# where is NM-B in code book



## RICK BOYD (Mar 10, 2008)

When I buy NM I can only find NM-B 
but can't find it listed in the book . 
I don't see it in 310-16, so what's it's ampacity? I know, but I want it in print
one supplier said it was NM with 90'F conductors but I can't find it in writing.
I like to read it cuz 
I don't believe anything I am told and only half of what I see.

Rick

ps: when I tell the salesman I want 12-2 nm 
he always says "do you want that with ground"
and I say NO and he says "we don't have it without ground"
and I say "DUH"


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## BEAMEUP (Sep 19, 2008)

look in 334


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## Bob Badger (Apr 19, 2009)

Article 334 covers all types of NM, in regards to temperature rating look at 334.80.

You can use 90 C as a starting point for derating but in no case may you exceed the 60 C rating.


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## RICK BOYD (Mar 10, 2008)

*I did your'e right*

Ok ,but what I find at the store is NM-B whether it is southwire or romex brand and that is not in the book, but I do see 334.8 and they referance NM , NMC and NMS but not NM-B

QUOTE=Bob Badger;137162]Article 334 covers all types of NM, in regards to temperature rating look at 334.80.

You can use 90 C as a starting point for derating but in no case may you exceed the 60 C rating.[/QUOTE]


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## Chris Kennedy (Nov 19, 2007)

RICK BOYD said:


> that is not in the book


Its in the book.




> 334.112 Insulation.
> 
> The insulated power conductors shall be one of the types listed in Table 310.13(A) that are suitable for branch-circuit wiring or one that is identified for use in these cables. Conductor insulation shall be rated at 90°C (194°F).
> 
> FPN: Types NM, NMC, and NMS cable identified by the markings NM-B, NMC-B, and NMS-B meet this requirement.


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## River Boy (Oct 26, 2009)

*Nm-b*

Years ago there was just NM or, non-metallic 60 C romex. Then sometime in the early 80s the NEC decided that NM needed to have a higher insulation rating for attics so they started putting 90 C THHN in the romex sheath and called it NM-B, as opposed to the old stuff which they temporarily named NM-A to differentiate between the two. They left a window of time for all the old stock, (NM-A) to be used up. When an inspector looks at a romex sheath and sees NM-B he knows he is looking at 90 C wire.


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## Briancraig81 (May 25, 2007)

I'm not trying to HiJack but can someone tell me what your supposed to do when your hanging a new fixture that say's use only 90 C conductors and what your connecting it is 60?

I asked my old boss this a few years back and he told me that they changed the temp rating back in the 80's (Which is what you guys are saying) and for me to just hang the fixture and not worry about it. He did tell me to always leave the fiberglass insulation on a fixture because it helps with the temp rating.

Can someone set me straight on this?, Thanks.


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## Dennis Alwon (May 9, 2009)

Briancraig81 said:


> I'm not trying to HiJack but can someone tell me what your supposed to do when your hanging a new fixture that say's use only 90 C conductors and what your connecting it is 60?


Most people don't worry about it but you can take a piece of #10 THHN insulation and sleeve it over the old 60C insulation. We do this alot when the old knob and tube is cracked beyond repair.


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## Bob Badger (Apr 19, 2009)

Code wise you can not hang the fixture,


I think most people do.


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## NolaTigaBait (Oct 19, 2008)

Dennis Alwon said:


> Most people don't worry about it but you can take a piece of #10 THHN insulation and sleeve it over the old 60C insulation. We do this alot when the old knob and tube is cracked beyond repair.


I've done this as well. I'm surprised Dennis would do this.:thumbsup:


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## Dennis Alwon (May 9, 2009)

NolaTigaBait said:


> I've done this as well. I'm surprised Dennis would do this.:thumbsup:


Wow- I didn't realize I set the standard so high. 

I look at it this way- what's a better install. If I can replace the wire I will but if we are between floors etc I find my solution to be the better of the two evils. The existing old fixture is probably a bigger hazard than the new fixture would create. So---- the lesser of the 2 evils is a good solution esp. with the higher temp. insulation.


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## RePhase277 (Feb 5, 2008)

Using some of the fiberglass high temp sleeves used in electric heaters and ranges over the old wires may be a good solution.


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