Which protective device is designed to prevent motors from overheating by interrupting current?

• A. Motor Starter
• B. Breaker
• C. Overload
• D. Encoder

Answer: (C)

Protecting a motor from heat buildup is achieved by an overload protection device. This device monitors the motor’s current (and often winding temperature) and will interrupt current when heat would exceed safe limits, stopping the motor before insulation damage or other heat-related failures occur. It’s usually a thermal overload relay wired in series with the motor through the starter, so when excessive current or temperature is detected, the relay trips and opens the circuit. A circuit breaker can also interrupt current but is intended to protect the electrical supply from faults or overloads in general, not specifically to guard the motor windings against overheating. A motor starter simply provides the means to start and stop the motor (and may include overload protection as part of a package), while an encoder measures speed or position and doesn’t provide protection. Therefore, the device designed to prevent motor overheating by interrupting current is the overload protection device.