Bundling NM

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gimpyfac

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How many NM cables are allowed to pass thruogh wood framing that is fire or draft-stopped? Hole size, 1, and 3/4.
 
Re: Bundling NM

there is a certain thing called temperature and it runs through wires common sense unless you figure to never turn power on
 
Re: Bundling NM

Clever. :roll:

Don, I see 310.15(B)(2)(a). It says "...where...bundled longer than 24 inches without maintaining spacing..." Is this what's supposed to apply, because it doesn't seem to. Is the fact that the cables are going the same way affect the "spacing" concept?

Thanks,
 
Re: Bundling NM

Its almost a non issue as the ampacity of 14-2 NM is 25 amperes. You derate from 25. It would take a lot of conductors to ge below 15 after derating.
 
Re: Bundling NM

From the 2005 code.
334.80 ... Where more than two NM cables containing two or more current-carrying conductors are bundled together and pass through wood framing that is to be fire- or draftstopped using thermal insulation or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a). [ROP 7?150a]
Click to expand...
 
Re: Bundling NM

So, to check my understanding: Hypothetically I have 5 14-2's through a hole, for ten conductors. The table states that for 10 conductors I must derate 50%, so in the 90 degree column in 310.16 I have 25 amps, derated to 12.5 amps. Hence, the maximum number of 14-2's I can run through a hole to be insulated (aren't they all?) is 4 cables.
Or 3 cables of 14-3. Same limits for 12 wire.

If that were exceeded for #14, I would have to install a "12.5" amp breaker (10 amp continous-load)...Right?

Wait: I thought I had seen 10 amp breakers on existing stuff in the field, but I don't find it in 240.6(A)? So, I flat couldn't put 5 14-2's through a hole then, ey?

Hypothetically. :)
 
Re: Bundling NM

Originally posted by channing123:
there is a certain thing called temperature and it runs through wires common sense unless you figure to never turn power on
Click to expand...
Could have sworn it was electricity that ran through wires in the wall...
 
Re: Bundling NM

Has there been any real field testing done to determine if multiple romex cables passing thru a single hole in a residential setting actually needs derating or is this just because too many people with word processors bounced the concept around soo much that it has become such an issue it finally made it into the code book?
 
Re: Bundling NM

Originally posted by macmikeman:
Has there been any real field testing done to determine if multiple romex cables passing thru a single hole in a residential setting actually needs derating or is this just because too many people with word processors bounced the concept around soo much that it has become such an issue it finally made it into the code book?
Click to expand...
Good question!
 
Re: Bundling NM

Code: 
334.80 Ampacity. The ampacity of types NM, NMC, and 
 NMS cable shall be determined in accordance with 310.15. 
 The ampacity shall be in accordance with the 60 degree C (140 F) 
 conductor temperature rating. The 90 C (194 F) rating 
 shall be permitted for ampacity derating purposes,
 provided the final derated ampacity does not exceed 
 that for a 60 C (140 F) rated conductor.
Jim, for derating, I can start with 90 degree ampacities.

It seems to me that crushing seven cables in a 7/8's hole should be against code (albeit against the laws of physics)--but this doesn't seem to address that. The only place this could have effect from what I have experienced is at the panel, where I drill a few 1.5" holes with a self feeder and the wires don't really come into contact with each other in a way that should require derating, but this would apply to that, wouldn't it? I do think this is a physical non-issue.

Has anyone been failed for bundling through holes?
 
Re: Bundling NM

I have been. A town that I was wiring a subdivision in, Finished my rough in on the first one, went to the next one, got a call from the inspector who told me I could only run 1 wire through each hole. And he didnt care if it was a 2" hole. Real intelligent guy huh??? :roll:
 
Re: Bundling NM

jimwalker

334.80 334.80 Ampacity.
The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60?C (140?F) conductor temperature rating. The 90?C (194?F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60?C (140?F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.
 
Re: Bundling NM

Out here in San Francisco, most of the inspectors insist on one-hole one-wire. It has always seemd rediculous to me. If you're running from a panel to a kitchen (2 applicance circuits, dish washer, disposal, refer, microwave..) you end up drilling 6 or 7 1/2 inch holes through every joist. Seems to me 2-3 wires through each hole would be fine if you drilled the peoper size.
I don't know of an NEC reference, but they say it's a "local variation."
 
Re: Bundling NM

Sorry, Jim, I didn't see this. I was confused because I had already written 334.80 out, and Tom reposted it. :)

1 cable per 1 hole? I'd steer clear of that or become a plumber. Man, what a PITA. :eek:
 
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