Arc flash hazard

Article By:

Das, J.C. AMEC, Inc., Tucker, Georgia.

Last reviewed:2008

DOI:https://doi.org/10.1036/1097-8542.YB084610

The arc flash hazard is a dangerous condition associated with the unexpected release of a tremendous amount of energy caused by an electrical arc within electrical equipment. This release of energy is in the form of intense light, heat, and blast of arc products, which may consist of vaporized components of enclosure material (copper, steel, and aluminum). Intense high sound and pressure waves also emanate from the arc flash, which resembles a confined explosion. Arcing occurs when the insulation between two live conductors breaks down, due to aging, tracking, tree formation, and human error during maintenance. Insulation systems are not perfectly homogeneous. Thermal aging, vibrations, impact damage, fractures, and abraded areas give rise to further development of cavities and partial discharges occur (partial discharge, PD, is a localized electrical discharge that partially bridges the insulation between conductors and which may or may not occur adjacent to conductors.) These discharge patterns, as they grow, resemble a tree and thus the term “treeing.” Ultimately the insulation resistance is much lowered and a breakdown occurs. Tracking occurs due to surface contamination. This provides a relatively low impedance path for the electrical arc to strike, say, between the line to ground. An example will be a contaminated insulator under high humidity conditions. Arc temperatures are of the order of 35,000°F (20,000°C), approximately four times the temperature on the surface of the Sun.

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