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My question is a bit more technical then most as I have narrowed the problem down to a bad neutral somewhere in the system. There is a service wire from the house overhead to a barn, then another line from the Barn panel to a pool house. (The Main service feed goes to the house) In the pool house, the homeowner was running a compressor that started idling dumb and not running properly. After investigating, I found that everything seamed normal until it was put under load and then the voltage between the two lines in the panel went crazy. I think it was like 50 and 170 instead of your normal 110/120.

After this I was pretty sure it was a bad neutral and it was backfeeding trying to run the compressor. I went back to the barn and checked the voltage there and it was the same as in the pool house. When I went into the house, the voltage at the breaker in the house to the barn was fine. I am trying to confirm that the issue is then between the house and the barn. The line had fallen and we raised it back up after a storm and it worked fine for a few months but maybe something broke in it and we can't see it?

The main thing I am wondering is if the wire is bad underground from the Barn to the pool house, can it still change the voltages at the barn panel even if the wire to the barn is ok? I don't want to focus on the wire between the house and the barn and the problem is between the barn and the pool house. I'm just trying to confirm my findings.

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  • So a service wire is the wire up to the meter, and it can be 3-wire. Generally it's the power company's responsibility. Everything past the meter is feeder and must be 4-wire (unless it's fairly old). Is that how your system is set up? How is grounding done at each building? How about neutral-ground bonds? Mar 29 at 16:09
  • I have looked at the wire connections and they seam ok. A bit rusted in the barn panel and so I was thinking that might be the problem. I didn't think about the grounding but it is a 3 wire from the house to the barn and from the barn to the pool house. I am assuming that both the barn and the pool house have their own ground rods but I am not sure of that anymore. As a note, this was a job I checked out last fall and he is now wanting it fixed before his pool gets green. Mar 29 at 16:16
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    I deleted the comment, and I'm sorry I was not clear. There was no sarcasm. I did not believe you had done the prior work. Specifically, I am warning you of the liability of being tangled up in this job. The current situation is a severe safety hazard, especially to pool users, and that creates huge liability for you, including jail if someone is killed. No sarcasm! I am saying either unhitch your wagon from this job, or if you are already involved, pull in a licensed electrician and have them write an action plan. That's for YOU: it's your "get out of jail free" card. Mar 29 at 18:34
  • This question does not appear to be about home improvement within the scope defined in the help center.
    – FreeMan
    Mar 30 at 11:10
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I'm sorry, but we have to talk about legalities.

Especially given the high risk here.

You are not a licensed electrician and that places limits as to what you may do.

  • You CAN do work the AHJ deems trivial, such as changing receptacles, switches and light fixtures.
  • You CAN diagnose and test, take deadfronts off panels and poke around with a voltmeter - basically anything a home inspector can do.
  • The homeowner is entitled to DIY (except a few jurisdictions like NYC), and you are allowed to genuinely assist under their supervision; but this can't be a sham.

But people will assume the worst, especially after an accident.

The problem here is that between the 3-wire feed which may be 40 years old (but is that documented?), the known lost neutral (pretty much the worst-case scenario), and the pool for Pete's sake. Read electrical drowning reports, and they always open with scenes like this. You're already involved, so it's a liability albatross for you.

Job One must be to sever yourself from that liability, and the path there is to have a licensed electrician review the site, write an action plan, and serve it on the customer. That shifts liability to the customer and gets you off the hook. Preferably get the customer to pay for it, but even if you have to eat it, it's a "get out of jail free" card.

Don't take my word on it. Ask your lawyer.

Based on what you say, I'd confirm your analysis

Given that the voltage swings are extreme at the barn and pool, and not at the house, it seems like a lost neutral somewhere between house panel and barn panel. Given that several splices are involved in the transition from panels to pole line, it could be any of them.

You say that the installation was previously done (before your time) with 3-wire "triplex" overhead service drop cable, with a bare neutral. That was legal prior to (I want to say) 1999, but not in every case; where there were parallel metal things e.g. water pipe, the ground was sometimes required to keep fault current from corroding the pipes. Since it was installed prior to that, it should be grandfathered by the inspector. Not by the reaper, though: neutral problems like this one are exactly why it was outlawed.

So the short-term quick-fix is to find and fix that poor neutral connection. Note that NEC 2017 requires use of a torque wrench/screwdriver for most connections, but larger connections such as feeder required it prior to that.

Simply doing the quick fix and walking away will still leave you with big liability exposure.

The next things to look at

And again, merely looking at these things yourself will not reduce your liability.

But I would start with the Grounding Electrode System inclusive of Ufer grounds, ground rods, and all the special grounding and bonding that must happen around a pool. I'll bet you a lot of that is out-of-order even for the time of original installation. If work was illegal at the time it was done, it is not grandfathered and must be done to current Codes.

Then I'd look at GFCI requirements especially around the pool areas.

Next, I'd look at running that fourth ground wire. The problem with a 3-wire feeder is exactly this: nothing really controls a "lost neutral", and if the GES is in good order, it can actually float the earth around the buildings to dangerous levels. (which can combine rather badly with things like fence lines).

The electrician's report would cover all that.

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