Which device detects imbalance between hot and neutral currents and trips to prevent shock?

• A. A surge protector.
• B. A circuit breaker.
• C. Ground-fault circuit interrupter (GFCI).
• D. A phase converter.

Answer: (C)

The concept being tested is sensing leakage current to ground by comparing the current in the hot and neutral paths and then tripping to prevent shock. A ground-fault circuit interrupter does this by continuously monitoring both conductors; under normal operation the currents return equally. If some current leaks to ground—such as through a person touching a live metal part—the balance is disrupted. The device detects that imbalance, activates a fast trip, and disconnects power to prevent a shock. The typical trip threshold is around 4 to 6 milliamps, which is fast enough to protect against harmful shocks but small enough to avoid nuisance trips.

This differs from a surge protector, which guards against voltage spikes but does not monitor current balance to ground. It also differs from a standard circuit breaker, which trips mainly for overloads or short circuits and not for small ground-leakage currents. A phase converter has no protective function related to electrical shock. So the device that detects hot-to-neutral current imbalance and trips to prevent shock is the ground-fault circuit interrupter.