How many wire per hole through studs

olly

Senior Member
I have been told my whole career that you can only run two romex through a hole in a stud. You are allowed to run as many wires as you want through a nipple, under 18" without derating the conductors. So as long as the studs don't add up to more than 18" you should be alright....? I ask because a buddy ran like 8 conductors through studs coming out of the breaker panel.
 

Coppersmith

Senior Member
Location
Tampa, FL, USA
The problem is running NM where it's touching and there is no cooling air space. I believe (and I have no code reference for you) that as long as there is at least a 1/8" air gap between cables, you can run as many as you want through the same hole. Look at cable stackers. They hold 8 or 10 cables in close proximity because each pair is separated by an air gap.

HOWEVER, I always run a maximum of two NM in a small (7/8") hole. If I need to run more than two, I make the hole bigger so the air gap is very apparent to the inspector. Hole size is obviously limited by board size per building code.
 

infinity

Moderator
Staff member
Location
New Jersey
If the hole is not fire-stopped or draft stopped there is no limit as to how many cables you can run through it. If it is filled then derating begins when you install more than two cables. You could possibly install 4-14/3 or 4-12/3 cables in a fire or draft stopped hole with no effect on the final conductor ampacity.
 

olly

Senior Member
If the hole is not fire-stopped or draft stopped there is no limit as to how many cables you can run through it. If it is filled then derating begins when you install more than two cables. You could possibly install 4-14/3 or 4-12/3 cables in a fire or draft stopped hole with no effect on the final conductor ampacity.
That's another question I had... Is firestop required?
 

Coppersmith

Senior Member
Location
Tampa, FL, USA
Firestop is required in the top plate but not the blocking. (Although some blocking is called firestop so IDK.) Not required for horizontal runs unless you are penetrating a firewall.
 
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infinity

Moderator
Staff member
Location
New Jersey
I have been told my whole career that you can only run two romex through a hole in a stud. You are allowed to run as many wires as you want through a nipple, under 18" without derating the conductors. So as long as the studs don't add up to more than 18" you should be alright....? I ask because a buddy ran like 8 conductors through studs coming out of the breaker panel.
Those who say that only two cables are allowed do not understand how to apply derating factors. Fact is if you had 10-2 NM cables on 20 amp circuits you could put 10 cables in a fire or draft stopped hole. (40 amps * 50%= 20 amps)
 
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I agree with Rob. There are two things going on here: 1st is whether derating applies. 2nd is derating properly.
To expand on the former, the code references are 334.80 and dont forget about the "bundling" provision in 310.15(B)(3)(a). This gets into what exactly "without maintaining spacing" means which will have different interpretations.

Regarding the latter, as noted but put another way, just because you have to derate, doesnt mean it will change anything in practice until you get over 9 CCC for sizes 12 and 14.
 

tom baker

First Chief Moderator
Staff member
I have heard the 2 cable limit before and maybe it was valid when we had 60 deg NM, plus the NM was larger than NM B.
Plus if you are 1 1/4 from the face of each side of a stud, 1 1/4 + 1 1/4 + 2 1/2, so a max 1" hole if centered, so most would drill a 3/4"
hole. I am not sure where the 2 cable limit started, its almost like MC cable requires a red head.
 

infinity

Moderator
Staff member
Location
New Jersey
I have heard the 2 cable limit before and maybe it was valid when we had 60 deg NM, plus the NM was larger than NM B.
Plus if you are 1 1/4 from the face of each side of a stud, 1 1/4 + 1 1/4 + 2 1/2, so a max 1" hole if centered, so most would drill a 3/4"
hole. I am not sure where the 2 cable limit started, its almost like MC cable requires a red head.
I'm guessing that it started with a lazy reading of the actual code wording. 334.80 does use the words "Where more than two" but to understand how it's applies you need to read the entire paragraph.

334.80 Ampacity.


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 sealed with thermal insulation, caulk, or
sealing foam, the allowable ampacity of each conductor shall
be adjusted in accordance with Table 310.15(B)(3)(a) and the
provisions of 310.15(A)(2), Exception, shall not apply.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
I'm guessing that it started with a lazy reading of the actual code wording. 334.80 does use the words "Where more than two" but to understand how it's applies you need to read the entire paragraph.
That's exactly it. I even had to expalin that to an inspector. Seems all he saw was "more than two conductors through a bored hole" and didn't read the whole thing. All it takes is one person reading it that way and others taking it as fact without looking for themselves. Then they pass it on with the same results.
 
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