Romex (NM) in PVC Conduit

[lkaufman]

I have a deck attached to my house and want to run a dedicated circuit to several new receptacles alond the perimeter. Is it permitted to run 14/2 NM inside of 3/4" PVC conduit underneath the deck. The PVC conduit would obviously terminate inside a PVC recetacle box. I would like to avoid having to run THHN and then transition it to NM inside the house back to the panel. I also am looking for the added protection of PVC as critters have been know to eat thru UF.

Thank you

 

[dpc]

Article 334 of NEC does not specifically address pulling NM cable in conduit, but I don't see why it would be a problem.

However, NM is listed only for dry locations. Since it will likely be damp under the deck, I think NMC would be more appropriate.

 

[lkaufman]

Thank you for the info. If NM will be in conduit, and all the connection watertight this should sufice? Also, does the NM need to be derated as it is in conduit?

Thanks

 

[dpc]

I don't think any de-rating is required for a single NM cable. But I'm not as optimistic about being able to keep moisture out of an outdoor PVC conduit system. I'd assume it was a damp location, especially if you have boxes involved. Moisture will condense inside even if it's sealed.

Don't forget the GFCI receptacles.

 

[lkaufman]

Thank you for the info. I was planning on using a GFCI breaker instead of a GFCI receptacle with additional receptacles on the load side.

 

[peebee]

A couple thoughts:

1) PVC deteriorates in sunlight. If you have any sunlight exposure, go with metal conduit instead. Also -- the squirrels around my house eat big holes in the plastic trash cans here -- I doubt the PVC conduit would stop them either. Might be another reason to go with metal conduit.

2) Check your local codes before you intall any PVC or Romex anywhere. Generally, they are prohibited in most cities, allowed in rural areas, and it's hit-and-miss in the suburbs.

3) Careful with the GFI breaker feeding multiple outlets. Keep in mind that the more outlets you put on the breaker, the more ground leakage current you'll get at each outlet. On a foggy day or dewey morning, you might experience a lot of nuisance tripping. You'll have much less problem with nuisance tripping if you put an individual GFI outlet at each location.

4) Romex, having a PVC jacket, will also deteriorate in sunlight. You might want to consider type SE cable or USE cable, (which are very similar to Romex) if you don't install this in conduit.

 

[dpc]

peebee,

Not sure where you live, but I have to disagree with some of your comments.

Sunlight resistance PVC conduit is approved for outdoor use, and is used all over the place. I agree it probably won't last as long as steel, but under a deck, I don't think it is going to see much daylight anyway. I don't use it for commercial or industrial outdoor use, but I would have no problem using it under my deck.

PVC conduit may be prohibited in some large cities, especially for high-rise construction, but it is used extensively in large cities and everywhere else all over the US.

Also, Romex (NM) cable is perfectly acceptable over vast parts of the US for residential wiring, which is what we're talking about. Again, there are some large cities, mainly in the East that might require conduit systems, but that is a minority.

I do agree that GFCI breakers can be problematic for long outdoor branch circuits and may cause nuisance tripping. With low cost of GFCI breakers these days, I'd use one at each outlet.

Cheers,

dpc

 

[peebee]

Re: PVC & Sunlight -- I didn't realize sunlight-resistant PVC was available (I don't use PVC too much). BUT -- it's certainly not ALL sunlight resistant -- you gotta check the label on it!!! From

http://ulstandardsinfonet.ul.com/scopes/0651.html

, (Schedule 40 and 80 Rigid PVC Conduit, UL 651) "1.4 Schedule 40 rigid PVC conduit and fittings are for aboveground use indoors or outdoors exposed to sunlight and weather, and for underground use by direct burial or encasement in concrete.Schedule 40 rigid PVC conduit, elbows, and other bends, marked in accordance with 20.9 are suitable for use only underground by direct burial or encasement in concrete." The second sentence makes it clear that not all PVC can be installed in sunlit areas.

Re: "but [PVC conduit] is used extensively in large cities and everywhere else all over the US." That's a bit of an overstatement. It's certainly permitted in many many places. But not everywhere all over the US. There are plenty of jurisdictions that recognize it for underground use ONLY. Even in residential locations. And I did realize his porch was probably in a residential location, but thanks for clarifying that.

Re: "Also, Romex (NM) cable is perfectly acceptable over vast parts of the US for residential wiring, which is what we're talking about. Again, there are some large cities, mainly in the East that might require conduit systems, but that is a minority." Dude, all I said was check with your local AHJ first. Again, there's plenty of places where it's ILLEGAL to install either Romex or PVC conduit. If I wasn't aware of this, I wouldn't have suggested SE cable now, would I?

Knob-and-tube is listed in the Code too. But there's not too many places that would let you put it in these days, even as an extension to an existing system. Many (most?) jurisdictions AMEND the code to PROHIBIT many installations that NEC indicate are A-OK.