# transformer



## dogdriver (Apr 23, 2014)

Why not? As long as the primary wiring and OCPD will take it and everything is compliant.

I do that kind of thing all the time because the people I work for like to just buy what they think they need without consulting anybody first and then say "hook it up". Most recently an 800 kva 480v generator to back up a 13.8 kv overhead line.


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## ponyboy (Nov 18, 2012)

You'll have an ungrounded secondary so you'll be required to ground one of the secondary phases or put ground fault monitoring on it.


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## dogdriver (Apr 23, 2014)

If he were to use a 240 delta to 480 wye xfmr and bonded the X4 to the building ground, wouldn't that satisfy the requirement?


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## ponyboy (Nov 18, 2012)

dogdriver said:


> If he were to use a 240 delta to 480 wye xfmr and bonded the X4 to the building ground, wouldn't that satisfy the requirement?


Yeah if that's what he has, which I doubt. Step up wyes aren't extremely common.


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## Chrisibew440 (Sep 13, 2013)

Tamas said:


> Hi
> I have client who bought some industrial equipment operating @ 480v,
> and in his building the only available service is 120/240v, 3phsae, delta, 4wire
> 
> ...


What's all the equipment amperage?


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## Chrisibew440 (Sep 13, 2013)

And the secondary windings are rated at 75kva not the primary. So in your case you'd be looking at 37,500 kva.


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## Chrisibew440 (Sep 13, 2013)

You could get 80 amps out of that set up.


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## Big John (May 23, 2010)

KVA rating is common to both sides of the transformer. 

Leave your low-side wye unbonded, ground one phase of your high side delta. Done and done.


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## Chrisibew440 (Sep 13, 2013)

Big John said:


> KVA rating is common to both sides of the transformer.
> 
> Leave your low-side wye unbonded, ground one phase of your high side delta. Done and done.


Really. How's that?


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## Big John (May 23, 2010)

Because you're changing amps at the expense of voltage. Except for inefficiencies in the transformer, total power needs to remain the same from primary to secondary. Any difference is lost as heat inside the transformer so designers work hard to eliminate that.

For a 1Ø tranny:
480V * 156A = 75kVA
208V * 360A = 75kVA


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## Chrisibew440 (Sep 13, 2013)

Big John said:


> Because you're changing amps at the expense of voltage. Total power remains basically the same.
> 
> For a 1Ø tranny:
> 480V * 156A = 75kVA
> 208V * 360A = 75kVA


Your still only getting a certain amount of amps though?


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## Big John (May 23, 2010)

Chrisibew440 said:


> Your still only getting a certain amount of amps though?


 Yeah, but it's always based on the kVA rating. In OP's case he'd get 90A.


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## Chrisibew440 (Sep 13, 2013)

Big John said:


> Yeah, but it's always based on the kVA rating. In OP's case he'd get 90A.


Ok, yeah i de-rated it a little for him. I said 80.


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## MaxH (Mar 12, 2014)

Yes,you can install a transformer in reverse as per the capacity of primary wiring...


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