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.

Power supply protector, also known as air circuit breaker, is a kind of circuit breaker. It is a switch that will automatically disconnect as long as the current in the circuit exceeds the rated current. Power protector is a very important electrical appliance in low-voltage distribution network and electric drive system, which integrates control and multiple protection functions. In addition to completing the contact and breaking circuit, it can also protect the circuit or electrical equipment from short circuit, serious overload and undervoltage, and can also be used to start the motor infrequently.