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IEEE & NFPA formulas
Posted by Michael from Portland, ME, US on May 8, 2008
The problem is though, IEEE and NFPA formulas are based on 3-phase bolted faults. HRG doesn’t even factor into the equation! Until they rewrite the formulas, there’s not much we can mathematically do.
According to IEEE 1584, using High Resistance Grounding System increases the Incident Energy by
approximately 30%. This is the only mathematical proof we have that High resistance Grounding
works. Now according to the Red Book 7.2.2 and the Green Book we can reduce the number of
Incidences that an Arc Flash may occur.
The purpose of IEEE 1584 is to calculate the Incident Energy in an Arc Flash. We can use the
information from the Red, Green, Buff Books to reduce the number of incidences.
An Arc Flash can occur on a High resistance Grounded System. When it does, we can calculate the
Incident Energy that we need to protect ourselves from, and wear the appropriate PPE. High
Resistance Grounding reduces the probability of a single phase fault escalating to a three phase fault
