The Thermal Relay is a protection instrument that is in charge of protecting the electric motors from possible abnormalities. The most frequent one is the overheating of the electric motor.
When the motor locks its shaft or is operating with too much load, it requests more current from the grid to seek to compensate for the required weight, in this way the engine ends up having to work with attributes that do not adhere to it.
This can cause faults in their coils causing heating and even a possible melting of their insulation, an action that is capable of closing a probable internal short circuit.
It is at the moment where the probable heating is happening that the relay comes into play. When this overheating occurs the bimetallic blades of different temperature coefficients heat up, causing deformation of the blades and allowing them to activate the relay, disarming the motor circuit, as well as the control circuit through its auxiliary contacts.
This relay is an important protection component, because after it is activated, it locks up, making it impossible to restart the motor. In this way the motor can only be started when there is a manual resetting action.