THHN: must it be run in conduit?
I have a bunch of 12 AWG red/black/white/green THHN. I am thinking about using it for some indoor wiring projects, and I don't know if I need to run in through plastic/metal conduit or not.
I have a 20 amp feed on 12 AMG Romex terminating in a metal 4 x 4 junction box in the basement. From this, I am planning to feed two ceiling fan/light combinations controlled from 3-way switches on opposite ends of the room. The round-trip circuit from the main panel (200 amp) would be about 100 feet.
The walls are open (panelling removed; drywall going in later) so access is not an issue. My intention is to not have to spend over $100 on 12/3 Romex.
1. Can the THHN be run like Romex (through drilled holes between joists, stapled to wall studs)? Or must they be run in conduit?
2. If conduit is a requirement, must I use metal conduit?
3. If I can use plastic conduit, may I tie in plastic conduit to the metal junction box which holds the feed?
Thanks in advance.