What device prevents overheating in an electric motor?

The thermal relay is specifically designed to monitor the temperature of an electric motor. It plays a crucial role in preventing overheating by detecting excessive heat that may arise during operation and automatically interrupting the power supply to the motor if the temperature exceeds a predefined threshold. This protective feature helps to avoid damage to the motor and enhances its longevity. The thermal relay operates based on the principle of thermal expansion; when the temperature rises, it triggers a mechanism that breaks the circuit, thereby protecting the motor from failure due to overheating.

In contrast, a rheostat is primarily used to control electric current and adjust resistance in a circuit, which can help regulate power but does not directly monitor temperature. A bus bar serves as a conductor to distribute electrical power within a system and lacks any protective temperature monitoring function. A solenoid is an electromechanical device that converts electrical energy into linear motion but is not involved in monitoring or protecting electric motors from overheating. Thus, the thermal relay is the appropriate device to use for preventing overheating in electric motors.