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I used a standard three-lamp outlet tester on an GFCI outlet, and it shows "open ground". Should I be worried?

This is not a special "GFCI tester"; it's just an ordinary plug-in three-lamp receptacle tester. I have tried multiple GFCI outlets throughout my house, and some of them show "correct", but two show "open ground". I'm not sure whether to be concerned about that.

My impression is that GFCI outlets are sometimes used in places where there is no true ground available. So, this makes me guess that the outlet tester might indeed show "open ground" on such an outlet, and that it won't be a problem. Is this correct?

(If it's relevant, these are pre-2016 GFCI outlets.)

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    If you push the "test" button on the tester, does it fail to trip the GFCI?
    – Harper - Reinstate Monica
    Feb 8, 2018 at 8:49
  • @Harper, unfortunately the tester I have doesn't have a "test" button. The GFCI outlet does shut off properly when I press the test button on the outlet. Thanks for the suggestion!
    – D.W.
    Feb 8, 2018 at 15:36
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    Just fyi, the test is that if you use an external 3-prong GFCI tester on a GFCI-protected outlet with no wired ground, the test button should not work. So if it does not trip, it passes the test. If it does trip, either it has a ground after all, or something has been bootlegged.
    – Harper - Reinstate Monica
    Feb 8, 2018 at 18:07

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You are correct, GFCI receptacles can be used to replace old 2-prong receptacles when there's no grounding conductor. If your home is old enough, you might assume that there is no ground at the receptacle. However, if you want to know for sure, you'll have to inspect the wiring inside the box.

A properly functioning GFCI receptacle, can provide ground-fault protection without a grounding conductor. So as long as you're not plugging in high-end audio/video equipment (or anything that requires surge protection), you're probably okay.

As @Harper mentions. Press the Test button on the GFCI, and make sure it trips and resets properly. Repeat this test every month, as these are likely not GFCIs that self test.

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  • I think what @Harpers is attempting to point out is that the test button on a “GFCI tester” doesn’t work correctly when plugged into a downstream outlet that doesn’t have a connected grounding conductor. In this case tho, the OP told us his tester is not a GFCI tester.
    – Tyson
    Feb 8, 2018 at 12:38
  • Most GFCI should have a test button, and that's probably something that should be checked in this instance, even if the outlet tester doesn't have a button.
    – poorplanning
    Feb 8, 2018 at 14:01
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    As I recall, GFCI outlets without connected ground must be marked as such. The outlets are packaged with stickers that say something like “No ground attached”. If you verify that there is no ground in the box, you should add that marking.
    – DoxyLover
    Feb 8, 2018 at 16:51
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    Yes it should be labeled. If the socket is known to be ungrounded, and you use a 3-prong GFCI tester, it is supposed to not work. Failing to trip the GFCI means it passes the "external tester" test.
    – Harper - Reinstate Monica
    Feb 8, 2018 at 18:00

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