Intermittent low voltage on one leg

[Clueless in Charlotte]

I have recently starting having an intermittent issue with low voltage but only on one 120V leg. My house is 2 years old, on a slab and the incoming power lines are underground. The first time it happened my kitchen overhead lights went out during the day so I thought we had lost all power. However, I soon discovered it was just some circuits that were down. I called the power company and they said to turn the range (220V) on. As soon as I did that the lights came back on. I didn't check any voltages because I assumed it was just an anomaly.

The next weekend the kitchen lights (LED bulbs) starting flickering and dimming. This time I turned off the main breaker, removed the circuit breaker panel cover and checked voltage on both legs. One leg was good (~123V) but the other leg was only 65V and only 37V if I swapped the test leads. Hot to hot read only 159V and dropped to 132V with the test leads reversed. Please note that I was reading the voltage with the main breaker off. I assume that means that it could not possibly be a bad breaker or loose connection in the panel or house wiring. If that is an incorrect assumption please let me know.

The main breaker was off for about an hour and when I turned it back on I noticed the digital HVAC thermostat didn't come back on. While I was researching that my wife noticed it came back on and the air conditioner started running. After that the voltage was back to normal. Both incoming legs read 123V and I get ~240V across legs. Readings are the same with the test leads reversed.

The next night 2 breakers tripped so I had an electrician come out the following day. After telling him my findings he said to call the power company. Customer service at the power company was supposed to put in a request for a monitor on the meter.

The next weekend the lights and circuits on the suspect leg went out again. One leg was normal but the other leg was low voltage just like before. I called the power company and they said they would dispatch technicians. After 5 or 10 minutes the power in the suspect leg was back to normal. The technicians arrived about an hour later but they didn't really do anything except read the (now good) voltages. They said the guy who would put the monitor on was out until Monday.

The circuit breaker panel and the meter are on opposite sides of the same wall, less than 1 foot apart. Again, when the problem is present, 1 leg reads low voltage with the main breaker off so I assume there is a bad connection or splice between the transformer and the meter. However, the technicians said there could not be an issue with the connection at the transformer (hard to believe).

Does anyone has any ideas on what the problem could be or how I should proceed? The power company hasn't been very helpful and still hasn't put a monitor on the meter as far as I know.

 

[Jadnashua]

Is your supply wiring copper or aluminum? If it's aluminum, two things: the panel must be approved for use with aluminum, and second, it needs the anticorrosion paste on the connection along with being properly torqued.

 

[Sponsor]

 

[Clueless in Charlotte]

The supply wiring is aluminum. The house is new (< 2 years old) and was subject to city building inspections during construction. The builder completed about 100 houses in our section of the development during the last 3 years so I assume they were all build to code with approved panels and anti-corrosion paste. I'm trying to rule out the panel and house wiring by reading the voltage with the main breaker off. Is it is a legitimate assumption that the panel and house cannot in any way effect the voltage reading on the suspect leg with the main breaker is off?

 

[DonL]

Does anyone has any ideas on what the problem could be or how I should proceed? The power company hasn't been very helpful and still hasn't put a monitor on the meter as far as I know.

It sounds like you have a loose connection in your breaker panel.

I would turn off the breakers that you do not need for test.

Arc fault breakers can trip and normally it is for a reason.

Call a Pro if you do not know.

 

[DonL]

The builder completed about 100 houses in our section of the development

That may be the problem, Over built for the power requirements, In your hood.

Builders have no clue. They think that shit flows uphill too.

Good Luck. I would ask the developer of the property.

 

[Clueless in Charlotte]

It sounds like you have a loose connection in your breaker panel.

I would turn off the breakers that you do not need for test.

Arc fault breakers can trip and normally it is for a reason.

Call a Pro if you do not know.

I probably didn't make it clear but the 2 breakers only tripped one time and the voltage on the suspect leg did not drop in that instance. That is what prompted me to call an electrician. The voltage on the suspect leg has dropped at least 3 times that I know of but does not trip any breakers. So, are you saying that a loose connection in the breaker panel could still cause one leg to be low voltage even with the main breaker off?

 

[DonL]

So, are you saying that a loose connection in the breaker panel could still cause one leg to be low voltage even with the main breaker off?

No. Unless it is a meter base problem.

You are on a shared transformer so other users on that transformer secondary will affect your voltage too.

 

[Clueless in Charlotte]

No. Unless it is a meter base problem.

You are on a shared transformer so other users on that transformer secondary will affect your voltage too.

Okay, thanks. That helps to know the problem isn't in the panel or house wiring. A lot of people were telling me it could be a breaker issue but I didn't see how that could have any effect with the main breaker off. Now I know I can look to the power company. Hopefully they will be willing to check the connections inside the meter housing as well as the transformer. I've asked my neighbors and no one else is having any issues.

 

[Bluebinky]

By "leg", do you mean the lug on the main breaker? What about the voltage on the incoming wire on that side? If there is no power on the wire itself, then it would be like others have said -- meter base, or power company feed from the transformer.

Be very careful, as this is a dangerous area to be working on, even if you know exactly what you are doing!

 

[Clueless in Charlotte]

It may not be the proper term but I'm using "leg" to mean one of the two 120v supply lines. I have checked it at the connection where the wire attaches to the main breaker and at the bare wire itself. The electrician tightened both supply lines and the neutral line on the main breaker but he said they weren't loose and there was no evidence of corrosion. To restate the problem, the voltage on one of the 120v supply lines drops intermittently (reads anywhere from 68v to 106v). It has happened 3 times in a 14 day period. The low voltage condition is always the same supply line and has lasted from 5 or 10 minutes to 1 or 2 hours. Thanks for the cautionary note.

 

[Jadnashua]

You have connections at the power meter that bring the power to the panel...those must be installed properly as well. It does not take much to convert an aluminum wire to an insulator. FWIW, aluminum almost instantly 'rusts', and AlO2 is a good insulator. The reason why Al doesn't just rust away to nothing like iron does is that the AlO2 coating actually seals the metal inside rather than being a larger molecule like FeO2, which then exposes more underneath as it flakes off. Without the proper torque and anticorrosion applied, it can look fine, but have issues, especially with thermal changes.

If you have access to a FLIR, or maybe even an IR thermometer, you might be able to locate the offending connection(s). They will be hotter than the side working normally, since they are acting like a resistor, dropping the voltage available.

 

[Bluebinky]

Bug the power company some more (tell them what you said in your last post)...

 

[Clueless in Charlotte]

You have connections at the power meter that bring the power to the panel...those must be installed properly as well. It does not take much to convert an aluminum wire to an insulator. FWIW, aluminum almost instantly 'rusts', and AlO2 is a good insulator. The reason why Al doesn't just rust away to nothing like iron does is that the AlO2 coating actually seals the metal inside rather than being a larger molecule like FeO2, which then exposes more underneath as it flakes off. Without the proper torque and anticorrosion applied, it can look fine, but have issues, especially with thermal changes.

If you have access to a FLIR, or maybe even an IR thermometer, you might be able to locate the offending connection(s). They will be hotter than the side working normally, since they are acting like a resistor, dropping the voltage available.

I do have an IR thermometer so I will see if I can determine anything using that. It's just so intermittent that I don't know when it may happen again. We've been in the house almost 2 years without any issues.

 

[Clueless in Charlotte]

Bug the power company some more (tell them what you said in your last post)...

Thanks - I will try them again. When I got home a while ago they had left a door hanger. They came out today but apparently didn't put a monitor on the meter. The hanger had generic check boxes that stated supply voltage was within normal range and if you have further problems, ... contact an electrician. Also, "our equipment is working properly". I can't seem to get through to them that the voltage is normal 99.9% of the time but one leg reads low intermittently. I'm in Charlotte, NC and Duke Energy is the power company - if anyone has any ideas on how to escalate this with them please let me know.

 

[WorthFlorida]

......I called the power company and they said to turn the range (220V) on. As soon as I did that the lights came back on. I didn't check any voltages because I assumed it was just an anomaly.

That is weird and it tells me the problem is from the circuit panel back to the house feed or meter. Since the stove heating elements are are 220v, and if one leg (L1) is low on voltage, the current will flow from high(L2) to low voltage, hence the L1 leg the voltage jump up. The LED lights will then turn on since their line voltage for full brightness is a very wide range. Dimmable LEDs are not dimmed buy a pure AC sine wave at a lower voltage as are incandescents. When you have the problem replace one of the LEDS with an incandescent or halogen light. If turning on the stove lights things up, look at the incandescent brightness.

Now why does things seem to work after this scenario? The electric elements of the stove take a lot of current and a bad connection or corrosion somewhere is arcing and corrosion burns off a bit making a better connection (I'm doubtful), then is starts to corrode again until is it bad again. As jadnashua above describe about aluminum corrosion.

Ask Duke Electric that your electric meter be inspected or replaced. If they seem to put it off tell a fib, report that you smell something burning at the meter. They'll jump on that. You might need your electrician to call Duke energy for this request. They will remove the meter and then the connections & the connecting blades can be inspected (safely). It would be doubtful that it's at transformer since it probably feeds several houses, however there could be a bad connection at the transformer for your house.

The thermostat thing is digital thermostats need usually at least 18-19 volts AC from the 24v transformer to work.
120v * .2 = 24v
65v * .2 = 13v

 

[Clueless in Charlotte]

That is weird and it tells me the problem is from the circuit panel back to the house feed or meter. Since the stove heating elements are are 220v, and if one leg (L1) is low on voltage, the current will flow from high(L2) to low voltage, hence the L1 leg the voltage jump up. The LED lights will then turn on since their line voltage for full brightness is a very wide range. Dimmable LEDs are not dimmed buy a pure AC sine wave at a lower voltage as are incandescents. When you have the problem replace one of the LEDS with an incandescent or halogen light. If turning on the stove lights things up, look at the incandescent brightness.

Now why does things seem to work after this scenario? The electric elements of the stove take a lot of current and a bad connection or corrosion somewhere is arcing and corrosion burns off a bit making a better connection (I'm doubtful), then is starts to corrode again until is it bad again. As jadnashua above describe about aluminum corrosion.

Ask Duke Electric that your electric meter be inspected or replaced. If they seem to put it off tell a fib, report that you smell something burning at the meter. They'll jump on that. You might need your electrician to call Duke energy for this request. They will remove the meter and then the connections & the connecting blades can be inspected (safely). It would be doubtful that it's at transformer since it probably feeds several houses, however there could be a bad connection at the transformer for your house.

The thermostat thing is digital thermostats need usually at least 18-19 volts AC from the 24v transformer to work.
120v * .2 = 24v
65v * .2 = 13v

Thanks - that explains certain aspects of the weirdness.

Does everyone agree that if the low voltage condition exists with the main breaker off then the issue is not the circuit breaker panel or house wiring?

If the issue is at the meter connection where it feeds to the circuit breaker panel is it my responsibility to clean, apply anti-corrosion paste and tighten the connections at the meter to the main breaker or is that Duke's responsibility?

 

[DonL]

Does everyone agree that if the low voltage condition exists with the main breaker off then the issue is not the circuit breaker panel or house wiring?

If the issue is at the meter connection where it feeds to the circuit breaker panel is it my responsibility to clean, apply anti-corrosion paste and tighten the connections at the meter to the main breaker or is that Duke's responsibility?

You should not mess with the meter.

If the breaker is off, There will be no load and no voltage drop that your breaker panel is causing.

Your neighbor can make your voltage drop, Because you have a shared transformer.

I would have them look/monitor voltage at the transformer.

If you are using a cheap harbor fright voltmeter, Get a better one to avoid embarrassment.

Good Luck.

 

[WorthFlorida]

You're not allowed to touch the meter and there is always power to the meter. You're going to have to have Duke Energy visit your meter with you there. The so call "monitor the meter" only takes it so far if it really is being monitored. More likely the standard smart meter reporting feature.

Do you have a smart meter? I would think that smart meters should be able to report a low voltage condition or the line voltage along with the wattage use. I did read, when my power company started the conversion, that at a power outage the meters would immediately report it and the power company would get the information for faster response times. Far better than waiting for phone calls.

 

[DonL]

Do you have a smart meter? I would think that smart meters should be able to report a low voltage condition or the line voltage along with the wattage use. I did read, when my power company started the conversion, that at a power outage the meters would immediately report it and the power company would get the information for faster response times. Far better than waiting for phone calls.

Seems that they would be smart enough to report voltage, At least on request.

They detect power outages when the meters stop answering update queries. I think mine updates every 15 minutes.

I can only see power usage, But can not see voltage readings using the web interface.

I use a P4330 Kill A Watt to monitor voltage, But it takes 2 to read both legs.

 

[Clueless in Charlotte]

Seems that they would be smart enough to report voltage, At least on request.

They detect power outages when the meters stop answering update queries. I think mine updates every 15 minutes.

I can only see power usage, But can not see voltage readings using the web interface.

I use a P4330 Kill A Watt to monitor voltage, But it takes 2 to read both legs.

View attachment 35277

I don't know if I have a smart meter or not but I'm using a Sperry multi-meter to read the voltages. When the problem occurs one supply line allows reads good (~125v) and the other supply line always reads low. I left a multi-meter plugged into an outlet on the suspect line so I can check voltages but just in real time. I called Duke Energy this morning and emphasized that the issue is intermittent and the low voltage condition only occurs on one of the supply lines. I think they're finally going to put a monitor on the meter.