Which statement best describes how a GFCI determines when to interrupt power?

Which statement best describes how a GFCI determines when to interrupt power?

• A. It detects an imbalance between current in the hot and neutral conductors and interrupts
• B. It measures ambient temperature to decide when to interrupt
• C. It slows current to a crawl under any fault condition
• D. It interrupts power only for short circuits

Answer: (A)

GFCI protection hinges on detecting current leakage to ground by comparing the currents in the hot and neutral conductors. Under normal conditions, the current leaving on the hot wire returns on the neutral wire, so there’s no imbalance. The GFCI uses a differential transformer to continuously monitor both paths. If some current leaks to ground—through a person, a faulty appliance, or another path—the currents no longer match. That small imbalance triggers the device to open the circuit within a fraction of a second, typically in the milliseconds range, to prevent electric shock. This mechanism is about leakage to ground, not about ambient temperature, not about slowing the current, and not solely about short circuits.

GFCI protection hinges on detecting current leakage to ground by comparing the currents in the hot and neutral conductors. Under normal conditions, the current leaving on the hot wire returns on the neutral wire, so there’s no imbalance. The GFCI uses a differential transformer to continuously monitor both paths. If some current leaks to ground—through a person, a faulty appliance, or another path—the currents no longer match. That small imbalance triggers the device to open the circuit within a fraction of a second, typically in the milliseconds range, to prevent electric shock. This mechanism is about leakage to ground, not about ambient temperature, not about slowing the current, and not solely about short circuits.