A thermal switch, or thermal protector, as used in an electric motor, is designed to

• A. Close the integral fan circuit to allow cooling of the motor.
• B. Reroute the circuit to ground.
• C. Open the circuit in order to allow cooling of the motor.
• D. Short the motor windings.

Answer: (C)

The main idea is that a thermal switch protects an electric motor by interrupting current when the motor overheats, so it can cool down safely. When the winding temperature rises above a safe limit, the switch opens its contacts, breaking the circuit and stopping motor current. This pause enables cooling and helps prevent insulation damage or winding failure. Some thermal protectors reset automatically after cooling, while others require manual reset.

This is why opening the circuit to allow cooling is the correct behavior. Closing a fan circuit, rerouting to ground, shorting the windings, or any action that keeps or redirects current faultily would not protect the motor and could cause damage or a safety issue. The thermal switch is there to cut power, not to keep it flowing.