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74 RICHARDSON'S BLUEBOOK OF PROJECTION
represented by 110 X 70 = 7,700 watts if current is taken through resistance. If we disregard the neutral and connect to the outside wires, then the wattage consumed would be 220 X 70 = 15,400 watts, or exactly twice as much as is required for the 110 volt connection.
(47) In Fig. 18 we have a diagrammatic representation of six house circuits fed by a 3-wire circuit, each wire of which is fused at 60 amperes. Circuit F is idle. Circuits A, B and C are each using 10 amperes, or a total of 30 amperes. Circuits D and E use a total of 20 amperes. Can we connect a projection arc circuit, the arc using 25 amperes, to circuit F? The offhand answer is: "No, the circuits are already using 50 amperes. A 25 ampere addition would overload the fuses/' This is an error for the circuits are not using 50 amperes, but 30, ten of which are handled individually by the generator attached between the upper wire and the neutral.
Circuits AB and DE will burn in series, so that instead of 40 amperes at 110 volts, the lamps or motors on A, B and DE will work in series on 220 volts, and only a total of 20 amperes will flow.
Circuit C will use 10 amperes at 110 volts as long as circuit F is idle. This will have the effect of causing the upper wire to carry 30 amperes, the lower 20 and the neutral 10. Thus the upper fuse will be loaded at 30 amperes, the neutral at 10 and the lower at 20. The system, therefore, is unbalanced by 10 amperes. The generator attached to the true positive and neutral has 10 amperes more load than the other.
If we now connect a 25-ampere load (the projector arc, for example) to circuit F, the condition of overload is reversed, and the generator attached to the lower two wires will be carrying 15 amperes more than the other. The upper fuse now carries 30, the center 15 and the lower 45 amperes. Therefore it is evident that instead of being overloaded, none of the fuses would be working to capacity.
Measuring Unbalance
(48) You may always ascertain exactly how much