According to 250.20(B) ('02 NEC), there should have been a grounded neutral brought in, if you were expecting, and spec'ed to the POCO, that you wanted 480/277 and a neutral. It sounds like you had a ground, but no neutral.

To answer the question directly, with no load, and the transformers' Y-connected secondaries' common point grounded, a meter should have read 277, but the impedance of earth is not low enough to assure 0 volts on the neutral with loads.

However, "straight 480" suggests a delta-connected secondary, which would limit you to either corner-grounding or a center-grounded secondary (both of which would show up on a voltage test), but the latter isn't done on 480.

I can't help but wonder how any competent electrician could not notice a service with no neutral conductor. Where did the panelboard neutrals go? Was this a simple main-breaker panel, or did the electrician assume the ground was "neutral'ed"?

Larry Fine
Fine Electric Co.