#ARC FLASH BOUNDARY HOW TO#
This example illustrates how to calculate the AFB for the 480-volt (V) panel that has been used for this series. T = Arcing time in seconds normally determined by the clearing time of the upstream protective device as discussed in part 3Ħ10 = Normalized distance of 24 inches converted to millimeters This is normally 5 J/cm 2, which is equal to 1.2 cal/cm 2.Ĥ.184 = Conversion from cal/cm 2 to J/cm 2 The distance exponent is a function of both voltage and the type of equipment.ĭ B = 1/x.Ĭ f = Calculation factor of 1.5 for voltages < 1 kV as discussed in part 3Į in = Normalized incident energy determined in part 3Į B = Incident energy in Joules per cm 2 (J/cm 2) at the AFB. The calculation is based on using the results of the normalized incident-energy calculations from part 3 of this series, and the rate at which the incident energy decreases with distance is defined by the distance exponent X found in the table above.
It can be calculated using an equation defined by IEEE 1584-IEEE Guide for Performing Arc Flash Hazard Calculations. The AFB must be determined as part of an arc flash risk assessment and a requirement for arc flash labels. The 2015 edition of NFPA 70E defines the arc flash boundary (AFB) as, “When an arc flash hazard exists, an approach limit at a distance from a prospective arc source within which a person could receive a second-degree burn if an electrical arc flash were to occur.”Īn energy exposure of 1.2 calories per centimeter squared (cal/cm2) is the widely accepted incident energy value considered to be where the onset of a second-degree burn could occur.
The first three parts appeared in the January, March and May 2016 issues of Electrical Contractor and can be found at Arc flash boundary This is the fourth article in a series that provides a step-by-step approach for performing arc-flash hazard calculations.
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