The physical plant I manage buys power from the POCO at primary. We have our own 3Mw substation. The beast was built c. 1935. It is, unfortunately, an operating electical museum. The secondary is 480v 3∅ Wye, 3 Wire, local grounds. We have a number of stepdown transformers running our buildings. We have a number of rotating loads up to 100 hp. Recently, we have observed some irregular voltage readings. We're seeing 460 to 495 between the three legs. Two legs fairly consistently measure 460 and 480 to ground. The third leg is 1.75 volts to ground. All rotating loads appear to be operating normally. Some transformers, depending on the legs they are connected across, are 120v on one side and 95 - 102 on the other. My Electricians are not certain of the source of the problem. I don't want them to waste a lot of time with hit or miss solutions. We know the system is out of balance from observed current draws. We know our local grounds vary in conductivity as the soil dries from a wet condition in the spring to dry in mid-summer. We are not sure if the balance issue is a cause or a symptom of the problem. Thoughts?