The wire inside NM cable

What kind of wire is used to manufacture NM cable? Is it THHN? or THWN ?
It can be any of the conductors in 310.13(A) that are suitable for branch circuit wiring or one that is identified for use in the cables and rated at 90 C.

It's up to the manufacturer.

Since the individual conductors in NM are not properly labeled, they can't be used in place of conductors not meant to be part of a manufactured cable.

Some companies will list on their web site what the conductor's equivalent type is, but that does not make a single conductor that type unless properly labeled.
 

edward

Senior Member
That would only apply to one manufacturer.
From Southwire:

The conductors inside of our Romex products are listed as THHN only. You are correct in the statement that most conductors are multi rated. Romex is listed as a complete product and the conductors SHALL NOT be used with out the outer jacket. It can only be used as Romex and where Romex is approved for use by the NEC.

New Products/Applications Engineer
Research Division
Southwire

Who else makes NM cable? we can check their specs as well.
 

templdl

Senior Member
Location
Wisconsin
What kind of wire is used to manufacture NM cable? Is it THHN? or THWN ?
This is somewhat of a loaded question in that NM basically stands for nonmetallic. But sense NM nonmetallic has been in use for a long time one must understand the difference between the older NM cable that the NM-B that we use today.
Would you be referring to the older NM or the newer NM-B? If NM then I would be inclined to say that it is TW 60degC rated and NM-B would signify that it is THHN 90degC rated wire.
How often have you attempted to change a light fixture where the insulation crumbles as you are trying to carefully remove the wire nuts where the home was wired with the original NM cable? It is quite interesting that they did not realize that the insulation would be damage because of the heat generated by the fixture. That compounded by replacing that fixture with a new fixture that requires 90degC wire.
That 60degC rated wire will get its butt whooped big time.
It must be remembered that copper is not only a good conductor of electricity but it is good conductor of heat as well. The heat in the junction box could likely be conducted by the copper outside the box deteriorating the insulation along the way.

Make sense?
 

480sparky

Senior Member
Location
Iowegia
From Southwire:

The conductors inside of our Romex products are listed as THHN only. You are correct in the statement that most conductors are multi rated. Romex is listed as a complete product and the conductors SHALL NOT be used with out the outer jacket. It can only be used as Romex and where Romex is approved for use by the NEC.

New Products/Applications Engineer
Research Division
Southwire

Who else makes NM cable? we can check their specs as well.
Even so, they say you can't use the conductors alone.
 

kwired

Electron manager
Location
NE Nebraska
It really doesn't matter because you can only use it as a cable assembly.
Best answer.

The cable is intended to be used as a "cable", not as individual conductors. The individual conductor insulation means nothing as they can not be used for anything except as part of the cable they come with, and is probably number one reason they are not marked.

It is likely they are same thing in most cases as THHN or even THWN, mostly because that is likely one of most popular production lines of insulated copper and would cost less to just make same thing - but maybe remove from the process any equipment used to mark the conductors.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Maybe it's just me but I find this whole process to be silly. Why can't the conductors be required to be THHN/THWN-2 and marked on the conductor like it is when I buy a spool of wire. From everything I've heard I would guess that dual rated (THHN/THWN-2) wire is more readily available and cheaper to manufacture than a plain old 90? conductor. So when needed one can strip a piece of NM and use the conductors individually. Even though this isn't permitted I'm guessing that it's a very common installation practice.
 

macmikeman

Senior Member
Strictly speaking according to the Southwire response , most all dwelling load centers have been ul violations if they utilize any removal of "romex" cable jacket in the installation. Same goes for inside of switch box, fixture outlet boxes, and receptacle outlet boxes. Same goes for any other location where the jacket is removed to expose conductors inside the cable for termination purposes. We best be getting busy going back and fixing all them bad installs. Chicago of course may ignore this post. No more laughing at the Chicago way, they were right all along.
 

TimK

Member
Location
Tacoma, WA
Romex/Outside?

Romex/Outside?

Agree that you have to use it as a cable assembly, but if the individual conductors are THWN then it can be used outside. (eg, sleeving romex through a liquid tight for an A/C unit).

The OP didn't ask if the conductors can be used outside of the cable.
I thought, (because of Katrina), that we learned Romex outside willnot work, the paper inside gets wet, molds and eats the insulation of the wire.
 

templdl

Senior Member
Location
Wisconsin
Maybe it's just me but I find this whole process to be silly. Why can't the conductors be required to be THHN/THWN-2 and marked on the conductor like it is when I buy a spool of wire. From everything I've heard I would guess that dual rated (THHN/THWN-2) wire is more readily available and cheaper to manufacture than a plain old 90? conductor. So when needed one can strip a piece of NM and use the conductors individually. Even though this isn't permitted I'm guessing that it's a very common installation practice.
Ditto. I have found it to be strange that the actual wire has no markings. I would see it as being simple where in the wire manufacturing process the wire is taken from. To purposely use unmarked wire is an interesting concept.
 

edward

Senior Member
Ditto. I have found it to be strange that the actual wire has no markings. I would see it as being simple where in the wire manufacturing process the wire is taken from. To purposely use unmarked wire is an interesting concept.
So you can buy two of the same product but think that they are different.

I believe code making panels do have manufacturing reps as well. :thumbsdown: Thats why we get to install things that don't make any sense.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
Strictly speaking according to the Southwire response , most all dwelling load centers have been ul violations if they utilize any removal of "romex" cable jacket in the installation. ....... We best be getting busy going back and fixing all them bad installs....
Rodger that. I got some leftover scraps of jacket that have not been split in half, a couple rolls of Scotch 33, and some Gorilla Glue.... Where do we meet?
 

PetrosA

Senior Member
To use NM-B outdoors, simply undersize the wire so it runs nice and hot (increase the load if need be), then slit the jacket along the entire length so the moisture can evaporate out. Works a charm... ;)
 
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