I'm going to running wire within a twelve inch wide concrete cavity wall. The exterior concrete faces are two inches wide, with each face having two inches of polyiso insulation bonded to it. So eight inches are used up. The middle four inches is where the wiring will go. Plastic outlet boxes are cast into the concrete walls. A cutout in the insulation allows access to the back of the box. Once the wire is into the box, it will be covered with another thinner insulation board, the wire passing through a hole in that board. Once the wiring and insulation is finished, the remaining four inch cavity is filled with sand, thus encasing the wire in sand. At corners which will have vertical concrete "L" shaped columns, 6" thick, the column will be sleeved with either 1" or 1.5" diameter conduit sweeps, so the outside diameter of the sweep is less than one third the column thickness.

I believe I can use regular romex wire for this. Between the concrete, insulation, and sand no air for combustion would be available. The concrete and sand is a fireproof encasement.

Any devil in the details that I'm missing? Thanks

No problem as long as all the locations the cable will be is dry. It cannot be embedded in poured concrete.

TK, would UF be better? Being buried in sand? Just curious. Thanks

I see your point, but as long as the void and sand remains perfectly dry it should be fine. But real good catch, if this sand can ever be even slightly damp for any reasons then UF type cable will be best as Strat recommends.

If one wanted to be conservative and use UF wire, how would one run three and four way switching circuits. I checked and did not find any UF 14/4 wire.

I had thought about having any multi switch lighting circuit be separate, but then so much more wiring is necessary. It seems smarter to carry a four conductor (not including ground) so an unswitched hot wire can share the neutral and ground to pick up outlets along the way of the switching circuit.

Things get complicated so harmlessly. Your experience and help is greatly appreciated.

There is #14-3 with a ground UF cable available, maybe only at electrical distributors, this will work just fine with the 3 ways. 4 wire with ground is relatively new in the NM cables, and not so popular in UF series, using UF will use just a bit more traditional method.

More 2 wire with ground will be needed.

Sand in a concrete cavity will evetually become damp especially if the concrete exterior is exposed to the windward side.

To use sweep conduit to go in and out of the back of a box, the radius is too large to be well accommodated within the cavity. For just direct box to box runs, can one substitute a tighter curved plumbing pvc ninety? Does conduit always imply metal boxes? Are there plastic boxes for conduit?

For recessed lighting cans embedded in a concrete slab (served by conduit), where can one find them, or is it possible to use like a juice can to cover a regular recessed type fixture?

I don't know about now, but 20 years ago when worked for a wire and cable manufacturer, the only difference in any of the Romex, NM, UF, UV resistant, etc. was the print wheel we labeled it with. As long as code doesn't require it, use whatever you can find. The wire was tested differently but always passed.

Can PVC be heated to position, and pull wiring through coduit completely. No Romex.