Page:Electricity (1912) Kapp.djvu/239

Rh By using an interconnected network, numerous feeding points, boosted feeders, and generally cables of ample cross section, it is thus possible to give a perfectly satisfactory service with a lamp voltage of 220 V. There remains, however, the question whether such a distributing system can be laid down at a reasonable cost? In most cases the answer is in the negative. With the low pressure of 220 volts the amount of copper required for feeders and mains would represent a prohibitive outlay. There is only one way in which we can economise copper, and that is by raising the pressure. Suppose we could get lamps which will work satisfactorily with double the pressure, or 440 volts, then for the same power we should only have to transmit half the current. If we also halve the cross sections of all cables we should have the same absolute voltage drop as before, but as the pressure is doubled, this means half the percentage drop. To get the same percentage drop as before we may again halve the cross section of all the cables, that is to say, by doubling the pressure the whole system will only require one quarter the amount of copper as before. This brings us into the region of the commercial possibility