Where in the codes doe it state what kind of sheathing is required for wiring through floor joists? I am going to pick a wire to run 220. I assume that single wires coated with plastic is not to code, when I say single wires I am referring to.typical house wiring, white and yellow Romex NM-B Cable, ie the three wires inside it, a bear copper wire and two covered wires and paper. When running wires through joists what is the code configuration? Is sheathing always required, I would assume it is.