What is the purpose of a ground fault circuit interrupter (GFCI)?

• A. To regulate voltage.
• B. To indicate wiring color.
• C. To detect current imbalance between hot and neutral and trip to prevent shock.
• D. To protect against overload.

Answer: (C)

The key idea is safety from electrical shock. A GFCI watches the current flowing through the hot conductor and the current returning through the neutral conductor. Under normal conditions those currents are equal. If some current leaks out—through a person or a fault path to ground—the two currents are no longer the same. The GFCI detects that imbalance and trips, cutting power in a fraction of a second to prevent a dangerous shock.

This device isn’t about regulating voltage, indicating wiring color, or protecting only against overload. Those functions belong to voltage regulators or color-coding standards and to circuit breakers or fuses, respectively. The GFCI specifically targets leakage current to ground to reduce the risk of shock.