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 Post subject: NESC Below 1000 Volts
PostPosted: Tue Apr 28, 2009 5:11 am 

Joined: Fri Jul 06, 2007 9:07 am
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Has anyone heard if there is anything proposed regarding NESC 410 Exception 2? This is the exception about systems below 1000 Volts ...

"in lieu of performing an arc hazard analysis, clothing or a clothing system with a minimum effective arc rating of 4 cal/cm2 shall be required to limit the liklihood of ignition."

I heard there might be a table in the works for less than 1000 Volts. 4 cal/cm2 seems like someone did not think this through.

Any Ideas?


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PostPosted: Wed Apr 29, 2009 8:37 am 
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http://www.arcflashforum.com/showthread.php?t=332


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PostPosted: Thu Apr 30, 2009 6:17 am 
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I was speaking at an electric utility conference earlier this week and this subject came up (several times). In talking with a few people there, it seems there is a movement underway to change 4 cal/cm2 to 20 cal/cm2 unless calculations are performed that indicate something less than 20 cal/cm2. Since 20 cal PPE is not people's first choice I am sure this will trigger calculations. Not sure if this will be an addendum, TIA or introduced in the next edition of the NESC but the overwhelming consensus was the 4 cal/cm2 was a very dangerous number to use.

As usual, stay tuned and I'll update everyone when more is known.

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PostPosted: Thu Apr 30, 2009 11:02 am 
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Are these folks aware of the lack of tools available to do arc in a box single phase calculations?


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PostPosted: Thu Apr 30, 2009 11:13 am 
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Yes, they are. I'm hoping that will be covered with the new tests although that doesn't help much right now. EPRI seems to be moving faster than IEEE so perhaps we'll know something sooner rather than later.

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PostPosted: Thu Apr 30, 2009 2:28 pm 
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Thanks for the info!


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