Will a GFCI detect line-to-line faults?

Will a GFCI detect line-to-line faults?

• A. Yes
• B. No
• C. Only for 3-phase faults
• D. Only at 120 V

Answer: (B)

A GFCI detects faults by sensing an imbalance between the current flowing in the hot conductor and the current returning on the neutral conductor. If all the current stays between hot and neutral, there’s no imbalance and the GFCI stays closed. A line-to-line fault, where current simply flows from one hot conductor to another hot conductor, does not create leakage to ground or return through neutral. The currents cancel through the device’s sensing path, so there’s no imbalance to trip the GFCI. This behavior holds regardless of whether the circuit is 120 V or 240 V, and regardless of how many phases are involved. In short, GFCIs protect mainly against ground faults, not line-to-line faults.

A GFCI detects faults by sensing an imbalance between the current flowing in the hot conductor and the current returning on the neutral conductor. If all the current stays between hot and neutral, there’s no imbalance and the GFCI stays closed. A line-to-line fault, where current simply flows from one hot conductor to another hot conductor, does not create leakage to ground or return through neutral. The currents cancel through the device’s sensing path, so there’s no imbalance to trip the GFCI. This behavior holds regardless of whether the circuit is 120 V or 240 V, and regardless of how many phases are involved. In short, GFCIs protect mainly against ground faults, not line-to-line faults.