delta-delta transformer

[bob52]

My company has to install a transformer 208 delta primary to 480 delta secondary. This is to provide 480v to a pump skid. I believe we need to ground the B phase to provide ground fault protection. Is that correct?

 

[augie47]

My company has to install a transformer 208 delta primary to 480 delta secondary. This is to provide 480v to a pump skid. I believe we need to ground the B phase to provide ground fault protection. Is that correct?

As far as the NEC is concerned you can ground one phase or you can operate it as an ungrounded system per 250.20. Note that if you elect to operate it as ungrounded, ground detectors are required per 250.21(B) and all the grounding requirements of 250.30(B) are applicable.
Some manufacturers have stipulations concerning grounded vs ungrounded systems, especially if drives are involved, and it might be well worth your time to discuss the situation with them

 

[pv_n00b]

Corner grounded deltas are pretty much legacy systems these days and have not been industry standard for a few decades. As augie47 wrote, check on the requirements for the pump grounding. I have seen a few examples of 480V deltas with a grounded center tap on one of the transformers to provide a ground reference. Otherwise ungrounded is an option at that voltage with a ground fault detection system that can trip the main OCPD.

 

[Smart $]

Another option is to use a 208VΔ – 480Y/277V transformer, ground X0 but not run a neutral conductor.

 

[templdl]

Another option is to use a 208VΔ – 480Y/277V transformer, ground X0 but not run a neutral conductor.

This is what I would do. Just because the OP only needs 480v 3ph doesn't mean that he is stuck using a delta. By using a 480y/277 and simply grounding the X0 ass you stated should there b a Line to ground fault it will be 277v unlike corner grounding a delta where there would be 480v from the ungrounded lines to ground.