High current on neutral with a balanced load

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
Hi, I have run into a strange issue and can't seem to find any good information on this so I am hoping someone here can help me understand how this can happen. We have been having some mild electrical issues in our home ranging from flickering lights to computer hardware damage. We have had 2 electricians out to check the electrical wiring in our panel and everything seems to check out. We then had our electrical provider out to check the wiring in our meter base and the guy they sent said all the wiring looks good, but he also measured the current on both of our hot legs and on our neutral and discovered that our neutral current is not equal to the difference of the two hot legs. I spoke to our electrician again and he told us to get both hot legs to 20 amps and check the neutral current again. I got phase A to 20.1 amps and phase B to 20.3 amps and our neutral current was still showing 7 amps. Clearly something isn't how it should be. So my question is how is this possible?
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Hi, I have run into a strange issue and can't seem to find any good information on this so I am hoping someone here can help me understand how this can happen. We have been having some mild electrical issues in our home ranging from flickering lights to computer hardware damage. We have had 2 electricians out to check the electrical wiring in our panel and everything seems to check out. We then had our electrical provider out to check the wiring in our meter base and the guy they sent said all the wiring looks good, but he also measured the current on both of our hot legs and on our neutral and discovered that our neutral current is not equal to the difference of the two hot legs. I spoke to our electrician again and he told us to get both hot legs to 20 amps and check the neutral current again. I got phase A to 20.1 amps and phase B to 20.3 amps and our neutral current was still showing 7 amps. Clearly something isn't how it should be. So my question is how is this possible?
With the currents at that level was the voltage even? Did you check voltage? It could be the voltage was extremely uneven to give those readings
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
I suggest shutting off all 2-pole breakers but leaving the main breaker ON. Then try to get the current on both hot legs equal to eachother again (around 15 to 30 amps would be OK) and measure the neutral current.
The reason for doing this is to check whether the house might be powered by two legs of a 3-phase wye configuration that are 120 degrees apart. If that's the case I would expect the neutral current to be about the same as the current on each hot leg.
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
With the currents at that level was the voltage even? Did you check voltage? It could be the voltage was extremely uneven to give those readings
We did check voltages. Both legs are at exactly 125 volts. I am going to try what synchro suggests and I will update.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
We did check voltages. Both legs are at exactly 125 volts. I am going to try what synchro suggests and I will update.
I had just assumed if you are an engineering student you would know if you were fed by a single phase XF or you are on a bank..
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
I am a sophomore industrial engineering student. I don't have much electrical experience. We have a single phase transformer. I understand the basics of electricity and wiring, but this issue is above my head and is why I am here.
 

Electricmo

Member
Location
Missouri
Occupation
Lineman
My bet is your house has LED lighting. Maybe a solar installation close also. My bet with what your seeing is a harmonic problem. Computer damage is commonly caused by harmonics. They also put a lot of harmonics on the system themselves. Only way to know for sure is to get a oscilloscope. This is becoming a common theme around my part of the world. LED lighting is a huge culprit.
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
My bet is your house has LED lighting. Maybe a solar installation close also. My bet with what your seeing is a harmonic problem. Computer damage is commonly caused by harmonics. They also put a lot of harmonics on the system themselves. Only way to know for sure is to get a oscilloscope. This is becoming a common theme around my part of the world. LED lighting is a huge culprit.
I happen to have an oscilloscope and spectrum analyzer. Would it be okay for me to post my results here?
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Interested in what you find, I'm not having any computer issues, only LED lighting flickering. Several different circuits, thought it might be worn switches, but that didn't help. My meter is not fast enough to catch the sag. Only affects the LED lights. Service lateral is about 28 years old, I'm thinking it may be going bad. Thermal scanned all my breakers including the main and transferswitch and no problem found. The problem did start when I upgraded to newer LED fixtures............
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
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.
 

Attachments

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.
All harmonics are at least 40dB down (i.e., 1% or less) which is quite good. What loads did you have going? Did it include all of your computer, entertainment, LED lighting, etc. that could generate harmonics?
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
All harmonics are at least 40dB down (i.e., 1% or less) which is quite good. What loads did you have going? Did it include all of your computer, entertainment, LED lighting, etc. that could generate harmonics?
This included my pc, most of the lights in our home which are all LED lights, several tvs, our ac unit, and a few other random things. Roughly 20 amps being drawn.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
This included my pc, most of the lights in our home which are all LED lights, several tvs, our ac unit, and a few other random things. Roughly 20 amps being drawn.
I would be interested to see what it was without the inductive loads such as the AC on.
Also, are you the only one on the transformer?
Neighbors having issues?

We had a bad neutral on the transformer at a customers house. The cable vision and telephone bond at a common point at the house service and the transformer pole at the street.
it could be a bad neighbors neutral just looking for the best place to earth return, which could be your circuits.
 

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.
The next test is to cause as much unbalanced current as you can and compare line voltages again.
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
I would be interested to see what it was without the inductive loads such as the AC on.
Also, are you the only one on the transformer?
Neighbors having issues?

We had a bad neutral on the transformer at a customers house. The cable vision and telephone bond at a common point at the house service and the transformer pole at the street.
it could be a bad neighbors neutral just looking for the best place to earth return, which could be your circuits.
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.
 
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