Thanks jghrist.
Let me reformulate, my information is a little confusing.
The electrical service in the building is 120/208V. Because they had some equipment that requires 480V (three wires), and it happened that they had available a 480/208-120V transformer (300 KVA, SquareD, Dry type), they...
I am experiencing the following situation: a 480/208-120V (delta-wye) transformer was used to step up voltage for 480V equipement. As such, 208-120 became primary, neutral x0 being connected as well to the neutral of the installation. Other single phase loads (and possible three phase) were...