How many wires per fire foamed 2" wood hole ?

GoldDigger

Moderator
Staff member
I dont get why deration is needed.In the code when they discuss drating isnt it ccc in conduit?Also you dont have to drate ccc when they are runing through a nipple witch is usualy longer than the lenth of the 2x4.So if you had two panels nippled together and instead of using thhn you used nm would you have to drate.
The article that GH cited describes a condition that was not prohibited by code when the study was published in 2003, but arguably should have been.

Art 334.80 of the 2008 NEC specifically calls out situations in which multiple current carrying conductors pass through a fire caulked hole in framing without some unspecified spacing between them, and it applies the same derating factors that are already specified for wires in conduit. For two NM runs, no problem because you have ampacity to spare. If the hole is large enough that the NMs do not touch each other, also no problem.

Only time you would have problems with cables going through the same opening in the framing member is if you bundled 10 or more current carrying conductors into the same conduit, cable assembly or in close proximity to one another because the derating factor would be at least 50% and could be higher if you had to double-derate for ambient temperatures as well.
From Southwire.com on 2008 code changes, we see that the 2008 code got even more restrictive than the 2005 code:

Type NM-B cable, NEC Section 334.80
Type NM-B cable is required to be derated when more than two cables are installed bundled together. NEC Section 334.80 specifically states that Type NM-B cable’s ampacity shall be derated when more than two NM-B cables are installed in thermal insulation without maintained spacing between the cables. This change was based on CDA studies of NM-B cable installed in walls with various thermal insulations. The study showed that without spacing the conductors, temperatures exceeded the maximum operating temperature of NM-B cable. This requirement is in addition to the 2005 NEC requirement for the derating of more than two cables installed through a draft stopped hole.
In NM cable the conductors are more effectively insulated than the same size individual conductors in conduit.
 
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infinity

Moderator
Staff member
Here's the original propsal to the 2005 NEC that caused the change. The 2008 NEC clarified that the 10'/10% exception does not apply.

Report on Proposals ? May 2004
NFPA 70
7-150a Log #CP700 NEC-P07
(334-80)
Final Action: Accept
Submitter: Code-Making Panel 7
Recommendation:
Add a new paragraph to 334.80 to read as follows:
"334.80 Where more than two NM cables containing two or more current-carrying conductors are bundled together and pass through
wood framing which 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)."
Substantiation:
Code-Making Panel 6 Rejected Proposal 6-31 to add the proposed text to 310.15(B)(2)(a) and provided the following Panel statement:
"The Panel agrees with the intent of the Proposal, however, this material is more appropriately addressed in 334.80 since the Proposal
only applies to one type of cable, and Code-Making Panel 6 covers all wiring methods. Therefore, Code-Making Panel 6 has forwarded
this Proposal to Code-Making Panel 7 for action."
The substantiation provided by the submitter, Travis Lindsey, of Proposal 6-31 was:
"Recent experimentation shows the possibility of dangerous conditions when loaded circuits are brought into close proximity to each
other inside a fire- or draft-stop, where the ability to dissipate heat is extremely limited. Cable temperatures well in excess of their 90?C
rating were encountered, with no overcurrent protection present for these conditions. Results indicate that immediate adjustments
should be made to the NEC to apply at least to the specific case represented by the experiment. Such a proposal is being made, with a
supplemental report offered as technical support."
Panel Meeting Action: Accept
Number Eligible to Vote: 15
Affirmative: 15
 

Rayme5037

Member
test does not relate

test does not relate

you may want to take a look at this..
This test was done in Nevada on an outside 2x4 wall with R11 insulation. This is VERY different than my house in Maine in an inside (butting the garage) 2x6 wall with R21 insulation. And for those who say it didn't, the test DID show that outside temperature effects the heating of conductors. I suggest you guys re-read that document. My bigger cavity (2x6), thicker wall insulation (R21), and being an inside wall in lower outside temperatures in Maine should all decrease the chance of over heating, right ??? Realistically I don't think i have an issue. But I understand the code and the point and obviously wont do this again.

Taking the wires out of the panel would be a nightmare trying to remember exactly where each one went (neutrals, grounds, what knockout and breaker....). You know i'll end up short on a few wires (long a others) and would have to junction in or above the panel. Talk about a mess and pain in the ass. I'm hoping the code enforcement officer will let me cut out the plate and piece one (will multiple holes) back in its place so I don't have to touch the panel. Well i'm actually hoping he lets its it go. But it doesn't sound very good from what you guys are telling me
 

kwired

Electron manager
This test was done in Nevada on an outside 2x4 wall with R11 insulation. This is VERY different than my house in Maine in an inside (butting the garage) 2x6 wall with R21 insulation. And for those who say it didn't, the test DID show that outside temperature effects the heating of conductors. I suggest you guys re-read that document. My bigger cavity (2x6), thicker wall insulation (R21), and being an inside wall in lower outside temperatures in Maine should all decrease the chance of over heating, right ??? Realistically I don't think i have an issue. But I understand the code and the point and obviously wont do this again.

Taking the wires out of the panel would be a nightmare trying to remember exactly where each one went (neutrals, grounds, what knockout and breaker....). You know i'll end up short on a few wires (long a others) and would have to junction in or above the panel. Talk about a mess and pain in the ass. I'm hoping the code enforcement officer will let me cut out the plate and piece one (will multiple holes) back in its place so I don't have to touch the panel. Well i'm actually hoping he lets its it go. But it doesn't sound very good from what you guys are telling me
Chances are your install runs cooler than the one in Nevada. I did not read through that very thouroughly and don't know all the details. Remember the insulation not only will keep external heat out it will also keep internal heat in. That was why I said I didn't think it would have a major impact on things. Actual loading conditions of the cables are what will make the bigger difference in internal temperature not the ambient temperature outside the wall. Cooler exterior ambient mostly just means it will take longer to warm it up. I have never been to Maine, but I'm sure it does get moderately warm or even down right hot at times in the summer months.
 

Rayme5037

Member
loading

loading

Chances are your install runs cooler than the one in Nevada. I did not read through that very thouroughly and don't know all the details. Remember the insulation not only will keep external heat out it will also keep internal heat in. That was why I said I didn't think it would have a major impact on things. Actual loading conditions of the cables are what will make the bigger difference in internal temperature not the ambient temperature outside the wall. Cooler exterior ambient mostly just means it will take longer to warm it up. I have never been to Maine, but I'm sure it does get moderately warm or even down right hot at times in the summer months.
I do agree, the loading conditions will make the bigger difference in heating vs the outside temperature. The Nevada test showed that at 87F outside, (with the 2x4 walls and R11 insulation) in combination with 73% loading, the bundle temperatures could reach excess of 194F. I understand the point but realistically here in Maine with my house conditions and loading conditions, I will never face a heating problem within the firestop foam. I guess this is why some enforce it and some don't. But code is code i guess.
 

kwired

Electron manager
I do agree, the loading conditions will make the bigger difference in heating vs the outside temperature. The Nevada test showed that at 87F outside, (with the 2x4 walls and R11 insulation) in combination with 73% loading, the bundle temperatures could reach excess of 194F. I understand the point but realistically here in Maine with my house conditions and loading conditions, I will never face a heating problem within the firestop foam. I guess this is why some enforce it and some don't. But code is code i guess.
Most of your general purpose circuits will not create very much heat, as they typically only have a small load on them, or if a larger load it is usually limited to short run times. Anything that is continuously loaded will be a difference maker.

Heating and air conditioning are most common things in a dwelling where you will notice heating of conductors. Most other loads are intermittent enough in nature that you seldom notice any any heating unless there is a problem with a connection or something like that, but it is there when conductors are loaded.

Go to an industrial place where many loads are continuous and you will notice there is heat inside panels, gutters, junction boxes, etc. Most of this heat is coming from within the conductors in panelboards there is some contribution from overcurrent devices.

Conductors do have resistance and where you have current flowing through a resistance you will have heat.
 

Rayme5037

Member
Most of your general purpose circuits will not create very much heat, as they typically only have a small load on them, or if a larger load it is usually limited to short run times. Anything that is continuously loaded will be a difference maker.

Heating and air conditioning are most common things in a dwelling where you will notice heating of conductors. Most other loads are intermittent enough in nature that you seldom notice any any heating unless there is a problem with a connection or something like that, but it is there when conductors are loaded.

Go to an industrial place where many loads are continuous and you will notice there is heat inside panels, gutters, junction boxes, etc. Most of this heat is coming from within the conductors in panelboards there is some contribution from overcurrent devices.

Conductors do have resistance and where you have current flowing through a resistance you will have heat.
Exactly! I do not have electric heat and AC is not needed in Maine ....... so another reason why realistically I wouldn't have any issues with heating inside the fire stopped 2" holes. ;-/ Where i'm from (Western Maine) this wouldn't bean issue at all but apparently here in Gorham (Southern Maine) they obviously enforce this code.
 

infinity

Moderator
Staff member
If it were my house I wouldn't care about those fire-stopped holes. The testing was done using heavily loaded cables. The real world application in a house will almost never duplicate the test.
 

kwired

Electron manager
If it were my house I wouldn't care about those fire-stopped holes. The testing was done using heavily loaded cables. The real world application in a house will almost never duplicate the test.
I agree, it likely is never going to be a problem, especially if there is never any heavy continuous loads on the conductors involved, but the OP has had it called out by an inspector, is that kind of testimony enough to make the problem disappear and make no changes?

To do it right the first time would not have taken much effort. I would still be in favor of consistency from the inspector. OP would not be the first person to have to redo or make some change to something like this because of a fairly simple mistake either.

Sorry to say it but keeping up with code changes every three years maybe would have changed his installation practices. Required CEU's to renew licensing around here results in taking classes on code related topics and I have not been to a single one where we did not go over changes in the most current code - especially the changes in chapters 1-4 that effect almost every installer to some extent.
 

Rayme5037

Member
All Fixed

All Fixed

I spoke with the local Code Enforcement Officer last night. He had me "trench" out the plates and spread the wires apart in groups of 3. I then re-firestopped the holes. This took about 4 hours of time to fix. It doesn't look quite as nice but it's to code. To untangle the wires I would have had to pull them from the panel.

1st Floor - Bottom Plate.jpg

1st Floor- Bottom Plate.jpg

1st Floor.jpg

I have no idea why he wanted "groups of 3." I tried to explain to him that I could have 9 conductors (i don't think he knew what that was) per hole. So instead of arguing I just did 3 instead of 4.

In conclusion:

334.80 Ampacity. The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The allowable ampacity shall not exceed that of a 60?C (140?F) rated conductor. The 90?C (194?F) rating shall be permitted to be used for ampacity adjustment and correction calculations, provided the final derated ampacity does not exceed that of 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 392.80(A). 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. Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a).


So basically if you have more than 2 wires in a fire stopped hole than you have to derate in accordance with Table 310.15(B)(3)(a). If you do the math in that table you will find that 14/2 is still good for 15 amps and 12/2 is still good for 20 amps until you bundle more than 9 current carrying conductors together. Each 14/2 or 12/2 wire has 2 conductors. If a 14/3 or 12/3 wire is used than it counts as 3 conductors. So, depending on what is used, you can place 3 or 4 wires per fire stopped hole.


I also did some reading and found that this code was most likely added to the NEC because a "test" was done in the western part of the U.S on an outside 2x4 wall with R11 insulation with outside temperatures reaching 120 degrees. The test found that at 73% loading, the wires and firestop foam showed signs over overheating. Realistically it would be impossible to get those test conditions in a residential house in Maine (and probably many other states) no matter how many wires were bundled in the same hole. This is probably why some inspectors don't enforce this code.

Thanks for all the help and input. This is a great forum. I'm sure i'll be back.
 

HoosierSparky

Senior Member
NEC - IRC

NEC - IRC

In a lot of jurisdictions the IRC takes precedence over the NEC for electrical. However, the ICC copied most of 334.80 so you still get caught.

From 2012 IRC:

E3705.4.4 Conductors of Type NM cable.
Conductors in NM cable assemblies shall be rated at 90?C (194?F). Types NM, NMC, and NMS cable identified by the markings NM-B, NMC-B, and NMS-B meet this requirement. The allowable ampacity of Types NM, NMC, and NMS cable shall not exceed that of 60?C (140?F) rated conductors and shall comply with Section E3705.1 and Table E3705.5.3. The 90?C (194?F) rating shall be permitted to be used for ampacity adjustment and calculations provided that the final corrected or adjusted ampacity does not exceed that for a 60?C (140?F) rated conductor. 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 E3705.3. Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table E3705.3.
 

GoldDigger

Moderator
Staff member
If a 14/3 or 12/3 wire is used than it counts as 3 conductors. So, depending on what is used, you can place 3 or 4 wires per fire stopped hole.
Specifically for an MWBC, containing L1 and L2 and N (and a common trip or handle tied breaker), 12/3 or 14/3 would only count as two current carrying conductors. But I doubt that your inspector could deal with that either.
 

Rayme5037

Member
Specifically for an MWBC, containing L1 and L2 and N (and a common trip or handle tied breaker), 12/3 or 14/3 would only count as two current carrying conductors. But I doubt that your inspector could deal with that either.
They didn't understand 9 conductors never mind 3-ways and 4-ways. haha
 

infinity

Moderator
Staff member
334.80 Ampacity. The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The allowable ampacity shall not exceed that of a 60?C (140?F) rated conductor. The 90?C (194?F) rating shall be permitted to be used for ampacity adjustment and correction calculations, provided the final derated ampacity does not exceed that of 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 392.80(A). 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. Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a).


So basically if you have more than 2 wires in a fire stopped hole than you have to derate in accordance with Table 310.15(B)(3)(a). If you do the math in that table you will find that 14/2 is still good for 15 amps and 12/2 is still good for 20 amps until you bundle more than 9 current carrying conductors together. Each 14/2 or 12/2 wire has 2 conductors. If a 14/3 or 12/3 wire is used than it counts as 3 conductors. So, depending on what is used, you can place 3 or 4 wires per fire stopped hole.




Thanks for all the help and input. This is a great forum. I'm sure i'll be back.
You're reading the requirement incorrectly, it says for more than two cables. And you only count the CCC's not every conductor. A 3 wire cable in this application will almost always only count as 2 CCC's.
 

kwired

Electron manager
You're reading the requirement incorrectly, it says for more than two cables. And you only count the CCC's not every conductor. A 3 wire cable in this application will almost always only count as 2 CCC's.
Might want to lower that percentage a little, for things like a cable carrying a 3 phase circuit (maybe not as likely with NM but not impossible), two phases and a neutral supplied by a wye system, or even switch loop with a common and two switched return conductors (which can still happen with switches controlling other than lighting outlets).
 

wireguy8169

Senior Member
I dont get why deration is needed.In the code when they discuss drating isnt it ccc in conduit?Also you dont have to drate ccc when they are runing through a nipple witch is usualy longer than the lenth of the 2x4.So if you had two panels nippled together and instead of using thhn you used nm would you have to drate.
Also bundling of conductors
 

kwired

Electron manager
I dont get why deration is needed.In the code when they discuss drating isnt it ccc in conduit?
Also applies to conductors and cables that are bundled together for more than 24 inches.


Also you dont have to drate ccc when they are runing through a nipple witch is usualy longer than the lenth of the 2x4.So if you had two panels nippled together and instead of using thhn you used nm would you have to drate.
Correct, nipple length can be up to 24 inches without derating. Same with NM or any other cable. The change is with NM cable and bundles that pass through a hole that is sealed by some manner for firestopping, air infiltration, etc. There is no mention of length, so it applies to any hole that gets sealed up. Pass same cables through a hole that does not get sealed up and you are back to the 24 inch nipple rule that has been around for a long time.
 
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