Redoing my kitchen and installing a new range while also moving the location of the range outlet (thus, I am required to bring it up to code). Existing range is 8/3 with no ground and a 3 prong outlet I will be changing to 4.
There are no other grounding sources nearby that can meet the requirements so I want to retrofit a ground back to the breaker box, which I can do fairly easily as my floor joists have an open structure.
I know that retrofitting a ground is acceptable practice. I know I need a 10AWG ground. I know that the NEC says I can run it unprotected through the sealed floor cavity. The problem is that I can't figure out exactly which type of wire to use.
Local HI stores only have THHN and bare copper. As far as I can tell, THHN can never be run without conduit and after extensive searching I can't find any other single-conductor wiring rated for in wall use. Do I really just run a bare ground 50ft through my floor? Is unprotected THHN acceptable in grounding applications (can't find an NEC reference)? I know it's not dangerous since it's just a ground but it just seems counterintuitive to not protect the wire itself from any basic threats (corrosion, etc.)