Diagnose cause of voltage fluctuation in house

Question

Background

• My house has 100 amp service with all copper wiring and all wiring contains a hot, neutral and ground wire.

• The past three weeks the lights in the house go dim and bright. The fridge makes a little noise when the voltage drops/spikes. It happens sporadically and some days it won't happen at all, other days it happens frequently throughout the day (no pattern to the time between occurrences).

• The load doesn't seem to affect when this happens.

• When the problem first appeared I started checking the voltage on the panel. When it happens one leg will drop down to around 118 volts for a few seconds, when it typically stays around 122 volts. One time one leg spiked to 169 volts.

• As i'm writing this message the fluctuation in voltage has happened at least five times, no load change in the house has occurred over that timeframe.

What I have done

• I had an electrician come check the panel and verify I have no loose neutrals. He said the power company is to blame. He checked out the panel and didn't find any issues. Unfortunately the spike / lowering of voltage didn't happen while he was here. I called power company.

Here is how my visits w/ power company has gone:

• Visit #1: Technician comes out, checks voltage at meter. Monitors voltage for a few minutes, no problems arise then leaves. Declares no problems on their end.

I start watching the neighbors house to see if they are getting any power fluctuations. I notice it is happening for them also. I speak with the neighbor and they claim it has been happening for months to them. They thought it was wiring in their house. Unfortunately they are renters and they can't be counted on for any help.

• Visit #2: Technician comes out, I'm home this time. He monitors voltage and has me put load on the system. Everything checks out, nothing happening. I tell him neighbors experiencing same issue. He says not seeing anything, will do a 'line trace' in a few days.

• Visit #3: Three technicians come out they check voltage at my meter, let it run for awhile. they check neighbors meter, find neighbor has issue in the meter and they fix the issue. They still don't see anything happening at my meter.

They say the transformer is relatively new and say it can't be the problem. As they are walking around the poles and other houses, I look at the volt meter they have installed at my meter and it drops down to 118 volts. I mention this to technician and he says that shouldn't happen.

I ask one of the technicians if something was going out in my neighbor's house could that impact my voltage? I said they have been running their AC all the time. He said it should have a thermal overload and not cause any issues w/ other neighbor's electricity, but he has seen where things fail and it can cause issues.

Technician's leave saying these things can take time and need to be patient.

What to do next?

I'm far from an expert on this, so any help is appreciated. I don't want voltage fluctuations harming things in the house.

Could something in my house be going bad which is causing the issue? Should I start turning off circuits in the house and see if the problem occurs? Would that be one way to troubleshoot the issue?

I'm afraid the burden of proof is on me now regarding the power company.

Answer 1

120v is supplied as two "legs" of 240v. In a perfect world, loads would be balanced and neutral would not be required. Neutral is there to assure the midpoint stays the midpoint even if the two legs are not balanced (and they are almost always not balanced).

A couple of volts of drift is no big deal, and is a normal and healthy effect of uneven loading on the legs (you could reduce it by using extra thick wire, but then you're wasting money).

However, tens of volts of drift says the neutral is not doing its job, you have an open neutral or lost neutral. This means balance is a matter of luck, and most of the time some appliances will see less than 120V while others see more than 120V, which is likely to damage the appliance and even start a fire.

240V loads such as oven, water heater, installed A/C unit, electric-car charger, heat pump, installed electric heat or electric dryer, will have no effect whatsoever on a neutral problem.

The fact that neighbors are also having the problem helps. What would help the most is if you have some sort of data-logging system actually recording leg voltages over an extended length of time. Significant shifts in leg voltage (I don't mean 2 volts) would absolutely reveal a damaged or lost neutral.

Answer 2

A loose or lost neutral for sure.

I had a similar problem at my house. It was the connection in my main meter panel. A previous homeowner had illegally upgraded the service and didn’t torque down the connections to the proper setting.

The transformer being new does not rule out the problem being there. We got a new transformer on our block and all houses connected were experiencing light flicker and sometimes outages just long enough to reboot Internet modems. Turns out the transformer was installed wrong. The crimps were aluminum and were corroding. Copper wire to copper wire connections should use copper crimps. The tech thanked me for calling the problem in because the connection would have corroded until it became more loose and likely would have melted away. I was lucky. This lineman was willing to be thorough with investigating possible issues.

Answer 3

Power company connections for sure, only way to know is bypass the meter and jump it out under load, measure the voltage, if there are inconsistencies it’s very likely it’s the pole connections or the house connections, I’ve had that happen many stupid times. If they rule that out, then it’s the meter connections/socket or very possibly the buss bar on the panel, I seen a mix of them all happen. 20yrs I thought I saw it all, but then comes more.