grounding transformers

[bman]

Can a 3 phase 480v/208v dry type transformer be used to as a step up transformer following the same wire sizing rules, etc. and if so must a neutral wire be fed to the transformer for your XO connection eventhough no neutral is needed, must the XO connection be grounded like a typical 480v to 208v connection?

 

[templdl]

Re: grounding transformers

Am I to understand that the transformer is a 480v delta-208y/120 and not a

3 phase 480v/208v

as would be assumed by your reference to an X0 connection.
If so, most DTDTs come standard with the Xo bonded to the enclosure with a copper strap or cable. Disconnect that bonding connection and simply supply the transformer with 208v via the X1, X2, and X3 bringing the EGC to ground the enclosure. NO NATURAL connection to the X0 is required.
Since it as normally assumed that transformers are applied as step down and fed from the HV side I would recommend that some means of labeling be used to identifiy that this transformer is being used to step up and is being supplied from the LV side.
However, you also must consider what to do about grounding the newly derived 3ph, 480v delta. It can be left ungrounded if there is a specific reason to do so. Otherwise I personally would strongly suggest that it be configured as a grounded 'B' phase.