Which component in a motor overload relay senses current?

• A. Control switch
• B. Sensing unit
• C. Mechanical trigger
• D. Reset mechanism

Answer: (B)

The component in a motor overload relay that senses current is the sensing unit. This critical part of the relay is designed to monitor the amount of current flowing through the motor circuit. When the current exceeds a predetermined threshold, the sensing unit activates a protective response to prevent damage to the motor, such as tripping the circuit to stop operation. The design of the sensing unit typically utilizes devices like thermistors or bimetallic strips that respond to increases in current, indicating overload conditions.

While other components of the overload relay play essential roles, such as the control switch that activates or deactivates the relay and the reset mechanism that enables the relay to be reset after a trip, they do not actually sense the electrical current. The mechanical trigger may respond to signals within the relay but does not directly measure the current. Therefore, the sensing unit is the key element responsible for monitoring and responding to electrical current levels in a motor overload relay.