Number of NM cables through hole

[jclint07]

I need help finding exact code section stating number of NM cables allowed through bored/drilled hole, regarding derating. I thought I had come across a section stating this. I believe 2 were allowed before derating, something to do with insulation being installed in hole as well. But I have been wrong before. Maybe this was not in actual NEC book but forum somewhere.

 

[acrwc10]

I need help finding exact code section stating number of NM cables allowed through bored/drilled hole, regarding derating. I thought I had come across a section stating this. I believe 2 were allowed before derating, something to do with insulation being installed in hole as well. But I have been wrong before. Maybe this was not in actual NEC book but forum somewhere.

2008 nec,
334.80 that will take you to 310.15(B)(2)(a)

then follow the chain of code sections,T310.16, 334.80, 310.15(B)(4)(a), 310.155(B)(5).

In a nutshell if you are working on a standard house, you can almost always put atleast 4 NM cables (sizes 14 and 12) in the same hole.

add- you can run four 14/3 and 12/3 also because, if they are MWBC the neutral is not a CCC and not counted. If they are used as 3-ways or 4-ways, one wire is always not being used as a CCC, because the switching moves the load from wire to another to make it work correctly.

 

[jclint07]

Thanks for code section I was looking for!

I still don't see how you can put 4 NM cables thru same bored/drilled hole, that is to be fire-stopped (thermal insulation)....
UNLESS drilled hole is considered an actual "raceway", then CCC conductors in each NM cable are derated per 310.15 (B)(2)(A).

So (5) 12/2 with ground NM cables could be stuffed through a 3/4" drilled hole (that is to be caulked) and NO derating is required because EACH cable has only (2) CCC conductors and NOT "more than 3 CCC cable" such as 310.15 (B)(2)(A) actually states?

 

[cowboyjwc]

You didn't say anything about the hole's being firestopped in your original post. For that you would have to go to the fire stopping product you are using and they will tell you how it shall be installed.

Look at 334.80 also.

 

[jclint07]

Why would the mentioning of firestopped make a difference?

I mentioned insulation being installed in holes in original post, which according to the code section being discussed (334.80), same rule applies to either.."to be fire-OR draft-stopped using thermal insulation...":?

 

[marti smith]

Think of heat dissipation...

 

[don_resqcapt19]

Thanks for code section I was looking for!

I still don't see how you can put 4 NM cables thru same bored/drilled hole, that is to be fire-stopped (thermal insulation)....
UNLESS drilled hole is considered an actual "raceway", then CCC conductors in each NM cable are derated per 310.15 (B)(2)(A).

So (5) 12/2 with ground NM cables could be stuffed through a 3/4" drilled hole (that is to be caulked) and NO derating is required because EACH cable has only (2) CCC conductors and NOT "more than 3 CCC cable" such as 310.15 (B)(2)(A) actually states?

It is my opinion that it is the total number of current carrying conductors in all of the cables that pass through the hole that is used for this purpose.

It appears based on the panel comment for proposal 6-44 for the 2014 code that panel 6 does not agree.

Section 310.15(B)(3)(a) is specific to conductors in raceway or cable. This section provides references to other sections, but contains rules for only conductors in raceways or cables.

 

[Dennis Alwon]

The reason you can install 4 12/2 cables in a hole that is firecaulked is because 12/2 nm is rated 90C. We start there and see that #12 is rated 30 amps at 90C. With 4 12/2 cables we have a total of 8 CCC. This must be derated to 70%. 70% of 30 is 21 so we are still good at 20 amps. Once you have10 CCC then you have problems because then we must derate at 50%

 

[jclint07]

Dennis...

How can you have a total of 8 CCC, as far as derating per 310.15(B)(2)?
(4) 12/2 NM cables is still only 2 CCC per cable.
Table 310.15(B)(2) clearly states at the top... "Adjustment Factor for More Than Three CCC in a raceway or CABLE

 

[cowboyjwc]

Why would the mentioning of firestopped make a difference?

I mentioned insulation being installed in holes in original post, which according to the code section being discussed (334.80), same rule applies to either.."to be fire-OR draft-stopped using thermal insulation...":?

Exactly, it mentions to be fire or draft stopped. What if it wasn't fire or draft stopped?

And again, the listing of the fire stopping product you use may only allow you to put in two cables in one hole or if you can put in four cables it will tell you how large the hole has to be so that you get the required anular space.

 

[don_resqcapt19]

Dennis...

How can you have a total of 8 CCC, as far as derating per 310.15(B)(2)?
(4) 12/2 NM cables is still only 2 CCC per cable.
Table 310.15(B)(2) clearly states at the top... "Adjustment Factor for More Than Three CCC in a raceway or CABLE

The title of this section was the very reason for my proposal (6-44). The section clearly applies to other than raceways or cables based on the following words in the section.

... or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, ...

Yes that includes the 24" rule, but in my opinion the intent of rule, when you are installing cables in draft or fire stoppped holes, that you derate on the total of all of the current carrying conductors in all of the cables that pass through a single hole.

 

[infinity]

Dennis...

How can you have a total of 8 CCC, as far as derating per 310.15(B)(2)?
(4) 12/2 NM cables is still only 2 CCC per cable.
Table 310.15(B)(2) clearly states at the top... "Adjustment Factor for More Than Three CCC in a raceway or CABLE

IMO it doesn't matter what the heading of that table is since 334.80 specifically directs you there when you have more than two NM cables.

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.
Where more than two NM cables containing two or more current-carrying conductors are installed, without maintaining spacing between the cables, through the same opening in wood framing that is to be fire- or draft-stopped using thermal insulation, caulk, or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a) and the provisions of 310.15(A)(2), Exception, shall not apply.

 

[Dennis Alwon]

Infinity nailed it. art. 334.80 specifically states to use the table 310.15(B)(2)(a) when you have more than 2 cables. If you bundle you look at the bundle as if they were in a raceway.

 

[jusme123]

2008 nec,
334.80 that will take you to 310.15(B)(2)(a)

then follow the chain of code sections,T310.16, 334.80, 310.15(B)(4)(a), 310.155(B)(5).

In a nutshell if you are working on a standard house, you can almost always put atleast 4 NM cables (sizes 14 and 12) in the same hole.

add- you can run four 14/3 and 12/3 also because, if they are MWBC the neutral is not a CCC and not counted. If they are used as 3-ways or 4-ways, one wire is always not being used as a CCC, because the switching moves the load from wire to another to make it work correctly.

Can you point out the code article that states these are not CCC if connected to 3 ways or 4 ways, IMHO I believe they count.

 

[acrwc10]

[/B]

Can you point out the code article that states these are not CCC if connected to 3 ways or 4 ways, IMHO I believe they count.

You are assuming they count, remember the NEC is a "permissive" document, if it doesn't say you can not do something then you can do it.
The point in saying you must count only CCC's is that, only a wire with current running through it will add heat to the bundle. If you look at how a 3 or 4 way switch works, one wire is ALWAYS dead, thus it is only a CCC when the other "traveler" is dead.
I had to write this out in long hand and submit it with a set of plans not that long ago, to the building dept. If you look at each code section I put down and think about it then move to the next code section (with a little math starting in the 90o column) you will see, 4 NM's in one hole is the magic number. The reality is most of the NM cables will never reach anywhere near their max (derated) load, in a house.

 

[jusme123]

You are assuming they count, remember the NEC is a "permissive" document, if it doesn't say you can not do something then you can do it.
The point in saying you must count only CCC's is that, only a wire with current running through it will add heat to the bundle. If you look at how a 3 or 4 way switch works, one wire is ALWAYS dead, thus it is only a CCC when the other "traveler" is dead.
I had to write this out in long hand and submit it with a set of plans not that long ago, to the building dept. If you look at each code section I put down and think about it then move to the next code section (with a little math starting in the 90o column) you will see, 4 NM's in one hole is the magic number. The reality is most of the NM cables will never reach anywhere near their max (derated) load, in a house.

I've been in the circus long enough to know how 3 and 4 way switches work. The code states that they are counted as CCC, it does not, however, state instanstances in which they do not count.

 

[suemarkp]

Do you have a reference to that in code prior to 2011?

I always treat NM cable in bored holes as bundled. Makes the whole insulated wall thing moot and avoids arguments as to whether the cables are bundled or not. Even if you want to do more than 4 cables per hole, it is difficult to do that in a 2x4 wall because if your bored hole is larger than 1" or other than perfectly centered, you need nail plates on both faces of each stud that you drilled. Much easier to drill a second hole instead of nail plating everything.

 

[infinity]

The code states that they are counted as CCC, it does not, however, state instanstances in which they do not count.

What specific code section would you cite to prove that they count?

 

[acrwc10]

I've been in the circus long enough to know how 3 and 4 way switches work. The code states that they are counted as CCC, it does not, however, state instanstances in which they do not count.

I know it is not easy to convince some inspectors to think logically but, the fact is one of the wires is always off (in a 3-4way) most inspectors, and logically thinking persons, would agree to. We do have a local builing dept. that will not allow more than two NM's through an insullated hole, unless you show them in writing that you have done the derating calculations. I have found 4 is the "always works" number for 12 and 14 NM If you want to run 3 NM's, just because it's a 3-4way switch, more power to ya. I'm just trying to answer your question, not insult you. I apoligize if you feel I was implying you didn't understand a 3way switch, but there are many others that read these posts and use this information, so I put in as much information as I feel is relevant.

 

[jusme123]

What specific code section would you cite to prove that they count?

Can heating and air conditioning be run in the same conduit without derating (3 phase, 220)?