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After a recent power outage i have serious power issues in my garage. With no load, i get solid 123vac from both channels in the box and a solid 240vac across both legs. As soon as i apply a load one channel drops to approx 100vac and the other shoots up to near 180vac. I have tried isolating individual circuit breakers, but so far only helps minimally and still have no usable power in the garage. It looks to me like multiple breakers were damaged. Is this plausible?

wsnbh
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    Sounds more like a damaged neutral connection. Is this garage directly utility fed with its own meter, or fed from another building where power is still good? – Ecnerwal Oct 23 '21 at 23:16
  • Yes, @Harper-ReinstateMonica very likely an open neutral. The OP didn't say if the garage was detached or had it's own sub-panel. If a sub-panel and the neutral was properly isolated from ground, I could see why there is no usable power there. In the main main panel, with the ground and neutral bonded, some of the current might be flowing thru the grounding system....as well as "heating up" grounded appliances and devices, creating a major shock hazard. My advice: Turn everything off and get the power company out there ASAP. – George Anderson Oct 24 '21 at 00:02
  • Fed from main building where power is still good. – wsnbh Oct 24 '21 at 00:19
  • @Harper and Ecnerwal thanks to you both for the feedback. I will have that checked out. – wsnbh Oct 24 '21 at 00:21
  • @George Anderson - the garage is detached and has its own sub-panel. Zero potential between ground and neutral that I could tell. Also, grounding stake is in place just outside the foundation with grounfing strap attached. Could this be a bad panel? – wsnbh Oct 24 '21 at 00:26
  • Then it's on you. It's probably a loose / mistorqued neutral connection in the garage subpanel or the main panel where the feeder attaches. – Harper - Reinstate Monica Oct 24 '21 at 00:27
  • One other note, I used a circuit checker on nearly every outlet, and I get two green lights every time. – wsnbh Oct 24 '21 at 00:46
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    Zero potential between ground and neutral is only relevant if you have a 4-wire feeder, and the neutral-ground bond in the sub panel has been removed (as it should on a 4-wire feeder). On a 3-wire feeder, your garage will have a local neutral-ground bond that will affix ground to neutral (which gets quite dangerous if you don't have local ground rods!) – Harper - Reinstate Monica Oct 24 '21 at 00:59
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    Crap. I screwed up. I missed that the power problem was only in the garage. But since isolated to the garage, the POCO is probably not to blame. I agree with @Harper-ReinstateMonica that you've got a bad neutral between the main panel and the sub-panel. Sorry for missing that point. I'll delete that comment after a bit. – George Anderson Oct 24 '21 at 01:06
  • "As soon as i apply a load ..." - How big is the load? – marcelm Oct 24 '21 at 08:08
  • Small load, just turning on a breaker, with maybe ceiling fixture on, or garage door opener plugged in (not activated) – wsnbh Oct 24 '21 at 20:01
  • Quick update, I replaced all the breakers in the garage panel. They were wuite corroded and not lookung very healthy. Alas, as expected did not resolve the issue. Ill call a different electrical company tomorrow. – wsnbh Oct 24 '21 at 20:02
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    Why are you risking so much asking a bunch of internet strangres, rather than paying a qualified expert? – Robbie Goodwin Oct 24 '21 at 20:42
  • @RobbieGoodwin maybe he has fire insurance – john Oct 25 '21 at 02:18
  • @RobbieGoodwin Sometimes getting a qualified expert is (a) expensive and (b) not so easy and/or more expensive on the weekend and (c) hard to do given the ongoing pandemic. (No COVID-19 doesn't cause electrical problems, but for a variety of reasons it has resulted in a shortage of qualified electricians to do small jobs in many areas.) So asking, in order to possibly self-fix and at least to know the right things to tell a professional, makes a lot of sense. – manassehkatz-Moving 2 Codidact Oct 25 '21 at 02:32
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    @manassehkatz-Moving2Codidact That does sound reasonable, and what I foolishly forgot to mention was, in this or any other technical situation the solution is to ask as many qualified experts as it takes to find one who is happy to first re-summarize the situation, then explain the answer in terms that suit whoever's asking… – Robbie Goodwin Oct 25 '21 at 18:21
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    Also worth noting, drawing any current from circuits affected by the wonky voltage problem is a pretty significant fire hazard. Wherever the neutral wire has high resistance it will be releasing heat (or even possibly arcing). – le3th4x0rbot Oct 26 '21 at 13:54

3 Answers3

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This sounds like a lost neutral. Assuming it affects everything on the same power company feed, CALL THE ELECTRIC UTILITY. NOW!!!. This is a serious problem that can affect safety and damage equipment.

The key is "everything". You mentioned "garage". If your power comes into your home (main panel) and from there feeds your garage (subpanel) and the circuits in the house are fine but the garage has problems, then you need to call an electrician as the problem is in the main panel (breaker to subpanel), subpanel or (more likely) the wiring in between.

However, if it is "everything" - i.e., house and garage, or the garage has its own meter, then call the power company first, because they will come for free and an electrician won't, and typically after outages (especially weather-related), the problem is more likely on utility-owned wires/equipment.

See Circuit Breakers on and outlets not working for more information.

manassehkatz-Moving 2 Codidact
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    thanks for the feedback, truly appreciated. Based ob the info you and others have provided, I think the issue may be lost or very weak neutral. Not sure how to test for that but i will chase that down. I will post updates as I progress. – wsnbh Oct 24 '21 at 00:36
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    @wsnbh First thing you do (before trying to test and investigate), disconnect all the loads in the garage or turn off all breakers there. Things like the 180V you see on a 120V circuit can easily fry your stuff. – TooTea Oct 24 '21 at 19:37
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    @wsnbh If this is the "everything" case - STOP. Don't chase anything down, turn everything electrical in your house OFF and call the power company first. – J... Oct 25 '21 at 13:57
  • When you call the power company, use the words "lost neutral". This may cause them to prioritise your call more highly than if you just talk vaguely about the voltages being wrong in your garage. – Dawood ibn Kareem Oct 26 '21 at 01:56
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    @TooTea don't disconnect the loads as there's some chance it will cause the voltage to shift more and break something that's not broken yet. Rather just turn the power off. – user253751 Oct 26 '21 at 16:45
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Based on my diy.se reading, you may have a damaged neutral wire to your garage or whole house, which is dangerous. See Loose Neutral or Poor Ground?

You may need to get an electrician to investigate.

The neutral wire balances the two opposite legs of the 240/120 split-phase power system, keeping both legs at approximately 120V despite different loads on each leg. If the neutral connection is weak or breaks, then the power from one leg goes through the loads on it, then through the loads on the other leg, and the different loads can have substantially more or less voltage than they are designed for, with the potential to destroy the devices and start a fire.

Triplefault
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First, make sure the house is OK. The "Lost Neutral" symptoms are slippery as can be, and are often mild enough to not be noticed. My cottage complex had an epidemic of appliance failures until my sweetie noticed a Crock Pot not heating well and the toaster being "slow".

But if the house has no trouble, this is a failure of the neutral wire on the feeder between house and garage. 90% of the time, wire failures are at the terminations (ends/lugs).

So, the right answer is to de-energize the feeder, then remove the neutral wire from its lug in the main panel, inspect the lug, inspect the wire end, clean it, refresh the anti-oxidation goop, put it back in and torque it to the panel specification.

And then, go out to the sub panel and do the exact same thing.

Chances are that'll nick it. If not, look for an intermediate splice that failed. If no splices have failed, then you have the less likely but more expensive case of a wire failure inline or underground, e.g. from a rock penetration (which is what you get when you do direct burial in rocky soil without lining the trench with sand above and below).

If you need to replace the feeder, remember that aluminum is a perfectly fine and safe choice for large feeder. The lugs are aluminum anyway.

Harper - Reinstate Monica
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    I'm not even American, and thought "lost neutral" while reading the question. It is scary how unrestricted the US power legislations are. – Criggie Oct 25 '21 at 00:44
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    @Criggie they are not "unrestricted", they have their honest share of rules and restrictions. And, losing neutral in an european 3-phase system (230/400V) is just as bad. Actually worse, because in US your expensive stuff is likely to have 100-240v universal psu and survive. Good luck with any electronics at 300V – fraxinus Oct 25 '21 at 06:40
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    Have you considered renaming your user account to The Lost Neutral Guy? – user253751 Oct 25 '21 at 09:17
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    @fraxinus I have had exactly this a few weeks ago in EU. The neutral wire was installed too deep in its clamp and had a bit of insulation wedged in. It ran on a weak connection at first, then a spark gap for almost a year, before the metal was finally eaten away. When I measured 400V on a power socket after multiple applicances died, I called the power company. Luckily, the emergency electrician diagnosed the botched installation of the neutral wire, so the original electricians' insurance paid the bill. – orithena Oct 25 '21 at 16:35
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    @Criggie and it can happen with European single-phase also, it just happens out at the transformer. People keep misestimating how US power works. – Harper - Reinstate Monica Oct 27 '21 at 19:20