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 Post subject: Arc Flash Incident - Calculation HelpPosted: Wed Jul 07, 2010 8:31 am

Joined: Wed Feb 17, 2010 1:08 pm
Posts: 4
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.

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 Post subject: Posted: Wed Jul 07, 2010 10:56 am
 Arc Level

Joined: Mon Jan 18, 2010 11:35 am
Posts: 557
Location: Wisconsin
Is this part of a lawsuit?

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 Post subject: Posted: Wed Jul 07, 2010 11:19 am

Joined: Wed Feb 17, 2010 1:08 pm
Posts: 4
JBD wrote:
Is this part of a lawsuit?

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

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 Post subject: Posted: Wed Jul 07, 2010 3:30 pm
 Arc Level

Joined: Mon Jan 18, 2010 11:35 am
Posts: 557
Location: Wisconsin
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.

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 Post subject: Posted: Thu Jul 08, 2010 6:39 am

Joined: Wed Feb 17, 2010 1:08 pm
Posts: 4
JBD wrote:
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?

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 Post subject: Posted: Thu Jul 08, 2010 6:46 am
 Sparks Level

Joined: Sun Dec 23, 2007 1:44 pm
Posts: 348
Location: Charlotte, NC
Have you checked to see if you already have a ground on one phase?

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