I had the entire HVAC system replaced at my house by a local contractor. The electrical inspection failed for a few reasons:

1. The 30A 2-pole breaker in it's own subpanel was labeled Service Disconnect, but not A/C Service Disconnect. OK, easy fix.
2. The circuit breaker panel was replaced and the furnace circuit breaker was not labeled. OK, easy fix. I had forgotten to get around to that.
3. Because the furnace circuit breaker wasn't labeled, the inspector couldn't verify that it was a 15A breaker. OK, that's fixed with the label.
4. The inspector said that NM-B cable was used in a wet location outside.

I'm struggling with #4 (I could just call the contractor, but I'd rather verify the problem than have them come out and waste time if there isn't a problem). I've traced the wires (well, I already knew where they were, but mostly read the insulation labeling) and have a separate meter box (interruptible electrical service) outside that feeds an aluminum 6 AWG XHHW-2 UV-rated cable that runs inside to a subpanel with a single 30A 2-pole breaker. More 6 AWG XHHW-2 UV-rated cable runs from the subpanel to a fuse box out next to the A/C compressor unit. The fuse box is connected to the A/C compressor with LFNC-B conduit and 3 individual wires inside, a black, red, and bare ground. I understand that the XHHW-2 isn't the problem as that's wet-rated and UV-rated. I also understand the LFNC-B is fine since it's not exposed to physical damage (protected behind the A/C), but it's outdoors and even though it's a liquid tight conduit, the inside is still considered a wet application which NM-B is not allowed for.

My problem is that the 3 wires inside the conduit only have maybe 3 inches exposed in the fuse box, and another 3 inches exposed in the A/C compressor's electrical panel. However, I can't see a single marking on either of the insulated wires to see what they are. They do not have a jacket like NM-B, and are separate wires. The black looks like it has clear shrink tubing along it's length and the white is taped red to indicate the second hot leg of the 240V circuit. Is there any way to tell what this wire is without pulling it out of the conduit?

The UF type romex will be inside a molded outer covering, the NM will have a loose outer covering, with a paper wrapping the conductors.

I knew that. It's not a cable though. It's 3 individual conductors. There is no outer insulation.

So they are possibly THHN/THWN, the only way to know for sure is pull them out.

It is a violation as described.
The cable jacket is required to be 1/4 inch inside the connector into the box.

If the conductors are in conduit from a stripped cable they are often unmarked and not suitable for use this way.

Is it not acceptable to use THWN? Then again, I would assume it's jacket would be marked.

It sounds like it is romex with the jacket stripped off, meaning the conductors are not marked, which is a no go.  Or it is romex that has the outer sheath stripped back until it is not visible, which is a no go.  Or it's just romex, which is a no go in a wet location.  If it was actually individual conductors with ground the ground wire would be insulated.

This is what has me so perplexed. The black conductor appears to have the black PVC insulation with a clear outer jacket like THWN would. However, the ground conductor is bare copper, and the second leg of the 240V is a white conductor with red electrical tape. The ground and second hot look like NM-B stripped of it's outer sheath. I think I'll just go to Home Depot and buy three lengths of THWN (which apparently HD stocks as THHN/THWN dual rated wire) in appropriate colors and rewire. It's only a few feet anyways.

It's a 2-pole 30A breaker, so based on ampacity tables, it looks like 10 AWG is the bare minimum and 8 AWG can handle slightly higher amps. Based on conduit fill charts, it appears the 1/2" LFNC conduit can hold three 8 AWG THHN/THWN conductors. I think I'll just rewire with three 8 AWG THWN conductors.

FYI... The grounding conductor   needs to be ... bare/stripped or solid (continuous) green in color if its awg is smaller then #4, marking tape if used is a violation of NEC 250.119. My Home Depots only sell #8 green by the roll plus you already have an adequate grounding conductor inplace

ETA.... for the thread readers, NEC 200.6 covers grounded (neutral) conductor identification requirements

Is this in emt or pvc conduit?  You can not just run THHN exposed

THWN is marked.

The insulation in NM is NOT marked on the individual conductors.

It's in 1/2" LFNC conduit. Currently has 3 conductors which I can't see markings on as they are exposed 3" or less on both ends of the conduit before they enter their final screw terminals. There is no outer sheath, but rather 3 individual conductors.

There is a black conductor which appears to have the colored and clear double layer insulation like THHN/THWN does. There's a white conductor wrapped in red electrical tape. And there's a bare solid copper ground conductor.

You didn't read the OPs original post did you. Since he said quote"The fuse box is connected to the A/C compressor with LFNC-B conduit"

OK, I've looked at it again. It's three 10 AWG solid conductors. The two hots appear to have the colored PVC insulation with the outer clear insulation like THWN would, but I can't find markings. So I'm guessing that's the problem. The ground is bare 10 AWG solid copper.

Probably, all wire must be labeled.

I did but apparently missed that part, thanks for pointing it out

Dude probably just used stripped NM

If you pull new THHN make sure to get it in the correct colors, reidentifying is a no-go on I think #6 and smaller.

I bought stranded copper 10 AWG THHN/THWN dual-rated wire tonight in black and red. I'm going to leave the solid 10 AWG bare copper ground conductor as it is. I'll pull it tomorrow.

What is strange to me is that I've never seen NM with this type of conductor in it. It has the dual layer insulation like THHN, and I've never seen that in an NM cable. Oh well, I have the proper wire now and I'll fix it. Inspector comes back on the 16th.

You can mark any gauge from neutral (grounded) to hot.

Marking grounding in smaller is not allowed.

Marking grounded gets touchy.