When testing whether the power supply protector is normal, professional personnel should be invited to use the leakage phase detector to test. If the power supply protector is in the normal protection state, the power supply protector of each circuit will trip separately, and the leakage protector will also trip together. If the power supply protector is in an abnormal state, only the main switch trips, the separate power supply protector does not trip, and the leakage protector does not trip.

The under-voltage release works on the contrary. When the voltage is normal, the main contact can be closed only when the electromagnetic attraction attracts the armature. Once the voltage drops seriously or the power is cut off, the armature will be released and the main contact will be disconnected. When the power supply voltage returns to normal, it must be switched on again before it can work, realizing the voltage loss protection.