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Ralph Lee equations from Reference [11] are as follows:

Maximum power in a three-phase arc is:

(1.5)

where MVA_bf is bolted fault mega-volt-ampere (MVA).

The distance in feet of a person from an arc source for a just curable burn, that is, skin temperature remains less than 80°C, is:

(1.6)

where t is the time of exposure in seconds.

The equation for the incident energy produced by a three-phase arc in open air on systems rated above 600 V is given by:

(1.7)

where:

 D = distance from the arc source in inches

 F = bolted fault short-circuit current, kA

 V = system phase-to-phase voltage, kV

 tA = arc duration in seconds.

For the low voltage systems of 600 V or below and for an arc in the open air, the estimated incident energy is:

(1.8)

where E_MA is the maximum open air incident energy in cal/cm², F is short-circuit current in kA, range 16–50 kA, and D_A is distance from arc electrodes, in inches (for distances 18 in and greater).

The estimated energy for an arc in a cubic box of 20 in, open on one side is given by:

(1.9)

where E_MB is the incident energy and D_B is the distance from arc electrodes, inches (for distances 18 in and greater).