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MANAGERS AND PROJECTIONISTS 87
exist. If we connect to wires D and F, then wire D will be just as truly positive as though dynamo A did not exist.
G — H and I are voltmeters. Voltmeters G and H will each register 110 volts and voltmeter I will register 220 volts.
Put in another way, in the three-wire system we have what is in effect two complete two-wire systems joined together in such way that they may either be used separately at 110 volts, or jointly at 220 volts. The reason for such a combination is that it is economical in installation cost and maintenance, since the same electrical energy can be transmitted over a three-wire system that could be conveyed over two separate two-wire systems having wires of equal size; also, there is the added advantage of being able to use 110 volt incandescent lamps (which are very much better than 220 volt lamps) and either 110 or 220 volt motors.
Assuming the system shown in Fig. 10 to be in operation, its electrical action will be as follows : First let us switch off lamps J, L and N, leaving only lamps K and M burning. Assuming the lamps to consume 55 watts each, the amperage passing through any one of them when burning alone on 110 volts pressure would be 55 H 110 = .5 of an ampere; also, the amperage passing through two such lamps when burning in series at 220 volts would be 110 -^ 220 = .5 of an ampere, each lamp consuming 55 watts or 110 watts in all.
A peculiarity of the three-wire system is that lamps or motors connected to opposite sides will always, when possible, operate in series, the current always seeking the true negative rather than the neutral wire.
It therefore follows that with only lamps K and M burning, they would burn "in series" at 220 volts' pressure, hence Yi ampere of current would pass out from generator A and along wire E to lamp K. The current would pass through lamp K to the neutral wire, 110 volts of its E. M. F. being consumed in forcing the current through the resistance of the lamp filament, along the neutral wire to lamp M, through lamp M and back to generator B along wire F, the true negative of the combination. Under this condition no current at all would pass over the neutral wire, except between the points at which lamps K and M are connected to it. ' Let us now switch on lamps L and N, whereupon instantly one ampere of current will follow along wire E up to the point where lamp K is connected to it. At this point th~ ampere will divide, one-half going through lamps K and M the other half continuing on and passing through lamps L