Derating NM cable

[coffeebean]

Does NM cable have to be derated when installed in a structure where spray foam insulation is used ?

 

[Dennis Alwon]

Does NM cable have to be derated when installed in a structure where spray foam insulation is used ?

The NEC is silent so the answer is "NO". Of course if more than 2 cables pass thru a plate that is foamed or sealed with fire caulk then you must derate but just embedded in spray foam-NO

 

[mcclary's electrical]

IMO, 334.12 (10) (b) will not allow you to do this. But that's a borderlined call. It goes on to derate for cables in bored holes that are fire caulked.

 

[raider1]

Does NM cable have to be derated when installed in a structure where spray foam insulation is used ?

What code cycle are you under?

A new paragraph was added to 334.80 that requires 2 or more NM cables that are installed in direct contact with thermal insulation without maintaining spacing to have their ampacities adjusted in accordance with 310.15(B)(2)(a).

Here is what that section says:

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)(2)(a).

Chris

 

[mcclary's electrical]

What code cycle are you under?

A new paragraph was added to 334.80 that requires 2 or more NM cables that are installed in direct contact with thermal insulation without maintaining spacing to have their ampacities adjusted in accordance with 310.15(B)(2)(a).

Here is what that section says:



Chris

Chris, is this 08' you're speaking of?

 

[raider1]

Chris, is this 08' you're speaking of?

Correct, Sorry I didn't make myself clear that this was a new paragraph to the 2008 NEC.

Chris

 

[jaylectricity]

Now I'm not saying that because I was allowed to do it, it must be OK, but the inspector in Lexington, MA is pretty much by-the-book. I used 15 amp breakers on my 14-2 runs and 20 amp breakers on my 12-2 runs. I used a 30 amp breaker on my 10-2 to the A/C condenser unit, and all of those became embedded in that spray in foam insulation.

I didn't even give it a thought. Would the derating have changed the allowable ampacities enough that I would have had to use 12-2 for all the lighting, bedroom recepts, etc and put it them on 15 amp breakers? What about the kitchen? 10-2 for the SABC on a 20 amp breaker? Does 10 AWG even fit into a GFI?

 

[Pierre C Belarge]

Chris
This is, in my opinion a dumb change to the NEC.
With the Style Manual and the NFPA/CMP members trying to make the NEC more user friendly, they use the phrase "MAINTAINING SPACING".


What does maintaining spacing mean?


I do not want to hear someone say the "intent is", because there is no definition, and no intent described in the ROPs/ROCs.


They should use a dimension in the paragraph. How could they not use a dimension, if they made this change...did I say this is a dumb change?


Now, I am wondering, how did they come to the conclusion? This is not a good thing? There are only about 200 million buildings built this way to date, what about those poor suckers.
Are the existing homes burning down?...Maybe we should let this be, you know generate more work during this slow economy.

 

[ibew501ed]

generally speaking you can get up to 9 current carrying conductors installed in a conduit or foamed wall before derating effects the c/b size.
using 14, 12, or 10

#14 thhn =25a
25a x 70% = 17.5a or 15 a c/b

90deg col. used for derating

 

[Pierre C Belarge]

generally speaking you can get up to 9 current carrying conductors installed in a conduit or foamed wall before derating effects the c/b size.
using 14, 12, or 10

#14 thhn =25a
25a x 70% = 17.5a or 15 a c/b

90deg col. used for derating

What about the wall space that is insulated, and is located above a panel?

 

[ibew501ed]

ouch
thats a lota wires
your a real downer pierre

 

[jaylectricity]

What about the wall space that is insulated, and is located above a panel?

Wow, that really makes your "maintaining space" argument very valid.

 

[suemarkp]

What about the wall space that is insulated, and is located above a panel?

Do you run all the cables in one giant bundle, or are they in smaller bundles of 2 to 4 that line up with the knockouts they go through. As you said, there is no definition of what "maintain spacing" means, but to me a bunch a 2 to 4 cables bundles side by side (but with some space between each) wouldn't have to be treated as a huge derated bundle.

Weren't we always required to derate NM cable when it was bundled? Isn't the only difference here that you get no forgiveness for less than 24" in the insulation or too many going through a bored hole that is fire stopped?

 

[cpal]

Now I'm not saying that because I was allowed to do it, it must be OK, but the inspector in Lexington, MA is pretty much by-the-book. I used 15 amp breakers on my 14-2 runs and 20 amp breakers on my 12-2 runs. I used a 30 amp breaker on my 10-2 to the A/C condenser unit, and all of those became embedded in that spray in foam insulation.

I didn't even give it a thought. Would the derating have changed the allowable ampacities enough that I would have had to use 12-2 for all the lighting, bedroom recepts, etc and put it them on 15 amp breakers? What about the kitchen? 10-2 for the SABC on a 20 amp breaker? Does 10 AWG even fit into a GFI?

Did you penetrate the structure with the 10/2 or did you change to thwn or uf before leaving the building??

Ma deleted the second parg of 334.80 and edits the first!

 

[Pierre C Belarge]

Do you run all the cables in one giant bundle, or are they in smaller bundles of 2 to 4 that line up with the knockouts they go through. As you said, there is no definition of what "maintain spacing" means, but to me a bunch a 2 to 4 cables bundles side by side (but with some space between each) wouldn't have to be treated as a huge derated bundle.

Weren't we always required to derate NM cable when it was bundled? Isn't the only difference here that you get no forgiveness for less than 24" in the insulation or too many going through a bored hole that is fire stopped?

What you have stated here is just what I am talking about. You have provided your opinion. Now an inspector comes behind your work and has a different opinion and asks you to derate the ampacity. Since there is no definition, then he may be correct.

The issue at hand is not in regards to bundling. It is about installing cables in the insulation and not maintaining spacing.

 

[hardworkingstiff]

Chris
This is, in my opinion a dumb change to the NEC.
With the Style Manual and the NFPA/CMP members trying to make the NEC more user friendly, they use the phrase "MAINTAINING SPACING".


What does maintaining spacing mean?


I do not want to hear someone say the "intent is", because there is no definition, and no intent described in the ROPs/ROCs.


They should use a dimension in the paragraph. How could they not use a dimension, if they made this change...did I say this is a dumb change?


Now, I am wondering, how did they come to the conclusion? This is not a good thing? There are only about 200 million buildings built this way to date, what about those poor suckers.
Are the existing homes burning down?...Maybe we should let this be, you know generate more work during this slow economy.

If you were doing an inspection, what would you use as a guide?

 

[rikthejman]

Happy Holidays everyone!!
I was reading the thread and had a discussion in a safety meeting a week ago about the spacing and insulation and derate of NMB into panels. The conclusion was that since the cables are stapled (1 or 2 together) at 12" and with 2 cables per 1/2" or 3/4" KO the cables remained "seperated". What was left is the 18" to 24" above the panel through the top plate. I usually go with 8-1 1/4" holes so thats 2-4 cables per hole. Derating would become an issue over 9 CCC's. You would think that seperating the cables with stapling avoids the issue all together. I think physical seperation is "spacing" in my humble opinion.

 

[suemarkp]

What you have stated here is just what I am talking about. You have provided your opinion. Now an inspector comes behind your work and has a different opinion and asks you to derate the ampacity. Since there is no definition, then he may be correct.

The issue at hand is not in regards to bundling. It is about installing cables in the insulation and not maintaining spacing.

So there's a good definition of bundling? To me, this is just an extension of an existing nebulous definition that the AHJ gets to define. As long as you have normal ambient temperatures, you need to run 4 or less cables through insulated walls and bored holes that are fire stopped. Because I can't get a good definition of bundled either, I limit all bored hole runs to 4 cables (9 CCC's), insulated cavity or not.

I would hope an inspector would consider groups of 4 cables spaced an inch from another bundle of 4 to have maintained spacing. But you're right, there is no set definition and he could say - no you've got to derate for 30 CCCs here... Add "maintain spacing" it to the list, along with bundling and subject to physical damage.

 

[jaylectricity]

Did you penetrate the structure with the 10/2 or did you change to thwn or uf before leaving the building??

Ma deleted the second parg of 334.80 and edits the first!

The 10/2 went right outside into the disconnect. That reminds me though that I frequently forget to check the MA amendments since I don't have a paper copy of them.

Found them at mass.gov though.