NM-B cables through studs

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oliver100

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Are two or more NM-B cables going through 3/4" to 1" stud holes considered bundled (as per 520.2 and 310.15) and have to be derated? How do the inspectors interpret this matter? Do they require cable spacers between the studs?
 
Re: NM-B cables through studs

Yes they are bundled. Derating begins at more than 3 current carryig conductors. You can bundle up to 9 current carrying conductors before derating forces you to reduce the ampacity. Neutrals count in 12-2. Neutrals don't count in 12-3 unless you're on the load side of a 3 phase service.

Cable spacers between studs? Never heard of them but in theory that would work. keeping your bundled distance to 24" or less.
 
Re: NM-B cables through studs

Larry, you are applying that provision without merit. The bundling is for 24". I have only seen this interpretation for inspectors who came out of tech courses, not from the field. A hole in a stud is not a raceway, and the bundling for the derating requires 24" and the ampacity allowed for the derating is from the 90 degree table which makes it possible to derate (for those who insist) to the amacity that is used for 12 and 14 normally, namely 20 amps and 15 amps. There is no code limitation on the number of wires thru stud holes.

persistence in taking this point of view, depite numerous proofs to the contrary, only points out that you have no real electrical experience in this matter. you might feel like the energizer rabbit, but you are dragging toilet paper behind you.

paul :p
 
Re: NM-B cables through studs

Originally posted by apauling:
persistence in taking this point of view, depite numerous proofs to the contrary, only points out that you have no real electrical experience in this matter. you might feel like the energizer rabbit, but you are dragging toilet paper behind you.

paul :p
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Paul that is rude and uncalled for.


In regards to the bundling you are just expressing your opinion not any code facts.

[ March 23, 2005, 05:12 PM: Message edited by: iwire ]
 
Re: NM-B cables through studs

2005 NEC

520.2 Bundled Cables or conductors that are physically tied, wrapped, taped or otherwise periodically bound together
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A number of NM cables run through a common hole in a line of studs would be otherwise periodically bound together.

[ March 23, 2005, 05:15 PM: Message edited by: iwire ]
 
Re: NM-B cables through studs

paul,
also new Change in 2005 in 334.80

Where more than two NM cable containing two or more current carrying conductors are bundled together and passing through wood framing..yada yada..the alowable ampacity of each conductor shall be adjusted w/ 310.15(b)2)a)

[ March 23, 2005, 05:26 PM: Message edited by: dillon3c ]
 
Re: NM-B cables through studs

Bob: yes it is rude, and I apologize for the rudeness. At this point though, i feel that this item having been brought up about twenty times (or more) in the last 2 years, tha answer is always the same, there is nothing NEC about derating for stud holes. Stud holes would have to be tabled for different size holes and different size wires. The believed-to-exist requirement that there be no more than three in a hole, does not make mention of cable sizes at all. AT ALL.

The proponents of said interps are not proposing making houses safer, though they think so. More holes have to be drilled in studs of deteriorating quality. This interp came from a few tech course teachers (junior college construction technology classes) and is not from any NEC code or explanation. It has no merit. It serves no real purpose. It's proponents accept no rebuttal, and has become more like a religous belief than a code interpretation.

you do not think that i have accepted being wrong in this forum but you are in error. I have made mistakes and admitted them several times, here, on this site. There has been mud on my face. But the proponents of this idea do not accept any rebuttal, cannot support their interp with any supporting code or information. Hence the frustration. You, yourself have used much less than kind words about me. I do not begrudge you your position, and have sought to grow a thicker skin. I did not deny you your right to be sarcastic, though you seem to have become much more polite in the last year.

I still think the image fits the situation, even if rude.

paul :cool:
 
Re: NM-B cables through studs

Originally posted by apauling:
i feel that this item having been brought up about twenty times (or more) in the last 2 years, tha answer is always the same, there is nothing NEC about derating for stud holes. Stud holes would have to be tabled for different size holes and different size wires. The believed-to-exist requirement that there be no more than three in a hole, does not make mention of cable sizes at all. AT ALL.
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Paul look above in this thread at the changes in the 2005 NEC.

And as far the intent of previous code additions I think you are mistaken in your opinion. The new code just makes that crystal clear.

Bob
 
Re: NM-B cables through studs

2002 says 24". period. 2005 means that it gets derated by 90 degree table.

derating means that a 12 conductor can only carry 20 amps (per tables).

14 conductor can only carry 15 amps.

so what is the constraint that stops several conductiors from passing thru a large hole. NOTHING.

it's a big hoohaw about nothing. It doesn't mean that there is any limit to the number of conductors in a hole. it doesn't mean for residential wiring that the cables are actually derated below their allowable ampacity.

2002 nothing that applies.
2005, in effect, nothing that applies.
nothing has changed.

if you think that 3 14-2 cables thru a 3/4" stud hole is the same as 3 8-3 cables thru a 3/4" stud hole, or even 3 6-3 cables thru a 3/4" stud hole, then i question your over all ability to reason clearly. That is the real problem with this idea, even if it were coded to have an impact on the amount of wires thru a stud hole. There is no perspective on actual hole size fill.

a big hoohaw.

paul :cool:
 
Re: NM-B cables through studs

Paul you do not seem like yourself today, how about coming back at this later with a clear head?

[ March 23, 2005, 05:57 PM: Message edited by: iwire ]
 
Re: NM-B cables through studs

Wow, things have been heating up since I was in the field all day dragging toilet paper behind me :p

Paul,
I think I actually understand why you went off. I hear of things that other inspectors call guys on and it drives me nuts because it lessens the profession.

Never heard of the "3 per hole" rule. I was talking about if someone managed to cram 5 - 12-2's or 5 - 12-3's through one hole then that mess would be subject to derating. Those cables between the studs would be bundled.
 
Re: NM-B cables through studs

________________________________________________
Re: also new Change in 2005 in 334.80

Where more than two NM cable containing two or more current carrying conductors are bundled together and passing through wood framing..yada yada..the alowable ampacity of each conductor shall be adjusted w/ 310.15(b)2)a)
_______________________________________________

Yada..yada.. is for wood framing that is to be fire- or draft- stopped using thermal insulation or sealing foam. Which is not our case. We are talking about regular studs with open holes or notches.

Based on that I assume that the definition of bundling by NEC means a very tight collection of wires, packaged together with no breeding space in between.

This brings the following question - what is the minimum distance between paralel stapled NM cables before derating is required?

If NEC is clear on the above, logically we can expect to find a table with the size of the holes/notches and the number of permitted wires through them similar to conduits and the number of wires in it.

If oveheating is to be expected as per NEC, it is obvious that the relationship between the hole/notch area and the number of cables should have been defined.

Since there is no definition or a table, is it save to assume that the creators of NEC covered all gray area isues, like this one, with the ruling that 90 degree cables must treated as 60 degree cables?

Since there is a lack of clear NEC definition on the subject, I would expect that a reasonable inspector, should not go to the extreme to claim that 2 cables through a good size hole/notch is a bundle of cables requiring derating.

So, how all colleagues are doing it and what do the inspectors say? Let's go to the field.
 
Re: NM-B cables through studs

Oliver,
I guess you'd be the one to know,being your question and all.I was sighting a 2005 code change in general,overall to the topic of NM cable through wood studs.
Come to think of it:
I don't remeber you not saying it wasn't wood studs.Did you? Don't remeber you saying Horizontal or Vertical run either.Just disregard my posting, sorry if I offended...
 
Re: NM-B cables through studs

With the utmost of respect Bob I do believe that the article that you have made mention to, 520.2 pertains to Theaters, Audience Areas of Motion Picture and Television Studios, Performance Areas, and Similar Locations, would pertain to that article only. We all know that 90.3 states that chapters 5, 6 and 7 supplements chapters 1, 2, 3, and 4 as they apply to chapters 5, 6 and 7.

310.15 (B) (2) (a) would better fit the bundling of cables than 520 for theaters. 334.80 address the bundling of NM cable through wood framing that is to be fire- or draft-stopped using thermal insulation or sealing foam.

Using the definition of bundling as outlined in chapter three at 310.15 (B) (2) (a) bundled longer than 600 mm (24 in.) without maintaining spacing, and put that with 334.80 where it clearly states bundled and fire stopped then I have a problem with bundling through studs.

The way I read 334.80 is that unless the conductors are bundled for more than 24 inches then the fire stop plays no part in the derating. Keep in mind that I am using the definition of bundled as outlined in chapter three (310.15) as it would apply to an article in chapter three (334.80)

I must therefore stand with Paul in his understanding of chapter three of the 2005 NEC. Paul I stand with your understanding not the way you displayed it here, although I have reacted the same way.

This is very clear and even those who have never installed a piece of NM cable can understand this simple and very precise statement in the NEC

:)

[ March 23, 2005, 07:39 PM: Message edited by: jwelectric ]
 
Re: NM-B cables through studs

JW can you or Paul explain the need for Exception No. 5: to 310.15(B)(2)(a) if bundled has to mean 'tied together?

If I run eleven 12/2 MC cables through bridle rings every 6' I am subject to a 60% derating.

The cables would be running through a hole (the bridle ring) only every 6' but that is enough to trigger the derating.

You can call me bias but that is because the inspectors here in MA enforce derating where cables are run through holes.

Most times this is a none issue in home wiring with 15, 20 and 30 amps circuits as you can have up to 9 current carrying conductors bundles together before the derating table reduces the ampacity to the point we need to use smaller breakers.
 
Re: NM-B cables through studs

Originally posted by jwelectric:


The way I read 334.80 is that unless the conductors are bundled for more than 24 inches then the fire stop plays no part in the derating. Keep in mind that I am using the definition of bundled as outlined in chapter three (310.15) as it would apply to an article in chapter three (334.80)


This is very clear and even those who have never installed a piece of NM cable can understand this simple and very precise statement in the NEC

:)
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JW,
It's true that I don't handle much NM cable.And I know this is opening a can of worms that will wiggle forever.
But I don't see this article of 334.80 as having to do w/ anything related (or described) with 24' in bundling.It takes it own description of bundling through the stud where NM passes through studs where need to be fire-rated (cauked) at stud hole opening. Nothing to do with 24' in length.And doesn't imply that..

[ March 23, 2005, 08:01 PM: Message edited by: dillon3c ]
 
Re: NM-B cables through studs

The word bundled is mentioned in four articles in the 2005 code in the following articles: 310, 334, 520 and 640.

520 pertains to Theaters, Audience Areas of Motion Picture and Television Studios, Performance Areas, and Similar Locations and 640 to Audio Signal Processing, Amplification, and Reproduction Equipment.

Chapter three is Wiring Methods and Materials. Article 310 pertains to Conductors for General Wiring and 334 is Nonmetallic-Sheathed Cable which would fall under a wiring method.

The first mention of bundling of conductors is in 310.15 Ampacities for Conductors Rated 0?2000 Volts. In (B) (2) (a) it states, 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)
This clearly states that they have to be bundled for more than 24 inches. Now there seems to be a misunderstanding about 334.80.

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 draft-stopped using thermal insulation or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a).

Note the reference in 334.80 to 310.15 where the definition for bundled is first mentioned and clearly states 24 inches.

Any inspector or other person can try and inject their opinion as much as they want and it will not change what is written in the NEC period. This is so clear that the high school kids in my class room can understand it so easy.

:) ;) :p
 
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