480v 3-phase unbalanced?

[CheezyBroccoli]

Newer to this field and while familiarizing myself with some of the machinery on a machine that was down for months for computer malfunction, I checked the phases. Phase A to B was 483v, A to C was 520v, B to C was 490v. A to ground was 285v, B to ground 285v, C to ground a little over 300v. Afterwards I checked the other machines in the vicinity and they were all balanced at about 480v phase to phase. What could cause this and could this be the root cause of the computer issues?

 

[TwoBlocked]

Are they all fed from the same transformer?

 

[zbang]

C is certainly high although not really out of spec (10% of 277). Is this actually a wye feed? Could be that the C phase is tapped differently than the others. Is this fed from a single three phase transformer or three one-phase units? (Again, could be tapped differently, or A and B might have heavier loads than C.)

When in unfamiliar territory, it's good to look at the entire supply, where it branches out, and what else might be seeing the same problem, don't just look at the place where you see the issues.

 

[CheezyBroccoli]

Are they all fed from the same transformer

C is certainly high although not really out of spec (10% of 277). Is this actually a wye feed? Could be that the C phase is tapped differently than the others. Is this fed from a single three phase transformer or three one-phase units? (Again, could be tapped differently, or A and B might have heavier loads than C.)

When in unfamiliar territory, it's good to look at the entire supply, where it branches out, and what else might be seeing the same problem, don't just look at the place where you see the issues.

Thank you for the reply. When I get back to it I will find out more