Selecting poles of Miniature Circuit Breaker
1P, 2P, 1P+N, 3P, 4P, 4P+N, P means that the miniature circuit breaker (MCB) is equipped with a protective pole (knife pole), N means that the neutral conductor is only equipped with knife pole, but no protection modules. Both 2P and 1P+N are called two pole switch, 4P and 3P+N are called 4 pole switch. Neutral conductor of 1P+N and 3P+N don't have protection, so they are much cheaper, the neutral conductor pole acts along with the phase line pole. Some circuit breakers divide 1P+N into two types: one adopts two module width, another adopts one module width (small size). For these poles, how to select a right miniature circuit breaker?
Selection of single pole, two pole, three pole and four pole of a miniature circuit breaker are determined by whether the neutral conductor needs to be broken. Generally, it can be judged by the following references:
Considering the maintenance safety
The neutral conductor needs to be broken when the TT system needs maintenance, so two pole and four pole circuit breaker are used. After the wires are well connected, the neutral conductor doesn't need to break apart from special circumstances, a single pole circuit breaker or three-pole circuit breaker is available. Four pole circuit breaker had better to avoid being used because it may cause the "neutral break" risk.
When there are two power sources, consider if it is necessary to isolate two grounding systems.
Moreover, 1P+N, 3P+N and 2P, 4P are used as two-pole switch and four-pole switch on electric. Then judge if the neutral conductor needs to be broken. But when the neutral conductor current can't exceed the phase line, the 1P+N and 3P+N shall be selected from the perspective of saving cost. If the neutral conductor current may exceed the phase line (affected by the harmonic wave), 2P or 4P circuit breaker shall be selected.
|1P||Single pole switch of circuit breaker: Only one connecting plug, it can only break one phase line, this switch is only suitable for controlling one-phase live wire.|
|2P||Two pole switch of circuit breaker: Two connecting plugs, one is connected to the phase line and the other is connected to the zero line.|
|3P||Three pole switch of circuit breaker: Three connecting plugs, which are connected to the live wires. This switch is suitable for controlling three-phase 380V circuit.|
|4P||Four pole switch of circuit breaker: Four connecting plugs, three are connected to the live wires and the remaining is connected to the zero line. This switch is suitable for controlling three-phase four-wire system circuit.|
|1P+N||Single pole switch with zero terminal (the zero line doesn’t break)|
|3P+N||Three pole switch with zero terminal (the zero line doesn’t break)|