Relay: As the bimetal deformation reaches a certain distance, the control circuit will be disconnected so that the contactor is about to lose power and the main circuit is also disconnected, that is how a relay realizes overload protection to the motor.

Fuse: As long as the current exceeds the specified value for a certain time, it will be melted by its own heat and cut off the power supply.

Circuit breaker: It can automatically cut off the circuit in case of serious overload, short circuit or undervoltage, whose function is equivalent to the combination of fuse switch and over-underheating relay.