What device is most frequently used to prevent an electric motor from being overloaded?

A thermal cut-out is designed specifically to prevent an electric motor from overheating due to overload conditions. It operates by monitoring the temperature of the motor, and when the temperature exceeds a predetermined limit, the thermal cut-out interrupts the electrical supply, thereby protecting the motor from potential damage caused by overheating.

This device is crucial in maintaining the longevity and functionality of electric motors, as excessive heat can lead to insulation breakdown, mechanical failure, and ultimately, motor burnout. The thermal cut-out ensures that the motor operates within safe temperature limits, enhancing reliability and safety in operations.

Other devices mentioned, such as warning signals, governors, and rheostats, serve different functions. Warning signals indicate a problem but do not take action to prevent damage; governors regulate speed but don’t protect against overloads; and rheostats control resistance and can modify motor speed but do not prevent overheating in the same manner as a thermal cut-out. Thus, the thermal cut-out is the most appropriate choice for protecting electric motors from overloads.