NESC Arc Flash Tables vs ArcPro Calcs

[dpc]

There was a thread on this several months ago, but it's locked, so I'll start a new one.

I'm trying to compare my results using ArcPro against the values in the NESC arc-flash table 410-2 at 69 kV. My results seem to be much less than the basis used for the NESC Table.

I thought I was using the arc gap and working distance as defined in the table footnotes, but something is obviously different. Most likely candidate seems to be the working distance. I used the 39" minimum approach distance from Table 441-1 minus twice the assumed arc gap and got about 31".

Has anyone been able to match the NESC table results using ArcPro?

 

[WDeanN]

dpc -
I know this is probably not necessary, but have you used the multipliers in ArcPro for single phase, three phase, etc? (It's been a while since I've used ArcPro, forgive me)

Also, although NESC says they were calculated using "commercially available software" is there a possibility they used the free Duke Energy calculator?

 

[dpc]

It's my understanding that ArcPro is what was used, but I could be wrong. For the table covering voltages from 1 kV up to 46 kV, the values in the tables exactly match my ArcPro calcs.

For the higher voltages, my results are consistently lower, although not by a consistent amount. If the footnotes in the tables are correct, there are some discontinuities in the assumptions made for arc gap. But I suspect the main discrepancy is what was used for the distance to arc and what was used as the Minimum Approach Distance.

I have not tried applying the factors for single-phase arc in box or three phase, but I don't see why they would start applying those at higher voltages when they apparently didn't apply them at 1-46 kV. But I'll take a look.

I traded e-mails with another engineer who is having similar issues. He has sent a request to NESC committee member who was said to be the expert on the tables, but has received no response.

 

[stevenal]

The '07 preprint proposals said "These calculations were derived using ARCPRO 2.0™"
The 07 code changed it to "...a commercially available software program."