one leg high one leg low...

[ritelec]

Hi all......

Reminds me of the Abbott and Costello skit ....up on the left leg.... " I Dream of Jeannie with...".. anyway

Read this and was wonder what this was about...... any thoughts......
thanks.

Residential Home 240v
About 200 feet from street
Meter and transformer on pole with underground 2/0 gauge cable approx 35 feet to panel in interior of home.
While loading one leg 15A I get a voltage rise on the other leg of 2.3 volts./While dropping the loaded leg roughly the same.
This would suggest a resistive neutral or improper size conductor.
However I am taking the measurement at the cables themselves which due to their size the rise on the unloaded leg should be negligible such as .25 volts.
With both legs unloaded and measuring at the cables I have 240V
One leg 121V the other 119V give or take a tenth or two.
I know the dangers of open or resistive neutrals I called the power company
Which came out and tightened up everything in the meter panel.
Who also had 121 and 119 leg voltages with no load.
The did not load test.
I still have the rise on the other leg when applying a load.
I was told as long as I didnt go over 125V on the other leg it wasnt a concern.
Which I could agree with except I am taking my measurements right at the cables,Which eliminates corrosion or a loose connection in the Main panel in the home
Since neutral has to only carry the imbalance in this case 15A and I am getting a fair rise I suspect an issue somewhere.
We already know we have an imbalanced {without load} transformer atop the pole.
Is this normal?
But more importantly the voltage rise{under load} is occurring from the meter back to transformer when a load is applied ...unless my underground cable is corroded and only has a strand or two left..which I highly doubt.

 

[ptonsparky]

Don't doubt the underground cable fault. We make a share of our wages finding and repairing those. If it looks like a duck, quacks like a duck...

Disconnect both ends and meg it.

 

[ritelec]

Cool..... thank you.

 

[GoldDigger]

Disconnect both ends and meg it.

The UG may have been provided by the owner, but the end of it connected to the transformer is under the control of POCO, so disconnecting it may not be simple.
And assuming your Megger also has a very low ohm function, it would be the right tool. An actual Megger test may not show anything or it may show a neutral to earth leak if the cable is faulty.
As for the initial voltage imbalance with no load, does the same secondary serve other customers?
Finally, if the UG run has a concentric neutral it would not be unexpected for it to corrode first in the event of a fault in the outer sheath.


Tapatalk!

 

[gar]

140212-2400 EST

ritelec:

There will be a ground rod at the transformer. Connect a long test lead, any reasonable wire size (#28 would work), possibly a couple hundred feet of #18 to #16 extension cords, from the transformer ground rod back to the home at where you have access to the neutral on the load side of the meter.

Measure the voltage drop between the pole ground rod and the house neutral with and without your only load of 15 A. This will provide a reasonable measure of the voltage drop along the neutral from the transformer center tap to the house neutral test point . Also it would be nice to know that there was little current in the center tap to pole ground rod path.

.

 

[ActionDave]

Hi all......
With both legs unloaded and measuring at the cables I have 240V
One leg 121V the other 119V give or take a tenth or two.
I know the dangers of open or resistive neutrals I called the power company
Which came out and tightened up everything in the meter panel.
Who also had 121 and 119 leg voltages with no load.....
.

Voltage measurements within this range could be showing nothing other than plain old voltage drop.

 

[ptonsparky]

The UG may have been provided by the owner, but the end of it connected to the transformer is under the control of POCO, so disconnecting it may not be simple.
And assuming your Megger also has a very low ohm function, it would be the right tool. An actual Megger test may not show anything or it may show a neutral to earth leak if the cable is faulty.
As for the initial voltage imbalance with no load, does the same secondary serve other customers?
Finally, if the UG run has a concentric neutral it would not be unexpected for it to corrode first in the event of a fault in the outer sheath.


Tapatalk!

Some day, maybe, I will get used to the thought that getting a POCO to work with you is more than just a phone call to them and a return call from their service guys asking where and when.

 

[gar]

140213-0820 EST

ActionDave:

Sure it is voltage drop. But the measurements imply a resistance of about 0.15 ohms, and that is very high for the distance and wire size. Thus, the implication of a problem. Suppose that instead of a 15 A load that the load was 200 A, then the neutral drop alone would be about 31 V.

.

 

[ptonsparky]

Change the applied load to the other Hot. A bad neutral should show up by a corresponding rise in voltage on the other leg.

Generally we don't find just one wire of a cable faulted. IMO it is usually one of the line conductors that faults first, or the worst, with the resulting heat damaging the insulation on the others. In sandy soils @ 480v the result can be glass. Hot enough.

Your close enough to the pole to just temp up an additional neutral. Even the extension cords Gar suggested would work. You have them stretched out anyway. In this case bigger would be better. Raising and lowering of voltage should disappear. Use your gloves.