Hot & Ground Reversed

[Zach Cross]

Hi folks, I'm trying to trouble shoot an electrical issue at my in-law's 1947 home. 

Apparently, they were using an extension cord at a living room receptacle, and yanked on the cord abruptly and the receptacle stopped working. 

I used my electrical tester and the receptacle reads hot and ground reversed. I pulled the receptacle out, checked all the connections and everything is secure. Wires coming into the box are energized. It is only when the mounting screws on the receptacle are fully tightened does the receptacle read with hot and ground reversed.  Otherwise, when the receptacle is pulled out from the metal box tester reads nothing, no power. 

It looks like some old armored BX cable running into a metal gang box. There are two other receptacles on the same circuit, on the same wall (exterior wall, inside receptacles) that also now display hot and ground reversed. 

I am wondering if there is a energized wire in contact with the armored cable somewhere in the circuit? 

Any insight would be much appreciated. 

[Bill Kibbel]

The 3-lamp tester isn't real accurate for analyzing a problem. A multi meter or even a wiggy would probably give better info. Of course, an experienced electrician would ve the safest 

Since everything was working before, I would suspect the individual outlet was the problem. Replacing it would be my first action.

[Zach Cross]

Thanks for the reply Bill. I forgot to mention that I did change out the receptacle with a brand new one, and no luck solving the problem.  I was getting roughly 114 volts with a multimeter between the hot and neutral when the receptacle was pulled out, but left off there. Went on some wild goose chasing looking for maybe some screws or nails they might have added on the wall somewhere. I got laser focused on something getting jostled from the extension chord, maybe should have thought about resistance?

They have an electrician to contact now, I was just hoping it was something easy. 

Edited December 1, 2023 by Zach Cross

[John Kogel]

Hello Zach. When the BX wiring was installed there was no ground prong on power cords and outlets had two identical slots. So it is normal for black and white wires to be mixed up a bit. If the outlets were changed to new 3-prong types, good chance they were installed wrong. Somebody got the white wire energized and didn't see a problem with that, probably. It only became an issue when the polarized 3-prong outlets were put in.

When you get a whole string of outlets in reverse, the first wrong one in the chain can be corrected and that should correct the polarity for all of them. This is a general statement because we can't see what you've got there.

Old BX wiring should all be checked by an electrician. He can check for leakage from damaged insulation,. fire hazards, over-fused circuits, etc.

[John Kogel]

Oops, I read your first post too quick. What I wrote above is not wrong, but your little tester is indicating worse than a simple hot and neutral reversed. Sorry, there is definitely an issue at that outlet, could be a broken neutral wire or something shorted to the outer shield. Get an electrician to check it out.

That wiring is 75 years old and is overdue to be replaced. They might be able to run some new wiring in the basement or attic to minimize fishing behind the lath and plaster. It is not something to ignore or put off till some other time.

[Jim Katen]

I suspect that the old receptacle was not "grounded" to the box. The new receptacle is - but only when you tighten the screws. 

You're probably on the right track looking for a fault to the cable jacket. 

Let us know what the electrician comes up with. 

 

 

[Zach Cross]

4 hours ago, Jim Katen said:

I suspect that the old receptacle was not "grounded" to the box. The new receptacle is - but only when you tighten the screws. 

You're probably on the right track looking for a fault to the cable jacket. 

Let us know what the electrician comes up with. 

 

 

Thanks Jim, will do. 

[Zach Cross]

On 12/4/2023 at 12:18 PM, Jim Katen said:

Let us know what the electrician comes up with. 

An update for anyone interested:

The culprit was a failed GFCI on the same circuit. I am a little surprised by this finding for a couple of reasons. 

1. There was still ~120v to the receptacles on that circuit. I guess if the GFCI wasn't tripped, but the internal components went bad, that's plausible?

2. The failed GFCI was no where near the receptacle that apparently was yanked on. Is it possible that a short damaged the internal circuitry of the GFCI? Or maybe just coincidence that the GFCI failed at/around the same time?

In any case, it is fixed and I trust that was the issue. I wasn't able to be at the house and pester the electrician with questions (unfortunately for me, great for them).  So that's about as much as I know. 
 

Edited December 12, 2023 by Zach Cross

[Jim Katen]

Thanks for the update. That makes sense. Some older GFCI receptacles would go faulty and produce a hot-ground-reverse reading in downstream receptacles. As I recall, it happens when you don't push the reset button all the way in and you can "fix" it by tripping the GFCI and fully pressing the reset button again.