What is ground fault protection and where is it typically applied?

• A. Thermal protection for switchgear.
• B. Automatic restoration of service after faults.
• C. Protection against faults from a conductor to earth, implemented with CTs and relays on feeders and buses.
• D. Protection against overvoltages on transformers.

Answer: (D)

Ground fault protection targets faults where a live conductor unintentionally comes into contact with the earth. When this happens, current no longer stays within the intended phase path and an imbalance appears among the phase currents. The protection scheme uses current transformers arranged around the conductors feeding a feeder or a bus; the relay monitors the sum of these currents (the residual or zero-sequence current). If a ground fault is detected, the relay trips the corresponding breaker to quickly isolate the fault.

This protection is typically applied on feeders and buses because those points carry the combined load of multiple circuits and are common locations to clear faults rapidly, minimizing damage and reducing arc-flash risk. Other options refer to different protective goals: thermal protection watches for overheating, automatic restoration deals with reclosers and restoring service after faults, and overvoltage protection handles voltage spikes—none of these describe ground faults.