Random brief voltage drops throughout the day impacting half the house

Question

For the past three months we've been experiencing lights flickering and certain electronics resetting due to voltage dips down to as low as 70 volts. This happens completely randomly regardless of new or existing loads and usually lasts a couple of seconds but can occasionally last longer and that's when electronics reset.

We have a single phase setup with two lines coming into the panel and this problem is only on one side. All circuits have now been replaced. I have mapped out all the circuits and have tested all receptacle for correct wiring. I have consulted with two electricians who haven't been able to figure this out. The dips don't cause any circuit breakers to trip. The power company has been out here a few times but of course when they come out, it doesn't happen. But just last week they installed a voltage monitor.

Amazingly this issue goes away for a few days wherever our electricity is shut down. It happened a couple of times due to storms and also when they came to install the monitoring meter and had to shut it down.

Any ideas?

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UPDATE: I was standing at the panel with my meter hooked to the fluctuating main line when I noticed another drop happening. Turned off all the main circuit breakers and voltage dropped very low and after a couple second was reading ZERO! It kept going to 15/16/30 back to 0. It was only after I turned the breakers on about 30 seconds later that the voltage was restored.

Answer 1

Finally after months I convinced the power company to open up the transformer and check for issues. And as soon as we opened it, the problem was obvious. The line going to our house was mistakingly disconnected by the power company instead of our neighbor's house where they had construction a few months back. But they didn't properly connect it back. One of the bolts was missing and the other one was very lose. This was completely the fault of the power company and they caused me months of misery.

Answer 2

It's the elephant in the room

I say that because you've replaced a whole ton of stuff, but there are a few things you have not replaced. Because they're hard. Those things are energized 24x7 and cannot be disconnected except by the power company coming out.

So it will be:

• the service entrance wire attachment to the main breaker
• the service entrance wire attachment to the meter
• the service lateral attachment to the meter
• bad connections between meter pan and meter
• (rarely) the connection between main breaker and panel bus bar or main feeder
• the service lateral attachment to the utility supply, which fortunately will be the ones they will be disconnecting so you can inspect the above
• both ends of the breaker-protected main feeder if you have one (easier to inspect)

The most likely cause of this is someone failing to set terminal torque with a torque wrench.

One might think "oh then I'll just torque it NOW and that will magically fix it" no, it's too late now. It has been arcing in there (not least you want to take it apart to witness the arc damage as conclusive proof that you found it). But you also want to clean out oxidation, soot and the other poorly conducting garbage that has gotten there because of the arcing.

So take it apart, clean it up, add NoAlox paste if you are mixing metals or on general principle (note those lugs are made of aluminum) and then with a proper torque wrench, torque to the spec.

One might presume the power company did at least some of that while installing their voltage monitor.