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.

The tripping mechanism of the switch is a set of connecting rod devices. When the main contact is closed through the operating mechanism, it will be locked in the closing position by the locking hook. If there is a fault in the circuit, the relevant release will act to release the locking hook in the release mechanism, and the main contact will quickly break under the action of the release spring. According to the different protection functions, the release can be divided into over-current release and voltage-loss release.