GFCI reading Hot/Ground Reversed

[DChambers772]

Good afternoon,

Hopefully I'm not violating any rules by posting. I read the pinned thread and I do not think it does. I also searched the forum and didn't find anything that really explained what I was seeing. I am currently working as electrician's apprentice since about May of 2022, so my experience is limited in the number of things I just simply haven't seen or just don't know what to look for yet.

I was hoping someone here might be able to shed a little light on something I came across this afternoon.

I was sent to take a look at a GFCI outlet at a car wash. There were two of them. I found the GFCI upstream which was obviously fried, and the insulation on the wires were blackened from the receptacle to where it met the conduit entering the box. I had been instructed just to clean the wires up as best I could and swap the GFCI out with a new one. Went ahead and did just that, double checked to make sure the line and load sides were correct, and then went ahead and wrapped it once over in electrical tape and went to put it back in.

The plug tester read correct, but as I screwed it down it would switch from reading correct to Hot/Ground reversed. I took it back out, double checked to make sure this was not the case. Went ahead and wrapped the hot wires with electrical tape where damaged just to make sure they weren't making contact with any other conductors, cut the screws down in length thinking maybe somehow, they were making contact with something inside of the box, and tested it again. Everything read correct. Went to screw it back down and the same thing happened. I could see it on the plug tester switch from correct to hot/ground reversed as I screwed it down.

I had been in contact with my boss the whole time and was eventually told to just leave it. He'd take care of it. I put it and the GFCI downstream back together and just decided to test them again to check. The top outlet on the first GFCI read correct. The bottom outlet and the downstream GFCI still read Hot/Ground reversed. I double checked my plug tester on another receptacle, and it was working correctly.

I was hoping someone could explain to me what might cause this, or if I had done something wrong in reinstalling it. I've been searching the internet and the only thing I could come up with was that maybe the neutral wire on the load side is just damaged to the point it is giving the plug tester a false reading there and downstream from it.

 

[augie47]

I don't recall the exact scenario ( I think it might be 'open ground' ) but the plug-in tester wll give a hot/ground reverse when that is not actually the problem. It is an indication of a problem but just not exact scenario.

 

[suemarkp]

An open neutral can cause this. Makes sense if the wires were burned -- maybe the neutral is mostly burnt and screwing the receptacle into the box is pushing on that wire breaking the connection.

Here is a site explaining the different readings you can get with a 3 light tester. Section 5.1 is the open neutral hot-ground reverse scenario: https://www.doityourself.com/stry/what-does-a-hot-ground-reverse-reading-mean

 

[DChambers772]

An open neutral can cause this. Makes sense if the wires were burned -- maybe the neutral is mostly burnt and screwing the receptacle into the box is pushing on that wire breaking the connection.

Here is a site explaining the different readings you can get with a 3 light tester. Section 5.1 is the open neutral hot-ground reverse scenario: https://www.doityourself.com/stry/what-does-a-hot-ground-reverse-reading-mean

Thank you, I think this is the best explanation. One of those things that I just don't know to look for or think about until I come across it. I'll add this to my notes for future reference!

 

[hillbilly1]

Check for voltage from the frame of the gfi to the box, I’m assuming it’s a metal box. Does it have a separate egc pulled? Or conduit is the egc? Car washes have a lot of caustic chemicals, and the conduit may be compromised. Does the box have a jumper to the egc if one was pulled? If not, the conduit may have become energized, which might explain the burnt wires

 

[DChambers772]

Check for voltage from the frame of the gfi to the box, I’m assuming it’s a metal box. Does it have a separate egc pulled? Or conduit is the egc? Car washes have a lot of caustic chemicals, and the conduit may be compromised. Does the box have a jumper to the egc if one was pulled? If not, the conduit may have become energized, which might explain the burnt wires

ECG was run through the conduit, connects to the grounding screw in the box. It is pigtailed to the ECG heading downstream to the other GFCI and the ECG going to the GFCI.

The guys at the carwash said they were running a kerosene heater inside the wash when it was -11 a few weeks back. Left the GFCI cover open with the heater plugged in while it warmed up and the ice on everything melted. I would assume the water from the melting ice or even just the hoses they were spraying there right next to it worked its way down into the box. If I get back out there, I will double check though.

 

[jaggedben]

An open neutral can cause this. ...

Not by itself. The tester would just give the open neutral indication. Something else was happening too.

 

[jaggedben]

I'm struggling with how this could likely happen without causing a short. I hope we're not being trolled. As best I can tell, it would have to be:

- as he tightens, the neutral opens
- downstream of where the neutral opens, the hot makes contact with the neutral
- the tester shows open neutral in between those two events, and either he isn't looking or it happens too fast for him to notice
- somehow the order and timing of those things is just so, and there's no short circuit that goes bang

It's the last part I'm struggling a bit to find plausible in the description, especially for it to happen the same way twice. But truth can be stranger than fiction I guess.

 

[DChambers772]

I assure you I am not trolling. I will admit I am not the most experienced when it comes to seeing anomalies like this, but I'm trying to figure out the possibilities. I could actually watch on the plug tester as it switches from correct to hot/ground reversed as I screwed it down. I have some photos I can try to upload later. At least of the burned up wires and GFCI. I didn't get one of it showing the hot and ground reversed though. I just didn't think to before I left in my frustration.

 

[DChambers772]

Wish I had taken a picture of the Hot and Neutral reversed, but hindsight is 20/20. Picture on the far right is the new one I installed.

 

[jaggedben]

Ideally that wiring gets replaced because of the damage.
I think you got incredibly lucky that nothing shorted and arced on you. I can't figure out a scenario where the tester does what you said without a high risk of that. Maybe someone else can explain it, but the LEDs simply light up between the three different combinations of wires, there's nothing smart about those testers. So there's a limited number of ways you could have gotten that reading.

 

[KyleDurham1221]

I don't recall the exact scenario ( I think it might be 'open ground' ) but the plug-in tester wll give a hot/ground reverse when that is not actually the problem. It is an indication of a problem but just not exact scenario.

Can confirm this. Even the seemingly nice klein plug testers with GFCI testing capability do not read the issues precisely every time. Often reading 30v when the only issue is open neutral. Slightly dangerous tbh