AUXILIARY APPARATUS 413 



set of contacts made by a copper foil finger pressing against 

 a copper block. When the breaker opens, these contact 

 surfaces open and the current goes through another pair 

 of copper contacts (not as carefully fitted as the first) and 

 when these open, a final pair of contacts carry the current. 

 This last contact is made between two carbon blocks, 



FIG. 270. A Double-pole Air-brake Circuit Breaker for Use on a 

 Low-voltage Circuit. General Electric Co. 



the separation of which finally ruptures the current. The 

 idea of thus breaking the circuit through a series of contacts 

 is to preserve the main pair of contacts in good condition. 

 If the current were ruptured by the main contacts, the 

 arcing would soon spoil the contact surfaces. The arcing 

 is really all done at the carbon blocks; when they are worn 

 away a new pair may be put in. 



