(civil residential buildings, from the meter box to the indoor distribution box when the single phase out of the line, why the distribution box line with 2P instead of 1P? No leakage of the switch?)

Answer: 1. 2P, easy to repair, safe!

2. 25.3/11 code for electrical design of civil buildings. When a single-phase power supply is used for every household, the household circuit breaker should have two poles. When three phase power supply is used, the three pole should be used for the household circuit breaker. And should be set from the double over-voltage protector.