Electrical Mystery

[Ken Rau]

Hi Folks - Long time lurker here who as learned much from the collective wisdom on this site.

This weekend I went to my shop that is remote from my home. Upon arriving I had multiple breakers tripped but not all (5 of 20). After reset everything works except for 1 breaker and I don't see damage to anything. I assume a lighting strike. Curious if there are other ideas.

The circuit that doesn't work is a 20A 120V circuit with 3 outlets. The first outlet is a GFCI. I replaced the breaker and GFCI to see if that was it and no improvement. No apparent arc/damage in main panel. Upon reset either the GFCI or breaker immediately trips (Breaker fine if GFCI is tripped but breaker will trip when GFCI is reset). After other checks I have found that the hot (Black) wire from the GFCI to the second outlet is the culprit. If unhooked all is good and if I hook it to the GFCI immediate trip of GFCI or breaker. That is with that wire disconnected completely (all 3 wires) from the second outlet. GFCI has power without that connected. I don't capture any continuity between the black wire and Neutral/Ground when measured wire to wire where the second outlet. I do find continuity between Neutral and ground but GFCI/Breaker don't trip if they are attached to GFCI without black wire.

This is an old barn and we upgraded electrical prior to insulation and putting up interior walls. Curious of what I might find and interested in any thoughts. Maybe a wire staple or drywall screw through the romex?

Second question - I'll replace the offending wire but not sure I need to pull it out of the wall. This is pole barn construction with the 2 outlets separated by a 4/6 post. 2x4 studs between the posts to add plywood and wall insulation. Do I need to remove cabinets, plywood and insulation and run correctly or could I fish a replacement wire. behind the wall and let it be loose? I have access at the top 10" that I didn't bother putting plywood on. Don't feel that is the way to go but not looking forward to doing it the right way.

[Bill Howatt]

Check for a connection between the neutral and ground - that can cause problems. I assume that you have everything unplugged.

[Cameron Wood]

9 times out of 10 the problems are at the ends & connections and not in the middle of a wire run, so carefully check at both ends, including for nicks where the wire exits the box.

If you do replace the Romex run, it's OK to run it some other way and not being fastened much is not a big issue IMO if it is protected. I have seen more problems from too much fastening (staples) than from too little.

[Jim Becker]

While physical damage to that hot conductor could certainly be because of a screw or something like that, it could also be a critter having a snack. Since you have post frame, if you have horizontal girts behind your wall, you should be able to fish a new cable through if you need to, although it might require a few "fishing holes", depending on the distance.

[Maurice Mcmurry]

The multiple tripped breakers does sound like you had a lightning strike. Did you have a storm? Lighting damage created several very puzzling problems for us. The strike at our house made its way to earth via several pathways and on more than one circuit. It fried a 120 volt circuit and the ethernet cable that ran from our house to our daughters house out back. Several parts of the PC were ruined. We think an extension cord left outside that was purged in during the storm was the culprit. It was near a big oak tree that died instantly.

IMG_2285.jpg
Lightning Casualty Tree

[Michael Schuch]

Is the breaker a GFI breaker? You can't have 2 GFI's on the same circuit (I mean the breaker + the outlet).

Pull the incoming wires off the GFI outlet (flip the breaker off first, of course). Put an ohm meter / continuity meter on the neutral and ground wires. They should be open, no continuity between them.

[Wayne Cannon]

Very similar symptoms from a mouse that followed a wire "runway" until it could no longer squeeze through the hole in a stud with an additional wire. It chewed the wire until it shorted, melted several feet of the wire's insulation, fried the mouse, and tripped the breaker, which kept tripping.

That wouldn't explain five breakers. A lightening strike at my brother's hit a ladder hanging horizontally on the outside wall, followed the ladder, jumped through the garage wall to a junction box, down the wall and across his driveway to the ground stake at the entrance meter & breaker box -- blistering the asphalt driveway above its path. That could definitely leave hidden damage to wiring tripping a GFCI.

My GFCI problems came from rain leaking into an exterior outlet box, unsealed after siding was replaced. All looked normal & there was no continuity across wires. It took a week after each storm to dry enough for the GFCI to
remain set.

Hopefully some ideas.

[Ken Rau]

A critter is very possible - This alone may be reason to dig deeper to ensure we don't have to take some other mitigation.

[Ken Rau]

The breaker is not a GFCI - only the first outlet. Line/Load are set correctly.

I have not put the meter on the ohm meter on the Neutral and ground at the GFCI yet but did on the next dowstream and did see continuity. That will be something else to check when I get back out there.

[Ken Rau]

Thanks for the input guys. Will share as I learn more.

This is an old barn with a separate meter and wire running directly from the pole to the barn outside. We have had storms but I unfortunately had not been to the shop for 2 weeks. I didn't look hard but didn't see anything odd outside or in the box and like I mentioned, everything else works fine. I'm wondering if a critter or nail on a staple could have reduced the integrity of the insulation and a lighting strike may have energized enough to make it where there is now an arc across the air gap.

Also wondering about continuity between neutral and ground I think they are bounded in the breaker box but will have to verify.

"Fun" brain teaser - just wish I had more time to look into it and more importantly to spend in the shop.

[Rollie Meyers]

Is the breaker a GFI breaker? You can't have 2 GFI's on the same circuit (I mean the breaker + the outlet).

Pull the incoming wires off the GFI outlet (flip the breaker off first, of course). Put an ohm meter / continuity meter on the neutral and ground wires. They should be open, no continuity between them.

The only reason you should not have two GFCI's is wasting money, not code prohibition on doing so.

[Bill Howatt]

Thanks for the input guys. Will share as I learn more.

...

Also wondering about continuity between neutral and ground I think they are bounded in the breaker box but will have to verify.

"Fun" brain teaser - just wish I had more time to look into it and more importantly to spend in the shop.

Yes, the neutral and ground are bonded at the panel - and in your case probably in the barn panel. When you have a sub-panel powered by the house's main panel, the bonding screw is left in the main panel but removed from the sub-panel. Your barn's panel is likely the "main" panel for its circuits.
Even though the neutral and ground are bonded, a GFCI will detect if there is any current going down the safety ground (or elsewhere) that should be going down the neutral.
I had a situation where the previous owner wanted a 3-way switch but didn't have the right cable so he used the ground wire as the third conductor (neutral). Only found out about this when installing a GFCI on the circuit that wouldn't power up without tripping. Electrically without the GFCI it worked but illegal.

[Frank Pratt]

I think he's referring to having a GFCI breaker feed a GFCI receptacle. Doing so can cause issues with the electronics in the GFCI devices.

[Rod Sheridan]

You may have had insulation damage to the line conductor caused by lightning, which in many cases is not detected by a conventional multimeter.

The insulation resistance should be checked with an insulation resistance meter, set it to apply 500 volts and check the line to ground and neutral.

Regards, Rod

[mike stenson]

so he used the ground wire as the third conductor (neutral)..

oof. I'd hate to find that out by touching a grounded case.