I'm replacing my kitchen, and as the sheetrock is removed, I got to see that the electrical wiring needed to be upgraded (lots of outlets sharing the same wire, not to mention bedrooms share the same wire with those as well...)

My house is in California and I've got a crawlspace. So I thought I would "simply" run wires from the outlets to the subpanel via the crawlspace.

(see picture: the 2 vertical wires go from the crawlspace to the house and will feed 2 outlets)

At the store I picked UF-B cables (20amps/12 awg) because it said "outdoor", so I imagined it would be stronger than indoor. After installing everything (of course) (which took 2 days + hundreds of $), I'm worried I picked the wrong kind of cables. So I searched the net and found lots of different answers.

These are example different things that I have read:

  • NM cables are ok in a crawlspace if it's dry
  • UF-B cables are not ok unless the crawlspace is damp
  • UF-B cables can become super hot (when not buried), so you should not use them in aluminum conduits
  • UF-B are ok in a crawlspace

So I'm a bit lost. I did NOT use conduits in the crawlspace (I tried to but after a few feet it was too hard to push the wire into the conduit, and I have like 30 feet). Also, I did NOT bury the wires, I just "stapled" them to the joists.

Note: My crawlspace is dry where the cables are (but damp elsewhere).


I've got a bunch of questions about this situation:

  • Regarding the heat: if the cable is hot and stapled to the joist, is it likely that the joist is going to burn?
  • What about where the cable goes through the wood (from the crawlspace to behind the drywall)? (see picture, I imagine the wire is in close contact for a few inches with the wood, so higher risk of damage if excessive heat)
  • Close to the subpanel there are lots of cables (and not so much space available to space them), is that an issue as well wrt. heat or should I not worry about it?
  • instead of this installation, I was thinking of keeping the majority of the UF-B lines that I ran in the crawlspace, but split the lines into NM wires just before they enter the floor (through aluminum conduit). This wouldn't take much longer since I could reuse the work
  • Despite that everything is probably not "by the book", should it be safe? Or would you redo the whole installation?
  • If I had to do everything again from scratch, what would be the proper way?

cable to switch

  • 1
    I am not an expert, but there are a few questions on here about using UF-B in a house. Most times in the last couple of years where because the people were doing wiring, went to buy NM-B but found they needed another mortgage. They then saw the cost of UF-B and it was a steal. The only bad thing I heard about using it was some makes were a pain to strip the ends.
    – crip659
    Commented Dec 13, 2022 at 11:44
  • Is the subpanel on an outside wall? Commented Dec 13, 2022 at 12:46
  • 1
    You've done the easy part. Wait until you start trying to strip back the water tight sheath on that UF-B to get to the wires inside! That is the hard part! Though, you should be pretty good at it by the time you're done. Lesson learned, though, ask before buying!
    – FreeMan
    Commented Dec 13, 2022 at 13:15
  • Do you need to be concerned about rodents gnawing on the cable?
    – Hot Licks
    Commented Dec 13, 2022 at 13:53
  • @ThreePhaseEel it is on the inside of an outside wall. On the outside of the wall there is a main panel (to which half of the wires will go as I'm maxing out my circuit breaker space)
    – Thomas
    Commented Dec 13, 2022 at 21:50

2 Answers 2


First off, there is nothing in the NEC that says that UF cannot be installed in a dry crawlspace, or even indoors for that matter -- 340.10(4) governs in this case. As to heat when stapled to studs or passing through bores, that's generally not a concern unless you're loading a bunch of cables into the same bore and then insulating around it, see NEC 334.80 for details. (Issues with cable damage at staples are due to poor stapling technique that causes cable damage, not due to heat.)


If I had to do everything again from scratch, what would be the proper way?

If you were willing to run conduit, you could have had a much easier time by buying THWN wires, which pull easily, are wet rated, but have to live in conduit, not out in the open on their own. You build the conduit complete, and then pull wires into it. Aluminum is an unusual choice for conduit - galvanized steel is generally stronger and cheaper.

To some extent this also means you can make changes later without having to rip the walls apart.

My personal primary reason for choosing conduit is rodent resistance - I've see way too many chewed-on cables in renovations. You can view that as "fire resistance" as electrical wires with the insulation stripped by rodents (or otherwise damaged) can arc and cause fires. Conduit protects wires from damage, and metallic conduit provides a ground path for any short that happens despite that, ensuring a quick trip of the breaker.

  • yeah I did purchase conduits for the rodents originally (although there doesn't seem to be any). I just was not aware that only specific kinds of cables would work with conduits. (I didn't know about THWN) :(
    – Thomas
    Commented Dec 13, 2022 at 15:46
  • 2
    @Thomas THWN is individual wires not a cable. So instead of trying to force a cable that's stiff because it has 3 wires reinforcing each other against bending you only have to feed 2 (the metallic conduit is ground so no need for a 3rd wire) separate and thus much more flexible wires through. Commented Dec 13, 2022 at 21:59
  • 1
    ..you can feed as many as 6 or 8 in (before getting into derating issues) if you have 3-4 circuits that can be served by one run of conduit, at least part of the way. And they will still pull easily. Wire: - metal core, solid or stranded, with or without insulation. Cable: several wires grouped by an additional layer of material around the outside, bundling and grouping the individual wires.
    – Ecnerwal
    Commented Dec 13, 2022 at 22:47

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