In the design of civil buildings, low-voltage circuit breakers are mainly used for line overload, short circuit, over current, loss of voltage, under voltage, grounding, leakage, automatic switching of dual power supplies, and protection and operation of motors when they are not frequently started. Principles In addition to complying with the basic principles of the use environment characteristics of low-voltage electrical equipment (see Industrial and Civil Power Distribution Design Manual), the following conditions should be considered:

1. The rated voltage of the circuit breaker should not be less than the rated voltage of the line;

2. The rated current of the circuit breaker and the rated current of the overcurrent release are not less than the calculated current of the circuit;

3. The rated short-circuit breaking capacity of the circuit breaker is not less than the maximum short-circuit current in the line;

4. The selection of type distribution circuit breaker needs to consider the short-time short-circuit making and breaking capacity and the coordination between the delay protection levels;

5. The rated voltage of the circuit breaker undervoltage release is equal to the rated voltage of the line;

6. When used for motor protection, the starting current of the motor should be considered when selecting the circuit breaker and it should not operate during the starting time; for the design calculation, please refer to the "Industrial and Civil Power Distribution Design Manual";

7. The selection of circuit breaker should also consider the selective coordination of circuit breaker and circuit breaker, circuit breaker and fuse.