In a basic three-phase motor control circuit, which component energizes the contactor coil to start the motor?

In a basic three-phase motor control circuit, which component energizes the contactor coil to start the motor?

• A. Stop button de-energizes coil
• B. Overload relay senses overcurrent
• C. Start pushbutton
• D. Thermal fuse

Answer: (C)

Starting a three-phase motor is accomplished by energizing the contactor coil through the control circuit. The start pushbutton is a momentary normally open switch in the control line; when you press it, it completes the circuit from the control power source to the contactor coil, energizing it and pulling in the contactor to connect the motor to the three-phase supply. Once the coil is energized, an auxiliary contact on the same contactor typically latches the coil in a energized state so the motor keeps running after you release the pushbutton. The stop button, normally closed, opens the circuit to de-energize the coil and stop the motor. The overload relay monitors current and will trip to interrupt the circuit if overcurrent occurs, providing protection, while a thermal fuse is a protection device in the motor windings, not something that energizes the coil.

Starting a three-phase motor is accomplished by energizing the contactor coil through the control circuit. The start pushbutton is a momentary normally open switch in the control line; when you press it, it completes the circuit from the control power source to the contactor coil, energizing it and pulling in the contactor to connect the motor to the three-phase supply. Once the coil is energized, an auxiliary contact on the same contactor typically latches the coil in a energized state so the motor keeps running after you release the pushbutton. The stop button, normally closed, opens the circuit to de-energize the coil and stop the motor. The overload relay monitors current and will trip to interrupt the circuit if overcurrent occurs, providing protection, while a thermal fuse is a protection device in the motor windings, not something that energizes the coil.