I have a 4" x 1-1/2" octagon box with 1/2" and 3/4" knockouts mounted to a 2x4" rafter in my shed located in Indiana.

I'm putting a NEMA 5-20 outlet in the box and I'll have a switch-controlled 12/2 NM-B going into the box to supply power and another leaving the box to supply power to the next box.

I need to run another 12/2 NM-b past the box to provide power to another box in another location. Unfortunately, as you can see by the picture, the 4" octagon completely covers the 2x4 so there's no room to slide the cable past on the outside of the box.

The options I've come up with:

  1. Run the "passing through" cable through the box behind the outlet. Do I have enough room to do this without over filling the box and is there enough room in the 3/8" grommets to allow this? This seems to be the easiest, at least until it's time to stuff everything into the box...

  2. Repeat the above, but rotate the box so I've got the 3/4" knockouts in the direction of cable travel. Again, not difficult until it's time to put the outlet in the box & put a lid on it.

  3. Drill a hole through the rafter on either side of the box and run the "passing through" cable to the other side of the rafter, then back to "this" side. Note that "either side of the box" could be near the top & bottom of the rafter so the cable makes almost the entirety of its run on the other side of the rafter. Not terribly difficult, but doesn't seem as "neat and tidy" or "professional looking".

  4. Run the cable along the bottom of the rafter as it bypasses the box. The shed will remain unfinished as long as I own it, so there won't be any concern about this interfering with interior covering, however, this wiring is above a loft storage area, so it would be more susceptible to bumps and bangs from boxes and other things being put into and taken out of the loft. Quite easy, but just seems... wrong.

Which of these is code acceptable? As a "bonus", opinion-based question, how would our resident pros do this or want to see it done?

Here's a "head on" view of the box showing that there's no room to squeeze another cable past without going through, behind or below. enter image description here

  • Without running the calcs (late, tired) I'm pretty sure you need a lot more box for the wire count you are running here. And then it gets easy. Octagons are tiny. 4 or 4-11/16 squares, plus raised device covers have all sorts of room.
    – Ecnerwal
    Jul 8, 2020 at 1:54
  • Remembered I have a prefilled spreadsheet. Tired, indeed. 12Ga, that box can have 6 wires - not cables, wires, as typically counted (all grounds count for one, each yoke device counts for 2, etc.)
    – Ecnerwal
    Jul 8, 2020 at 2:02
  • Why not just run the bypassing NM through some PVC conduit that you can clamp to the rafter?
    – Huesmann
    Jul 8, 2020 at 13:45

1 Answer 1


Any reason you can't install a 2"x4"x2.5" deep junction box horizontally at this location and just run your additional 12/2 above the box?

enter image description here

  • Because stupid? It's a box, it goes on the ceiling (well, it was supposed to originally, the rafter mount was an "ah ha!" moment), and well... because stupid... I was stuck thinking inside the octagon. :(
    – FreeMan
    Jul 8, 2020 at 11:39
  • I think this is less volume than needed even without the pass-through cable. 2 for device, 1 for grounds, 2 in, 2 out, 7 - times 2.25 cubic inches.
    – Ecnerwal
    Jul 8, 2020 at 13:02
  • 1
    @Ecnerwal Thanks. The 2.5" deep box is 18.3 cu in so that should be ok. I edited my answer, typed in wrong size.
    – JACK
    Jul 8, 2020 at 14:11
  • 1
    @FreeMan Don't be so hard on yourself.... we've all had our days..lol :-)
    – JACK
    Jul 8, 2020 at 15:55
  • 1
    Have you got actual splices? The description you gave (assuming no pass-through cable) would be (in a normal implementation) 4 wires terminating on the device (power in, power on to next box) with no separate splice to count (all grounds being 1.) The fact that the wires are in effect "spliced" by being on the device is not counted twice.
    – Ecnerwal
    Jul 8, 2020 at 16:45

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