Thermal overload units conduct the motor load current through heater elements.

Thermal overload units are designed to protect motors from overload and overheating by interrupting the supply voltage when the load current exceeds the rating of the motor. This is done by conducting the motor load current through heater elements that are sensitive to temperature. When the temperature exceeds a certain limit, the heater elements cause the contacts of the thermal overload unit to open and interrupt the power supply to the motor.