174 



ELECTRICAL MACHINERY 



in Fig. 105. The lever, or arm by means of which the 

 resistance is cut out as the motor speeds up, is so connected 

 to a spring that it constantly tends to fly back to the " off " 

 position, thus opening the armature circuit. 



Special Features cf a Starting Rheostat. There are two 

 conditions under which the armature circuit should be 

 opened, and the starting box, shown in Fig. 105, is designed 



FIG. 105. Front View of a Motor-starting Rheostat. 



Company. 



Ward-Leonard 



to take care of these automatically. If too much load is 

 put on the motor, a dangerously large current may flow 

 through the armature circuit; under such a condition the 

 armature should be opened, thus stopping the motor and 

 warning the operator of the over-load. The " over-load 

 release " of the starting box, shown in Fig. 105, actuates 

 a stop which releases a small circuit breaker located on the 

 face of the starting box, thus opening the circuit when the 

 safe current is exceeded, 



