Single pole circuit breaker and 2 pole circuit breaker
A single pole circuit breaker is only one point in the switch circuit, that is, the incoming line of the FireWire.
The 2 pole circuit breaker simultaneously turns off the firing line and the zero line, so if the 2 pole circuit breaker controls the incoming and outgoing lines of the single-phase circuit, there will be no current in the circuit after shutting down.
Some original parts of the some device are very sensitive, and the zero line may cause damage to the original parts. so it is necessary to cut off the fire line and zero line with 2 poles; some circuits do not need to turn off the fire line and zero line, but must be opened and closed at the same time. In this case, the 2 pole circuit breaker is also used to ensure synchronization.
Circuit breaker with leakage protection are generally more than 2 poles, because leakage protection must measure the currents of incoming and outgoing poles.
If there is leakage protection in the circuit, but it need to be controlled by a single pole switch the single pole circuit breaker can be used.