What is the purpose of a thermal switch (thermal protector) in an electric motor?

• A. To start the motor
• B. To short the circuit
• C. To open the circuit to allow cooling
• D. To regulate voltage

Answer: (C)

A thermal switch in an electric motor acts as an overheating safeguard for the windings. It senses temperature and, when the windings get too hot—often due to overload, poor cooling, or a stall—it opens the circuit to stop current flow. This interruption gives the motor a chance to cool down before damage can occur. In many designs, the switch auto-resets after cooling so the motor can start again if conditions have improved; some require manual resetting. This protection helps prevent insulation damage and reduces fire risk. It isn’t used to start the motor, it doesn’t short the circuit, and it doesn’t regulate voltage.