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Discussion Starter · #1 ·
Hi Folks,

We are adding an outdoor lampost in our backyard. The plan is to tie into an exterior GFI outlet, add a weatherproof switch, and run the wire to the lampost. To get around the concrete patio, I need to run the wire about 6' horizontally across the exterior of the fireplace, before I can go down and run out to the lamp post.

I'd like to use 12/2 UF in the trench to the light, but obviously will need conduit on the back of the house where the wire is above ground. I am planning on using 1/2" PVC conduit. I know that you're not supposed to run UF or NM cable in a conduit because of temp issues.

So, if I run UF cable from the light, can I just strip off the sheathing and run the conductors in teh conduit when I get above ground, or do I need a box to transition from THHN to UF? Or do I need to run conduit the whole way?

While I'm thinking of it, is code still min 18" below ground?
 

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It is fine to run the uf through the pvc to the box.
Do not strip the uf to run in the conduit.
If the uf is gfci protected, then 12" is ok.
 

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I know that you're not supposed to run UF or NM cable in a conduit because of temp issues.
This isn't really true. The fill calculation is based off circular area even for flat cables, so you can't put very many in a conduit, but other than that, there's not really a problem.
 

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This isn't really true. The fill calculation is based off circular area even for flat cables, so you can't put very many in a conduit, but other than that, there's not really a problem.
He's right. You can run romex/UF in conduit, as long as the fill calculations are met. UF is thicker than romex, so you might want to use 3/4 rather than 1/2 inch, just to make it easier to push or pull through.
 

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Discussion Starter · #5 ·
Thanks for the info! I always thought that NM or UF automatically exceeded fill ruls because of its sheathing, good to know that's not true.

So, if the NEC allows UF in conduit I'm good to go! I will go with 3/4" PVC in that case also.

Thanks!:thumbup:
 

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Why not go all the way with the PVC and use individual conductors? Seems to me like a waste of time to go part way with cable and part way with PVC. Conduit is cheap, and individual conductors are much easier to install (pull). Your call.

Ps....Use extra straps on the exposed section of PVC. It sags something terrible.
 

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I probably will, I feel better with conduit underground than just wire, even if it's down 18"

Minimum depth for buried UF is 24 inches.
 

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Discussion Starter · #9 · (Edited)
Is that 24" for just exposed UF or does that apply to conduit as well?

So happens I got lucky last night...:yes: I was digging the hole for the lamp post base and hit a pipe that almost perfectly bisected the hole...I remembered that it was abandoned conduit that ran out to an outlet for a pool filter the previous owner had installed. I had long ago disconnected the circuit from the box and pulled the wires out of the conduit, but just left the conduit there.

Interesting stuff, looks like 1/2" galvanized steel conduit, but it's not the thinwall you buy at the home center, the walls on this stuff are at least 1/16" thick.

Anyway, cut it with the sawz-all, snaked it through to the basement, and was able to fish #12/2 UF through it. Now I can add a switch inside the back door, and forget that conduit running on the outside of the house.
 

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Ah... I wish all jobs turned out like that. I'd give an arm, or at least some fingers, if every time I needed a conduit somewhere, there already was one empty where I was digging.

There are few things in life that I disdain as much as digging a trench. Even with a machine, it still sucks pretty bad.
 

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Discussion Starter · #11 ·
I had forgotten all about it, we had an inground pool put in about 15 years ago and I know they tore up a bunch of sprinkler pipe when they dug that hole. Turns out the likely path of this conduit misses the pool by about 4' based on where it enters the house. [All the pool wiring was professionally done and inspected, not messing with that...]

We had a concrete patio poured across the back of the house after the pool was put in and silly me never thought about running electric out there for future use...we had wanted a light fixture in this spot for years and I put the job off for exactly that reason, dreading the trench that seemed inevitable....

Interesting when they ran the conduit, instead of coming up the outside of the foundation and through the rim joist with a pull elbow, they ran the conduit straight through the foundation 2' below grade! I had cut the conduit off flush with the inside of the basement wall and left it, meaning to fill it at some poiint but never did. I'm thinking I'll just mount a junction box on the concrete wall over the end of the conduit, connect to NM and run up to the switch.
 

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Interesting when they ran the conduit, instead of coming up the outside of the foundation and through the rim joist with a pull elbow, they ran the conduit straight through the foundation 2' below grade! I had cut the conduit off flush with the inside of the basement wall and left it, meaning to fill it at some poiint but never did. I'm thinking I'll just mount a junction box on the concrete wall over the end of the conduit, connect to NM and run up to the switch.
Really no need for the junction box, just run the UF to the switch.
 

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24 inches for direct buried UF
If it is gfci protected then it can be buried at 12 inches.
Column 4, table 300.5 2005 nec.
 

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If it is gfci protected then it can be buried at 12 inches.
Column 4, table 300.5 2005 nec.
That's interesting. I thought the 24 inch requirement was more to do with physical protection than anything else. 24 inches down and it's unlikely somebody with a shovel will cut your line. Thanks for the code reference. I'll look it up when I get a chance.
 
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