414 ELECTRICAL MACHINERY 



The arm of the breaker is held in the " closed " position 

 by a catch; it is tripped by the impact of a small plunger 

 or similar device which is operated by a solenoid located 

 in the breaker. This solenoid carries a current proportional 

 to that which the feeder is supplying and when this current 

 gets too large the solenoid lifts up the plunger, trips the 



FIG. 271. The Breaker of Fig. 270 is here Shown in the " Open " 

 Position. General Electric Co. 



catch, and a spring forces the breaker to quickly snap 

 open. Fig. 271 shows the breaker in the " open " position. 

 Procedure in Closing a Circuit Breaker. Each breaker 

 in a station has a knife switch or oil switch in series with it. 

 When a breaker opens it must not be closed until the sivitch 

 in the same feeder has been opened. The circuit breaker is 

 for the protection of apparatus etc., and cannot operate 

 if the attendant has hold of the handle, hence while it is 



