I was asked to look at a family friend home with an electrical issue. The homeowner had an issue with all the appliances in home suddenly not working or causing electrical issues like flickering lights or not working at all. They said during windy weather they experience flickering lights. I open electrical panel and took a voltage reading, on one leg i got 109-120 the voltage bounced when taking the measurement and the other phase was 134volts. I didnt know what to think of the issue. I took reading on line side of breaker so i think its coming from POCO. I also notice the home had no ground rod attached. i kinda suspect the home got struck by lighting which damaged appliances. The voltage issue is what i cant make sense. I have never seen a voltage above 130v for 120/240 single phase. Is this common for voltages like this? I remember and issue along time ago where i had kinda similar problem with voltage difference in the phases and it was on POCO side.
Voltage reading
- Thread starter MBLES
- Start date
- Status
JFletcher
Senior Member
- Location
- Williamsburg, VA
You have probably lost the service neutral. without it, you have 240V across your loads in series vs 120V in parallel.
If the resistances of the loads on leg A = leg B, you will still have 120V in each leg. IF, however, there is a resistance imbalance from the loads on leg A vs leg B, the voltage on one leg will go high and the other low. You could see readings like 165V/75V on leg a and b, even on the line side of the main breaker.
Find and fix the issue before you start letting the magical smoke out of your 120V appliances
http://forums.mikeholt.com/attachment.php?attachmentid=15740&d=1474598581
If the resistances of the loads on leg A = leg B, you will still have 120V in each leg. IF, however, there is a resistance imbalance from the loads on leg A vs leg B, the voltage on one leg will go high and the other low. You could see readings like 165V/75V on leg a and b, even on the line side of the main breaker.
Find and fix the issue before you start letting the magical smoke out of your 120V appliances
http://forums.mikeholt.com/attachment.php?attachmentid=15740&d=1474598581
Last edited:
My first thought was a neutral problem. i wasnt brave enough to touch the service drop on riser at home to simulate wind moving line. and i couldnt see the XFMR or line coming off transformer because the XFMR was a distance from home in another yard. I had homeowner contact POCO see if they could reattach the neutral on line side to riser. In our area a permit is needed to open meter box. The POCO night charge them a fee but i told them its worth it not to loose any more appliances
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
I'd be unplugging the expensive appliances until the PoCo fixes things.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
190208-2504 EST
MBLES:
The measurements you made were inadequate and incomplete. I would think that electricians would have more complete training on troubleshooting voltage problems at a main panel.
I assume your voltage measurements were from hots to neutral. If only one phase showed the large voltage changes, then neutral is not the primary problem. But on your apparently stable side the 134 V is abnormal.
If both hot supply lines are good including the transformer and all terminations and devices between the transformer and the main panel, then you should have a fairly steady 240 V ( or some other reasonably stable value ) reading line to line. My home voltage looks like, 1 second resolution, --- see photo P26 at http://www.beta-a2.com/EE-photos.html .
The voltage readings you take should be from probes directly on the line side wires, not on the breaker lug, or other termination.
Is the neutral bus connected to earth by any other means than the nonexistent ground rod, such as a copper water pipe, vs only at the power company transformer? Using a high impedance DVM what is the voltage of the incoming neutral wire, again directly on the wire, relative to a screwdriver in the earth outside? I believe mine is below 1 V. There should no major fluctuation like your 10 V or 1/2 of this. If there is, then there is a neutral problem back to the transformer. My ground rod is 150 ft of 1" diameter copper water supply line.
Your 134 V reading is suspect, but if it is stable while the other phase to neutral jumps around, then your primary flicker problem is from the hot line of the flickering phase from main panel to the transformer, and could even be inside the transformer.
When you have this degree of voltage variation and suspect a neutral problem, then two 120 V low wattage ( easier to look at ) incandescent bulbs may be more useful than two meters to simultaneously monitor the two phase voltages to neutral.
If your 134 V reading was stable and read with a meter of adequate accuracy, then you need the power company to find out why.
.
MBLES:
The measurements you made were inadequate and incomplete. I would think that electricians would have more complete training on troubleshooting voltage problems at a main panel.
I assume your voltage measurements were from hots to neutral. If only one phase showed the large voltage changes, then neutral is not the primary problem. But on your apparently stable side the 134 V is abnormal.
If both hot supply lines are good including the transformer and all terminations and devices between the transformer and the main panel, then you should have a fairly steady 240 V ( or some other reasonably stable value ) reading line to line. My home voltage looks like, 1 second resolution, --- see photo P26 at http://www.beta-a2.com/EE-photos.html .
The voltage readings you take should be from probes directly on the line side wires, not on the breaker lug, or other termination.
Is the neutral bus connected to earth by any other means than the nonexistent ground rod, such as a copper water pipe, vs only at the power company transformer? Using a high impedance DVM what is the voltage of the incoming neutral wire, again directly on the wire, relative to a screwdriver in the earth outside? I believe mine is below 1 V. There should no major fluctuation like your 10 V or 1/2 of this. If there is, then there is a neutral problem back to the transformer. My ground rod is 150 ft of 1" diameter copper water supply line.
Your 134 V reading is suspect, but if it is stable while the other phase to neutral jumps around, then your primary flicker problem is from the hot line of the flickering phase from main panel to the transformer, and could even be inside the transformer.
When you have this degree of voltage variation and suspect a neutral problem, then two 120 V low wattage ( easier to look at ) incandescent bulbs may be more useful than two meters to simultaneously monitor the two phase voltages to neutral.
If your 134 V reading was stable and read with a meter of adequate accuracy, then you need the power company to find out why.
.
Last edited:
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Yep. See post #3.
- Occupation
- Licensed Electrician
It's gotta be underground. Windy weather causing the problem was my first clue.
ptonsparky
Tom
- Occupation
- EC - retired
I think Dave was sleepy or sarcastic. I can’t see from here.
Here's a nice video of what happens in the event of a loose or open neutral in a multiwire circuit.
https://www.youtube.com/watch?v=eVamt9IdQd8
https://www.youtube.com/watch?v=eVamt9IdQd8
Had this on my old house fought with poco, followed wires from xfmr talked to all on street who were feed from same. Called poco back talked with same "engineer " he told me I couldn't read the flux of incoming voltage, I told him that the gas station on the same line was having electronics reset on gas sales and diagnostic repair testing and as a master with 20 yrs. in and sitting watching two meters one on each phase they should send out a strip chart recorder and take a look at the pcb bomb that by size alone is too small for the loads plus so old it can't be read with a pair of binoculars; and could he send me the paperwork to recoup my losses on my new tv, frig, wellpump, furnace, stereo, etc.
They were out the next day monitor installed, wife made the old timer lunch and when he left at the end of the day told here "looks like a problem with the xfmr neutal" be back tomorrow to get info. for engineers, had new xfmr on pole 2 days later.
They were out the next day monitor installed, wife made the old timer lunch and when he left at the end of the day told here "looks like a problem with the xfmr neutal" be back tomorrow to get info. for engineers, had new xfmr on pole 2 days later.
- Status