Step up transformer grounding

[TXMaster]

I have a situation that requires a step-up transformer from 3ph 208V to 3ph 480V. The transformer proposed is wye input and delta output. The load does not use a neutral. How can I meet code without intentionally grounding one leg of the delta output? The load cannot handle a corner ground. Is there any advantage to using a wye input? The load is a VFD with a dual motor output for A/C fans in an air handler.

 

[jim dungar]

I have a situation that requires a step-up transformer from 3ph 208V to 3ph 480V. The transformer proposed is wye input and delta output. The load does not use a neutral. How can I meet code without intentionally grounding one leg of the delta output? The load cannot handle a corner ground. Is there any advantage to using a wye input? The load is a VFD with a dual motor output for A/C fans in an air handler.

Not all VFDs are rated to be used with an ungrounded delta. You best choice would be th Wye output, which should be a standard design from all major manufacturer. Some manufacturer will list the output as 460Y or may call their unit a Drive Isolation transformer.

 

[augie47]

Unless I am misreading your transformer nameplate the output is 480Y/277

 

[TXMaster]

Man guys. Its been a long day. I already figured this out last week and that's why I chose this wye output. Sorry!!! Arrrgh. Time to go home. SMH.

 

[TXMaster]

Thanks for smacking my eyes and brain back straight!

 

[LarryFine]

Glad we could help.