was doing a mall store recently and noticed the 480 was around 510. I was just there helping finish up, so I didn't mess with any of the trannies (the 208 was a little high). At what point do you feel responsible to start fiddling with the taps ? 10% ?
Motors don't mind 10% higher voltage, but no load loss in transformer goes up and magnetic ballasted fluorescent and HIDs operate at increased power leading to increased power consumption. Simple HX reactor type HIDs are affected substantially by line voltage, so +10% will substantially increase power consumption of parking lot lights operating on 480 or 277.
If you're reading +10% with heavily loaded transformer and its consistently high, then you might consider changing taps. If output at 208Y/120v is +10% consistently, 120v light bulbs will fail at 25-50% of rated life.
Office equipment uses switching power supply and they're not really affected by +10% voltage.