Investigation of Arc Flash in Single-Phase Vertical Conductors in a Box

NFPA 70E and IEEE 1584 are defining standards for arc flash hazard analysis. Both assume three-phase faults for calculations since three-phase power distribution is predominant in utility and industrial applications; however, arc flash in single-phase systems is excluded. Single-phase faults to neutral or ground or single phase-to-phase faults can occur in a variety of circumstances. Such events may have the potential to produce arc flash and blast that would pose a significant safety concern. This paper describes a recent doctoral research investigation of arc flash in one single-phase configuration. Experiments were sponsored by UL and performed at the Schneider Electric High-Power Laboratory in Cedar Rapids, Iowa. This facility provided a test article; a full suite of voltage, current, and temperature instrumentation; and high-speed video recording. Experimental work revealed incident energy values less than 0.2 cal/cm2 for 240-volt single-phase arc fault events though there was still significant flash and splatter of molten wire residue. 480 V single-phase events produced an order of magnitude greater heat energy, and at 22 kA sustained arcing until interrupted by the test cell controller. Results suggest that 240 V single-phase panels and equipment common in residential and light commercial applications may be at very low risk of yielding arc flash burn-related injuries. However, 480 V single-phase faults can produce levels of incident heat energy known to cause burns, flash, and blast pressure at available fault currents between 10 and 22 kA.