I am running a 6/3 wire for a hot tub and need advice. Is it better to run the wire inside the exterior wall or have it come out the soffit and run on the outside? Also general advice welcome!

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    Are you using NM (black presumably, with the paper separator), UF (grey stuff, no paper separator), or some type of armored cable? Dec 7, 2021 at 3:17
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    Are you running to a subpanel? Because if so, you may be better off (save $) with aluminum wiring a size larger. Dec 7, 2021 at 3:25
  • If you're running copper NM or UF, you need 6/3. If the lugs on the disconnect are rated 75C thermal, you can run #8 in any other kind of copper, or #6 aluminum. That is because all wires except NM and UF are allowed higher thermal rating and thus higher ampacity. Dec 7, 2021 at 4:54
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    Most cable cannot be run out in the open on the outside of a building without being in conduit or protected from damage in some other way— and some cable cannot be run in conduit. It’s not a question of better, it’s a question of what kind of wire did you buy and how easy is it to access the inside of the wall to pull the wire. Dec 7, 2021 at 5:58
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    NM cable isn't allowed outside at all, so it won't be able to get to your hot tub. If you post some pictures of your proposed hot tub location and where you're running wire from, we might be able to suggest what conduit/wire/cable you need.
    – kg333
    Dec 8, 2021 at 17:38

1 Answer 1


If you're using NM, then you'll have to run it inside the wall

NM isn't rated for exterior exposure at all; if you try, the paper separator will wick up any water that gets in and carry it into boxes, where it'll cause failures down the road. Furthermore, the jacket on NM cable will get damaged if left out in the sun, which'll simply accelerate the deterioration process.

So, you'll need to run the cable inside the wall, bringing it into the back of the "spa box" disconnect/GFCI on the outside wall. If that's not practical, then you'll need to consider a different wiring method.

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