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I've gone over this in my head a few times, and I think this is the best solution given the problem at hand. Just want to get some feedback and see if anyone has an alternative idea.

This is going to be all new electrical for a detached garage, from a 60A sub panel inside the garage. AHJ follows NEC 2017 with no amendments.

I'm planning to use metal boxes that will house 2 duplex receptacles each and run 1/2" EMT conduit between the boxes. Each duplex in a box will be on a separate GFCI protected circuit (two receptacle circuits total) because it is a workshop and in case tools close together need to be operated simultaneously. EMT is probably overkill and I could just use MC, AC, or even NM-B (can't get a clear answer on whether NM-B is allowed for a detached garage); but I think EMT will be a good exercise and I don't mind doing some extra work here.

The garage is unfinished and uninsulated, with 24" OC 2x4 framing along the exterior walls. I don't have current plans to finish the walls but want to leave that opportunity open in the future, hence not running along the surface.

Here is a primitive and absolutely not to-scale drawing of my plan:

Box mounted on blocking between studs with conduit entering bottom

The boxes will be mounted on 2x4s cut to length and screwed between studs. Conduit will travel through holes in the center of the studs and come up to the boxes with 90 degree elbows (based on this table the 90 in 1/2" EMT will be 5 7/8" from horizontal to vertical center, so should be plenty of room within 24" OC framing).

Questions:

  • Is there a better way to mount these boxes when using EMT?
  • I plan to make the depth between the surface of the framing and the front of the box about 5/8" to account for drywall. Is that appropriate for using the crushed corner metal box covers? I can't find any images of a 4x4 box going through drywall and what the cover would look like.
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  • Are the receptacles facing the wood cross member? With a crushed corner box centered you would screw the back of the box to the cross member, humm a solid stick of emt through studs how are you going to put it in? Most of the US allows nmb in garages through bored holes but a guard strip will be needed. MC they usually are ok with exposed. Some things to think on. – Ed Beal Jan 13 at 21:02
  • @EdBeal re: how are you going to put it in? Probably with a lot of connectors. At first look I'm not seeing any MC that has both a white and grey. I want to run two circuits to each box (workshop environment so want each duplex in a box on separate circuits). Can't do MWBC (afaik, maybe I'm wrong) because each run will start with GFCI receps – Ivan G. Jan 13 at 21:33
  • Can't do MWBC with GFCI receps.. but you can use a two-pole GFCI circuit breaker to protect a MWBC. Alternatively, you could use a high-current two-pole GFCI breaker to feed a subpanel filled with normal breakers. (Don't power the lights from that subpanel though; it's no good to have the room go dark when a ground fault happens with a power tool!) – Greg Hill Jan 13 at 22:25
  • @GregHill ok good idea, so a GFCI breaker protected MWBC on 12/3 MC is a viable alternative to using EMT here. I'll have to evaluate how excited I am about bending all that EMT when it comes time for this – Ivan G. Jan 13 at 22:35
  • Can you drill holes through the exterior at the end of the wall? If so then you could feed straight sticks of EMT into the wall from outside. Then you could cut the straight tube and add connectors and pre-formed elbows at each box location. – Greg Hill Jan 13 at 22:48
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If you can drill straight through to run longer chunks (or if not able to, a bunch of shorter chunks, and couplers, and perhaps slightly oversized holes in some studs to facilitate getting them in) you can just run the conduit in a straight line at the elevation you want the boxes at, and run straight into the sides of the boxes, rather than using a bunch of elbows up into the boxes. This does involve working your way along to do the install, since you can't easily insert one in the middle of a run that way. But if you build it as you go, it works perfectly well, and is shorter, with fewer bends.

The "crushed corner covers" are exposed work covers, intended for use without drywall or trim plates. There are different covers intended for use with drywall or plaster, commonly known as mud rings and coming in various depths/extensions - and then used with normal trim plates for the devices to finish the opening around the devices in the drywall/plaster surface.

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  • Of course, there is absolutely nothing in the NEC that prohibits boxes from protruding from a wall – ThreePhaseEel Jan 14 at 1:02
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    Indeed, I'd more likely run a strip of wood/plywood on the face of the framing and mount the boxes and conduit out there - if you insulate and enclose the wall later, the board is easily insulated behind and sheathing/drywall can butt up to it above or below. Just working with the expressed desire to do it in the cavity, but trying to simplify that. – Ecnerwal Jan 14 at 1:16
  • TIL: Mud rings aren’t just for low voltage, and have extensions. This helps out a lot with your idea of running EMT into the sides of the boxes, because I can push the box further back so that the EMT runs closer to the center of the studs – Ivan G. Jan 14 at 1:56
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    A low voltage ring (self-mounting to drywall) and a mud ring for a box (screws to the face of the box) are different...as I hope you learned when you went looking. – Ecnerwal Jan 14 at 3:09
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    @IvanG. they make stand-off mounts for EMT that will (I think) hold the conduit at the right distance from the wall for it to feed directly into the knockout in the side of the box. This would eliminate needing to put an offset on each side of every single box and would cover securing the conduit to the wall at the same time. – FreeMan Jan 14 at 14:40

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