Quick question for all the electricians out there. I'm in the states and looking to make a couple new electrical runs for the outside of my house.

The runs will be done inside my crawl space inside schedule 80 pvc. Once I reach the exit point I will drill a hole through the block wall and hook it to an electrical box on the outside of the house.

Here is my question.

Does the wire need to be rated for moisture seeing as how it's under the house, or will the fact that its in the pvc negate that requirement?

  • Thanks I adjusted it as the recommendation and pvc sizing issue are the easiest of the three to figure out.
    – hcker2000
    Commented Nov 29, 2017 at 21:13
  • When you say "runs" and "wire", are you referring to single conductors or multiple conductors in a cable of some sort, and if so, what type of cable?
    – Upnorth
    Commented Nov 29, 2017 at 22:17
  • I was looking at Romex 12-2 wire but I hear that is harder to pull if I need to use conduit. By run I mean I'm going to be doing multiple circuits
    – hcker2000
    Commented Nov 30, 2017 at 0:45

2 Answers 2


Simply use dual-rated THHN/THWN and call it a day

Just about all THHN made and sold today is dual-rated THHN/THWN-2 -- this means that you'll be getting wet location performance "for free" when you use THHN in conduit.

  • Having never worked with THHN wire. I see there is stranded and there is solid. Previous experience with electronics tells me the stranded is easier to pull but what needs to happen at the outlet side of things? I know most have the usual screw fasteners but I'm guessing its not code to just stick the strands under that and fasten it down.
    – hcker2000
    Commented Nov 30, 2017 at 14:46
  • 1
    I did some more research and I guess from what I'm seeing it is ok to just stick the strands under the screw and fasten it down.
    – hcker2000
    Commented Nov 30, 2017 at 20:40
  • @hcker2000 You can also use ferrules to crimp the wire bundle together so it acts as solid wire at the termination. From what I understand, this is common in other parts of the world (and even in the US on PLC control cabinets and heavy machinery)
    – Hari
    Commented Jun 17, 2018 at 2:42
  • 1
    @HariGanti -- ferrules are for use with spring-compression type terminations though (Eurostyle terminal blocks) -- they aren't needed or useful with the screw-type terminations used on North American wiring devices Commented Jun 17, 2018 at 3:09
  • 1
    I just use back and side outlets in both cases of stranded or solid , with both the clamp is solid and there is no need for ferrules I have not had a recall ever with these outlets but have had many calls to repair back stabs over the years.
    – Ed Beal
    Commented Nov 7, 2018 at 3:25

The answer is no. Nor does it need to run inside a conduit. It would not be subject to physical abuse as long as it was kept between the joists. The standard NM cable of today has conductors with a THHN rating. This insulation is rated for damp environment.

  • I should have noted that the majority of the cable has to run along the block wall. Is that an issue? I also know that if I have to go at an angle to the joists it either needs to be run inside a conduit or holes drilled into joists. The underside of the floor is insulated and has a vapor barrier so fastening the wire between the joists means cutting into that, fastening and then closing it up. That might be more work than simply running pvc.
    – hcker2000
    Commented Nov 29, 2017 at 21:30
  • Are you sure you know that? Surface-mounted wiring is permissible in some cases.
    – isherwood
    Commented Nov 29, 2017 at 21:36
  • I was going based off of NEC 334.15 Exposed Work.
    – hcker2000
    Commented Nov 29, 2017 at 21:50
  • 2
    Perhap THHN is "rated for damp" but my NEC 2014 seems to say "Type NM ... shall not be used under the following conditions or in the following locations:...(4) In wet or damp locations." 334.12(B).
    – Upnorth
    Commented Nov 29, 2017 at 22:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.