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My home is older, and while 1st floor is grounded, basement has older 2-prong outlets. I decided that at a minimum I should put in a gfci in the laundry room. Inside box there are 3 wires however it does not appear the the ground wire is actually grounded. Test wires, black is hot, white is neutral as they should. Hook up black wire to the HOT LINE side GFCI, and hook up white wire to the other. But it says hot and neutral are reversed on my tester.

If I flip them around, which I can tell is wrong from the screw colors and directions, tester shows it's technically correct with open ground. That just seems off to me.

What could cause that false polarity reversal reading? Dont think it's the tester, I've tried it on other outlets and it's fine. Would no ground throw off the reading? Or just a bad GFCI?

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    Did you actually connect the ground wire? Without a ground connection, a three-light tester should not be able to detect hot/neutral reversal.
    – DoxyLover
    Commented Mar 29, 2020 at 22:02
  • Can you post a photo of the inside of the outlet box please?
    – ThreePhaseEel
    Commented Mar 29, 2020 at 22:14
  • I determined it was a faulty gfci. I exchanged and reinstalled and it checked out correctly, reading "open ground". Then ran a ground wire from some conduit about 12" above the outlet. Everything checked out correctly with the testers. Voltage checked out correct H-N at 118V, N-G at 0V. And it tripped the gfci when I did H-G.
    – Bobby Quam
    Commented Mar 29, 2020 at 23:16
  • You know hot is brass screw and white is silver screw right? I could imagine a GFCI putting them on the opposite/unexpected side of the recep (e.g. brass on the tall-prong side), and that would not be faulty.
    – Harper - Reinstate Monica
    Commented Mar 29, 2020 at 23:29
  • Yes, I'm aware of the color of the screws and what goes where. When I returned the first one to ace hardware, the cashier said I was the second person that returned a gfci the same day for the same reason, so they must've gotten a bad batch that somehow had reverse polarity.
    – Bobby Quam
    Commented Mar 30, 2020 at 9:45

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enter image description hereI determined it was a faulty gfci. I exchanged and reinstalled and it checked out correctly, reading "open ground". Then ran a ground wire from some conduit about 12" above the outlet. Everything checked out correctly with the testers. Voltage checked out correct H-N at 118V, N-G at 0V. And it tripped the gfci when I did H-G.

When I returned the first one to ace hardware, the cashier said I was the second person that returned a gfci the same day for the same reason, so they must've gotten a bad batch that somehow had reverse polarity.

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