ELECTRIC DISTRIBUTION AND WIRING. 



295 



Modifications of Cases I. and II. Every practical case of wiring 

 in the constant-voltage system of distribution can be treated as a 

 slight modification of Cases I. and II. above described. Thus Fig. 

 167 shows two groups of lamps each exactly like the single 



Fig. 167. 



group in Fig. 163 ; and Fig. 168 shows a combination of Figs. 

 163 and 164, that is, the portion, pa, of the group of lamps 

 in Fig. 1 68 is arranged in conformity with Fig. 163 and the 

 portion, pb, is arranged in accordance with the return loop 

 scheme. 



Fig. 168. 



120. The economic balance between loss of power and the cost 

 of copper in the distribution of electric current. The original 

 cost of erection of a distributing line consists of two nearly inde- 

 pendent parts, namely (a) the cost of the copper and (&) the cost 

 of poles, cross-arms, pins and insulators and the cost of erection. 

 That is to say, even if one were to double the size of wires to be 

 used the cost of item (b) would not be increased to any consider- 

 able extent. The disadvantage of using large wires lies, there- 



