Learn me: Latent voltage in my house

Neither A/C  unit has an identifiable ground?

TRoglodyte said:

Neutral is finding ground through appliances, be very careful, something is very jacked up. If you cant move through it slowly and methodically call a pro

Agreed.

Have you ever had some taillights or trailer lights that go all wonky on you?  Like the running lights work fine, but when you hit the brakes, one lights up and the other one goes out?  In that case, it's a bad ground and it causes all kinds of odd potentials through the filaments of the bulb.  It's also only 12v.  In this case, you have 120v worth of "I'm going to zap you or potentially cause a fire."  This is why things are grounded in your house.  If something in an appliance fails and causes a voltage leak, its easiest path is back that bare copper wire instead of through you.  When you get the symptoms you're describing, it's like the messed up taillights finding the simplest path through whatever filament it can find, except it's 120v, and you could end up being one of the filaments, or an arc/spark could ignite something flammable.

I hate to sound apocalyptic because it might be a simple thing and not hurt anything, but I also don't want you or your family to get hurt.  I would rather you panic-dial an electrician and find out it was simple than to sit on it a few days and end up with someone getting hurt.

You might also have a failing leg.  One of the two 120v lines coming in might be loose, corroded, or failing somewhere before the panel (between your house and the pole).  When you activate the A/C (which uses both legs) it more or less shares that conductor which is why the other half of your house comes back to life.

While this low-voltage thing is happening, test voltage at the main lines coming in to the panel, and then test the voltage on two adjacent breakers.  They should be the same.

Just get it looked at ASAP so I can sleep sometime soon, m'kay?  :)

What Curtis said. This is a Thing that Needs Fixing.

I am with Curtis on this. Bad wiring has a real potential to cause injury, fire, or worse. I like to do stuff around the house as much as the next guy and have installed lights, ceiling fans, outlets, etc... 

A brown out and back feed through the AC unit, powering a large swath of the house... yeah, that is scary. 

Yup.  Loose something somewhere.  That narrows it down to "yikes."

tuna55 said:

Well that was fun, everything appeared normal, but when I power in the house back on only how half of the house came back on. Now I'm stuck with an angry family. I'm guessing some GFCI somewhere is not happy but I can't tell where. I've got at least eight circuits that aren't behaving despite everything looking fine.

Call the power company again, this sounds like a bad connection on your service entrance.  It's not unheard of for them to not find it the first time and/or just tell you there isn't a problem - it happened to me once and I had to get them out a second time to actually fix the problem.

TRoglodyte said:

Neutral is finding ground through appliances, be very careful, something is very jacked up. If you cant move through it slowly and methodically call a pro

It may also be a bad main breaker and one of the 120v legs is transmitting through the 240v appliances. The resistance of the appliances is why you get a brownout condition. 

With all the breakers off, flip the main back and forth 5-6 times and see if that takes care of the issue. If so, get someone to change the main breaker or call the power company to pull the meter and change it yourself. 

That also appears to be aluminum entrance cable. It is renowned for failing and the lugs working loose. Is it an underground feed or is the meter on the other side of the wall? If any of it is underground, it is suspect. 

tuna55 said:

Well that was fun, everything appeared normal, but when I power in the house back on only how half of the house came back on. Now I'm stuck with an angry family. I'm guessing some GFCI somewhere is not happy but I can't tell where. I've got at least eight circuits that aren't behaving despite everything looking fine.

Been there not too long ago. 
 

edit: recommend leave all 220v breakers OFF if possible until this is figured out. 

All of the above with ghost voltage on a good day is a complex compounding problem, better off calling a licensed professional  IMO

Also, a precursor to help expectations.  Once it's fixed, don't expect zero ghost voltage.  Expect minimal ghost voltage.  All of the unshielded wiring with AC current running next to each other can cause significant inductance.  I was able to get my worst circuit down to about 9V, but when I first discovered it I had 90V in one.

Electrician says it sounds like a bad main breaker losing a phase. He recommended I buy one, though I asked him to come and change it. 

Bad memories.  

Soon after moving to a new house, we had a bad storm in the middle of the night that brought down the crown of a HUGE oak.  It landed, of course, across our service line.  We woke up, assessed the situation, and realized we were lucky to still have power.  I turned on some lights, then tried the TV.  Weird flickering screen and bursts of audio.  Hmmm, that don't look right.  Turned it off, and suddenly the lights in the living room got really bright while the kitchen lights went out.  The outlet by the TV began making a sizzling sound, so I unplugged the power strip.  Nope, whatever is happening is IN the outlet.  Smoke, terror, then it stops.  Whew.  Surprise, now the same thing is happening to an outlet in the kitchen!  Sparks, smoke, then silence.  WTF?  Now the next outlet in the kitchen starts up.  When this happens at 2AM in a house you've barely lived in, it starts to feel like a horror movie.  Or maybe the Money Pit.  No, this is not funny.  Something finally clicked in my head and I ran downstairs and flipped off the main breaker which stopped the madness. 

When the branch took the service line down, it broke the neutral.  Things stayed stable for a few minutes, but then floating voltages and currents began wreaking havoc, destroying nearly all of my GFCI outlets and most of my light bulbs.  Thankfully, that was the extent of the carnage.  

I feel for you.  Get it fixed ASAP.

tuna55 said:

Electrician says it sounds like a bad main breaker losing a phase. He recommended I buy one, though I asked him to come and change it. 

TIL... please keep us updated?

In reply to 11110000 :

jeebus man that's *terrifying*... Seeing's how I'm in the process of wiring up my brand new shop, I've been following this thread with too much interest. And although I don't even have ghost volts where they shouldn't be, thanks for making it so I prolly won't get much sleep tonight! 

In reply to 11110000 :

Had lightning strike the house a hand full of years ago. Not a direct hit. Came in through cable tv.   Similar issues. 

TRoglodyte said:

tuna55 said:

Electrician says it sounds like a bad main breaker losing a phase. He recommended I buy one, though I asked him to come and change it. 

TIL... please keep us updated?

So was it just a bad breaker? 

Finally had a good day for both of us and he came. He found:

The main breaker connections are Allen key. It's likely the original electrician didn't have the key, and so used a big flat head. The connections weren't arcing but they were barely hand tight. 

The rest of the box seemed fine, but he remade the connections in the breaker box and the meter panel. 

He replaced the main breaker and everything seems to be working fine now. I probably could have removed the meter myself, but I would have been unwilling to remake the connections in that panel due to the inability to shut off those connections. 

$250 for service maybe two hours long, I think it's worth my money. 

In reply to tuna55 :

It was worth every penny.