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Joined: Dec 2004
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I am wiring a new house that is using I-joists'. have wired other houses with these. and usually will drill a 2 1/2" or 3" hole towards the top about 3" down and run most of my wires through that hole.. My question is, how many wires are allowed through that hole? and do you get into a derating problem? my inspector says it is ok. I have about 20 wires through it, and most are #12... what do you guys think?
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Joined: Feb 2004
Posts: 494
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Hi,
Watch out...there are strict rules about WHERE you can drill in manufactured beams!
For the most part do not get out of dead center.
As for the wires...20 is too many for one hole no mater what the cable is feeding!
Check 334.80
310.15(B)(2)(a) Adjustment Factors.
(a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). (the preceeding was copied from another post on the subject)
-regards
Mustang
[This message has been edited by mustangelectric (edited 12-07-2004).]
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Joined: Nov 2004
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I assume that the wiring method is Type NM cable. Installing 20 No. 12awg cables through a 2-1/2" hole is OK, provided that they are not bundled (secured together) for a distance in excess of 24". See 310.15(B)(2)Exception No. 3.
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Joined: Dec 2003
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Where did you get the definition of bundling as "secured together"?
It has been explained by Mike Holt, and etc. that multiple cables installed in bored holes are bundled. Don't you think that the bored holes every 16 or 24 inches secure the cables together?
Earl
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Joined: Oct 2000
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Bundled.
Cables or conductors that are physically tied, wrapped, taped or otherwise periodically bound together.
Joe Tedesco, NEC Consultant
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Joined: Dec 2004
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thanks for your input guys. didnt want to get all roughed in and have to tear everything back out. wayne
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Joined: Dec 2003
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So, Joe, are you saying that NM cables installed in bored holes are not bundled, and therefore we can install as many as we want in a large hole?
I don't see a definition in Article 100, is that from the dictionary?
Earl
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Joined: Apr 2001
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If the bored hole is through a piece of wood in excess of 24 inches, I would say the cables need derating just as through a raceway. If it is a series of holes through 1/4" wood members every 16-24 inches I don't believe derating is needed. If the cables are stuffed tightly where they pass through the holes I think the issue would be physical damage to the cables rather than derating.
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Joined: Feb 2004
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SKI-Thanks for that reference. Now we know!
-regards
Greg
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