TOPIC: GFCI in non grounded house

If a house has a non grounded system and you install a GFCI outlet, will the GFCI trip (work) if the power supply deviates? In other words, does the GFCI provide any protection if it is not grounded?

No, because the system is not grounded.

Doesn't the built in circuitry of the GFCI detect a current fluctuation and shut off the power at that outlet?

Qoute is from Propex Consulting:

"Normally, the difference in potential between the hot and neutral conductors is zero. The component in a GFCI device that monitors current and senses an imbalance or difference between the current flowing out on the hot conductor and the current flowing back to ground on the neutral conductor is referred to as a differential current transformer. In the event that some of the current returning to ground is passing through you instead of the neutral conductor, the transformer will sense the imbalance and open the internal contacts to stop the flow of current through the GFCI device and through you. This also explains why GFCI receptacles (which are three-pin type receptacles) can replace two-pin type receptacles in two conductor wiring systems and still provide ground fault protection. Attachment of an equipment grounding conductor is not necessary for a GFCI device to sense a ground fault and to trip. However, the “test” button function of a GFCI cube-type receptacle tester is designed to use the system grounding to create a difference in potential and to trip causing the receptacle to become internally electrically disconnected on both the hot and neutral sides when the cube “test” button is depressed. In a two-wire system there is no means for the GFCI receptacle to connect to a grounding source through the receptacle’s grounding terminal. This is why depressing the “test” button on a GFCI cube-type will not trip and will not disconnect a receptacle installed in a two-wire system."  ME: AS an inspector, GCCI recepteacle on a two wire sustem, a handheld tester (little box testors?)will not work. Action: TRip the GFCI receptacle using test buttons on the receptacle and then test for current flow using a light or voltage tester. The question here is "how to test" not whether or not the device will function as intended if an event occurs.

I ran into the same problem recently, Stephen. My trip device did not trip the GFCI, but the test button did. One of the pre-typed conditions on my report is "GFCI failed to trip using inspector's trip device". So that's what I put in my report. Upon searching the subject, I found out that when receptacles test "open ground condition", one fix is to install a GFCI per the NEC code book. I'm still confused as to how an ungrounded receptacle (the GFCI) does anything to help the ungrounded condition. My background is in Standby Emergency Generators, and I have wired 2000 amp transfer switches for Lowe's, Sprint/Nextel, and Home Depot, hospitals, colleges, etc., so I have a fairly good understanding about AC power. However, I am still not sure installing a GFCI is better than grounding. We used to say in the Standby business- "when in doubt, ground". No circuit is more powerful than its grounding wire, which I saw lots of technicians try on DC automotive and truck equipment. They would have a 2/0 welding cable for battery charging, and a 14 ga wire for the ground. I always had a hard time convincing them that the 14 ga wire was carrying the whole load.

That's all really helpful information but the essence of my question is: On a non grounded house, will the GFCI prevent shock/electrocution if some lady drops here hair dryer in a sink with running water?