Electrical Wiring in the Home/GFCI's on a 2 wire system
QUESTION: Will a GFCI function correctly on an older house wiring system that is 2 conductor based (i.e. no separate bare/green ground conductor)?
ANSWER: Yes, it will function properly if the wiring is good and the hot and neutral are not crossed.
You need to use the sticker "No Equipment Ground" on the face of the GFCI.
This is the approved way of making a two wire system have 3 prong outlets.
---------- FOLLOW-UP ----------
QUESTION: Thanks Greg, you were very helpful, and very quick. I am surprised that the GFCI will still function (i.e. trip) as designed without the equipment ground (green wire/bare wire) for a reference.
The GFCI monitors for a difference on the two legs (hot and neutral).
Your circuit breaker is looking for a short circuit.
The ground wire ensures a path to ground if your equipment ground comes in contact with the hot side of the circuit.
Lets say you have no gfci protection on a circuit and there is a small short not big enough to trip the circuit breaker. This creates a dangerous situation.
If you install a gfci protector it should pick up on the unbalance and shut the circuit down.
This is why you sometimes get a nuisance trip on a gfci on an inductive circuit. It detects an unbalance.
About Electrical Wiring in the Home
This site answers questions related to home electrical wiring, home wiring, general electrical help,and other electrical questions related to aleternating current (AC). You can find help on the National Electical Code, home electrical issues, wiring electrical outlets, installing lighting, electrical grounding, and general electrical help for do-it-yourself projects not require an electrician. If you do not see your home electrical wiring question answered in this area then please ask your electrical wiring question here