Three phase floating neutral?

[leggo]

I looked at a residential job that has a separate service for a pole barn that supplies 120/240v 3phase with a 208v high leg. My voltages read fine with no load.My problem is that any 120v. load you put on the A or C phase (B phase is the 208v) I get different voltages. ie. A phase drops to 60 volts and C phase increases to about 180v. The 500 watt halogen light that I was using to test was always dim.
I tried to reconnect the neutral at the service mast where it connects overhead from the poco. This didn't chang anything. Please advise.
Ed

 

[peter d]

Re: Three phase floating neutral?

Maybe one of the windings in the transformer is open?

 

[bob]

Re: Three phase floating neutral?

You have a bad neutral connection on the bank pole of at the service. When this occurs the voltage on 1 leg goes up and the other leg drops with added load.

 

[leggo]

Re: Three phase floating neutral?

Bob,
Do you mean that it is bad at the power company pole. I am not sure what you meant about the bank pole.

 

[charlie]

Re: Three phase floating neutral?

Call the serving electric utility, there is an open neutral (grounded conductor) somewhere and it needs to be repaired. I am betting that it is on the line side of the service point.

 

[bob]

Re: Three phase floating neutral?

Leggo and Charlie
I had a typo. What I ment to say was that there is a bad neutral connection on the bank pole or at the service conductors. Leggo, by bank pole I mean the pole with the transformer bank. You may have a service pole also. As Charlie said have
the utility check.

 

[LarryFine]

Re: Three phase floating neutral?

Actually, the bad neutral connection may be anywhere from the transformer, even inetrnally, to the branch-circuit panel, even internally again.

This points out why earth can not serve as the return path; the impedance is too high.

 

[leggo]

Re: Three phase floating neutral?

Thanks for all your help. I will let you know what I find.

 

[leggo]

Re: Three phase floating neutral?

Thank you for the help. Yes, it was the power company's problem. They came out and fixed it and everything is back to normal.
Thanks again