Electrical – What conduit to use for later use

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Reference picture below.

The electrical boxes for the switches can be adjusted in/out for different thickness of drywall.

I want to run conduit from the 2-gang switch box though the top-plate and into the attic for about 3 feet. The reason is so that I can come back later and run NM cable to the switch box. The conduit must allow the box to be adjusted in/out to meet the thickness of the drywall or other wall covering.

  1. Does the NEC allow this?
  2. If so, what options are available?

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Revision:

I am undecided on the wall covering at this point. At least 5/8 Type X Drywall. Had considered maybe 2 x 5/8 Type X Drywall for sound.

The box is Arlington Industries FA102:

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Best Answer

NM-B ("Romex" is a brand name...) in conduit is a pain. Conduit fill calculations treat "oval" cables like a round cable of the largest dimension, so if you need more than one you need HUGE conduit.

So, use a junction box in the attic to transition from NM-B to THHN in conduit, which makes life MUCH easier.

Properly attached rigid conduits (which can be a confusing term, since "rigid" (RMC) is the heaviest class of steel conduit, but in this case I mean "non-flexible" to include IMC, EMT and PVC) will not allow much, if any flex, since it's supposed to be attached near boxes/termination points.

So, you need a flexible product. ENT or "smurf tube" is a corrugated plastic conduit. ENT picture from Carlon

Flexible metallic conduit (steel or aluminum) is also reasonable. Flexible aluminum conduit picture from home depot

Liquid-tight flexible conduit is probably acceptable, but insanely expensive and something you don't need, so it's unreasonable.

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