Backfeed a 480Y to 240delta transformer... Awkward scenario.

[SPJPROD]

I recently came across a peculiar scenario when the attached transformer was purchased to backfeed a piece of machinery. The piece of equipment only need a 480V delta, and transformer clearly states that it has a 30 degree phase shift from Y to Delta. If this transformer were backfed with 240v delta could a grounded B phase configuration be used? There is obviously no tap on the 480V side for a neutral or ground as primary sides aren't grounded. Anyone have any thoughts on this. Clearly the best answer would be to get the right transformer for the job, but I want to hear what you folks have to say about this.

Thanks.

 

[jumper]

I will first ask if the transformer is listed by the manufacturer for backfeeding.

NEC 2014

450.11(B) Source Marking.
A transformer shall be permitted to
be supplied at the marked secondary voltage, provided that
the installation is in accordance with the manufacturer’s
instructions.

 

[SPJPROD]

I called the manufacturer and they said that it can be backfed.

Thanks,

 

[ActionDave]

You can use it and corner ground it and everything will work fine. The only problem with corner grounds is they freak people out who think you are grounding a ''hot".

 

[jumper]

You can use it and corner ground it and everything will work fine. The only problem with corner grounds is they freak people out who think you are grounding a ''hot".

The secondary will be a wye. I do not think you can corner ground it like a delta.

 

[SPJPROD]

Thanks ActionDave. I run into into corner grounded systems on occasion and have some familiarity with them. Don't see it too frequently where I am at.

 

[jumper]

I called the manufacturer and they said that it can be backfed.

Thanks,

Okay. Then if the machinery does not need a neutral and can run as ungrounded you could do that. You would need fault indicators and still install a GES.

 

[ActionDave]

The secondary will be a wye. I do not think you can corner ground it like a delta.

He's reverse feeding a delta wye transformer so his secondary is going to be delta and he'll float the XO on the primary and corner ground the secondary.

 

[SPJPROD]

I'm actually reverse feeding a Wye Delta transformer. See images above.

He's reverse feeding a delta wye transformer so his secondary is going to be delta and he'll float the XO on the primary.

 

[jumper]

He's reverse feeding a delta wye transformer so his secondary is going to be delta and he'll float the XO on the primary and corner ground the secondary.

You sure. I thought he was reverse feeding a wye-delta.

 

[ActionDave]

You sure. I thought he was reverse feeding a wye-delta.

:slaphead: I didn't look at the pictures. You are correct.

 

[ActionDave]

I'm actually reverse feeding a Wye Delta transformer. See images above.

That's weird. I would expect to see an center tap on the wye side.

 

[jumper]

That's weird. I would expect to see an center tap on the wye side.

Why would a primary wye need one?

 

[ActionDave]

Why would a primary wye need one?

Why have a wye at all unless you need a center tap? I'm not arguing, I'm asking.

 

[GoldDigger]

Why have a wye at all unless you need a center tap? I'm not arguing, I'm asking.

Because the transformer was on hand?

Sent from my XT1585 using Tapatalk

 

[jumper]

Why have a wye at all unless you need a center tap? I'm not arguing, I'm asking.

I am asking also. I is clueless. Ungrounded wye is too weird for me, but they exist somehow.

 

[ActionDave]

Because the transformer was on hand?

Sent from my XT1585 using Tapatalk

If you look at the pictures in the op it says sqd is making them as a regular item. Sounds like they have found a way to package their old Delta wye stepdown as a new stepup to meet current code.

 

[ActionDave]

I am asking also. I is clueless. Ungrounded wye is too weird for me, but they exist somehow.

I was just looking through 250 and it seems you could ground B phase and be legal so it's just like a corner ground only the inside of the transformer would know the difference.

 

[SPJPROD]

I guess the question is. Can you corner ground a Y configuration if the neutral is eliminated?

 

[ActionDave]

I guess the question is. Can you corner ground a Y configuration if the neutral is eliminated?

Looking through 250.30 I say yes.