The effect of this paper was to realize the need to protect people from the hazards of arc flash. In the early 1980’s a paper “The Other Electrical Hazard: Electric Arc Blast Burns” by Ralph Lee was published in the IEEE Transactions on Industrial Applications. The challenge is to sense the arc fault current and shut off the voltage in a timely manner before it develops into a serious arc flash condition. The transition from arc fault to arc flash takes a finite time, increasing in intensity as the pressure wave develops. The electrical equation for energy is volts x current c time. Unless these devices have been selected to handle the arc fault condition, they will not trip and the full force of an arc flash will occur. The arc fault current is usually much less than the available bolted fault current and below the rating of circuit breakers. This fiery explosion devastates everything in its path, creating deadly shrapnel as it dissipates. This massive energy discharge burns the bus bars, vaporizing the copper and thus causing an explosive volumetric increase, the arc blast, conservatively estimated, as an expansion of 40,000 to 1. The plasma will conduct as much energy as is available and is only limited by the impedance of the arc. The cause of the short normally burns away during the initial flash and the arc fault is then sustained by the establishment of highly-conductive plasma. An arc fault is similar to the arc obtained during electric welding and the fault has to be manually started by something creating the path of conduction or a failure such as a breakdown of insulation. Lower voltage levels normally will not sustain an arc. Arc faults are generally limited to systems where the bus voltage is in excess of 120 volts. During an arc fault the air is the conductor. Arc Flash is the result of a rapid release of energy due to an arcing between a phase bus bar and another phase bus bar, neutral or a ground.
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