High current on neutral with a balanced load

hillbilly1

Senior Member
Location
Atlanta,Ga
Underground service? May be the lateral going bad. Lightning usually blows pin holes in the insulation, so it usually takes a while to show up.
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
Underground service? May be the lateral going bad. Lightning usually blows pin holes in the insulation, so it usually takes a while to show up.
We do have an underground service. How would insulation damage manifest itself in my home? And how would I test for something like that?
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
We share our transformer with one neighbor. I asked them if they were having similar problems and they said everything is working perfectly on their end. Our power company swapped our transformer about a month ago because we have been complaining about flickering lights. Its been really bad recently. They check our connections at the meter and at the trasnformer but I don't think they have checked anything at our neighbor's home. We also share a well with our neighbor and the breaker for it is on the pole with the transformer. The well pump was struck by lightning a few years ago and that is about when all of our problems started but we had the wiring checked and they said it looked good.
Take your oscilloscope and check it without and with the water running
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
We do have an underground service. How would insulation damage manifest itself in my home? And how would I test for something like that?
That would generally show up as low voltage. The time to check it is when it is acting up.
Also loading a single phase at a time will show it better.
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
That would generally show up as low voltage. The time to check it is when it is acting up.
Also loading a single phase at a time will show it better.
Okay thanks for the response. I will test with my oscilloscope as soon as I get home. It will be a couple hours from now.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I will give this a try. Thanks for the suggestion. What exactly am I looking for?
You're looking to see whether a current imbalance causes a voltage imbalance. Only a resistance in the neutral pathway can cause the voltage to neutral on one line to rise as the voltage on the other line reduces.

And, yes, measure the line-to-line voltage while you're at it. The guys above are looking to see whether the two line-to-neutral voltages add up to the line-to-line voltage at any given moment.
 
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Another C10

Electrical Contractor 1987 - present
Location
Southern Cal
Occupation
Electrician NEC 2020
I got phase A to 20.1 amps and phase B to 20.3 amps and our neutral current was still showing 7 amps.
This may of been answered above but, Being that you have 7 amps between a pretty balanced load the question obviously is why is there a +- 7 amp return.

I would systematically shut off each branch or solar circuit while noting the amperage difference on the service neutral to see when the excessive neutral return drops, then turn the questioned circuits back on to recreate the improper amp imbalance, that should determine which branch circuit/s should be focused on.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Here are my oscilloscope and spectrum analyzer results. I am not sure what would be considered a bad level of harmonics. This was measured in my panel from each leg to ground. Both hot legs showed the same wave and frequencies.
If you have a 2-channel Picoscope I suggest measuring each hot leg on a separate channel at the same time. Then you can see what relative phase relationship the two legs have to each other. If there's a 120 degree difference then the neutral current you measured with balanced loads has an explanation. If it's 180 then you have to dig deeper for the cause of this.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I haven't tested that before, but phase A shows 124.8 and phase B shows 124.6. Load was about the same on both legs when I measured. Within 1 amp of each other.
So, inquiring minds want to know whether L-L was 249.4v at the time.
 

oldsparky52

Senior Member
This may of been answered above but, Being that you have 7 amps between a pretty balanced load the question obviously is why is there a +- 7 amp return.
It could be as simple as he has a 120/208 service and that neutral current is normal with a combination of 1 pole and 2 pole circuits. I kind of discount the current coming from a neighbor since there was zero current on the neutral with the main turned off. Since only one neighbor shares the transformer, it's kind of doubtful he has a 120/208 service too.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
It could be as simple as he has a 120/208 service and that neutral current is normal with a combination of 1 pole and 2 pole circuits. I kind of discount the current coming from a neighbor since there was zero current on the neutral with the main turned off. Since only one neighbor shares the transformer, it's kind of doubtful he has a 120/208 service too.
See post #9
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
Our POCO diagnostics stop at the meter. Once it leaves there, the problem is yours. We fixed one yesterday where the POCO was out for the third time at owners request to check their connections. I had them wait for us. I megged the customers underground and found both lines at about .01 meg that came up to 14 volts. This lateral had been partially functioning for quite a few weeks. Six old repairs had failed after 10-15 years.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
We use Fluke 1507 Insulation Testers. The POCO had the transformer fuse pulled, with meter out when I got there and were waiting for me. The customer owns and is responsible for the lateral. The owner had turned the Main breaker off on his panel. Service was 4/0 4/0 2/0 direct bury Al. First check was from meter can load lugs to pole ground. Reading was .010 meg with a voltage maintained at 14v. Test range was 500 volts. I removed all the load wires at the meter can, removed the neutral in the service panel and confirmed the main was off. Readings were the same. Faults were where whoever buried a private propane line years ago and had cut through the lateral. Two splices on each side for all three conductors.

Readings after repair were >550 M @ 526 VDC.

The buried maker tape didn’t appear to have prevented any damage
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Since the poco only pulled the fuse, which is on the primary side, how did you test with the poco transformer still connected? They had the neutral floating at the transformer?
 
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