What is the purpose of a GFCI?

• A. To regulate voltage levels in a circuit.
• B. To measure electrical resistance of a conductor.
• C. To detect ground faults and quickly interrupt current to prevent electric shock.
• D. To protect against arc faults in wiring.

Answer: (C)

A GFCI is designed to protect people from electrical shock by sensing leakage of current to ground and then quickly interrupting the circuit. It continuously compares the current flowing through the hot conductor and returning on the neutral. If there’s a ground fault—meaning some current is taking an unintended path to ground, such as through a person or water—the currents no longer balance. When the imbalance exceeds a small threshold (about 4–6 milliamps), the device trips in a fraction of a second and cuts power to the outlet or circuit. This rapid shutoff helps prevent a dangerous shock, especially in wet locations or where contact with water is possible.

It isn’t meant to regulate voltage or measure resistance, and it doesn’t specifically protect against arc faults (that’s the job of an AFCI device). Some devices combine both protections, but their primary functions remain distinct: GFCI guards against ground faults and electric shock, AFCI guards against arcing faults.