[Electric engineering.] . wo-wire system. In this case, two main wires A, Arun from the dynamo, the various switches and measuringinstruments being here omitted for the sake of clearness,and the lamps are either connected directly across thispair of mains or are connected across branch mains, asshown at B, B and C, C. The lamps are, therefore, simply S 16 ELECTRIC LIGHTING. 43 connected in parallel, as explained in Art. 46. This arrange-ment answers very well for small plants, where only a smallnumber of lamps are operated and where they are notscattered very widely. 51. Feeders and Mains.—If
[Electric engineering.] . wo-wire system. In this case, two main wires A, Arun from the dynamo, the various switches and measuringinstruments being here omitted for the sake of clearness,and the lamps are either connected directly across thispair of mains or are connected across branch mains, asshown at B, B and C, C. The lamps are, therefore, simply S 16 ELECTRIC LIGHTING. 43 connected in parallel, as explained in Art. 46. This arrange-ment answers very well for small plants, where only a smallnumber of lamps are operated and where they are notscattered very widely. 51. Feeders and Mains.—If the lamps are scatteredover a considerable area, it is best to run out feeders, asshown at A and B, Fig. 26, to what is known as centers ofdistribution, as at C and D, and then at these pointsattach mains E, F to the feeders. These centers of dis-tribution should be selected so as to lie near the pointswhere the bulk of the light is used. It will be noticed thatno lights whatever are attached to the feeders; they simply. mv. convey current from the station to the center of distribu-tion, which becomes, as it were, a kind of substation. Bythis method, a considerable drop can be allowed in thefeeders without causing any trouble at the lights. Forexample, suppose 110-volt lamps were to be operated and adrop of 15 volts was allowable between the dynamo and thelast lamp on the line. We may, for example, figure thecross-section of the feeders so that a drop of 13 volts willoccur in them. This large drop will allow comparatively 44 ELECTRIC LIGHTING. § 16 small feeders to be used and will not be injurious to thelamps, because the pressure at the point C will be main-tained at 112 volts, and the variation in pressure along themains would be but 2 volts, or the balance of the totaldrop of 15 volts allowed. It is evident that when no cur-rent is flowing, there can be no drop in the line, because thedrop is the product of the current and the line the current increases, th
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