Which device is primarily used to switch power to a motor on and off in normal operation?

Which device is primarily used to switch power to a motor on and off in normal operation?

• A. Breaker
• B. Contactor
• C. Relay
• D. Switch

Answer: (B)

To control a motor in normal operation, you need a device that can handle the motor’s current and be driven by a low-power control circuit. A contactor fits this role: it’s an electromechanical switch with heavy-duty contacts that close to supply motor current when its coil is energized by a control circuit, allowing automated on/off control. The coil is fed from a low-voltage control circuit (like a pushbutton, PLC output, or control relay), so you can start and stop the motor remotely or automatically while the motor current flows through the contacts. This setup is common in motor starters and is often paired with an overload relay to protect the motor. A breaker is primarily a protective device that interrupts current during faults, not the normal on/off switch for motor control. A switch can manually operate the motor but isn’t suited for automation or frequent operation. A relay handles control signals or lower currents and isn’t rated for the high motor current; for motor power you use a contactor. In short, the contactor is designed to switch the motor’s power during normal operation while being controlled by a low-power signal.

To control a motor in normal operation, you need a device that can handle the motor’s current and be driven by a low-power control circuit. A contactor fits this role: it’s an electromechanical switch with heavy-duty contacts that close to supply motor current when its coil is energized by a control circuit, allowing automated on/off control. The coil is fed from a low-voltage control circuit (like a pushbutton, PLC output, or control relay), so you can start and stop the motor remotely or automatically while the motor current flows through the contacts. This setup is common in motor starters and is often paired with an overload relay to protect the motor. A breaker is primarily a protective device that interrupts current during faults, not the normal on/off switch for motor control. A switch can manually operate the motor but isn’t suited for automation or frequent operation. A relay handles control signals or lower currents and isn’t rated for the high motor current; for motor power you use a contactor. In short, the contactor is designed to switch the motor’s power during normal operation while being controlled by a low-power signal.