Selection principle of low-voltage circuit breaker:

1) Determine the type and protection form of the circuit breaker according to the protection requirements of the line-determine the choice of frame type, device type or current limiting type.

2) The rated voltage UN of the circuit breaker should be equal to or greater than the rated voltage of the protected circuit.

3) The rated voltage of the undervoltage release of the circuit breaker should be equal to the rated voltage of the protected circuit.

4) The rated current of the circuit breaker and the rated current of the overcurrent release should be greater than or equal to the calculated current of the protected circuit.

5) The ultimate breaking capacity of the circuit breaker should be greater than the effective value of the maximum short-circuit current of the circuit.

6) The protection characteristics of the upper and lower circuit breakers in the distribution line should be coordinated, and the lower protection characteristics should be located below the upper protection characteristics and do not intersect.

7) The long-time tripping current of the circuit breaker should be less than the allowable continuous current of the wire.