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.

Under normal conditions, the armature of the overcurrent release is released; In case of serious overload or short circuit fault, the coil connected in series with the main circuit will generate strong electromagnetic attraction to draw the armature down and lift the locking hook, making the main contact disconnected.