# A very common question



## Hexamexapex (Jun 9, 2012)

Ok guys I'm back. Bare with me as I'm not as dumb as some of my previous post may have lead on. Working on my LLE and need clarification. 

Please excuse the redundancy of this question. Im pretty sure it's been discussed many a time. 
Art. 334.80 Ampacity of NM cable. In this case type NM-B. 
"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 fire or draft stopped using thermal insulation caulk, or sealing foam the allowable Ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a) And the provisions of 310.15(A)(2), exception, shall not apply."

So for example I install three 14-2 NM-B cables through a single bored hole. Using table 310.16, under the 90C column I see an ampacity of 25 amps. I go back to table 310.15(B)(2)(a) and use 80% ampacity adjustment. Please exclude any ambient temp adjustments. So now this puts my ampacity at 20 amps. Now according to 240.4(D) my overcurrent device must not exceed 15amps for 14AWG.....so we use a 15A breaker and my brach circuit conductors have ampacity of 20A. I guess my question is have I missed anything? My loads are not continuous so I didn't think I need to derate according to 210.19(A)(1). Any suggestions? Am I on the right track?

Thanks for any and all assistance.


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## Bulldog1 (Oct 21, 2011)

Hexamexapex said:


> Ok guys I'm back. Bare with me as I'm not as dumb as some of my previous post may have lead on. Working on my LLE and need clarification.
> 
> Please excuse the redundancy of this question. Im pretty sure it's been discussed many a time.
> Art. 334.80 Ampacity of NM cable. In this case type NM-B.
> ...



You only have to derate if you use fire stopping. If you do and your math is correct then yes you are correct.


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## Hexamexapex (Jun 9, 2012)

Bulldog1 said:


> You only have to derate if you use fire stopping. If you do and your math is correct then yes you are correct.


What if my wires are running through walls that will be insulated? I interpret the codes "thermal insulation" reference to mean the standard insulation everyone has in there home....most newer homes anyway.


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## Bulldog1 (Oct 21, 2011)

Hexamexapex said:


> What if my wires are running through walls that will be insulated? I interpret the codes "thermal insulation" reference to mean the standard insulation everyone has in there home....most newer homes anyway.



You are wrong and it says thru bored holes not insulated walls.


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## Hexamexapex (Jun 9, 2012)

Hexamexapex said:


> What if my wires are running through walls that will be insulated? I interpret the codes "thermal insulation" reference to mean the standard insulation everyone has in there home....most newer homes anyway.


I think I forgot to place a comma between "thermal insulation, caulk"


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## Dennis Alwon (May 9, 2009)

You have it correct. The fact is you can have up to 4 two wire nm cables thru a hole that has insulation or caulk without it affecting anything. Once you get above 9 current carrying conductor's then you have an issue.


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## Hexamexapex (Jun 9, 2012)

Bulldog1 said:


> You are wrong and it says thru bored holes not insulated walls.


Ok "draft stopping thermal insulation". That's not your normal wall insulation? Also the bored hole I spoke of is coming down through a top plate. Regardless, whether through wall studs or down top plate the wire could be in contact with insulation. So can you explain to me what draft stopping thermal insulation is?


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## ohiosparky99 (Nov 12, 2009)

Hexamexapex said:


> I think I forgot to place a comma between "thermal insulation, caulk"


I think thermal insulation caulk is fire caulk, not wall insulation


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## Dennis Alwon (May 9, 2009)

Hexamexapex said:


> Ok "draft stopping thermal insulation". That's not your normal wall insulation? Also the bored hole I spoke of is coming down through a top plate. Regardless, whether through wall studs or down top plate the wire could be in contact with insulation. So can you explain to me what draft stopping thermal insulation is?


Every hole that penetrates thru ceiling or floor plate must be sealed with a foam or caulk that is listed for draft stop.


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## Bulldog1 (Oct 21, 2011)

Hexamexapex said:


> Ok "draft stopping thermal insulation". That's not your normal wall insulation? Also the bored hole I spoke of is coming down through a top plate. Regardless, whether through wall studs or down top plate the wire could be in contact with insulation. So can you explain to me what draft stopping thermal insulation is?



Draft stopping is to keep fires from spreading and insulation is to keep the heat and ac inside.


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## Dennis Alwon (May 9, 2009)

Imo, if you have more than 4 cables travelling thru studs in insulation I would say that is bundling. This has been argued forever but.....


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## Hexamexapex (Jun 9, 2012)

ohiosparky99 said:


> I think thermal insulation caulk is fire caulk, not wall insulation


Verbatim, "through the same opening in wood framing that is to be fire- or draft-stopped using thermal insulation, caulk, or sealing foam,"


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## Hexamexapex (Jun 9, 2012)

Bulldog1 said:


> Draft stopping is to keep fires from spreading and insulation is to keep the heat and ac inside.


Ok...thank you. So damn I guess I shouldn't have to derate my three 14-2 nm cables. We are not required to caulk or fire-protect any of our holes through top plate in our local jurisdiction. That would mean caulking every light hole in house, among other things.


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## Hexamexapex (Jun 9, 2012)

Dennis Alwon said:


> Imo, if you have more than 4 cables travelling thru studs in insulation I would say that is bundling. This has been argued forever but.....


Where in the NEC is "Bundling" discussed?


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## Dennis Alwon (May 9, 2009)

Hexamexapex said:


> Where in the NEC is "Bundling" discussed?


The last sentence in 334.80 talks about current carrying conductor's in contact with thermal insulation without maintaining spacing between cables.--- that is bundling. I don't believe the NEC uses the word bundling


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## Hexamexapex (Jun 9, 2012)

Dennis Alwon said:


> You have it correct. The fact is you can have up to 4 two wire nm cables thru a hole that has insulation or caulk without it affecting anything. Once you get above 9 current carrying conductor's then you have an issue.


So my actual ampacity of these wires would be still be 25 since no derating required. 15amp breaker is a must though.


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## Dennis Alwon (May 9, 2009)

Hexamexapex said:


> So my actual ampacity of these wires would be still be 25 since no derating required. 15amp breaker is a must though.


No, you have to derate at 70% for 9 current carrying conductor's however 9 times 25 is 17.5 amps so a 14 gauge wire is still compliant on a 15 amp breaker. Hopefully you are not putting 17.5 amps on that wire with a 15 amp breaker


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## Hexamexapex (Jun 9, 2012)

Dennis Alwon said:


> The last sentence in 334.80 talks about current carrying conductor's in contact with thermal insulation without maintaining spacing between cables.--- that is bundling. I don't believe the NEC uses the word bundling


Ah.....there it is right in front of me. Gotta try not to overthink this. Easy to get crossed up. So my original derating was correct....like you said.


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## Dennis Alwon (May 9, 2009)

Hexamexapex said:


> Ah.....there it is right in front of me. Gotta try not to overthink this. Easy to get crossed up. So my original derating was correct....like you said.


IMO, yes.... some would argue if boring thru the studs would constitute bundling but IMO, it does.


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## Bbsound (Dec 16, 2011)

But if you did need to derate, you would not change anything as you are limited to a 15 amp breaker anyway.


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## Hexamexapex (Jun 9, 2012)

Dennis Alwon said:


> No, you have to derate at 70% for 9 current carrying conductor's however 9 times 25 is 17.5 amps so a 14 gauge wire is still compliant on a 15 amp breaker. Hopefully you are not putting 17.5 amps on that wire with a 15 amp breaker


So we won't have an issue till we try and cram 10 or more conductors through that bored hole. Then our ampacity would be less than 15 at which point we would be in violation. Not that we would cram that many wires through one hole.


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## Hexamexapex (Jun 9, 2012)

So 334.80 will eventually lead us to table 310.16 for conductor ampacity. I initially looked for type NM in a column, no dice. This could be confusing to some, no? I kinda assumed my 14-2NM-B fell under the general copper column. Just curious as to why no specific mentioning of NM. I guess they are all a form of NM no? Maybe not necessarily Romex.


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## Dennis Alwon (May 9, 2009)

Hexamexapex said:


> So 334.80 will eventually lead us to table 310.16 for conductor ampacity. I initially looked for type NM in a column, no dice. This could be confusing to some, no? I kinda assumed my 14-2NM-B fell under the general copper column. Just curious as to why no specific mentioning of NM. I guess they are all a form of NM no? Maybe not necessarily Romex.



All we need to know is that the wire is rated 90C based on art.334.112 and that the final amp is 60C


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## Hexamexapex (Jun 9, 2012)

Dennis Alwon said:


> All we need to know is that the wire is rated 90C based on art.334.112 and that the final amp is 60C


Understood.


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## Hexamexapex (Jun 9, 2012)

Hexamexapex said:


> Understood.


So am I correct in saying, that according to general electrical installation requirements, all conductor ampacity shall be based on 60C and any higher rating is simply used for derating purposes?


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## KGN742003 (Apr 23, 2012)

Using Mineral wool or even fiberglass insulation is pretty common here for draft stopping. Normally holes bored through stud bays used as cold air returns are fire-caulked.


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## A Little Short (Nov 11, 2010)

Hexamexapex said:


> So am I correct in saying, that according to general electrical installation requirements, all conductor ampacity shall be based on 60C and any higher rating is simply used for derating purposes?


No you are not correct in saying that all conductors are 60C. 
NM is generally the only conductors that are 60C.
Look at the table in 310.13.

You are correct in saying that the 90C is for the most part, only used for derating.


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## Hexamexapex (Jun 9, 2012)

Little-Lectric said:


> No you are not correct in saying that all conductors are 60C.
> NM is generally the only conductors that are 60C.
> Look at the table in 310.13.
> 
> You are correct in saying that the 90C is for the most part, only used for derating.


Thank you. Got a lot to learn.


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## Hexamexapex (Jun 9, 2012)

Dennis Alwon said:


> All we need to know is that the wire is rated 90C based on art.334.112 and that the final amp is 60C


Keeping with my ampacity theme of the week I have a wiring method that must be scrutinized for code compliance.....and also to further my understanding of type SE cable ampacity derating. Here is the situation:
We (my company) wire an 8 unit apartment building about once a month. Our service entrance cable is #2 XHHW aluminum rated at 90C. We use 100 amp breakers on our service equipment for the main disconnect. I may have missed something but according to NEC we must use the 60C column for type SE cable. According to table 310.16 this puts out #2 XHHW aluminum at 75amps. Am I wrong in thinking we need to move up to 1/0? We have done at least 15 of these and everyone passes. Local jurisdiction?


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## A Little Short (Nov 11, 2010)

Hexamexapex said:


> Keeping with my ampacity theme of the week I have a wiring method that must be scrutinized for code compliance.....and also to further my understanding of type SE cable ampacity derating. Here is the situation:
> We (my company) wire an 8 unit apartment building about once a month. Our service entrance cable is #2 XHHW aluminum rated at 90C. We use 100 amp breakers on our service equipment for the main disconnect. I may have missed something but according to NEC we must use the 60C column for type SE cable. According to table 310.16 this puts out #2 XHHW aluminum at 75amps. Am I wrong in thinking we need to move up to 1/0? We have done at least 15 of these and everyone passes. Local jurisdiction?


If each unit has a 100A service, then take a look at Table 310.15(B)(6)

Keep on studying!


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## Hexamexapex (Jun 9, 2012)

Little-Lectric said:


> If each unit has a 100A service, then take a look at Table 310.15(B)(6)
> 
> Keep on studying!


If you don't mind could you take a look at the thread titled "#2 XHHW aluminum". Tell me what you think.


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## chicken steve (Mar 22, 2011)

Hexamexapex said:


> Art. 334.80 Ampacity of NM cable. In this case type NM-B.
> "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 fire or draft stopped using thermal insulation caulk, or sealing foam the allowable Ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a) And the provisions of 310.15(A)(2), exception, shall not apply."
> 
> .


The bold is the key issue , at least to me Hex

I define _'space'_ as _'not touching each other' _

ergo, _'space'_ between conductors

I think that a reasonable enough interpetation in plain English to forgo any NFPA translator's intervention into art 100

~CS~


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## Hexamexapex (Jun 9, 2012)

chicken steve said:


> The bold is the key issue , at least to me Hex
> 
> I define 'space' as 'not touching each other'
> 
> ...


I understand that portion. I'm using 2008 NEC. The very first paragraph of 334.80 is what I'm using to come to this conclusion. 
"The ampacity of types NM, NMC, and NMS cable shall be in accordance with 310.15. The ampacity shall be in accordance with the 60C conductor temperature rating. And so on.....your cited portion comes after that first paragraph and I viewed your cited portion as additional provisions to be aware of, but not to discount first paragraph of said section. Is that first paragraph negated by the second which you cited?


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## Hexamexapex (Jun 9, 2012)

chicken steve said:


> The bold is the key issue , at least to me Hex
> 
> I define 'space' as 'not touching each other'
> 
> ...


Sorry chicken Steve, my response to your post had to deal with a thread entitled "#2 XHHW aluminum". Take a look at that one if you get a chance.


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