[Electric engineering.] . n feeder, and thus admits ofeach section being controlled independently from the station. 53. Three-Wire System.—The simple two-wire sys-tem, even if operated on the feeder-and-main plan, requiresaltogether too much copper to admit of very extendeduse. For moderate distances, the three-wire system is 27 shows this system using feeders and mains as appliedto lighting work. A large amount of lighting is carried outon this plan in New York, Philadelphia, and other largecities. It is not confined to direct current alone, but is alsolargely used in connection wit
[Electric engineering.] . n feeder, and thus admits ofeach section being controlled independently from the station. 53. Three-Wire System.—The simple two-wire sys-tem, even if operated on the feeder-and-main plan, requiresaltogether too much copper to admit of very extendeduse. For moderate distances, the three-wire system is 27 shows this system using feeders and mains as appliedto lighting work. A large amount of lighting is carried outon this plan in New York, Philadelphia, and other largecities. It is not confined to direct current alone, but is alsolargely used in connection with alternating current. Wehave here the two dynamos A and B connected in series andsupplying current through the feeders 1, 2, 3, etc. to thedifferent centers of distribution where the mains a, b, c are §16 ELECTRIC LIGHTING. 45 attached. The use of this arrangement effects a consider-able saving in copper over the two-wire system; the pressurecommonly used is 110 volts on each side of the circuit, or <®sj\. Fig. 27. 220 volts between the outside wires. In some recent plants,220-volt lamps are used, thus giving 440 volts between theoutside wires. 54. Special Three-Wire Systems.—The ordinary three-wire system has the disadvantage of requiring two the load were absolutely balanced, one 220-volt dynamowould alone be sufficient, but in most cases an accuratebalance cannot be obtained. A number of different systemshave been devised whereby a large 220-volt dynamo can beoperated on the two outside wires and the unequal distribu-tion of the load taken up by a balancing arrangement ofsmall capacity compared with that of the dynamo.
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