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I'm experiencing some electrical issues with the apartment I'm subletting. While connecting up a projector/speaker setup using outlets from different sides of the room, we discovered (through means of frying our electronics) that the grounds on each side of the room are at different potentials.

When measured with a multimeter from the ground pin of one outlet to the ground of the outlet across the room, we get 120VAC. Keeping the same reference ground pin across the room, neutral also measures at 120VAC and power measures at 0VAC.

It seems like one of the outlets must have it's wiring backwards, but a visual inspection of the wires (at least the outlet side) checks out and an outlet tester claims they are all correct.

Will that outlet tester detect if neutral and ground are powered and power is grounded? Is that condition particularly dangerous?

Note: I'm not proposing that I do any of the electrical work myself, I'm just curious about what went wrong and where.

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  • When you say ground, you are talking about the middle, somewhat rounded hole in the outlet, right? Not trying to be a smart alec. It is just that I am kind of surprised that anyone would have a hot ground on an outlet. But it sounds like you do.
    – mkeith
    Jul 5, 2016 at 16:30
  • Please post a picture of the outlet and indicate which pin you consider ground. Or tell us where you live and the type of plugs you use.
    – Ariser
    Jul 5, 2016 at 16:47
  • @Ariser considering the outlet tester pointed by the link, it looks like US and NEMA.
    – Dmitry Grigoryev
    Jul 5, 2016 at 16:52
  • Compare the voltage on the ground pins to a "true" ground such as the cold water pipes (make sure those are metal all the way to the inlet).
    – Carl Witthoft
    Jul 5, 2016 at 17:26
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    Sounds like one of the outlets has a swapped neutral/hot, and someone took an extremely unsafe shortcut when installing grounded outlets by "faking" a ground by connecting the outlet ground to the "neutral", which in this case is actually a hot. I'd turn off the power and unplug everything until an electrician can inspect it.
    – Johnny
    Jul 5, 2016 at 18:45

2 Answers 2

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Use a non-contact voltage detector pen on the outlet by holding it near the face -- if it lights up, you likely have what Johnny is describing in the comments, a so-called "reverse polarity bootleg ground".

(On a properly wired outlet, the voltage detector should not trigger until you stick its tip into the hot slot on the outlet.)

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No, simple outlet tester which doesn't sense hot wire alone won't detect the fault you describe. You may want to check the ground contact with an AC sensing screwdriver or a similar device to confirm.

If that's the case, then yes, this condition is dangerous as hell. When someone plugs a grounded appliance (like a microwave oven or a toaster) in that socket, they will get electrified on contact with the case.

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  • IF they are grounded. Which, of course, they often are, but by no means always.
    – mkeith
    Jul 8, 2016 at 22:04

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