High current on neutral with a balanced load

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
If you have common metallic water lines some current will flow on them to the neighbors, then back to the transformers. A bad or missing neutral at the neighbors will cause the current to flow on the water lines. Some current will go through earth to the transformers, but not much. It will prefer any common metallic path.
 

kwired

Electron manager
Location
NE Nebraska
I think it is likely. What would cause a neighbor's current to reach my home though? We share a transformer. Also, shouldn't the current coming from a neighbor bleed off to ground? Whatever is causing this is damaging my electronic equipment, so it is getting past the ground rods and into our panel. I have lost several computer power supplys now.
Current takes all possible paths, paths of lesser resistance do carry more of the current though. Current isn't "bleeding off to ground" it is seeking the neutral terminal of the source. Lowest resistance paths to get there is where the bulk of the current will flow. Earth is a good conductor, but connecting to earth with low resistance is usually not that easy therefore any current that does take an earth path to get there is usually somewhat negligible (will likely be in milliamp ranges) as long as there is other lower resistance paths.

If on a metallic water piping system you typically will have low enough resistance path that there will be current from elsewhere, if your neighbor has compromised supply neutral you very well can be carrying nearly all of the neighbor's neutral current through the water piping and then back to the source via your supply neutral conductor.

I don't see this being a reason to damage your electronics there has to be more than just that going on.
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
If you have common metallic water lines some current will flow on them to the neighbors, then back to the transformers. A bad or missing neutral at the neighbors will cause the current to flow on the water lines. Some current will go through earth to the transformers, but not much. It will prefer any common metallic path.
We share a well with our neighbor and the pipes are plastic.
 

McLintock

Senior Member
Location
USA
Occupation
Electrician
When did that start? What were the conditions when this started? I would check your 240v appliances to see if a neutral is being back fed, because if everything is shut off and get no current the problem, I would think, is in the house itself. Also do you have a pic of the panel?


“ shoot low boys their riding shetland ponies”
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
I think it is likely. What would cause a neighbor's current to reach my home though? We share a transformer. Also, shouldn't the current coming from a neighbor bleed off to ground? Whatever is causing this is damaging my electronic equipment, so it is getting past the ground rods and into our panel. I have lost several computer power supplys now.
Something shared... cable vision line shield, old phone line shield, metal water piping, etc...
If POCO N is bad, it’s coming in through a shared whatever type of conductor trying to get back to source.
Did you try Larry Fines suggestion? Cut off mains and check N current?
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
Something shared... cable vision line shield, old phone line shield, metal water piping, etc...
If there N is bad, it’s coming in through a shared whatever type of conductor trying to get back to source.
Did you try Larry Fines suggestion? Cut off mains and check N current?
I have tried that. In fact, when we had the power company here a week ago, they removed the meter to kill power completely and we were still seeing 1-3 amps on the neutral. We do not have any form of solar power or battery that would cause this. Our home is small and simple. We only have one neighbor and we share a well pump and transformer with them.
 

McLintock

Senior Member
Location
USA
Occupation
Electrician
I have tried that. In fact, when we had the power company here a week ago, they removed the meter to kill power completely and we were still seeing 1-3 amps on the neutral.
If that’s the case, it’s on the POCO side of the meter and THEY have a problem with their neutral hook up,


“ shoot low boys their riding shetland ponies”
 

mikeames

Senior Member
Location
Germantown MD
Occupation
Teacher - Electrician - 2017 NEC
I have tried that. In fact, when we had the power company here a week ago, they removed the meter to kill power completely and we were still seeing 1-3 amps on the neutral. We do not have any form of solar power or battery that would cause this. Our home is small and simple. We only have one neighbor and we share a well pump and transformer with them.
There's the answer Larry was referring to. The problem lies outside your house. 1-3 amps with main off is significant enough to say there is an issue with utility or neighbor.
 

McLintock

Senior Member
Location
USA
Occupation
Electrician
I have tried that. In fact, when we had the power company here a week ago, they removed the meter to kill power completely and we were still seeing 1-3 amps on the neutral. We do not have any form of solar power or battery that would cause this. Our home is small and simple. We only have one neighbor and we share a well pump and transformer with them.
Is the well pump hook up in your house?


“ shoot low boys their riding shetland ponies”
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
There's the answer Larry was referring to. The problem lies outside your house. 1-3 amps with main off is significant enough to say there is an issue with utility or neighbor.
POCO denies responsibility. How do I find or fix this type of problem?
Is the well pump hook up in your house?


“ shoot low boys their riding shetland ponies”
No, it has its own meter and breaker on the pole with our shared transformer.
 

kwired

Electron manager
Location
NE Nebraska
I have tried that. In fact, when we had the power company here a week ago, they removed the meter to kill power completely and we were still seeing 1-3 amps on the neutral. We do not have any form of solar power or battery that would cause this. Our home is small and simple. We only have one neighbor and we share a well pump and transformer with them.
What comes in must go out or the other way around.

If there is 3 amps on the grounded supply conductor there has to be 3 amps on another conductor or at least a net 3 amps on multiple other conductors that connect at same node. Check current on GEC.

What you don't know is if current is flowing to or from the grounded supply conductor, just that it is flowing. Disconnect the grounded conductor then check voltage to "earth", both on supply side and on load side of the opened connection. This will tell you which direction from that point has a rise in voltage over what normally should be little or nothing.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
If you have cable for TV or internet, a phone line, etc. coming in the house then a clamp-on ammeter should be put around the cable to see if there's any significant current. The clamp should be put around the entire cable or phone line including any shield that it may have.
As was mentioned by others, the current you've been observing on the neutral with the main breaker off has to be returning on some other conductor(s) in order to complete the circuit.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
My thoughts, in no particular order:

Pulling the meter still does not interrupt the neutral (obviously), but I wonder what the voltage would be across the gap.

I wonder how the POCO explains the stray current with the meter pulled, and the voltage if opened as I mentioned above.

Is it possible the POCO's neutral is so poorly maintained that some of its current is using your electrodes for continuity?

What electrodes are there, and have you clamped them to see if any current is traveling in the earth through them?
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
What electrodes are there, and have you clamped them to see if any current is traveling in the earth through them?
It could also be worth putting a clamp meter on any cable or conduit exiting the breaker panel to check whether there's any measurable current. Perhaps an equipment grounding conductor (aka EGC) of an individual branch circuit is connected to a cable shield for TV/internet at a cable modem. This might enable current from the service neutral conductor to flow through the bond between neutral and EGC in the panel and then into a branch circuit EGC, to the TV/internet cable shield, and then to the other house through it's cable or to the provider's distribution system.

I thought a little about a return through the earth but it would have to be a very low resistance GES to conduct the observed current on the neutral without a relatively large voltage drop. In the picture that the OP provided with the three clamp meters the difference between the line currents is 6.7A - 4.97A = 1.73A. So depending on the polarity of this difference current relative to the "foreign" current source, either 7.63A -1.73A = 5.9A or 7.63A + 1.73A = 9.36A is unaccounted for in the neutral current. Even when using the lower 5.9A value the resistance to earth would have to be about 1.7 ohms to limit the GES voltage rise from earth to 10V, and so without additionaI data I think conduction through the earth seems to be a less likely explanation for the measured neutral current.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
POCO denies responsibility. How do I find or fix this type of problem?

POCO doesn’t deny responsibility. The service lineman they sent out there doesn’t understand what’s going on because they are little more than glorified construction workers.
I would discuss this with someone in a responsible position with a little education in electrical theory.
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
You guys are all very wise and I appreciate your comments. You have given me several ideas on ways to troubleshoot this. Is there any additional information I can provide that might help? I do have cable tv and internet and I have put a clamp meter on the coax cables and there is no significant amperage. Roughly .25 amps. Disconnecting the coax cables at the service entrance does not fix the amperage issue on the mains.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
The only way to cause a current on a conductor is to have a voltage difference between the ends.

Something is causing that voltage. You need to determine the source.

At least one end of your neutral pathway is at other than zero volts to earth, either the POCO neutral or your local earth.

"Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth." ~ Arthur Conan Doyle
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
You guys are all very wise and I appreciate your comments. You have given me several ideas on ways to troubleshoot this. Is there any additional information I can provide that might help?
I suggest putting your clamp meter around any Romex cable, conduit, or grounding electrode conductor that exits the breaker panel, to the extent there are clearances to do so. Somewhere there has to be a return conductor for the stray current that's flowing on the service neutral.
 
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