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:

log~{I_a}~=~K~+~0.662~log~I_{bf}~+~0.0966~V~+~0.000526~G~+
~~~~~~~~~~~~~~~~~~~~0.5588~V~(log~I_{bf})~-~0.00304~G~(log~I_{bf}).....[1]

where:
log = log10
Ia = arcing current (kA)
K = –0.153 for open configurations or
K = –0.097 for box configurations
Ibf = 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:

log~I_a~=~0.00402~+~0.983~log~I_{bf}.....[2]

Table 2—Classes of equipment and typical bus gaps
Classes of equipment Typical bus gaps (mm)
15 kV switchgear 152
5 kV switchgear 104
Low-voltage switchgear 32
Low-voltage MCCs and panelboards 25
Cable 13
Other Not required

Source: IEEE 1584-2002 IEEE Guide for Performing Arc-Flash Hazard Calculations

7614 = 7598 = 7631

About the Author

Ver Pangonilo
A Filipino Engineer, Registered Professional Engineer of Queensland (RPEQ) - Australia and Professional Electrical Engineer (PEE) - Philippines with extensive experience in concept select, front-end engineering, HV & LV detail design, construction and commissioning of Hazardous and Non-Hazardous Area electrical installations in water and waste water pipeline and pumping facilities, offshore platforms, hydrocarbon process plants and pipelines including related facilities. Hazardous area classification and design certification (UEENEEM015B, UEENEEM016B, UEENEEM017B).
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