100 amp residential house service panel unbalanced voltage and power drain under load. Causing power outage

Question

About a month ago I had my service interrupted - half the house lost power, one leg of breaker box had no power, then while trying to troubleshoot the issue I lost all power to both legs.
Completely rewired the house with brand new 100A service (was way overdue for updating).

Everything has run perfectly fine for the past 3 weeks. All of a sudden half of house lost power again and power was jumping from one leg back to the other, swapping controlling sides. Low voltage on one side and high voltage on the other leg.
Killed all power at the breaker and started one circuit at a time trying to diagnose the issue. Every time I would get to a certain load capacity it would drop to 5V on one leg and jump to 243V on the other leg.

Had an electrician come out to look today and I'm in no better shape then yesterday. He checked all the breaker box and only issue found was a faulty arc breaker. Had the electric company come out a month ago to check if it was an issue on their side but they stated no it is getting correct voltage, but all of this was checked without a load on it. I'm almost positive it's a neutral open but not sure where.
Drainage happens even if there is only 1 circuit on in the breaker box and put a load on it. Can opener drains voltage from 122 volt to 96 volts on every circuit tried without any other load than that. Need help and insight

Answer 1

Typical symptoms of an open neutral. At your main panel measure between the two hots (or any 240v breaker), you should get 240v or close. Then measure between one hot and neutral at the main panel, then the other, varying loads, small space heaters make good loads since they take quite a bit of current. As you move it around and take repeated readings from both hots to neutral, document the readings. It's almost certainly a PoCo issue. This is very serious, open neutrals can do a lot of damage.

EDIT: I should have added that if you decide to do this testing, unplug all your electronics, IE cable box, routers, PCs, laptops, satellite boxes, cell phone chargers, etc. turn off breakers to your heating system, then, one circuit at a time do your testing.

ONE MORE EDIT: (sorry, still recovering from Thanksgiving dinner!) Trying to make my answer as complete and informative as possible. Counterintuative as this may seem, low voltage can be as damaging as over voltage. A motor expecting 120v and now only getting 70 (just an example), is going to over-heat, melt the insulation on the windings and die. All this sucks, but your vacuum cleaner won't anymore! Also light bulbs, esp. incandescent, that are expecting 120v but getting 160 are going to burn out in short order. I'm not sure how CFLs and LEDs respond to wide voltage variations.

AGAIN, THIS IS SERIOUS, TURN OFF EVERYTHING YOU CAN AND GET IT FIXED, MOST LIKELY A PoCo issue, maybe a failing transformer, or bad connection from the transformer to your home.

Answer 2

That is a classic Lost Neutral.

Usually, this is a problem on the power company's end. The triplex cable carrying power from the poletop to your weatherhead uses the bare wire both as the physical carrier wire and as the neutral. Steel has a fatigue limit: don't exceed it and a spring will last forever. Aluminum and copper have no fatigue limit* which means every flexure causes metal fatigue. That overhead line whips in the wind, it is a matter of time before something goes SNAP and it's more likely the neutral wire.

The power company cannot check neutral with the smart meter. It is a 4-jaw meter (2 in, 2 out) and that means the meter has no access to neutral. That would require a 5-jaw meter. So when they check it remotely, of course it looks peachy keen.

However. The second possibility is a faulty neutral connection at a panel or in the meter-panel wiring. If this past work was DIY'd, it often happens that the amateur torques it "gud-n-tight" and does not use a torque wrench per the spec. That is the #1 cause of a connection problem.

I don't like having to buy a torque screwdriver, but these service lugs are generally in the working range of an automotive torque wrench. And I have one of those. If not, a 1/4" beam-type torque wrench typically handles up to 80 inch-pounds, is inexpensive, and never needs calibration. (back to "steel has a fatigue limit and the wrench stays within it"). Just watch out - most of those lugs are hot all the time. Electrical supply houses sell socket extensions certified as non-conductive.

Extreme swings indicate a problem

Note that in a Lost Neutral situation, neutral current seeks an alternate path - through the service Neutral-Ground bond, to the grounding electrode and rods, through the dirt, and back to neighbors' and the transformer's ground rods then on to their neutral-ground bonds. If your voltage swings are excessive, take a close hard look at the integrity of your Grounding Electrode System.

However, if the Lost Neutral is between the main panel and the loads, then the extremes of swing are completely normal. The alternate path through the Grounding Electrode System is not available, after all. So if you are confident in your GES, then look at connections between main and subpanel - that kind of thing.

Answer 3

Sounds like an open neutral; concur with precautionary shutoffs per @GeorgeAnderson answer.

One possible cause: aluminum feeder wires to the breaker panel or elsewhere. Two major concerns:

1. Aluminum oxidizes over time. With (obviously) power off, cleaning the wire ends where they come into the panel would be wise.
2. During heating and cooling cycles, aluminum and copper expand at different rates. Over time, especially with large load changes (especially an issue with electric heat, dryers and hot water tanks), the aluminum will squish out of the (usually copper) clamp attaching it to the panel bus. I saw arcing at the panel in our old place. These need periodic checks for whether they need tightening (every 5..10 years or so).