NM cable thru holes

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nizak

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Has there been any change to the current code that prohibits running more tha 3 nm cables thru drilled holes?

I am not asking about where caulk or insulation is applied, just simply drilled holes thru floor joists.

On 2 occasions I have had other contractors tell me that they are being questioned about drilling a 2" dia. hole for instance and pulling their home runs back to the panel.

I have never had a job turned down for this ever. 12" 16" 24" joists on center I've always done this way.

Both have asked to get a code reference and have been told it's just not a good practice.

BTW, this is the same inspector in both townships.

Thanks.
 
nizak said:
Has there been any change to the current code that prohibits running more tha 3 nm cables thru drilled holes?

I am not asking about where caulk or insulation is applied, just simply drilled holes thru floor joists.

On 2 occasions I have had other contractors tell me that they are being questioned about drilling a 2" dia. hole for instance and pulling their home runs back to the panel.

I have never had a job turned down for this ever. 12" 16" 24" joists on center I've always done this way.

Both have asked to get a code reference and have been told it's just not a good practice.

BTW, this is the same inspector in both townships.

Thanks.
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No, there has not been a change to the NEC in which a limit has been placed on the no. of nm's run thru framing members in the non caulked, insulated, non fire stopped etc situation you described.

Unless there is a written local amendment covering this, the 'spector is in fantasy land and/or making up his own code.:)

The opinion of "good practice" is different than being required.
 
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See 310.15(B)(3)(a) and note that (B)(3)(a)(4) does not apply. The inspector is correct about the installation described. You can do it, but 10s and 8s are generally cost prohibitive for 15A and 20A circuits.
 
The limitation isn't how many cables can run in a hole, the limitation becomes cost and practicality of having to adjust ampacity if you have more then three current carrying conductors in the same group, bundle, etc.

We used to drill 2 inch holes and put all the home runs in them a long time ago, but it has been about 20 years now since an inspector made us stop doing that, or derate the conductors, our choice.
 
kwired said:
The limitation isn't how many cables can run in a hole, the limitation becomes cost and practicality of having to adjust ampacity if you have more then three current carrying conductors in the same group, bundle, etc..
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310.15(B)(3) mentions that the derating only applies if the nms were installed w/out "maintaining spacing" for longer than 24 inches and it doesn't tell us what that means (1/8, 1/16, 1/4 of an inch between cables along the entire 24"???)- so up to AHJ, but in the eyes of the NEC, imo, the op is fine.

The nm derating that would come from 334.80 also does not apply b/c the op said no caulk, fire stop, insulation etc.
 
user 100 said:
The nm derating that would come from 334.80 also does not apply b/c the op said no caulk, fire stop, insulation etc.
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True however...........

310.15 said:
(3) Adjustment Factors.
(a) More Than Three Current-Carrying Conductors.
Where the number of current-carrying conductors in a raceway
or cable exceeds three, 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, the allowable ampacity of each
conductor shall be reduced as shown in Table 310.15(B)(3)(a).
Each current-carrying conductor of a paralleled set of conductors
shall be counted as a current-carrying conductor.
Click to expand...
 
nizak said:
Has there been any change to the current code that prohibits running more tha 3 nm cables thru drilled holes?

I am not asking about where caulk or insulation is applied, just simply drilled holes thru floor joists.

On 2 occasions I have had other contractors tell me that they are being questioned about drilling a 2" dia. hole for instance and pulling their home runs back to the panel.

I have never had a job turned down for this ever. 12" 16" 24" joists on center I've always done this way.

Both have asked to get a code reference and have been told it's just not a good practice.

BTW, this is the same inspector in both townships.

Thanks.
Click to expand...

You could run 4 or 5 NM, say from a switchbox, thru the same top plate**, but not thru 2 joists (over 24").

Ive seen a lot of older installs where large holes were drilled near the panel and numerous (7-15+) homeruns were pulled thru them, so I'm guessing it was allowed at some point in the past.

There doesnt have to be much separation as cable stackers apparently provide sufficient distance between conductors. If a 1/4" is fine, I would think that one could put numerous cables thru one bored hole, then come back thru and put a barrier of sorts between the wires (like an 8 sided plastic piece that looks like an asterisk from the end view, with 8 channels between, providing a fixed separation between cables) and that would be code compliant. Probably just easier and cheaper to drill 1" holes and stick to few conductors/cables per hole.

** NOPE. See the last paragraphs of 334.80 to see why people are sticking to 2 NM cables/hole. That said, having a lot of cable briefly come together, like a bored hole thru a top plate, isnt going to cause a fire, esp on something like switch legs where the overall current thru all of those wires would be generally limited to 15A (one residential lighting circuit).
 
Its often said you can't run more than 3 NMs thru one bored hole. I hear this a lot, but there is no code rule on this, but the derating issue does come in, however remember you derate from the 90 deg C rating.

However for a 2 x 4, which is 3 1/2, the distance from the face of the stud for the hole is 1 1/4", 2 x 1/1/4 " = 2 1/2", leaving a 1" hole. Before 1984, NM was made with THW insulation so the overall jacked was larger, perhaps it was just a physical limit to get that may NMs thru a hole
 
user 100 said:
310.15(B)(3) mentions that the derating only applies if the nms were installed w/out "maintaining spacing" for longer than 24 inches and it doesn't tell us what that means (1/8, 1/16, 1/4 of an inch between cables along the entire 24"???)- so up to AHJ, but in the eyes of the NEC, imo, the op is fine.

The nm derating that would come from 334.80 also does not apply b/c the op said no caulk, fire stop, insulation etc.
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Quite frankly I have no issue with general lighting and outlet circuits in dwelling unit and drilling a 2 inch hole and putting in multiple cables. especially if not surrounded by any thermal insulation. Such cables seldom are loaded very much or when they are not for very long.

I do have concerns with HVAC loads or maybe a pool pump or other continuous duty circuit that is sized for minimum ampacity required as I have experienced feeling some heat in those cables when the load has been running for a long time.

But it says what it says and I try to deep the current carrying conductor count in one hole below nine so deration is not an issue.
 
kwired said:
Quite frankly I have no issue with general lighting and outlet circuits in dwelling unit and drilling a 2 inch hole and putting in multiple cables. especially if not surrounded by any thermal insulation.
Click to expand...

Really, aside from limiting use to 60C, just about all these rules are nonsense. But code is code, and to deviate is to invite rejection of the installation.
 
kwired said:
Quite frankly I have no issue with general lighting and outlet circuits in dwelling unit and drilling a 2 inch hole and putting in multiple cables. especially if not surrounded by any thermal insulation. Such cables seldom are loaded very much or when they are not for very long.
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That wouldn't be an issue unless the cables going to and from that hole are bundled. You can put as many as you can fit in a hole if there is no fire stop or draft stop material within the hole since no adjustment is required.
 
The problem is that one inspector may consider the install bundling while another does not. I used to do exactly what the op stated-- 2" hole with many homeruns run thru them. It never was considered bundling but I can understand how it would be considered so.
 
That's exactly right. I like to do things consistent. In certain areas one way is acceptable and in the next county you have to change your routine.
 
Building codes have to have some limit on how big of hole you can make in a joist.I remember seeing a chart of some sort on it. the closer you get to the bearing point the smaller the hole allowed.
 
George Stolz said:
Actually, if you read the bag they come in, they do tell you to observe 310.15(B)(3)(a), oddly enough.
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Can you elaborate on this? I don't touch Romex if I can help it.:p So I don't see those bags, but I would think those stackers "maintain spacing" and in between studs would be enough to satisfy the bundling requirement. Saying to "observe" 310.15 doesn't necessarily mean the stackers don't maintain spacing. If it does mean that, then at what point are wires or cables no longer "bundled"?
 
Galt said:
Building codes have to have some limit on how big of hole you can make in a joist.I remember seeing a chart of some sort on it. the closer you get to the bearing point the smaller the hole allowed.
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Type of framing member can have differences as well.

But a 2 inch hole in a floor joist is usually not too big as long as it is not too close to top or bottom "chord" of the joist.
 
I do have concerns with HVAC loads or maybe a pool pump or other continuous duty circuit that is sized for minimum ampacity required as I have experienced feeling some heat in those cables when the load has been running for a long time.

I feel that this would be the case with "most" loads that carry a load for an extended period.
 
JDB3 said:
I do have concerns with HVAC loads or maybe a pool pump or other continuous duty circuit that is sized for minimum ampacity required as I have experienced feeling some heat in those cables when the load has been running for a long time.

I feel that this would be the case with "most" loads that carry a load for an extended period.
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What I was getting at is a conductor for such loads that hasn't had an ampacity adjustment made to it.

Go to about any dwelling on a hot day where the AC has been running all day and open the panel and the AC breaker and it's conductors are about the only ones that are warm, and may even be close to too hot to touch. This is because it was continuously loaded and also very likely to near the ampacity of the conductor. Similar happens on really cold days with electric heating circuits sometimes. Most other circuits in a dwelling are not continuous enough or if continuous are such a light load in comparison to the branch circuit rating that you don't see this kind of heating. But go to commercial or industrial facilities and you see more of this sort of heating at times.
 
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