I have a structural steel stud condo with 5/8 Fireguard Sheetrock wall. Ref the picture below - I am wondering about grounding requirement given the metal box + steel stud + ENT. There are three conductors in the ENT, (W, B, G; 12 gauge THHN). The outlet at bottom (green) is original with a grounding screw on the box. The NM 2-gang outlet box (blue) is for a light switch and receptacle. The switch will feed the metallic sconce box at top and another one.

Given that none of the metal boxes at Lowe’s seem to have grounding screws, I’m wondering what to do with the ground wire in the sconce boxes, or if I should switch those to NM. My difficulty is that this is a 1hr firewall and that 11gauge steel studs SUCK to work with.

Any and all advice appreciated. This is a short-term vacation rental on coastal Carolina.

various outlet boxes in wall

Edit: this is the wiring I’m planning to follow - switch is a Lutron Caséta dimmer, and will be powering LED bulbs.

  • 2
    I'm going to bet that you need to use a metal box in this wall, not a wood-frame residential blue plastic one. How many stories is this condo building?
    – Ecnerwal
    Dec 30 '19 at 0:16
  • 3 stories. The only 18 of the 50+ units are steel stud, the rest are wood frame - our part of the building was rebuilt after a hurricane.
    – benmarks
    Dec 30 '19 at 12:24

As for grounding screws, you buy a bag of 50 of them (or generic 10-32 screws), and the (threaded) holes for them are in virtually every metal box, usually in a "dimple" so that the grounding screw can be screwed in even if the back of the box is hard up against a wall as mounted. They are not supplied with the box.

  • Ah, I was using a screw from an outlet, but after your advice I see what you mean!
    – benmarks
    Dec 30 '19 at 15:19

Forget about plastic boxes, they are a wild misfit. They are generally kitted up to nail to wood joists. Can't nail to a steel joist.

Your best bet is a metal box. As Ecnerwal says, virtually all metal boxes going back 50 years have a smaller-than-the-others hole. This is pre-tapped #10-32 for a machine screw of that size. That is your ground screw. The boxes don't include them, because EMT, IMC or Rigid surface mount work doesn't require them. I have a factory full of EMT with hundreds of steel boxes, and not a ground screw among them.

Any 10-32 machine screw will do, or if you're fancy, you can go for the green ground screws they sell in packs of 10 for a buck.

As far as Smurf tube, conduit is awesome. Go with what is already in the building, unless you want a class act, in which case EMT is hard to install but very, very easy to fit wires into. No inspector will have a problem with EMT here.

  • Swapping some of the original metal boxes for plastic due to rust (esp by the door), but yes, I agree they are a bit... wobbly. Sticking with smurf for now, but agree EMT is better, especially when I have to pull the 3/1 6 gauge THWN for the range.
    – benmarks
    Dec 30 '19 at 15:22
  • 1
    I asked a separate question based on this
    – Machavity
    Dec 30 '19 at 16:40

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