what to do with the neutral from a wye 480V source on a delta-Wye transf

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cortgal

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I have a Wye 480V line-line source conneted H1,H2 and H3 on a delta-wye 220V line-line/127V Line-neutral dry stepdown transformer. what to do with the neutral from the source? should it be connected to XO on the transformer?
 
A 'delta' load, such as a 3 phase motor or the primary of a transformer, uses only the 3 phase conductors from the source. It doesn't matter if the source is wye or delta, the load uses only the 3 phase conductors, and does not use the neutral. This is true even if the load internally actually has a 'wye' connection (very common for some types of motor).

The X0 terminal of a delta/wye transformer will be _grounded_ using a proper GEC to your grounding electrode system. If your 480V supply happens to be a grounded wye, then the neutral of the 480V system will be grounded in the same way and thus connected to X0, but only indirectly, not by a current carrying circuit conductor.

-Jon
 
If the source neutral is pulled with the ungrounded conductors to the transformer primary then one might think it would not be a problem to just simply land it on the X0. After all, it should not have any current flowing through it anyway. And if the source for this feeder is the service panel where bonding occurs then this conductor could be re-labeled as a grounding conductor (green tape, etc). However, if the source for the feeder is not the service panel and the transformer feeder neutral is connected to the neutral bar (not bonded) of a sub-panel or other load distribution device, then having the neutral conductor landed to the X0 will create a parallel path for neutral currents from elsewhere returning to the source panel or device to jump onto the grounding grid....which is not permitted by code. As always, if I am missing something here please tell me...I'm always ready to learning something new!
 
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