What is the purpose of a motor overload device in a motor control circuit?

• A. It protects the motor from overheating by opening the control circuit if the motor current exceeds its rated value for a set period.
• B. It reduces motor speed during overload by throttling voltage.
• C. It indicates overload by flashing a warning light only.
• D. It resets automatically when current returns to normal.

Answer: (B)

Overload protection is about preventing motor damage from overheating when the motor draws more current than it should for too long. The overload device senses excessive current (often with a thermal element that heats up as current increases) and, after a short delay, trips the motor contactor to open the circuit and cut power to the motor. This interruption stops the motor before insulation, windings, or bearings get damaged from heat.

It’s not about slowing the motor down by reducing voltage—that’s a speed-control function (soft start or a variable-frequency drive). It isn’t merely an indicator light, since the primary job is to protect by disconnecting power when overload is detected. Some overload relays can reset automatically after cooling or require manual reset, but the main purpose remains protecting the motor by opening the circuit when overload occurs.