GFCI in non grounded house

[Michael Sedillo]

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?

[Stephen Stange 3270]

No, because the system is not grounded.

[Michael Sedillo]

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

[Stephen Stange 3270]

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.

[Michael A Clark]

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.

[Michael Sedillo]

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?

[Stephen Stange 3270]

Like anything else, "if it is functioning as intended" it will open the circuit thus protecting the woman in the bathtub." How much current she gets, a little or a lot, is the variable. AS an inspector, you are there to test or inspect the devices as functioning or deficent.

You, as an inspector, and in my opinion, would not want to warrant or gaurantee that she will be protected from harm inclusiveley. Any more than if the house DID have a three wire system AND three pronged receptacles AND was grounded.
So either way, the lady, as far as we all know will be protected to some degree IF the device functions as it is intended to function. If she takes a current and the device does not open as it should, what do you think will happen?
But your job is to inspect. Maybe I misunderstood you as my original comments involved the need for special attention will inspecting GFCI functionality in two and three wire systems. 

[Stephen Stange 3270]

Hi Michael. The answer to your reply# 2 is No. A handheld testor works off the circuit ground wire ONLY. That's why wire with an ungrounded circuit (two wire), you test the receptacle by pushing its test button, then check for current with a light or voltage tester to make sure the circuit is open. In other words, on two wire circuits, it is a good practice not to use handheld testers, in my opinion. I'm sure others might disagree, but that's what I do. Challenging ourselves with questions like these keeps us sharp! Thanks.

[Stephen Stanczyk]

Two wire systems MUST be tested using the test button on the receptacle or circuit breaker only.  If it trips using the built in test button, report it as functional and move on.  If your wife throws the hair dryer or radio into your tub, the GFCI protection will be the same regardless if it is a 2 wire or 3 wire system.  Even if you use a 3 light tester or bigger SureTest, always test using the built in button as well.  I always test both top and bottom of the receptacle.  You would be surprised how many will trip with one and not the other.

[Michael A Clark]

Thanks guys. I have an older house that does not have a GFCI in the bathroom. Now if I can just find the darn hair dryer while my wife is taking her bath.....

[Dan Musielski]

YES..Micheal, it still will Work!
The GFCI  measures current incoming on the hot wire and compares it to the returning current on the neutral wire.

[Michael Sedillo]

Thanks Dan, and thanks to all who replied. Dan's answer was the best, he was precise and cogent. "Brevity is the soul of wit".

[Dan Musielski]

Thanks for the compliment Michael...I see your out in the OC.  Love it out there...was trying to plan a motorcycle run there this summer...but they may not happen.  But hopefully will just have to do it without the bike.

[Dominic Maricic]

Dan, don't go too far. I'm going to Chicago in July to do an 8 hour talk!

[Gary L. Rusk]

The GFCI will work as intended. All such installations should be labeled "No Equipment Ground" on each receptacle that applies.

[Dan Musielski]

Dominic- That is Awesome! I will be there:)

[Richard Overton]

As a  note, One recognized solution to installing  3 prong outlets to replace 2 prong ones in houses with no ground wire, is to install a GFCI outlet at the beginning of the branch circuit (first outlet from the panel)wired correctly with line and loads. All down stream outlets must be labeled non grounded GFI protected. These labels come with the GFIC in its box. All down stream outlets are protected and the gfic will still work as a ground is not required for it to function properly.

[doug diller]

This was a really helpful discussion. Thanks for everyones input.

[James A. Wood]

I agree this is great information. Thanks to all who put there experience out there for others to learn from.