Which device should be opened to ensure de-energization of the circuit?

• A. Ground fault detector
• B. Main breaker
• C. Turn off / open disconnect device
• D. Lockout device

Answer: (C)

To de-energize a circuit you must interrupt the path of power by opening the device that provides electrical isolation—the disconnect. This action physically breaks the connection to the power source, ensuring no voltage is present in the circuit you’re about to work on. A ground fault detector is a protective sensor that can trip if a fault occurs, but it does not by itself remove power, so it cannot guarantee de-energization. The main breaker can also stop power, but the instruction to open the disconnect device emphasizes using the designated isolation point for proper de-energization. A lockout device is used after the circuit is de-energized to prevent accidental re-energizing by securing the disconnect in the open position. So, opening the disconnect device is the step that reliably achieves de-energization.