If the impedance of the ground-fault current path is too high, what is a likely consequence?

• A. Fault current may be insufficient to trip protective devices
• B. Fault current will be excessive
• C. No fault current flows
• D. The equipment will automatically reset

Answer: (A)

When the ground-fault current path has high impedance, the current that can flow back to the source during a fault is limited. Protective devices rely on reaching a certain current level (or, for some devices, a certain imbalance) to trip and shut off power. If the fault current is kept low by the high impedance, it may not reach that trip threshold, so the device won’t trip and the fault can persist. This is why a high-impedance fault path is dangerous: the fault may not be cleared promptly, leaving energized equipment and a potential shock or fire hazard. In contrast, a low-impedance fault path allows a large enough fault current to flow to reliably trip the protective device and isolate the fault quickly.