Open Neutral

[Jayaygee]

We have what we think is an open neutral at a customer's residence. We have a difference of voltages between the A and B phases to ground. The path of this system is from the utility pole to a bussed gutter (3 phase delta source) to a 1 phase meter for the house and a 3 phase meter for the water pump and AC units. From the house meter 100 ft. to the house sub panel then to two other sub panels down the line.
1. If I tested the voltage at the house sub panel, is there any way that the neutral could be the problem on the load side of where my tester is? Isn't an open neutral in this case always on the line side of wherever I'm testing the voltage-assuming the problem exists at that point?
2. Is there any other condition that might cause the same symptoms--high voltage on one leg to neut, low voltage on the other? (adding/subtrtacting load changes voltages too)

 

[steve66]

Re: Open Neutral

Sounds right to me. If the voltage difference is at the main panel, I would suggest shutting of the power and calling the POCO.

If the voltage is OK at the main panel, and different at the sub panel, you would have an open neutral between the two panels.

The only other thing I can think of to cause this would be a bad transformer (still reason to shut of the power and call the POCO), a large voltage drop (due to a long run or a heavy load), or even a short circuit somewhere on the load side.

Steve

 

[Paul B]

Re: Open Neutral

You said you are testing from the line to grd. How much difference are you seeing between the two phases? Check the neutral to grd at the sub panel, what are you reading there?

 

[southernboys]

Re: Open Neutral

Ran into something similar a few years back as a hot shot apprentice. Had 160v on one leg to ground 60 on the other. Took me two weeks of scratching my head and saying whatdafunk before I noticed that at the service some idiot wannabe homeowner had cut several of the darn strands of the ground wire off and put the ground under one of the small screws. Damn screws were so rusted I ended up cutting the ground wire putting a blue wire nut and mounting a new ground bar to refeed the trailer. Still dont know if what I did was 100% to code but aint had a call back yet. Great learning experience.