Electric circuits are protected against overloads and short circuits by means of a/an （）.

A.amount of temperature rise with no load
B.temperature of the compartment where the motor is located
C.normal operating temperature, less the room temperature
D.amount of temperature developed by an operating motor

A.higher than the bus frequency
B.lower than the bus freouencv
C.the same as the bus frequency but out of phase with it
D.the same as the bus frequency, and the circuit breaker may be closed at any pointer position

A.visual inspection for dirt accumulation
B.high megger readings
C.low operating temperature
D.the time period since the last cleaning