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Before starting any DIY electrical work in my new (to me, built circa 1990) house, I picked up and used an outlet tester, and promptly discovered the "hot ground reverse" error occurring for every outlet on the property (house with service box + main panel, and a detached garage with sub-panel served by 3+1 wire with no grounding rod of its own). However, every outlet works.

Since then I've replaced some receptacles and switches, moved kitchen MWBC lines onto GFCI breakers, had an electrician upgrade the sub-panel and add circuits to both panels, shuffled around everything in my main panel, and fixed an issue I found with the main panel (ground was connected only to neutral busses leaving ground isolated, now connected only to ground busses since neutral and ground are already bonded in the service box).

Throughout all these changes the hot ground reverse issue persists, and all known electrical service paths are "working" in so far as connected devices receive power and work. I say all known paths, because I have a circuit which was originally marked "microwave" which seemingly goes nowhere and remains a mystery. The fault even appears when every circuit is off (but meaning only hot disconnected) except the one being tested (and pick any one).

How concerned should I be about this fault? Unless it is truly trivial (an assessment that I feel requires a good explanation), what steps can I take to trace the root cause? What kind of tests might I perform to verify the problem isn't just with the outlet tester itself, other than getting another one? (I do have a multimeter and two-prong bulb-style tester as well.)

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  • The isolated ground was particularly surprising, because the original electrician clearly took pride in his work, and did a beautiful job overall. I had to do a lot of research and investigation to convince myself that wiring was truly wrong, but there wasn't even a way present to connect the box or ground bars to the ground line (no strap, bar, or lugs). Sep 11, 2021 at 3:15
  • Hot-ground reverse is a lie. That's not the problem. Sep 12, 2021 at 2:13
  • Hence the quotes. ;) Sep 12, 2021 at 13:23
  • Are you getting this indication from a simple and dumb 3-light tester giving red and outer yellow (no indication from middle yellow)? Or is this a "smart"/"computer assisted" tester who does the interpretations for you and doesn't let you see the raw lights? Have you tried the tester at work/friend's modern house where grounds are known to be good? Sep 12, 2021 at 21:03
  • It's the simple, cheap 3-light type. I am aware that "hot ground reverse" typically actually means open neutral and ground electrified by something else closing the circuit, except that doesn't square with all working receptacles. But I've also confirmed the tester is wrong both by using it elsewhere and using a bulb probe tester, and accepted the given answer accordingly. Sep 13, 2021 at 13:27

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IMO by far the most likely explanation here is that the outlet tester is defective.

Given that multiple people have worked on the installation at different times, it seems very unlikely that every outlet would be miswired, and if you had swapped a hot conductor with the neutral in the "240V" parts of the installation you'd probably know about it when some equipment went up in smoke because it received 240V and was expecting 120V.

If you want to assure yourself that things are ok, measure the voltages with your multimeter, you should see very little voltage between neutral and ground and full voltage between either of those and the hot conductor.

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    Yes my thought too. Perhaps OP can take the outlet tester to a friend's house, neighbour, cafe... Also same neutral to ground and live to ground tests can be performed with the two-prong bulb tester.
    – P2000
    Sep 11, 2021 at 5:16
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    Bulb probe test found current between hot and neutral, between hot and ground, and not between neutral and ground. The outlet tester produced same result for a receptacle at the local home center, so I'm ordering some gear that includes a new one. Sep 11, 2021 at 14:47

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