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Does MC cable need a raceway, e.g. PVC conduit, when passing from a crawlspace through a mudsill and stucco and terminating in a surface-mount exterior receptacle box?

I am going to install several receptacles surface mounted to the exterior stucco wall of my house at the height of the rim joist. I am using MC cable for this circuit, running it through the crawlspace, the rim joist, the stucco wall, into the back of a surface mounted 1-or-2 gang weatherproof outlet box.

I repurposed a picture below to illustrate. Can the orange "hole" through the rim joist/stucco be just a hole or do I have to provide conduit protection. If I use conduit, the conduit becomes the interface to the back of the box, and how/do I need to secure the MC cable sheath to the box as well? What kind of PVC termination does there need to be at the free end of the conduit inside the crawlspace?

Illustration of MC cable through exterior wall

Image Source

Edit: Added Image Source

aerospark
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  • Is PVC your "go-to" for any and all conduit work, or is there a reason you see PVC as particularly appropriate here? – Harper - Reinstate Monica Oct 21 '20 at 16:24
  • I'm not clear why you would want to put MC cable inside a PVC or other type of conduit. – jwh20 Oct 21 '20 at 16:43
  • MC cable isn't necessarily rated for wet locations. You need to check the 1) cladding; 2) insulation on the wires within the cladding; and 3) the MC/AC threaded connector which you'll screw into the exterior box; to ensure all are wet-rated. It might be easier for you to use PVC & THHN for the penetration and put a junction box or conduit body on the inside; then none of those MC parts has to be wet-rated. If you're doing that, might as well consider PVC instead of MC for the whole run? – Jeff Wheeler Oct 21 '20 at 16:54
  • @jwh20 because the OP isn't a licensed electrician and hasn't read 10000 questions here tagged [tag:electrical]? Better that he ask than potentially kill himself or burn down her house. We get loads of questions that are silly for those who do this daily, but are mystifying to those who are new. – FreeMan Oct 21 '20 at 16:54
  • @aerospark - it is requested that you post your image sources, even if you've edited it before posting. – FreeMan Oct 21 '20 at 16:57
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    Oh, separately, do not put MC inside of PVC or EMT conduit. This doesn't make it suitable for wet locations. You can't take a non-waterproof wire or cable and run it in a conduit to make it waterproof; that's not allowed. It sounds silly, but the rationale is, conduits will get water in them, therefore, the insulators inside them shouldn't degrade when subjected to wet conditions. – Jeff Wheeler Oct 21 '20 at 16:58
  • @Harper-ReinstateMonica Not married to PVC although I would at least have some familiarity with handling it, whereas I have no experience with EMT. I was partially basing my setup on Tester101's answer here: https://diy.stackexchange.com/questions/14600/how-do-i-install-electrical-through-existing-stucco-e-g-old-work – aerospark Oct 21 '20 at 17:10
  • @JeffWheeler Thank you for your response and your explanations! I had forgotten you have to treat conduit in a wet location as being filled with water for the purposes of wire/cable suitability within that conduit. I wanted to minimize the number of interfaces/junctions/splices to make the job more tenable for DIY. I had read that MC cable can now be "clotheslined" running perpendicular along the bottom edge of floor joists, which makes the install much easier: https://www.jadelearning.com/blog/330-15-new-standards-for-installing-mc-cable/ – aerospark Oct 21 '20 at 17:13
  • @FreeMan First of all thank you. I have added a link to the image source. – aerospark Oct 21 '20 at 17:17
  • @jwh20, Per my comment to JeffWheeler, I was hoping to use MC cable throughout the circuit to keep the installation simple. I was hoping to run the MC all the way to the exterior outlet, but my readings here on Stack Exchange clued me in that I have to be careful running cable/wire through an exterior wall, and I can't find an existing question or demonstration of what I want to do here or elsewhere online so I have to ask. Is conduit everwhere + THWN within really the easiest code-compliant way to do this, or, how would you do it? – aerospark Oct 21 '20 at 17:20
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    You can hang PVC conduit under joists perpendicularly similar to the MC. The reason you call that "clotheslined" is the rule `334.15(C)` is actually there to *prevent* occupants from running 12-2 NM-B everywhere and then *literally hanging their clothes from those small cables* and causing damage. That's why it's okay to do it with a larger-gauge cable or one protected by a conduit. Just support the PVC every 4 feet (every 3 joists if 16" OC.) Or rent a joist drill and drill holes, whatever you prefer. You have a lot of options. – Jeff Wheeler Oct 21 '20 at 18:17

2 Answers2

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The outdoor recep does not need to be a "GFCI Receptacle". It can be a plain recep that is GFCI protected from a GFCI device in the nice dry indoors where it'll last a lot longer.

If able, I would stick another junction box on the interior. Now, they make conduit nuts, and chances are the outside box (if it's watertight) has a threaded hole. It takes standard pipe thread, which is used by IMC and Rigid conduit.

So, I would fit a piece of Rigid conduit there. Get it the right length so it screws into the outside box, and pokes through a knockout on the inside box by about 1/2". Either put the inside box on shims/spacers, or have the pipe cut to the right length and have the hardware store thread it.

On the outside box it screws into the box body. On the inside box, clamp it down with a conduit nut.

This will NOT be a valid grounding path so you need to run a ground wire. Use the inside box to switcheroo from non-outdoor wiring method to several THWN wires. (must be green ground, white or gray neutral, and any other color for hot. So just buy a couple feet of by-the-foot THWN.

Harper - Reinstate Monica
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    Basically, er, no, _exactly_ what I did for my wall penetrations this summer. Oh, I added some silicone around the outside of the box against the wall in an attempt to keep water out of the wall (not the wiring). I ran NM-B inside the garage to the box, then out the wall with THHN/THWN or UF-B (two different applications). – FreeMan Oct 21 '20 at 17:47
  • Are you referring to the MC armor not being a grounding means, or the RMC into the outdoor box's hub not being a grounding means? – ThreePhaseEel Oct 21 '20 at 23:12
  • @ThreePhaseEel I feel the RMC would be an unreliable path. You'd be using the conduit nut in the interior box to compress a huge stack of ??? building materials that could slacken over time, leaving the RMC nut slack, and not getting any tooth to get a reliable ground. – Harper - Reinstate Monica Oct 22 '20 at 00:18
  • @Harper-ReinstateMonica -- hm, wouldn't there be two nuts at the indoor junction box though, one on the inside and one on the outside? Or at least, that's my understanding of how it's done – ThreePhaseEel Oct 22 '20 at 01:55
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    @ThreePhaseEel That would be better, yes... but it would require getting the Rigid conduit length just right, so there's threads in the places threads need to be for that to work. Ib believe Rigid is pipe threaded, so it's on a taper. (know alot about that from restoring a riDgid machine). – Harper - Reinstate Monica Oct 22 '20 at 02:08
  • @Harper-ReinstateMonica -- radical idea -- chop the RMC blunt then use a setscrew RMC fitting (Appleton SNTC-50 or equivalent) on the indoor box – ThreePhaseEel Oct 22 '20 at 03:27
  • Harper-ReinstateMonica, @ThreePhaseEel, thanks, this is really solid input. Does the interior junction box need to back up flush with the rim joist or can I get one of those junction boxes with an integral bracket that can be hammered to or screwed in to the mudsill? ThreePhaseEel's setscrew RMC fitting would naturally require a standoff from the rim joist, perhaps a little more than I want to "shim". Just trying to make it so there's not much calculation that has to go on – aerospark Oct 22 '20 at 04:44
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If you run conduit as a sleeve between the cable and the box, the conduit need not connect to the box; the cable however should enter the back of the box on the outside with a clamp / box connector.

If you run conduit as a raceway, connected to the box on the outside, then the simplest thing to do is put another box on the other side of the wall, also properly connected to the inside box. Enter the box with a clamp on the inside, with enough stripped to reach through the wall and terminate on the other side.

batsplatsterson
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