The following points should be considered when selecting a circuit breaker.

(1) The rated current and rated voltage of the circuit breaker should be greater than or equal to the rated current and rated voltage of the circuit.

(2) The rated current of the trip unit of the circuit breaker should be greater than or equal to the load current.

(3) The rated short-circuit making and breaking capacity of the circuit breaker should be greater than the maximum short-circuit current in the circuit.

(4) Molded case circuit breakers can be used for short-circuit currents not too large; current-limiting circuit breakers can be used for large short-circuit currents; frame circuit breakers can be used for large rated currents.

The selection principles of circuit breakers for motor protection are as follows.

(1) The operating current setting value of the long delay inverse time overcurrent release should be equal to the rated current of the motor.

(2) The instantaneous operating current setting value of the trip unit of the circuit breaker protecting the cage asynchronous motor should be equal to 8 to 15 times the rated current of the motor.

(3) The returnable time of the 6 times long delay action current setting value should be greater than or equal to the actual starting time of the motor.