spacing between duct

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frenchcomp

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Annex B, article B.310.15 (B)(6) NEC 2005: "if spacing between electrical ducts in figure B.310.2 is less..... the ampacity...need not to be reduced".
Does it mean it is acceptable to have for example 9 (3x3) touching underground ducts between 2 pulling chambers and that with this configuration we conform to B.310.2 and dedicated NEC table calculation? Is mutual heating effect of underground duct the same from 0 to 7.5in.?
 
Re: spacing between duct

NEC 2002:

If spacing between electrical ducts, as shown in Figure B.310.2, is less than specified in Figure B.310.2, where electrical ducts enter equipment enclosures from underground, the ampacity of conductors contained within such electrical ducts need not be reduced.
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So IMO, just for that one case it is allowed. :D

Edit: Allowed is the wrong terminology, as Appendices are not enforceable. "Advised" would be a better word.

[ January 12, 2005, 09:21 AM: Message edited by: wirenut1980 ]
 
Re: spacing between duct

I agree with David. Mutual heating is in fact higher, the closer any two (or more) ducts get to each other. However, that impact is minimal for the short distance associated with entering an equipment enclosure. This is just a way of recognizing that many (if not most) equipment enclosures do not have room for a 3 x 3 array of ducts to enter at 7.5 inch spacing.

And to be clear, a pair of consecutive ?pulling chambers? does not meet this rule. The rule only addresses the final entry into the equipment enclosure.
 
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