Properly Testing GFCI Outlets

Mornin All,
I have a question I need with about GFCI outlets replaced in 2-wire systems & haven’t seen this addressed or missed it when it was. I live in Wyoming & there are probably more 2 prong outlets here than in the whole rest of the world. A lot of “wet areas” that I’ve tested that have 2 prong outlets (numerous 2 prong outlets present throughout the rest of the house)replaced with GFCI outlets show “open ground” & won’t trip when challenged with any external tester I’ve tried ( the ones w/black button on top), BUT will when their own “test” button is pushed on the outlet. Is this a “false positive” or am I missing something?? Don’t these external testers (like I use) cause a direct short to similiate an actual short in an appliance?? How accurate are they?
T.J. " 2-prong " Christopher

most simple testers just cause a small ground fault.
no ground to fault to, no trip.

this is how most testers will behave.

no trip with tester.
test button trips and resets fine.

T.J., the plug-in GFCI testers function by simulating a “fault” to the ground pin. In a 2 wire outlet there is no available “ground” so the tester can’t simulate the fault.
If the GFCI’s own test button produces a “tripped outlet” it is working fine.

edited: Chris beat me to it.:slight_smile:

Yes, T.J. …GFCI replacement receptacles on 2-wire ungrounded circuits do work, but as everyone says, won’t “test” for the reasons already stated. I make a habit of recommending them…not only in “wet” locations, but suggesting that they can be installed at the upstream receptacle in each branch circuit for added child safety. Clients appreciate that info. Here’s a suggested comment:

“The home has a two-wire, ungrounded system, which was the norm when the home was built. Modern standards call for GFCI (Ground Fault Circuit Interruptors) in kitchens, outdoor locations, and other wet locations such as pools and spas. AFCI (Arc Fault Circuit Interruptors) are now required for bedroom circuits. While these upgrades are not a requirement in this particular home, I strongly recommend consulting a licensed electrician about installing GFCI receptacles in all the locations and conditions mentioned above that may be present in this home.”

I recommend GFCI upstream on bedroom circuits simply because AFCI won’t work on an ungrounded system, and installation of GFCI renders more protection than simply leaving it alone. I have found that people usually follow up on this, as it is relatively inexpensive…and even the agents like it!

It’s a win win.

Jimmy B.

Can I ask where you received that information?

AFCI’s have superior performance protection over a standard circuit breaker when it comes to low-level line-to-neutral faults. In an old house I would surely install them and recommend them, even though they are not required by the NEC because the code is not retrocative…But safety is.

No, no, no, Paul. Safety is not retroactive. Just read the newspaper each day or watch your local news. :mrgreen: :shock: :cool:

As we have joked about in the past:

fill the sink with water
put one hand in the water
put one finger in the small plughole
does it trip?

If the circuit does not have a ground at the plug, you must become ground for the device to work.
I don’t personally practice this test procedure, nor do I endorse it! :slight_smile:

I never trust the test buttons on GFCI outlets. They lie all the time! So when you report it, describe how you tested the device (with the devices internal test circuit) and report the results of the test. Do not report that all GFCI’s were tested and functional (because you don’t know).

GFCI’s will not work properly with out a ground. The ground provides a reference point for the internal circuitry of the GFCI, removing the reference point from the circuitry anything goes…


Hey All,
Thanx for the replies (more are welcome)

  1. Can you properly test a GFCI outlet? If so how…(within reason & not extending your inspection into a full blown electrical evaluation.)
  2. Also is there anyway to test 2 prong outlets to see if grounded??

Hey, John.

I think every electrician here in San Diego will disagree with you. In fact, a common fix for two-prong outlets without rewiring a house is simply to replace the two-prong outlets with GFCI outlets since they don’t need to be grounded.

I test GFCI outlets using the manufacturer’s test button, just like the manufacturer recommends in their installation instructions. If it’s good enough for the manufacturer, it’s good enough for me.

Two-prong outlets, by definition, are not grounded.

I dislike seeing the myth, that GFCI’s require a ground to function. This scares people off from upgrading older homes with them, and put many people at risk.

How do we get rid of this type of thinking, when those ‘who should know’ perpetuate it?

Also, where did the idea that AFCI’s require a ground? They don’t even accept an equipment grounding conductor. Did this stem from that AFCI’s now have a lower ground fault detection like a GFCI, but not as low?

Would you not recommend Smoke Detectors in homes built prior to their being required? Ofcouse not. So always include information about the personal safety of GFCI’s and property/personal safety of AFCI’s in all your reports for homes that don’t have any. We might just save some one’s home or life.



We just have to keep educating everyone, sometimes even our own. Hec, one of the reasons why I stick around NACHI is because the education here is great.

NACHI rocks!
NACHI rolls!
NACHI rules!

lol…thats what I mean RRay…thats the HI’s job to demand safety and ignore the fact NEC guys ( like myself ) will say it fine…as it was CODE at the time of installation…when in fact codes change because of safety issues and news findings…thats why i favor AFCI’s so much…

And yes they DO work without a " Grounding " conductor, not sure now who made that statement but it is false.

Hey Paul, T.J. here, the original poster, is there any way or need to test these GFCI (that show open ground on my tester) outlets other than with their own trip buttons & just list as GFCI outlet w/open ground.
P.S. If you ever sit on a toilet seat in Wyoming, you better tap it with the back of your hand first to make sure it’s grounded, LOL!!!

Not without rigging something.

A note of caution on using a plug in GFCI tester on ungrounded GFCI load side receptacles…The plug in GFCI tester shunts about 6ma of current to the ground pin of the receptacle. If that receptacle is not grounded, the GFCI will not trip when using a plug in tester. HOWEVER… if that receptacle happens to be mounted in a metal box, has a metal faceplate, a metal weatherproof cover, or has conduit associated with it, those metal parts will potentially be energized with about 6ma of current. You can potentially get a handsome shock if you happen to be touching a metal part while you press that button, under the right circumstances. This can easily happen if a metal flipper lid weatherproof cover is resting against your hand while you have the tester engaged and you’re pressing the button. At this test current level, 50% of people cannot let go.

Thanks for the booklet, Marc. Very nice.


If you are speaking of downstream receptacles then just test them at the original device ( GFCI Receptacle )…to ensure those downstream are working as they should…TRIP the GFCI at the GFCI receptacle and then go check to ensure that the receptacles downstream are actually OFF…this should be all you need to do…to ensure they are working properly per the manufacturer.