Fault Current

The current from the connected power system that flows in a short circuit.

Comment: The amplitude, phase angle, and rate of rise of a fault current resulting from an SPD failure (which might not necessarily be a complete short‑circuit) have a significant effect on the failure mode. It has been observed that more objectionable failure modes can result from a rela­tively low available fault current because overcurrent protection in an actual installation takes longer to clear the fault, increasing the length of exposure of surrounding materials to the high‑temperature arc. In the lost neutral scenario, where the current trough the failed SPD is limited, the branch circuit overcurrent device will not provide disconnect.

Source: UIE Guide to Quality of Electrical Supply for Industrial Installations, Part VI: Transient and Temporary Overvoltages and Currents