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480 volt 3-phase Arc Flash Demonstration

An electrical explosion, or "arc flash", occurs when one or more high current arcs are created between energized electrical conductors or between an energized conductor and neutral ground.  Once initiated, the resulting arc(s) can bridge significant distances even though the voltage is relatively low. In the above demonstration, arcs were intentionally initiated by bridging #28 AWG wires across three 1 inch copper bus bars in a testing laboratory. When power is applied, the wires immediately explode, forming a conductive plasma which creates high current power arcs between the bus bars.  In the above example, three one inch copper bus bars were separated by one inch, and were connected to a 480 volt open circuit source (a delta-connected distribution transformer). During the 842 millisecond event, the average short circuit current was 17 kiloamperes, and the peak current exceeded 30 kiloamperes.

The energy dissipated within a power arc is limited only by the fault current capability of the upstream power source and the duration before protective hardware will "clear" (interrupt) the short circuit. In many low voltage (480 - 600 volt) electrical power distribution systems, fault currents can exceed 70,000 amps. The thermal energy liberated within a high current arc can be many tens of megawatts, and the arc core may reach 35,000 degrees F (four times that of the surface of the sun!). As the arc "roots" vaporize portions of the copper bus bars, the vapor explosively expands to over 60,000 times its solid volume. It then combines with oxygen in the atmosphere, forming dense clouds of cupric oxide, blackening the air and covering nearby objects with black "soot". Globules of molten copper are also violently ejected, showering the immediate vicinity with 2,000 degree droplets that can approach speeds of 700 miles per hour. Magnetic forces propel the arc along the bus, extending it in the process, and magnetic forces on the bus  bars and cables may be sufficient to bend bus bars and rip them from their mountings, sometimes creating additional shrapnel.  An unprotected individual unlucky enough to be anywhere near this event would be seriously injured or killed. Because of the extreme danger,  most countries now require electrical workers to wear protective clothing and headgear whenever working near energized high energy equipment.


Arc Flash Information Guide

OSHA requires that all
“Non-Dwelling”facilities have an
Arc Flash Hazard Analysis done

Arc Flash Evaluation

NFPA 70E
COMPLIANCE GUIDE



Arc Flash Evaluation

Arc Flash Video

See this 480 volt 3-phase Arc Flash Demonstration Video

Arc Flash Evaluation

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