I run across a large number of installations where the electrician installs NM cable in Liquid-tight conduit to outside equipment such as A/C units and well equipment.

I have failed these jobs and have required the installation of cables or condutors listed for wet location based on 225.4 / 310.8 of the NEC.

Some have argued that the conductors in NM cable is thhn, however even so, 310.8(C) does not list thhn as listed for wet location and 334.10(A) also states "normally dry location."

I discussed the issue with UL and they claim any insulation type listed in Table 310.13 and is rated at 90° C. will comply. Its basically up to the manufacturer.

I called one NM manufacturer whom stated their conductors are insulated with basically THHN without the nylon jacket. They also confirmed NM is not to be used outdoors or in wet locations.

So, it appears I have the code on my side, however I don't know if common sense is. Is the inside of a raceway listed for a wet location also a wet location? Yes or no, the code indicates it doesn't matter.

From a practical sense I doubt you will have any dead babies from Romex inside sealtite in a wet location but it is still a code violation. I have seen Romex that survived decades direct buried. It held a GFCI OK but it is certainly not legal.

I agree, it is a violation. THHN is not for use in a wet location.

A semi-good way to remember what is listed for wet:
If it has a 'W' in it, then it is probably listed for use in a wet location (but remember that the W doesn't necessarily stand for "wet"). Check the charts to see if I'm right.

What about UF?

"W" does mean wet. UF is Underground Feeder, "wetter than wet". It could be in your Carflex too, outside.

Where are you getting that W means wet? I researched this once, oh about 4 years or so ago.

You are correct Bryan, I spoke with an old friend who is on CMP-8, and although the raceway you install the NM cable in is liquid-tight and is used to protect conductors in a wet location, that does not apply to outside, since the problem is condensation due to temperature changes...just like underground raceways per 356.10(2).

Please excuse my not posting often, I am one of the inspectors for the TV show build project Extreme Makeover. Just got off a 22 hour tour.

Very cool! That must be an interesting experience...

I had a chart from one of the manufacturers that had all the codes on it. "W" usually means wet or water resistant. Machine Tool Wire (MTW) is one exception. I think it is always true in "building wire" conductors tho. The safest way is still to look it up if you see an unknown wire type.