ECN Forum Forums General Topics of the Trade General Discussion Area Dazed and confused in Texas

I work for a POCO where we got a complaint of "partial power". The customers' service comes off of an "underbuilt" service (where the leads from the transformer go from pole to pole and several services tap off of them).
The two services closest to the transformer have good voltage (121 on each leg to ground). At the end of the underbuilt there are four services that all are getting 114 and 126 volts.

"Aha, sez I. Classic neutral problem".

Trouble is, we check and/or redo every connection and still can't correct the problem.

As it turns out, another underbuilt from another transformer terminates on this same pole and it is not having any problems. The neutral for both services is the system neutral and is continuous between both transformers . So we transfer the end services to the other underbuilt and now that one goes from 120/120 to 114/126.

"What the ....???"

So in desperation, the serviceman starts opening the main breakers of each customer and on one, the problem suddenly goes away.
So now, with one guy off, everyone else has good voltage.

My dilemma is what do I tell this guy to fix?
Turning his main off wouldn't impact the neutral.
Any ideas?

P.S. unfortunately, nobody took any amp readings, but they're going back to get some.

Check the meterbase and ground at his meter. If that is ok turn off all the breakers in the panel; turn them on one at a time till the problem shows up. Then he has a starting point. Good luck Rod

That sounds wierd that it would be so precisely offset with varied parallel loading of the source. The only thing that comes to mind is a chance that it could be feeding the primary of a 240/??? transformer with a fault or improper primary tap to neutral. Then you could have two center tap references fighting each other for neighborhood domination. I would expect alot of neutral current there though. I also suppose it would be possible that a damaged surge arrestor could be clamping at a reduced voltage. A scope would reveal a pretty ugly waveform if that were the case.
Joe