The motor thermal protection is usually called overload protection, which is realized by the motor thermal protector or the long delay protection of the circuit breaker.

Motor thermal protector is composed of two connected to the terminal on the heating element and bimetallic strip, we according to the rated current of the motor to setting good thermal relay current action, once the working current is greater than the motor protector of action current hot components fever, bimetallic strip is heated, according to the motion curve of constant movement after a certain period of time will be to cut off the protection circuit. The double metal sheet of the motor thermal protector is made up of two pieces of metal sheet with different thermal expansion coefficients. Because of the different expansion coefficients, the metal sheet will be bent. The contact will be disconnected from the driving rod to cut off the power supply of the AC contactor coil, and the AC contactor will be released to cut off the main circuit.

Some small power motors do not configure motor thermal protection and choose circuit breakers as thermal protection.The thermal electromagnetic circuit breaker action principle is similar to themotor thermal protector, but he is disconnected the main contact of the circuit breaker, to cut off the power supply, the action time is corresponding to the current time curve. An electronic circuit breaker is also used to be called thermal protection, in fact, is called long delay protection, electronic circuit breaker without thermal components, but through the resistance of the current transformer induction current value, and then passed to the CPU, according to the action time we set to protect the action.

Thermal protection elements need to pay attention to the wiring end of the primary loop, the nose of the wire and the terminal should be tightly combined, the wire should be able to meet the requirements of rated current, otherwise due to the contact resistance and wire too thin caused by heat will also lead to trip, we should pay more attention to.