What Causes an Arc Flash

Published on January 2017 | Categories: Documents | Downloads: 12 | Comments: 0 | Views: 96
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What causes an arc flash?
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Accidental contact with energized parts Inadequate short circuit ratings Tracking across insulation surfaces Tools dropped on energized parts Wiring errors Contamination, such as dust on insulating surfaces Corrosion of equipment parts and contacts Improper work procedures

The vast majority of arc faults occur when the door is open or being opened.
An arc faults happens when electric current flows through air gaps between conductors. Insulation failure and accidents caused by touching a test probe to the wrong surface or slipped tool are the most common causes of an arcing fault. The fault current magnetic fields make conductors to separate producing an arc. In other words, arc flash is caused by uncontrolled conduction of electrical current from phase to ground, phase to neutral, and/or phase to phase accompanied by ionization of the surrounding air. Because of the expansi e aporization of conducti e metal, a line!to!line or line!to!ground arcing fault can escalate into a three phase arcing fault in less than a "/"### of a second. The heat energy and intense light at the point of the arc is called arc flash. $hort circuits and arc faults are extremely dangerous and potentially fatal to personnel. The product of arc fault current and oltage concentrated in one place, results in enormous energy released in se eral forms. Arc fault generates large amounts of heat that can se erely burn human skin and set clothing on fire. Temperatures at the arc can reach four times the temperature of the sun%s surface. The high arc temperature aporizes the conductors in an explosi e change in state from solid to apor. &opper apor expands to '(,### times the olume of solid copper. &onducti e apors help sustain the arc and the duration of the arc is primarily determined by the time it takes for o er current protecti e de ices to open the circuit. )or example, fast acting fuses may open the circuit in * ms or faster while other de ices may take much longer to operate and open. +etal is blasted and splattered from the fault location. The arcing faults also produce large shock wa es that can blow personnel off their feet. The other exposure risks to arcing faults include flying debris, se ere sound wa es, shock hazard due to touching energized conductors etc.

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