Teacher Guo covered up.

This is a question for Mr. Guo. I'll try to answer. If I do it right, it will be a review. If I understand it wrong, please ask Teacher Guo for guidance.

On the transformer side, PE line and N line are grounded at the same time, and the zero potential of neutral point is established at this grounding point. If a small grounding system is made at the load end, once grounded, the grounding current will reach the transformer neutral point through the shell-protective ground wire PE line, instead of through the shell-protective ground wire-large grounding system resistance-earth-small grounding resistance neutral point-neutral point. In another five-wire power supply system, the leakage protector is used as a circuit breaker. Its working principle tells us that the neutral point is not allowed to be grounded, and the neutral point is not grounded. When a certain phase leaks electricity, the leakage current returns to the neutral point of the transformer through the PE line, resulting in that the sum of the three-phase current and the N-line current is not equal to zero. The protector detects this electromotive force and amplifies it to drive the mechanical mechanism to open the circuit breaker. In addition, after the neutral point of the load end is connected to the shell, if there is unbalanced current in three phases, such as non-three-phase welding machine, lighting lamp and other single-phase loads, there will be current in the neutral line, which will inevitably return to the neutral point through the PE line, so that the sum of the three-phase line and the N-line current is not equal to 0, and the circuit breaker will act. Therefore, in the five-wire power supply circuit, repeated grounding is not allowed. A small leakage current is enough to open the circuit breaker.

The N line of the secondary neutral point of the transformer is connected to the grounding line PE where the transformer is located, and the grounding is good. When the N line and the PE line pass through the user leakage switch, they are not allowed to be connected again. When I say non-repeated grounding, I mean that the zero line N is not allowed to be connected to the PE line after passing through the user's leakage switch, that is, zero protection and grounding protection cannot be used. In some four-wire power supply systems, in order to achieve the effect of five-wire system, PE line is separated from PE line before entering the house, and N line is not allowed to be connected with PE line after entering the house.