ELECTRIC DISTRIBUTION AND WIRING. 



293 



The return loop scheme of wiring evidently requires three 

 wires of a given length instead of two, and therefore it requires 

 much more copper than the simple parallel wiring scheme for the 

 same total voltage-drop. The advantage of the return loop 

 scheme however is that a 

 very large total drop is per- 

 missible, so that the size of 

 the wires may always be de- 

 termined from economic 

 considerations. 



The return loop scheme 

 is usually employed in the 

 wiring of churches, lecture 

 halls and theaters, where 

 the lamps are either all in 

 use or all out of use, or where the lamps in certain groups 

 are either all in use or all out of use. 



In many cases the lamps in a group are arranged in a circular 

 or reentrant row. In such a case the return loop scheme is 

 carried out as shown in Fig. 165, or as shown in Fig. 166. 



Fig. 165. 



Fig. 166. 



Return loop scheme with wires of uniform size. When the 

 wires used in the return loop scheme are of uniform size (not 

 tapered) the middle lamp, /, Fig. 1 64$, has the lowest voltage of 



