Circuit breakers for motor protection can be divided into two categories:

1) The circuit breaker is only for protection and not for normal operation.

2) The circuit breaker is used for both protection and infrequent operation.

Selection principle:

(1) Isd = In

Where ISD -- setting value of long delay current, a;

In -- rated current of motor, a.

(2) Instantaneous setting current in

1) When protecting cage asynchronous motor

2)Protection of wound rotor asynchronous motor