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.

There are three kinds of tripping modes: thermal tripping, electromagnetic tripping and multiple tripping. When a general overload occurs to the line, although the overload current cannot make the electromagnetic release act, it can make the thermal element generate a certain amount of heat, make the bimetallic sheet bend upward under the heat, push the lever to disconnect the hook from the latch, disconnect the main contact, and cut off the power supply. When the short circuit or serious overload current occurs in the line, the short circuit current exceeds the instantaneous tripping setting current value, and the electromagnetic release generates enough suction to absorb the armature and impact the lever, so that the hook rotates upward around the rotating shaft base and disengages from the latch, and the latch breaks the three main contacts under the action of the reaction spring, cutting off the power supply.