What does a Ground Fault Circuit Interrupter (GFCI) do?

• A. It Increases Current Temporarily
• B. It Measures Energy Usage
• C. It Protects by Detecting Surges
• D. It Shuts Off Electric Power in the Event of a Ground-Fault Within as Little as 1/40 of a Second

Answer: (D)

GFCIs protect people by quickly disconnecting power when a ground fault is detected. They monitor the current flowing through the hot and the neutral wires; under normal use, these currents are equal. If some current leaks to the ground path—such as through a person touching a live surface—the imbalance is detected. The device then trips in a fraction of a second, typically within about 25 milliseconds (as little as 1/40 of a second), cutting off the electrical supply to prevent shock. This rapid shutoff is what makes GFCIs effective at preventing serious injury from electric faults. They aren’t about measuring energy usage or handling voltage surges, and they don’t increase current; they act to interrupt power whenever a ground fault occurs.