NMB

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physis

physis

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This might be really stupid but it's been bugging me for a long time. All the NM I use is NM"B", the NEC doesn't recognise the "B".

Does it designate anything, is there a purpose.

The same thing with some other wire types.
 
Re: NMB

This from the 2005 NEC:
Type NMC Insulated conductors enclosed within a overall, corrosion resistant nonmetallic jacket.

Type NMS Insulated power or control condctors with signaling, data, and communications conductors within an overall nonmetallic jacket.

I have never seen any of the "C" or "S" though.
 
Re: NMB

I asked about this once and thought the "B" was in reference to the conductors being THHN and 90 degree C rated..,

Don't have a reference but just trying to throw some direction towards the answer ......again I am just taking a shot at this one from the hip .
 
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It's been a while & the details are kinda hazy, but wasn't the "B" added some time ago when manufacturing standards went to using 90 degree conductors in the "Romex" ?
 
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Sam
I can?t remember the year off the top of my head but nonmetallic cable was produced with sixty degree conductors. Then the standards were that NM cable had to have ninety degree conductors. Well this caused a problem because no code official knew how to tell the difference between the two. The letter ?B? was printed on the sheath so it could be recognized as ninety degree conductors
 
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Hello John, you have been away for awhile. ;)

Roger
 
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Hi Roger, been around but found it more benefical to" listen to folk" like you and many others here who " really know and understand" the trade. You guys have helped a great deal.

Appreciate your input and exsperinec like always :D
 
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The "B" indicates that it is rated for 90 degrees C................but you still must use the 60 degree table for the proper ampacity.
 
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Since you guy's are talking about the 60 degrees and 90 degrees I'm stumped on something! When the code says "ambient air temp." what excactly is meant? Is that just for lugs or actual air temp or what? Whenever I read the code handbook and I come across it, i get a little confused. For instance, I was studing up a little on derating and load calculation's on table 310.16 and it always talk's about.
 
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NM, NMC, and NMS cable all come with a bare or insulated conductor for equipment grounding purposes only and then they are identified as NM-B, NMC-B, and NMS-B and this is as of 336-30(b) FPN 99 code. where provided the grounding conductor shall be sized with article 250.
 
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elect36 - Ambient air temperature is the air temperature of the immediate area surrounding the cable. Lugs have their own temperture ratings just like conductors do.
 
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Wait a second Bryan, now I'm confused all over again. 334.80 refers to only NM, NMC and NMS.

Roger's link doesn't provide temperatures on those types. I'm guessing they're not 90?. If they're not you're not going to be able to derate from 90?, right?
 
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Please, someone explain when they used any NM cable / derating.......I have been in situations where it could have been applied...but its looked over for the most part.

Where other than the branch circuits being fed through a conduit longer than 24 inches going to a panel would you use this ???? Even then would you derate....think about that for a moment.

I would bet some( the majority) have talked about derating NM but never have or will.

My opinion.

Spelling corrections .

[ January 13, 2005, 11:52 PM: Message edited by: drg ]
 
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