Electrical Confusion Question

I came across a personal situation yesterday while helping a friend. Looking for a little feedback.
He called me over because he knew i had some electrical background and was studying for my CPI with InterNACHI.
He recently purchased a really old home thats been somewhat rewired (an electricians nightmare) and he has a mini plug in tester and during testing a receptacle showed REVERSED POLARITY and all outlets fed downstream from it (3) showed same as well of course. Issue is when i pulled the receptacle out from the box everything was hooked up properly (Hot and Neutral, not reversed) and grounds were done properly. When i put the receptacle back in and tested it again with the mini tester it stilled showed reversed polarity. So i once again pulled it out to see if I was missing something and when I tested it outside of the box the tester showed OPEN GROUND and so did all the others downstream now. To make a long story short, every time i fasten the receptacle back in the box properly it and all downstream show reversed polarity and when unscrewed and pulled out from the box they all go back to open ground. Seems that its the top screw that holds receptacle in is the one causing the change. I cleaned in behind the box where the receptacle fastening screw extends because there was some dirt and plaster in there and now i only have OPEN GROUND. So I seemed to have eliminated the REVERSED POLARITY which is very puzzling on its own, but now still have the OPEN GROUND. I checked every where in the boxes, sub panels, main panel and junction boxes and cannot find anything that is not grounded. I have instructed him to get an electrician in to locate the OPEN GROUND but am curious why the REVERSED POLARITY from the tester when all was hooked up right?

Are the wires Romex or BX?

They are romex

Are the ground wires properly joined? To each other and the devices.

Metal boxes?

You need a circuit analyzer or meter to perform diagnostics, not a three light tester.

They all seem to be yes. I pulled the cover from the junction box in the attic (assuming it was indeed the right one) that we think feeds the box in question and all grounds are together and back to the ground screw. They are all wound together but no connector. I didnt like it but i dont think it would be the issue since wound tight together. Told him it needs a connector tho.

Yes metal boxes

That is the time to call in an electrician

Thats what i said too

I just wondered if any of you had come across one of the mini testers giving a false REVERSED POLARITY indication before when all is hooked up right? There is another grounding issue for sure and must be the reason for the false reverse polarity reading. I just never came across it before.
Thanks for the input guys.

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You are getting a correct reading. The problem is just hidden from you. Trust the readings.

Call the electrician

Just because the outlet was the first to indicate a problem in the series doesn’t mean the issue isn’t one more receptacle upstream.

Make sure to be there when the electrician comes so you can see what s/he does and get some education paid for by your friend :slightly_smiling_face:

What hasn’t been pointed out yet is that your three light tester can’t depict both situations at the same time. It’s either hot/neutral reversed or no ground. If you think about it you can see why. The ground is essential for determining hot/neutral reversed. Without it all the tester can tell you is open ground. Most test equipment is reliable only within certain parameters. Your three light tester has limitations.

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