What is a Ground Fault Circuit Interrupter?

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A ground fault circuit interrupter is a fast-acting protective device that detects any leakage of current to ground and quickly interrupts power. It works by constantly comparing the current in the live and neutral conductors; under normal conditions those currents are equal. If some current escapes to ground—such as through a person touching a live conductor—the currents become unbalanced. The GFCI senses that imbalance, typically in the order of a few milliamps, and trips in milliseconds to cut off power, reducing the risk of serious electric shock. This sensitivity and rapid response are its defining protections, especially in wet or exposed areas common on ships. It’s not simply about regulating voltage, nor is it a fuse, and while there are DC-rated devices, the essential purpose is protection against ground faults by monitoring current balance.