Hello guys.

We had an incident where a 480V cable was run overhead for temporary power. A large vehicle was passing underneath the cable and the cable got caught on the vehicle. The insulation on the cable was damaged and caused arcing to the vehicle.

I have been asked to analyze the arc flash potential from this incident and I am a little confused on how to go about this for this situation.

The cable is fed from a delta-delta connected transformer so there should be no single-line-to-ground fault current. We have both SKM and ArcPro software programs. I was planning on using ArcPro for the analysis since it occured in open air but ArcPro is based on a single-phase model and since there is no SLG fault current I was not sure if using the three-phase fault current would give an accurate value. I also had questions as to the arc gap since it is a cable and not a bare wire installed overhead. Typically I would use a 2 inch arc gap for an overhead 480 V line.

Any help would be appreciated.

Is this part of a lawsuit?

Nope. I believe our safety department would just like to know how serious this could have been.

Unless all three phase conductors were damaged and the arcing was phase-phase-phase, doing a standard arc flash analysis may provide meaningless results. Normal SKM calculations, based on IEEE-1584, are not valid for single phase (either L-L or L-G) faults.

Would ground faults even produce an arc flash due to the source being a delta-delta transformer?

Have you checked to see if you already have a ground on one phase?