Hawkins Electrical Guide v. 04 (of 10) Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications

XXXVI. DISTRIBUTION SYSTEMS

The selection of the system of transmission and distribution of electric energy from the generating plant to lamps, motors, and other devices, is governed mainly by the cost of the metallic conductors, which in many electrical installations, is a larger item than the cost of the generating plant itself. This is especially true in case of long distance transmission, while in those of the lighting plants, the cost of wiring is usually more expensive than that of the boilers, engines, and generators combined.

The principal distribution systems, are classed as:

1. Series; 2. Parallel; 3. Series-parallel; 4. Parallel-series.

=Ques. What is the characteristic feature of each class?=

Ans. In the series systems the current is constant, but the voltage varies. In the parallel systems, the voltage is constant, but the current varies.

=Series System of Distribution.=—A series system affords the simplest arrangement of lamps, motors, or other devices supplied with electric energy. The connections of such a system are shown in fig. 783. The current from the terminal of the dynamo passes through the lamps, L, L, L, L, one after the other and finally returns to the terminal. The current remains practically constant, but the voltage falls throughout the circuit in direct proportion to the resistance, and the difference in pressure between any two points in the circuit is equal to the current in amperes multiplied by the resistance in ohms included between them.

For example. Each open arc lamp requires about 50 volts. In the system shown in fig. 783, the pressure measured across the brushes of the dynamo is assumed to be 1,000 volts. As this current flows through the circuit 45 volts will be actually lost in each lamp, and as the drop on the line wire is usually about 10 per cent. of the total voltage, there will be a drop of 5 volts on the conductor between any two lamps. In the circuit shown, there are twenty lamps, therefore, the difference in pressure between either terminal of the dynamo and middle point A of the circuit will be 10 lamps × 50 volts = 500 volts. Likewise, the difference in pressure between any two points on the circuit will be equal to 50 volts multiplied by the number of lamps included between them.

=Ques. Describe the danger in a series arc light system?=

Ans. Since the total voltage of the system is equal to the sum of the volts consumed in all of the lamps, it is high enough to be dangerous to personal safety.

This is illustrated in fig. 783. If the line be grounded at B owing to defective insulation, the pressure of the circuit at that point will be zero, and therefore, a man standing on the ground could touch that point without receiving a shock, but if he should touch the line at the point C, he will receive a slight shock of 150 volts, as there are three lamps between the point C, and the ground connection B. Therefore, the danger of touching the circuit increases directly with the resistance between the point touched and the ground connection, so that if a man touch the circuit at the point D, he will receive a dangerous shock of 16 × 50 = 800 volts. In practice, sixty lamps are often placed on a single arc lighting circuit, so that its total pressure is about 3,000 volts, thus greatly increasing the danger of the system.

=Ques. What is a constant current system?=

Ans. The series system is a constant current system, and is so called because the current remains practically constant, while the voltage falls throughout the circuit in direct proportion to the resistance.

=Ques. What are the principal applications of the series system?=

Ans. For arc lighting, and telegraphic circuits.

=Ques. What are the advantages of the series system?=

Ans. In the case of telegraphic circuits only one wire is required, and for lighting and power transmission and distribution, only two wires; therefore, it is simpler and cheaper than any other system.

=Ques. What is the disadvantage of the series system?=

Ans. The danger due to the high voltage in installations such as arc lighting circuits.

=Parallel System.=—Parallel or multiple systems are usually more complicated than series systems, but since the voltage can be maintained nearly constant by various methods, practically all incandescent lamps, electric motors, and a large proportion of arc lamps are supplied by parallel systems.

The general principle of the parallel system is shown in fig. 784. With six lamps on the circuit, each requiring one-half ampere of current, at 110 volts, the dynamo will have to supply a current of 3 amperes at a pressure of 112 volts, and this current will flow through the circuit and distribute itself as shown on account of the lesser resistance of the wire relatively to that of the lamps. At the first lamp, the 3 amperes will divide, ½ ampere flowing through the lamp and the remaining 2½ amperes passing on to the next lamp and so on through the entire circuit. The reduction of pressure from 112 volts across the brushes to 110 volts at the last lamp is due to the resistance of the conducting wires.

=Ques. What three effects are due to this drop in pressure?=

Ans. 1, All the lamps or motors in the circuit receive a lower voltage than that at the dynamo, 2, some lamps or motors may receive a lower voltage than the others, and 3, the voltage at some lamps or motors may vary when the others are turned on or off.

The first is the least harmful and may be counteracted by running the dynamo at a little higher voltage; but the second and third are very objectionable and difficult to overcome. They are counteracted successfully in practice, however, by various methods of regulation, the use of boosters, and the operation of dynamos in parallel.

=Ques. What are the principal applications of parallel or constant pressure systems?=

Ans. They are used on practically all incandescent lamp and electric motor circuits, and on some arc lamp circuits.

=Ques. Why is it specially applicable to incandescent lamp circuits?=

Ans. Incandescent lamps cannot be made to stand a pressure much over 220 volts, and therefore have to be operated on low voltage systems.

=Ques. What is the principal disadvantage of a parallel system as compared with a series system?=

Ans. The greater cost of the copper conductors.

=Ques. What is the usual arrangement of parallel systems?=

Ans. Conductors known as a feeder run out from the station, and connected to these are other conductors known as a main to which in turn the lamps or other devices are connected as shown in fig. 785.

=Ques. In what two ways may feeders be connected?=

Ans. They may be connected at the same end of the mains, known as parallel feeding, or they may be connected at the opposite end of the main, called anti-parallel feeding.

The main may be of uniform cross section throughout, or it may change in size so as to keep the current density approximately constant. The above condition gives rise to four possible combinations:

1. Cylindrical conductors parallel feeding, fig. 786; 2. Tapering conductors, parallel feeding, fig. 787; 3. Cylindrical conductors, anti-parallel feeding, fig. 788; 4. Tapering conductors, anti-parallel feeding, fig. 789.

=Series-Parallel System.=—This is a combination of the series and parallel systems, and is arranged as indicated in fig. 790. Several lamps are arranged in parallel to form a group, and a number of such sets are connected in series, as shown. It is not necessary for the groups to be identical, provided they are all adapted to take the same current in amperes, which should be kept constant, and provided the lamps of each set agree in voltage. For example, on the ordinary 10-ampere arc circuit, one group might consist of 5 lamps, each requiring 2 amperes at 50 volts; the next might be composed of 10 lamps, each taking 1 ampere at 100 volts, and so on.

=Parallel-Series System.=—In this method of connection, one or more groups of lamp are connected in series and the groups in parallel as shown in fig. 791.

=Ques. When is a parallel-series system used?=

Ans. When it is desired to operate a number of lamps or motors on a line where voltage is several times that required to operate a single lamp or motor.

The parallel-series system is employed chiefly in the lighting circuit on electric traction lines; here, usually five 110 volt lamps are connected to the source of supply which has a pressure of 550 volts.

=Center of Distribution.=—It is important to determine the point at which the feeders should be attached to the mains in order to minimize the amount of copper required. The method employed is similar to that used in determining the best location of a power plant as regards amount of copper required. The center of distribution may be called the electrical center of gravity of the system, and is found by separately obtaining the center of gravity of straight sections and then determining the total resultant and point of application of this resultant of the straight sections.

Feeders (feeding cables or conductors) are run from the source of supply to the distributing centers, and, as these feeders are in many cases of considerable length, a substantial loss of pressure generally occurs in them. The pressure at the source of supply, however, is so regulated as to compensate for the drop in the feeders, and the pressure at the distributing centers is thus kept constant; or the same result is obtained by the use of regulating devices in the feeders. The essential condition in most systems is that the pressure at the distributing centers shall be kept practically constant, irrespective of the load.

=Edison Three Wire System.=—In electric lighting systems used up to about 1897, it was not considered practicable to use incandescent lamps requiring a pressure exceeding 120 volts. This limited the operating voltage of parallel systems, and necessitated the use of conductors of large size and weight, especially where the current had to be transmitted a considerable distance.

The effect of this limiting voltage is more apparent when it is clearly understood that the size of wire required to carry a current depends upon the amperes and not upon the volts.

A wire capable of carrying a current of 10 amperes at 20 volts, can carry 10 amperes at 20,000 volts or any other voltage. Therefore, since the amount of electric energy or power transmitted through a conductor is equal to the amperes multiplied by the volts, it is clear that by increasing the voltage, the power transmitting capacity of a current can be almost indefinitely increased without increasing the size of the conducting wire. This is the reason why considerations of economy dictate the use of the highest voltages possible in long distance transmissions. The voltage of the current is determined, however, by the requirements of the apparatus to be operated.

Incandescent lamps usually require a pressure of 110 volts, and the current required by a 16 candle power lamp at that voltage is about ½ ampere. Therefore if the lamp be designed for a pressure of 220 volts, the current will be reduced to ¼ ampere, and the same size of wire could be used to feed twice as many lamps.

The saving of copper is the sole merit of the three wire system, and the object which led to its invention was to effect this economy with the use of 110 volt lamps.

=Principle of the Three Wire System.=—In fig. 792, two dynamos A and B are shown supplying two independent incandescent lighting circuits, each circuit receiving 3 amperes of current at a pressure of 110 volts. It is evident that the dynamos could be connected with each other in series, and the lamps connected in series with two each, as shown in fig. 793, thus making the two wires K and L of the two independent circuits unnecessary, as the pressure will be increased to 220 volts while the current will remain at 3 amperes, and each lamp will require ¼ ampere.

The amount of copper saved will be 100 per cent., but this arrangement is open to the objection, that when one of the lamps is turned off, or burned out, its companion will also go out. This difficulty is avoided in the three wire system by running a third wire N, from the junction O, between the two dynamos, as shown in fig. 794, thus providing a supply or return conductor to any one of the lamps, and permitting any number of lamps to be disconnected without affecting those which remain. If the system be exactly balanced, no current will flow through the wire N, because the pressure toward the - terminal of the dynamo A, will be equal to the pressure from the + terminal of dynamo B, thus neutralizing the pressure in the wire. For this reason the middle wire of a three wire system is called the neutral wire, and is usually indicated by the symbol O or ± the latter meaning that it is positive to the first wire and negative to the second. If the system be unbalanced, a current will flow through the neutral wire, to or from the dynamos, according to the preponderance of lamps in the upper or lower sets. When the number in the lower set is the greater, the current in the neutral wire will flow from the dynamos as shown in fig. 797, and toward the dynamos under the reverse condition.

In the case represented in fig. 797, there are five lamps in circuit, requiring 2½ amperes of current at a pressure of 110 volts. The two lamps in the upper set will require 1 ampere, and the three lamps in the lower set, 1½ amperes. Since a pressure of 110 volts can force only a current of one ampere through resistance of the two lamps in the upper set, it is evident, that the additional ½ ampere required by the three lamps in the lower set will have to be supplied through the neutral wire, as shown.

=Balancing of Three Wire System.=—In practice it is impossible to obtain an exactly balanced system, as the turning on and off of lamps as required results in a preponderance of lamps in the upper or lower sets, and furthermore, even when the number of lamps in the two sets are equal, they may be located irregularly, thereby causing the currents to flow for short distances in the neutral line. Therefore, the larger the number of lamps in the circuit, the easier it will be to keep the system in a balanced condition.

=Copper Economy in Three Wire Systems.=—Theoretically, the size of the neutral wire has to be only sufficient to carry the largest current that will pass through it. A large margin of safety, however, is allowed in practice so that its cross section ranges from about one-third that of the outside line, in large central station systems, to the same as that of each outside line in small isolated systems.

If the neutral wire be made one-half the size of the outside conductor, as is usually the case in feeders, the amount of copper required is 5/16 of that necessary for the two wire system. For mains it is customary to make all three conductors the same size increasing the amount of copper to ⅜ of that required for the two wire system.

=Modifications of the Three Wire System.=—By the employment of suitable arrangements, it is possible to operate a three wire system with only one dynamo. Some of the various arrangements which have been used or proposed in this connection may be briefly mentioned as follows:

=Three Wire Storage Battery System=, in which a storage battery is connected between the two outside wires, and the pressure of the neutral wire varied to balance the system by shifting the point at which it is connected to the battery.

=Three Wire Double Dynamo System=, in which a double dynamo having two armature windings upon the same core, connected to two separate commutators, is used in the same manner as two separate dynamos connected in series.

=Three Wire Bridge System=, in which a resistance is connected across the two outside wires, and the neutral wire is brought to a point on the resistance through a movable switch. The pressures on the two sides of the circuit are equalized by adjusting the arm of the switch for any change of load.

=Three Wire Three Brush Dynamo System=, in which the neutral wire is connected to a third brush on the dynamo.

=Dobrowolsky Three Wire System=, in which a self-induction coil is connected to two diametrically opposite points of the armature of an ordinary direct current dynamo. The principle of this system is illustrated in fig. 795.

=Three Wire Auxiliary Dynamo System=, in which the neutral wire is connected to an auxiliary dynamo which supplies a pressure one-half as great as that of the main dynamo. The auxiliary dynamo is usually belt driven by the main dynamo, and acts as a dynamo when the load is greater on the negative side of the circuit, and as a motor when the excess of load is on the positive side.

=Three Wire Compensator System=, in which two auxiliary dynamos A and B called compensators or equalizers, are coupled together and connected to the system as shown in fig. 796. Each compensator generates one-half as much pressure as the main dynamo D, and serves to equalize the pressure and the load, the compensator on the lightly loaded side operating as a motor and driving the other as a dynamo. When the system is exactly balanced, both compensators run as motors under no load, therefore, consume very little energy. In this arrangement only one booster E, is required for both sides of the system, as the compensators are connected to the outside wires at a point beyond the boosters, and therefore, sub-divide the increased difference of pressure equally between the two sides of the system.

=Extension of the Three Wire Principle.=—In order to attain still greater economy in copper, the principles of the three wire system may be extended to include four, five, six, and seven wire systems. The comparative weights of copper required by such systems are as follows:

Two wire system 1.000 Three " " all wires of equal size .370 Three " " neutral wire one-half size .313 Four " " all wires of equal size .222 Five " " " " " " " .156 Seven " " " " " " " .096

The four wire system requires about two-ninths as much copper, and the seven wire system about one-tenth as much copper, as an equivalent two wire system; but neither is desirable, as their operation involves too much inconvenience, too many unavoidable complications, and create a possibility of accident, which more than offsets the saving in copper.

=The Five Wire System.=—This system is employed advantageously in many places in England and Europe, but has not as yet been introduced to any extent in America. It is very probable that in the future the three wire 440 volt system will be selected in preference to the five wire system.

=Dynamotor.=—This is a combination of dynamo and motor on the same shaft, one receiving current and the other delivering current, usually of different voltage, the motor being employed to drive the dynamo with a pressure either higher or lower than that received at the motor terminals.

The dynamotor in the direct current circuit corresponds to the transformer in the alternating current circuit.

=Ques. How is the dynamotor used as an equalizer in the three wire system?=

Ans. When thus used, the machine is connected as in fig. 798. When both sides of the system are balanced, there will be no current in the neutral lead N, and a small current will pass through the two armature windings of the dynamotor in series, both armatures acting as motors. If the load on one side of the system become larger than the load on the other side, there will be a greater drop in the leads connected to the overloaded side and consequently a lower voltage will exist over the larger load than exists over the smaller load. The armature winding of the dynamotor connected to the higher voltage will act as a dynamo, whose pressure will tend to raise the voltage of the more heavily loaded side.

The direction of the currents in an unbalanced three wire system that is being supplied with energy from a main dynamo is shown in the figure. The commutator at G is connected to the dynamo winding of the dynamotor and is supplying current to the upper or larger load, and the lower commutator is connected to the motor winding of the dynamotor and is taking current from the lightly loaded side.

=Motor-Dynamo or Balancing Set.=—A balancing set or balancer consists of a motor mechanically connected to a dynamo used to balance a three wire system. The operation of such a combination is practically the same as the dynamotor just described. The balancer is connected as shown in fig. 799.

When an unbalanced load comes on, the voltage on the lightly loaded side rises and on the heavily loaded side drops. The machine on the light side then takes power from the line and runs as a motor driving the machine on the heavy side as a dynamo, supplying the extra current for that side. This action tends to bring the voltage back to normal and gives good regulation.

In some cases the field of each machine is connected to the opposite side of the system which gives a quicker action. This regulation is automatic and the set takes care of unbalanced loads in either direction without adjustment.

=Balancing Coils.=—Another method of balancing a three wire system which does away with any additional rotating machines makes use of balance coils.

=Ques. Describe the type of dynamo used with balancing coils?=

Ans. The regular two wire dynamo is used supplying power to the outside wires, but there are collector rings connected to the armature. These rings are much lighter than they would be for a converter as they carry only about ⅛ of the dynamo load. These rings being light are usually placed at the end of the commutator and are connected directly to the commutator bars.

=Ques. How are the balancing coils constructed?=

Ans. They are built of standard transformer parts, and are placed in cases similar to those of ordinary small transformers.

[Illustration: FIGS 802 and 803.—Distribution by dynamo-motor sets. Fig. 802, sets in parallel; fig. 803, sets in series. In fig. 802, current produced by the main dynamo G, is carried to the machines by the conductors A and B to which the motor portions M are connected in parallel. These motors are provided with shunt wound field coils which may be connected to the primary or to the secondary circuit, consequently the machines run at a practically constant speed. The dynamo portions D of the transformers are connected to the secondary circuits which supply the lamps, etc., L, as indicated. The field magnets of these dynamos may also be fed by the main circuit AB, or they may be self-excited by shunt or compound winding. In fig. 803, the motors M are all connected in series with the main dynamo G, and the dynamo elements D of the transformers, connected to the lamps, etc., L. If the current be kept constant (the dynamo G having a regulator like a series arc dynamo), and the motors M are simple series wound machines, they will exert a certain torque, or turning effort, which will be constant. It follows, therefore, that if the dynamos D be also series wound, each will generate a certain current which will be constant. If lamps or other devices, designed for that particular current, be connected in series on the secondary circuits, the dynamos D will always maintain that current, no matter how many lamps there may be. When lamps are added, the resistance of the local circuit is raised, and the current in it decreases, so that the dynamo increases its speed until it generates sufficient pressure to produce practically the same current as before. Hence this constitutes a system which is self-regulating, when lamps, etc., are cut in or out of the secondary circuits. No harm results even if the secondary be short circuited, since only the normal current can be generated. But if the secondary circuit be opened, then the machine will race, and probably injure itself by centrifugal force, because the torque of the motor M has its full value, and there is no load upon the dynamos D. To guard against this danger, some automatic device should be provided to short circuit the field or armature of the motor when its speed or reverse voltage rises above a certain point.] The coil has a straight continuous winding, both ends and a connection from the middle point of the winding being brought out of the case.

=Ques. How are the coils connected to the dynamo?=

Ans. Two coils are used and are connected to the collector rings as shown in fig. 801, one coil across each phase. The connections from the middle points of the coils are connected together and to the neutral wire of the system.

=Ques. What is the action of the coils in equalizing the load?=

Ans. On balanced load, the coils take a small alternating exciting current from the collector rings as any transformer does when connected to an alternating current line with its secondary open. When an unbalanced load comes on, the current in the neutral divides, half going to each coil. This enters the coil at the middle point and half flows each way through the coil and the slip rings into the armature winding. The unbalanced current is thus fed back directly into the dynamo armature continuously.

The coils are small and can be placed back of the switchboard or below the floor, as they require no attention. The current flowing to each slip ring is 25% of the direct current in the neutral wire with the small exciting current taken by the coil added.

The coils are usually built to take care of current in the neutral equal to 25% of full load current of the dynamo with a voltage regulation not to exceed 2 per cent.

=Ques. Upon what does the operation of the balancing coil system depend?=

Ans. It depends on the following points: First, the impedance[1] of the coils keeps the exciting current which they take from the collector rings down to a small value as it is alternating current. At the same time the current from the neutral wire flows through the four half coils in parallel, and being direct current is impeded only by the ohmic resistance of the coils, which is low, giving only a slight loss in the coils. The common point to which the neutral wire is connected must at all times be neutral to the - and + direct current brushes.

[1] NOTE.—The term impedance means the total opposition in an electric circuit to the flow of an alternating current, being made up of the actual or ohmic resistance and the apparent resistance due to self-induction, or if the circuit contain also capacity, the resultant apparent resistance due to self-induction and capacity.

That this common point is at all times neutral is readily shown. Referring to fig. 804, let AE, BF, CG and DH represent the balance coil and its connection for different positions of the armature of a bipolar machine. Let O be the tap to the middle point of the winding.

Take the instant when the balance coil taps are directly under the direct current brushes as shown at position AE. It is evident that since the point O is the middle point of the coil, it is neutral between A and E. When the armature turns so that the balance coils take the position BF, the voltage drop between A and E may be divided into 4 parts, AB, BO, OF and FE. As in the first instance, O is neutral between the ends of the coil, and the voltage drop over OF equals that over OB.

Since the space AB includes the same number of armature coils as space FE and they are in fields of equal strength, the voltages across the two spaces will be equal, and the voltage over AB equals that over FE. Then adding equals: AB + BO = FE + FO and O is neutral between A and E as in the first case.

In the same way it can be shown that O is neutral between the direct current brushes for any position of the balance coil taps. One coil will operate the system, but two coils, giving four points spaced 90 electrical degrees apart, give better distribution of the current to the armature winding and better regulation of the voltage.

=Boosters.=—A booster may be defined as, a dynamo inserted in a circuit at a point when it is necessary to change the voltage. A booster is generally driven by a motor, the two armatures being directly coupled, although boosters are sometimes driven from the engine or line shaft.

=Ques. Explain the use of a booster?=

Ans. When a number of feeders run out from a station, the longest and those carrying the heaviest loads will have so much drop on the line that the pressure at distant points is too low. It is therefore necessary to raise the pressure to compensate for the drop and this is done by inserting a booster in the circuit.

It would not be economical to raise the voltage on all the lines by supplying current from the main dynamo at higher pressure, hence the voltage is raised only on the lines which need it by means of the booster working in series with the main dynamo.

=Ques. For what other service are boosters employed?=

Ans. They are used in connection with storage battery plants for the purpose of raising the voltage of the bus bars to the pressure necessary for charging storage batteries.

=Ques. What is an auxiliary bus bar?=

Ans. An extra bus bar which is kept at higher pressure than the main bar.

=Ques. What is the object of an auxiliary bus bar?=

Ans. It is used in place of a booster as shown in fig. 806. One or more dynamos maintain the pressure between the auxiliary bar and the common negative bar. The feeders which need boosting are connected to the common negative bar and the auxiliary bar as shown.

Spotted a typo or a problem in this chapter? Tell us

XXXVII. WIRES AND WIRE CALCULATIONS

The wireman who is called upon to plan and install a system of wiring will find it necessary first to have a knowledge of the various kinds of wire so as to select the one best suited for the work, and to be able to make simple calculations in order to determine the proper sizes of wire for the various circuits.

Wires are generally made of circular cross section. The process of manufacture consists in drawing the material through steel dies, when its properties permit this treatment. In the case of some substances, as for instance, tin and lead, difficulties arise in the drawing process, and these are therefore "squirted."

The metals most extensively used for wires are copper and iron; German silver, tin and lead are also employed, but only at points where it is desirable to have a comparatively high resistance in the circuit.

=Copper Wire.=—Copper is used in nearly all cases of wiring because it combines high electrical conductivity with good mechanical qualities and reasonable price. In conductivity it is only surpassed by silver, but the cost of the latter of course prohibits its use for wiring purposes.

Copper wire is used for electric light and power lines, for most telephone and some telegraph lines, and for all cases where low resistance is required at moderate cost.

Hard drawn copper wire is ductile, and has a high tensile strength; these properties allow it to be bent around corners and drawn through tubes without injury.

Pure annealed copper has a specific gravity of 8.89 at 60° Fahr. One cubic inch weighs .32 pound; its melting point is about 2,100° Fahr.

Good hard drawn copper has a tensile strength of about three times its own weight per mile length. Thus, a number 10 B. & S. gauge copper wire, weighing 166 lbs. per mile, will have a breaking strength equal to approximately 3 × 166 = 498 lbs.

=Iron Wire.=—This kind of wire is largely used for telegraph and telephone lines, although it is rapidly being replaced by copper in long lines.

There are three grades of iron wire:

1. =Extra best best (E. B. B.)= which has the highest conductivity and is the nearest to being uniform, in quality, being both tough and pliable;

2. =Best best (B. B.)=, which varies more in quality, is not so tough, and is lower in conductivity. It is frequently sold as =E. B. B.=;

3. =Best (B.)=, which is the poorest grade made, being more brittle, and lowest in conductivity. Iron wire should be well galvanized.

=German Silver Wire.=—German silver is an alloy consisting of 18 to 30% nickel, and the balance about four parts copper to one part zinc. It is very largely used as a resistance material in making resistance coils, and is sold in the form of wire, and strip. The resistance of this wire varies with its composition.

The resistance of the 18% alloy at 25° C. is 18 times that of copper, and of the 30% alloy about 28 times that of copper.

The safe carrying capacity of the wire in spirals in open air for continuous duty is such that the circular mils per ampere varies from about 1,500 in No. 10 wire to about 475 in No. 30. For intermittent duty the capacity is twice as great.

=Standard of Copper Wire Resistance.=—Matthiessen's standard for resistance of copper wire is as follows: A hard drawn copper wire one meter long, weighing one gramme, has a resistance of .1469 B. A. unit at 32° Fahr. Relative conducting power: silver, 100; hard or un-annealed copper, 99.95; soft or annealed copper, 102.21.

A committee of the Am. Inst. Electrical Engineers recommends the following form of Matthiessen's standard, taking 8.89 as the specific gravity of pure copper: A soft copper wire one meter long and one millimeter in diameter has an electrical resistance of .02057 B. A. unit at 0°C.[2] From this the resistance of a soft copper wire one foot long and .001 in. in diameter (mil-foot) is 9.72 B. A. units at 0°C.

[2] NOTE.—The international ohm ÷ B. A. ohm = 1 ÷ .9866. The B. A. ohm ÷ International ohm = 1 ÷ 1.0136. Hence, to reduce British Association ohms to International ohms, divide by 1.0136. or multiply by .9866.

For every degree Fahr., the resistance of copper wire increases .2222%. Thus a piece of copper wire having a resistance of 10 ohms at 32°, would have a resistance of 11.11 ohms at 82°.

Relative Conductivity of Different Metals and Alloys.

(According to Lazare Weiler.)

Pure silver 100 Pure copper 100 Alloy, ½ copper, ½ silver 86.65 Telephonic siliceous bronze 35 Pure zinc 29.9 Brass with 35% zinc 21.5 Swedish iron 16 Pure platinum 10.6 Copper with 10% nickel 10.6 Pure lead 8.88 Pure nickel 7.89 Phosphor-bronze, 10% tin 3.88

=Conductors.=—Copper is used more than any other metal for transmitting electrical energy, and for interior wiring it is used exclusively. Copper conductors should be of the highest commercial conductivity, not less than 97%.

For conductors up to sizes as large as No. 8 B. & S. gauge, single conductors may be used, but for larger sizes the necessary conductivity should be obtained by conductors made up of strands of smaller wires. The size of these strands depend upon the size of the conductors and the conditions under which they are to be used.

Where conductors are very large (as for instance dynamo leads), and where it is essential that they should be as flexible as possible, strands as small as No. 20 or 22 B. & S. gauge may be used.

Conductors for flexible cords, pendants, fixtures, etc., should also consist of very fine strands, so that they may be perfectly pliable and flexible.

The individual strands for instance, for a No. 16 B. & S. gauge flexible cord should be as fine as No. 30.

=Covered Conductors.=—For most conditions of service, wires are protected with an insulating covering. Wires used in interior circuits should have a covering which shall act both as an electrical insulator and as a mechanical protection. In some instances, however, the insulating qualities are of secondary importance.

The various forms of covering now in use commercially for wires are:

1. Rubber; 2. Weather proof; 3. Slow burning; 4. Slow burning weather proof; 5. Armoured.

=Rubber Covered Conductors.=—This class of conductor consists of a tinned copper wire with a rubber covering, protected by an outside braiding of cotton saturated with a preservative compound.

=Ques. What are the advantages of rubber insulation for conductors?=

Ans. It is waterproof, flexible, fairly strong, and has high insulating qualities.

=Ques. What are the disadvantages of rubber insulation?=

Ans. It deteriorates more or less rapidly and is quickly injured by temperatures above 140° Fahr.

=Ques. For what service are rubber covered conductors adapted?=

Ans. For interior wiring.

=Ques. Is pure rubber used?=

Ans. No. The covering should be made from a compound containing from 20 to 35 per cent. of pure rubber.

It would be difficult to place pure rubber on a wire, and moreover a covering made of pure rubber would not be durable and would deteriorate very rapidly, particularly at temperatures above 120° Fahr. Accordingly, it is mixed with other materials, such as French chalk, silicate of magnesia, sulphur, red lead, etc.

=Weather Proof Conductors.=—In this class of conductor, the wire is protected from the weather by a waterproof covering, consisting usually of braided cotton of two or three thicknesses saturated with a moisture resisting insulating compound.

=Ques. Where are weather proof conductors used?=

Ans. In places subject to dampness, such as cellars, tunnels, open sheds, breweries, etc.

=Ques. What are the advantages of weather proof conductors?=

Ans. The insulation is cheap, very durable, and does not deteriorate unless exposed to high temperatures such as will melt the compound.

=Ques. State the disadvantages.=

Ans. The covering is more or less inflammable and is not very efficient as an insulator.

=Ques. What precaution should be taken in using weather proof conductors?=

Ans. On account of the inflammable character of the covering, care should be taken in wiring at points where any considerable number of conductors are brought together, or where there is much woodwork or other combustible material.

=Ques. For what use are weather proof conductors especially adapted?=

Ans. For outside wiring where moisture is certain and where fireproof quality is not necessary.

Obviously conductors of this class should not be used in conduits, nor in fact, in any way except exposed on glass or porcelain insulators.

=Slow Burning Wire.=—This class of conductor is defined as: one that will not carry fire. The covering consists of layers of cotton or other thread, all the interstices of which are filled with the fireproofing compound, or of material having equivalent fire resisting and insulating properties. The outer layer is braided and specially designed to withstand abrasion. The thickness of insulation must not be less than that required for slow burning weather proof wire and the outer surface must be finished smooth and hard.—Underwriters' requirements.

=Ques. Where should slow burning wires be used?=

Ans. In hot dry places, where ordinary insulations would be injured, and where wires are bunched, as on the back of a large switchboard or in a wire tower.

A slow burning covering is considered good enough when the wires are entirely on insulating supports. Its main object is to prevent the copper conductors coming into contact with each other or anything else.

=Ques. What must be done before using weather proof wire?=

Ans. Permission to use the wire must first be obtained from the local Inspection Department.

=Slow Burning Weather Proof Wire.=—The covering of this type wire is a combination of the underwriters and weather proof insulations. The fireproof coating comprises a little more than half of the total covering. When the fireproof coating is placed on the outside, the wire is called "slow burning weather proof."

=Ques. How does slow burning weather proof wire compare with weather proof wire?=

Ans. It is less inflammable and less subject to softening under heat.

=Ques. Where should slow burning weather proof wire be used?=

Ans. In places where the wires are to be run exposed and where moisture resisting quality is desired, also where at the same time it is desirable to avoid an excess of inflammable covering.

=Ques. How should it be installed?=

Ans. It should be set on glass or porcelain insulators.

=Miscellaneous Insulated Conductors=

+————————————-+————————————+————————-+——————————————+——————————+——————————-+ | No. of | Gauge of | No. of | Gauge of | Outside | Weight | | Conductors | Conductors | Armour | Armour Wires | Diameter | per 1,000 | | | (B. & S.) | Wires | B. W. G. | (inch) | Feet | +————————————-+————————————+————————-+——————————————+——————————+——————————-+ | | | | | | | | 1 | 14 | 12 | 8 | ⅞ | 1,150 | | 2 | 14 | 16 | 8 | 1-31/32 | 1,675 | | 3 | 14 | 14 | 6 | 1¼ | 2,400 | | 4 | 14 | 16 | 6 | 1-5/16 | 2,750 | | 5 | 14 | 19 | 6 | 1⅜ | 3,100 | | 6 | 14 | 21 | 6 | 1½ | 3,500 | | 7 | 14 | 21 | 6 | 1½ | 3,600 | | 10 | 14 | 22 | 4 | 1⅞ | 4,600 | | | | | | | | +————————————-+————————————+————————-+——————————————+——————————+——————————-+

NOTE.—The above specifications refer only to river and harbor cables. Ocean cables are of an entirely different character, and consist of "shore end," "intermediate" and "deep sea" types.

=Ques. For what service is slow burning weather proof wire not suited?=

Ans. It is not adapted to outside work.

=Safe Carrying Capacity of Wire.=—All wires will heat when a current of electricity passes through them. The greater the current or the smaller the wire, the greater will be the heating effect. Large wires are heated comparatively more than small wires because the latter have a relatively greater radiating surface.

The temperature of a wire increases approximately as the square of the current, and inversely as the cube of the diameter of the wire.

The elevation in temperature of a wire carrying a current represents so much lost energy.

From these considerations it must be clear that it is important not to overload conductors in order to secure efficient working, and to avoid risk of fire on inside installations.

The Board of Underwriters specifies that the carrying capacity of a conductor is safe when the wire will conduct a certain current without becoming painfully hot.

In the following table of carrying capacity, prepared by the underwriters, a wire is assumed to have a safe carrying capacity when its temperature is not increased by the given current over 30° Fahr. above that of the surrounding air.

SAFE CARRYING CAPACITIES OF WIRES

(Maximum amperes allowed by the Underwriters.)

+————————+——————————————-+————————————+————————————+ | Brown | | Rubber | Other | | and | | insulation | insulations| | Sharpe | Circular mils | —————— | —————— | | Gauge | | Amperes | Amperes | | | | | | +————————+——————————————-+————————————+————————————+ | | | | | | 18 | 1,624 | 3 | 5 | | 16 | 2,583 | 6 | 8 | | 14 | 4,107 | 12 | 16 | | 12 | 6,530 | 17 | 23 | | 10 | 10,380 | 24 | 32 | | 8 | 16,510 | 33 | 46 | | 6 | 26,250 | 46 | 65 | | 5 | 33,100 | 54 | 77 | | 4 | 41,740 | 65 | 92 | | 3 | 52,630 | 76 | 110 | | 2 | 66,370 | 90 | 131 | | 1 | 83,690 | 107 | 156 | | 0 | 105,500 | 127 | 185 | | 00 | 133,100 | 150 | 220 | | 000 | 167,800 | 177 | 262 | | 0000 | 211,600 | 210 | 312 | | | 200,000 | 200 | 300 | | | 300,000 | 270 | 400 | | | 400,000 | 330 | 500 | | | 500,000 | 390 | 590 | | | 600,000 | 450 | 680 | | | 700,000 | 500 | 760 | | | 800,000 | 550 | 840 | | | 900,000 | 600 | 920 | | | 1,000,000 | 650 | 1,000 | | | 1,100,000 | 690 | 1,080 | | | 1,200,000 | 730 | 1,150 | | | 1,300,000 | 770 | 1,220 | | | 1,400,000 | 810 | 1,290 | | | 1,500,000 | 850 | 1,360 | | | 1,600,000 | 890 | 1,430 | | | 1,700,000 | 930 | 1,490 | | | 1,800,000 | 970 | 1,550 | | | 1,900,000 | 1,010 | 1,610 | | | 2,000,000 | 1,050 | 1,670 | | | | | | +————————+——————————————-+————————————+————————————+

The lower limit is specified for rubber covered wires to prevent gradual deterioration of the high insulations by the heat of the wires, but not from fear of igniting the insulation. The question of drop is not taken into consideration in the table on page 731.

The carrying capacity of Nos. 16 and 18 B. & S. gauge wire is given, but no smaller than No. 14 is to be used, except as allowed under rules for fixture wiring.—Underwriters' Rules.

=Circular Mils.=—The unit of measurement in measuring the cross sectional area of wires is the circular mil; it is the area of a circle one mil (.001 in.) in diameter.

The area of a wire in circular mils is equal to the square of the diameter in mils.

Thus a wire 2 mils in diameter (.002 in.) has a cross sectional area of 2 × 2 = circular mils. Accordingly to obtain the area of a wire in circular mils, measure its diameter with a micrometer which reads directly in mils or thousandths of an inch, and square the reading.

The circular mil (abbreviated C.M.) applies to all round conductors, and has a value of .7854 times that of the square mil, that is, 1 circular mil = .7854 square mil. If the diameter be expressed as a fraction of an inch, as for instance ⅓ in., the circular mil area may be found as follows: Reduce the fraction ⅓ to the decimal of an inch, multiply the result by 1,000 to express the diameter in mils, and square the diameter so expressed, thus: ⅓ = 1,000 ÷ 3 = .333. .333 × 1,000 = 333 mils; 333 × 333 = 110,889 circular mils.

The diameter of any wire may be found when its circular mil area is known by extracting the square root of the circular mil area.

=Square Mils.=—For measuring conductors of square or rectangular cross section, such as bus bars, copper ribbon, etc., the square mil is used. A square mil is the area of a square whose sides are one mil (.001 in. long) and is equal to .001 × .001 = .000001 square inch.

EXAMPLE.—A copper ribbon for a field coil measures ⅝ inch by ⅛ inch. What is its area in square mils? What is its area in circular mils?

⅝ = .625 in., or 625 mils; ⅛ = .125 in., or 125 mils.

Area in square mils = 625 × 125 = 78,125.

Area in circular mils= { 78,125 ÷ .7854 } {or 78.125 × 1.2732} = 99,469.

=Mil Foot.=—This unit is used as a basis for computing the resistance of any given wire. A mil foot means a volume one mil in diameter and one foot long.

The resistance of a wire of commercially pure copper one mil in diameter and one foot long is taken as a standard in calculating the resistance of wires, and has been found to be equal to 10.79 ohms at 75° Fahr.

The calculation is made according to the following rule:

The resistance of a copper wire is equal to its length in feet, multiplied by the resistance of one mil foot (10.79 ohms) and divided by the number of circular mils, or the square of its diameter.

Expressed as a formula:

length of wire in ft. × 10.79 resistance in ohms = —————————————————————————————— (1) circular mils

EXAMPLE. What is the resistance of a copper wire 1,500 feet long and having a transverse area of 10,381 circular mils?

Substituting these values in formula (1)

1,500 × 10.79 resistance = ———————————————————— = 1.559 ohms. 10,381

The transverse area of a copper wire is found by multiplying the resistance of a mil foot (10.79) by its length in feet and dividing the result by its resistance in ohms.

This is obtained directly from the formula (1) by solving the equation for circular mils, thus:

length of wire in ft. × 10.79 circular mils = ——————————————————————————————- (2) resistance in ohms

EXAMPLE. What is the circular mil area of a wire 1,500 feet long and having a resistance of 1.559 ohms?

Substituting the values in equation (2)

1,500 × 10.79 circular mils = ————————————- = 10,381 1.559

=Lamp Foot.=—This unit facilitates laying out wiring and calculating the drop. A lamp foot is defined as one 16 candle power lamp at a distance of one foot from the point of supply. Accordingly the number of lamp feet in any circuit is equal to the number of 16 candle power lamps (or equivalent in other sizes) in the circuit multiplied by the distance in feet from the fuse block to the center of distribution.

When no point is specified, the feet are always measured from the supply point to the center of distribution. When other than 16 c.p. lamps are in the circuit they must be reduced to 16 c.p. lamps. Thus two 8 c.p. lamps would be counted one 16 c.p. lamp, one 32 c.p. lamp would be counted two 16 c.p. lamps, etc.

=Ampere Foot.=—From the foregoing explanation of lamp foot, the significance of ampere foot is easily understood—the two terms are in fact self-defining.

An ampere foot may be defined as the product of one ampere multiplied by one foot.

The unit ampere foot is used in figuring motor circuits or currents designed to carry a mixed load.

The ampere feet of a main are found by multiplying the maximum load in amperes by the distance from the fuse block to the electrical center of the load.

Thus if the center of distribution be 50 feet from the fuse block and the maximum load is 9 amperes, the number of ampere feet is equal to 9 × 50 = 450.

=Electrical Center of Distribution.=—The electrical center of a circuit depends upon the distances between the lamps and the fuse block; also the relative sizes of the lamps.

It may be defined as the sum of the lamp feet for each section divided by the number of 16 candle power lamps in the circuit.

If the lamps be of uniform capacity, and placed at equal distances apart, the center of distribution will coincide with the geometrical center of the group of lamps. However, if the lamps vary in size, and be irregularly spaced, the electrical center will not coincide with the geometrical center unless the lamps be symmetrically arranged so as to compensate for the difference in sizes and spacing.

In such cases, as shown in fig. 821, the electrical center can be determined by adding together the lamp feet of the several sections A, B, C, etc., of the main and dividing the result by the 16 c.p. units. Thus the lamp feet of

Section A = 10 lamps × 10 feet= 100 " B = 9 " × 5 " = 45 " C = 7 " × 6 " = 42 " D = 6 " × 4 " = 24 " E = 5 " × 5 " = 25 " F = 4 " × 10 " = 40 " G = 2 " × 5 " = 10 ——- which added together gives a total of 286 lamp feet.

This when divided by the ten 16 c.p. units comprising four 16 c.p. lamps and three 32 c.p. lamps, gives a little over 28½ feet as the distance from the fuse block to the center of distribution, the position of which is shown by the line M N in fig. 821, while that of the geometrical center is shown by the line K L.

When the center of distribution is at a considerable distance from the supply circuit, and it becomes advisable to divide the wiring into two distinct elements—a feeder and one or more mains, the junction of the feeder and the mains should be located at the electrical center of the mains whenever possible. When this is done, it is obvious that the wire size of only one half the main needs to be calculated, as both halves of the main are identical.

=Wire Gauges.=—For the purpose of facilitating the measurement of wire, a number of gauges have been designed by various wire manufacturing concerns. The principal gauges used in the United States are the American or Brown & Sharp's gauge; the English standard or Birmingham gauge; Washburn & Moen's standard gauge; Imperial wire gauge; Stubs' steel wire gauge, and the U. S. Standard wire gauge.

The several gauges are here given with explanation of their use.

=The American Standard or Brown and Sharp's Gauge.=—This gauge is commonly designated as A. W. G. or B. & S., and has been adopted by brass manufacturers and is used mostly in measuring brass, copper, silver, German silver, and gold in both wire and plate.

=Birmingham or Stub's Wire Gauge (B. W. G.).=—Old English Standard and Iron Wire Gauge. _Birmingham or Stubs' Iron Wire Gauge is not the same as Stubs' Steel Wire Gauge_. A table of Stub's Steel Wire Gauge is given on page 741.

=Washburn and Moen's Standard Wire Gauge.=—Commonly designated as W. & M. G. has been adopted by the U. S. Steel Corporation in making their wire.

=New British Standard (N. B. S.).=—British Imperial English Legal Standard and Standard Wire Gauge, and is variously abbreviated by S. W. G. and I. W. G.

=Roebling Gauge.=—Washburn Moen, American Steel & Wire Co.'s Iron Wire Gauge.

=U. S. Standard Wire Gauge.=—This gauge is used for measuring sheet and plate iron, and steel, by the U. S. Government in assessing duties, and in making requisitions for supplies.

=Old English Standard Wire Gauge.=—The old English gauge is the same as the Birmingham or Stubs' standard gauge, commonly designated as B. W. G. It is used chiefly for measuring sheet iron and steel, also soft steel and iron wire.

=London Gauge.=—Old English (not Old English Standard).

From the foregoing it is seen that great confusion exists with such a multiplicity of gauges and emphasizes the importance of specifying the gauge and of knowing what gauge to use.

In using the gauges known as Stubs' Gauges, there should be constantly borne in mind the difference between the Stubs' Iron Wire Gauge and the Stubs' Steel Wire Gauge. The Stubs' Iron Wire Gauge is the one commonly known as the English Standard Wire, or Birmingham Gauge and designates the Stubs' soft wire sizes. The Stubs' Steel Wire Gauge is the one that is used in measuring drawn steel wire or drill rods of Stubs' make and is also used by many makers of American drill rods.

=STUBS' STEEL WIRE GAUGE=

——————-+————————-++——————+————————-++——————+————————-++——————+———————- | Size of || | Size of || | Size of || | Size of Letter.| Letter ||No. of| Number ||No. of| Number ||No. of| Number | in || Wire | in || Wire | in || Wire | in |Decimals.||Gauge.|Decimals.||Gauge.|Decimals.||Gauge.|Decimals. ——————-+————————-++——————+————————-++——————+————————-++——————+———————- Z | .413 || 1 | .227 || 28 | .139 || 55 | .050 Y | .404 || 2 | .219 || 29 | .134 || 56 | .045 X | .397 || 3 | .212 || 30 | .127 || 57 | .042 W | .386 || 4 | .207 || 31 | .120 || 58 | .041 V | .377 || 5 | .204 || 32 | .115 || 59 | .040 U | .368 || 6 | .201 || 33 | .112 || 60 | .039 T | .358 || 7 | .199 || 34 | .110 || 61 | .038 S | .348 || 8 | .197 || 35 | .108 || 62 | .037 R | .339 || 9 | .194 || 36 | .106 || 63 | .036 Q | .332 || 10 | .191 || 37 | .103 || 64 | .035 P | .323 || 11 | .188 || 38 | .101 || 65 | .033 O | .316 || 12 | .185 || 39 | .099 || 66 | .032 N | .302 || 13 | .182 || 40 | .097 || 67 | .031 M | .295 || 14 | .180 || 41 | .095 || 68 | .030 L | .290 || 15 | .178 || 42 | .092 || 69 | .029 K | .281 || 16 | .175 || 43 | .088 || 70 | .027 J | .277 || 17 | .172 || 44 | .085 || 71 | .026 I | .272 || 18 | .168 || 45 | .081 || 72 | .024 H | .266 || 19 | .164 || 46 | .079 || 73 | .023 G | .261 || 20 | .161 || 47 | .077 || 74 | .022 F | .257 || 21 | .157 || 48 | .075 || 75 | .020 E | .250 || 22 | .155 || 49 | .072 || 76 | .018 D | .246 || 23 | .153 || 50 | .069 || 77 | .016 C | .242 || 24 | .151 || 51 | .066 || 78 | .015 B | .238 || 25 | .148 || 52 | .063 || 79 | .014 A | .234 || 26 | .146 || 53 | .058 || 80 | .013 | || 27 | .143 || 54 | .055 || | ——————-+————————-++——————+————————-++——————+————————-++——————+———————-

The following table gives the diameters, in decimal parts of an inch, of the various sizes of wire corresponding to the number of gauge numbers of the different standard wire gauges used in the United States.

=TABLE OF VARIOUS WIRE GAUGES=

=In decimal parts of an inch=

————————+————————-+————————-+——————————+——————-+——————-+——————-+——————- Number | Ameri- | Birming-| Wash- | Tren- |G.W. | Old | Brit- of | can, or | ham, or | burn & | ton | Pren- | Eng- | ish Wire | Brown & | Stubs | Moen | Iron | tiss, | lish, | Stan- Gauge | Sharpe | (B.W.G.)| Mfg. Co.,| Co., | Holy- | From | dard | (B.&S.) | | Worces- | Tren- | oke, | Brass | (S.W.- | | | ter, | ton, | Mass. | Mfrs' | G.) | | | Mass. | N.J. | | List | ————————+————————-+————————-+——————————+——————-+——————-+——————-+——————- 0000000 | | | | | | | .500 000000 | | | .460 | | | | .464 00000 | | | .430 | .450 | | | .432 0000 | .46000 | .454 | .393 | .400 | | | .400 000 | .40964 | .425 | .362 | .360 | .3586 | | .372 00 | .36480 | .380 | .331 | .330 | .3282 | | .348 0 | .32486 | .340 | .307 | .305 | .2994 | | .324 1 | .28930 | .300 | .283 | .285 | .2777 | | .300 2 | .25763 | .284 | .263 | .265 | .2591 | | .276 3 | .22942 | .259 | .244 | .245 | .2401 | | .252 4 | .20431 | .238 | .225 | .225 | .2230 | | .232 5 | .18194 | .220 | .207 | .205 | .2047 | | .212 6 | .16202 | .203 | .192 | .190 | .1885 | | .192 7 | .14428 | .180 | .177 | .175 | .1758 | | .176 8 | .12849 | .165 | .162 | .160 | .1605 | | .160 9 | .11443 | .148 | .148 | .145 | .1471 | | .144 10 | .10189 | .134 | .135 | .130 | .1351 | | .128 11 | .090742 | .120 | .120 | .1175 | .1205 | | .116 12 | .080808 | .109 | .105 | .1050 | .1065 | | .104 13 | .071961 | .095 | .0920 | .0925 | .0928 | | .0920 14 | .064084 | .083 | .0800 | .0800 | .0816 | .08300| .0800 15 | .057068 | .072 | .0720 | .0700 | .0726 | .07200| .0720 16 | .050820 | .065 | .0630 | .0610 | .0627 | .06500| .0640 17 | .045257 | .058 | .0540 | .0525 | .0546 | .05800| .0560 18 | .040303 | .049 | .0470 | .0450 | .0478 | .04900| .0480 19 | .035890 | .042 | .0410 | .0400 | .0411 | .04000| .0400 20 | .031961 | .035 | .0350 | .0350 | .0351 | .03500| .0360 21 | .028462 | .032 | .0320 | .0310 | .0321 | .03150| .0320 22 | .025347 | .028 | .0280 | .0280 | .0290 | .02950| .0280 23 | .022571 | .025 | .0250 | .0250 | .0261 | .02700| .0240 24 | .020100 | .022 | .0230 | .0225 | .0231 | .02500| .0220 25 | .017900 | .020 | .0200 | .0200 | .0212 | .02300| .0200 26 | .015940 | .018 | .0180 | .0180 | .0194 | .02050| .0180 27 | .014195 | .016 | .0170 | .0170 | .0182 | .01875| .0164 28 | .012641 | .014 | .0160 | .0160 | .0170 | .01650| .0148 29 | .011257 | .013 | .0150 | .0150 | .0163 | .01550| .0136 30 | .010025 | .012 | .0140 | .0140 | .0156 | .01375| .0124 31 | .008928 | .010 | .0130 | .0130 | .0146 | .01225| .0116 32 | .007950 | .009 | .0120 | .0120 | .0136 | .01125| .0108 33 | .007080 | .008 | .0110 | .0110 | .0130 | .01025| .0100 34 | .006305 | .007 | .0100 | .0100 | .0118 | .00950| .0092 35 | .005615 | .005 | .0095 | .0095 | .0109 | .00900| .0084 36 | .005000 | .004 | .0090 | .0090 | .0100 | .00750| .0076 37 | .004453 | | .0085 | .0085 | .0095 | .00650| .0068 38 | .003965 | | .0080 | .0080 | .0090 | .00575| .0066 39 | .003531 | | .0075 | .0075 | .0083 | .00500| .0052 40 | .003145 | | .0070 | .0070 | .0078 | .00450| .0048 41 | | | | | | | .0044 42 | | | | | | | .0040 ————————+————————-+————————-+——————————+——————-+——————-+——————-+——————-

NOTE.—The sizes of wire are ordinarily expressed by an arbitrary series of numbers. Unfortunately there are several independent numbering methods, so that it is always necessary to specify the method or wire gauge used. The above table gives the numbers and diameters in decimal parts of an inch for the various wire gauges in general use.

=Wiring Terms.=—The various members of a complex wiring installation are designated feeders, sub-feeders, mains, branches, and taps.

A feeder is a stretch of wiring to which no connection is made except at its two ends.

A sub-feeder is of the same class as a feeder, but is distinguished either by being one of two or more connecting links between the end of a single feeder and several distributing mains, or by constituting an extension of a feeder.

A main is a stretch of wiring supplied from one or more feeders or sub-feeders and distributing current to a number of taps, or else to a number of branches.

A branch distributes current among a number of lamps, etc.

A tap almost invariably delivers current to a single lamp or other device.

Reference to fig. 826 will make these definitions clearer. This diagram is intended merely to illustrate the above definitions and does not represent any special plan of wiring.

The simplest possible wiring installation is one in which a single lamp or compact cluster of lamps is located at the end of a main, as shown in figs. 827 and 828. In such cases calculations are almost always unnecessary, for the reason that No. 14 wire, the smallest size allowed by the underwriters, will supply several lamps at a long distance (as interior wiring goes) with a very moderate drop. For example, if the three lamps shown at the end of the main in fig. 828, be of 16 candle power each, and the voltage of the supply circuit be 110 volts, a main of No. 14 wire would supply the lamps at a distance of 135 feet from the fuse block with a drop of only 1 per cent.

When the lamps are strung along the main, however, as in fig. 826, it is sometimes necessary to choose the size of wire with regard to the drop, and in order to do this the main must be measured for either "ampere feet" or "lamp feet."

=Wire Calculations.=—The problem of calculating the size of wire will be presented here in as simple a form as possible, with explanation of the various steps so that any one can understand how the formula is derived.

In determining the size of wire, there are four known factors which enter into the calculation, viz.:

1. Length of circuit in feet; 2. Maximum current in amperes; 3. Drop or volts lost in the circuit, in % of the impressed voltage; 4. Heating effect of the current.

The calculation is based on the mil foot, which as previously explained, is a foot of copper wire one mil in diameter and whose resistance is equal to 10.79 ohms at 75° Fahr.

The first step is to find an expression for the resistance of the wire which may be later substituted in Ohm's law formula. Accordingly, the resistance of any conductor is equal to its length in feet multiplied by its resistance per mil foot and the product divided by its area in circular mils, thus:

length in feet × resistance per mil foot resistance in ohms = ————————————————————————————————————————— circular mils

feet × 10.8 or ohms = ————————————- (1) circular mils

(calling the resistance per mil foot 10.8 instead of 10.79 to facilitate calculation).

LAMP TABLE FOR RUBBER COVERED WIRES

Showing the maximum number of 16 candle power 110 to 240 volt lamps in parallel that may be carried by the various sizes of wire without violating the underwriters' rules.

+——————————+———————+——————————————+————————————————+————————————-+ |Wire size |Amperes|3.1-watt lamps|3.5-watt lamps. |4-watt lamps.| |B. & S. | +——————————————+————————————————+————————————-+ | gauge | | At 110 220 | At 110 220 | 220 230 240 | | | | volts V. | volts V. | V. V. V. | +——————————+———————+——————————————+————————————————+—————————————+ |0000 | 210 | 462 924 | 412 825 | 722 754 787 | | 000 | 177 | 389 778 | 347 695 | 608 636 663 | | 00 | 150 | 330 660 | 294 589 | 515 539 562 | | | | | | | | 0 | 127 | 279 558 | 249 499 | 436 456 476 | | 1 | 107 | 235 470 | 210 420 | 367 384 401 | | 2 | 90 | 197 396 | 176 353 | 309 323 337 | | | | | | | | 3 | 76 | 167 334 | 149 298 | 261 273 285 | | 4 | 65 | 143 286 | 127 255 | 223 233 243 | | 5 | 54 | 118 237 | 106 212 | 185 194 202 | | | | | | | | 6 | 46 | 101 202 | 90 180 | 158 165 172 | | 8 | 33 | 72 145 | 64 129 | 113 118 123 | | 10 | 24 | 52 105 | 47 94 | 82 86 90 | | | | | | | | 12 | 17 | 37 74 | 33 66 | 58 61 63 | | 14 | 12 | 26 52 | 23½ 47 | 41 43 45 | | 16[3] | 6 | 13 .. | 11 .. | 20 21 22 | +——————————+———————+——————————————+————————————————+—————————————+

[3] This size can be used only in the shape of flexible cord.

Now, according to Ohm's law,

volts = amperes × ohms (2)

hence, substituting in (2) the value for the resistance in ohms, as obtained in (1):

feet × 10.8 volts = amperes × ————————————- circular mils

or using the usual symbols

feet × 10.8 E = I × ————————————- (3) circular mils

or expressed in words, formula (3) means that the volts lost or drop between the beginning and end of a circuit is equal to the current flowing through the circuit multiplied by the product of the conductors' length in feet multiplied by the resistance of one mil foot of wire, divided by the area of the conductor in circular mils.

LAMP TABLE FOR WEATHER PROOF WIRES

Showing the maximum number of 16 candle power 120 to 240 volt lamps in parallel that may be carried by various sizes of weather proof wire without violating the underwriters' rules.

+———————+————————+———————————————+———————————————+———————————————-+ |Wire |Amperes |3.1-watt lamps.|3·5-watt lamps.| 4-watt lamps. | |size | +——————————————-+——————————————-+————————————————| |B. & S.| | 110 220 | 110 220 | 220 230 240 | |gauge | | V. V. | V. V. | V. V. V. | +———————+————————+———————+———————+————————+——————+———————————————-+ | 0000 | 312 | 686 | 1372 | 612 | 1225 | 1072 1121 1170 | | 000 | 262 | 576 | 1152 | 514 | 1029 | 900 941 982 | | 00 | 220 | 484 | 968 | 432 | 864 | 756 790 825 | | | | | | | | | | 0 | 185 | 407 | 814 | 363 | 726 | 636 665 693 | | 1 | 156 | 343 | 686 | 306 | 612 | 536 560 585 | | 2 | 131 | 288 | 576 | 257 | 514 | 450 470 491 | | | | | | | | | | 3 | 110 | 242 | 484 | 216 | 432 | 378 395 412 | | 4 | 92 | 202 | 404 | 180 | 361 | 316 330 345 | | 5 | 77 | 169 | 338 | 151 | 302 | 264 276 288 | | | | | | | | | | 6 | 65 | 143 | 286 | 127 | 255 | 223 233 243 | | 8 | 46 | 101 | 202 | 90 | 180 | 158 165 172 | | 10 | 32 | 70 | 140 | 62 | 125 | 110 115 120 | | | | | | | | | | 12 | 23 | 50 | 101 | 45 | 90 | 79 82 86 | | 14 | 16 | 35 | 70 | 31 | 62 | 55 57 60 | +———————+————————+———————+———————+————————+——————+———————————————-+

Now, since the length of the circuit is given as the "run" or distance one way, that is, one half the total length of wire in the circuit, formula (3) must be multiplied by 2 to get the total drop, that is:

feet × 10.8 X 2 I × feet × 21.6 E = I × ——————————————- = ———————————————- (4) circular mils circular mills

Solving the last equation for the unknown quantity, the following equation is obtained for size of wire:

I × feet × 21.6 amperes × feet × 21.6 circular mils = ———————————————- = ————————————————————— (5) E "drop"

The following practical example is given to illustrate the application of the formula just obtained:

EXAMPLE.—What size wire should be used on a 250 volt circuit to transmit a current of 200 amperes a distance of 350 feet to a center of distribution with a loss of three per cent. under full load?

The volts lost or drop is equal to 250 × .03 = 7.5 volts.

=PROPERTIES OF COPPER WIRE=

+————————+————————+——————————+—————————————————————————————+———————————————————————-+ | Number |Diameter| Area in | Weight in pounds | Resistance at 68° Fahr.| |of gauge| in | circular |——————————————————————————————————————————————————————| |B. & S. | mils | mils | 1,000 feet| mile |feet per| 1,000 feet | mile | | | | | | | pound | | | +————————+————————+——————————+———————————+—————————————————+———————————————————————-+ | 0000 | 460 | 211,600 | 640.5 |3,381 | 1.561 | .04893 | .2583 | | 000 | 409.6 | 167,800 | 508 |2,682 | 1.969 | .06170 | .3258 | | 00 | 364.8 | 133,100 | 402.8 |2,127 | 2.482 | .07780 | .4108 | | 0 | 324.9 | 105,500 | 319.5 |1,687 | 3.130 | .09811 | .5180 | | | | | | | | | | | 1 | 289.3 | 83,690 | 253.3 |1,337 | 3.947 | .12370 | .6531 | | 2 | 257.6 | 66,370 | 200.9 |1,062 | 4.977 | .1560 | .8237 | | 3 | 229.4 | 52,630 | 159.3 | 841.1 | 6.276 | .1967 | 1.0386 | | 4 | 204.3 | 41,740 | 126.4 | 667.4 | 7.914 | .2480 | 1.3094 | | | | | | | | | | | 5 | 181.9 | 33,100 | 100.2 | 529.0 | 9.980 | .3128 | 1.6516 | | 6 | 162.0 | 26,250 | 79.46 | 419.5 | 12.580 | .3944 | 2.0824 | | 7 | 144.3 | 20,820 | 63.02 | 332.7 | 15.87 | .4973 | 2.6257 | | 8 | 128.5 | 16,510 | 49.98 | 263.9 | 20.01 | .6271 | 3.3111 | | | | | | | | | | | 9 | 114.4 | 13,090 | 39.63 | 209.2 | 25.23 | .7908 | 4.1754 | | 10 | 101.9 | 10,380 | 31.13 | 166.0 | 31.82 | .9972 | 5.2652 | | 11 | 90.74| 8,234 | 24.93 | 131.6 | 40.12 |1.257 | 6.6370 | | 12 | 80.81| 6,530 | 19.77 | 104.4 | 50.59 |1.586 | 8.374 | | | | | | | | | | | 13 | 71.96| 5,178 | 15.68 | 82.79| 63.79 |2.000 | 10.560 | | 14 | 64.08| 4,107 | 12.43 | 65.63| 80.44 |2.521 | 13.311 | | 15 | 57.07| 3,257 | 9.858 | 52.05|101.4 |3.179 | 16.785 | | 16 | 50.82| 2,583 | 7.818 | 41.28|127.9 |4.009 | 21.168 | | | | | | | | | | | 17 | 45.26| 2,048 | 6.200 | 32.74|161.3 |5.055 | 26.690 | | 18 | 40.30| 1,624 | 4.917 | 25.96|203.4 |6.374 | 33.655 | | 19 | 35.89| 1,288 | 3.899 | 20.59|256.5 |8.038 | 42.440 | | 20 | 31.96| 1,022 | 3.092 | 16.33|323.4 |10.14 | 53.540 | +————————+————————+——————————+———————————+—————————————————+———————————————————————-+

Substituting the given value in formula (5)

350 × 200 × 21.6 circular mils = —————————————————— = 201,600. 7.5

Diameter = 2 √201,600 = 449 circular mils or .449 in.

From the table (on page 731 or on page 742) the nearest (=larger=) size of wire is 0000 B. & S. gauge.[4]

[4] =CAUTION.=—The size thus obtained should be compared with the table of carrying capacity of wires as given on page 731 to see if the wires would have to carry more than the allowable current.

WIRING TABLE FOR LIGHT AND POWER CIRCUITS

===================+======================================================= VOLTS | PERCENTAGE OF LOSS ===================+======================================================= 2000 | 1.7 1.5 1.4 1.2 1.1 1.0 0.75 0.5 1000 | 3.4 2.9 2.7 2.4 2.2 2.0 1.5 1.0 500 | 6.5 5.7 6.2 4.8 4.3 3.9 2.9 2.0 220 | 13.7 12.0 11.0 10.3 9.3 8.3 6.5 4.4 110 | — — 20.0 18.5 17.0 15.4 12.0 8.4 52 | — — — — — — 22.4 16.1 ===================+======================================================= ACTUAL VOLTS LOST =========+=========+======================================================= Carrying | | Capacity | Size | 35 30 27.5 25 22.5 20 15 10 Amperes. | B. & S. | =========+=========+======================================================= 300 | 0000 | 345800 296400 271700 247000 222300 197600 148200 98800 245 | 000 | 274400 235200 215600 196000 176400 156800 117600 78400 215 | 00 | 217525 186450 170912 155375 139837 124300 93225 62150 190 | 0 | 172550 147900 135575 123250 110925 98600 73950 49300 160 | 1 | 136850 117300 107525 97750 87975 78200 58650 39100 135 | 2 | 108500 93000 85250 77500 69750 62000 46500 31000 115 | 3 | 86100 73800 67650 61500 55350 49200 36900 24600 100 | 4 | 68250 58500 53625 48750 43875 39000 29250 19500 90 | 5 | 54250 46500 42625 38750 34875 31000 23250 15500 80 | 6 | 43050 36900 33825 30750 27675 24600 18450 12300 60 | 8 | 26965 23130 21202 19275 17347 15420 11565 7710 40 | 10 | 16975 14550 13337 12125 10912 9700 7275 4850 30 | 12 | 10675 9150 8388 7625 6862 6100 4575 3050 22 | 14 | 6720 5760 5280 4800 4320 3840 2880 1920 5[5] | 16 | 4235 3630 3328 3025 2723 2420 1815 1210 ————————-+————————-+——————————————————————————————————————————————————————-

===================+===================================================== VOLTS | PERCENTAGE OF LOSS ===================+===================================================== 2000 | 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 1000 | 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 500 | 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 220 | 3.9 3.5 3.1 2.7 2.2 1.8 1.4 0.9 0.45 110 | 7.6 6.8 6.0 5.2 4.4 3.5 2.7 1.8 0.9 52 | 14.7 13.3 11.8 10.3 8.8 7.1 5.5 3.7 1.9 ===================+===================================================== ACTUAL VOLTS LOST =========+=========+===================================================== Carrying | | Capacity | Size | 9 8 7 6 5 4 3 2 1 Amperes. | B. & S. | =========+=========+===================================================== 300 | 0000 | 88920 79040 69160 59280 49400 39520 29640 19760 9880 245 | 000 | 70560 62720 54880 47040 39200 31360 23520 15680 7840 215 | 00 | 55935 49720 43505 37290 31075 24860 18645 12430 6215 190 | 0 | 44370 39440 34510 29580 24650 19720 14790 9860 4930 160 | 1 | 35190 31280 27370 23460 19550 15640 11730 7820 3910 135 | 2 | 27900 24800 21700 18600 15500 12400 9300 6200 3100 115 | 3 | 22140 19680 17220 14760 12300 9840 7380 4920 2460 100 | 4 | 17550 15600 13650 11700 9750 7800 5850 3900 1950 90 | 5 | 13950 12400 10850 9300 7750 6200 4650 3100 1550 80 | 6 | 11070 9840 8610 7380 6150 4920 3690 2460 1230 60 | 8 | 6939 6168 5397 4626 3855 3084 2313 1542 771 40 | 10 | 4365 3880 3395 2910 2425 1940 1455 970 486 30 | 12 | 2745 2440 2135 1830 1525 1220 915 610 305 22 | 14 | 1728 1536 1344 1152 960 768 576 384 192 5[5] | 16 | 1089 968 847 726 605 484 363 242 121 ————————-+————————-+————————————————————————————————————————————————————-

[5] NOTE.—In case a larger loss than any given in the table is required, proceed as follows:—Divide the ampere feet by 10 and then refer to column of Actual Volts Lost divided by 10, from which the size of wire is found as before.

RULE.—Multiply current in amperes by single distance and refer to the nearest corresponding number under column of actual volts lost, to find size of wire. It should also be noted that the underwriters prohibit the use of wire smaller than No. 14 B. & S. gauge, except as allowed for fixture work and pendant cord.

TABLE OF WIRE EQUIVALENTS

GAUGE NUMBER OF WIRES B. & S. 2 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16384

0000 0 3 6 9 12 15 18 21 24 27 30 33 36 39 000 1 4 7 10 13 16 19 22 25 28 31 34 37 40 _____ 00 2 5 8 11 14 17 20 23 26 29 32 35 38| 0+6 0 3 6 9 12 15 18 21 24 27 30 33 36 39| 1+7 1 4 7 10 13 16 19 22 25 28 31 34 37 40| 2+8 _____| 2 5 8 11 14 17 20 23 26 29 32 35 38|3+9 4+6 3 6 9 12 15 18 21 24 27 30 33 36 39|4+10 5+7 4 7 10 13 16 19 22 25 28 31 34 37 40|5+11 6+8 _____| 5 8 11 14 17 20 23 26 29 32 35 38|6+12 7+9 6 9 12 15 18 21 24 27 30 33 36 39|7+13 8+10 7 10 13 16 19 22 25 28 31 34 37 40|8+14 9+11 _____| 8 11 14 17 20 23 26 29 32 35 38|9+15 10+12 9 12 15 18 21 24 27 30 33 36 39|10+16 11+13 10 13 16 19 22 25 28 31 34 37 40|11+17 12+14 _____| 11 14 17 20 23 26 29 32 35 38|12+18 13+15 12 15 18 21 24 27 30 33 36 39|13+19 14+16 13 16 19 22 25 28 31 34 37 40|14+20 15+17 ____| 14 17 20 23 26 29 32 35 38|15+21 16+18 15 18 21 24 27 30 33 36 39|16+22 17+19 16 19 22 25 28 31 34 37 40|17+23 18+20 ____| 17 20 23 26 29 32 35 38|18+24 19+21 18 21 24 27 30 33 36 39|19+25 20+22 19 22 25 28 31 34 37 40|20+26 21+23 ____| 20 23 26 29 32 35 38|21+27 22+24 21 24 27 30 33 36 39|22+28 23+25 22 25 28 31 34 37 40|23+29 24+26 ____| 23 26 29 32 35 38|24+30 25+27 24 27 30 33 36 39|25+31 26+28 25 28 31 34 37 40|26+32 27+29 ____| 26 29 32 35 38|27+33 28+30 27 30 33 36 39|28+34 29+31 28 31 34 37 40|29+35 30+32 ____| 29 32 35 38|30+36 31+33 30 33 36 39|31+37 32+34 31 34 37 40|32+38 33+35 ____| 32 35 38|33+39 34+36 33 36 39|34+40 35+37 34 37 40|36+39 ___| 35 38|37+39 36 39|38+40 37 40|

=Ques. If the calculated size of wire be larger than any in the table how is the required area obtained?=

Ans. By using two or more smaller wires in parallel, whose combined area is equal to the required area.

To facilitate finding the equivalent sizes the above table of wire equivalents has been prepared.

=Ques. How is the table of wire equivalents used?=

Ans. To use the table, find in the vertical column at left the size of conductor desired; then follow along horizontally until the size of wire that is desired to use for the strands, and the corresponding number at top of column will give the number of strands of that size wire required.

=Ques. What is the significance of the zig-zag line?=

Ans. The figures below this line give the gauge numbers of two wires which will have the same conductivity as the corresponding conductor in left hand column.

TABLE OF CABLE CAPACITIES

=Incandescent Lamps on 660 Watt Circuits.=—The standard incandescent lamp is rated as equivalent to the light given by 16 candles, and may consume, according to type and make, from 50 to 56 watts, or from 3.1 to 3.5 watts per candle power. Therefore, a 660 watt circuit will carry thirteen 16 candle power 49.6 watt lamps, or eleven 56 watt lamps.

The proper size of wire for a 660 watt circuit will depend upon the voltage for which the lamps are made. For example: a 16 candle power lamp which consumes 56 watts on 110 volt circuit will take, 56 ÷ 110 = .5 or ½ ampere of current, while the same lamp, if made for 220 volts, will take only 55 ÷ 220 = .25 or ¼ ampere. Therefore, eleven 16 candle power 56 watt lamps will require a current of 5½ amperes at 110 volts, or 2¾ amperes at 220 volts.

According to the laws of resistance, the resistance of a round wire is inversely proportional to the square of the diameter, and if the circuit be taken at 100 feet, and the allowable percentage of drop at 1 volt, then according to formula, (5) on page 748, the wire required for a circuit carrying eleven 16 candle power 56 watt 110 volt lamps, will have a cross sectional area of,

5.5 × 100 × 21.6 ———————————————— = 11,880 circular mils. 1

while the same number of lamps on a 220 volt circuit will require wire having a cross sectional area of,

2.75 × 100 × 21.6 ————————————————- = 5,940 circular mils. 1

In order to conform to the underwriters' requirements, No. 8. B. & S. gauge, wire must be used for the circuit carrying the 110 volt lamps, while No. 12, B. & S. wire, would be sufficient for the 220 volt circuit.

In the case shown in fig. 829, the branch circuits A and B are identical, each supplying four 16 candle power lamps requiring 3.5 watts per candle power at 110 volts or carrying a load of 4 × 16 × 3.5 = 224 watts, = 224 ÷ 110 = 2 amperes.

The distance from the feeder junction or cut out to the electrical center of each branch circuit is 12.5 feet. The compact area of distribution permits the reduction of the loss of volts to 1 per cent, or 110 × .01 = 1.1 volts "drop." Then substituting in formula (5) on page 748 the values for amperes, feet and drop as obtained above

2 × 25 × 21.6 ————————————- = 981 circular mils, 1.1

or a value far below that of even No. 18 wire, B. & S. gauge (see table on page 731), but the smallest wire allowed by the underwriters for the mains A and B is No. 14, B. & S. gauge.

In calculating the size of wire for the feeders the total load must be considered. This is equal to eight 16 candle power lamps, requiring 3.5 watts per candle power at 110 volts = 8×16×3.5 = 448 watts = 4 amperes.

The distance from the entrance cut out to the feeder cut out is 200 feet. The drop should not be greater than 1.5 per cent. or 110×1.5 = 1.6 volts. Then,

4×200×21.6 —————————— = 10,800 circular mils 1.6

a value which indicates that No. 8 wire, B. & S. gauge, must be used for the feeders in order to keep the drop within the limit of predetermined value.

TABLE FOR TAPS, BRIDGES OR OTHER WIRES AT NEGLIGIBLE DROP

————————————————————————————————————————————————————————————————————————— Wire Nos. |0 |1 |2 |3 |4 |5 |6 | 7 |8 |10 |12 |14|16|18 ————————————————————————————————————————————————————————————————————————— Lamp Feet|52 v.| 300| 260|200|160|130|100| 80| 65| 50| 38| 24|15| 9| 6 |110v.|1,280|1,085|860|680|560|435|345|280|220|160|100|60|40|25 —————————————————————————————————————————————————————————————————————————

NOTE.—In using this table, it is only necessary to calculate the lamp feet of the tap and take the size of wire corresponding to the nearest greater number of lamp feet in the table. The lamp feet specified by this table should not be exceeded by more than 10 per cent. Thus, if a tap measure 108 lamp feet, in 110 volt lamps, No. 12 wire would be used. But if it measure 115 lamp feet, it would be advisable to use No, 10 wire.

=Constant Voltage Arc Lamp Circuits.=—The branch conductor should have a carrying capacity about fifty per cent. greater than the normal current required by the lamp, so as to provide for the heavy current required when the lamp is started. The underwriters prohibit the use of any size wire under No. 12 for parallel connected arc light circuits.

=Constant Current Series Arc Lamp Circuits.=—The wiring for series connected arc lamps should never be concealed nor encased unless requested by the electrical inspector.

For all interior wiring of this class, approved rubber covered wire should be used, and the wire should always be rigidly supported on porcelain or glass insulators which will hold the wires at a distance of at least one inch from the surface wired over. The wires on all circuits up to 750 volts, should be kept at least 4 inches from each other, and 8 inches apart on circuits of over 750 volts. No wires carrying a current having a pressure exceeding 3,500 volts should be carried into or over any building except central stations and sub-stations.

=Wire Calculations for Motors.=—The proper size of wire for a motor may be readily determined by means of the following formula:

H.P. × 746 × D × 21.6 circular mils = ————————————————————- (6) E × L × K

in which

H.P. = horse power of motor; 746 = watts per H.P.; D = length of motor circuit from fuse block to motor;

21.6 = ohms per foot run in circuit where wires are one mil in diameter; E = voltage at the motor; L = drop in percentage of the voltage at the motor; K = efficiency of the motor expressed as a decimal.

The average values for K are about as follows: 1 H.P., .75; 3 H.P., .80; 5 H.P., .80; 10 H.P. and over, 90 per cent.

EXAMPLE.—What is the proper size of wire for a 10 H.P. motor, run at 220 volts, allowable drop 2 per cent. on 200 foot circuit.

Substituting the given values in the formula on page 758:

10 × 746 × 200 × 21.6 Circular mils = ————————————————————- = 36,991. 220 × 4.4 × .9

The nearest larger value to this result, in the table of carrying capacities of copper wire (page 731), is 41,740, corresponding to No. 4 wire, B. & S. gauge.

In all cases the size of the wire thus formed should be compared with that allowed by the underwriters for full load current of motor, plus 25 per cent. of that current, and if the size calculated happen to be smaller than the allowable size, it should be increased to the latter, otherwise it will not pass inspection.

TABLE OF AMPERES PER MOTOR

——————————————————————————————————————————————————————————————————————————————- H.P. Per Cent. Eff. Watts Input 50 Volts 100 Volts 220 Volts 500 Volts ¾ 70 800 16 7 4 2 1½ 70 1600 32 15 7 3 3 75 2980 60 27 14 6 5 80 4660 93 42 21 9 7½ 85 6580 132 60 30 13 10 85 8780 176 80 40 18 15 85 13200 264 120 60 26 20 85 17600 352 160 80 35

25 85 21900 438 199 100 44 30 90 24900 498 226 113 50 40 90 33200 664 301 151 66 50 90 41400 828 376 188 83

60 90 49700 994 452 226 99 70 90 58000 1160 527 264 116 80 90 66300 1330 608 302 133 90 90 74600 1490 678 339 149

100 90 82900 1660 755 377 166 120 90 99500 1990 905 453 199 150 90 124000 2480 1130 564 248 ——————————————————————————————————————————————————————————————————————————————-

TABLE OF AMPERES PER DYNAMO

——————————————————————————————————————————————————————————————————————————————- Appx. Appx. K.W. 125 Vs. 250 Vs. 500 Vs. H.P. K.W. 125 Vs. 250 Vs. 500 Vs. H.P. 1. 8 4 2 1.3 30. 240 120 60 40. 2. 16 8 4 2.7 37.5 300 150 75 50. 3. 24 12 6 4.0 40. 320 160 80 53. 5. 40 20 10 6.7 50. 400 200 100 67. 7.5 60 30 15 10. 60. 480 240 120 80. 10. 80 40 20 13. 75. 600 300 150 100. 12.5 100 50 25 17. 100. 800 400 200 134. 15. 120 60 30 20. 125. 1000 500 250 167. 20. 160 80 40 27. 150. 1200 600 300 201. 25. 200 100 50 34. 200. 1600 800 400 268. ——————————————————————————————————————————————————————————————————————————————-

To determine the current required for a motor, as for instance, the 10 H. P. motor under consideration, multiply the horsepower by 746, and divide the product by the voltage of the motor multiplied by its efficiency as follows: (10 × 746) ÷ (220 × .90) = 37.6 amperes.

This value increased by 25 per cent. of itself (37.6 × .25 = 9.4 amp.) is equal to 37.6 plus 9.4 = 47 amperes. In the table of carrying capacities of copper wire (page 731), 46 amperes is given as the allowable carrying capacity of No. 6, B. & S. gauge, rubber covered wire; therefore No. 5 wire must be used.

=Calculations for Three Wire Circuit.=—In all cases of interior conduit work, and in most cases of inside open work, the main feeders from a three wire source of supply are installed on the three wire plan, and the sub-feeders and distributing mains, on the two wire plan, except where the application of the method necessitates the use of unwieldy sizes.

In laying out sub-feeders and mains, the total load, under normal operating conditions, should be divided as nearly as possible into two equal parts, and one part connected on each side of the neutral part of the entrance cut out, or the neutral bus bar of the switch board or panel board in an isolated plant, thus making the load on each side of the neutral wire of the feeder as near equal as possible.

Fig. 841 shows a three wire panel board with connection for 12 mains; those shown in solid lines as A, B, C, etc., being connected between the neutral wire and the negative wire of the feeder, and those shown by dotted lines as G, H, I, etc., being connected between the neutral wire and the positive wire of the feeder. The total load consists of ninety-one 16 candle power lamps, which are so distributed that the positive wire of the feeder carries the current for 46 lamps, and the negative wire, 45 lamps, the neutral wire carrying the difference or current for 1 lamp.

The proper size of wire for the mains may be calculated as already explained, but in calculating the outer wires of the three wire feeder, the neutral wire should be disregarded and the outer wires connected as a two wire circuit carrying the total load of 91 lamps at the over all pressure of 220 volts.

EXAMPLE.—Ninety-one 16 candle power lamps consuming 3.1 watts per candle power at a pressure of 110 volts, will require a current of

16 × 3.1 × 91 ————————————- = 41 amperes. 110

The distance from the entrance cut out to the main or feeder switch is 200 feet, then for a 2 per cent. drop, or a loss of 110×.02=2.2 volts, the cross sectional area of the wire will be,

41 amperes × 200 feet × 21.6 ———————————————————————————— = 80,509 circular mils. 2.2 volts

The joint resistance of the lamps on a three wire system, however, would be four times greater than on a two wire system; consequently the resistance of the outer wires of the feeder in this case will be four times greater for the same percentage of loss, and the cross sectional area of each of the outer wires will be, 80,509÷4=20,127 circular mils. According to the underwriters' rules, this value compels the use of No. 6 B. & S. gauge wire.

If the lamp voltage, 110 volts, be used, the two wire formula (5) given on page 748 must be modified to,

amperes × feet × 21.6 circular mils = ————————————————————- drop × 4

but if an over all voltage, (that is, the voltage between the outer wires), of 220 volts be used, the two wire formula does not require any modification.

The proper size of wire may also be calculated by means of the formula

drop ———————————————————————- = resistance per foot . . . . (1) 2 × distance × amperes

Example.—If in calculating a three wire feeder, the over all voltage be 220 volts, the drop = 4.4 volts, twice the distance = 400 feet, and the current = 20.5 amperes, then,

4.4 volts ————————————————————————- = .0005365 ohms per foot. 400 feet × 20.5 amperes

In the table of the properties of copper wire which gives the resistance of various sizes of wire, it will be noted that at all of the given temperatures No. 8 wire has a resistance greater than the value just calculated, therefore, No. 6 B. & S. gauge wire should be used for the outer wires of the feeder. In the table the resistance is given per 1,000 feet, hence it is only necessary to move the decimal point to obtain the resistance per foot.

If the calculation be based on the lamp voltage, 110 volts, the formula (1) must be modified to

drop × 4 ———————————————————————— = resistance . . . .(2) 2 × distance × amperes

In this case, drop = 2.2 volts, 2 × distance = 400 feet, and current = 41 amperes, then,

2.2 volts × 4 8.8 ———————————————————— = ———————— = .005364 ohms. 400 feet × 41 amp. 16,400

=Size of the Neutral Wire.=—In three wire circuits, the size of the neutral wire will depend to a great extent upon operating conditions. In the case of installations which occasionally have to be worked as two wire systems, the cross section of the neutral wire should be equal to the combined cross section of the two outer wires.

For interior wiring which must pass inspection, the neutral wire must always be twice the size of one of the outside wires. However, for general distribution, if it be reasonably sure that the system will always be worked three wire and that the drop in the two outer wires does not exceed 1½ per cent., the cross section of the neutral wire may be made smaller than that of one of the outer wires. In such a case the size of the neutral wire may be calculated for a maximum unbalancing of 25 per cent., when the current in one of the outer wires is 75 per cent. of the current in the other outer wire.

For instance, suppose that in a balanced system, the total load on each of the outer wires of a feeder be 211 amperes, and that on account of certain operating conditions, this load has to be divided unequally so as to put 242 amperes on one of the outer wires, and 181 amperes on the other outer wire. In this case the neutral wire will carry 60 amperes, or 25 per cent. of the current carried by the heavier outer wire.

If the drop in the outer wires exceed 1½ per cent., the cross section of the neutral wire will have to be equal to or larger than that of each of the outer wires, otherwise the drop in the neutral wire will exceed ½ volt with an unbalancing of 25 per cent.

Spotted a typo or a problem in this chapter? Tell us

XXXVIII. INSIDE WIRING

The term wiring is commonly understood to mean the methods employed in laying the conductors used for the transmission and distribution of electrical energy for lighting, power, and other purposes. Interior wiring, comprises the various methods of installing the conductors from the entrance devices in the walls or other parts of the buildings to the lamps, motors, and other electrical apparatus within the buildings.

The different methods of interior wiring may be conveniently grouped into the following general classes:

1. Open or exposed wiring; 2. Wires run in mouldings; 3. Concealed knob and tube wiring; 4. Rigid conduit wiring; 5. Flexible conduit wiring; 6. Armoured cable wiring.

=Open or Exposed Wiring.=—This method of wiring possesses the advantages of being cheap, durable and accessible. It is used a great deal in factories, mills and buildings where the unsightly appearance of the wires exposed on the walls or ceilings is of no consequence.

=Ques. What kinds of wires are suitable for this method of wiring?=

Ans. Either rubber covered or slow burning weather proof wire.

Rubber insulation should always be used where the wire is in a damp place, such as a cellar, and either weather proof or rubber insulation may be used to protect it against corrosive vapors.

=Ques. How are the wires installed?=

Ans. They are laid on some cornice, wainscoting, beam, or other architectural feature suitable for the purpose, by means of porcelain knobs and cleats, as shown in figs. 842 to 844.

Porcelain knobs should preferably be of the two piece type (fig. 863) in which the wire is carried between the upper and lower portions rather than being tied to a one piece knob with a tie wire as in fig. 860. Various porcelain knobs and cleats are shown in figs. 860 to 866.

=Ques. What are the disadvantages of open wiring?=

Ans. The wiring is not sufficiently protected from moisture, and the effects of fire which will destroy the insulation of the wires; it is also liable to mechanical injury.

=Ques. How far apart should the wires be placed?=

Ans. When installed in dry places and for pressures below 300 volts, the insulators should separate the wires 2½ inches from each other and ½ inch from the surface along which they pass. For voltages from 300 to 500, the wires should be separated four inches from each other and one inch from the surface along which they pass.

If the wiring be in a damp place, the wires should be at least one inch from the surface.

=Ques. How should wires be protected when run vertically on walls?=

Ans. They should be boxed in or run in a pipe as shown in fig. 854, the covering extending 6 feet above the floor.

When placed inside a box there should be a clearance of at least one inch around the wires; the box should be closed at the end as shown, and the wires protected where they enter the top with bushings. When the wires are placed in a pipe they should be first encased in a piece of flexible tubing that will extend from the insulator below the end of the pipe to the first one above it.

=Ques. What kind of incandescent lamp receptacle or wall socket is best adapted to exposed wiring?=

Ans. One which does not have exposed contact ears, an approved form being shown in fig. 859.

=Practical Points Relating to Exposed Wiring.=—Some of the principal points which should be remembered in this connection, together with the methods which may be applied to special cases, may be briefly stated as follows:

1. In interior wiring no wires smaller than No. 14 B. & S. gauge should be used, except as allowed by the underwriters, and no more than 660 watts should be allowed to a circuit.

2. Tie wires should have an insulation equal to that of the conductors which they secure.

3. In all cases, whether the wires be run on knobs, split insulators, or cleats, the wires should be supported at intervals of at least 4½ feet, and if exposed to mechanical injury, the supporters should be placed at closer intervals.

4. Wires run on bare ceilings of low basements, especially where they are liable to injury, should be protected by two wooden guard strips as shown in fig. 858. The protective strips should be at least ⅞ inch in thickness and slightly higher than the knobs, insulators, or cleats. The two circuit wires should not be run closer than 6 inches apart, and wires run near water tanks must be rubber covered so as to render them moisture proof.

5. Cleats should be used for the wiring of stores, offices, or buildings having flat ceilings, provided the wiring is installed in dry locations.

6. When the installation is exposed to dampness or acid fumes such as those developed in stables, bakeries, etc., the wires should run on knobs or split insulators, and should be rubber covered.

7. When wires are run at right angles to beams which are more than 4½ feet apart, a running board should be used and the wires cleated to it as shown in fig. 843. It is desirable, however, to avoid the use of running boards, whenever possible by running the wires parallel with the beams, thus reducing the cost of insulation.

8. In factories or other buildings of open mill construction, mains of No. 8 B. & S. gauge or larger wire, where they are not exposed to injury, may be placed about 6 inches apart and run from timber to timber, not breaking around, and may be supported at each timber only.

9. The best location for feeders is on the walls. In dry buildings the fire and weather proof wire can be used with safety; but covered wire must be used on buildings subject to any form of dampness. In all cases where feeders are run on the walls, they should be protected from mechanical injury by boxings at least 6 feet high on each floor. If floor switches be used, they may be mounted on the front of the boxing. In such cases, the holes in the boxing through which the wires pass to the switches should be provided with porcelain bushings.

10. The rosettes, receptacles, sockets, snap switches, etc., used in connection with exposed wiring should conform in all respects to the standards specified by the underwriters.

=Wires Run in Mouldings.=—Wooden mouldings are extensively used in connection with the wiring of stores, factories and buildings. The advantages of this type of construction are: simplicity, cheapness, and accessibility, and when the moulding is run straight and accurately mitred it makes a neat job. Any class of wooden moulding wiring, however, is not sufficiently impervious to moisture to render it suitable for use in damp places, and it is liable to be crushed or punctured. Furthermore, it is naturally very combustible. These difficulties are overcome to a certain extent by impregnating the moulding with some kind of moisture repellant, or by coating it both inside and out with water proof paint. Hardwood moulding should be used wherever possible, but soft wood moulding usually conforms much better to the wall line.

=Ques. For what conditions is wiring in mouldings suitable?=

Ans. It is adapted to installations in which the wires have to be laid after the completion of the buildings.

=Ques. Describe the moulding usually employed.=

Ans. It is made of hardwood in two pieces, a backing and cap, so constructed as to thoroughly encase the wire.

It should provide a one-half inch tongue between the conductors and a solid backing which should not be less than three-eighths of an inch in thickness under the grooves; it should be able to give suitable protection from abrasion.

The inside of the moulding and the cap must have at least two coats of waterproof material, or else the whole moulding must be impregnated with moisture repellant.

Only one conductor is placed in a groove.

The backing is secured to the walls or ceilings by means of wire nails. The wires are then laid in the grooves and the capping put in place and fastened by small brads.

The wires should be continuous, and only rubber covered wire should be employed.

Wooden moulding is made in a great variety of size and design. The general appearance of this type of moulding being shown in fig. 869.

=Ques. What other kind of moulding is used?=

Ans. Metal moulding, as shown in figs. 870 to 872.

Metal moulding is permitted on circuits requiring not more than 660 watts and where the pressure is not over 300 volts. Special fittings must be used with this class of moulding so that it is continuous both mechanically and electrically. The moulding should be grounded. The installation rules are practically the same as those governing conduit work.

=Ques. What is a kick box?=

Ans. A fitting, as shown in fig. 873, for protecting wires at the points where they enter or emerge from the floor.

=Ques. How is moulding work installed on brick or plaster walls which are liable to dampness?=

Ans. A backing board must be put on before the moulding is used.

=Ques. How should moulding be placed on a ceiling with respect to appearance?=

Ans. The appearance is improved if the moulding be carried through to the side of the room, even if part of it be not used. This will give a neat and finished appearance to the ceiling as shown in fig. 874.

Moulding should always be run in as inconspicuous position as possible, and if it be necessary to run it on the open ceiling, it should be arranged so as to form regular panels. Often it can be run so as to take the place of a picture moulding or as a part of the baseboard so that it becomes merely a part of the wooden trim of the building; and in certain cases it should be made of material to match the rest of the trim.

=Ques. What is the usual character of moulding work?=

Ans. Usually, a certain part of the work will be run as concealed, that is, inside the partitions, the wires being "fished" from the moulding to the outlet.

=Practical Points Relating to Wiring in Mouldings.=—The following practical points will be found useful in the satisfactory execution of any class of wiring with wooden moulding:

1. Wooden moulding should never be concealed, and should not be used in damp places or in buildings subject to acid fumes, such as ice houses, breweries, or stables, etc.

2. Wooden moulding selected for use should be formed of good straight stock and free from knots, knot holes and other imperfections. The saving effected in the lower cost of second hand moulding does not compensate for the additional cost increase in its working.

3. When wooden moulding is used in connection with solid pipe or flexible tube conduit, an iron box or conduitlet must be installed where the system of wiring changes, as shown in fig. 875. The pipe conduit is secured to the box by means of lock nuts, with porcelain bushings or flexible tubes protecting the wires. In all cases the loom should run up to the moulding.

=Arc Light Wiring.=—All wiring for high voltage arc lighting circuits should be done with rubber covered wire. The wires should be arranged to enter and leave the building through an approved double contact service switch which should close the main circuit and disconnect the wires in the building when turned "off" and be so constructed that they will be automatic in their action, not stopping between points when started and to prevent arcing between points under any circumstances, and should indicate plainly whether the current is "on" or "off." Never use snap switches for arc lighting circuits. All arc light wiring of this class should be in plain sight and never enclosed, except when required, and should be supported on porcelain or glass insulators which separate the wires at least one inch from the surface wired over. The wires should be kept rigidly at least eight inches apart, except, of course, within the lamp, hanger board or cut out box or switch. On side walls, the wiring should be protected from mechanical injury by a substantial boxing, retaining an air space of one inch around the conductors, closed at the top (the wires passing through bushed holes) and extending not less than seven feet from the floor. When crossing floor timbers in cellars or in rooms, where they are liable to be injured, wires should be attached by their insulating supports to the under side of a wooden strip not less than one-half an inch in thickness.

=Arc Lamps on Low Pressure Service.=—For this service there should be a cut out for each lamp or series of lamps. The branch conductors for such lamps should have a carrying capacity about 50 per cent. in excess of the normal current required by the lamp or lamps to provide for the extra current required when the lamps are started or should a carbon become stuck without over fusing the wires. If any resistance coils be necessary for adjustment or regulation, they should be enclosed in non-combustible material and be treated as sources of heat; it is preferable that such resistance coils be placed within the metal framework of the lamp itself. Incandescent lamps should never be used for resistance devices. These lamps should be provided with globes and spark arresters, as in the case of arc lamps on high voltage series circuits, except when the closed arc lamps are used.

4. Wooden moulding should never be run in elevator shafts, or shafts of any kind, and should never be run on the inner side of the outside walls of the buildings, as these locations are usually subject to dampness.

5. In laying out feeders it is usually cheaper to use iron conduit in a shaft, than to run moulding through the floor timbers.

6. When tapping outlets for feeder circuits, an iron outlet box with cover should be used, as shown in fig. 886. The one splice box is held up to the outlet box already installed by means of two long screws, and the loom is run right up to the moulding so as to leave no exposed wire.

7. Wherever fixture outlets are installed, a circular fixture block as shown in fig. 876 should be used, to give a good support for the fixture and to make a neat backing for the fixture canopy. The wires should be brought through the fixture without cutting and disfiguring the canopy.

=Concealed Knob and Tube Wiring.=—This method of wiring should be discouraged as far as possible, as it is subject to mechanical injury, is liable to interference from rats, mice, etc. As the wires run according to this method are liable to sag against beams, laths, etc., or are likely to be covered by shavings or other inflammable building material, a fire could easily result if the wires become overheated or short circuited.

Concealed knob and tube wiring is still allowed by the Underwriters, although many vigorous attempts have been made to have it abolished. Each of these attempts has met with strong opposition from electric light companies and contractors, especially in small villages and towns the argument being that it is the cheapest method of wiring, and if forbidden, many places which are wired according to this method would not be wired at all, and the use of electricity would therefore be much restricted, if not entirely dispensed with in such communities. This argument, however, is only a temporary makeshift obstruction against progress, and in the near future, no doubt, concealed knob and tube wiring will be forbidden by the underwriters.

=Ques. Describe the method of concealed knob and tube wiring.=

Ans. It consists in running the wires concealed between the floor beams and studs of a building, knobs being used to support the wires when run parallel to the beams or studs, and porcelain tubes, when run at right angles through the beams, or studs as shown in fig. 877.

In this method of wiring, usually nothing need be disturbed on the first floor as the various outlets can be reached from the basement and from the second floor.

For instance, if it be necessary to make an outlet for the center fixture in the parlor, a strip of flooring can be removed from the floor above so as to expose the beams. Then the wireman can bore two holes through each of the beams, insert porcelain tubes therein, slip the wires through the outlet and replace the strip of flooring.

Various simple methods may be employed for carrying the wires to the outlets on the side walls. For example: a small hole can be made in the wall, and the wire may be dropped through the spaces between the walls, or they may be pulled up from the basement by means of a cord lowered with a weight attached to its end. Outlets for switches and base receptacles may be provided for, in a similar manner.

=Ques. What are the advantages of concealed knob and tube wiring?=

Ans. Its cheapness, especially in wiring completed buildings, and the absence of any wires or casings on the walls or ceilings.

=Ques. What kind of wire must be used?=

Ans. Wire having an approved rubber insulating covering.

=Rigid Conduit Wiring.=—The installation of wires in conduits not only affords protection from mechanical injury, but also reduces the liability of a short circuit or ground on the wires producing an arc which would set fire to the surrounding material; the conduit being of sufficient thickness to blow a fuse before the arc can burn through the conduit.

=Ques. Describe the unlined type of conduit.=

Ans. It consists of an iron or steel pipe, similar in size, thickness, and in every other way to gas pipe, except that special precautions are taken to free it inside from scale or any irregularities; it is then coated inside with enamel, outside it is sometimes enameled and sometimes galvanized.

=Ques. Describe the lined type of conduit.=

Ans. It usually consists of a plain iron pipe lined with a tube of paper which has been treated with an asphaltic or similar compound; this paper tube is cemented or fastened to the inside of the iron pipe so that it forms practically an integral part of the same.

=Ques. What are the advantages of unlined conduit?=

Ans. It is cheaper, because having no lining a smaller size of conduit can be used for any given size of conductor; it is also cheaper to install, as it can be bent, threaded, and cut more readily than the lined conduit. Wires may be more easily inserted and withdrawn as the inside is smoother than that of the lined conduit.

NOTE.—Conduits for inside wiring which are subject to inspection, must have an inside diameter of not less than ⅝ inch. They must be continuous from outlet to outlet or to junction bores, and must properly enter and be secured to all fittings, and the entire system be mechanically secured in position. In case of service connections and main wires, this involves running each conduit continuously into a main cut out cabinet or gutter surrounding the panel board as the case may be. Conduits must first be installed without the conductors, and be equipped at every outlet with an approved outlet box or plate. Outlet plates must not be used where it is practicable to install outlet bores. The outlet box or plate must be so installed that it will be flush with the finished surface, and if this surface be broken, it shall be repaired so that it will not show any gaps or open spaces around the edge of the outlet box or plate. In buildings already constructed where the conditions are such that neither outlet box nor plate can be installed, these appliances may be omitted by special permission, providing the conduit ends are bushed and secured. It is suggested that outlet boxes and fittings having conductive coatings be used in order to secure better electrical contact at all points throughout the conduit system. Metal conduits where they enter junction boxes, and at all other outlets, etc., must be provided with approved bushings or fastening plates, fitted so as to protect wire from abrasion, except when such protection is obtained by the use of approved nipples, properly fitted in boxes or devices. Conduits must have the metal of the conduit permanently and effectually grounded. Conduits and gas pipes must be securely fastened in metal outlet boxes so as to secure good electrical connections. If conduit, couplings, outlet boxes or fittings having protective coating of insulating material, such as enamel, be used, such coating must be thoroughly removed from threads of both couplings and conduit and from surfaces of boxes and fittings where the conduit is secured in order to obtain requisite good connection. Where boxes used for centers of distribution do not afford good electrical connection, the conduits must be joined around them by suitable bond wires. Where sections of metal conduit are installed without being fastened to the metal structure of buildings or grounded metal piping, they must be bonded together and joined to a permanent and efficient ground connection. Junction boxes must always be installed in such a manner as to be accessible. All elbows or bends must be so made that the conduit or lining of same will not be injured. The radius of the curve of the inner edge of any elbow must not be less than three and one-half inches. Must have not more than the equivalent of four quarter bends from outlet to outlet, the bends at the outlets not being counted.

=Ques. What are the disadvantages of the unlined conduit?=

Ans. The Underwriters require the use of double braided conductors instead of single braided which are allowed for lined conduits.

=Ques. Where may unlined conduits be used?=

Ans. In buildings where the conduit is not liable to corrosive action.

=Flexible Conduit Wiring.=—Flexible conduits are used to advantage in many cases where rigid conduits would not be desirable. It is especially adapted to completed buildings where it is desired to install the wiring by "fishing" without greatly disturbing the walls, floors, or ceilings.

=Ques. How is a flexible conduit installed by "fishing"?=

Ans. It is "fished" under floors, in partitions between the floor and ceiling, by making pockets in the floors, walls or ceilings, say every 15 or 20 feet, and fishing through first a stiff metal wire called a "snake," and then attaching the conduit to same and pulling the conduit in place from pocket to pocket.

=Ques. How is the conduit fished on vertical runs?=

Ans. A chain or weighted string is used which is dropped from the outlet to the floor and its lower end located by sound of the chain end or weight striking the floor.

=Ques. What is the difference between flexible conduit and flexible tubing?=

Ans. Flexible conduits are made of metal while flexible tubing is non-metallic.

=Ques. Describe a flexible conduit.=

Ans. It is a continuous flexible steel tube composed of convex and concave metal strips, wound spirally upon each other in such a way as to interlock their concave surfaces.

=Ques. What are the advantages of this form of flexible conduit?=

Ans. It possesses considerable strength and can be obtained in long lengths (50 to 200 feet); elbow fittings are not required as the conduit may be bent to almost any radius. The fissures of the conduit provide some ventilation; this is an advantage in some places and a disadvantage in others.

=Ques. In what places are flexible conduits not desirable?=

Ans. In damp places.

=Ques. Why?=

Ans. Because of the fissures.

=Practical Points Relating to Inside Conduit Wiring.=—The following instructions apply to the installation of wiring in both rigid and flexible conduit:

1. All conduits should be made continuous from one junction or outlet box to another, or to the various fixtures. A conduit installation is made a complete system by the use of outlets, outlet boxes, switch or junction boxes, and panel boxes with doors and locks, which serve to thoroughly protect the circuit at all points.

2. In the installation of interior conduit wiring, the tubes are usually put in place as soon as the partitions of the buildings have been constructed. In non-fireproof buildings, the tubes are usually supported from the underside of the floor beams, but in fireproof buildings they are placed on top of the floor beams and under the floor as in fig. 902.

3. When conduit is used in damp places, lead encased wires should be used, and the wires drawn in very carefully so as to prevent any injury to the casings.

4. For wiring installations in buildings constructed entirely of reinforced concrete, the preliminary work should be laid out during the progress of the building operations so as to avoid, as much as possible, the necessity of drilling holes in the finished concrete work.

5. For concealed wiring, the location of all the outlets should be marked by sheet iron tubes large enough to hold the conduits. These tubes should be properly plugged, and set in the false work before the concrete is poured in. In a similar manner, threaded pieces of conduit of the proper size, should be placed in the false work for risers.

6. For exposed wiring on concrete walls and ceilings, suitable cast iron supports should be set in the moulds at regular intervals. When liberally used, these supports will also serve as good supports for other pipes.

7. Where a conduit line terminates on the outside of a building some suitable fitting such as a pipe cap should be used, as shown in fig. 903, to prevent the entrance of moisture into the conduit system. A variety of devices suitable for this purpose are available at supply houses; but those having porcelain covers which spread the wires the proper distance apart are the most satisfactory.

8. Where it is desirable or necessary to continue open wiring from conduits, or where the character of the wiring makes it necessary to bring the wires over from the conduit, as in an arc lamp, neat and safe work can be done by use of a suitable form of condulet as shown in fig. 904.

9. Where a conduit line terminates in a switch or panel box, the lining or casing of the panels should be of iron, and the conduit firmly secured to it so as to make good electrical contact. Vertical lines of conduit should be fastened to the wall or other supports in such a manner as to prevent the weight of the conduit coming on the panel box, and each length of conduit installed should be fastened so as to bear only its own weight. The best method of fastening conduit to brick walls is by the use of expansion bolts and screws. In the case of fire brick ceilings or other plastered walls, toggle bolts should be used. When conduits are run on wooden or iron beams, various kinds of pipe hanger may be employed.

10. There are numerous devices on the market for bending conduit for the making of elbows, offsets, etc., but the majority possess the disadvantage that the conduit must be taken to them to be bent. In the case of the smaller sizes, this difficulty is avoided by the use of some form of conduit bender such as shown in figs. 910 and 911.

11. In all cases, the interior diameter of the conduit installed should be amply sufficient to permit of the wires being drawn in easily, thus providing a substantial raceway for the conductors. The practice of pulling wires through conduit by means of a block and tackle is very objectionable. It is evident that if the wires be pulled in by the application of much force the insulation is very liable to become damaged; furthermore, much difficulty will be experienced in pulling them out again, especially in warm places where the heat tends to soften the lining of the conduit, and also the rubber covering of the wire. Powdered soapstone put in the pipe while the wires are being drawn in will lessen the friction and permit the wire to go in more readily.

=Armoured Cable Wiring.=—Where a conduit system cannot be conveniently installed, armoured cable is used. Armoured cable is made by winding steel strips over the insulated conductors, the latter being permanently retained inside the steel casing. Armoured cable is manufactured in long lengths, the actual lengths being determined by convenience in handling.

=Ques. What are the features of armoured cable?=

Ans. It is flexible and the conductors are well protected from mechanical injury. While this form of wiring has not the advantage of the conduit system—namely, that the wires can be withdrawn and new wires inserted without disturbing the building in any way whatever—yet it has many of the advantages of the flexible steel conduit, and it has some additional advantages of its own. For example, in a building already erected, this cable can be fished between the floors and in the partition walls, where it would be impossible to install either rigid conduit or flexible steel conduit without disturbing the floors or walls to an extent that would be objectionable.

=Ques. How should armoured cable be installed?=

Ans. It should be continuous from outlet to outlet, without being spliced and installed on the loop system. Outlet boxes should be installed at all outlets, although, where this is impossible, outlet plates may be used under certain conditions. Clamps should be provided at all outlets, switch boxes, junction boxes, etc., to hold the cable in place, and also to serve as a means of grounding the steel sheathing.

=Ques. Is armoured cable wiring expensive?=

Ans. It is less expensive than the rigid conduit or the flexible steel conduit, but more expensive than cleat wiring or knob and tube wiring, and is strongly recommended in preference to the latter.

Spotted a typo or a problem in this chapter? Tell us

XXXIX. OUTSIDE WIRING

In the equipment of lighting and power plants, the cost of the outside wiring represents a considerable proportion of the total investment, sometimes costing more than the engines, boilers and dynamos.

A thorough knowledge of outside wiring is therefore necessary to properly proportion and install the wires so that the system will prove economical and safe.

=Materials for Outside Conductors.=—Copper wire is now considered to be the most suitable material not only for the transmission of current for electric light and power purposes, but also for telegraph and telephone lines, in place of the iron wire formerly employed.

Hard drawn copper wire is used in outside construction, because its tensile strength ranges from 60,000 to 70,000 pounds or about twice that of soft copper. This is desirable to withstand the stresses to which the wire is subjected which, in the case of long spans, are considerable.

The table on the next page gives the tensile strength, in pounds per square inch of cross section, hard drawn copper wire of various sizes B. & S. gauge.

The metal aluminum possesses certain advantages as a material for overhead wires. Its conductivity is about .6 that of copper. The specific gravity of aluminum is about 2.7, while that of copper is 8.89, so that a given volume of copper will weigh 3.3 times more than an equal volume of aluminum, and copper wire of given length and resistance would be about twice as heavy as an aluminum wire of equal length and resistance.

There are several disadvantages, such as, low tensile strength, high electro-positive quality of the metal, higher electrostatic capacity, etc.

TENSILE STRENGTH OF COPPER WIRE

+——————————————-+————————————————+——————————————-+————————————————+ | Size of wire | Tensile | Size of wire | Tensile | | B. & S. gauge | strength, lbs. | B. & S. gauge | strength, lbs. | +——————————————-+————————————————+——————————————-+————————————————+ | 0000 | 9971 | 9 | 617 | | 000 | 7907 | 10 | 489 | | 00 | 6271 | 11 | 388 | | 0 | 4973 | 12 | 307 | | 1 | 3943 | 13 | 244 | | 2 | 3127 | 14 | 193 | | 3 | 2480 | 15 | 153 | | 4 | 1967 | 16 | 133 | | 5 | 1559 | 17 | 97 | | 6 | 1237 | 18 | 77 | | 7 | 980 | 19 | 61 | | 8 | 778 | 20 | 48 | +——————————————-+————————————————+——————————————-+————————————————+

=Pole Lines.=—In the majority of cases overhead conductors are supported by wooden poles. In tropical countries, however, such as India, Central America, etc., where wood is rapidly destroyed by the ravages of white ants and other insects, iron poles are almost exclusively used for telegraph, telephone, and other electric transmission lines. The form of iron pole generally adopted consists of tapering shells of sheet iron of convenient length, riveted together at their ends and set into cast iron base plates which are buried in the ground.

=Wooden Poles.=—On account of their size and straightness, various species of northern pine, cedar and cypress are especially suitable for large poles. Chestnut, which can be readily sawed and hewed is a very good material for smaller poles. Sawed redwood is extensively used in California.

=Preservation of Wooden Poles.=—The preservation of wooden poles employed in line work is a matter of importance. Decay of the pole at or near the soil line is caused primarily by various forms of bacteria or fungi, and in some cases by insects. Bacteria and fungi attack either dead or living timber. In the case of dead timber, such as that of poles, they attack the walls of the cells and cause the familiar rot or decay which eventually destroys the usefulness of the pole.

It is well known that the rapid multiplication or action of the bacteria and the growth of the fungi are induced by a certain per cent. of moisture and the heat of the sun, that is, the portion of the pole at or near the soil line is alternately moistened and dried. Therefore, in order to protect it against this action, it is necessary to sterilize the pole by the application of an antiseptic which will penetrate the pores of the wood.

=Preservation Processes.=—There are several processes which may be successfully employed for the preservation of poles or other exposed timber. The best known of these are the creosoting, burnettizing, kyanizing, carbolizing, and vulcanizing processes.

In England, creosoted poles showed no sign of decay at the end of 35 years of service. In the United States they have an average life of 22 years. In Europe impregnation with copper sulphate has been extensively used, but this impregnation must take place within a few days after cutting down the tree.

Uniformly good results have been obtained by impregnation with corrosive sublimate, involving simply immersion in the liquid from ten to fourteen days. German authorities state that the average life of such poles is about 17 years, compared with 14 years for natural or untreated poles.

The application of pitch and tar oftentimes results in more harm than good. It is authoritatively stated, however, that in Europe wooden poles are effectively protected by painting them with tar up to about 2 feet above, and down to about 1½ feet below the soil line. The painted parts of the pole are then covered with a cloth which after being nailed to the pole, is also painted with tar. Finally a zinc plated sheet of iron painted on both sides with tar, is placed around the cloth and tightened to the pole.

The saving due to the use of sterilized poles is 40 per cent. of the cost of unsterilized poles. The comparison is made on the following basis: Cost of pole, $5 each; sterilizing, $1.25; renewal of sterilized pole in 24 years, unsterilized pole, in 12 years.

=Methods of Setting Wooden Poles in Unsuitable Soil.=—In places where salt is plentiful and cheap, such as the Great Salt Lake region in Utah, it has been found that the liberal use of salt mixed with the dirt filling tamped in around the foot of the pole is very effectual in preventing decay below the soil line.

Where poles have to be planted in low, swampy ground, or where the climatic conditions are such that timber decays rapidly, it has been found advantageous to place the poles in concrete settings. This method is extensively employed in various parts of the Southern States, square poles being placed in settings about 7 feet deep and 3½ feet square. In very soft ground the employment of a concrete setting is sometimes impracticable. In such cases piles are driven deep into the soil, and the pole bolted to the part of the pile extending above the ground.

=Reinforced Concrete Poles.=—The strongest point in favor of concrete poles is their durability. Untreated wooden telephone and telegraph poles have to be replaced by new poles about every six or seven years, depending on the percentage of moisture in the soil, the drier the soil, the longer being the life of the pole. Concrete poles are not affected by soil conditions, and if properly made will last indefinitely.

One form of reinforced concrete pole consists of a skeleton frame work of four corrugated iron rods covered with ordinary concrete. The pole is octagonal in shape, 30 feet long, and provided with mortises for cross arms, the latter being fastened in place by means of iron bolts. It is stated that they are less expensive than pine poles, and that each pole can be manufactured at the point on the line at which it is to be installed or planted.

In Canada, reinforced concrete poles are made square on account of the ease of making, and also on account of the steel economy permitted thereby. All poles are made at the point of erection. They are moulded in wooden forms, in a horizontal position, the top side being left open and finished with a trowel. The concrete is composed of one part of Portland cement, two parts clean sharp sand, and four parts broken stone. A 35 foot pole for ordinary line work weighs about 2½ tons and a 50 foot pole about 5 tons.

=Cross Arms.=—The familiar cross arms for stringing wires are usually attached to the poles before they are erected. They are commonly made from yellow pine wood, generally 3¼ x 4¼ inches, and are freely coated with good mineral paint as a preservative. Attachment is made to the pole by cutting a gain one inch deep and of sufficient breadth to allow the longest side of the cross arm to fit accurately. It is then secured in place by a lag screw, with a square head, so that it may be driven into place with a wrench.

The cross arm is further secured to the pole with braces. These are flat strips of wrought iron or low carbon steel, 30 inches long, ¼ inch thick and 1¼ inches wide, according to standard specifications. Holes are bored at points one inch from either end, one for attaching to the pole, the other for attaching to the cross arm; two braces forming a triangle with the cross arm for the base and with the apex at the point of connection to the pole. Like all other iron work used on pole lines, the braces are carefully "galvanized," so as to stand three immersions of one minute each in a saturated solution of copper sulphate without showing copper deposits, the color being black at the completion of the test.

Before the cross arm is set in place the gain is carefully painted with white lead. As it is important that cross arms on a line of poles, particularly when there are several on each pole, should be at equal distances from the ground as well as being uniformly spaced, it is necessary that some measuring instrument should be used to accomplish this. Such an instrument is the ordinary template, which is a length of board carrying a pointed block at one end, to correspond exactly with the top of the pole, and also cross cleats nailed at precisely the same intervals below it as it is proposed attaching the cross arms. The template, laid upon a pole, shows where to cut the gains.

In planting the poles it is customary to so arrange them that the cross arms on alternate poles shall face in opposite directions, for the purpose of equalizing the strain on the line. On curves, however, all cross arms are placed on the side of the pole facing the middle of the curve.

=Ques. What provision is made for attachment of the wires?=

Ans. The cross arms are bored with holes for the insertion of the insulator pins, which are made of locust wood and threaded at the upper end to receive the glass insulator.

The cross arm is made of such a length as to accommodate the number of pins to be inserted. An arm for two pins is made three feet long, according to the standard usually followed, with holes for the pins at center points three inches from either end and a space of 28 inches between them in the center.

=Ques. How must electric light and power wires be placed when wired on telephone or telegraph poles?=

Ans. They must not be put on the same cross arm with the telegraph, telephone, or similar wires, and when placed on the same pole with such wires the distance between the two inside pins of each cross arm must not be less than twenty-six inches.

=Poles for Light and Power Wires.=—In selecting the style of pole necessary for a certain class of work, the conditions and circumstances should be considered. Poles may be divided into three classes, the size of wire to be carried being one of the important considerations.

First Class.—Main line of poles should range in length of from 30 to 35 feet with 6 inch tops. The height of trees, of course will have to be considered in many cases.

Second Class.—Town lighting by arc lights. All poles should have at least 6 inch tops. The corner poles should have 6½ inch tops, and wherever the cross arms are placed on a pole at different angles, the pole should have at least a 6½ inch top. A 30 foot pole is sufficiently long for the main line, but it would be advisable to place 35 foot poles on corners.

Third Class.—Where heavy wire, such as No. 00, is used for feeder wire, the poles should have at least 7 inch tops. Where mains are run on the same pole line the strain is somewhat lessened, and poles of smaller size will answer.

Cull Poles.—All poles that are smaller at the top than the sizes agreed upon, are troubled with dry rot, large knots and bumps, have more than one bend, or have a sweep of over twelve inches, should certainly be classed as cull poles. Specifications for electric light and power work should be, and in many cases are, much more severe than those required by telegraph lines. A cull pole, one of good material, is the best thing for a guy stub, and is frequently used for this purpose. A cedar pole is always preferable to any other, owing to the fact that it is very light in comparison to other timber, and is strong, durable, and very long lived.

Pole Setting.—In erecting poles, it seems to be the universal opinion of the best posted construction men that a pole should be set at least five feet in the ground, and six inches additional for every five feet additional length above thirty-five feet; also additional depths on corners. Wherever there is much moisture in the ground, it is of much value to paint or smear the butt ends of the pole with pitch or tar, allowing this to extend about two feet above the level of the ground. This protects the pole from rot at the base. The weakest part of the pole is just where it enters the ground. Never set poles further than 125 feet apart; 110 feet is good practice.

Painting.—When poles are to be painted, a dark olive green color should be chosen, in order that they may be as inconspicuous as possible. One coat of paint should be applied before pole is set, and one after pole is set. Tops should be pointed to shed water.

=Spacing the Poles.=—In general, the spacing of poles, like their dimensions, is regulated by the weight of the lines they are designed to carry—the heavier the lines the greater the number of poles. The spacing of poles also depends on their liability to injury from storms and wind in any given locality, and the nature of the service. Poles for a telephone line may be spaced twenty to fifty to the mile—that is, from about 260 to 100 feet apart.

=Erecting the Poles.=—Since each pole on a properly constructed line is sawed to the right length and carefully shaped before it is finally inserted in the ground, it is necessary that the holes be dug to as nearly the required depth as possible. Holes for poles are dug very little wider than their diameter at the butt, and the depth is usually computed according to the nature of the soil and the weight of the proposed line. Excavation, while sometimes accomplished with patent post hole augers, or even dynamite, is usually done with a long handled digging shovel, and the earth removed with a spoon shovel, such as is shown in fig. 921.

Wherever required by the nature of the soil, a "grouting" or foundation of loose stones is formed in the bottom of the hole, and, in marshy or springy ground, a base of concrete and cement is laid, with filling of the same material around the pole, when raised.

=Ques. How are the poles transported to the holes?=

Ans. They are rolled or carried on hooks similar to those used for carrying blocks of ice, except for a long handle for lifting the load at either side.

=Ques. How are the poles raised and placed in the holes?=

Ans. A piece of timber is inserted in the hole as a slide to prevent crumbling of the earth as the pole is slid into place. The end is raised by hand sufficiently to allow the "dead man," or pole hoist, to be placed beneath, and this is moved along regularly as the pole is lifted with pike poles, until it slides into place through the force of gravity.

This accomplished, the pole is held in a perpendicular position by pikes in the hands of assistants, or planted in the ground around it, while the earth is carefully shoveled into the hole and thoroughly packed down with a tamper.

=Guys for Poles.=—Where poles are subject to severe strains which might throw them down and break the wires, guy cables are largely employed, these being attached near the top and secured either to the base of the next pole, to a suitable guy stub or post, or to a guy anchor, which is buried about eight feet in the earth and held down by stones and concrete.

=Ques. Under what conditions is it necessary to guy poles?=

Ans. They are guyed at corners in order to thoroughly secure the poles so that no strain may come on the cornerwise span. It is also necessary to guy a line where it is to be deflected from a straight path, as when rounding a hill, water course or railway curve, in order to neutralize the pull of the wires, tending to incline the poles toward the center on which the arc is described; also when descending a hill.

=Guy Stubs and Anchor Logs.=—In guying a line under such conditions, each pole is connected by a suitable cable to a guy post or "stub," or to an anchor log. Standard rules specify stubs between 18 and 25 feet, with exact limits as to circumference measures at the top and at a point 6 feet from the butt, according to the kind of wood used.

Thus, guy stubs of cedar or juniper, either 18 or 25 feet in length, must have a circumference of 22 inches at the top and of 32 inches 6 feet from the butt; stubs of chestnut must measure 24 inches in the first, and 34 in the second, while those of cypress require 28 in the first, and in the second, 39 inches for an 18 foot length, and at least 41 for a 25 foot length. In planting guy stubs the same rules are followed as hold for poles, every means being adopted to promote security of construction except that the stub is raked or tilted against the strain on the guy cable.

=Wiring the Line.=—The erection and guying of the poles of a line as well as the attachment of the cross arms and the screwing on of the insulators are completed before the stringing of the line is begun. It is particularly essential that the pull on poles of a given line be accurately calculated, and that each one be guyed accordingly before the line is strung, in order to avoid the danger of an undue strain upon the wires in attempting to rectify the condition afterward. It is a good working rule that the wires should be subjected to no stress other than the weights of their own spans after they have been attached to the poles.

=Ques. Describe how the wires are strung.=

Ans. In stringing the lines, either one or the full number of wires may be put up at the same time. When one line only is to be strung, the operation consists simply in reeling the wire and running it off from a hand reel, such as is shown in fig. 953 or 954. At each pole the wire is drawn up to its place, pulled out to the desired tension, and attached to the insulator.

In the operation of stringing a number of lines at once, the method is different. The reels are placed at the beginning of a section, each wire being inserted and secured through a separate hole in a board, which is perforated to correspond with the spacing of the insulators on the cross arms. A rope is then attached to this running board, which is drawn by a team of horses through the stretch to be wired, being lifted over each pole top in turn. When a certain length has thus been drawn out the wires are drawn to the required tension between each pair of poles and secured to the insulators.

=Ques. How much tension must be put upon the wires?=

Ans. In applying tension to the wires as they are strung on the poles, it is the rule to allow some sag. The amount of sag to be allowed varies with different line hangers.

A typical case quoted by one or two authorities gives a sag of four inches at the center of each 130 foot span for a given size of wire, at a given temperature. A more general rule is to make the tension on a wire as it is drawn up between each pair of poles equal to one-third of its breaking weight. Thus No. 10 B.& S. gauge, would be drawn to about 163 pounds, and No. 12 to about 102 pounds. The temperature at the time of stringing and the distance between the poles are, however, important considerations in applying tension and allowing for sag. Thus, one construction company specifies a dip of 10 inches in summer and 8 inches in winter for spans of 130 feet, or 40 poles to the mile. Several authorities specify figures about as given in the above table for No. 14 iron or copper wire.

SAG TABLE

+——————+————————————————————————————-+ | | Temperature Fahr. | | Span +————————-+————————-+————————-+ | in | 30° | 60° | 80° | | Feet +————————-+————————-+————————-+ | | Sag in Inches | +——————+————————-+————————-+————————-+ | 75 | 1¾ | 2½ | 3⅛ | +——————+————————-+————————-+————————-+ | 100 | 3 | 4¼ | 5⅜ | +——————+————————-+————————-+————————-+ | 130 | 5⅛ | 7 | 8⅝ | +——————+————————-+————————-+————————-+ | 150 | 6¾ | 9 | 11¼ | +——————+————————-+————————-+————————-+

=Ques. How is the wire drawn out?=

Ans. In drawing out the wire, it is customary to use a wire clamp, or "come along." This tool is attached to a block and tackle, or drawn in by hand, and, as soon as the proper force has been applied, the wire is held, while the lineman secures it to the insulator.

Another contrivance for this purpose is the pole ratchet, by which the wire is drawn tight and held until attached to the pole.

=Ques. How are the wires attached to the insulators?=

Ans. An approved method is shown in figs. 959 and 960. Standard rules specify that all wires shall be tied to the side of the insulators toward the pole, except on the insulators next to the pole, where they are to be attached on the opposite side. On curves, however, it is required that all wires shall be arranged so that the strain shall be against the insulator and not on the wire.

=Ques. How are the wires spliced?=

Ans. There are several methods of splicing wires. Fig. 961 shows the American wire joint, and fig. 963 the McIntire sleeve joint. In making a joint, the two ends are gripped by come alongs and drawn up to the proper tension with tackle as shown in fig. 958. The joint is then made as shown in the illustrations.

=Transpositions.=—In some classes of circuit, as for instance telephone lines, the current is often seriously affected by electrostatic induction from other lines, and also from power circuits, owing to the fact that the surfaces of the wires form, as it were, so many charging plates of an electrical condenser, with the intervening air as the insulating layer or dielectric.

The telephonic current changes the pressure of its own charging surface as frequently as it alternates, and this fact in itself is amply sufficient to account for a vast weakening of the current before it reaches its destination. The only practicable method of overcoming this annoyance in pole lines is by the arrangement known as "transposition," which is, briefly, the practice of regularly shifting the relative position of the two limbs of each circuit as regards other wires in the same pole system, as shown in fig. 965.

For short lines and pole systems with only a few wires it is not necessary to transpose very frequently. On longer lines it has been found amply sufficient to transpose once every quarter mile; that is to say to change the relative position of the wires of the different circuits at posts situated about that distance apart. This does not mean, however, that each pair of wires is transposed so often, but that on ordinary sized systems, the transposition of some one circuit is amply sufficient to secure balanced relations and effectually counteract the effects of cross induction. It is a matter which must be carefully calculated and planned in each particular instance in order to secure the best advantages.

=Insulators.=—Glass and porcelain are employed almost universally for supporting overhead wires. Insulators made of these materials are superior to those made of other material such as hard rubber, or various compounds of vegetable or mineral matter, with the exception perhaps of mica insulators used on the feeders of electric railway lines.

Glass insulators are generally used on low tension lines, and porcelain insulators on high tension lines, the latter type being usually stronger and less brittle. Porcelain is more expensive than glass, and its opacity prevents the detection of internal defects which would be readily observed through glass.

=Ques. What is a petticoat insulator?=

Ans. An insulator which has one, two or three deep flanges or "petticoats" around the base for the purpose of increasing the leakage path from the line to the pin.

Both glass and porcelain insulators may be the double or triple petticoat type which may be cast or moulded solid, or made in two or more parts which are subsequently cemented together.

=Service Connections and Loops.=—Whenever it is necessary to tap an overhead conductor for service connection, the method of connection will depend upon the character of the circuit. In the case of a parallel circuit, an extra insulator must be placed on the cross arm so as to prevent the service main putting a side strain on the main line conductor. In the case of a series circuit the main line conductor is usually dead ended at the nearest pole and a loop taken to the point of service, as shown in fig. 972.

=Ques. What are service wires?=

Ans. Wires which enter a building.

Spotted a typo or a problem in this chapter? Tell us

XL. UNDERGROUND WIRING

In large cities, the best method of running wires for all varieties of electrical power transmission is to place them underground. Many city authorities have made this method of wiring compulsory by law, because of the difficulty in approaching a burning building, the danger from crossed and falling wires, and the disfigurement of the streets where there is a network of overhead wires.

The expense of installing an underground system is very great in comparison with that of overhead construction, but the cost of maintenance is much less and the liability of interruption of service greatly reduced.

=Underground Systems.=—An underground system of electrical conductors is composed of three essential elements:

1. The conductor itself, which is almost invariably of copper;

2. The insulation, which is either in the form of a complete covering of insulating material, or simply insulated supporting points;

3. The tube or conduit, which constitutes the mechanical protection against the effects of the severe shocks, weather conditions, etc., to which the system is naturally exposed.

The various underground systems may be divided into three classes:

1. Lead encased cables laid directly in the ground; 2. Solid or built in systems; 3. Drawing in systems.

=Ques. What may be said of the first mentioned construction?=

Ans. Where cables are laid directly in the ground, the metallic covering, consisting usually of a lead tube, which is placed over the insulation is depended upon for mechanical protection. Such cables are largely used for short private lines and the first cost is less than that of the others, but in case of repairs it has to be dug up.

=Ques. Describe the drawing in system.=

Ans. In this construction the cables are drawn in after the conduits are built. The conduit of the drawing in system may consist of various forms of pipe or troughs of iron, earthenware, concrete, wood or fibre, while those of the solid or built in systems are composed of either iron tubes or concrete trenches.

=Conduits.=—The principal qualifications of a good conduit are freedom from disintegration by the action of fire, water, acids, alkalies, or electrolysis; second, a smooth interior surface so as to permit of the easy drawing in of the cables; and third, a design which will permit of its economical installation in crowded streets. There are numerous kinds of conduit of which may be mentioned:

1. Vitrified clay pipe conduits; 2. Vitrified clay or earthenware trough conduits; 3. Concrete duct conduits; 4. Wooden duct conduits; 5. Wooden built in conduits; 6. Wrought iron or steel pipe conduits; 7. Cast iron pipe and trough conduits; 8. Fibre conduits.

=Vitrified Clay Pipe Conduit.=—Various forms of vitrified clay conduit appear to possess the qualifications, desirable in underground construction, to a higher degree than any other type. They are made in both single and multiple duct, as shown in fig. 975, the single type being about 3½ inches in diameter, or 3½ inches square, and 18 inches long. Multiple conduit is made in two, three, four, six and more sections, ranging from 2 to 3 feet in length.

=Ques. For what conditions is the single conduit especially adapted?=

Ans. It is most suitable for use where the sub-surface conditions are characterized by a great crowding of gas, water, and other pipes, as the conduits can be divided into several layers so as to cross over or under such pipes, and many other sub-surface obstructions which are present in the streets of large cities and towns.

=Ques. What are the features of the multiple duct conduit?=

Ans. It can be laid somewhat cheaper than the single duct type, especially in lines of about two to four ducts; it is, therefore, most suitable for use in outlying communities where the streets are comparatively free from many sub-surface obstructions.

=Ques. How is the conduit laid?=

Ans. In laying conduit, a trench is dug, usually sufficiently wide to allow the placing of three inches of concrete on each side of the ducts, and sufficiently deep to hold at least thirty inches of concrete on top of the upper layer of concrete forming the conduit, and to allow for three inches of concrete in the bottom. The trench is graded from some point near the middle of the block to the manhole at each intersection, or from one manhole to the next manhole, at a gradient not less than 2 inches to 100 feet.

=Ques. How are single duct conduits laid?=

Ans. The tiles of the several ducts are placed close together, and the joints plastered and filled with cement mortar consisting of one part of Portland cement to one part of sand. When the conduit is being laid, a wooden mandrel about four or five feet long, three inches in diameter, and carrying a leather or rubber washer from three to eight inches larger at one end is drawn through each duct so as to draw out any particles of foreign matter or cement which may have become lodged in the joints, and also to insure good alignment of the tiles, as shown in fig. 977.

Single duct conduits are usually laid by bricklayers. This fact accounts for the somewhat greater cost of the single over the multiple conduit which is usually laid by ordinary laborers. One good brick-layer and helper, however, will lay from 200 to 300 feet of single duct conduit per hour.

Practically the same standard of construction is maintained on all conduit lines from two ducts up to twenty-five ducts, as many of the smaller lines may extend for miles into the outlying districts, and contain transmission lines of the maximum working voltage.

=Vitrified Clay or Earthenware Trough Conduit.=—It consists of troughs either simple or with partitions as shown in fig. 976. They are usually made in tiles 3 or 4 inches square for each compartment, with wall about one inch thick. The length of the tiles ranges from two to four feet. Each of the two foot form duct troughs weighs about 85 pounds. When laid complete, the top trough is covered with a sheet of mild steel, about No. 22 gauge, made to fit over the sides so as to hold it in position, and then covered over with concrete.

=Joints in Multiple-duct Vitrified Clay Conduit.=—In laying multiple duct earthenware conduit, the ducts or sections are centered by means of dowel pins inserted in the holes at each joint, which is then wrapped with a six inch strip of asphalted burlap, or damp cheese cloth, and coated with cement mortar as shown in fig. 978. Economy of space and labor constitutes the principal advantages derived from the use of multiple duct conduit.

=Concrete Duct Conduits.=—These are usually constructed by placing collapsible mandrels of wood or metal in a trench where the ducts are desired and then filling the trench with concrete. After the concrete has solidified, the mandrels are taken out in pieces, leaving continuous longitudinal holes which serve as ducts. Some builders produce a similar result by placing tubes of sheet iron or zinc in the concrete as it is being filled into the trench. These tubes have just enough strength to withstand the pressure to which they are subjected, and are, therefore, very thin and liable to be quickly destroyed by corrosion, but the ducts formed by them will always remain unimpaired in the hardened mass of concrete.

=Wooden Duct Conduits.=—In this type of conduit, the ducts are formed of wooden pipe, troughing, or boxes, and constitute the simplest and cheapest form of conduit. A pipe conduit consists of pieces of wood about 4½ inches square, and three to six feet long, with a round hole about three inches in diameter bored through them longitudinally. As shown by fig. 979 a cylindrical projection is turned on one end of each section, which, when the conduit is laid fits into a corresponding recess in one end of the next section. The sections are usually laid in tiers, those of one tier breaking joint with those of the tiers above or below.

The trough conduit consists of ducts about 3 inches square made of horizontal boards and vertical partitions, usually of yellow pine about one inch in thickness. This form of conduit can be laid in convenient lengths of 10 or 12 feet, or it can be built along continuously.

=Ques. What is the objection to the use of wood for conduits?=

Ans. The decay of the wood tends to form acid which corrodes the lead sheath of the cable.

=Ques. How can this be prevented?=

Ans. The decay of the wood can be prevented to a certain extent by the application of sterilizing processes, thereby preserving it in fairly good condition for about ten to fifteen years.

=Ques. For what service is wooden conduit best adapted?=

Ans. For temporary installations which will be discontinued before the wood decays.

=Wooden Built-in Conduits.=—Within recent years several forms of wooden built-in conduit have been designed and successfully used for permanent work. They possess several advantages over any of the duct systems, the chief of which are high insulating quality, the capability of using bare wire and rods for underground conductors, and reduced cost. An approved form of wooden built-in conduit is shown in fig. 980.

=Ques. How are wooden built-in conduits installed?=

Ans. A wooden trough is laid in a trench about 18 inches deep. Porcelain carriers as shown in figs. 981 and 982 are placed in the trough at intervals of 4 to 5 feet, to act as bridgework for supporting the conductors. This bridgework is placed on and is surrounded by impregnated felt or similar material, and the spaces between the carriers, after the conductors have been placed in position on them, is filled with voltax, which hardens rapidly and forms a solid insulating material throughout the conduit.

=Wrought Iron or Steel Pipe Conduits.=—These are formed of pipes similar to gas or steam pipes, with screw or other connections. They are laid either simply in the earth, or in hydraulic cement, and are the strongest and one of the most satisfactory forms of underground conduit. An appropriate standard of this kind of work is shown in fig. 983.

=Ques. What is the ordinary method of construction?=

Ans. A trench, the width of which will depend upon the number of pipes to be laid, is first dug in the ground, and after its bottom has been carefully leveled, is braced with side planking and filled to the depth of two to four inches with a layer of good concrete, consisting of two parts of Rosendale cement, three parts of sand, and five parts of broken stone capable of passing through a one and one-half inch mesh. This concrete is well secured in place and forms the bed for the lowermost layer or tier of pipes. Ordinary wrought iron pipe is employed, in 20 foot lengths about three to four inches in diameter, depending upon the size and number of cables they are intended to carry. After the last tier of pipes have been put in place, and a layer of concrete from two to four inches placed over it, a layer of two inch yellow pine planking is laid over the whole.

The pipe connections consist of a taper screw thread coupling which can be easily made up as the pipes are laid, and which forms a tight joint.

The pipes in each tier are usually laid from ½ to ¾ of their diameter apart, and when the first tier is in place, the spaces between and around the pipes are filled in with concrete which is carried up over the pipes to a depth of about one-half a diameter to form the bed for another tier of pipes.

=Ques. What is the principal object of the top covering of planks.=

Ans. To protect the conduit against the tools of workmen making later excavations.

Practical experience shows that workmen will dig through concrete without stopping to investigate as to the character of the obstruction, but under similar circumstances, will invariably turn away from wood.

=Ques. How are the pipes treated before being laid?=

Ans. They are dipped in tar to protect the outside surface from rust.

=Ques. What is the most satisfactory form of lined iron pipe?=

Ans. Pipe lined with cement. The internal surfaces of these pipes are usually covered with a lining of pure Rosendale cement about ⅝ inch thick and containing no sand. The internal surface of the cement lining does not offer much friction to the introduction or withdrawal of the conductors.

These pipes are laid in cement or concrete in the same manner as plain iron pipe, and are given a coating of tar on the outside to prevent rusting.

=Cast Iron Pipe and Trough Conduit.=—Cast iron pipe for underground conduits is similar to ordinary wrought iron pipe, except that it is thicker. The additional thickness is necessary to make the strength equal to that of wrought iron; it is therefore heavier to handle and more expensive.

=Ques. Describe a cast iron trough conduit.=

Ans. It consists of shallow troughs of cast iron in six foot lengths, laid directly in the earth so as to form a system of continuous troughing in which the conductors are placed and then covered over by cast iron covers which are bolted to the trough.

=Ques. What advantages does this form of conduit possess over the duct type?=

Ans. First, the cables can be laid directly in place, thus eliminating any chance of injury during the process of drawing in, and second, the cables are easily accessible at any point by simply removing one or two of the sectional cast iron covers, thus permitting of their being readily inspected and repaired.

Branch connections can be made with greater facility than in the case of any duct system, so that it is especially suitable for distribution systems were it not for the fact that it is so expensive as to be practically prohibitive.

=Fibre Conduits.=—This form of conduit consists of pipes made of wood pulp impregnated with a bituminous preservative and insulating compound. These pipes are laid in concrete in a manner similar to iron pipe. Fibre conduits are made in sizes ranging from 1 inch to 4 inches in diameter and from 2½ to 5 feet in length, with walls ranging from ¼ to ½ inch in thickness.

=Ques. Name the three types of fibre conduit.=

Ans. The socket joint type, as shown in fig. 984, the sleeve type, fig. 985, and the screw joint type, fig. 986.

=Ques. What is the usual method of laying the socket joint type of fibre conduit?=

Ans. After the trench has been dug to the required width and depth, depending upon the number or pipes to be placed in a tier and the number of tiers, a bed of concrete about 3 inches deep is placed on the bottom and a line drawn on one side for the alignment of the first line of pipes. The other lines of pipe or ducts are laid parallel to the first line, and are separated from it and from each other by means of ¼ inch or ½ inch wooden or iron pegs. The pipes are well grouted and covered with a layer of concrete to the depth of ¼ or ½ inch, and the next tier laid in place in the same manner. When the final tier of pipes has been installed, it is covered with a layer of concrete about 2 to 3 inches deep.

=Ques. What is done when it is necessary to cut a length of pipe to break joints, or to enter a manhole?=

Ans. The remaining part of the length may be utilized by using a fibre conduit sleeve having an inside diameter ½ inch greater than the pipe being used on the system.

These sleeves are furnished by the manufacturers at a nominal charge per foot. They are about four inches in length and fit over the ends of the abutting pipes, so that they make tight joints and give perfect alignment.

Although its employment is not permitted where fireproof regulations are in force, fibre conduit is now being extensively used in other places, and is giving satisfactory service. It is not affected by moist earth and is impervious to the action of acids, alkalies, and gases. As it is not subject to expansion and contraction, leakage is practically eliminated, and since it is a very good insulator, troubles due to stray currents are reduced to a minimum. It is extremely light, comparatively non-breakable, and can be accurately laid at the rate of 12,000 duct feet per day by a gang of common laborers, consisting of two layers and three helpers.

=Edison Tube System.=—Of the various built in or solid underground conduit systems other than those already described under wooden conduit systems, the most satisfactory are the Edison tube system, the Crompton naked conductor system, the Kennedy system, which is a modification of the Crompton and the Callender systems.

=Ques. Describe the Edison tube system.=

Ans. It consists of a series of iron tubes or pipes containing one or more copper conductors which are placed therein before each complete section or pipe leaves the factory, so that they only need to be joined together to form a continuous line of underground conduit with conductors in place. The arrangement of wires and the details of the Edison tube system are shown in figs. 987 to 989.

=Underground Cables.=—Electric light and power cables for use in conduit may be divided into two classes: moisture proof, and non-moisture proof, according to the character of the insulator. In the moisture proof cables, the insulation consists of some form of rubber, or of bitumen, and a metal sheath or covering, usually of lead, is provided to protect the cable from mechanical or chemical injuries. The non-moisture proof cables are insulated with paper impregnated with oil, wax, or resinous compounds.

=Metal Sheaths on Underground Cables.=—Metal sheaths are used on rubber covered cables to protect the insulating compounds from the deteriorating effects of electrolysis and various kinds of acids and gases which, under present methods of construction, are ever present in the underground conduits. It is a fact, however, that the lead sheath on a low tension cable, which is used as one side of a grounded circuit, has been, in some cases the cause of, instead of, cure for electrolysis. The proper cure lies in the omission of the sheath altogether, but as this is not practical except in the case of very large conductors, the best thing that can be done is to interrupt the continuity of the sheath by some form of insulating joint.

=Pot Heads.=—The upper end of a lateral cable is equipped with a discharge bell, which is commonly called a pot head. The purpose of a pot head is to hermetically seal the end of the cable and bring the conductors out in such a manner as to permit of their being conveniently connected to the primary service boxes.

=Ques. How are pot heads made?=

Ans. They are usually made in three parts, the base being of cast brass, having a diameter depending upon the size of the conductors, with a hole in the lower end threaded within in such a manner as to make a tight fit on the cable.

=Ques. How is a pot head connected to a cable?=

Ans. After the cable has been bent in to the proper position, the brass base is slipped down over it with the larger end up, and then screwed down on the lead sheath. The threads cut down into the lead sheath to a distance of about ½ inch along the sheath, thus making an air tight connection without necessitating the making of a wiped joint.

The separate conductors are now bared of their insulation for a distance of about two inches, and then spliced to heavy rubber covered braided wire of sufficient length to reach the primary service boxes. The joints connecting these rubber covered wires and the cable conductors are spliced in the same manner as straight splices, the paper sleeves used being of sufficient diameter to be backed out of the way over the rubber insulation. When the splice is completed a brass shell threaded at one end to fit a female thread in the upper end of the brass base, is slipped over the end of the rubber covered wire and screwed into the base. A hood of sheet copper having the form of a quarter section of a ball is slipped over the top of the frame and its lower edge tracked in position below the horizontal shelf. This hood makes the pot head water, snow, and insect proof.

Spotted a typo or a problem in this chapter? Tell us

XLI. WIRING OF BUILDINGS

In laying out the circuits for a dwelling house, the cut out cabinets should be located first. In many houses only one cut out cabinet is necessary, but in large houses it is convenient to have one on each floor, with vertical mains running through them from the top to the bottom of the house.

If only one distributing point be used, it should be either in the cellar or attic and risers run to the different floors.

=Ques. How should the distributing centers or cut out cabinets be located?=

Ans. They should be installed near a partition that is so located as to make the running of risers easy, and should be on an inside wall to guard against dampness.

=Ques. What instructions are usually given the electrician who does the wiring?=

Ans. In many cases simply a plan showing the location and number of lights, from which he must figure out how to install them using the least amount of material and labor consistent with a good installation that will pass inspection.

=Ques. What provision should be made in rooms where lamps are suspended from the ceiling?=

Ans. A switch should be placed at a point where it will be convenient for any one entering to turn on the light.

=Ques. Where are receptacles usually placed?=

Ans. In the baseboard.

A receptacle is a convenient device which permits any one to connect a lamp to the electric lighting system by inserting a plug which is connected by flexible cord to the lamp.

=Ques. What provision should be made in wiring a hallway?=

Ans. The switching arrangement should be so designed that the lights may be turned on or off either from the hall or floor above.

=Ques. What is this arrangement called?=

Ans. A two way switch, as shown in fig. 992.

=Ques. How can a two way switch be distinguished?=

Ans. It has three binding screws, two on one end and one on the other.

=Ques. How may a group of lights be controlled from three points?=

Ans. By the use of a 4 way switch and two 2 way switches connected as shown in fig. 993.

=Ques. Before laying out the wiring system for a building, what should be done?=

Ans. It is necessary to ascertain whether power will be supplied from the central station, or whether a private plant is to be installed.

=Ques. What wiring system should be used with a private or isolated plant?=

Ans. The two wire multiple system as shown in fig. 994.

=Ques. When the central station is to supply power as an auxiliary in case of break down, how should the connection be made?=

Ans. The supply from the central station should be connected to the wiring system through a double throw switch, as in fig. 995, so that either source may be thrown into circuit.

=Ques. How are the connections made when the auxiliary supply is brought in through a three wire system?=

Ans. A double throw three pole switch is used as shown in fig. 995.

=Ques. When power from an outside source only is to be used what must be determined before wiring?=

Ans. The system of wiring of the supply. If a three wire system be used, the general arrangement will be as shown in fig. 997.

=Ques. Would it be expensive to change a regular three wire system to a two wire system?=

Ans. It would require the reinforcement of all mains and feeders by an additional wire. This wire would be connected with the neutral wire so as to make the capacity of the neutral equal to the sum of the other two. If a three wire two wire system had been originally installed, no change in the wiring system would be necessary. The only change would be at the service end of the switchboard, and the doubling of the size of the center fuses.

=Ques. Is a three wire system desirable with an isolated plant?=

Ans. It is more expensive to install than one for a two wire system, as it is necessary to add a balancer in connection with a 240 volt dynamo. This balancer set should have one-tenth the capacity of the plant. Such an equipment has its advantages when 240 volt motors and 120 volt lamps are connected to the system. With this plant no changes in the motors are necessary, whereas in a straight 120 volt system, the motors would have to be changed from 240 to 120 volt machines.

=Ques. After deciding on the system of wiring to be used, how should the electrician proceed with the work?=

Ans. He should lay out the mains, feeders and branches of the wiring system. The outlets are first located and then the distributing centers. There is no fixed rule or plan by which to go, but the current density and source of supply are the main points to be considered in locating these centers. He must also consider the construction of the building and select runways and shafts which provide easy runs for feeders.

=Ques. How should panel boards be placed?=

Ans. Panel boards in loft buildings or in any building requiring 8 to 10 circuits to a floor should be distributed one to a floor. In private houses it is sometimes advisable to install only one panel for the entire house. This is good practice for a three-story house not requiring over twelve circuits.

In a building covering a large area it is often advisable to install two panels or centers to a floor, with two sets of feeders. It is advisable to keep circuit lengths down to 100 feet or less, and the judicious laying out of circuit centers will save many feet of wiring.

=Ques. How should the arrangement of feeders for a large building be determined?=

Ans. A good method is to draw an elevation of the building as in fig. 999, and note on each floor the current requirements.

The best plan is to furnish a feeder for every floor, especially in large installations. In smaller installations one or two feeders are sometimes all that are required.

=Ques. How should feeders for motors be installed?=

Ans. They should be independent of the lighting feeders.

=Ques. What is the largest size of feeder that should be used?=

Ans. Feeders requiring over 2 inch pipe should not be used. It is better to subdivide them, especially if there be many bends or offsets, since two inch pipe is about the limiting size for economical handling.

=Ques. How should feeders be arranged?=

Ans. They should radiate from a distributing panel, having a proper sized switch and fuse for each feeder.

If the system of wiring be such that auxiliary power is taken from a local lighting company, it is a good plan to have each circuit controlled by a double throw switch so that in case of overload any circuit can be fed from the illuminating company's mains as in fig. 1,000.

=Ques. How should feeders and mains be run?=

Ans. It is advisable to install them in iron pipe even though the circuit wires be run otherwise. Since the former carry the main supply of current it is important to have them well protected as they usually run up side walls.

The underwriters make numerous restrictions against open or moulding work on brick walls and require good protection, and this is an additional reason for piping the mains and feeders.

=Ques. How much load should be placed on the branch circuits?=

Ans. In laying out the branch circuits, it is not good practice to use up the underwriters' circuit allowance of 660 watts.

If a circuit be wired with the full allowance of lamps, no additions could be made without violating the underwriter's requirements.

=Ques. If concealed wiring is to be installed in a finished building what should be done first?=

Ans. The outlets should be marked on the ceilings and walls with a pencil cross at the spot, marking also the location of switches, etc.

=Ques. If an outlet is to be placed at the center of a room, how is the center of the ceiling located?=

Ans. It is first located on the floor, then transferred to the ceiling by means of a plumb bob.

=Ques. What is the first operation in making a ceiling outlet?=

Ans. A small hole is bored through the ceiling and the bit pushed up till it comes in contact with the flooring of the room above, this flooring is also bored, as in fig. 1,001.

A long bit about ¼ inch in diameter and about 18 inches long is used. The hole bored in the floor above will show where to take up the board to install the wires.

=Ques. How is a pocket opened above the hole bored for ceiling outlet?=

Ans. One-quarter inch holes are bored to insert a keyhole saw through the joint between two boards at each end of the pocket, and as near the beams as possible, then the board is cut at an angle as indicated in fig. 1,001. Having sawed across the board at both ends, it is pried out with a chisel as shown.

=Ques. How are the holes bored through the beams for the tubes?=

Ans. They are bored about two inches from the top with a 9/16 inch bit, slanting downward just enough to give clearance for the brace.

=Ques. How are the knobs fastened?=

Ans. Screws may be used but stout wire nails are satisfactory and are inserted with less labor.

Leather nail heads are slipped on the nails to protect the porcelain.

=Ques. How is a ceiling outlet completed after the work has reached the stage shown in fig. 1,002?=

Ans. A baseboard is next installed as in fig. 1,003 to have a secure hold for the screws used in fastening the fixtures. Two holes are then bored diagonally with a 11/16 inch bit inserting the bit in the small hole bored in the ceiling as in fig. 1,001. The outlet wires are then tied around the knobs and the upper ends being bared and tapped on to the main wire. A piece of loom is slipped on each outlet wire after which it is thrust through the outlet as in fig. 1,003.

=Ques. How are the mains secured to the knobs?=

Ans. By taking a turn around the intermediate knobs and a dead end hitch at the end knobs, or they may be hitched at each knob. The main may be secured also by use of a tie wire.

=Ques. What is the difference between a splice and a tap?=

Ans. A splice is the joining of two wires at their ends; a tap is the joining of the end of one wire with an intermediate point of another wire.

=Ques. What precaution should be taken in making joints?=

Ans. All wires joined together should be soldered as this insures good electrical contact.

Unsoldered wires are both unreliable and dangerous, since they will corrode from dampness, thus increasing the resistance of the joint so that it may become heated.

=Ques. How should joints be finished after soldering?=

Ans. They should be covered with rubber tape twisted tightly while it is hot. When the rubber has melted it will adhere to the joint and can be moulded with the fingers. Adhesive tape is then wound over the rubber, the insulation thus being made equal to that which was removed to unite the wires.

=Wiring for Heating Appliances.=—There are now on the market a great number of heating appliances which absorb such small amounts of energy that they can be used readily on the lighting circuit. These appliances include the coffee percolator, chafing dish, heating pad, small water heater, cigar lighter and many other miscellaneous devices. By adapting these smaller devices to the lighting circuit, not only is the cost of wiring decreased, but the convenience and cleanliness of the electrical system is secured.

The location of the outlets for the heating appliances is not of the least importance. For many purposes, the flush receptacle in the baseboard of the room answers many requirements. In other places, for instance, a receptacle placed beneath the bracket lamp in the bathroom upon the same circuit as the lamp, is very convenient as a connection for the electric shaving mug or the massage motor. Similarly, a suitable outlet placed near the head of the bed is most convenient for operating a heating pad as it does not necessitate unscrewing a lamp at night.

The house illustrated in figs. 1,006 to 1,008 is an example of the use of a single electric heating circuit with a restricted use of the lighting circuit for heating purposes.

As can be seen in the basement plan, the main supply circuit enters the basement and from this the heating circuit and lighting circuits branch, as shown by the arrows. The heating circuit runs direct to the basement laundry, a branch running to the flat iron. Connections are made with the kitchen on the first floor and with the dining room by branch circuits running through the partitions to the respective rooms. The heating circuit at the dining room is provided with flush wall receptacles, to which connection is made for the chafing dish and percolator.

In the kitchen the electric baking outfit is arranged as shown. This electric outfit is used for auxiliary cooking, such as a gas range would be, and the oven, placed by itself on the opposite side of the coal range, is controlled from the main table.

Upstairs the heating circuit, upon which the dining room appliances are operated, is extended to supply current to the electric luminous radiator, either in the chamber or bathroom.

The arrangements for the lighting circuits are shown in the figures. Landing and basement lights are controlled by three way switches to make them convenient.

In the living room a flush floor receptacle is installed so that the reading lamp, chafing dish or coffee percolator can be operated without necessitating the use of a long cord. A few of the electrical outlets suitable for the purposes mentioned are illustrated.

Where several heating circuits are used it is essential that an appliance taking a large current be not placed on the regular lighting circuit. To guard against this possibility, special receptacles should be installed, constructed for plugs which will not fit any other receptacle.

Spotted a typo or a problem in this chapter? Tell us

XLII. SIGN FLASHERS

The devices used for giving the flashing and changeable effects to electric lights in any form are called "flashers." The mechanism may be constructed to flash a sign by spelling the words out, one letter at a time, flashing border lights around a window, changing colors in glass signs, or in fact in any way to attract the eye.

There are two advantages in favor of using a flasher: 1, it causes the passerby to look at the sign, and 2, reduces the cost of electricity, because the lamps are switched off periodically.

There are numerous kinds of flasher, and they may be classified, according to construction of the switch contacts, as:

1. Carbon type; 2. Brush type; 3. Knife type.

Again, with respect to operation or the electrical effects, they may be classified as

1. Simple on and off flashers; 2. High speed flashers; 3. Lightning flashers; 4. Script breakers; 5. Chaser flashers; 6. Thermo flashers; 7. Carriage calls; 8. Talking signs; 9. Electric clocks.

=Carbon Flashers.=—In this type of flasher, carbon breaks are provided, that is, the arc which is formed when the circuit is broken, falls on carbon, while metal switches are provided to carry the load. Thus the carbon gets the arc which prevents the switches burning, while the switches carry the load to prevent the carbons becoming heated and disintegrated. The carbons must be adjusted occasionally according to the load they are carrying. Carbon machines are made either double, triple, or series break.

=Brush Flashers.=—These machines are provided with brush contacts. These bear on cams constituting a drum, and they are usually made of several strips of copper. Brush flashers are generally used for spelling out signs one letter at a time, or work of a similar nature.

=Knife Flashers.=—This type of construction is cheaper than the carbon type. The switches are of the knife type with metal contacts. One manufacturer states that it is not advisable to build knife flashers for more than 15 amperes per double pole switch, as they cannot be depended upon to break a greater load for any length of time.

=Simple On and Off Flashers.=—These are used for flashing whole signs or heavy loads on and off. A flasher of this type consists essentially of a revolving double pole switch with reducing gear and connection to a small motor for operating same.

The machine may have only one switch or any number of switches. The connection to motor may be by belt or chain, or the motor may be directly connected to the worm gear.

* * * * *

=Flash System of Gas Lighting=—This system for simultaneously lighting a large number of gas burners, is used in large halls, churches, theatres, etc. Two sparking points, each insulated one from the other and from the burner, are arranged at each burner, so that a spark between the points passes through the jet of gas and ignites it. A number of sparking points and the secondary of an induction coil are connected in series. When the circuit through the primary of the induction coil is closed, sufficient pressure is induced in the secondary to cause sparks to jump across every jet in the series. Since the voltage is high, the wires must be installed with great precaution. The wire should be enclosed in glass tubing wherever it comes within less than 1¼ in. from the gas piping, except where purposely grounded.

=High Speed Flashers.=—Machines of this type are used for giving what is generally known as high speed effects, such as fountains, water, steam, smoke and fire effects, whirling borders, revolving wheels and work of a similar nature.

=Lightning Flashers.=—These machines are for giving the appearance of a streak of lightning going across a display. There is very little expense attached to their operation, because not more than two-thirds of the lamps are turned on at one time, and this number for only about one-sixth of the time, as compared with the sign burning steadily.

Lightning strokes can be utilized in various ways, either alone or with other advertising pieces. Alone they can be placed along a cornice, across the front of a building, up and down the corners leading to a doorway, etc. They can be used in the center of a sign with letters above and below. In this case, it is best to alternate the stroke with the letters, that is, flash the wording on and then off. As soon as it goes out, the stroke flies across in the darkness, then the wording comes up again, say six times a minute.

In the case of a sign already in use, on the front of a building or over the sidewalk, a stroke can be placed leading to the sign from any point above. The flash goes down and when it hits the sign the latter lights up, holds a few seconds, goes out, and repeats about four times a minute.

Lightning flashes are not usually constructed for heavy loads, the one shown in fig. 1,025 being designed for two amperes.

=Script Breakers.=—Flashers of this type are used for breaking large script signs, one socket at a time; that is, each lamp is lighted one after another until all are on. After a few seconds they all go out simultaneously and repeat. This gives the appearance of an invisible hand, writing the name in the darkness, and is very effective. The result can be accomplished only with script, and to get the proper effect the smallest letter in a sign should be not less than two feet high; the larger the letter, the better the effect.

Script breakers are also used for fancy border signs of other kinds, and in order to produce these results, it is necessary that the return wire of every lamp go back to the flashers independently, which means a wire for each lamp.

=Chaser Flashers.=—This class of flasher is designed to operate signs whose lamps are arranged to give the effect of snakes chasing each other around the border. This peculiar effect is produced by having a separate wire and a separate switch on the flasher for each two lamps in the border, and the mechanism so arranged that when the tenth lamp is lighted (assuming the snake to be ten lamps long) the first lamp goes out; when the eleventh is lighted, the second goes out, etc., progressing in this way around the entire border.

In operation, the lamps are turned on and off so rapidly that it produces the effect of snakes.

It is not advisable to build these signs small nor cheaply, as in order to produce the desired effect, the curved path taken by the snake should cover at least 10 inches width, which would mean a total of 20 inches lateral space for the snake in addition to the electric letters in the center. In order to get the proper effect, the sign should be at least ten feet long.

=Ques. Why are chaser signs expensive?=

Ans. It is on account of the care required in their construction, large amount of wiring necessary and large flasher required.

A sign four by ten feet outside dimensions, would require in the neighborhood of 150 lamps in the border alone on each side. This would require a flasher with 75 switches and about 82 wires to run between the sign and flasher.

=Ques. How are chaser signs worked?=

Ans. There are several ways of operating these signs. The border is generally working continuously, while the center can be flashed or not, as may be desired. Flashing the wording reduces the current expense, which offsets in a measure the extra cost of the sign.

The border, although working continuously consumes very little current.

=Ques. What is the relative cost of a one snake sign as compared with a two snake sign?=

Ans. One snake running around the border would cost twice as much for flasher and wiring as a two snake flasher.

Three snakes would cost about 25 per cent. less for flasher and wiring than for two snakes. The smaller the number of snakes travelling around the border at one time, the greater the expense of wiring and flasher.

=Ques. How many snakes should there be for best effect?=

Ans. Two is considered best. Three may be used on some signs, but more than four would, in most cases, so crowd them as to spoil the effect entirely.

=Thermo Flashers.=—These flashers work on the thermo or heat expansion principle, that is, the movement of the contact points of the flasher necessary to open and close the circuit is obtained automatically by the alternate heating and cooling of the metal of the flasher, which causes it to expand and contract.

=Carriage Calls.=—These are used to avoid the confusion and noise at the theatre, club house or department store when vehicles are called by a megaphone.

The call itself consists of two or more sheet steel boxes, one of which is shown in fig. 1,032, with incandescent lamps arranged in metal compartments in such order that any number may be produced by lighting the proper lamps.

The flashing of the number is controlled by a keyboard or switch which may be placed in any convenient location. When the switch and call are connected together, any numeral may be flashed by pressing the corresponding key. The numeral automatically remains lighted until the releasing button is pressed.

=Talking Signs.=—This type of electric sign automatically flashes out in brilliant letters, different phrases or announcements. These are flashed out repeatedly and continuously during the operation of the sign and the changes follow each other without intermission of darkness.

The talking sign consists of any desired number of monograms or units, in each of which any letter or figure can be formed by lighting certain combinations of incandescent lamps. A unit is shown in fig. 1,032. The lamps are controlled by a simple mechanical arrangement operated by a small motor. Any reading matter can be flashed by properly setting the mechanism.

The flashing of the letters or numerals in the monogram is controlled by commutators, one commutator being required for each monogram, except for a double faced sign where the corresponding monogram on each side is controlled by the same commutator.

Spotted a typo or a problem in this chapter? Tell us

XLIII. LIGHTNING PROTECTION

A lightning arrester is an apparatus designed to provide a path by which lightning disturbances or other static discharges may pass to earth. Lightning arresters may be divided into three classes, according as their action depends upon the effects of:

1. Sharp points; 2. Air gaps; 3. Sharp turns.

=Lightning Rods.=—This form of arrester consists of a conducting rod or cable erected on the outside of a building and connected to earth, in order to afford protection from lightning by carrying the lightning discharge into the ground; or to prevent lightning by leading the electricity from the earth to the cloud without disturbance.

=Ques. Why do lightning rods terminate in sharp points?=

Ans. The action of the rod depends on the discharging effect of a sharp point as follows: When an electrically charged cloud approaches a building provided with a lightning rod, it induces an opposite charge in the earth and in the rod which is connected to the earth. As soon as the charge on the point becomes strong enough to break apart the molecules of the air in front of it, a stream of electrified particles, opposite in sign to that of the charge on the cloud, passes from the neighborhood of the rod to the cloud and thus neutralizes the charge of the cloud.

=Ques. How should a lightning rod be erected?=

Ans. The conductor should be carried to all high points of the building it is to protect and should be well insulated from the latter and grounded in deep wet earth, independent of gas or water pipes. Sharp bends and corners should be avoided.

=Ques. Why have lightning rods fallen into disfavor?=

Ans. On account of numerous failures due to faulty installations, and non-maintenance of the rod in good condition, also because of the excessive prices charged by unscrupulous dealers for rods and their erection.

A lightning rod with defective insulation or broken ground connection is a danger rather than a protection.

=Air Gap Arresters.=—Many of the lightning arresters used for the protection of electrical apparatus depend upon the fact that lightning discharges will jump across air spaces that are good insulators for the regular working current, while they find difficulty in passing through circuits containing electromagnets.

The principle of air gap arresters is illustrated in fig. 1,039. There are two brass plates slightly separated; one is connected to the line and the other is grounded. The air gap between the plates is very small and the resistance thus interposed, while sufficient to prevent the regular working current jumping across, is not great enough to interfere with a lightning discharge which readily jumps the gap and passes off to earth.

=Ques. Why are teeth provided on the plates?=

Ans. For the same reason that points are used on lightning rods. That is, when electricity at high pressure accumulates at such points the surrounding air is electrified and the charge escapes by means of the charged air particles.

=Ques. For what kind of service is the form of arrester just described used?=

Ans. It is suitable for telegraph and telephone lines where currents of very low voltage are employed.

=Ques. Why is it not used on lines employing higher voltage, such as in electric light and power stations?=

Ans. Current at high pressure would follow the lightning across the gap and establish an arc or continuous flame from one plate to the other thus quickly destroying the plates and causing other more serious damage.

=Ques. What provision is made to prevent the destruction of arresters by the line current?=

Ans. Lightning arresters used on heavy duty circuits are designed to rupture the arc as soon as formed.

=Ques. How is this done?=

Ans. There are several methods, of which may be mentioned the variable gap method described in fig. 1,042, and the magnetic blow out method shown in fig. 1,043.

=Ques. Where should lightning arresters be placed?=

Ans. They should be placed as near as possible to the point where wires enter a building, and in an easily accessible place away from combustible material.

=Ques. What should be avoided in installing lightning arresters?=

Ans. Kinks and sharp bends in the wire running from the outdoor lines to the arresters and from arresters to ground should be avoided as far as possible.

=Ques. Why should kinks and sharp bends be avoided?=

Ans. Because they offer resistance to the lightning discharge.

=Ques. How should lightning arresters be grounded?=

Ans. They should be connected to ground with No. 6 B. & S. gauge copper wire or larger. Gas pipes within a building must not be used for a ground connection.

Ground connections may be made with a one inch galvanized iron pipe driven about 8 feet or until it reaches permanently moist earth, and extending at least 7 feet above ground. The ground wire should be securely soldered to a brass plug firmly screwed into the pipe, and both strongly stapled to the pole so there will be little danger of the connection being broken.

A good ground is important, as the efficiency of the protection would be impaired if the ground connection were poor. Wherever the earth is dry and a good ground cannot surely be obtained, an excavation 4 or 5 feet deep should be made, and after placing the copper ground plate or iron pipe in the hole, it should be filled with crushed coke or charcoal about pea size. This improves the electrical connection between pipe or plate and earth.

=Ques. Does lightning often strike telephone or electric light lines?=

Ans. No, the lines become charged to a high pressure by induction from lightning flashes or from the passing of clouds that are highly charged.

Spotted a typo or a problem in this chapter? Tell us

XLIV. STORAGE BATTERIES

=Introduction.=—The practical development of the storage battery is comparatively recent, although a knowledge of the phenomena upon which its actions are based, dates back to 1801. In 1800, the year made memorable by Volta's discovery of the galvanic battery, Nicholson and Carlisle found that a current from Volta's cell could decompose water.

In 1801, Gautherot discovered that if two plates of platinum or silver, immersed in a suitable electrolyte, be connected to the terminals of an active primary cell and current be allowed to flow, a small current could be obtained on an outside circuit connecting these two electrodes as soon as the primary battery had been disconnected.

Erman found that the positive pole of such a cell, was the pole which had been connected to the positive pole of the battery.

In 1803, Ritter observed, with gold wire, the same phenomenon as Gautherot, and constructed the first secondary battery, by superposing plates of gold, separated by cloth discs, moistened with ammonia.

Volta, Davy, Marianini, and others added somewhat to the knowledge on the subject, and in 1837, Schoenbein found that peroxide of lead could be used in secondary batteries.

Sir William Grove next came forward with the discovery that metal plates, with a layer of oxide on them, acted better than the plain metallic plates, and Wheatstone and Siemens found still later that peroxide of lead was the best for such purposes.

In 1842, Grove constructed a gas battery, in which the electromotive force came from the oxygen and hydrogen evolved in the electrolysis of water acidulated with sulphuric acid. By means of fifty such cells, he obtained an arc light.

Michael Faraday, when electrolyzing a solution of lead acetate, found that peroxide was produced at the positive, and metallic lead at the negative pole, and in his "Experimental Researches," he comments on the high conductivity of lead peroxide, and its power of readily giving up its oxygen. Although he made no apparent use of this discovery, it may be considered as the next important step in the development of the storage battery.

According to Niblett, Wheatstone, de la Rue, and Niaudet were well aware that peroxide of lead was a powerful depolarizer, but nobody appears to have made use of this fact until 1860, when M. Gaston Plante constructed his well known cell with coiled plates. Plante's researches extended up to 1879, and practically determined the state of the art.

As to the theory at this time, it may be stated that Clerk Maxwell, although the leading electrician of his time, speaks of the storage battery as storing up a quantity of energy in a manner somewhat analogous to the ordinary condenser; hence the use of the word "accumulator" for storage battery.

In 1879, R. L. Metzer did away with the tedious forming process, by mechanically applying the active material. This important discovery was not, however, generally known, until 1881, when Camille Faure obtained important patents concerning the method of shortening the time of formation.

Charles F. Brush, working independently of either Faure or Metzer, arrived at the same result, and the United States courts have decided, after long litigation, that to him belongs the priority of invention in this country.

=Ques. To what use is the storage battery sometimes put in electric lighting or power stations?=

Ans. To carry the "peak" of the load; that excessive portion of the load which, for instance, in electric lighting stations has to be carried only for two or three hours a day. To carry the entire load at minimum hours. To act as equalizer or reservoir. Also for equipment of annex or substations.

=Theory of the Storage Battery.=—The action of the storage battery is practically the same as that of the primary battery and it is subject to the same general laws. The cells of a storage battery are connected in the same way as primary cells, and when charged is capable of generating a current of electricity in a manner similar to that of a primary battery. It differs, however, from the primary battery in that it is capable of being recharged after exhaustion by passing an electric current through it in a direction opposite to that of the current on discharge. This difference constitutes the principal advantage of the storage battery over the primary battery.

=Ques. Describe a storage cell.=

Ans. A storage cell consists of plates or of grids in an electrolyte, of such a character that the electrical energy supplied to it is converted into chemical energy (a process called charging). The chemical energy can be reconverted into electrical energy (a process called discharging).

=Ques. Describe the electrolyte generally used.=

Ans. It consists of a weak solution of sulphuric acid which permits ready conduction of the current from the primary battery, the greater the proportion of acid within certain limits, the smaller the resistance offered.

=Ques. What is the effect of the current passing through the electrolyte?=

Ans. It decomposes the water into oxygen and hydrogen; this is indicated by the formation of bubbles upon the exposed surfaces of both plates, these bubbles being formed by oxygen gas on the plate connected to the positive pole of the primary battery, and hydrogen on the plate connected to the negative pole.

Because, however, the oxygen is unable to attack either platinum or silver under such conditions, the capacity of such a device to act as an electrical accumulator is practically limited to the point at which both plates are covered with bubbles. After this point the gases will begin to escape into the atmosphere.

=Ques. What is the prime condition for operation of a storage battery?=

Ans. The resistance of the electrolyte should be as low as possible in order that the current may pass freely and with full effect between the electrodes. If the resistance of the electrolyte be too small, the intensity of the current will cause the water to boil rather than to occasion the electrolytic effects noted above.

=Ques. What happens when the charging current is discontinued, and the two electrodes joined by an outside wire?=

Ans. A small current will flow through the outside circuit, being due to the recomposition of the acid and water solution. The process is in a very definite sense a reversal of that by which the current is generated in a primary cell.

Hydrogen collected upon the negative plate, which was the cathode, so long as the primary battery was in circuit, is given off to the liquid immediately surrounding it, uniting with its particles of oxygen and causing the hydrogen, in combination with them, to unite with the particles of oxygen next adjacent. The process is continued until the opposite positive plate is reached, when the oxygen collected there is finally combined with the surplus hydrogen, going to it from the surrounding solution.

This chemical process causes the current to emerge from the positive plate, which was the anode, so long as the primary battery was in circuit. The current thus produced will continue until the recomposition of the gases is complete; then ceasing because these gases, as before stated, do not combine with the metal of the electrodes.

=Types of Storage Battery.=—There are three classes of storage cell which are commercially important:

1. Plante cells; 2. Faure cells; 3. Alkaline cells.

According to construction secondary cells may be classified as follows:

1. Lead sulphuric acid cells; 2. Lead copper cells; 3. Lead zinc cells; 4. Alkaline zincate cells.

The lead sulphuric acid type includes all those cells belonging to the Plante and Faure groups.

Lead copper cells consist of sheets of metal coated with lead oxide, serving as the positive electrode, and copper plates for the negative electrodes. These plates are immersed in a solution of copper sulphate. Cells belonging to this class are not employed in commercial practice, being useful only for laboratory experiments.

Lead zinc cells are similar to the preceding type, but differ by having zinc for the negative electrode, and zinc sulphate for the electrolyte. The voltage of these cells is slightly higher than that of the ordinary cell, and their capacity per unit of total weight is high, but they are apt to lose their charge on open circuit, besides they possess most of the disadvantages of the Plante cells.

Alkaline zincate cells have copper for the positive, and iron for the negative electrode. The electrolyte is composed of sodium, or potassium, zincate. Cells of this type are used to some extent for traction purposes.

In addition to the above there are some special forms of cell which do not belong to the four preceding types.

=Ques. Describe the Plante type.=

Ans. In the Plante type the lead is chemically attacked and finally converted into lead peroxide, probably after it has gone through several intermediate changes. The plates are all formed as positive plates first and then all that are intended for negative plates are reversed, the peroxide being changed into sponge lead.

=Ques. What is done to make the Plante plate more efficient?=

Ans. The surfaces are finely subdivided, the following methods being those common: scoring, grooving, casting, laminating, pressing, and by the use of lead wool.

=Ques. Describe the Faure or pasted type.=

Ans. This form of plate is constructed by attaching the active material by some mechanical means to a grid proper. The active material first used for this purpose was red lead, which was reduced in a short time to lead peroxide when connected as the positive or anode, or to spongy metallic lead when connected as the cathode or negative, thus forming plates of the same chemical compound as in the Plante type.

The materials used at the present time by the manufacturers for making this paste are largely a secret with them, but in general they consist of pulverized lead or lead oxide mixed with some liquid to make a paste.

=Ques. How do Faure plates compare with those of the Plante type?=

Ans. They are usually lighter and have a higher capacity, but have a tendency to shed the material from the grid, thus making the battery useless.

Many ways have been tried for mechanically holding the active material on the grid, the general method involving a special design in the shape of the grid. Some of these designs are: 1, solid perforated sheets of lattice work; 2, corrugated and solid recess plates not perforated; 3, ribbed plates with projecting portions; 4, grid cast around active material; 5, lead envelopes, and 6, triangular troughs as horizontal ribs.

=The Electrolyte.=—Sulphuric acid is generally used as electrolyte; the acid should be made from sulphur and not from pyrites, as the latter is liable to contain injurious substances.

=Ques. How is the electrolyte prepared?=

Ans. One part of chemically pure concentrated sulphuric acid is mixed with several parts of water. The proportion of water differs with several types of cell from three to eight parts, as specified in the directions accompanying the cells.

=Ques. What test is necessary in preparing the electrolyte?=

Ans. In mixing the water and acid, the hydrometer should be used to test the specific gravity[6] of both the acid and the solution. The most suitable acid should show a specific gravity of about 1.760 or 66° Baumé.

[6] NOTE.—Specific gravity is the weight of a given substance relative to an equal bulk of some other substance which is taken as a standard of comparison. Water is the standard for liquids. In the laboratory the specific gravity bottle is often used in determining the specific gravity of a liquid. The capacity of the bottle is 1,000 grains of pure water. When it is filled with spirits of wine and weighed in a balance (together with a counterpoise for the weight of the bottle, which of course is constant), it will weigh considerably less than 1,000 grains; in fact, the bottle will contain only about 917 grains of proof spirit; therefore, taking the specific gravity of water as unity, 1 or 1.000, the specific gravity of spirits of wine is 0.917. If, on the other hand, the bottle be filled with sulphuric acid, it will weigh about 1,850 grains; hence, the specific gravity of sulphuric acid is said to be 1.850. A more convenient method for the automobilist is by the use of the hydrometer.

=Ques. In preparing the electrolyte, how should the water and acid be mixed?=

Ans. The mixture should be made by pouring the acid slowly into the water, never the reverse. As cannot be too strongly stated, in mixing, the liquid should be stirred with a clean wooden stick, the acid being added to the water slowly; the latter is corrosive and will painfully burn the flesh.

Distilled or rain water should be used in preparing the electrolyte. When made, the solution should be allowed to cool for several hours or until its temperature is approximately that of the atmosphere (60 being the average). At this point it should have a specific gravity of about 1.200 or 25° Baumé. If the hydrometer show a higher reading, water may be added until the correct reading is obtained; if a lower reading, dilute acid may be added with similar intent.

The electrolyte should never be mixed in jars containing the battery plates, but preferably in stone vessels, specially prepared for the purpose. Furthermore, it should never be placed in the cell until perfectly cool.

=Ques. What is the effect of mixing the acid and the water?=

Ans. The mixture becomes hot.

Before using, the mixture should be allowed to cool.

=Ques. What kind of a vessel should be used?=

Ans. The vessel should be of glass, glazed earthenware, or lead.

=Ques. At what density is the resistance of dilute sulfuric acid at a minimum?=

Ans. At 1.260.

The percentage of concentrated sulphuric acid and of water per 100 parts of the electrolyte for various specific gravities is given by the following table:

SPECIFIC GRAVITY TABLE +——————————————+————————————+————————————————+ |Sulphuric acid| Water |Specific gravity| | (Per cent.). |(Per cent.).| of Mixture. | +——————————————+————————————+————————————————+ | 50 | 50 | 1.398 | | 47 | 53 | 1.370 | | 44 | 56 | 1.342 | | 41 | 59 | 1.315 | | 38 | 62 | 1.289 | | 35 | 65 | 1.264 | | 32 | 68 | 1.239 | | 29 | 71 | 1.215 | | 26 | 74 | 1.190 | | 23 | 77 | 1.167 | | 20 | 80 | 1.144 | | 17 | 83 | 1.121 | | 14 | 86 | 1.098 | | 10 | 90 | 1.068 | +——————————————+————————————+————————————————+

The electrolyte of the desired specific gravity may be purchased ready for use, but in cases where it is desirable to save freight, the acid may be diluted at the point of installation.

=Ques. What is the effect of a deep containing vessel?=

Ans. Parts of the plate surface may do more than their share of the work due to the difference in the density of the electrolyte at the top and bottom. The containing vessel should, therefore, never be deeper than about 20 inches unless some artificial means of acid circulation be used.

=Ques. What is the effect of changes in temperature on the electrolyte?=

Ans. The resistance of the electrolyte is changed, being less for increase of temperature.

=Ques. How should the cells be filled?=

Ans. Enough of the electrolyte should be poured into the jars to completely cover the plates, or to within about a half inch of the top edge of the jar. Large cells should be filled by means of an acid proof pump and rubber hose.

=Ques. What change takes place after filling the jars?=

Ans. The specific gravity of the electrolyte will fall considerably, but will rise again when the battery is charged.

=Ques. What may be said with respect to the density of the electrolyte?=

Ans. It should never exceed 1.200 when the battery is fully charged.

=Ques. How much electrolyte is used per 100 ampere hours battery capacity, on an 8 hour rating?=

Ans. About ten pounds; in automobile batteries, about four pounds is sufficient.

=Ques. What may be said with respect to impurities in the electrolyte?=

Ans. The electrolyte should be free from chlorine, nitrates, acetates, iron, copper, arsenic, mercury, and the slightest trace of platinum.

Mercury alone has no injurious effect unless it be present in sufficient quantity to amalgamate the plates, but in combination with any other metal, may cause local action.

The following tests should be made for impurities before the electrolyte is poured in the cells:

=Chlorine.=—To a small sample of the electrolyte add a few drops of silver solution (20 grains of silver dissolved in 1,000 cu. cm. of water). A white precipitate indicates chlorine.

=Nitrates.=—Place some of the electrolyte in a test tube, and add 10 grains of strong ferrous sulphate solution. Carefully pour down the side of the test tube a small amount of chemically pure concentrated sulphuric acid. A brown stratum between the electrolyte and the concentrated acid indicates the presence of nitric acid.

=Acetic acid.=—Neutralize the electrolyte with ammonia, then add ferric chloride. If the solution turns red, and is afterwards bleached by the addition of hydrochloric acid, acetic acid is present.

=Iron.=—Neutralize a sample of the electrolyte with ammonia; boil a small portion with hydrogen peroxide, and add ammonia or caustic potash solution until the mixture becomes alkaline. If a brownish red precipitate forms, it indicates iron.

=Copper.=—If copper be present, a bluish white precipitate will be formed when ammonia solution is added to the electrolyte.

=Mercury.=—This is indicated by an olive green precipitate when a solution of potassium iodide is added to the electrolyte, or by a black precipitate when lime water is added.

=Platinum.=—A rough test for traces of platinum is made by pouring the electrolyte into a cell in which the battery plates are immersed. If gassing take place for some time on open circuit, it is an indication of the presence of platinum.

=Ques. What should be done with old electrolyte?=

Ans. When a battery is taken down the electrolyte may be saved and used when re-assembling the battery, providing great care be exercised when pouring it out of the jar, so as not to draw off with it any of the sediment. It should be stored in convenient receptacles, preferably carboys, which have been thoroughly washed and never used for any other purpose.

The electrolyte saved in this manner will not, however, be sufficient to refill the battery, and as some new electrolyte will be required, in general it is recommended that the old supply be thrown away and all new electrolyte (1.200 specific gravity) be used when re-assembling.

=Voltage of a Secondary Cell.=—This depends on the density of the electrolyte, the character of the electrodes and condition of the cell; it is independent of the size of the cell.

The voltage of a lead sulphuric acid cell when being charged is from 2 to 2.5 volts. While the cell is being discharged, it decreases from 2 to 1.7 volts. The voltage due to the density of the electrolyte may be calculated from the following formula:

V = 1.85 + .917 (S - s)

in which

V = voltage; S = specific gravity of the electrotype; s = specific gravity of water at the temperature of observation.

=Connection for Charging.=—The dynamo cable connections may be made either before or after filling the cells. In making these connections great care should be taken to be sure that the positive terminal of the battery is connected to the positive lead of the dynamo, and that the negative terminal of the battery is connected to the negative lead of the dynamo. In order to insure that the reverse connections are not made accidentally, the dynamo leads should be tested by a pole tester, and the positive and negative poles marked red and black respectively.

The polarity of the dynamo wires being determined, they may be joined to the proper terminals by means of suitable clamps or by solder.

Wherever possible the dynamo should be of the direct current, shunt wound, or special compound type, but in cases where only alternating current can be obtained, suitable rectifiers or converters should be used for changing it to direct current.

=Charging.=—Before beginning to charge a storage battery, it should be gone over carefully, and any cell that is not up to the standard should be disconnected and put in working order before being replaced. In general, if the current used in charging be too large, it will waste energy by evolving an excess of heat and gas; if too small, an insulating deposit of white lead sulphate will be formed on the positive plate, thereby preventing the formation of the proper amount of lead peroxide.

=Ques. How should a battery be charged for the first time?=

Ans. It is essential that the current be allowed to enter at the positive pole at about one-half the usual charging rate prescribed, but after making sure that all necessary conditions have been fulfilled, it is possible to raise the rate to that prescribed by the manufacturers of the battery.

=Ques. What is the usual period for charging a new battery?=

Ans. With several of the best known makes of storage battery the prescribed period for the first charge varies between twenty and thirty hours.

=Ques. How is the electrolyte affected by the first charge?=

Ans. A change of specific gravity occurs. The specific gravity should be about 1.200 when the solution is poured into the cells.

At the completion of the first charge, it should, on the same scale be about 1.225. If it be higher than this, water should be added to the solution until the proper figure is reached, if it be lower, dilute sulphuric acid should be added until the hydrometer registers 1.225.

At the first charging of a cell, when the pressure has reached the required limit, the cell should be discharged until the voltage has fallen to about two-thirds normal pressure, when the cell should again be recharged to the normal voltage (2.5 or 2.6 volts).

The manufacturers of a well known cell of the Plante genus prescribe for the first charge, half rate for four hours, after which the current may be increased to the normal power and continued for twenty hours successively.

=Ques. What strength of current should be used in charging a cell?=

Ans. It should be in proportion to the ampere hour capacity of the cell.

Thus, as given by several manufacturers, the normal charging rate for a cell of 40 ampere hours should be five amperes, or one-eighth of its ampere hour rating in amperes of charging current.

=Ques. What should be the voltage of the charging current before closing the charging circuit?=

Ans. The voltage should be at least ten per cent. higher than the normal voltage of the battery when charged.

=Ques. What indicates the completion of a charge?=

Ans. When a cell is fully charged the electrolyte apparently boils and gives off gas freely. The completion of a charge may be determined by the voltmeter, which will show whether the normal pressure has been attained.

=Ques. How should the voltage be regulated during the first charge?=

Ans. It should be allowed to rise somewhat above the point of normal pressure.

Electrical Data Edison Cell +——————————————————————————————————————————————————————————————+ | =B-2= =B-4= =B-6=| |Normal output, ampere hours 40 80 120 | | | |Maximum output, ampere hours 48 95 142 | |Normal rate of discharge, amperes for | | five hours 8 16 24 | | | |Average voltage on normal discharge 1.2 1.2 1.2 | | | |Normal rate of charge, amperes for | | seven hours 8 16 24 | | | |Maximum rate of "boosting charge" | | (for short time only) 50 100 140 | | | |Length of containing can (determined | | by number of plates) 1½ 2⅝ 3-13/16 | | | |Width of containing can 5⅛ 5⅛ 5⅛ | | | |Height " " " 7-15/16 7-13/16 7¾ | | | |Height over all 8¾ 8¾ 8⅞ | | | |Weight of each cell alone, lbs. 4.6 7.4 10.5 | | | |Average weight per cell of battery, | | assembled in trays 5.5 8.7 11.8 | +——————————————————————————————————————————————————————————————+

=Ques. How often should a battery be charged?=

Ans. At least once in two weeks, even if the use be only slight in proportion to the output capacity.

In charging a storage battery, it is essential to remember the fact that the normal charging rate is in proportion to the voltage of the battery.

Thus, a 100 ampere hour battery, charged from a 110 volt circuit at the rate of ten amperes per hour, would require ten hours to charge, and would consume in that time an amount of electrical energy represented by the product of 110 (voltage) by 10 (amperes) which would give 1,100 watts, or 1⅒ kw.

=Ques. If in charging a battery, one or more of the cells do not boil at the completion of the charge, or fail to show the proper voltage, what should be done?=

Ans. The charging must be continued until the cadmium test shows the required voltage, but if the prolonging of the charge be liable to damage the plates in the other cells, the defective cell or cells should be cut out of circuit when the battery discharges and then placed in circuit again when the battery is recharged. If the desired result cannot be attained by this method, the plates which require additional charging may be charged in a separate cell.

=Ques. How is the cadmium test made?=

Ans. A plate of cadmium is mounted in a hard rubber frame and immersed in the electrolyte. The test consists in taking voltage readings between the cadmium plate and the positive or negative plates of the cell. During charge the cadmium plate reads negative to the negative plate, until the cell is about full, when the reading should be zero; the charge should be continued until the cadmium reads 0.2 volt positive to the negative while charging at the normal rate.

=Ques. Name some portable instruments that should be provided for testing batteries.=

Ans. 1, a hydrometer syringe (specific gravity tester); 2, an acid testing set (can be used instead of the syringe); 3, a low reading voltmeter; 4, suitable prods, and 5, a thermometer.

=Ques. What precaution should be taken in charging a battery?=

Ans. Care should be taken not to have a naked flame anywhere in its vicinity.

To either charge or discharge a battery at too rapid a rate involves the generation of heat. Thus, while this is not liable to result in a flame under usual conditions, the battery may take fire, if it be improperly connected or improperly used.

=Ques. What is the effect of varying the charging current?=

Ans. In charging a storage cell, particularly for the first time, a weaker current than that specified may be used with the same result, provided the prescribed duration of the charge be proportionally lengthened. The battery may also be occasionally charged beyond the prescribed voltage, ten or twenty per cent. overcharge effecting no injury, although if frequently repeated, it shortens the life of the battery.

=Ques. What are the charge indications?=

Ans. The state of the charge is not only indicated by the density of the electrolyte and the voltage of the cell, but also by the color of the plates, which is considered by many authorities as one of the best tests for ascertaining the condition of a battery.

=Ques. What are the colors of the plates?=

Ans. In the case of formed plates, and before the first charging, the positives are of a dark brown color with whitish or reddish gray spots, and the negatives are of a yellowish gray. The whitish or reddish gray spots on the positive plates are small particles of lead sulphate which have not been reduced to lead peroxide during the process of forming, and represent imperfect sulphation.

As a general rule, the first charging should be carried on until these spots completely disappear. After this the positive plates should be of a dark red or chocolate color at the end of the discharge, and of a wet slate or nearly black color when fully charged. A very small discharge is sufficient, however, to change them from black to the dark red or chocolate color.

If the battery has been discharged to a pressure lower than 1.8 volts, the white sulphate deposits will reappear, turning the dark red color to a grayish tint in patches or all over the face of the plate, or in the form of scales of a venetian red color.

The formation of these scales while charging indicates that the maximum charging current is too large and should be reduced until the scales or white deposits fall off or disappear, after which the current can be increased again.

During charging, the yellowish gray color of the negatives changes to a pale slate color which grows slightly darker at the completion of the charge. The color of the negatives always remains, however, much lighter than that of the positives.

=Ques. How are the best results obtained in charging?=

Ans. The rate of charge should be normal, except in cases of emergency. At such a rate, unless the constant voltage method be employed, the cell may be considered full when the voltmeter reads 2.5 volts during charge. The electrolyte should be kept at uniform density throughout the cell; when water is added, because of evaporation, it should be added by means of a funnel reaching to the bottom of the cell. Care should be taken never to add acid after evaporation; otherwise the electrolyte will be too heavy. Hydrometer readings should be taken regularly; the reading is an excellent indication of the amount of charge in the battery. Hydrometer readings are useless, however, unless the precaution be taken to keep the electrolyte of uniform density.

=Ques. What voltage should be used in charging?=

Ans. At the beginning of the charge the voltage should be about 5 per cent. higher than the normal voltage of the battery, unless the latter has been overdischarged, in which case the difference of pressure should not exceed 2 per cent., otherwise the current might be too large.

=Ques. In what two ways may batteries be charged?=

Ans. They may be charged either at constant current or at constant voltage.

Although the latter method is considered the better one by many authorities, it is a fact, nevertheless, that if the charging current be normal at the beginning of the charge, and no means be provided for keeping it constant, it will diminish as the charging progresses, thereby greatly increasing the length of the time required for charging, and resulting in serious injury to the plates.

=Ques. How may the charging current be kept constant?=

Ans. Its voltage should be gradually increased, first to about 10 or 15 per cent. above the voltage of the battery, and kept at that point nearly to the end of the charge, where in consequence of the rapid rise of pressure in the battery it might become necessary to increase the voltage of the current to 30 or 40 per cent. above the normal of the battery.

=Ques. What tests should be made while charging?=

Ans. Occasional voltage and cadmium readings of each cell should be taken for the purpose of ascertaining their condition and the behavior of the separate plates.

=Ques. What tests should be made after charging?=

Ans. Each cell should be tested with a low reading voltmeter and hydrometer about once a week. If any cell read low, it should be cut out and examined to see if any material has been introduced which would cause a short circuit. If this trouble do not exist, the cell should be given an independent charge.

=Charge Indications.=—The state of the charge is not only indicated by the density of the electrolyte and the voltage of the cell, but also by the color of the plates, which is considered by many authorities as one of the best tests for ascertaining the condition of a battery.

In the case of formed plates, and before the first charging, the positives are of a dark brown color with whitish or reddish gray spots and the negatives are of a yellowish gray. The whitish or reddish gray spots on the positive plates are small particles of lead sulphate which have not been reduced to lead peroxide during the process of forming, and represent imperfect sulphation.

As a general rule the first charging should be carried on until these spots completely disappear. After this, the positive plates should be of a dark red or chocolate color at the end of a discharge and of a wet slate or nearly black color when fully charged. A very small discharge is sufficient, however, to change them from black to the dark red or chocolate color.

If the battery has been discharged to a pressure lower than 1.8 volts, the white sulphate deposits will reappear turning the dark red color to a grayish tint in patches or all over the surface of the plate, or in the form of scales of a venetian red color.

The formation of these scales during charging indicates that the maximum charging current is too large and should be reduced until the scales or white deposits fall off or disappear, after which the current can be increased again.

=Ques. Describe the behavior of the electrolyte during discharge.=

Ans. There is a definite change in the density of the electrolyte for a given amount of discharge.

The density of the electrolyte is, therefore, one of the best indications of the state of charge, provided, of course, no internal discharge due to local action takes place. If, when the cell is charged, it show a density of 1.200, and when discharged 1.130, the difference .07 represents the total charge. If at any time the density be 1.165, then just one half the amount of capacity has been taken from the cell.

It is necessary to stir the electrolyte well, in order for these observations to be reliable.

If the discharge has taken place at a high rate, the cell must stand for an hour or more before the electrolyte will completely diffuse so that the density readings are correct.

=Ques. Define the term "boiling."=

Ans. Boiling means the rapid evolution of gas when a cell is nearly charged.

=Ques. What causes boiling?=

Ans. The amount of sulphate to be converted into peroxide becomes less and less as the charge progresses and the plates therefore become virtually smaller, so that the current becomes too large for the work demanded of it. The result is, that part of the current not actually used in the formation of peroxide decomposes the electrolyte into its constituent elements.

=Ques. Why do the gases evolved produce a less milky appearance of the electrolyte when a battery has been in use for a considerable time?=

Ans. The plates are better formed; consequently a larger charging current can be used without producing "boiling".

=Ques. What may be said of charging a battery as quickly as possible?=

Ans. As a general rule, such a procedure should not be adopted unless the battery be thoroughly discharged.

=Ques. What precaution should be taken?=

Ans. The danger to be avoided in rapidly charging a cell is its tendency to heat.

=Ques. What apparatus is necessary in charging a battery?=

Ans. The battery may be charged from direct current mains having the proper voltage. A current as near uniform as possible is required, and existing conditions must be met in each separate case. Sometimes a motor dynamo set with a regulating switchboard is used. Such an apparatus consists of a direct current dynamo, driven direct from the shaft of a motor, which, in turn, is energized by current from the line circuit.

With a direct current on the line, a direct current dynamo may be used; but with an alternating current an induction motor is required. The speed of the motor is governed by a rheostat, and the output of the dynamo is thus regulated as desired.

=Charging Through the Night.=—If an electric vehicle, after a late evening run, is to be used in the morning, the battery may be charged during the night without an attendant being present; but in doing this great care must be taken not to excessively overcharge.

A careful estimate of the amount of current required should be made and the rate of charge based on this estimate.

If, say, 72 ampere hours be required to recharge, and the time available is nine hours, the average rate of charge must be 8 amperes.

If charging from a 110-volt circuit, the rate at the start should be about 10 amperes; if from a 500-volt circuit, about 9 amperes; as, in charging from a source with constant voltage, such as a lightning or trolley circuit, the rate into the battery will fall as the charge progresses. This also applies if the charging be done from a mercury arc rectifier without attendance.

=Ques. What precautions should be taken in charging a battery out of a vehicle?=

Ans. When a battery is being overhauled, the cells must be connected together in series and to the charging source in relatively the same manner as if they were in the vehicle; that is, the positive (+) terminal of one group of cells must be connected to the negative (-) terminal of the next group, and the two free terminals, one positive and the other negative, must be connected respectively to the positive and negative terminals of the charging circuit, but not until all of the groups have been connected in series. Great care must always be taken to have the polarities correct and the wire or cable for the connections of ample size to carry, without heating, the heaviest current used in charging.

=Charging Small Cells.=—For cells of the portable type, having capacities from 10 to 100 ampere hours, the normal charging and discharging rate should be about one-tenth the stated capacity, but the discharging rate may be increased to double this value, in case of necessity.

If the cells be provided with formed plates and not charged, the jars should be filled with the proper electrolyte, and then charged for at least 10 hours steady, or until they boil, then they may be discharged.

In the case of unformed plates, the charging should be from 30 to 40 hours, until the cells boil, and the plates assume their proper color.

=Ques. How are small cells easily charged from 110 or 220 volt circuits?=

Ans. This may be conveniently done by inserting in one of the charging leads an incandescent lamp which will pass the required quantity of current. If the current required be as large as 10 amperes, a suitable resistance or 10 lamps in parallel, each passing one ampere, may be used. Great care should be taken to see that the battery is connected properly.

=Period of Charging a New Battery.=—In the case of batteries provided with formed plates, the first charge should extend over a period of not less than 30 consecutive hours, without stopping, if possible, or for periods of not less than 10 hours a day for three consecutive days. The electrolyte will then commence to "boil" or "gas," assuming a milky appearance due to the ascending bubbles of gas. At this stage the density of the electrolyte as shown by the hydrometer placed in each cell should be at least 1.200; it is essential that the charging should be continued until every cell boils equally. From this point the charging should be prolonged until the pressure, as determined by a voltmeter or a cadmium tester, rises to about 2.55 volts.

The charging of unformed plates is similar in all respects to that of formed plates, except that the first charging should extend over a period of at least 70 consecutive hours without stopping, at the end of which time the plates should have the characteristic colors of those of a fully charged battery. If they do not, the charging should be prolonged and the cell tested for density of electrolyte, and voltage, as already described until the desired conditions are attained. Then the battery may be discharged and recharged.

It is probable that a total of 300 to 400 hours of charging with intervening discharges will be required to form the plates until they acquire a good color, and the density of the electrolyte becomes stable.

In regular charging, the rate should be rapid when the battery is nearly exhausted, but it should be greatly reduced at the end of the charge after passing the point of boiling. Charging at too low a rate is always injurious.

=Ques. What may be said with respect to the capacity of a new battery?=

Ans. A new battery will never give its full capacity till after about twenty discharges. During this time it should be given about 25% overcharge. After that, 10% overcharge, that is, 10% more charge than was taken out, will be sufficient for ordinary work.

=High Charging Rates.=—Occasionally it is desirable to charge a battery as quickly as possible. As a general rule, such a procedure should not be adopted unless the battery be thoroughly discharged, and not then, unless done by a person who thoroughly understands what he is about; battery makers will always furnish data and directions to meet emergencies.

In charging a battery at a high rate, the danger to be avoided is the tendency of the cells to heat. The troubles that might arise from this cause may be prevented by immediately reducing the current strength. The proper rate of charge for a given battery of cells may be thus discovered by experiment. A battery should never be charged at a high rate unless it be completely exhausted, since it is a fact that the rate of charge that it will absorb is dependent upon the amount of energy already absorbed.

For rapid charging, when a battery has to be charged in four hours, the current should vary about as follows:

40 per cent. of total 1st hour 25 " " " " 2nd " 20 " " " " 3rd " 15 " " " " 4th "

For quick charging in three hours the rates should be: 50 per cent. 1st hour; 33⅓ per cent. 2nd hour; 16⅔ per cent. 3rd hour.

=Mercury Arc Rectifier.=—This is a device for obtaining direct current from alternating current for use in charging storage batteries. The transformation is obtained at a low cost, because the regulation is obtained from the alternating side of the rectifier, while the current comes from the direct current side.

The theory is as follows: In an exhaust tube having one or more mercury electrodes, ionized vapor is supplied by the negative electrode or cathode, when the latter is in a state of "excitation." This condition of excitation can be kept up only as long as there is current flowing toward the negative electrode.

If the direction of the voltage be reversed, so that the formerly negative electrode is now positive, the current ceases to flow, since in order to flow in the opposite direction it would require the formation of a new negative electrode, which can be accomplished only by special means. Therefore, the current is always flowing toward one electrode—the cathode, which is kept excited by the current itself. Such a tube would cease to operate on alternating current voltage after half a cycle if some means were not provided to maintain a flow of current continuously towards the negative electrode.

=Ques. Describe the construction and operation of a mercury arc rectifier.=

Ans. Fig. 1,135 is an elementary diagram of connections. The rectifier tube in an exhausted glass vessel in which are two graphite anodes A, A´, and one mercury cathode B. The small starting electrode C is connected to one side of the alternating circuit, through resistance; and by rocking the tube a slight arc is formed, which starts the operation of the rectifier tube. At the instant the terminal H of the supply transformer is positive, the anode A is then positive, and the arc is free to flow between A and B. Following the direction of the arrow still further, the current passes through the battery J, through one-half of the main reactance coil E, and back to the negative terminal G of the transformer. When the impressed voltage falls below a value sufficient to maintain the arc against the reverse voltage of the arc and load, the reactance E, which heretofore has been charging, now discharges, the discharge current being in the same direction as formerly. This serves to maintain the arc in the rectifier tube until the voltage of the supply has passed through zero, reversed, and built up such a value as to cause the anode A to have a sufficiently positive value to start the arc between it and the cathode B. The discharge circuit of the reactance coil E is now through the arc A'B instead of through its former circuit. Consequently the arc A'B is now supplied with current, partly from the transformer, and partly from the reactance coil E. The new circuit from the transformer is indicated by the arrows enclosed in circles.

=Ques. How is a mercury arc rectifier started?=

Ans. A rectifier outfit with its starting devices, etc., is shown in figs. 1,132 to 1,134. To start the rectifier, close in order named line switch and circuit breaker; hold the starting switch in opposite position from normal; rock the tube gently by rectifier shaker. When the tube starts, as shown by greenish blue light, release starting switch and see that it goes back to normal position. Adjust the charging current by means of fine regulation switch on the left; or, if not sufficient, by one button of coarse regulation switch on the right. The regulating switch may have to be adjusted occasionally during charge, if it be desired to maintain the charging current approximately constant.

=Capacity.=—The unit of capacity of a storage cell is the ampere hour, that is, the ability to discharge one ampere continuously for one hour. For instance, a 100 ampere hour battery will give a continuous discharge of 12½ amperes for eight hours. It should theoretically give a discharge of 25 amperes continuously for four hours, or 50 amperes for two hours, but in reality, the ampere hour capacity decreases with an increase of discharge rate.

It requires, theoretically .135 ounces of metallic lead on either element reduced to sponge lead or to lead peroxide to produce one ampere hour; in practice, from four to six times this amount is required.

The reason for this is because it is impossible to reduce all the active material, to bring every particle in contact with the electrolyte, or to cause every part to be penetrated by the current.

Experiments show that from .5 to .8 ounces of sponge lead, and from .53 to .86 ounces of metallic lead converted into peroxide, are required on their respective elements to produce a discharge of one ampere hour at ordinary commercial rates.

The capacity increases with the temperature, being about one per cent. for each degree Fahr. increase in temperature.

Battery capacity depends on the size and number of plates; the quantity of active material present, and the quantity of electrolyte.

For an eight hour rate of discharge and 60 degrees temperature, the capacity of American batteries varies from 40 to 60 ampere hours per square foot of positive plate surface ( = 2 × number of positive plates in parallel × length × breadth).

The following table gives the variation of capacity for different rates of discharge:

Capacity Variation for Different Discharge Rates

+——————————-+——————————————————————+ | Discharge | Per cent of capacity | | rate | at 8 hour rate | +——————————-+——————————————————————+ | | =Plante= | =Faure= | | 8 hour | 100% | 100% | | 6 hour | 96% | 96% | | 4 hour | 80% | 88% | | 2 hour | 61% | 70% | | 1 hour | 56% | 48% | +——————————-+——————————+——————————-+

=Ques. How may the capacity of a battery be increased?=

Ans. By mixing organic materials with the lead oxide, but any such mixture is always accompanied by a rapid deterioration of the plates.

=Discharging.=—In discharging a battery its voltage should never be allowed to fall below 1.8 volts, under load, thus leaving about 30 per cent. of the total capacity unused. The normal discharging current may be equal to the normal charging current, but a discharge equal to 3 or 4 times the normal may be given without injury to the plates. Some types may be discharged at even six or seven times the normal rate. In such cases, however, the capacity will be reduced in the same proportion, as before explained in the paragraph dealing with battery capacities.

=Ques. What is the effect of discharging too rapidly?=

Ans. It tends to break the plates, and in the case of pasted plates, a very sudden discharge will dislodge the paste.

=Ques. How is the discharge capacity of a storage battery stated?=

Ans. In ampere hours. This, unless otherwise specified, refers to its output of current at the eight hour rate. Most manufacturers of automobile batteries specify only the amperage of the discharge at three and four hours. Thus, at the eight hour rate, a cell which will discharge at ten amperes for eight hours is said to have a capacity of eighty ampere hours. It does not follow that eighty amperes would be secured if the cell were discharged in one hour. It is safe to say that not more than forty amperes would be the result with this rapid discharge.

As a general rule, the one hour discharge rate is four times that of the normal, or eight hour discharge, and considerations of economy and prudence suggest that it should never be exceeded, if, indeed, it ever be employed. The three hour discharge, which is normally twice that of the eight hour, is usually the highest that is prudent, while the four hour discharge is the one most often employed in vehicles for the average high speed riding.

=Ques. What should be the maximum rate of discharge?=

Ans. The one-hour rate; this when used, should not extend over fifteen or twenty minutes. In the case of regulating batteries a forty-five minute rate of discharge may be allowed for one or two minutes during great fluctuations of load.

=Ques. How does the capacity decrease?=

Ans. It decreases with the increase in current output.

An 80 ampere hour cell, capable of delivering 10 amperes for 8 hours, would, when discharged at 14 amperes, have a capacity of 70 ampere hours; when discharged at 20, its capacity would be 60; and when discharged at 40, its capacity will have decreased from 80 to 40 ampere hours.

=Ques. What, in general, are the indications of the quantity of electricity remaining within a cell?=

Ans. The voltage, and the density of the electrolyte.

=Ques. What should be done after discharging?=

Ans. Whenever possible the battery should be immediately charged.

=The Battery Room.=—Precautions should be taken to prevent any direct sunlight falling on the battery cells in glass jars, as the breakage of such jars due to unequal expansion of the different portions of the glass, is a source of constant trouble and danger.

The exclusion of direct sunlight also tends to keep the evaporation of the electrolyte at a minimum.

Operation of Edison Rectifier

The operation of the Edison rectifier may be explained as follows with the aid of figs. 1,154 to 1,156 (the parts being uniformly lettered in the figures): The primary circuit taken from the alternating current mains by the cord B, embraces the primary winding of the transformer T, a condenser C, and the coils P, of the vibrating units, fig. 1,155.

The secondary circuit from the transformer embraces the massive carbon and copper contacts (N and O, fig. 1,156) which pass only the positive waves of the alternating current, for charging batteries or other duty.

An ammeter and rheostat may be placed in this charging circuit if the current is to be varied, or a fixed connection may be substituted on the base of the rectifier if it is to be used for the maximum duty of 8 or 16 amperes.

The vibrating unit (fig. 1,155), which operates in a manner similar to the well known action of a polarized relay, includes a permanent magnet M; the coil in the primary circuit P; the vibrating armature of steel with removable carbon contact N; the stationary copper contact with comb top for heat radiation O, and the screw Q for adjusting the amplitude of the armature vibration.

The vibrating armature of each unit is divided into two parts, which gives flexibility, affords increased current capacity and minimizes sparking, the two leads shown being connected together in one circuit.

A primary relay and a secondary switch (E and F, figs. 1,154 and 1,156), close their contacts when current is flowing.

Upon failure of the main alternating current line they operate to open the charging circuit. A storage battery is thus prevented discharging through the rectifier.

Upon resumption of the main alternating current, the rectifier starts automatically.

Every battery room should be provided with a water tap and sink. The floor should be paved with vitrified brick, preferably blue or yellow in color, of diamond pattern and sloping in all directions toward suitable drains. A floor of this type can be easily washed by flooding with water, and its patterns tend to keep it dry under foot at all times. Wooden floors are rotted very quickly by acid spillings and by the spray.

The room should be kept absolutely clear of everything, which may be injured, by the sulphuric acid fumes and it should be well ventilated to insure the safety and good health of the attendants.

A battery, even at rest, gives off hydrogen which when diluted with air forms a mixture which is very liable to explode if brought in contact with any kind of flame. Unless proper ventilation be provided, the breaking of the connection when a current is flowing, or the lighting of a bare flame lamp in the battery room would be dangerous.

=Battery Attendants and Workmen.=—Those employed in setting up batteries are liable to suffer from soreness of hands and the destruction of clothing unless proper precautions be taken to prevent the same. In order to avoid these troubles, the boots should be painted with paraffine mixed with an equal quantity of beeswax.

The clothing should be of woolen material, which, unlike cotton, is practically unaffected by the acid. If cotton shirts be worn, they should be dipped in a strong solution of washing soda and then rough dried.

An apron of sacking, backed with flannel should be worn over all the other clothes. A bottle of strong ammonia should be kept in the battery room at all times, and in case of an accidental splash of acid on the clothes, the immediate application of a small quantity of the ammonia, by means of the stopper, will at once neutralize the acid and prevent it burning a hole in the material. A pail containing water made strongly alkaline with washing soda should also be kept conveniently at hand during all operations in the battery room. The hands should be dipped occasionally in this water in order to prevent the skin smarting and becoming sore under the action of the acid.

If a splash of acid should happen to enter the eye, it should be washed at once with clean water, warm water preferably, and then put one or two drops of olive oil into the eye. If olive oil be not immediately available, any kind of engine oil is better than none at all.

=Points on Care and Management.=—In setting up storage cells, they should be placed in as few tiers as possible, and in such a manner that the direct rays of the sun are not allowed to fall upon the cells. The rays of the sun are likely to crack the glass. This is probably due to the unequal expansion of the glass, for it has been found that jars which are carefully annealed never crack in this manner. Of course, the latter precaution does not apply to large batteries, where lead lined wooden tanks or solid lead boxes are used.

In installing plants where expert attendance is not to be had, it is well to place in the circuit two magnetic cut outs, one set for maximum current, and the other for minimum voltage, so that the battery cannot be discharged too low.

=Ques. How should the cells be placed?=

Ans. They should be placed as shown in fig. 1,151, on insulators A, resting on wooden stringers B, and supporting pieces C placed on the floor. The insulators are usually of glass or porcelain, which in certain patterns may be filled with oil, to insure better insulation as shown in figs. 1,165 and 1,166.

In setting up a battery, it should be remembered that plates deteriorate on standing exposed to the air. They should, therefore, be unpacked and set up immediately on arrival. When they are entirely connected up, they are ready for the addition of the electrolyte, and for the forming charge, which they should receive immediately.

=Ques. How should the wooden stringers, shelves, cell boards, and trays be treated?=

Ans. They should be thoroughly varnished to insure cleanliness as well as good insulation.

Outside of each cell and close to the mouth, melted paraffine should be applied by means of a brush, so as to form a band about an inch wide, for the purpose of preventing the electrolyte creeping over the top of the jar, wetting the outside, and thereby impairing the insulation.

=Ques. What should be done to avoid waste of current by leakage?=

Ans. Each cell of the battery must be thoroughly insulated.

=Ques. What is the effect of verdigris which forms on the terminals?=

Ans. It is a poor conductor and should therefore be removed and the terminals kept bright and clean to insure the proper flow of the current.

=Ques. What precautions should be taken in unpacking cells?=

Ans. The plates should be handled carefully. When they are sent out from the factory already built into sections, they should be unpacked without disturbing a single plate. In all cases, every particle of packing, straw, hay and any chips and bits of parts should be carefully removed, and all the dust should be blown out of the spaces between the plates by means of a bellows or other similar device.

NOTE.—Champion directions for repairs. To replace broken jars in a battery remove the lid and lift out elements bodily. Empty the good jars with a syringe or by tilting the battery over. Never put the acid in any vessel except glass, stone or lead. Put new jars in place same as others and run melted paraffine around the edges. The wax must be broken off the elements that are to go into new jars and be poured on again. Fill the jars with acid to ¾" from tops. Melt the broken wax in a tin ladle and pour over the acid about ½" thick. Do not fill with wax to tops of jars. When the wax gets cold it will be found to have shrunk away from the edges of the jars. Fill up the opening with a little melted paraffine wax by means of a squirt can. Cut a small hole in the middle of the wax seal for a vent. Smear the brass posts and terminals and inside of case with vaseline to prevent creeping of the acid. The "6-25-G" requires one-half gallon of acid and the "6-50-G" one gallon.

Although such particles are good non-conductors, the action of the sulphuric acid electrolyte carbonizes them, giving them conducting properties which tend to produce leakage.

=Ques. How should the cells be assembled?=

Ans. In placing the plates or plate sections in the containing jars or tanks, care should be taken to see that the supporting frame of paraffined wood bears evenly on the bottom of the jar. If they do not, wedges of paraffined wood should be placed under the frame, so as to distribute the weight of the section equally. Each section should be lowered gently into the jar until it rests fairly upon the frame, and care should be taken to see that none of the plates have shifted, and that the section is situated centrally in the jar, with a small clear space all around.

=Ques. How should the cells be arranged?=

Ans. They should be so placed that the battery attendant can see the edges of the plates and consequently the spaces between them at the same time.

=Ques. Describe the method of connecting the cells.=

Ans. This is accomplished by means of solder, bolts and nuts, or clamps, according to circumstances. The use of solder is not essential if there be a good surface of the lead strip of one cell in contact with that of the next, and provided these contact surfaces have been well cleaned. Usually, the ends of the lead strips are turned up so that the junction of two cells takes the form of an inverted T as shown in fig. 1,162.

=Ques. What precaution should be taken in joining the terminals of the cells?=

Ans. The contact at the junctions should be very thorough, otherwise they will become heated when a current is flowing, and it is desirable that the connections should include as little lead strip in the circuit as possible, thereby reducing the amount of useless resistance.

Brass or gun metal clamps may be kept clean by brushing them over with melted paraffin after they have been screwed up tightly. When thus treated they serve to indicate points of bad contact by heat, generated at such points, when the current is flowing, softening the paraffin and changing its normal color. Vaseline and different kinds of anti-sulphuric acid varnishes, or preparations that are not attacked by the electrolyte, may also be used for this purpose. It is a good plan to color the varnish with vermillion or lamp black and paint the positive connections red and the negative connections black, and also other parts of the installation for distinguishing the polarities.

=Cell Connections.=—The cells may be connected together either in series or parallel, or in parallel-series or series-parallel combinations, according to the requirements, but in all cases it is best to use the simplest arrangement practicable.

For instance: if the cells employed in an installation requiring 110 volts, have only half the capacity required, and 55 cells give the desired voltage, then the number of cells must be increased to 110, and theoretically the required number of amperes hours at 110 volts may be obtained in one of two ways: 1, by connecting the cells in pairs in parallel and then coupling the pairs together in series, and 2, by arranging the 110 cells in two complete batteries of 55 cells each connected in series, then coupling the two batteries in parallel.

The first method is quite impracticable, however, as the slightest difference between the voltages of the two cells of any pair will result in the one having the greater pressure discharging into the other, thereby causing the entire battery to quickly deteriorate.

NOTE.—To determine the positive wire. Without a voltmeter, the positive terminal of the charging circuit can be determined by attaching a piece of clean lead to each wire which is to be connected to the battery, and immersing them, without touching each other, in a glass or other insulating vessel containing water to which is added a drop or two of sulphuric acid. After the current has passed through the circuit for a short time, the positive lead will commence to discolor, and, if left long enough, will turn brown. Bubbles will arise from the two terminals immersed, the larger and more frequent ones being from the negative, the smaller ones from the positive.

NOTE.—Method of disconnecting "National" cells. There are two methods of disconnecting the cells employing link connectors. First a ⅝ inch bit or twist drill may be used, boring down into the top of the posts about ¼ inch. The link will then be loosened and can be removed. This leaves the link, as well as the post, in good condition for reburning. Second the link may be cut in the center. A flame should be played on the top of the post, at the same time grasping the end of the half link firmly with pliers. When the connection has become warmed (care being taken not to melt the lead) the half link can be twisted loose from the port. New links may be used if desired in re-assembling the cells. It is not necessary to remove the covers from the element, the links may be cut in the center and the plates removed from the jars without removing the links from the ports. The links can be afterwards reburned together in the center. When the cells are equipped with "T" or "L" straps, they should be cut apart with hack saw or chisel midway between the cells, and in re-assembling, burned together at this point.

=Battery Troubles.=—To successfully cope with faults in storage batteries, there are two requisites: 1, a thorough knowledge of the construction and principle of operation of the battery, and 2, a well ordered procedure in looking for the source of trouble. The faults which are usually encountered by those who operate storage batteries are here given.

=Short Circuiting.=—A form of derangement that may occasionally affect storage batteries is short circuiting. It may be caused by some of the active material—if the cell be of the pasted variety—scaling off and dropping between the plates, or by an over collection of sediment in the bottom of the cell.

Should the operator suspect trouble with his battery he may discover a short circuited cell by the marked difference in color of the plates or of the specific gravity of the electrolyte, as compared with the other cells. No particular damage will be caused, if the trouble be discovered and removed before these symptoms become too marked.

If a foreign substance has become lodged between the plates, it may be removed by a wood or glass instrument.

If some of the active material has scaled off, it may be forced down to the bottom of the jar. If excessive sediment be found, the jar and plates should be washed carefully, and reassembled.

A cell that has been short circuited may be disconnected from the battery and charged and discharged several times separately which may remedy the trouble.

=Ques. How are internal short circuits indicated?=

Ans. Short circuits in a cell are indicated by short capacity, low voltage and low specific gravity, excessive heating and evaporation of the electrolyte.

=Ques. How are internal short circuits located?=

Ans. If the trouble cannot be located by the eye, the battery should be connected in series and discharged at the normal rate through suitable resistance. If a suitable rheostat be not available, a water resistance may be used.

This consists of a receptacle (which must not be of metal) filled with very weak acid solution, or with salt water in which are suspended two metal plates, which are connected by wires through an ammeter. The current may be regulated by altering the distance between the plates, or by varying the strength of the solution. As the discharge progresses the voltage will gradually decrease, and it should be frequently read at the battery terminals; as soon as it shows a sudden drop, the voltage of each cell should be read with a low reading voltmeter.

While the readings are being taken, the discharge rate should be kept constant and the discharge continued until the majority of the cells read 1.70 volts; those reading less should be noted. The discharge should be followed by a charge until the cells which read 1.70 volts are up, then the low cells should be cut out, examined, and the trouble remedied.

=Overdischarge: Buckling.=—On account of unequal expansion of the two sides of a plate, or certain portions thereof, the strains thus set up may distort it and cause it to assume a buckled shape, that is, bent so one side is concave.

Buckling is due always to over discharge on either the whole, or some portion of the plate. Occasional buckling may occur with too rapid charge and discharge.

=Sulphation of Plates.=—During discharge a storage cell deteriorates on account of the formation of lead sulphate over the surface of the plates. This lead sulphate is the product of the chemical combination of active material with the electrolyte. It is a non-conductor, white in color and of greater volume, in proportion than the active material. When the discharge is over prolonged, sulphation is evidenced by the electrodes becoming lighter in color, because of the sulphate which lessens the active surface.

=Ques. Name some causes of sulphation.=

Ans. It is sometimes caused by a too weak or too strong acid solution, but more generally by continued over discharging, or too rapid discharging of the batteries, or by allowing them to remain uncharged for long periods of time.

=Ques. What is the effect of sulphation?=

Ans. It tends to cause shedding of the active material, buckling of plates, loss of capacity, increase of resistance and consequent reduction of efficiency, and increase of temperature with flow of current. A sufficient amount of lead peroxide and sponge lead must be retained on the plates to reduce this resistance, otherwise the charging current cannot flow through the active material and regenerate the battery.

=Ques. What should be done in case of sulphation?=

Ans. Charge the battery below the maximum rate, necessarily prolonging the charge, until the plates assume the proper color. This is a tedious task, but it must not be hastened, as rapid charging will cause serious buckling.

* * * * *

NOTE.—How to destroy acid vapor in storage battery rooms: The best remedy is a good system of thorough and rapid ventilation; failing this the evil effect of the acid may be minimized by the fumes of a powerful alkali such as ammonia, which will readily combine with the sulphuric acid to form sulphate of ammonia, an inert and harmless salt. If the use of liquid ammonia be objectionable, the granulated carbonate of ammonia will do equally well. The ammonia fumes are best obtained by placing dilute ammonia in shallow dishes, so that an extensive evaporating surface is obtained. In the same way the corroding dew which is so frequently deposited on the lugs and connectors of storage battery elements may readily be neutralized by the application of a solution of ammonia, or even common washing soda. A good method of protecting metal work in battery rooms is to smear it over evenly with vaseline.

The charging should be done at low rates. Discharge should not be carried below 1.8 volts per cell, and the charging current should be stopped when each cell shows 2.4 volts.

If the plates be in a very bad condition, a little of the white sulphate deposit on each of the positive plates may be removed with a stick, thus exposing a part of the good surface to the action of the electrolyte.

If the positive plates cannot be restored to their proper color as directed, it is cheaper to replace them by a new set, rather than to attempt their recovery by means of reversals.

Electrical Data on "National" Cells (Size of plate 4⅞" × 8⅝")

======================================+=======+=======+========+======== Number of Plates per cell | 5 | 7 | 9 | 11 ——————————————————————————————————————+——————-+——————-+————————+———————— {for 4 hours |12 |18 | 24 | 30 Discharge in amperes {for 5 hours |10¼ |15¼ | 20½ | 25½ {for 6 hours | 9¼ |13¾ | 18½ | 23 | | | | {at 4 hour rate|48 |72 | 96 |120 Ampere hour capacity {at 5 hour rate|51 |76 |102 |127 {at 6 hour rate|55 |83 |110 |138 | | | | Outside measurements of rubber {Length| 1⅞ | 2⅝ | 3⅜ | 4-3/16 jar, in inches {Width | 5-5/16| 5-5/16| 5-5/16| 5-5/16 {Height|11¾ |11¾ | 11¾ | 11¾ | | | | Weight of cell complete, in lbs |14¼ |19¼ | 24¼ | 29¾ | | | | Weight of electrolyte, in lbs | 1 | 2 | 3½ | 5 ——————————————————————————————————————+——————-+——————-+————————+————————

=Lack of Capacity.=—This is usually due to the clogging of the pores in the plate with sulphate which is invisible because the surface of the plate is maintained in proper condition but the interior portions of the active material have not been thoroughly reduced. To correct this condition, the battery should be given a prolonged overcharge at low current rates, say about one fourth the normal 8 hour charging rate.

NOTE.—Oxide of lead, litharge, or plumbic oxide is sometimes found native as lead ochre, and may be artificially made by heating the carbonate or nitrate. It is usually prepared on a larger scale by heating the lead in air. When the metal is only moderately heated, the oxide forms a yellow powder which is known as massicot, but at a higher temperature the oxide melts, and on cooling, it forms a brownish scaly mass, which is called flake litharge. The scaly pieces are afterwards ground between stones under water, forming buff or levegated litharge. The litharge of commerce often has a reddish yellow color, due to the presence of some of the red oxide of lead, and frequently from one to three per cent. of finely divided metallic lead is found mixed with it. When heated to dull redness litharge assumes a dark brown color, and becomes yellow again on cooling. At a bright red heat it fuses and readily attacks clay crucibles, forming silicate of lead. Litharge is a most powerful base, and has a strong tendency to form basic salts. Hot solution of alkalies, as potash or soda, readily dissolve it, and on cooling, it crystalizes out in the form of beautiful pink crystals.

Falling off in the capacity may be caused by a dry cell, due to a leaking jar; some or all of the cells may be in a state of incomplete charge, due to the battery having been run too low and not sufficiently charged; or the plates may be short circuited, either by the sediment (deposit in the bottom of the jar) getting up to the bottom of the plates or by something that has fallen into the cell.

Electrical Data on "American" Cells

+————————+——————————————————————————————————————————-+ | Normal | Number of 30 volt Tungsten lamps that can | |Capacity| be run with 16 cells in series for | | | 2, 4, 6 or 8 hours | +————————+——————————+——————————+——————————+——————————+ | Ampere | | | | | | hours | 2 hours | 4 hours | 6 hours | 8 hours | | 40 | 14 | 9 | 8 | 7 | | 60 | 17 | 14 | 12 | 10 | | 80 | 28 | 18 | 15 | 14 | | 120 | 42 | 27 | 24 | 21 | | 160 | 57 | 37 | 31 | 28 | | 200 | 71 | 45 | 40 | 35 | | 250 | 88 | 56 | 50 | 44 | | 300 | 106 | 70 | 60 | 52 | | 350 | 124 | 81 | 71 | 62 | | 400 | 142 | 91 | 81 | 71 | +————————+——————————+——————————+——————————+——————————+

=Ques. What action takes place when a battery stands idle for some time?=

Ans. It loses part of its charge, due to local losses in the cells.

=Ques. How should batteries be treated, when used but occasionally?=

Ans. If a battery is not to be used for several days, it should first be fully charged before standing; if it continue idle, a freshening charge should be given every two weeks, continuing the charge when the cells begin to gas freely.

=Ques. What should be done in case of lack of capacity?=

Ans. If the current consumption be normal, there may be poor connections or trouble in the battery; there may be a dry cell, due to a leaking jar; some or all of the cells may be in a state of incomplete charge, due to the battery having been run too low and not sufficiently charged, or the plates may be short circuited, either by the sediment (deposit in the bottom of the jar) getting up to the bottom of the plates or by something that has fallen into the cell.

Electrical Data on "Autex" Cells (Standard plates; size, 5¾" x 8⅝")

+————————————————————————————————+————————+————————+————————+————————+ |Number of Plates | 7 | 9 | 11 | 13 | +————————————————————————————————+————————+————————+————————+————————+ |Discharge in Amperes for 4 hours| 21 | 28 | 35 | 42 | +————————————————————————————————+————————+————————+————————+————————+ | {Length | 2¾ | 3½ | 4¼ | 5 | |Outside Measurements { +————+————+————+————+ | {Width | 6⅛ | 6⅛ | 6⅛ | 6⅛ | |Rubber Jars in inches. { +————+————+————+————+ | {Height | 12⅜ | 12⅜ | 12⅜ | 12⅜ | +————————————————————————————————+————————+————————+————————+————————+ | {Element | 15¾ | 20¼ | 24¼ | 29¾ | | { +————————+————————+————————+————————+ |Weight in Pounds {Electrolyte | 4½ | 5 | 5¾ | 6¼ | | { +————————+————————+————————+————————+ | {Complete Cell | 22 | 28 | 34¼ | 40½ | +————————————————————————————————+————————+————————+————————+————————+

Electrical Data on "Autex" Cells(continued) (Standard plates; size, 5¾" x 8⅝") +————————————————————————————————+————————+————————+————————+————————+ |Number of Plates | 15 | 17 | 19 | 21 | +————————————————————————————————+————————+————————+————————+————————+ |Discharge in Amperes for 4 hours| 49 | 56 | 63 | 70 | +————————————————————————————————+————————+————————+————————+————————+ | {Length | 5¾ | 6½ | 7¼ | 8 | |Outside Measurements { +————————+————————+————————+————————+ | {Width | 6⅛ | 6⅛ | 6⅛ | 6⅛ | |Rubber Jars in inches. { +————————+————————+————————+————————+ | {Height | 12⅜ | 12⅜ | 12⅜ | 12⅜ | +————————————————————————————————+————————+————————+————————+————————+ | {Element | 34 | 38½ | 43 | 47½ | | { +————————+————————+————————+————————+ |Weight in Pounds {Electrolyte | 7 | 7¾ | 8½ | 9¾ | | { +————————+————————+————————+————————+ | {Complete Cell | 47 | 53¼ | 59½ | 66 | +————————————————————————————————+————————+————————+————————+————————+

NOTE.—Peroxide of lead, pure oxide or plumbic dioxide is the true active material in all forms of lead storage cell. This lead salt is found native as the mineral plattnerite. It is a heavy lead ore, forming black, lustrous, six sided prisms. It may be prepared from the red oxide by boiling it in fine powder, with nitric acid diluted with five parts of water, or by treating the carbonate when suspended in water with a stream of chlorine gas, and then thoroughly washing and drying it. It is reduced to a lower oxide on heating or by exposure to bright sunlight. This salt readily imparts oxygen to other substances; it becomes heated to redness when thrown into sulphuric dioxide, and takes fire when triturated with sulphur—hence this oxide is a common ingredient in lucifer match composition. When used in primary or secondary batteries it readily imparts its oxygen to nascent hydrogen, forming water, and thus it acts as a powerful depolarizer. When robbed of its oxygen, it readily becomes reoxidized, if subjected to the action of nascent oxygen liberated by the electrolytic decomposition of water.

If the trouble cannot be located by the eye, connect the battery in series, and discharge it at the normal rate, through suitable resistance. If a suitable rheostat be not available, a water resistance may be used.

This consists of a receptacle (which must not be of metal) filled with very weak acid solution or salt water in which are suspended two metal plates, which are connected, by wires through an ammeter.

Electrical Data on "Autex" Cells (Light weight plates; size, 5¾" × 8⅝")

——————————————————————————+——————————+————————-+——————————+————————+————————-+ Number of Plates | 7 | 9 | 11 | 13 | 15 | ——————————————————————————+——————————+————————-+——————————+————————+————————-+ Discharge in Amperes for | | | | | | 5 hours | 15¾ | 21 | 26¼ | 31½ | 36¾ | ——————————————————————————+——————————+————————-+——————————+————————+————————-+ Outside {Length | 1-29/32 | 2-7/16 | 3-31/32 | 3½ | 4-⅟32 | Measurements { +——————————+————————-+——————————+————————+————————-+ {Width | 6⅛ | 6⅛ | 6⅛ | 6⅛ | 6⅛ | Rubber { +——————————+————————-+——————————+————————+————————-+ Jars in in. {Height | 12⅜ | 12⅜ | 12⅜ | 12⅜ | 12⅜ | ——————————————————————————+——————————+————————-+——————————+————————+————————-+ Weight {Element | 11½ | 14¾ | 18 | 21¼ | 24½ | in { +——————————+————————-+——————————+————————+————————-+ Pounds {Electrolyte | 2¼ | 2½ | 3 | 3¾ | 4¼ | { +——————————+————————-+——————————+————————+————————-+ {Comp. Cell | 15¾ | 20 | 24¼ | 28½ | 33¼ | ——————————————————————————+——————————+————————-+——————————+————————+————————-+

——————————————————————————+——————————+————————-+——————————+————————+————————-+ Number of Plates | 17 | 19 | 21 | 23 | 25 | ——————————————————————————+——————————+————————-+——————————+————————+————————-+ Discharge in Amperes for | | | | | | 5 hours | 42 | 47¼ | 52½ | 57¾ | 63 | ——————————————————————————+——————————+————————-+——————————+————————+————————-+ Outside {Length | 4-9/16 | 5-3/32 | 5⅜ | 6-5/32| 6-11/16 | Measurements { +——————————+————————-+——————————+————————+————————-+ {Width | 6⅛ | 6⅛ | 6⅛ | 6⅛ | 6⅛ | Rubber { +——————————+————————-+——————————+————————+————————-+ Jars in in.|{Height | 12⅜ | 12⅜ | 12⅜ | 12⅜ |12⅜ | ——————————————————————————+——————————+————————-+——————————+————————+————————-+ Weight {Element | 27¾ | 31 | 34¼ | 37¼ | 40½ | in { +——————————+————————-+——————————+————————+————————-+ Pounds {Electrolyte | 4¼ | 5½ | 6 | 6¾ | 7¼ | { +——————————+————————-+——————————+————————+————————-+ {Comp. Cell | 38 | 42 | 46¼ | 51½ | 56 | ——————————————————————————+——————————+————————-+——————————+————————+————————-+

The current may be regulated by altering the distance between the plates or by varying the strength of the solution. As the discharge progresses, the voltage will gradually decrease and it should be frequently read at the battery terminals. When it shows a sudden drop, the voltage of each cell should be read with a low reading voltmeter.

While the readings are being taken, the discharge rate should be kept constant and the discharge continued until the majority of the cells read 1.70 volts; those reading less should be noted. The discharge should be followed by a charge until the cells which read 1.70 volts are up; then the low cells should be cut out, examined and the trouble remedied.

NOTE.—How to prevent lead poisoning. Workmen employed in the manufacture of lead or lead salts are always liable to lead poisoning, both by inhaling the dust and by contact of the materials with the hands. Various preventives for this have been employed, and of these, the most simple seems to be a careful washing of the hands in petroleum. It is said that three washings a day are sufficient to prevent all serious danger of poisoning. The benzole in the petroleum appears to scour the skin and remove the loose lead dust, and the fatty substance in the oil fills up the pores of the skin and prevents the absorption of the deleterious salts. The employment of petroleum has given such good results that it has been proposed to use this material as a guard against poisoning in other industries where the salts of copper or mercury are employed.

=Ques. What causes low specific gravity when there are no short circuits?=

Ans. 1, sloppage or a leaky jar (the loss having been replaced with water alone), 2, insufficient charge, 3, over discharge, or 4, a combination of these abuses. Any of these mean that there is acid in combination with the plates.

In this case the acid should be brought out into the electrolyte by a long charge at a quarter of the normal discharge rate.

=Ques. How should weak cells be treated?=

Ans. They should be grouped by themselves and charged as a separate battery, care being taken that the positive strap of one cell, is connected to the negative strap of the adjoining cell and that the charging connections are properly made. If there be not sufficient resistance in the charging rheostat to reduce the current to the proper point, a water resistance should be used.

NOTE.—Pole testing paper. Make a thin solution of white starch and soak strips of thin white blotting paper in it, and set aside in a clean, dry place to dry. Dissolve ½ oz. of potassium iodide in one pint of water. Immerse the strips in the solution for a few seconds and again dry. This paper, when moistened and used in the usual way, turns violet at the positive pole.

While a cell is being treated, when possible, the cover should be removed (if sealed, the compound can be loosened by using a hot putty knife).

=Disconnecting Cells.=—The best method of disconnecting cells assembled with pillar straps, for the purpose of replacing broken jars, cleaning or taking out of commission, is to use a five-eighth inch twist drill, in a carpenter's brace, boring down into the top of the pillar about one-quarter inch; then pull off the connector sleeve from the pillar. By following this method, all parts may be used again.

When cells are equipped with top straps, the straps should be cut with a sharp knife or chisel midway between the cells.

=Taking Batteries out of Commission.=—Where a battery is to be out of service for several months, and it is not convenient to give it the freshening charge every two weeks, it should be taken out of commission.

COMPARISON OF THE BAUMÉ AND SPECIFIC GRAVITY SCALES AT 60° FAHRENHEIT +————————-+——————————+————————-+——————————+————————-+——————————+————————-+——————————+ |Degrees|Specific|Degrees|Specific|Degrees|Specific|Degrees|Specific| | Baume |Gravity | Baume |Gravity | Baume |Gravity | Baume |Gravity | +————————-+——————————+————————-+——————————+————————-+——————————+————————-+——————————+ | 0 | 1.000 | 17 | 1.133 | 34 | 1.306 | 51 | 1.542 | | 1 | 1.007 | 18 | 1.142 | 35 | 1.318 | 52 | 1.559 | | 2 | 1.014 | 19 | 1.151 | 36 | 1.330 | 53 | 1.576 | | 3 | 1.021 | 20 | 1.160 | 37 | 1.342 | 54 | 1.593 | | 4 | 1.028 | 21 | 1.169 | 38 | 1.355 | 55 | 1.611 | | 5 | 1.036 | 22 | 1.179 | 39 | 1.368 | 56 | 1.629 | | 6 | 1.043 | 23 | 1.188 | 40 | 1.381 | 57 | 1.648 | | 7 | 1.051 | 24 | 1.198 | 41 | 1.394 | 58 | 1.666 | | 8 | 1.058 | 25 | 1.208 | 42 | 1.408 | 59 | 1.686 | | 9 | 1.066 | 26 | 1.218 | 43 | 1.421 | 60 | 1.707 | | 10 | 1.074 | 27 | 1.229 | 44 | 1.436 | 61 | 1.726 | | 11 | 1.082 | 28 | 1.239 | 45 | 1.450 | 62 | 1.747 | | 12 | 1.090 | 29 | 1.250 | 46 | 1.465 | 63 | 1.768 | | 13 | 1.098 | 30 | 1.261 | 47 | 1.479 | 64 | 1.790 | | 14 | 1.107 | 31 | 1.272 | 48 | 1.495 | 65 | 1.812 | | 15 | 1.115 | 32 | 1.283 | 49 | 1.510 | 66 | 1.835 | | 16 | 1.124 | 33 | 1.295 | 50 | 1.526 | | | +————————-+——————————+————————-+——————————+————————-+——————————+————————-+——————————+

NOTE.—The characteristic properties of concentrated sulphuric acid are very marked. Its freedom from odor, oily appearance, and its great weight, distinguish it from other liquids. The pure concentrated commercial acid has a density which usually reaches 1.842, and its boiling point is about 640° F. The absolutely pure acid is perfectly colorless, but usually even that used in laboratories has a peculiar grayish color, due to slight traces of organic matter. Sulphuric acid is exceedingly hydroscopic, and when exposed to the air it rapidly increases in bulk, owing to absorption of atmospheric moisture.

NOTE.—Clamps not made of metal similar to that of the connecting strips, frequently give trouble from the galvanic action due to the contact of dissimilar metals in the presence of moisture which causes the destruction of either the connecting strip or the clamp. Such troubles can be avoided by placing a thin strip of sheet zinc between the lead strip and the clamp. Under these circumstances the zinc will crumble away, and can be replaced without much inconvenience and very little expense, while the clamps and connecting strips will remain uninjured.

Strength of Dilute Sulphuric Acid of Different Densities at 59° Fahr. +————————————————+——————————+————————————————+——————————+ | Per cent. | Specific | Per cent. | Specific | | of | | of | | | Sulphuric Acid | Gravity | Sulphuric Acid | Gravity | +————————————————+——————————+————————————————+——————————+ | 100 | 1.842 | 23 | 1.167 | | 40 | 1.306 | 22 | 1.159 | | 31 | 1.231 | 21 | 1.151 | | 30 | 1.223 | 20 | 1.144 | | 29 | 1.215 | 19 | 1.136 | | 28 | 1.206 | 18 | 1.129 | | 27 | 1.198 | 17 | 1.121 | | 26 | 1.190 | 16 | 1.116 | | 25 | 1.172 | 15 | 1.106 | | 24 | 1.174 | 14 | 1.098 | +————————————————+——————————+————————————————+——————————+

=Ques. Describe the method of taking a battery out of commission.=

Ans. The battery is charged in the usual manner, until the specific gravity of the electrolyte of every cell has stopped rising over a period of one hour (if there be any low cells, due to short circuits or other cause, they should be put in condition before the charge is started, so that they will receive the full benefit of it). The cells may now be disconnected and covers and elements removed from the jars, (if sealed, the compound is loosened with a hot putty knife). The elements are placed on their sides with the plates slightly spread apart at the bottom, the separators withdrawn, and the positive and negative groups pulled apart. The electrolyte is washed off with a gentle stream of water and the plates allowed to drain and dry.[7] The positive plates are ready to be put away. When dry, the negatives are completely immersed in electrolyte (of about 1.275 specific gravity), and allowed to soak for three or four hours. The jars may be used for this purpose. After rinsing and drying, they are ready to be put away; wash also the rubber separators.

[7] NOTE.—If the active material in the negative plates extend beyond the ribs of the grid (the supporting frame), it should be at once pressed back into place, care being taken to prevent the plates drying before this is done. The most suitable and convenient method for pressing, is to place between the plates smooth boards of a thickness equal to the distance between the plates and then put the groups under pressure.

Wood separators, after having been in service, will not stand much handling and had better be thrown away. If it be thought worth while to keep them, they must be immersed in water or weak electrolyte, and in re-assembling, the electrolyte must be put into the cells immediately, as wet wood separators must not stand exposed to the air.

=Ques. What precaution should be taken with the jars?=

Ans. They should be thoroughly cleaned with fresh water, no sediment being allowed to remain.

=Putting Batteries into Commission.=—When re-assembling a battery, it should be treated in the same manner as if it were new and the regular instructions for assembling and putting a new battery into commission followed.

=Cleaning Jars.=—The jars should be thoroughly cleaned with fresh water, no sediment being allowed to remain.

Table of Voltage Change as Affected by Discharge Rate[8]

[8] NOTE.—The voltage increase or decrease with change in current is practically constant in a given type of cell for any size of cell when the current is referred to a given time rate of charge or discharge; that is, the drop in a large cell or in a small cell, when each is discharged at its four, six or eight hour rate, will be the same. The drop varies somewhat for the condition of the battery charge. For batteries which are one-third discharged, the temperature 60° Fahr., and plates in good condition, the changes in pressure which may be expected between open circuit voltage and the voltage on charge or discharge are given in the above table.

8 hour rate .05 volt 6 " " .065 " 4 " " .09 " 3 " " .11 " 2 " " .14 " 1½ " " .18 " 1 " " .21 "

=Condensed Rules for the Proper Care of Batteries.=—The following general instructions should be followed in the care and maintenance of batteries:

1. A battery must always be charged with "direct" current and in the right direction.

2. Be careful to charge at the proper rates and to give the right amount of charge; do not undercharge or overcharge to an excessive degree.

3. Do not bring a naked flame near the battery while charging or immediately afterwards.

4. Do not overdischarge.

5. Do not allow the battery to stand completely discharged.

6. Voltage readings should be taken only when the battery is charging or discharging; if taken when the battery is standing idle they are of little or no value.

7. Do not allow the battery temperature to exceed 110° Fahr.

8. Keep the electrolyte at the proper height above the top of the plates and at the proper specific gravity. Use only pure water to replace loss by evaporation. In preparing the electrolyte never pour water into the acid.

9. Keep the cells free from dirt and all foreign substances, both solid and liquid.

10. Keep the battery and all connections clean; keep all bolted connections tight.

11. If there be lack of capacity in a battery, due to low cells, do not delay in locating and bringing them back to condition.

12. Do not allow sediment to get up to the plates.

Spotted a typo or a problem in this chapter? Tell us

XLV. STORAGE BATTERY SYSTEMS

Storage batteries are used for many purposes, such as to supply current for electric vehicles, gas engine ignition, lighting, and in connection with power stations and distribution work.

* * * * *

The latter is an important field, the storage battery being used in connection with the power station for the following purposes:

1. To carry the peak load, during hours of maximum demand; 2. To carry the entire load during hours of minimum demand, or for a short time in case of emergency; 3. To act as an equalizer; 4. For regulation of load and voltage; 5. As compensation for feeder drop; 6. As a preventive against shut downs.

In almost every electric lighting plant there are long periods during the day and late at night when the number of lamps lighted is so small that it may not pay to run the generating machinery. In such cases, storage batteries may usually be used to advantage to aid in carrying the maximum load and to supply the entire current at minimum load as illustrated in fig. 1,179. In other words, batteries are substituted for a certain portion of the machinery plant or are used in place of the latter.

=Ques. What provision must be made in power plants when storage batteries are not used?=

Ans. The capacity of the generating machinery must be sufficient for the heaviest overloads which may occur, and it must be operated continuously for 24 hours a day in the majority of central stations supplying current for lighting and power.

=Ques. What results are obtained with this method of working?=

Ans. The engines working under very variable loads, not only operate at low efficiency, but are continually subjected to severe mechanical strains.

=Ques. How may greater efficiency be secured with steam engines under variable loads?=

Ans. Judicious selection of the number and sizes of the engines enable them to be worked in most cases at a considerable fraction of their full capacity nearly all the time.

=Ques. What further improvement is secured in most cases with the storage battery?=

Ans. The plant is made more flexible, and the economy of the engines is increased by making their loads nearer uniform, and nearer to full capacity while they are running.

=Ques. What is the effect of a battery connected in parallel with a dynamo, as in fig. 1,180?=

Ans. It is not necessary for the dynamo to have a capacity exceeding that which is sufficient for the average daily load, at which it may be worked practically all the time.

When the load is below the average, the dynamo charges the battery, and when the load rises above the average, during the hours of maximum demand, the battery discharges into the line in parallel with the dynamo. During the hours of minimum demand the engines may be shut down and the necessary current supplied from the battery alone, thus not only increasing the efficiency of the plant, but serving to maintain a steadier pressure under fluctuating loads.

=Ques. What is understood by the expression "floating the battery on the line"?=

Ans. A storage battery is said to float on a line when connected across the circuit at some distance from the power station, so that a heavy load on the line, within the range of the battery influence, causes sufficient line drop to allow the battery to discharge, while with a light load on the line, the drop is small and the impressed voltage at the battery high enough to charge the battery. This usage is confined chiefly to electric railway service, where large voltage changes are permissible.

=Ques. When the battery is floated on the line, how may the amount of charge be made to approximately equal the amount of discharge?=

Ans. By properly proportioning the number of cells in series.

=Connections and Circuit Control Apparatus.=—When a storage battery is used in an electric lighting plant, provision must be made for feeding the lamps, etc., from either the dynamo or battery separately, or from the two working in parallel, and it should be possible to charge the battery at the same time the lamps are being supplied. To accomplish these results requires three switches, for the following connections:

1. To connect the lamps to the dynamo; 2. To connect the lamps to the battery; 3. To connect the battery to the dynamo.

In some plants, the first switch is omitted, because the lamps are always fed by the battery alone, the latter being charged during the day, when no lamps are in use.

It is desirable, however, to have all three switches in every plant in order to be able to supply lamps and charge the battery at any time.

In the battery circuit there should be an ammeter having a scale on both sides of zero, to show whether the battery is being charged or discharged, as well as the value of the current. Another similar ammeter is required in the circuit between the dynamo and the battery, to show the direction and amount of current. A third ammeter is desirable in the lamp circuit, to show the total current supplied to the lamps, but it need only indicate on one side of zero, since the current there always flows in the same direction.

A voltmeter is required with a three-way switch to connect it to the dynamo, battery or lamps, and a circuit breaker must be inserted in the battery circuit in order that it may be opened when the current becomes excessive.

A discriminating cut out or reverse current circuit breaker is required between the dynamo and the battery to open the circuit when the charging current falls below a certain value, and thus avoid any danger of the battery discharging through the dynamo, if from any cause the voltage of the latter drop below that of the battery. This completes the ordinary measuring and circuit controlling apparatus employed with storage batteries.

=Methods of Control for Storage Batteries.=—As the external voltage of a storage battery varies with the amount of charge it contains and with the direction of the current, it is necessary to employ some means for compensating this variation in order to maintain a constant voltage on the line supplied by the battery. The various devices used for this purpose are as follows:

1. Variable resistances; 2. End cell switches; 3. Reverse pressure cells; 4. Boosters.

The particular method selected will depend upon the size of the battery, the purpose for which it is used, the allowable limits pf current and voltage variations, the cost of the system, etc.

=Variable Resistance.=—Regulation by variable resistance may be used advantageously only with batteries of small capacity, and in small lighting plants such as those of yachts, where the space available for battery auxiliaries is limited, and where the cost of energy is so low that the loss of power in the resistance is not objectionable.

The connections for one of the simplest methods is shown in fig. 1,185. The battery is divided into two halves, which are connected in series for discharging and in parallel for charging. Since the voltage of each cell at the end of a discharge should not be lower than 1.8 volts, a battery intended for use on a 110 volt lighting circuit will require 110 ÷ 1.8 = 62 cells. The voltage necessary, however, for each cell at the end of a charge is about 2.6 volts, or a total of 2.6 × 62 = 161 volts for the battery, a value which is far above the line voltage. By dividing the battery into two halves and connecting them in parallel only 80.5 volts are necessary for charging. The excess voltage of the line, 29.5 volts is taken up by the resistance, which also controls the output of the battery on discharge.

=End Cell Switches.=—These may be used to advantage in small installations where there is not demand for current during the day, or where the charging is done by means of boosters.

=Ques. What is an end cell switch?=

Ans. A form of switch employed in connection with a storage battery in order to control the end cells for regulating the voltage.

=Ques. Describe the construction of an end cell switch.=

Ans. This is shown in fig. 1,187. The switch contact arm is made in two parts, A and B, which are insulated from each other as shown, and connected with each other through the protective resistance R. The end cell contacts are so spaced that when the main current carrying part A of the switch arm is squarely on one end cell contact such as X, the part B, does not touch any other contact such as Y, but when the switch arm is advanced for cutting into circuit another end cell, the part B, reaches the contact Y before the part A, leaves the contact X, thus keeping the battery circuit closed, while the resistance R, limits the current in the short circuited cell at the instant the switch arm passes from one end cell contact to the next.

=Ques. How should the conductors joining the end cells to the end cell switch contacts be proportioned?=

Ans. They must have the same sectional area as the conductors of the main circuit.

The reason for this is that when any end cell is in use, the conductor connecting it to the switch becomes a part of the main circuit. An allowance of 1,000 amperes per sq. in., when the battery is discharging at the two-hour rate, is considered good practice.

=Ques. Describe some of the features of end cell switch construction.=

Ans. Those of small capacity are made circular; the larger sizes are made horizontal in form, and both types may be either operated by hand or motor driven.

=Ques. Where are end cell switches of large capacity located?=

Ans. Generally they are placed as near the battery room as possible to avoid the cost of running the heavy conductors, and when such switches are motor driven, the usual practice is to control their operation from the main switchboard.

In fig. 1,188 is shown the method of regulation with an end switch. The diagram shows the battery being charged with the main switch open, and the voltage of the dynamo raised to the charging pressure. During discharge the cells are connected in series, and as the voltage of each cell at the beginning of discharge is at least 2.1 volts, only 52 or 53 cells are required to give the desired pressure of 110 volts, but as the discharge continues, and the voltage of each cell decreases, the end cells, 1, 2, 3, 4, etc., are cut into circuit successively by means of the end cell switch, thereby adding to and compensating the drop in the total voltage until, at the end of discharge when the voltage of each cell has fallen to 1.8 volts, the entire 62 cells are in series to supply the required line pressure.

For a 110 volt circuit, the number of cells required is 110 ÷ 1.8 = 61, and the number in series when the battery begins to discharge is 110 ÷ 2.1 = 52. Hence, in a 110 volt circuit an arrangement must be provided whereby 61 - 52 = 9 cells may be cut out or switched in, one by one.

The number of end cells for any voltage may be obtained by the following formula:

Number of end cells = (E/1.8) - (E/2.1)

E = voltage of supply circuit; 1.8 = minimum voltage of cell during discharge; 2.1 = voltage of fully charged cell.

=Reverse Pressure Cells.=—These consist of unformed lead plates immersed in the ordinary electrolyte of dilute sulphuric acid. As they have no active material, they possess no capacity, but are capable of setting up an opposing pressure of about 2 volts each to the discharging current flowing through them, thereby cutting down the total voltage of the battery, so that the net voltage across the line depends on the number of reverse current cells in series in the battery circuit. As the voltage of the battery falls during discharge, the reverse pressure cells are cut out, successively, thus keeping the external or line voltage constant.

It is obvious, that as these cells do not possess any capacity, the number of active cells required in the battery will be the same as when end cell control is employed. Therefore, the reverse pressure cells represent an increase in equipment, which entails an additional expense of at least 8 per cent. For this reason, and also on account of the fact that the amount of energy lost in discharging against reverse pressure cells, is the same as when the resistance methods of controlling the discharge are employed, the use of cells for this purpose is now practically obsolete.

=Boosters.=—In general, a booster may be defined as a dynamo inserted in series in a circuit, to change its voltage. It may be driven by an electric motor, in which case it is sometimes called a motor-booster. The function of a booster is to add to an electric pressure derived from another source.

For instance, if a storage battery be used in conjunction with one or more dynamos to supply current to an electric light installation, the battery cannot be charged from the machines which are feeding the lamps, because it requires a pressure higher than that required for the lamps to complete the charge. A small dynamo is therefore connected in series, with the main machines and the battery, acting in conjunction with the former to provide the necessary pressure.

The power for running such a dynamo is obtained in various ways. The dynamo or charging booster may be belt driven or arranged on an extension of the armature shaft of the main dynamo; again, it may consist of a single armature with a double winding (fig. 1,191), or a motor and dynamo coupled together on one bed plate as in figs. 800 and 805. Boosters may be divided into several classes as follows:

1. Series boosters; 2. Shunt boosters; 3. Compound boosters; 4. Differential boosters; 5. Constant current boosters; 6. Separately excited boosters.

=Series Boosters.=—The series booster acts so as to compound the battery, and tends to maintain a constant voltage on the line, whatever the load may be. Its operation depends on the fact that the dynamo voltage must rise and fall with the load. It can, therefore, be used only with a shunt dynamo or its equivalent as the source of supply.

=Ques. What use is made of the series booster system?=

Ans. It is suited to power, but not to incandescent lighting purposes, being similar in operation to a floating battery. It is not extensively used as the other types give better service, under the same conditions.

=Ques. Describe some characteristics of the series booster.=

Ans. It is automatic and adjusts its voltage to produce the proper ratio of charge or discharge with varying external load, and it also tends to maintain a constant voltage across the line, under all conditions of change in circuit.

=Shunt Boosters.=—This type of machine is simply a shunt dynamo, having its armature circuit in series with the line from the main dynamo to the battery. A rheostat controls the field excitation. Its function is to send charge into the battery. It is used in plants where the battery is not designed to take up load fluctuations, but is in service only to carry the peak of the load, being charged during periods of light loads and discharged in parallel with the dynamo.

The shunt booster acts to increase the voltage applied to the battery so that the charging current will flow into the latter.

=Ques. How is a battery used with a shunt booster proportioned?=

Ans. Usually sufficient battery is provided to carry the entire load during the light load period.

=Ques. Explain the use of the rheostat controlling the field excitation.=

Ans. It is used to vary the booster voltage so as to hasten the charging of the battery if desired.

=Ques. For what service is the shunt booster not suited?=

Ans. It is not adapted to circuits where there are sudden fluctuations that are great compared with the capacity of the dynamo.

=Ques. What is its action in changing from charge to discharge?=

Ans. It is not automatic, the switching must be done by hand.

=Ques. How may it be used reversibly?=

Ans. It will give a pressure to assist the battery to discharge when excited from the bus bars and provided with a reversing rheostat.

In this case it will assist the battery to discharge when the direction of the field magnetization is changed. When so used, no end cells are necessary, but the booster must be run continuously during the entire period of discharge.

=Ques. What should be the battery capacity on a 110 volt circuit with a reversible booster?=

Ans. 56 cells will be sufficient.

The voltage to fully charge is 56 × 2.6 = 146, or 36 volts above dynamo voltage. Minimum voltage of discharge = 1.8 × 56 = 100 volts, or 10 volts less than that of the line. Hence, the booster need give only 36 volts maximum, and is required to add 10 volts to the battery voltage toward the end of battery discharge. In this case, the booster voltage is only 36/49 or about ¾ of that required in the preceding case; five cells less of battery are necessary and the end cell switches and leads are eliminated.

The machine will be larger, however, than it would be if used only for charging, because the discharge current is unusually greater than that of charge, and the current carrying of the armature must be great enough to take care of the heaviest currents.

=Compound Boosters.=—These machines are used on railway and power circuits where there are great fluctuations in load, the battery acting to prevent excessive drop and to assist the generating machinery in carrying the load, relieving it from the strain of sudden rushes of current.

The connections are shown in the diagram fig. 1,197. Under ordinary working conditions, the shunt field of the booster creates an electric pressure in the same direction as that of the battery, tending to discharge it.

When no current is flowing into or out of the battery, the following relation exists:

Dynamo voltage = booster voltage + battery voltage

In this case the dynamo carries the whole external load. If the load increase, the dynamo voltage decreases, so that the booster voltage + battery voltage is greater than the dynamo voltage, and the battery begins to discharge.

In discharging, the current passes through the series field of the booster and produces a proportional pressure acting with the shunt field to raise the voltage of the booster, thus increasing the battery discharge and shifting more of the load from the dynamo, until the system becomes balanced.

If the load on the external circuit be small, the dynamo voltage rises and current flows into the battery. In this case the series field acts against the shunt field and decreases the booster voltage so that the pressure at the dynamo is greater than booster and battery voltage combined, thus increasing the rate of charge of the battery until the load causes the dynamo voltage to drop to normal and the system is again balanced.

The battery and booster can be placed at the power house or where the greatest drop is likely to occur. As this system, like the series booster, depends for its action upon the drop of voltage with increase of load, it is only adapted to shunt wound dynamos.

From the foregoing description it will be seen that the compound booster is automatic within certain limits of battery charge. Any marked change of battery voltage will be followed by a corresponding change in dynamo current, unless the rheostat be manipulated to bring battery voltage + booster voltage back to normal.

While the theoretical dynamo current variation is small for a given change of load, there is always a sudden, momentary, current rush from the dynamo on increase of load, the duration of which is equal to the time lag of magnetization of the booster field.

Lights on a circuit with variable load will "wink" on sudden changes of load. In this respect the compound booster is not so satisfactory as the constant current booster, as in the latter all dynamo current passes through the series fields, which, by reason of their self-induction, oppose and check any sudden current rush, giving the booster field time to change its magnetization to the proper degree.

=Differential Boosters.=—In this type of booster, a series coil energized from the main current, tends to discharge the battery, and a shunt coil, excited from the battery, tends to charge the cells. These two coils are opposed to one another, and the difference in their respective strengths represents the net strength available for boosting. In order to produce quicker reversal, additional compound coils are sometimes added.

=Ques. For what service is the differential booster adapted?=

Ans. It is suited to power and railway circuits where the load fluctuates widely and suddenly.

There are several varieties of this type of booster, and many patents have been issued covering the different methods of varying the voltage of the machine.

=Constant Current Boosters.=—In installations where it is desired to supply both an approximately constant load and a fluctuating load from the same dynamos (as for instance, in office buildings or hotels, where it is necessary to supply lights and elevators from the same source), the fluctuations in the power circuits must not interfere with the lighting circuits and to prevent this, two sets of bus bars are provided.

The dynamos are connected in the usual manner to one set of bus bars, and the lighting circuits are connected across these.

Across the other set of bars are connected the circuits supplying the fluctuating load, and the battery is also connected directly across these power bars.

The power bars are supplied with current from the lighting bars, a non-reversible or so called constant current booster being interposed between the two as shown in fig. 1,202. Since this permits only a constant current to pass from the lighting bus bars, the load on the dynamo does not vary, although the load on the power busses may vary widely.

=Separately Excited Boosters.=—In some forms of booster the field excitation is secured by a small exciting dynamo. An example of this class is shown in fig. 1,203. The exciter is provided with a single series coil, through which the station output or a proportional part thereof passes. The armature of the exciter is connected to the exciting coil on the booster, and thence across the mains as shown.

NOTE.—Reversible boosters should be used where the average total current to the fluctuating load is greater than the battery discharge current, and where the pressure of the power bus bars must not fall off with increase in load. Electric railway and lighting plants having long feeders are examples of the systems to which reversible boosters are suited. Non-reversible boosters should be used where the average total load is less than the battery discharge current, and where a drop in the voltage of the power bus bars is of advantage. Examples of such plants are hotels or apartment houses where electric elevators are operated from the lighting dynamos. Boosters are usually driven by electric motors directly connected to them, though any form of driving power may be used.

With the average current passing through the field coil or the exciter, its armature generates a voltage which is equal to that of the system, and in opposition to it. These two opposing pressures balance, and no current flows in the booster field coils.

With an increase in external load above the average, the tendency is for an increase to take place through the exciter series coil, augmenting its field strength and consequently the exciter armature voltage. This latter now being higher than that of the line, causes current to flow in the booster field coil in such a direction as to produce a pressure in the booster armature which assists the battery to discharge, and is of a magnitude to compensate for the battery drop occasioned thereby.

When the load decreases below the normal, the current in the exciter field is decreased, and its armature voltage falls below that of the system. Current will now flow in an opposite direction in the booster field coil, generating a voltage in the booster armature to assist charge. Since the exciter always generates a voltage in opposition to that of the line, this system is known commercially as the counter pressure system.

HAWKINS PRACTICAL LIBRARY OF

=ELECTRICITY=

IN HANDY POCKET FORM PRICE $1.00 EACH

They are not only the best, but the cheapest work published on Electricity. The books are sold at $1 each. Each number being complete in itself. They are guaranteed in every way or your money will be returned. The new numbers will be supplied for $1 each, as published.

NOW READY

=ELECTRICAL GUIDE, NO. 1=

Containing the principles of Elementary Electricity, Magnetism, Induction, Experiments, Dynamos, Electric Machinery.

=ELECTRICAL GUIDE, NO. 2=

The construction of Dynamos, Motors, Armatures, Armature Windings, Installing of Dynamos.

=ELECTRICAL GUIDE, NO. 3=

Electrical Instruments, Testing, Practical Management of Dynamos and Motors.

=ELECTRICAL GUIDE, NO. 4=

Distribution Systems, Wiring, Wiring Diagrams, Sign Flashers, Storage Batteries.

=ELECTRICAL GUIDE, NO. 5=

Principles of Alternating Currents and Alternators.

=ELECTRICAL GUIDE, NO. 6=

Alternating Current Motors, Transformers, Converters, Rectifiers.

=ELECTRICAL GUIDE, NO. 7=

Alternating Current Systems, Circuit Breakers, Measuring Instruments.

=ELECTRICAL GUIDE, NO. 8=

Alternating Current Switch Boards, Wiring, Power Stations, Installation and Operation.

=IN WORK (Ready Soon)=

=ELECTRICAL GUIDE, NO. 9=

Telephone, Telegraph, Wireless, Bells, Lighting, Railways.

=ELECTRICAL GUIDE, NO. 10=

Modern Practical Applications of Electricity and Ready Reference Index of the 10 Numbers.

=Theo. Audel & Co., Publishers= =72 FIFTH AVENUE.=

[Transcriber's Note:

Where possible, unicode characters are used. Some of the fractions do not have a unicode character which will cause some inconsistencies in the display.

Inconsistent spelling and hyphenation are as in the original.]

Spotted a typo or a problem in this chapter? Tell us