Unbalanced voltage from utility on High Leg Delta

Status
Not open for further replies.

BigMike

Member
At the job site, we have a 240V high leg delta transformer that feeds numerous buildings. We added some three phase roof top units and they are not functioning properly. We measured the L-L voltage at the panel and it had:

A-B: 254V
B-C: 242V
A-C: 243V

We told the utility about the problem and they don't seem willing to help the client out saying their voltage is "within spec". One option I was thinking of was installing a single phase transformer between A-B to reduce the voltage. Someone else mentioned using a UPS ($$$$$$$) which Im not even sure that would work. Should I just push back and say to replace with single phase roof top units? Anyone else have a better solution?
 

jtester

Senior Member
Location
Las Cruces N.M.
Re: Unbalanced voltage from utility on High Leg Delta

If your utility is required to meet ANSI standards for voltage regulation, you should continue to press them. They should meet nominal +/- 5% which is a maximum of 252 volts.

A second argument is that motors suffer greatly with voltage imbalances of the magnitude you are experiencing. Put their claims department on notice that there will likely be claims filed, and your problem will probably be take care of. I did just that recently, and when claims got involved, the transformer bank was replaced and the problems went away.

Not all utilities, particularly some municipalities, are not bound by the ANSI standard for voltages.

Jim T
 

delton

Member
Re: Unbalanced voltage from utility on High Leg Delta

Commercial/Industrial limits are usually 7 1/2 %. The limits are 222/258 or as they are saying "within specs". However, there is also an ANSI requirement to be at 3% current imbalance or less. That may help you solve this problem. See if the utility will work with you on establishing the current imbalance, which will be your problem to solve. You may have to look at this customer paying the utility to close the Delta Bank if possible.
 

jbwhite

Senior Member
Re: Unbalanced voltage from utility on High Leg Delta

The HVAC contractor may be able to install an adjusable chiv on the air handler belt. I have had this work sometimes in the past.
 
Status
Not open for further replies.
Top