liquidtite
Senior Member
- Location
- Ny
gotcha
How many wires per fire foamed 2" wood hole ?
- Thread starter Rayme5037
- Start date
- Status
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
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.
From Southwire.com on 2008 code changes, we see that the 2008 code got even more restrictive than the 2005 code:
In NM cable the conductors are more effectively insulated than the same size individual conductors in conduit.
Last edited:
- Location
- New Jersey
- Occupation
- Journeyman Electrician
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.
test does not relate
test does not relate
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
test does not relate
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
- Location
- NE Nebraska
- Occupation
- EC
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.
loading
loading
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.
loading
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
- Location
- NE Nebraska
- Occupation
- EC
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.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
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
- Location
- NE Nebraska
- Occupation
- EC
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.
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.
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.
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.
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 Plans Examiner, MEP
- Location
- Scottsdale AZ
- Occupation
- Senior Plans Examiner
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.
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.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
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
- Location
- New Jersey
- Occupation
- Journeyman Electrician
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
- Location
- NE Nebraska
- Occupation
- EC
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).
RustyShackleford
Senior Member
- Location
- NC
- Occupation
- electrical engineer
Or perhaps more commonplace still, a neutral/hot/switched to a split outlet.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
yes:thumbsup:
wireguy8169
Senior Member
- Location
- Southern Maine
Also bundling of conductors
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Also applies to conductors and cables that are bundled together for more than 24 inches.
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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