Can I use a GFCI on an ungrounded 2-wire circuit at the terminus?

Question

I mistakenly ran 18ga twin lead through plastic conduit out to power 12 volt lights. Never hooked up. Now I want to power a .68 amp 120V pump on a water feature. Too many 90 degree elbows to be able to pull and replace the wire, I believe.

I read in my 1999 electical manual that I can safely use a GFCI on this ungrounded circuit at the terminus.

1. I want to make sure this is OK.

2. What about making a separate ground via a earth rod at the terminus?

Don't want to create a hazard for anyone of course, but I am trying to avoid having to but a new 12V pump and transformer or running all new service to the location.

TIA

Answer 1

The wire needs to be designed to handle the capacity of the circuit it's attached to, not the device that is plugged in. Otherwise, if anything is plugged into the end, or if there is a short, that draws more power, but not in excess of the circuit breaker, you would have a fire risk. I don't have a copy of the NEC, but to the best of my knowledge, in the US, a 15 amp circuit needs a 14 gauge wire, a 20 amp circuit requires a 12 gauge, and a 30 amp circuit requires a 10 gauge. Therefore, your 18 gauge wire is insufficient to attach to any standard circuit breakers that I've seen.

To answer your second question, you could install a separate ground for the other end of the connection and wire a gfci to that, assuming that the existing wiring were adequate for the circuit.

To fix the conduit, I would eliminate any sharp 90 degree turns and if it runs over a long enough distance, break the run by going up to an access panel.