Type NM-B Ampacities

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Sierrasparky

Sierrasparky

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Electrician ,contractor
nakulak said:
I have never seen thhn in romex. All I have seen is what appears to be hhn.
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I don't mean to be a pest on this but charlies post in number 4 does not give a reason that NM-B C f G or whatever is not allowed to have the ampacity of it's counterpart. Mc , Ac, EMT, RNMC, RMC and so on.
 
charlie

charlie

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Indianapolis
Sierrasparky said:
. . . does not give a reason that NM-B C f G or whatever is not allowed to have the ampacity of it's counterpart. MC, Ac, EMT, RNMC, RMC and so on.
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Sorry, I didn't know that you had asked that question. The -B designation is for the higher temperature conductors. The NMC-B designation is for the corrosion resistant outer jacket. The NMS-B designation is for the cable that has signaling, data, and communications conductors inside the outer jacket.

MC, AC, and the various other cable, raceway, and tubing wiring methods have a containment method in the case of damaged cable. Type NM has nothing except for the overall outer jacket and many people feel like type NM is a very inferior type of wiring method. Some places, notably Chicago, has even deleted Article 334 from their local code. :)
 
Sierrasparky

Sierrasparky

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Electrician ,contractor
charlie said:
Sorry, I didn't know that you had asked that question. The -B designation is for the higher temperature conductors. The NMC-B designation is for the corrosion resistant outer jacket. The NMS-B designation is for the cable that has signaling, data, and communications conductors inside the outer jacket.

MC, AC, and the various other cable, raceway, and tubing wiring methods have a containment method in the case of damaged cable. Type NM has nothing except for the overall outer jacket and many people feel like type NM is a very inferior type of wiring method. Some places, notably Chicago, has even deleted Article 334 from their local code. :)
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So how does reducing the ampacity result in less damage (less containment from a damaged Cable. I would think a damaged cable is a damaged cable. The only thing that would be different is that the one carrying a Higher current will show a problem sooner. The one carrying the low current will just take longer to show a problem. Giving the EC more days or years to get far away from repsonsibility.
 
charlie

charlie

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I think you are being too concrete. The higher current could result in a damaged cable . . . correct. Why are AFCIs now required for NM cable and not for other wiring methods . . . NM cable is more fragile? Perhaps. Think what you wish but the rules are what they are and they will not change unless you make a proposal with solid documentation to change the perception. Just saying, "I would think . . ." is not going to cut it with a code making panel or an AHJ. :)
 
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hurk27

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Location
Portage, Indiana NEC: 2008
charlie said:
I think you are being too concrete. The higher current could result in a damaged cable . . . correct. Why are AFCIs now required for NM cable and not for other wiring methods . . . NM cable is more fragile? Perhaps. Think what you wish but the rules are what they are and they will not change unless you make a proposal with solid documentation to change the perception. Just saying, "I would think . . ." is not going to cut it with a code making panel or an AHJ. :)
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The "2008" doesn't require AFCI's for conduit ?

I know here in Indiana it's been removed , but I didn't know that it was changed to just requiring it for NM?:confused:
 
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scottam99

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Vero Beach Florida
1 inspectors comment

1 inspectors comment

A friend of mine was an inspector in the county I live in. He said it is because of the paper in the NM-B cable. I asked where I could find this in the code book but he couldn't tell me. ANyone else know where this might be stated? Or maybe it's the code book that only Inspectors are allowed to see!!!!!
 
ivsenroute

ivsenroute

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Location
Florida
scottam99 said:
A friend of mine was an inspector in the county I live in. He said it is because of the paper in the NM-B cable. I asked where I could find this in the code book but he couldn't tell me. ANyone else know where this might be stated? Or maybe it's the code book that only Inspectors are allowed to see!!!!!
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He may have attended a seminar or learned that some other way. Code books don't tell you why so you won't find that type of info in there. Some of the information that I have found out was by talking to panel members who actually listen to testimony and change the code.

The rest is just hearsay
 
charlie

charlie

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Location
Indianapolis
hurk27 said:
The "2008" doesn't require AFCI's for conduit? . .
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It wasn't intended to mean that. The intent of the AFCIs is to protect not only the circuit but anything that is connected to the circuit from arcing faults.

scottam99 said:
. . . He said it is because of the paper in the NM-B cable. . .
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It has been a long time since I have stripped out type NM cable but I don't believe the cable is built with paper anymore. :)
 
H

hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
charlie said:
It wasn't intended to mean that. The intent of the AFCIs is to protect not only the circuit but anything that is connected to the circuit from arcing faults.
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Had me worried there, thought I missed out on somthing:grin:

charlie said:
It has been a long time since I have stripped out type NM cable but I don't believe the cable is built with paper anymore. :)
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All the NM we been getting have the paper, not only around all the conductors but around the EGC too. UF is the only one I havent seen the paper in.;)
 
mivey

mivey

Senior Member
charlie said:
It used to be that way years ago but, I thought the manufacturers went to a cellophane type of filler. :)
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Might be, but I could swear I saw cases of paper and reels of it spooling into the winding machines in a cable manufacturing plant the other day. I thought it looked liked coated paper, but I did not play with a sample to see up close or feel the texture.
 
mivey

mivey

Senior Member
charlie said:
I am not disputing you because I do not know. I am just relating what I though I knew. :)
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You may be absolutely right. I just remembered thinking "look at all the paper they use".

It may not have been paper, but I'll check the next time I'm over there, if I don't forget.
 
N

nakulak

Senior Member
I'm using nm on a hotel right now (unfortunately). I've got paper and plastic (didn't notice which manuf)
 
G

gndrod

Senior Member
Location
Ca and Wa
cable vs. wire rating

cable vs. wire rating

Gentlemen,
NM-B 60 deg C is for the cable rating only, the conductor wire in the cable = 90 deg C rated and noted in table 310.14 for dry locations (THHN). Note that NM, UF, SE, MC,...etc. type cables are not rated in the Table 310.16 for the reason that they are not conductors but cables.

You can see UF cable is also rated at 60 C and wire within the cable in T310.14 still rated 90 C but for wet locations (THWN). The ambient condition 90 C derating for the wire is allowed regardless of it being NM-B, UF, SE...etc. rbj
 
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