I want to run power from a sconce in our patio to a fan. My original plan is to put UF in conduit. As I’ve been reading I came across condensation issues in conduit. I’m a bit confused about what is the right way to do this.

Should the line from the sconce come out of the box toward the ground and then turn up to the ceiling? Is there an alternative to this?

For a run that will total about 11 feet in total distance do I need a conduit drain or breather or both? If so where is the best place to put it?

Instead of UF I believe I can use THHN as this location is considered damp and not wet. Any issues with that?

Any other things I should be considering?

Thank you!

  • 1
    As noted toward the end of this answer, you will have water in your conduit. Period. Use the proper wire and don't worry about it. Don't pull UF through conduit - it's too much work! As I understand it, most THHN is also THWN which is wet rated. Run your conduit with the minimum number of bends possible - there's a max of 360° allowed in a run before you have an access point. Wait for one of the electricians to confirm all this.
    – FreeMan
    Commented Jul 18, 2020 at 14:26
  • 1
    Would the condensation in the conduit be due to the warmer air from the house migrating through the space around the electrical connections into the conduit? If so would sealing the exiting wire at the house side fix this?
    – Elmo
    Commented Jul 18, 2020 at 14:30
  • I read through the question you marked. I’ll use THHN/THWN. If conduit fills with water how does one keep it from flowing back into the house where non-wet rated wiring is located?
    – Elmo
    Commented Jul 18, 2020 at 14:36

3 Answers 3


Condensation isn't as much of an issue with conduit as water intrusion, usually in buried conduit. But there is no point in running UF in conduit. THHN/THWN (they are almost always the same now) would be much easier to pull and allow you to use smaller conduit. 11' isn't much of a run, so size or difficult pulling probably isn't an issue. Still, THHN/THWN is a lot easier to work with than UF.

I doubt you'll have a condensation issue bc the pipe will be at the same temp as surrounding area. Condensation occurs when things are colder than surrounding area (like a glass of ice water).

  • A few sub-questions. Does warm air from the house leak into the conduit causing issues? Should I seal it with conduit sealer? Can I run the conduit into the sconce box from the top since water is less of a concern? Should I leave the bottom plug of the sconce box off for drainage or does it not matter? The answer in the link referenced by Freeman above states that THHN has to be continuous between boxes. So would it be acceptable to run an additional length of conduit to an outlet from the fan connecting in the fan box via wire nuts? Or does this require another run from the sconce box?
    – Elmo
    Commented Jul 18, 2020 at 14:46
  • You added something here that I need to clarify. Where is the sconce now? And is it switched? If switched do you have power to the sconce and the switch is on a switch leg or does power go to the switch and then to the sconce? Is the sconce indoors or outdoors? How did you plan on controlling the fan? Remote? Wall switch? Commented Jul 18, 2020 at 14:55
  • I agree that pvc conduit is not as big of an issue but emt really connects water above ground but 11’ will not be long enough to have a big problem. Wire nuts at the boxes are fine (no splices inside pipes) the last thhn I got was thhn / thwn2 / mtw there may have been another listing but thhn /thwn has been dual certified for decades. A trick for stranded wire around screws is twist the strands counter clock wise this helps when wrapping around the screw 66-75% .
    – Ed Beal
    Commented Jul 18, 2020 at 15:10
  • The sconce is switched. Power goes from the switch to the sconce. The sconce is outdoors. The switch is always on and the lights controlled by it automatically turn on and off based on ambient light. The fan and built in fan light would be controlled by remote.
    – Elmo
    Commented Jul 18, 2020 at 15:17
  • While I appreciate your thoughtfulness and care on this project, I do believe you are over-thinking this and will be fine. Just run the conduit, use THHN/THWN wire (like Ed said, they are the same for decades now), hook it up and enjoy your new outdoor fan/space! Commented Jul 18, 2020 at 15:23

UF is a bad idea on so many levels - use THWN. Most THHN is also THWN and a few other listings. UF is hard to pull and requires larger conduit in most cases.

All exterior conduit is wet by definition, and in reality.

You can minimize condensation in conduits by using duct seal (a usually gray, non-hardening putty) to minimize air movement, but you can't eliminate it. If you don't go nuts trying to seal up the boxes, any water that forms by condensation will happily leak out.


If you run UF in conduit, the conduit ID needs to be 138% of the widest width of the UF. UF is pretty wide, so that makes the conduit pretty big.

I gather you've done enough wiring to know how ridiculously stiff NM and UF cable are. The stuff you want is THWN, which is individual wires, and if you get it stranded, it's very flexible and an easy pull.

The only snag with stranded is it can be tricky to place on screw terminals, it takes a fairly well-developed skill to get the twisted wires to hold shape as you tighten, and not turn into a bad hair day. You can sidestep that by choosing outlets that attach with pigtails/wirenuts, or use the screw-and-clamp system.

Condensation is because air changes temperature faster than objects. It can happen anywhere. Simply assume that all outdoor conduit is 100% full of water 100% of the time.

  • 1
    For an 11 foot pull, I doubt solid THWN will be a problem at all for the pull, and it can be simpler to terminate.
    – Ecnerwal
    Commented Jul 18, 2020 at 14:48
  • @Ecnerwal Agreed. I only go to stranded when I get to 10ga. wire. Solid isn't bad and for such a short pull, should be no problem, esp. if 14 ga. Commented Jul 18, 2020 at 14:51

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