THE POLYPHASE CIRCUIT. 



297 



dotted forming the return wire for the current carried by 

 the conductor just above it. 



Then the current in A l is equal and oppositely directed 

 to the current in A at every instant, and similarly for the 

 remaining pairs. 



It will be shown later that the special characteristic of 

 a 3-phase system is that the sum of the currents in any two 

 circuits at any instant is equal and oppositely directed 

 to the current in the third circuit. Thus, the sum of the 

 currents in B and C is always equal and opposite to the 

 current in A. Consequently, if a suitable connection were 

 made between the conductors A, B, and C, the conductors 

 B and C might, without any change in the current flowing 

 in them, provide the return path for the current in A. 

 That is, the current supplied by the generator to the 

 circuits B and C may be looked upon as being the return 

 current of the circuit A. Thus the conductor A 1 might be 

 dispensed with, without the current in A being affected. 



FIG. 145. COBVES OP CURRENT IN A S-PHASE CIRCUIT. 



Similarly, the conductors A and B carry an equal and 

 opposite current to that in the conductor C, and the 

 conductor C 1 may be dispensed with without altering the 

 current in C, if A and B are so connected to C that they 

 can form the return path for the current in it. 



In this way no circuit requires a separate return 

 conductor, and the 3-phase currents can be transmitted 

 along three conductors instead of six. 



The simplest way of showing that the sum of the 

 Qurrents in two circuits is equal and opposite to that in 



