What is a contactor and its typical use in motor control?

• A. Light-duty switch for signaling
• B. Sensor for speed measurement
• C. Transformer for stepping voltage
• D. High-current switches for motors controlled by a low-voltage coil

Answer: (D)

A contactor is a heavy-duty electromagnetic switch used to control motors. It is designed so that a low-voltage, low-current control coil energizes the device and closes the high-current power contacts that supply the motor. This lets you start and stop large motors from a simple control circuit, and contactors are often used with overload relays to protect the motor.

That’s why the description of a high-current switch for motors that is controlled by a low-voltage coil best fits. The other options describe devices with different roles—signaling switches, sensors, or transformers—none of which match the motor-control function of a contactor.