Looking at the IE calculation there is a variable for grounding depending on what type system you have installed, and noticed that the grounding type can have a significant effect on the calculated IE energy on ungrounded vs grounded systems. Just curious if anyone can shed some light or point me in the direction of some literature that would better explain the cause of increased IE on ungrounded systems. I see the variable change in the calculations and there is a brief statement about this and found some articles that discuss the grounding types etc. but could not find any technical literature on the “why’s� any information is greatly appreciated. Thanks…

I've seen some reports that anecdotally mention that they do NOT see any differences compared to the IEEE 1584 calculation. It might be simply a numerical anomaly or not. The calculation itself is purely an empirical curve fit so there is no theoretical explanation as to any physical meanings behind the IEEE 1584 empirical equation because by nature, there isn't one.

The article below is actual testing that tested the ungrounded/resistance grounded concept and found that you get a 3 phase arcing fault but that the A-C fault is actually more like A-N-B where N is the surrounding housing. Given that in a solidly grounded system it can just as form A-G or C-G as the third arc and there is no need for a double line-to-ground fault (LGL), the reduction in the amount of arcing columns might provide some explanation here. Obviously impedance (through the grounded connections) plays a role for the third and fourth arcs. This is purely a guess on my part. I have no documentation to back it up.

http://www.neiengineering.com/wp-conten ... esting.pdf

It was more of the erratic nature of the 3 phase arcing current getting established. It it didn't always initially act as a "balanced" three phase event even though the calculations assume all three phases are equal. The IEEE 1584 Working Group has been looking into this but at the moment I'm not able to say much else. Stay tuned!