1. In the circuit, it plays the role of switching power supply and undervoltage release. When the loop pressure is 0, the control capacity is large, which is used to control the loop and has a long service life, reducing the influence of the loop on the whole power grid.

2. AC contactor is used for electric power, which can let it pass when the current is relatively large, so it actually has overcurrent or protection function.

3. When it thunders, if there is lightning in the wire, it can automatically cut off the power supply to protect the electrical appliances at home from being damaged. The most direct manifestation is the tripping problem.