What principle does a ground fault circuit interrupter work under?

A ground fault circuit interrupter (GFCI) operates based on the principle of sensing the difference in current entering and leaving a circuit. When a GFCI is connected to a circuit, it continuously monitors the electrical current flowing through the hot (live) wire and the neutral wire. Under normal operating conditions, the current in both wires should be equal. However, if there is a ground fault—meaning some of the current is leaking to the ground or an unintended path, which can occur through a person—this creates an imbalance.

The GFCI detects this disparity in current flow, and when it senses that the amount of current going out does not match the amount returning, it quickly interrupts the circuit, shutting off power to prevent electric shock or fire hazards. This rapid response is typically within milliseconds, providing essential protection in environments where electricity and moisture may coexist.

In contrast, the other options do not accurately describe the function of a GFCI. Increasing circuit voltage does not contribute to fault protection. Halting all electrical flow suggests a complete shutdown of a circuit rather than responding to specific imbalances, and grounding all electrical equipment does not represent the specific action of a GFCI. The crucial aspect is the GFCI's sensitivity to