I have a contractor putting a pocket door in a wall in our 1925 house. He removed plaster from one side of the wall and exposed a single strand of K&T wire right where the door needs to go.

This conductor was feeding a 3-way-switched ceiling light, carrying current routed through our 2nd-story floor, up the wall, through our attic to the ceiling box (where it was simply hanging through a knock-out, no extra insulation, grommet, or clamp). It seems to be always hot, and was attached to the hot wire of our light fixture.

I needed to allow the contractor to keep working, so shut off the circuit (which also feeds several of our original first-floor lights), and then carefully pried off all knobs and pulled the wire -- maybe 25 feet -- through our attic, down the wall, and into the floor cavity (I cut an access through exposed subfloor I'll eventually be covering). I snipped, capped, and taped the end, then rolled it up neatly inside the joist bay while I figured out how to proceed.

I now know I can use the last stud bay on the other side of this wall -- the one that's getting the new door -- to re-route. Originally, I thought about possibly reusing all the knobs and tubes I saved to keep this wire taught and held on insulators just up into the stud bay, where I'd put in a box and splice to Romex to feed back into the attic. But I think it will be difficult to reattach knobs without seriously opening up the floor, and I know I can't make a junction inside the joist bay (or without an accessible box, in general).

I started to think it might be safest, actually, to get non-metallic conduit and run the wire through that all the way from the tube in the floor joist where it's originating to a tube I've put in the new hole I've drilled in the base plate of the stud cavity. I thought this would provide support and protection of this one wire -- the only one in the whole space -- over about 5 feet, and that I could use conduit clamps to keep the entire run safely centered in the joist bay.

But I can't find any reference for whether there would be any safety concerns doing this. I can't imagine it's less safe than trying to reinstall it with old knobs, but just not sure. Wondering if anyone has any thoughts on this.

Thanks