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starrapido 11-27-2012 01:11 AM

Romex in Conduit Outdoors
I have been reading threads regarding romex in conduit and romex in wet/damp locations and how they are a no-no. I was going to install some outdoor GFI outlets and a couple of lights under a deck and was wondering why I could not use Romex NM in 3/4" sch 40 grey conduit.

If the romex got wet ot GFI's would they not trip and so prevent any danger??

Also I read over heating might occur, but if I used 14/2 Romex in 3/4" Sch 40conduit I doubt it would get to temperatures above 90 degrees celsius or as warm as romex that ran through onsulation or insulated areas.

What am I missing? Is it dangerous or just code being overkill? I am not a licensed electrician just a DIYer so any advice is greatly appreciated. Thanks.

mpoulton 11-27-2012 01:42 AM

Romex (NM cable) is not rated for use in wet locations because the jacket, paper liner, and (arguably) conductor insulation isn't designed to be water resistant. It's not an issue of some sort of temporary problem that a GFCI would fix - the problem is that the cable degrades and can eventually fall apart if it stays moist. When a conduit is installed in a wet location, the inside of the conduit is also considered a wet location. This makes sense in practice, because conduits DO NOT keep water out. Sometimes they even accumulate condensation inside them. Basically, conduit provides only physical protection from damage, not protection from environmental conditions. So if you can't use NM cable in a certain location due to water, putting it in conduit doesn't help. Note that there is usually no reason you can't run NM in conduit - but it's hard to do and only provides protection from damage.

UF cable is made specifically for this kind of situation. Use it instead.

bob22 11-27-2012 06:33 AM

Or use THWN individual wiring in conduit.

electures 11-27-2012 10:00 AM

My vote is for UF.

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