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 Post subject: Minimum Approach Distances - Which ones?
PostPosted: Fri Feb 06, 2009 8:46 am 
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Joined: Fri Feb 06, 2009 7:49 am
Posts: 1
Location: Lower Willamette Valley in Oregon
While minimum approach distances are unrelated to arc flash boundaries, they come into play for utility distribution voltages: If the arc flash boundary is less than the MAD, then it becomes a moot topic because the line worker will be futher away than the boundary. My question is this: Which MAD should utilities use? :confused: The numbers listed in OSHA 1910.269(I)(10), Table R-6 are different from those listed in the NESC, Tables 441-1 and 441-2, especially in the 15kV to 25kV range. Also, the separation of single phase and three phase distances in Tables 441-1 and 441-2 seems non-sensical. :eek:


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PostPosted: Fri Feb 06, 2009 12:36 pm 
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Joined: Tue Jan 13, 2009 5:00 pm
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Note that the MAD is measured from the conductor, while the arc flash boundary is measured from the arc. Looks like NESC is more restrictive. If both apply, use the most restrictive. NESC usually leads OSHA. I expect the next OSHA revision will match NESC. There is an NESC Arc flash forum here.


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