With the given values:

C_{f} = 1.5 for voltages at or below 1 kV.

E_{n} = 5.26 J/cm^{2}

E_{n} = 4.4126 J/cm^{2} *(reduced incident energy)*

t = 0.025 s *(from Table 1, See note 1)*

x = 1.641 *(from Table D.4.2)*

D = 455 mm *See Table 3.*

J/cm^{2}

cal/cm^{2}

For the reduce incident energy

J/cm^{2}

cal/cm^{2}

Now that the incident energy has been determined, the Arc Flash Boundary can be calculated. Arc Flash Boundary is the distance at which a person is likely to receive a second degree burn. The onset of a second degree burn is assumed to be when the skin receives 5.0 J/cm^{2} of incident energy.

For the empirically derived equation,

.....[3]

For the theoretically derived equation,

.....[4]

**where:**

D_{B} = distance (mm) of the arc flash boundary from the arcing point

C_{f} = calculation factor

C_{f} = 1.0 for voltages above 1 kV

C_{f} = 1.5 for voltages at or below 1 kV

E_{n} = incident energy normalized

t = time, sec

x = distance exponent from Table D.4.2

E_{B} = incident energy in J/cm^{2} at the distance of the arc flash boundary

V = system voltage, kV

I_{bf} = bolted three-phase available short-circuit current

The above equations could be used to select personal protective equipment (PPE), to ensure that it is adequate to prevent thermal injury at a specified distance in the event of an arc flash.

For our example, using the reduced arcing current and equation [3], the calculated arc flash boundary (AFB) is 506.4 mm requiring Category 1 PPE (see Table 130.7(C)(15)(A)(b)).

**Notes:**

1. This need to taken from the time-current curve of the protective device. In the absence of such information, Table 1 can be used. Latest models of MCCB can clear faults in 0.5 - 1 cycle. As per NFPA 70E, 2 seconds is a reasonable maximum time for calculations.