1. The rated voltage of ABB miniature circuit breaker must be greater than or equal to the voltage of the line.

2，ABB微型断路器热脱扣器额定电流要稍大线路中的负载电流，（如果保护对象是导线，则断路器额定电流稍小于导体的安全载流量。）

2. The rated current of ABB miniature circuit breaker thermal release shall be slightly larger than the load current in the line. (if the protection object is a conductor, the rated current of the circuit breaker shall be slightly smaller than the safe current carrying capacity of the conductor.)

3，ABB微型断路器的极限分断电流要大于电路可能出现的最大短路电流。

3. The limit breaking current of ABB miniature circuit breaker shall be greater than the maximum short-circuit current that may occur in the circuit.

4，如果保护对象线路里冲击电流比较大要考虑断路器瞬时脱扣值的大小和动作时间，例如电动机回路，一般启动电流是额定电流的4一7倍，如果是重载时启动电流会更大，选择ABB微型断路器作侏护时，应选择额定电流稍大于电动机额定电流（是电机额定电流的1.2倍一1.5倍）而瞬时动作值大于电动机最大启动电流的ABB微型断路器。

4. If the impulse current in the line of the protection object is relatively large, the instantaneous tripping value and action time of the circuit breaker shall be considered. For example, the starting current of the motor circuit is generally 4-7 times of the rated current. If it is heavy load, the starting current will be greater. When ABB miniature circuit breaker is selected as low protection, ABB miniature circuit breaker with rated current slightly greater than the rated current of the motor (1.2-1.5 times of the rated current of the motor) and instantaneous action value greater than the maximum starting current of the motor shall be selected.

5，极数的选择，根据需要控制的相线和零线数量合理选择ABB微型断路器极数，单相电用1P或2P的，三相电用3P或4P的。

5. Selection of the number of poles: the number of poles of ABB miniature circuit breaker shall be reasonably selected according to the number of phase lines and zero lines to be controlled. 1p or 2p for single-phase power supply and 3P or 4P for three-phase power supply.