NFPA 70E Example Arc Flash Calculations Annex D

Provided for Educational Purposes Only

Contact a qualified engineer to calculate arc flash hazards.

Ralph Lee Calculation Method D.2

Short Circuit Calculation D.2.3a
Isc = {( MVA x 10⁶ ) / (1.732 x E)} x { 100 / %Z }

Power of the Arc D.2.3b
MW = 1.732 x E x Isc x 10^-6 x 0.707²

Distance to a 2nd Degree Burn D.2.3c
D_inches = { 2.65 x [ 1.732 x Isc x E x 10^-6 ] x 0.1 }^1/2

Distance to a 2nd Degree Burn D.2.3d (Alternative Method)
D = [ 53 x MVA x t ]^1/2

Energy in Open Air D.2.4 (Use for MORE than 600 Volts)
cals/cm² = ( 793 x (Isc /1000) x (E / 1000) x t ) / D²

Doughty Neal Paper D.3

Energy in Open Air D.3.2b (Use for 600 Volts or LESS)
cals/cm² = 5271 x D^-1.9593 x t x {[0.0016 x (Isc/1000)²] - [0.0076 x (Isc/1000)] + 0.8938}

Arc in a Cubic Box D.3.3b (Use for 600 Volts or LESS)
cals/cm² = 1038.7 x D^-1.4738 x t x {[0.0093 x ( (E/1000)²) ] - [0.3453 x (E / 1000)] + 5.975}

MVA
Voltage, "E"
Impedance, "Z"
Seconds, "t"
Distance, Inches, "D"