MC and RX conductors

[nerspellsner]

I have heard too many different answers for this question. I thought I might ask it again and get a 100% correct answer from you. What type and temperature ratings are the conductors in NM and MC? I thought that NM (romex) had type TW conductors inside the cable, but TW is only rated for 60C. If the conductor type includes a W does that mean they are all rated for wet locations? If romex is TW or THW or THHW then why cant it be used in a underground conduit?

 

[iwire]

Officially we do not 'know' what the individual conductors are in NM. I think it is a safe bet they are very similar to THHN/THWN but we do not have any listing or labeling to tell us that.

334.80 tells us that we must treat NM as 60 C except for the purposes of derating which we can use the 90 C rating for.

330.80 tells us the rules for MC

 

[nerspellsner]

What do we do when installing light fixtures in a building using Romex as a wiring method when the light fixture says to use only 90C wires for a connection? Should we splice pigtails of 90C THHN to the Romex, or just connect the light fixture directly to the Romex?

 

[bphgravity]

The conductors in NM cable are 90?C rated. You just can't load them to that rating.

 

[celtic]

What do we do when installing light fixtures in a building using Romex as a wiring method when the light fixture says to use only 90C wires for a connection? Should we splice pigtails of 90C THHN to the Romex, or just connect the light fixture directly to the Romex?

We should read 334.80


I tried searching for a thread where I said RX wasn't allowed in a fixture...someone corrected me (citing 334.80) and also provided a link (to UL?).

If that "someone" could splash that link in this thread it would be appreciated

 

[busman]

I have often wondered if part of the reason that type NM is not allowed in wet locations is the paper that is contained in the cable. This paper could wick moisture into enclosures. Thoughts?

Mark

 

[wireman3736]

Talking wire rating I'm not sure what temprature rating some of the old wire is, does anyone know for sure what k&t, bx or old romex was rated at, I always assumed 60 deg c but that word assumed sometimes gets me in trouble.

 

[dlhoule]

I'm not sure what if any temp rating it had/has. I can tell you that it took a serious overload to damage the insulation. Most of the K&T that I have seen were #14 wire; typically fused at 30 amp.

I have seen insulation damage on it a few times but most of the time that was due to a penny behind the fuse. Even the 15 amp fuses held up quite well with a penny behind them.