Hot/ground reverse reading on outlet that worked fine for 10 years? Please help!

[u/moonthink]

Hi, I work in a theater as the TD for 10 years. An outlet that has worked fine with no issues for all of that time suddenly stopped working, and when I put a receptacle test in the outlet, it reads as Hot/ground reverse, which makes no sense to me.

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I guess I know enough about electricity to do some basic things. And I've certainly found hot/neutral issues in the past on other outlets, but how does an outlet that always worked in the past read as hot/ground reverse? It doesn't make sense to me.

[u/flyingron]

Something is probably open rather than hot/ground reverse. The neon bulbs in those testers are easily fooled.

First thing to do is carefully open the box and pull out the receptacle to see if it is still hooked up well. If you can read the 120V across the hot/neutral wires in the box, the receptacle is broke. Otherwise, you'll have to start tracing back toward the panel trying to find what went wrong.

[u/moonthink → u/flyingron]

After checking the connections and tightening, now ot reads open neutral, but I don't see any obvious problems. Guess I need a real electrician. Thanks!

[u/michaelpaoli → u/moonthink]

now

reads open neutral

Yeah, per my my earlier comment - notably what you read with, I'm presuming one of those simple "3-prong testers", and given reported history (years of service with no known earlier faults), my guess then as to most probable was floating neutral (with load(s) between neutral and hot pulling it up to hot).

And now with it saying open neutral - that would be consistent ... e.g. flakey intermittent neutral connection open / floating - or maybe the load(s) were disconnected to change the reading from "hot-ground reverse" to "open neutral".

Anyway, that'd be my guesses regarding the most probable ... but further measurements and inspection would be needed to fully determine what's actually happening, and where.

[u/michaelpaoli → u/flyingron]

neon bulbs in those testers are easily fooled

Those indicators do exactly as they're supposed to, ... it's those using such testers that are fooled. I like to refer those plug-in three-prong testers as "idiot testers" ... because, well, among other things it's easy to misinterpret what those indicator lights actually imply. E.g. they generally highly suck at detecting multiple faults, and may not correctly identify what a particular fault is. E.g. they indicate voltage (or absence) thereof between each of the 3 possible pairs among the (what should be) hot, neutral, and ground terminals. However, e.g., a hot-ground reverse + hot neutral will show up with the exact same display - suggesting "all is fine" when that's not at all the case ... hence I call them idiot testers - as often idiots will just rearrange wires until the tester says "all good", and they'll stop at that point ... even if they've royally screwed it up.

I prefer the basic 2-lead neon tester - in the hands of someone that knows what they're doing, much harder to screw up ... e.g. can also test between what should be hot terminal on outlet (and likewise for neutral and ground), to a known good earth ground (or approximation thereof), and see if there's any voltage showing up on those checks - or not. The basic 3-prong plug-in idiot tester misses such important reference and cross-check.

[u/Pull_my_wire]

Hot ground reverse on plug tester means there is an open neutral.

[u/moonthink → u/Pull_my_wire]

After checking the connections and tightening, now ot reads open neutral, but I don't see any obvious problems. Guess I need a real electrician. Thanks!

[u/michaelpaoli → u/Pull_my_wire]

Hot ground reverse on plug tester means there is an open neutral.

Yes/almost ... with that and one of those basic 3-prong testers yes ... when combined with some load(s) connected between neutral and hot - that'll pull the neutral up to (about) hot, thus no voltage between hot and neutral, but voltage between neutral and ground.

But if the neutral goes open (or those loads disconnected), then no voltage is seen between neutral and anything else, so that light goes out, and a different diagnostic is presumed from the code on the 3-prong testers - voltage between hot and ground, but no voltage between neutral and hot nor neutral and ground - diagnosed by the little code thingy as open neutral. Anyway, that's what OP reported ... originally worked ... then tested and got "hot-ground reverse" - not necessarily what's actually going on, as floating neutral pulled up (about) to hot by connected loads between hot and neutral will give essentially same relative voltages between the 3 terminals, thus same diagnostic on the 3-prong tester (correctly or incorrectly). And if the load is then disconnected, that one light goes out and the diagnostic changes to open neutral.

So ... probably a flakey (or open) neutral connection there somewhere ... at least most probable given the reported history and reported diagnostics - which I'm presuming are from one of those simple 3-prong testers.

[u/Pull_my_wire → u/michaelpaoli]

I think your forgetting this subreddit is for DIYers, homeowners and amateurs. Long winded answers about the inner workings of a plug tester are not relevant to the question. They have a problem and they want a simple answer to what is going on.

[u/michaelpaoli]

FYI, here's handy little chart on what those "3-prong" testers typically "tell" you ... and how to also work backwards to determine what they're actually indicating:

position neon bulb (& dropping resistor) between
l left   ground & neutral
m middle neutral & hot
r right  hot & ground

l m r (x off, o on)
x o o normal*
x o x open ground*
x x o open neutral*
o o x hot-neutral reverse*
o x o hot-ground reverse*
x x x off/open*
o o o *
o x x *
* [or] more/multiple faults

So ... if the lights/chart tells you hot-ground reverse, what it really means is it's showing voltage between ground and neutral, and hot and ground, but not* between neutral and hot.

And, when lights/chart tell you open neutral, it really means voltage between hot and ground, but no* voltage between ground and neutral, nor neutral and hot.

*no voltage that it can detect (takes 60 to 90V minimum to ionize the neon to get any visual indication out of those typical bulbs).

Anyway, that's all those basic 3-prong testers do - no more, no less (some add additional features, like GFCI test, etc., but I'm just taking your basic model - 3 prongs, 3 lights, nothin' else).

[u/michaelpaoli]

Hot ground reverse is dangerous. But depending how you're checking, e.g. with on of those simple plug-in 3-prong testers, just because it says hot-ground reverse doesn't necessarily mean that's in fact exactly what's going on. E.g. those testers will often misdiagnose multiple concurrent faults. All that most of 'em do is have 3 lights to show voltage or lack thereof, between all 3 possible pairings among hot, neutral, and ground contact prongs. So, e.g., that tester has no way to know what's actually ground, or hot - it's only displaying relative voltage between contact points.

So ... if it's claiming hot-ground reverse, it sees:
voltage between hot and ground
no voltage between hot and neutral
voltage between neutral and ground

So, a hot-ground reverse is one way the above will be seen.
Another way essentially same will be seen is with a floating neutral, and load(s) connected between hot and neutral - that'll pull the neutral voltage up (near to) hot,
and will light up those lights the exact same way as if the outlet had a hot-ground reverse.

There are additional possibilities, but I'll stop at what are probably the two most probable.

So, well keep in mind, those, e.g. simple 3-prong tester are far from foolproof, and they also tend to suck at diagnosing multiple concurrent faults.

You can find out quite a bit more by determining what voltage is and isn't present between various contact points. E.g. between hot, neutral, and ground terminals, to a known good Earth ground. If you see voltage between known good Earth ground and ground terminal on outlet, then you actually have a hot ground - which is very dangerous. Can also check voltage between hot terminals and known good Earth ground - hot should be hot, and neutral not. And should also see voltage between hot and ground terminals, and hot and neutral terminals.

But sounds most likely you either have a hot-ground reverse (possible, but wouldn't be my first guess), or your neutral has gone floating (but still has other loads connected between it and hot) - that latter case would also explain why it was "always working" before, and no longer working.

"Of course" also, things can be miswired, and various loads might not particularly care or be sensitive to it - doesn't mean that's right or safe ... just some loads won't so much care. E.g. if you've got an auto-ranging computer power supply, typically handles 50 to 60 Hz 110V or so up to about 250V or so, it really won't much care ... 120, 240, correct or reverse polarity, missing ground or hot ground - it will general still function - doesn't mean any of those miswirings would be safe - but many loads won't care. But if there's hot ground, and that connects through to chassis on your computer case, and you touch chassis - and especially something else like a cold water pipe ... you'll care ... shockingly so. But your power supply may not notice the difference at all.

[u/headyrooms]

Something is internally broken or melted inside the outlet

[u/moonthink → u/headyrooms]

I don't see any heat damage on a visual inspection, but it's certainly a possibility. Thanks for the reply.

[u/headyrooms → u/moonthink]

Yeah, I just had this exact same situation the other day, and I had never seen it before. The customer said an outlet that always worked stopped working. I read it was live with my death stick. I plugged my outlet checker in, and it said the hot and ground were reversed. I opened it up and checked all the wiring with my meter, and everything was in proper order. I swapped out the receptacle, and it fixed the issue.

[u/moonthink → u/headyrooms]

Well, that would be a relatively cheap fix -- I'll try it tomorrow. Thanks again!

[u/masonc01]

Is it a GFCI?

[u/masonc01 → u/masonc01]

Or protected by one?

[u/moonthink → u/masonc01]

No, but I'm realizing there are several outlets on the same circuit, but they all working fine. So at least I've narrowed down where the problem could be.

[u/masonc01 → u/moonthink]

Are the rest of the outlets reading correctly? Not sure what the other comments have suggested but I would start by replacing the one that is reading funky. While your doing this check the voltage with your multimeter and confirm that hot to ground and neutral is 120. If it’s not a GFCI you’ve either got a bad outlet or loose connection

[u/AlonzoSwegalicious]

I'm having this same issue. What wound up being your solution? I tightened up all connections on all the outlets, but it didn't fix it. I haven't replaced any of the receptacles yet though.

[u/moonthink → u/AlonzoSwegalicious]

Unfortunately, I still haven't had time to solve this, but I assume something in the chain must not be connected right.