Line fault at the outlet -- do I need an electrician?

almarg9,456 posts

03-22-2020
2:11pm

@Hilde45, when you measured the 4 volt difference between safety ground and the miswired "hot" terminal on the outlets was some or all of the equipment plugged in at the time? If so, I think it would be worthwhile to repeat that measurement with the equipment unplugged. In addition to the possible causes Erik has cited for the 4 volt measurement I’m thinking that applying 120 volts to the neutral of whatever equipment was plugged in could have resulted in AC leakage to ground within the component(s) that might have been responsible.

Jim ( @jea48 ), does that sound plausible to you?

I’m thinking that applying 120 volts to the neutral of whatever equipment was plugged in could have resulted in AC leakage to ground within the component(s) that might have been responsible.

Jim ( @jea48 ), does that sound plausible to you?

Al, (almarg), yes I would think that is a possibility too. Any connected load along the entire length of the branch circuit.


Also as I said previously.

1) VD, (Voltage Drop), on the neutral conductor due to the connected load on the branch circuit.

2) An induced voltage that is/may be created by the hot and neutral current carrying conductors onto the equipment grounding conductor.

4Vac would be pretty high in my opinion though.

Here is another possible reason:
IF there was a decent size load connected to the circuit at the time the 4 volts was measured it could be caused by a slightly loose and or corroded neutral connection anywhere from the panel neutral bus connection to the outlet the OP measured the 4 volts.

It would be interesting to know if the other branch circuit the OP measured 124Vac on is fed from the same Line,Leg, as the circuit he is experiencing the problem on. If yes, the 4V could very well be caused by a slightly loose and or corroded neutral wire connection in the branch circuit. That is one of the problems with using the duplex outlets for making the in and out connections for the branch circuit wiring. Though I have seen the same thing happen with a slightly loose and or corroded joint where a cheap hard plastic wirenut was used.


Though none of the above has anything to do with the AC reversed polarity problem the OP is experiencing.

Jim.

hilde45 OP

As far as finding the outlet closest to the panel is a bit tricky, as the wire which feeds things disappears into the ceiling and I'm not sure where it goes first. I'm sure where the 3rd, 4th outlets are, but not the 1st, 2nd ones. If the problem was at the panel, that's at least clear. If it's not at the panel, then I suppose I can just *try* what might be outlet #1, first, and see what I find.

Turn off the breaker and start checking for everything that is Dead. Including ceiling lighting. For the wall receptacle outlets a 120V drop light works great.  You can move pretty fast from one outlet to the next.

Use a piece of masking tape on the cover plate showing you have checked the outlet/s. You might want to make a second pass to make sure you didn't miss one.

Jim

" So, our house is a mixture of old/DIY and new (renovation); the problem is with the old part of the house."


Hmm, that’s telling eh miller?

Thanks, all.
I ran out of time today, but I'm going to
(a) unplug all things on that chain
(b) measure again to see if the 4v are still there
(c) turn off the breaker and measure everything before (and more) again to see if there's leakage
(d) perhaps take off the breaker cover and see how that breaker is wired — WITHOUT touching anything.

I'll try to report back in case you all are still interested in interpreting.
This is really helpful.

Correction:

jea483,299 posts

03-22-2020
2:57pm


Also as I said previously.

1) VD, (Voltage Drop), on the neutral conductor due to the connected load on the branch circuit.

2) An induced voltage that is/may be created by the hot and neutral current carrying conductors onto the equipment grounding conductor.

4Vac would be pretty high in my opinion though.

"4Vac would be pretty high in my opinion though."

That statement was meant for #2 only.
( An induced voltage that is/may be created by the hot and neutral current carrying conductors onto the equipment grounding conductor. )
It does not apply to #1.

hilde45 OP286 posts

03-22-2020
2:35pm

So, our house is a mixture of old/DIY and new (renovation); the problem is with the old part of the house.

If you would have said the branch circuit wiring you were having the problem with is DIY, I would tell you to hire an electrician to find and fix the problem/s.



Is the wiring in the old part of the house original wiring? Any idea what year that part of the house was built?

Just a guess the branch circuit wiring you have been troubleshooting is 14 gauge. The breaker in the panel is a 15 amp.
Just a guess there is maybe 6 to 8 duplex receptacles on the circuit. At present you have not posted if there are any ceiling light fixtures on the circuit.

By chance do you know what type of wiring the branch is? Is any of it exposed where you can see it? Maybe a back side of an unfinished wall? Maybe in the room the electrical panel is located?
Examples of the type of the branch circuit wiring:
Romex?
Thin wall rigid (EMT) Conduit and wire?
BX? (Wire with an outer flexible interlocked steel armor).