How many wires per fire foamed 2" wood hole ?

Rayme5037

Member
Im new to the forum. I currently hold a JIT license and have just completed the hours for my Journeyman's and am in the process of sending in for the license. I have worked as an electrician for 5-6 years and am now working as an engineer in Portland, Maine.

I am having a house built (for myself) and just finished the rough-in this past weekend and the Code Enforcement Office did their initial (before insulation) inspection yesterday (Monday, Feb 4th). I was not there for the inspection but apparently the Code Enforcement Office has said they want clarification from a State Inspector and want to know if what I did was ok. What do you guys think?

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What you are looking at is two 2" holes through the top and bottom plate that contain the feeds from from the panel (directly below). The holes are fire foamed. One 2" hole has ten 12/2's & four 14/2's and the other 2" hole has twelve 12/2's & four 14/2's. They are supported to the 2x6 wall using cable stackers on both sides. This was common practice and i've seen/done this hundreds of times with no issues.

The code is slightly confusing:

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).

From my interpretation of the code, as long as the wires "maintain spacing" then what I did here is fine. The code does not define "maintaining space" ??? Above the panel has plenty of spacing and the cable stackers allow spacing up the entire 2x6 wall. The 2" holes pass through the plates (about 3" thick) and allow plenty of spacing around the wires. In reality I don't see an issue here, especially seeing how I wired my own house.

The feeds are already made up in the panel. Obviously any change would be a pain in the ass :sick:

Apparently the Code Enforcement Office is waiting to get clarification before I can Insulate. I guess they wanted me to drill 30 1" holes (talk about ugly and destroying my wall). Please share you opinions and help clarify this code for me.
 

Attachments

kwired

Electron manager
If you did not foam the holes you would be just fine. The section in violation is 334.80 and it was modified in 2011 NEC. You must derate those conductors in this case. Up to 16 2 wire cables in one hole is 32 current carrying conductors in the hole, deration factor of 40%. Sorry to give you the bad news. I have seen some lab testing that shows there is some fairly significant heating in NM cable when it is encapsulated in foam insulation like that with much fewer conductors in the testing, there is no place for the heat to dissipate. You do not need a hole for every cable, deration starts at the 90C ampacity level. For most cases you can easily get up to 9 current carrying conductors before deration will require larger conductors.
334.80 Ampacity.
Changed From 2008
• 334.80: Revised to clarify the use of ampacity adjustment and correction calculations.


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).
You said you maintained spacing, but did you maintain spacing while passing through the hole? If so how?
 
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Rayme5037

Member
Maintain Spacing

Maintain Spacing

Well "maintaining space" is not defined in the code ? Could mean as long as they are not touching.... could mean as long as they are not continuously touching..... could mean a 1" gap ...... who knows.

And the basement is not finished..... so obliviously their will be plenty of air flow above the panel. I am not concerned at all ..... just curious what others think or usually do in residential houses.

I would never hack up my wall with 30 1" holes ..... maybe if it was someone else house.
 

Gregg Harris

Senior Member
Im new to the forum. I currently hold a JIT license and have just completed the hours for my Journeyman's and am in the process of sending in for the license. I have worked as an electrician for 5-6 years and am now working as an engineer in Portland, Maine. I am having a house built (for myself) and just finished the rough-in this past weekend and the Code Enforcement Office did their initial (before insulation) inspection yesterday (Monday, Feb 4th). I was not there for the inspection but apparently the Code Enforcement Office has said they want clarification from a State Inspector and want to know if what I did was ok. What do you guys think? View attachment 8047 View attachment 8048 View attachment 8049 View attachment 8050 View attachment 8051 What you are looking at is two 2" holes through the top and bottom plate that contain the feeds from from the panel (directly below). The holes are fire foamed. One 2" hole has ten 12/2's & four 14/2's and the other 2" hole has twelve 12/2's & four 14/2's. They are supported to the 2x6 wall using cable stackers on both sides. This was common practice and i've seen/done this hundreds of times with no issues. The code is slightly confusing: 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). From my interpretation of the code, as long as the wires "maintain spacing" then what I did here is fine. The code does not define "maintaining space" ??? Above the panel has plenty of spacing and the cable stackers allow spacing up the entire 2x6 wall. The 2" holes pass through the plates (about 3" thick) and allow plenty of spacing around the wires. In reality I don't see an issue here, especially seeing how I wired my own house. The feeds are already made up in the panel. Obviously any change would be a pain in the ass :sick: Apparently the Code Enforcement Office is waiting to get clarification before I can Insulate. I guess they wanted me to drill 30 1" holes (talk about ugly and destroying my wall). Please share you opinions and help clarify this code for me.
Calculation Example Four 2-conductor, size 12 AWG, copper with ground, Type NM cables are installed in direct contact with thermal insulation according to the requirements of 334.80. Calculate the ampacity of the conductors and determine the maximum overcurrent protection permitted for these four circuits. Solution Step 1. Determine the number of current-carrying conductors. According to 310.15(B)(3)(a), the number of current-carrying conductors is Step 2. Determine the initial ampacity of 12 AWG using 334.80 and Table 310.15(B)(16). Using the 90?C copper ampacity from Table 310.15(B)(16) for derating purposes, the ampacity (prior to derating) is 30 amperes. Step 3. Determine the adjusted ampacity of each NM cable due to direct contact with thermal insulation using Table 310.15(B)(3)(a), eight current-carrying conductors require an adjustment factor of 70 percent: Step 4. Determine the maximum permitted overcurrent device for each NM cable circuit in this example. Section 334.80 does not allow an ampacity greater than given in the 60?C column of Table 310.15(B)(16). And, according to the footnote of Table 310.15(B)(16), conductor sizes of 14 AWG through 10 AWG must also comply with 240.4(D). Section 240.4(D) limits a 12 AWG copper conductor to a maximum of 20 amperes. Therefore, the 21 amperes of adjusted ampacity must be further reduced or limited by being protected by an overcurrent device not to exceed 20 amperes. Thus, 20 amperes is the final ampacity for each current-carrying conductor of this problem, and the maximum overcurrent device permitted for each of the four circuits in NM cable is 20 amperes. Conclusion: This example points out that NM cable can be installed without spacing and placed within thermal insulation by not exceeding nine current-carrying conductors [70 percent adjustment factor of Table 310.15(B)(3)(a)]. By following similar installation practice as outlined in this example, this requirement will have little impact on most installations, whether installing groups of NM cable from panelboards or installing multiple NM cables down to ganged switches, as long as the quantity is limited to not more than nine current-carrying conductors.
 

cowboyjwc

Moderator
Staff member
You have to install the fire caulk per it's listing. Each manufacturer will have it's own requirements. They are not all the same.
 

kwired

Electron manager
You have to install the fire caulk per it's listing. Each manufacturer will have it's own requirements. They are not all the same.
I don't see that he has fire caulk here, it is just thermal insulation isn't it? Either way deration of conductors is necessary though.
 

kwired

Electron manager
Well "maintaining space" is not defined in the code ? Could mean as long as they are not touching.... could mean as long as they are not continuously touching..... could mean a 1" gap ...... who knows.

And the basement is not finished..... so obliviously their will be plenty of air flow above the panel. I am not concerned at all ..... just curious what others think or usually do in residential houses.

I would never hack up my wall with 30 1" holes ..... maybe if it was someone else house.
You are willing to burn down the house though?

I will agree that in most cases there will never be a problem with this installation, but how do you know you are not one of those in the small percentage that do have a problem someday?

As I said in earlier post, I have seen a lab test - not with extreme controlled conditions just a setup in a lab at the local community college's electrician program lab where they placed several NM cables through a foamed hole in a typical wood framed wall and stuck some temperature probes inside the cable bundles and come up with some temps that make you think about what can happen in worst case scenarios. The cables were heavily loaded for several hours but not overloaded. They fed resistance heat loads for several hours. Granted most of the time dwelling loads have a pretty good load diversity and this heat likley doesn't build up just too much, but for heating or cooling loads the diversity of those loads changes to a more constant load most of the time.

I don't see you needing 30 holes either. 7-9 conductor deration of 70% allows for 4 two wire cables per hole, so that cuts you down to only needing 8 holes - that is not that hard to do other than the fact you have everything already made up.
 

GoldDigger

Moderator
Staff member
I will agree that in most cases there will never be a problem with this installation, but how do you know you are not one of those in the small percentage that do have a problem someday?

As I said in earlier post, I have seen a lab test - not with extreme controlled conditions just a setup in a lab at the local community college's electrician program lab where they placed several NM cables through a foamed hole in a typical wood framed wall and stuck some temperature probes inside the cable bundles and come up with some temps that make you think about what can happen in worst case scenarios. The cables were heavily loaded for several hours but not overloaded. They fed resistance heat loads for several hours. Granted most of the time dwelling loads have a pretty good load diversity and this heat likley doesn't build up just too much, but for heating or cooling loads the diversity of those loads changes to a more constant load most of the time.
The floor penetrations may be OK, but the double or maybe triple top plate means that the conductors at that point in the wall will be closely spaced and insulated over a longer distance, making heating problems worse.
 

infinity

Moderator
Staff member
IMO the stackers provide enough spacing to forget about derating if the wall is uninsulated. The fire or draft stop in the hole required that those conductors be derated. As far as Swiss cheesing the wood you can put 4 -3 wire homerun cables in each hole before you surpass the magic number of 9 CCC's.
 

Rayme5037

Member
Dont forget im located in Maine (the outside temps will be MUCH less than Nevada).

Dont forget im located in Maine (the outside temps will be MUCH less than Nevada).

you may want to take a look at this..
Dont forget im located in Maine (the outside temps will be MUCH less than Nevada where the test's were done). I do understand the point though.

Everyone i know in Western Maine does there panel's like this and as far as i know have never had an issue. This house im building (and now wiring) is located in Southern Maine and apparently they interpret the code different or just enforce it more.
Seeing how thee panel is already made up, I don't have many choices. :? I guess i will need to contact the code enforcement officer and see what he is willing to let me do. I may need to cut the 2" hole into a larger section (carefully around the wires) and place a new plate with multiple holes (in pieces). That if he will let me cut the plate. My only other option is to pull all the wires out of the panel.:ashamed1:
idea.png
Anyone follow me?

I guess i will wait and see what he says before I go ding anything. I would rather take a chance of my house burning then deal with this.
 

kwired

Electron manager
Dont forget im located in Maine (the outside temps will be MUCH less than Nevada where the test's were done). I do understand the point though.

Everyone i know in Western Maine does there panel's like this and as far as i know have never had an issue. This house im building (and now wiring) is located in Southern Maine and apparently they interpret the code different or just enforce it more.
Seeing how thee panel is already made up, I don't have many choices. :? I guess i will need to contact the code enforcement officer and see what he is willing to let me do. I may need to cut the 2" hole into a larger section (carefully around the wires) and place a new plate with multiple holes (in pieces). That if he will let me cut the plate. My only other option is to pull all the wires out of the panel.:ashamed1:
View attachment 8053
Anyone follow me?

I guess i will wait and see what he says before I go ding anything. I would rather take a chance of my house burning then deal with this.
People had done it like that in many places for years. In more recent years, many have been filling these holes with foam insulation and that is really what introduces a problem with it.

Outside temp doesn't really have much impact on what the temp inside that bundle may reach - it is completely encapsulated in insulation and the heat developed within has a hard time escaping is the problem.

I was thinking of suggesting cutting out the plate and piecing something back in with multiple holes in it.

I guess you can do what you want with your own house, but don't you still need to pass inspection?
 

GoldDigger

Moderator
Staff member
Outside temp doesn't really have much impact on what the temp inside that bundle may reach - it is completely encapsulated in insulation and the heat developed within has a hard time escaping is the problem.
But the main heat escape route is conduction down the wires, so if the rest of the wires in the cavity are hotter, the bundle will be correspondingly hotter too.
For an interior wall, probably no effect from outside temperatures. :)
 

liquidtite

Senior Member
I don't see that he has fire caulk here, it is just thermal insulation isn't it? Either way deration of conductors is necessary though.
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.
 

kwired

Electron manager
But the main heat escape route is conduction down the wires, so if the rest of the wires in the cavity are hotter, the bundle will be correspondingly hotter too.
For an interior wall, probably no effect from outside temperatures. :)
I fully understand that, so can you explain why NEC decided foamed holes in framing members need conductor derating even if cables are to be separated on both sides of the hole? Apparently there was convincing enough evidence that heat can build up to dangerous levels here, otherwise in the past the 2 foot nipple rule was justification to allow all those conductors in the same hole, now they are saying if that hole is filled with a "sealant" of any type you must derate the conductors.
 

liquidtite

Senior Member
i could see that but I even heard this befor without out the firefoam in the holes that if you have more than three ccc through a 2x4 its called bundling and you could get flaged for it. So thats why I never put more than 3 nms in a hole it never made sense to me.
 

kwired

Electron manager
i could see that but I even heard this befor without out the firefoam in the holes that if you have more than three ccc through a 2x4 its called bundling and you could get flaged for it. So thats why I never put more than 3 nms in a hole it never made sense to me.
But if they only pass through one hole and then are separated they are not bundled for more than 2 feet and deration is not necessary, the change was the adding of the derating requirement when the hole is filled with caulk, foam, etc. If you don't fill the hole with a "sealant" the rules have not changed at all.
 
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