Which device interrupts a circuit when a leakage to earth is detected?

• A. Surge protector
• B. OCPD
• C. AFCI
• D. Ground fault circuit interrupter (GFCI)

Answer: (D)

Ground fault protection relies on detecting leakage current to earth and trips to cut power. A ground fault circuit interrupter watches the current flowing in the hot and neutral conductors; under normal operation those currents are equal. If some current escapes to the ground path—such as through a person or a faulty appliance—the currents are no longer equal, and the GFCI quickly opens the circuit to prevent an electric shock. The typical leakage threshold is a few milliamps, which is enough to sense a hazardous fault but small enough to keep most harmless loads safe.

Surge protectors are designed to withstand and divert voltage spikes, not to sense ground leakage. Overcurrent protective devices (OCPD) respond to excessive current to protect wiring from overheating, but they don’t detect a ground fault. Arc fault circuit interrupters (AFCI) look for arcing conditions that can heat and ignite conductors, a different fault mode. Devices can also be combined, but when the goal is interrupting a circuit due to leakage to earth, the responsible device is the ground fault circuit interrupter.