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?
