I recently did the electrical design for a small municipal wellhouse. The service entrance is 277/480vac three phase, feeding a motor control center. A branch circuit from the MCC feeds a transformer, which then feeds a panelboard for general loads like HVAC, lights, receptacles and so forth.
The transformer is 480V:120/208V three phase. The problem is that I called out a 120/240V single phase panelboard (I don't know how I let that one slip by :mad: .) I wasn't lucky enough to have the contractor or supply house catch my mistake, so all the equipment was delivered and now the electrician is on site wondering what to do.
So, my question is: can we safely go ahead and use the three phase transformer and single phase panelboard? We'd end up with 120/208V in the panel instead of 120/240V, and one leg of the transformer would not connected to anything.
The panelboard is pretty lightly loaded, and the two pole devices connected to it (a couple small electric unit heaters, an a/c unit and a small electric water heater) are all rated for use at either 208V or 240V so they should be okay, but my main concern is the transformer - will there be circulating currents generated in the windings of that unused leg that will cause problems with heating, harmonics or ?
I think the correct answer is to get the right transformer, but it would be nice if I didn't have to spend any more money.