I have a house built in the 1950’s with fabric covered NMC wiring still present in most circuits. Those original wires are all 12/2 with no ground. I am currently in the process of replacing some of my old switch loops with new 12/3 romex from the light fixture to the switch box in order to bring in a neutral for “smart” switches. The existing switch box is metal.
I want to go from a typical switch loop (ignore the green ground wire in this diagram, my old wiring only has line and neutral)
To one that supplies neutral from the fixture to the switch box
My question is, what is the proper way per NEC to terminate the ground wire inside the new 12/3 romex? The light fixture itself has a ground wire that is currently floating. Should I leave the ground wire disconnected and just cap it by itself? Should I attach the ground wire at the fixture to the ground at the new cable in the event that ground may someday be brought to that receptacle? (This seems more dangerous to me since it’s definitely not currently grounded.) Should I clip it up to the romex jacket and pretend it isn’t there?
I know the technically correct thing to do would be to pull new 12/2 wire from the existing fixture back to the panel (basically rewire the whole house), but that is not economically feasible. I am looking for the most code-compliant way to handle this ground wire, but I am not having any luck searching through the 2017 NEC. Any advice on the proper way to handle my scenario would be appreciated, especially if they can point to the relevant section(s) of the electrical code.