What is a ground fault and how is it normally detected?

• A. Ground fault occurs when current flows along the normal path; GFCIs detect other issues.
• B. Ground fault occurs when current flows along a normal path; GFCIs ignore imbalances.
• C. Ground fault current is detected by measuring voltage on the equipment ground conductor.
• D. A ground fault occurs when current finds an unintended path to ground; GFCIs detect imbalance between conductors and trip to prevent shock.

Answer: (D)

A ground fault happens when current finds an unintended path to ground, such as through a person, water, or a damaged insulation path, instead of returning through the normal neutral conductor. GFCIs work by continuously comparing the current flowing in the hot conductor with the current returning in the neutral conductor. Under normal conditions these currents are equal, so no difference is detected. If some current leaks to ground, the currents become unbalanced. The GFCI senses that imbalance and trips, cutting power to prevent a shock.

This isn’t about measuring voltage on the equipment ground conductor; GFCIs monitor the difference between the hot and neutral currents. The key idea is that any leakage to ground creates an imbalance, which the GFCI detects and uses to quickly interrupt the circuit.