I have installed 9 "QuiteWarm Radiant Heat Film for under subfloor" to heat the floor above a crawl space off the the basement. The crawl space has a concrete slab and is tempered. This subfloor system is a 120v. system, with a total load of 900 watts, 7.5 amps for the 9 panels. Each radiant heat film panel comes with a separate black and white 12 ga. wire. The instructions say to run all the wires (black and white)to a junction box, wire them in parallel and run a 12/2 Romex to the Thermostat. The Thermostat gets power from a separate 15 amp breaker circuit. The thermostat has a built in GFI. My question concerns the single 12 ga. wires from the film panels to the junction box. Can the single 12 gauge wires be run exposed in the crawl space(fastened per code along joist or 2x6) or do they need to be put in conduit or something else?. Thanks

  • 1
    Where do you live? At minimum I would suggest to use UFB wire since a crawl space is technically a wet location and is exposed to the elements/wildlife. If you have a rodent problem and fear it will get chewed then use conduit.
    – MonkeyZeus
    Dec 14 '20 at 18:53
  • By "single wires" do you actually mean the cable (what you call "Romex")?
    – isherwood
    Dec 14 '20 at 19:06
  • @MonkeyZeus, you can't make that assumption about crawl spaces. Many I've worked in are every bit a basement including floor slab, albeit with shorter walls.
    – isherwood
    Dec 14 '20 at 19:09
  • As I understand you, each panel has 2, shortish, individual #12 wires that you then connect to the "house wiring". Are you asking about these short, individual wires, or are you asking about the "house wiring" (that I understand you're adding new)? Pics of what you've got would be quite helpful.
    – FreeMan
    Dec 14 '20 at 19:14
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    It is a dry location with insulated concrete walls and concrete floor with access directly from the basement. The crawl is about 4ft in height and has been dry for 25 years and I have not seen any signs of pests. I would say it is no different that a basement only shorter( height). The location is in Wisconsin. The 12 ga. wire are single insulated wires that are part of the heating element panel and are each about 20' long. It is not romex. It is similar to one of the insulated wires in 12/2 romex cable but with out the outer sheating.
    – Gene Post
    Dec 14 '20 at 19:32

Yes a crawl space can have your 12/2 attached directly to the floor joists if going along the joist if going perpendicular a rat run is needed for smaller than 2 ea #6 or 3 ea #8 wires see exhibit 334.1 in the code , nmb in this location has been code for decades. Rat run or 1/2” plywood minimum. Note bored holes need no protection.

  • Sorry but this doesn't address OP's concern about the individual cables which come from the panels per "My question concerns the single 12 ga. wires from the film panels to the junction box."
    – MonkeyZeus
    Dec 14 '20 at 20:12
  • what is a 'rat run'? Never heard this expression before
    – peinal
    Dec 14 '20 at 20:54
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    A rat run is a board or plywood nailed to the bottom of the joists when going perpendicular to the joist (or exposed below the joist) sorry it’s an electrician slang term. Placed on top of ceiling joist is the other location the term rat run is used. @ monkeyzeuse as only the op referred to “12-2 cable” and Romex are at the boxes my answer directly answers the question with the code reference. Of wiring in a crawl space as required by code you can say it doesn't answer it but the cable coming from the breaker to the junction boxes go according to my answer and code reference let the OP decide
    – Ed Beal
    Dec 14 '20 at 21:10

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