Romex in conduit

[Ole Anderson]

I am running a 30 amp 220 circuit for an a/c compressor. Panel is in the garage so I will be running 10-2/wg romex to the point it exits the wall to the outside, where I will run the wires in about 10 feet of 3/4" PVC conduit (above ground) to the disconnect. Previously I would have likely just continued the romex in the conduit to the disconnect. But being outside and being considered a wet location, I suppose that is a no-no so I need to put a JB where I transition from romex to thhn? Seems silly in that the pvc conduit is watertight.

[Phil Thien]

I am running a 30 amp 220 circuit for an a/c compressor. Panel is in the garage so I will be running 10-2/wg romex to the point it exits the wall to the outside, where I will run the wires in about 10 feet of 3/4" PVC conduit (above ground) to the disconnect. Previously I would have likely just continued the romex in the conduit to the disconnect. But being outside and being considered a wet location, I suppose that is a no-no so I need to put a JB where I transition from romex to thhn? Seems silly in that the pvc conduit is watertight.

10-2 NM shouldn't exceed the fill limit of 3/4" PVC. So if it doesn't, I don't see why you wouldn't continue the NM right through the plastic and up to the disconnect. I think this makes it pretty clear that you can run NM in conduit (below). BUT, if this job will be inspected, you may want to check with your local inspector to make sure they aren't going to have a cow. And when you check with an inspector, don't ask if it is okay. Say, "hey, I was reading this section of the code and it says yada yada yada. Now, that seems like it is okay to run NM right through the plastic up to the disconnect, but I wanted to check with you, first."

334.30 Securing and Supporting.
Nonmetallic-sheathed cable shall be supported and secured by staples, cable ties, straps, hangers, or similar fittings designed and installed so as not to damage the cable, at intervals not exceeding 1.4 m (4½ ft) and within 300 mm (12 in.) of every outlet box, junction box, cabinet, or fitting. Flat cables shall not be stapled on edge.

Sections of cable protected from physical damage by raceway shall not be required to be secured within the raceway.

[Ole Anderson]

Thanks Phil, I also came to that conclusion, but my real question: is that out the door because the conduit is outside in a wet location thereby requiring wires that are rated for a wet location (romex isn't as I understand). And is being in a sealed PVC conduit then make it ok?

[Phil Thien]

Thanks Phil, I also came to that conclusion, but my real question: is that out the door because the conduit is outside in a wet location thereby requiring wires that are rated for a wet location (romex isn't as I understand). And is being in a sealed PVC conduit then make it ok?

Oh, good point!

Well installing the extra box removes all doubt, I guess. No way you will have any disagreement from an inspector over the extra box and switching media.

[Anthony Whitesell]

I had never given any thought to NM in PVC conduit in a wet location. What about running UF-B instead of NM-B? 340.10(3)

You will have to put the transition in the dry side. How far between the panel and the transition? Does it make more sense to add more PVC conduit and THHN and run it to/from the panel?

[Art Mann]

People run insulated single strand copper wires underground in conduit all the time to places like well pump houses and out buildings. In fact, that is how underground service to new houses is done around here. Why would it not be acceptable to do it in your case? There may be special rules about running double insulated wires in conduit in some locations but I haven't come across it yet.

[Julie Moriarty]

Seems silly in that the pvc conduit is watertight.

Electrical PVC isn't watertight. I thought it was until, when as an apprentice, I was told to blow the water out of the pipe before we pulled the wire. And then the next and the next and the next. It wasn't just that job either. Practically every underground PVC conduit run I've ever been involved pulling wire through was wet.

[Anthony Whitesell]

Electrical PVC isn't watertight. I thought it was until, when an apprentice, I was told to blow the water out of the pipe before we pulled the wire. And then the next and the next and the next. It wasn't just that job either. Practically every underground PVC conduit run I've ever been involved pulling wire through was wet.

I was perusing the NEC regarding this install (as I have a similar task to be done this summer, but I will be using UF-B) and the books says the inside of the conduit in a wet condition is considered wet. I guess you have helped us find out why. FWIW. It also says that conduit in wet locations is required to be self draining.

[Steve Meliza]

Practically every underground PVC conduit run I've ever been involved pulling wire through was wet.

Do you think it was ground water seeping through the joints or humid air condensing on the cool pipe walls?

[Art Mann]

What I have seen with underground service installations is the people who bury the conduit seldom make provisions to prevent rain or runoff water from getting in there before the wires are pulled. As for the smaller grey plastic conduit, it isn't very different from PVC plumbing pipe. Obviously, you can make it absolutely waterproof if you glue the joints and seal the ends adequately. That is especially true in the OP's situation because the conduit is above ground. I think the real issue is whether the practice is acceptable to the inspector. The answer to that question is probably as easy as a 5 minute phone call. I would not go by what the NEC says because the final authority is the utility inspector.

[Frank Pratt]

What Julie said. My experience has been the same. No matter how well the PVC is glued, moisture always seems to get in, either by seepage or condensation.

[Bob Coleman]

Back when I was familiar with this sort of thing, out here "sections of cable" was interpreted as less than two feet. FWIW.

[Jeff Fischer]

My electrician explained to me that watertight fittings were needed for use with NM cable in conduit outdoors, and the water tight fittings were necessary due to the paper wrapping the ground wire possibly getting damp/wet could cause corrosion and could lead to shorting and fires. This was not for an underground use, just a ceiling fan and lighting in a covered porch setting outdoors, above ground.
HTH,
Jeff

[Ole Anderson]

I ended up running NM in the 3/4" PVC conduit about 18" above grade under an eve. Fittings were glued and the pull ell coming out of the house was gasketed and no belly in the run. Thanks for all of your comments. As always a little touchy not getting a permit, but like many of our small shop projects, the permit could cost more than the materials, not to mention the time factor. Really needed it done today.

[Julie Moriarty]

Do you think it was ground water seeping through the joints or humid air condensing on the cool pipe walls?

Usually it's ground water seeping in. That job I mentioned when I was an apprentice had miles of 5" concrete encased PVC. The pipe was completely full of water. The pipes went from manhole to manhole and I only remember one occasion water in the manhole was above the pipe level. I asked the journeymen I was working with how concrete encased PVC, that I knew was well glued together (because I did most of that) could fill with ground water. I got answers like, "You think concrete is waterproof?" or "It's not plumbing pipe. We don't use a cleaner and the couplings aren't designed to be watertight."

I did hear some guys talking about condensation but most of the time there was so much water, sometimes dirty and sometimes silty, that it had to be seeping in. I've sopped the joints with glue to see if I could create a watertight environment but when we came back to pull the wire, water and sometimes dirt had seeped in. After a while, I stopped trying to prevent it and just accepted it as fact.