Arc Flash – Calculating Arcing Current

Arcing current is used to calculate the incident energy from an arc flash. The predicted three-phase arcing current, which is lower than the bolt fault current, must be determined so that operating time for protective devices can be set.

For a system with a voltage under 1000 V, equation (1) will be used:

.....[1]

where:
log = log₁₀
I_a = arcing current (kA)
K = –0.153 for open configurations or
K = –0.097 for box configurations
I_bf = bolted fault current for three-phase faults (symmetrical RMS) (kA)
V = system voltage (kV)
G = the gap between conductors, (mm) (see Table 2)

For system voltage of 1000 V and higher, equation (2) is applicable:

.....[2]