ECN Forum Forums Code Related Discussion NEC & other Code issues Old issue

I haven't seen THHN that wasn't also THWN labled, at least not since I can remember.
I assume manufacturing expediency probably makes the conductor in NM-b the same wire, without the marking. Unfortunately that keeps us from ensuring compliance so we are obligated to fail it or 90-4 it.
I believe the paper packing is probably why NM is not OK in wet/damp locations.

A telling thing is when I search "wire" manufacturer sites for NM-c I get UF.

I just read Article 334 on NM cable and it's starting to become clear to me that NM cable or more properly identified as NM-B is only suitable for interior wiring. It specifically mentions "in" buildings or structures. Not even suitable for damp location. Dry locations only. I'm not willing to say that the inside of LFNC is dry. Might not be wet but for sure damp. NM cable is a no no for use outside the building. There I said it. So let it be written- So let it be done.

The ban on NM in damp locations is new - and, as far as I'm concerned, absurd. Eveb the older cloth-wrapped version worked just fine in such 'damp' locations as crawl spaces and under decks.

"NMC" differs from plain "NM" in being 'corrosion resistant.' For the life of me, I cannot see how the current PVC jacket is not 'corrosion resistant.' Having actually done the relevant tests, I have no doubt it would pass. So why isn't the common product marked "NMC-B?" Only Southwire knows for sure.

That an inquire would be referred to UF is silly; UF has it's own code section.

Ditto for the practice of using unmarked wires inside the jacket. Why? If the manufacturers are using this practice to limit the use of their product, let's just change the code to ban it, marked or not.

The NEC seems - and I've said this before - a bit bi-polar regarding NM. Some recent changes (expanded list of approved occupancies) suggest it's a reliable, proven, safe method; others (damp location ban, AFCI's) suggest it's the 'tobacco' of the trade.

Getting back to 'where the rubber meets the road,' we have to make the judgement call: just where is the problem? If the conductors are otherwise proper, where's the introduced hazard?

The same approach applies as well to the running of the t-stat wire. Why not run it with the power wires? The t-stat wire I see is rated at least 150 volts - more than either power conductor to ground. Most has a 300 volt jacket. Wouldn't you rather see the wire in the power conduit, than encased in the foam insulation of the very hot line set?

The hazard with the t-stat wire in the same raceway with the power is not the wires but what they are connected to. A failure of one system to the other could put 120 V to the thermostat. That could be a real surprise.

You need TWO failures to get 120 V to the thermostat. Failure of the line voltage insulation PLUS the failure of the T-Stat insulation.

Larry C

Reno, I still believe it is the paper packing in RX that is not water friendly. It might wick water into boxes etc.
That seems to be the concern when you read the "flooded house" articles. Maybe someone has a link to the NOLA article in IAEI News.
As far as I can determine, NM-C is NM with a plastic packing instead of paper. I have never actually seen any NM-C and I do not think Southwire really makes it, hence routing me to UF when I try to look it up (assuming I want to buy a pallet I guess).

In regards to UF/NMC, I found this on Southwire's website:

"Southwire Type UF-B cable is generally used as feeder to outside post lamps, pumps, and other loads or apparatus fed from a distribution point in an existing building as specified in the National Electrical Code1. UF-B cable may be used underground, including direct burial. Multiple conductor UF-B cable may be used for interior branch circuit wiring in residential or agricultural buildings at conductor temperatures not to exceed 90°C (with ampacity limited to that for 60°C conductors) as specified by the National Electrical Code. UF-B can be used in applications permitted for NMC in Section 334.10(B) of the National Electrical Code. Voltage rating for UF-B cable is 600 volts."