Grounding 208 Y pri.240 Delta sec. transformer

[ddekruyf]

We are installing a 208 volt Y pri to 240 delta sec. to feed a single machine. There is some disscussion on what to do with X\O on the primary. What does NEC require?

 

[augie47]

Re: Grounding 208 Y pri.240 Delta sec. transformer

act like its not there

 

[infinity]

Re: Grounding 208 Y pri.240 Delta sec. transformer

Just wondering how you'll ground the Delta secondary of this transformer?

 

[LarryFine]

Re: Grounding 208 Y pri.240 Delta sec. transformer

Originally posted by augie47:
act like its not there

Augie, are you saying that the primary neutral should not be run back to the supplying-panel's neutral?

Why not?

 

[iwire]

Re: Grounding 208 Y pri.240 Delta sec. transformer

Larry that is exactly what he is saying.

It is unneeded and under certain circumstances like a blown fuse on one of the ungrounded primarys it can burn up.

 

[LarryFine]

Re: Grounding 208 Y pri.240 Delta sec. transformer

So it's more like an ungrounded delta?

 

[iwire]

Re: Grounding 208 Y pri.240 Delta sec. transformer

I am guessing that this transformer is actually designed to be used as a 240 delta primary with a 208Y/120 secondary. I am also guessing they plan to use it backward which may be fine.

Used in this way the the XO terminal has no purpose.

 

[LarryFine]

Re: Grounding 208 Y pri.240 Delta sec. transformer

It seems that any imbalance on the delta secondary would swing the primary's X0 point away from zero volts to ground, resulting in unbalanced voltages among the three primary windings.