Delta to wye

[Twbaskin]

I have an industrial customer who I am adding a sub-panel for. He often buys large equipment himself from a source we have used for years and I install and provide everything else.
The building has two services, one 480, one 208/120. Both are wye services. The equipment being fed is 30 KVA and rated for 200-240 volts.
We are running out of room so I am feed this panel from the 480 service through a transformer.
His supplier sent us a transformer listed for a delta primary and wye secondary. I know you can hook a wye source to the primary, but I am curious about whether I am connecting my secondary properly. Do I not have to bond from the 0(N) secondary terminal in the transformer to the grounding electrode conductor? In this case I have both a grounding conductor coming from the 480v feed, and I have solid building steel just a couple feet away.
Thanks!

 

[Twbaskin]

I have an industrial customer who I am adding a sub-panel for. He often buys large equipment himself from a source we have used for years and I install and provide everything else.
The building has two services, one 480, one 208/120. Both are wye services. The equipment being fed is 30 KVA and rated for 200-240 volts.
We are running out of room so I am feed this panel from the 480 service through a transformer.
His supplier sent us a transformer listed for a delta primary and wye secondary. I know you can hook a wye source to the primary, but I am curious about whether I am connecting my secondary properly. Do I not have to bond from the 0(N) secondary terminal in the transformer to the grounding electrode conductor? In this case I have both a grounding conductor coming from the 480v feed, and I have solid building steel just a couple feet away.
Thanks!

Worth adding - the equipment is strictly 3-phase, but I would like the option to be able to run 110volt circuits out of this sub-panel. We oversized the transformer to allow for other loads to come out of this panel.

 

[don_resqcapt19]

Assuming the transformer is intended to be a 480-208Y/120 step down transformer and you are reverse wiring it, you do not connect anything to the XO terminal. You will have a 3 wire secondary with no provisions for any line to neutral loads. You will either have to provide ground detectors on the 208 secondary or make it a corner grounded system.

 

[jim dungar]

The devil.is in the details.
Are you going down from 480V?
What is the transformer wiring diagram?

Typically the secondary side of a transformer is isolated from the primary and so is considered a separately derived system (buck-boost connections are typical exceptions).

 

[LarryFine]

Welcome to the forum.

Yes, the secondary neutral should be connected to building steel, as long as it is in turn properly bonded.

The transformer should be 480D to 208Y/120. This will give you both 208v 3ph (and 1ph) and 120v 1ph.

 

[tortuga]

In this case I have both a grounding conductor coming from the 480v feed, and I have solid building steel just a couple feet away.
Thanks!

Yes equipment grounding conductor with 480V feeder then a grounding electrode conductor per 250.30(A)(5) to building steel and consider if there is a metal water pipe see 250.104(D)

 

[augie47]

This is a typical install:

 

[Twbaskin]

Assuming the transformer is intended to be a 480-208Y/120 step down transformer and you are reverse wiring it, you do not connect anything to the XO terminal. You will have a 3 wire secondary with no provisions for any line to neutral loads. You will either have to provide ground detectors on the 208 secondary or make it a corner grounded system.

Not reverse wiring it. I am feeding the primary from a 480v wye source. I am stepping down to 208/120V and intend for that that to be a wye connection so I can have a neutral present for 110v loads. At this time I'm not sure there will actually be any. But I want to be able to if the need arises. It seems per below responses that I am on the right track. Just wanted to get a second, (or more) opinion.

 

[Twbaskin]

Welcome to the forum.

Yes, the secondary neutral should be connected to building steel, as long as it is in turn properly bonded.

The transformer should be 480D to 208Y/120. This will give you both 208v 3ph (and 1ph) and 120v 1ph.

Thank you. I think this answers my question. I have certainly wired transformers many times in my 50 years or so in the business. I'm just not sure I've ever been handed a transformer that shows a delta primary and a wye secondary. The truth is - I may have, and just not really noticed it. But it made me question myself and I don't like to take chances with this type of installation. There's a butt-load of VERY expensive equipment being connected to this.

 

[Twbaskin]

Thanks to all.
I believe I have confirmed what I thought I already knew. Just looking for a bit of assurance.
As I noted in a reply above - I have certainly wired transformers many times in my 50 years or so in the business. I'm just not sure I've ever been handed a transformer that shows a delta primary and a wye secondary. The truth is - I may have, and just not really noticed it. But it made me question myself and I don't like to take chances with this type of installation.
This is my first time on this forum, and I appreciate the quick and obviously knowledgeable replies. I have already bookmarked it for future reference.

 

[don_resqcapt19]

Thanks to all.
I believe I have confirmed what I thought I already knew. Just looking for a bit of assurance.
As I noted in a reply above - I have certainly wired transformers many times in my 50 years or so in the business. I'm just not sure I've ever been handed a transformer that shows a delta primary and a wye secondary. The truth is - I may have, and just not really noticed it. But it made me question myself and I don't like to take chances with this type of installation.
This is my first time on this forum, and I appreciate the quick and obviously knowledgeable replies. I have already bookmarked it for future reference.

That is by far the most common configuration for a step down transformer.
Don't forget about the supply side bonding jumper and the grounding electrode system for the secondary side.

 

[jim dungar]

Delta-Wye transformers are probably far and away the most common configuration used for stepping down 480V, in non-utility applications. If you told me 75-80% I would believe you.

 

[Twbaskin]

I looked last night for tech data on some transformers that I've hooked up. Two of them at this same business. They both were this same configuration. I just didn't ever notice it.
And after reading comments and thinking a bit more, it makes sense that the primary side doesn't really care whether or not the incoming line originates as a wye or a delta wired source. It is creating it's own derived voltage and system neutral. Regardless
Thanks again.

 

[augie47]

I looked last night for tech data on some transformers that I've hooked up. Two of them at this same business. They both were this same configuration. I just didn't ever notice it.
And after reading comments and thinking a bit more, it makes sense that the primary side doesn't really care whether or not the incoming line originates as a wye or a delta wired source. It is creating it's own derived voltage and system neutral. Regardless
Thanks again.