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I need to figure out what size box to mount in the corner where the wall meets the ceiling (actually, a soffit) inside my garage. I'm going to have one 2" conduit entering from the top, carrying 6 (5, if I share the neutral) 1/0 wires, separating them into two 2" conduits exiting from the bottom going to 2 separate subpanels.

+------|2"|------+
|    ___/\___    |
|   /        \   |
+-|2"|------|2"|-+
  |  |      |  |
+-|  |-+  +-|  |-+
|panel1|  |panel2|

Looking at 314.28(A)(1) it seems that the only size that matters is the vertical that needs to be 8 times 2", which is 16". The ceiling height there is 80", and the panels are 39", so that should work. However, I'd prefer a slimmer box on the top and to spread the panels a bit, so I'm wondering if I can use a wire trough instead:

+------------------|2"|------------------+      +-|2"|-----------------------------------+
|    /--------------/\--------------\    |  or  |  \\======\-----------------\           |
+--|2"|----------------------------|2"|--+      +---------|2"|--------------|2"|---------+
 +-|  |-+                        +-|  |-+               +-|  |-+          +-|  |-+
 |panel1|                        |panel2|               |panel1|          |panel2|

From 376.23(A), it looks like I can use Table 312.6(A) and get away with a 4"x4" trough for the 1/0 wire. If so, I still have a question about the length of the trough. Should I be sizing it as for an angle pull box and have the minimum of 6 times 2" between the top and the bottom holes? Or that doesn't matter as long as I deflect the wires at least 30 degrees?

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    I use wire troughs or gutter all the time the advantage with gutter is you don’t have to derate until 30 current carrying conductors but the max fill is 20% usually easier but you still need it to be large enough for the bend.
    – Ed Beal
    Nov 4, 2020 at 23:30
  • 2
    How about running 2" conduit direct from each box to the meter-main? That also gets you around the 310.15(B)(3)(a) derate, and allows #1 instead of 1/0, which in turn allows much smaller conduit.
    – Harper - Reinstate Monica
    Nov 5, 2020 at 0:04
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    How long is the 2" nipple carrying the wires from the outside into the back of the trough?
    – ThreePhaseEel
    Nov 5, 2020 at 0:34
  • (being a long time lurker, I'm so happy that all my favorite pros are noticing my question :))
    – Dr.No
    Nov 5, 2020 at 0:48
  • I'm fishing FMC through a soffit between finished basement and the upper floor. It is running from one side of the house, where my main panel is sitting in the finished basement, to the opposite side, where the garage is. There's space for one flex 2", but another one might be a problem. I've got the wire already, so it's sunk cost now. The nipple from the soffit to the top of the trough can be any length. I hope to mount the trough on the surface in the corner where the wall meets the soffit, so the nipple hides in the soffit.
    – Dr.No
    Nov 5, 2020 at 1:00

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