What does the thermal overload protect in a starter or MCC?

The thermal overload relay in a starter or Motor Control Center (MCC) is designed specifically to protect motors from overheating due to prolonged overload conditions. When a motor operates at a current level above its rated capacity, the thermal overload relay activates to cut off power to the motor. This is critical because excessive heat generated by an overcurrent can damage the motor’s windings and insulation, leading to motor failure.

Thermal overload relays typically function by using a bimetallic strip that bends in response to the heat produced by the overload condition. Once the temperature reaches a certain threshold, the relay opens the circuit, stopping current flow to the motor and preventing any further damage. By ensuring that motors are safeguarded from excessive temperatures, these devices significantly enhance the lifespan and reliability of motor operations within industrial settings.

The other options, while important components in electrical systems, do not serve the direct protective role that thermal overload relays perform for motors. Wires can be protected by circuit breakers, transformers have their own specific protection methods, and switches are typically designed to manage electrical flow rather than protect motors.