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ekstra   ara
 Post subject: NFPA 70E Annex D Flash Boundary Calcs
PostPosted: Thu Aug 12, 2010 8:37 am 
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Joined: Thu Aug 12, 2010 6:51 am
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Why does the sample calculation in Annex D, Paragraph D.4 of the 2009 edition of the NFPA 70E, not match the result in Table D.2 for the same parameters used in the sample calculation? The sample calculation, which refers to Table D.2, comes up with results of 7.00 ft and 7.28 ft., while Table D.2 for the same transformer reports a value of 9.7 ft. A difference 2.4 ft is significant!

Also, has anyone looked at the use of significant figures in these calculations? It seems that the rounding and reporting of figures is not consistent or practical.

Examples: the sample calculation reports a result of "6.9 or 7.00 ft" (converting two to three significant figures).

And how is it practical to report Flash Boundaries to hundredths of a foot, such as 7.28 ft (from Sample calc.), or 0.61 ft (from Table D.2)? How do you comply with that, a micrometer?


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PostPosted: Thu Aug 12, 2010 1:44 pm 
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Joined: Tue Feb 24, 2009 7:05 am
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You're not the only one: see [url="http://www.arcflashforum.com/showthread.php?t=347"]this thread[/url] (without answers).

But since almost everybody uses IEEE1584 up to 15kV, I didn't push the issue more.


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