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Test Sequence 1: Arcing Fault
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An arc flash occurs so quickly and generates such a blinding light, the human eye sees little but the aftermath. This sequence of photos, taken from high-speed, specially filtered digital video shot during testing at Ferraz Shawmut's high-power lab, illustrates the development of an arc flash and the hazards it generates.
Based on the IEEE Standard 1584 setup for "in the box" testing, the test uses a 20" x 20" x 20" steel box (photo 1). Three-phase power is supplied through the top of the box via three ¾" copper electrodes spaced 1¼" apart. The tips of the electrodes are 10" from the top and 4" from the back of the box. The seven disks mounted on the horizontal poles are calorimeters used to measure heat.*
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Test is based on IEEE 1584 setup for "in the box" testing
View Test Sequence
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An arcing fault usually begins with an inadvertent connection between a phase conductor and ground or between two phases. In this test sequence, a wire connects all three phases, or electrodes (photo 2). The test lab is configured to deliver 23kA RMS to a bolted fault at the tips of the electrodes. When the conductors are energized, the wire vaporizes and initiates an arcing fault.
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Although all of the events shown here occur in 100 milliseconds, the heat, light and thermoacoustic energy created during an arc flash is more than the human body can survive.
Analyses of power systems indicate that heat densities from arcing faults can range from 0.3 cal/cm² to over 100 cal/cm², depending on the electrical system values, equipment design and protective equipment in place. In this test, heat energy densities in excess of 6.8 cal/cm² were measured at typical working distances (18").
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To initiate an arcing fault, a wire connects all three phases.
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*For the video frames show, the calorimeters were moved to 4' to improve visibility. Measurements cited at 18" were from a similar test.
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