In the design of civil buildings, low-voltage circuit breakers are mainly used for protection and operation of overload, short circuit, overcurrent, loss of voltage, undervoltage, grounding, leakage, automatic switching of dual power supplies, and infrequent starting of motors. Principles In addition to complying with basic principles such as the use environment characteristics of low-voltage electrical equipment (see Industrial and Civil Power Distribution Design Manual), the following conditions should also 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 line;
3) The rated short-circuit breaking capacity of the circuit breaker is not less than the maximum short-circuit current in the line;
4) Selective distribution circuit breakers need to consider the short-delay short-circuit on-off capability and the coordination between delay protection levels;
5) The rated voltage of the circuit breaker undervoltage release is equal to the rated voltage of the line;
6) When it is used for motor protection, the starting current of the motor should be considered in the selection of the circuit breaker and it should not act within the starting time; for the design calculation, see “Industrial and Civil Power Distribution Design Manual”;
7) The selection of circuit breakers should also consider the selective coordination of circuit breakers and circuit breakers, circuit breakers and fuses.
Post time: Jul-18-2023
