I'm replacing some electrical wiring in a shed attached to my house (it's in an enclosed area under the deck with a cement slab. It has doors and windows. It's not wet, but it isn't a sealed area like it inside the house (lots of gaps around the shed door leading to the outside). I'm guessing it qualifies as a damp area. The existing wiring was just NM sheathed cable stapled around the walls.

I'm planning on using one of these boxes:

PVC Electrical Box with 1/2" threaded knockouts

It's a single-gang PVC electrical box with 3 threaded 1/2" knockouts (top, bottom, and back). Presently the NM sheathed cable (coming from the house) just sticks out through a in the wall. I'd like to place this box on the wall where the NM sheathed cable comes out, and terminate the NM sheathed cable in it. However, I should probably install some sort of strain relief. I can think of a few options:

  1. Push in plastic strain relief. I think those are made for metal boxes though. I can't really get them to fit a threaded hole
  2. Metal threaded NM clamp. The threads don't really fit the PVC threads all that well. I'm also not sure if the clamp would need to be bonded.
  3. Threaded nylon strain relief: threaded strain relief This kind of seems like overkill. It would have to go inside the box.

Am I using the wrong box?

  • 2
    You're using the wrong cable NM is not rated for outdoor use, period.
    – Ecnerwal
    Commented Feb 27, 2023 at 0:17
  • 2
    Why not use metal boxes? The cable choice might be iffy if just the door/s are not weather proof. Metal boxes have better grounding choice and fire resistance to plastic for similar cost.
    – crip659
    Commented Feb 27, 2023 at 1:25
  • @crip659 - I wasn't sure if regular metal boxes were OK for damp locations. I could use aluminum boxes with threaded knockouts--but then I'd have the same problem I have now.
    – watkipet
    Commented Feb 27, 2023 at 2:29
  • @Ecnerwal -- Thus the reason I'm switching out the wiring. I don't have access to the location the wire comes from. From the shed, it goes straight into (what used to be) the exterior wall--right through the siding into the joist cavity (up and over some architectural elements). I can draw it if you'd like.
    – watkipet
    Commented Feb 27, 2023 at 2:32
  • Does this answer your question? what kind of cable connector do I use on an outdoor junction box?
    – Armand
    Commented Feb 27, 2023 at 4:53

1 Answer 1


(posting as answer to include photo)

I think "hubs" may be the term rather than knockouts, as these are threaded. A better-quality "weatherproof" box (metal) should have hubs with good threading, and plugs for the hubs you aren't using. The metal threaded NM clamp should fit the hub threads fine, or allow you to later run conduit, whether metallic or something like nonmetallic liquid tite.

enter image description here

  • how to include photos in Comment section: i.sstatic.net/303eY.png
    – Traveler
    Commented Feb 27, 2023 at 4:33
  • @Ruskes Yes, but how do I get the photo as an i.stack.imgur.com file without pasting it in an answer?
    – Armand
    Commented Feb 27, 2023 at 4:39
  • Show me the link where you got your photo originally, since stackexchange automatically coverts it to imgur
    – Traveler
    Commented Feb 27, 2023 at 5:28
  • example hvacrschool.com/wp-content/uploads/2017/08/…
    – Traveler
    Commented Feb 27, 2023 at 5:30
  • 1
    @Armand, simply put the link to the image (at its original location) into your comment. Works a treat. There's no need for imgur to host it when someone else is, particularly if it's just a comment.
    – FreeMan
    Commented Feb 27, 2023 at 13:59

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