Weird one

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Fred B

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
So had a service call the other day that overnight lost power on portion of circuit. (Did have storms overnight.) Customer states they had tried to use the shredder in the morning and nothing, assumed the shredder was shot but decided to try a different receptacle, and it worked. He then stated he knew the receptacle had some damage so he decided to replace it. He did the replacement and then the TV on same line stopped working. That is when he called me. First thing was to check the receptacle that he replaced to see if it was wired correctly, connection in correct place. But when I metered first with the circuit tester it showed hot/groung reversed. Put on the volt meter checked Hot-neutral, 6V; hot-ground, 0V; gound-neutral, 116V. Started tracking back toward the origin of circuit next receptacle also showed hot-ground reversed, etc until I got to a good reading. Now he hadn't per his statement changed any other receptacle. Started to open up to see if it had a wire disconnect and make a short that wasn't tripping breaker. Found none, all were wire correctly. Ground-hot did show continuity from the load side at the 4th receptacle but not on line side, so I've isolated the area. Working my way back checking each receptacle for the shorted connection an found none, it did have a gas fireplace that used a connection in between the tested points. Assuming this load had gotten damaged in the storm disconnected it (plug-in unit). Reconnected the everything except the fireplace. Turned on power and retested. All receptacles tested ok, no reversals. Plugged in the power strip for the TV and suddenly got a reversal on the lines again. Unplug the power strip, and still have the reversal. Now really puzzled. Shut off power and re-metered, everything metered correctly between receptacles. So thought could it be power strip, so just plugged in the TV and the cable box (the loads on that circuit) Turned on power and no further reversal. Plugged additional load on line and it still held. So it seems to be related to the power strip.

But the question that puzzling is why did the tester still read as a reversal when I removed the power strip until I turned off breaker and then turn it back on? But if the condition is load related, as that seems to be a more logical situation given the reversal remains until breaker is turned of then reset, does it only present when the loads are applied via the power strip?
 
hillbilly1 said:
Probably a capacitive load on that line somewhere bleeding back enough voltage to fool the tester.
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Would the power strip have something of that nature? The multimeter test also showed the ground voltage after the introduction and removal of the power strip, but not by introducing the loads that were on the power strip. That is what is puzzling. The voltage issue remained until turning breaker off then back on, and only reappeared with the powerstrip use.
 
Fred B said:
Would the power strip have something of that nature? The multimeter test also showed the ground voltage after the introduction and removal of the power strip, but not by introducing the loads that were on the power strip. That is what is puzzling. The voltage issue remained until turning breaker off then back on, and only reappeared with the powerstrip use.
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If the power strip was equipped with some sort of surge suppression device it might provide high impedance paths involving hot, neutral, and EGC.
 
Little Bill said:
Those plug-in testers will, a lot of times, show hot /ground reversed when it's actually a lost neutral. You might have a loose neutral somewhere that is making intermittent contact.
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I ran into the same issue a few months ago with a garage GFCI circuit. Tester was showing hot/ground reversed, but the problem was a loose neutral in the panel.

For what it's worth, on that particular service call, it was a 400 amp service with two separate 200 amp panels in finished exterior studded walls. I had recently wired that house brand new

Over half of the neutrals were loose in both panels. And it was the second time I found loose wires in the panels.

The only explanation I could come up with was expansion and contraction
 
Little Bill said:
Those plug-in testers will, a lot of times, show hot /ground reversed when it's actually a lost neutral. You might have a loose neutral somewhere that is making intermittent contact.
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That's my initial thought that's why I also used my meter. That's is when I had gotten L-G 0V, N-G 117V, L-N 6V. Removed power strip, then only after resetting breaker, I had gotten L-G 116V, N-G 0V, L-N 117V.
Plug in the power strip then after about a minute it reverted back to the bad reading that I had at first. So I thought it might have been associated with the loads on the strip. So removed power strip, reset breaker and all read ok so put loads back on to circuit but without the power strip and readings remained in normal status. That stayed that way for over half hour, then started to pack up as it was late. So far no call back, just puzzled by those bad readings and the fact it held that way even after removing the power strip until I reset the breaker, off then back on, then readings were once again normal.
 
Little Bill said:
Those plug-in testers will, a lot of times, show hot /ground reversed when it's actually a lost neutral. You might have a loose neutral somewhere that is making intermittent contact.
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Particularly if there is load connected between hot and neutral, the open circuit in the neutral leaves all points ahead of that open spot at full volts to ground, which gives your plug in tester wrong reference points for it to indicate what is going on.
 
James L said:
I've done that plenty of times. Even if you have to drop a temporary receptacle out of the front of the panel
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My temp receptacle for that is a test cord with 5-15 connector on one end and alligator clips on the other. Only need reliable ground reference, connect all three leads to grounding/grounded conductor and at end of your extension cord any terminal is a ground reference.
 
Got thinking about these measurements, could there be a possibility of this scenario? This system has the old romex with undersized ground, the last box that I opened in tracing the issue showed evidence that a mouse had been in wall at the location but didn't find any damage to conductors inside the box.
Could the power strip have enough issue with it in combination with a conductor that had a rodent damage to the hot, that the circuit when under load the NM conductors are close enough to make the induction draw the hot to ground and make contact, making the ground - hot down stream, as well as make the voltage reading between hot and ground 0V, and ground to neutral 117V?
Got this odd thought when looking at the readings for a corner grounded delta, that you would get 0V reading on the hot/ground of that one phase, but phase to phase would be "normal" for whatever rating of the xfer.
 
Just guessing, but perhaps there's an open EGC somewhere on the branch circuit and a MOV surge protector in the power strip (mentioned by GoldDigger in post #4) was damaged. The MOV might then have a leakage current across L-G which then led to your readings of L-G 0V, N-G 117V. The damaged MOV might be flaky and not always consistent in operation, such as a breakdown in the semiconductor material that was initiated by a prior voltage transient which is continuing to draw current until the power source is removed.
Was the 6V L-N measured at the output of the power strip? If so and the power strip has a circuit breaker, perhaps the circuit breaker might also be damaged.
 
synchro said:
Was the 6V L-N measured at the output of the power strip? If so and the power strip has a circuit breaker, perhaps the circuit breaker might also be damaged.
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That measurement was downstream of where the powerstrip was. The measurement remained the same even after removing powerstrip until the circuit's breaker was turned off then back on. Then the measurements returned to normal. Plug in the powerstrip and voltages go all wonky again. Plug in all the loads without the powerstrip and all the voltage readings stay normal. Powerstrip does seem to have a breaker or surge protection, no markings other than a lit switch with reset printed on it, so can't be sure.
 
KdogSparky said:
I assume when you wired the house "brand new" those loose neutrals were a "pre-existing condition"?
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I'm not sure what you mean.

I wired the house in February 2020 and did the finish in July.

Then this past winter I had two call backs.
The first one was because their electric furnace stopped working and they call the HVAC company back. At that time they found the wires were loose at the breaker. That's when I got called back and found loose neutral wires in both panels (400 amp service).

Then about 5 weeks later I got called back because of a GFCI not working correctly. That's when it was showing hot and ground reversed. It ended up being a loose neutral in the panel, and about half of them were loose again 🤔🤔🤔

I couldn't figure it out because I had just been there a month earlier and tightened all of them. The homeowner even watched me do it, and concurred when I mentioned it on the second call back.

I haven't had any more calls about it since then.
 
Maybe you just have a light touch. I tighten terminals enough to deform the wire a bit, which increases contact area.
 
LarryFine said:
Maybe you just have a light touch. I tighten terminals enough to deform the wire a bit, which increases contact area.
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James L said:
I do the same thing. It needs to be smashed just a bit. Not paper thin, though
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I have a suspicion that in receptacles with clamp type terminals, solid wire is susceptible to loosening when everything is pushed back into the box because the end of the wire may rotate if it hasn't been smashed to some extent. Compressing the wire end with a pliers first could be done also.
Wire wrapped around screw terminals wouldn't be susceptible to loosening in this way.
 
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