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Have you ever used NESC Table 410-1 for arc flash studies?
Yes
No
No - Never heard of it
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 Post subject: Use of NESC Table 410-1
PostPosted: Sun Mar 21, 2021 12:42 pm 
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Joined: Mon Sep 17, 2007 5:00 pm
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Location: Scottsdale, Arizona
The National Electrical Safety Code (IEEE Std. C2) Table 410-1 lists Minimum Arc Ratings of clothing and clothing systems for working on specific equipment and voltages. Some line items in this table are based on industry testing by two major US utilities.

In particular, two items from Table 410-1 include:

Panelboards 50V to 250V – Three Phase >100A = 4 cal/cm2 minimum arc rating
Panelboards 50V to 250V – Single Phase (all) / Three Phase (<100A) = 4 cal/cm2 minimum arc rating


I am not advocating any one method over another but simply asking this week’s question:

Have you ever used NESC Table 410-1 for arc flash studies?
Yes
No
No - Never heard of it

Your thoughts about this table are appreciated!


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 Post subject: Re: Use of NESC Table 410-1
PostPosted: Mon Mar 22, 2021 8:54 am 

Joined: Mon Nov 10, 2014 11:01 am
Posts: 23
Your question was about NEC table 410.1 which does not exist.


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 Post subject: Re: Use of NESC Table 410-1
PostPosted: Mon Mar 22, 2021 10:47 am 
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Your question was about NEC table 410.1 which does not exist.

No, it really is the NESC - National Electrical Safety Code. Back in 2007 when arc flash surfaced in this standard used by utilities, there was a statement that less than 1000 volts defaulted to 4 cal/cm^2 for incident energy which cause a bit of panic by some. Then the next edition introduced the subject table 410-1 based on equipment tests with the line items that I quoted. Some use this when on the secondary side of transformers.


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 Post subject: Re: Use of NESC Table 410-1
PostPosted: Mon Mar 22, 2021 4:16 pm 
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Joined: Tue Jan 13, 2009 5:00 pm
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Quote:
Have you ever used NEC Table 410-1 for arc flash studies?
Yes
No
No - Never heard of it
You may select 1 option


Jim,
We know from the subject line and your post that you meant the NESC. The actual question, however, left out that all important S.

I said yes, since my organization meets the scope of the NESC. I understand OSHA has a problem with a few of the entries.


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 Post subject: Re: Use of NESC Table 410-1
PostPosted: Mon Mar 22, 2021 4:29 pm 
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stevenal wrote:
Quote:
Have you ever used NEC Table 410-1 for arc flash studies?
Yes
No
No - Never heard of it
You may select 1 option


Jim,
We know from the subject line and your post that you meant the NESC. The actual question, however, left out that all important S.

I said yes, since my organization meets the scope of the NESC. I understand OSHA has a problem with a few of the entries.

Whoa! :o Thanks to you and JCP for pointing out my typo. Yes it is NESC and not NEC, I did miss the "S". I corrected it. Thanks!


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 Post subject: Re: Use of NESC Table 410-1
PostPosted: Wed Mar 24, 2021 1:00 pm 
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Joined: Sat Nov 21, 2009 10:23 pm
Posts: 113
Location: Ohio
Jim

You already know my thoughts, the IEEE calculation at 208V are so far out of wack it becomes misleading. I review a lot of studies and when I see a 120/208V, 30 kVA transformer feeding a 100A panelboard with a 20 cal/sq cm label I cringe. When I do the training for that company/study, I have to walk a very narrow line.

In addition, I think I have read most IEEE papers trying to test for incident energy at 208V, a large percentage of the tests cannot even maintain an arc. Most of the papers fall short of any real direction. The most interesting reads relate to the NESC findings. Those tests are very clear, they are testing real equipment, unlike the IEEE tests which mostly uses the arc-in-a-box.

This is just an opinion, when a study is done, the < 250V equipment should not totally use the IEEE calculations. One way to moderate the the process is to provide generic 4 cal labels (NESC Method) for all circuits (=> 100A) fed by < 125 kVA through 30 kVA transformers. The 15 kVA transformers are treated differently since they fall under the 2000 amp IEEE threshold. The > 125 kVA transformer circuits are completed using a modified IEEE method which typically provides results near or under 4 cal. Again, this last paragraph is all opinion.


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 Post subject: Re: Use of NESC Table 410-1
PostPosted: Sun Mar 28, 2021 3:13 pm 
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Flash wrote:
Jim

You already know my thoughts, the IEEE calculation at 208V are so far out of wack it becomes misleading. I review a lot of studies and when I see a 120/208V, 30 kVA transformer feeding a 100A panelboard with a 20 cal/sq cm label I cringe. When I do the training for that company/study, I have to walk a very narrow line.

In addition, I think I have read most IEEE papers trying to test for incident energy at 208V, a large percentage of the tests cannot even maintain an arc. Most of the papers fall short of any real direction. The most interesting reads relate to the NESC findings. Those tests are very clear, they are testing real equipment, unlike the IEEE tests which mostly uses the arc-in-a-box.

This is just an opinion, when a study is done, the < 250V equipment should not totally use the IEEE calculations. One way to moderate the the process is to provide generic 4 cal labels (NESC Method) for all circuits (=> 100A) fed by < 125 kVA through 30 kVA transformers. The 15 kVA transformers are treated differently since they fall under the 2000 amp IEEE threshold. The > 125 kVA transformer circuits are completed using a modified IEEE method which typically provides results near or under 4 cal. Again, this last paragraph is all opinion.


Thanks for your comments! Exactly what I was hoping to hear and the reason for my question last week - To bring attention to the NESC Table. I have to walk a fine line too - especially because of my position.


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