GEC required for 208-480 delta transformer?

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greenspark1 said:
...
I just learned that contractors have obtained a real 208Y-480D step up transformer. ...
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greenspark1 said:
Nope, wye-delta. Square D model V28M48T1516. Still need to ground a leg? Surprised the unit's wiring diagram doesn't show this.
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Got a picture of that diagram/nameplate?

Three phase transformers typically have delta primaries, step up or down. I couldn't find any info online for that particular model number.

Transformer diagrams do not show corner grounding of a delta configuration. Wye neutral and delta high leg grounding are the only grounding I've seen indicated on diagrams.

It has been said on this forum that the neutral of a wye primary should be left floating (i.e. not connected). I've never quite grasped the reasoning, so perhaps someone that does will explain it...
 
FWIW, cranes are often powered with ungrounded systems with ground fault detectors. This is so a single line to ground fault doesn't trip the OCPD. This allows suspended loads to be discharged prior to performing the necessary maintenance.
 
Smart $ said:
Got a picture of that diagram/nameplate?

Three phase transformers typically have delta primaries, step up or down. I couldn't find any info online for that particular model number.

Transformer diagrams do not show corner grounding of a delta configuration. Wye neutral and delta high leg grounding are the only grounding I've seen indicated on diagrams.

It has been said on this forum that the neutral of a wye primary should be left floating (i.e. not connected). I've never quite grasped the reasoning, so perhaps someone that does will explain it...
Click to expand...

Most every one knows that you bond the XO secondary neutral connection to the case/ground if your wiring a standard 480v Delta to 120/208v secondary xfmr, but, If one bonds the XO neutral connection to the case of a standard 480v delta to 120/208v secondary, like they usually always do out of habit, but back feed that transformer with 208v delta, please let me know so I'm not close to it when they throw the power to it.


JAP>
 
Smart $ said:
FWIW, cranes are often powered with ungrounded systems with ground fault detectors. This is so a single line to ground fault doesn't trip the OCPD. This allows suspended loads to be discharged prior to performing the necessary maintenance.
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That's very interesting.

JAP>
 
jap said:
Most every one knows that you bond the XO secondary neutral connection to the case/ground if your wiring a standard 480v Delta to 120/208v secondary xfmr, but, If one bonds the XO neutral connection to the case of a standard 480v delta to 120/208v secondary, like they usually always do out of habit, but back feed that transformer with 208v delta, please let me know so I'm not close to it when they throw the power to it.


JAP>
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I don't think you need to back off too far. Most cases I have heard of just have high currents in the 208 volt side if the neutral point is connected to the supply neutral, they don't blow up. Some of them maybe take days or even weeks before the unit fails as well.

A unit intended for step down will typically have higher inrush current though when energizing it, presumably because the high voltage side is wound closer to the core, where one intended for step up the low voltage side would be wound closer to the core.
 
kwired said:
I don't think you need to back off too far. Most cases I have heard of just have high currents in the 208 volt side if the neutral point is connected to the supply neutral, they don't blow up. Some of them maybe take days or even weeks before the unit fails as well.

A unit intended for step down will typically have higher inrush current though when energizing it, presumably because the high voltage side is wound closer to the core, where one intended for step up the low voltage side would be wound closer to the core.
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You've heard of it,,,, I've witnessed it.
They don't blow up, its a dead short to ground and its instantaneous should that connection be made and backfed.
It wont take a day or a week to tell you about it.

JAP>
 
Let me rephrase not so much a dead short, but, the insulated bonding jumper that was installed from XO to the case shredded all of its insulation of in all of about 1/2 of a second. :)


Jap>
 
jap said:
Let me rephrase not so much a dead short, but, the insulated bonding jumper that was installed from XO to the case shredded all of its insulation of in all of about 1/2 of a second. :)
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I think that installation had a problem more significant than connecting the primary neutral to X0.
 
Smart $ said:
Got a picture of that diagram/nameplate?

Three phase transformers typically have delta primaries, step up or down. I couldn't find any info online for that particular model number.

Transformer diagrams do not show corner grounding of a delta configuration. Wye neutral and delta high leg grounding are the only grounding I've seen indicated on diagrams.

It has been said on this forum that the neutral of a wye primary should be left floating (i.e. not connected). I've never quite grasped the reasoning, so perhaps someone that does will explain it...
Click to expand...

Ask and you shall receive (attached). It is indeed a 208Y-480D step up transformer. So, how do we hook up this bad boy?
I propose: connect all 5 (A,B,C,N,EGC) wires on the LV side and 3 hots and a ground on the high side. Add a GEC. Bond one 480V phase to ground.
 

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greenspark1 said:
Ask and you shall receive (attached). It is indeed a 208Y-480D step up transformer. So, how do we hook up this bad boy?
I propose: connect all 5 (A,B,C,N,EGC) wires on the LV side and 3 hots and a ground on the high side. Add a GEC. Bond one 480V phase to ground.
Click to expand...

My whole point in all of this is I don't think anyone should try to explain how to hook up a transformer more or less "Over the Phone".

A qualified electrician with experience will know how.

Jap>
 
greenspark1 said:
But we're not backfeeding this transformer. It's made as 208V -> 480V.
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In your first post you indicated you had a "Standard" transformer that you were going to feed backwards.
Leading me to believe it was a V48M28T1516.

With this new information given that's not the case.

The picture is of an Eaton Custom XFMR 208Y Primary to 480v secondary.

Although I don't see why you needed a 208v Y Primary it still doesn't change the fact that suggestions on how to hook it up should not be given.

JAP>
 
I notice now in your later post you indicated you all got a "Real" Transformer.

Good decision.

:thumbsup:

JAP>
 
jap said:
I notice now in your later post you indicated you all got a "Real" Transformer.

Good decision.

:thumbsup:

JAP>
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Yup, should be safer! So now that we have a 'real' one, I would like to be able to confirm that the electricians are hooking it up correctly. They have not run a GEC so I already think that's an omission. And I suspect do not have much experience with step up transformers for 480V cranes. I will not be following the instructions given here verbatim but I do want to understand how it should be hooked up and why. That's why this forum is great!
 
greenspark1 said:
Ask and you shall receive (attached). It is indeed a 208Y-480D step up transformer. So, how do we hook up this bad boy?
I propose: connect all 5 (A,B,C,N,EGC) wires on the LV side and 3 hots and a ground on the high side. Add a GEC. Bond one 480V phase to ground.
Click to expand...
That looks like a delta wye transformer that is allowed to be reverse fed. In your case there should be nothing connected to the X0.
 
ActionDave said:
That looks like a delta wye transformer that is allowed to be reverse fed. In your case there should be nothing connected to the X0.
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Actually it is a 208v Y Primary 480v Delta secondary just as the OP has stated.

JAP>
 
Smart $ said:
I think that installation had a problem more significant than connecting the primary neutral to X0.
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me too.

ActionDave said:
That looks like a delta wye transformer that is allowed to be reverse fed. In your case there should be nothing connected to the X0.
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Actually it is a 208v Y Primary 480v Delta secondary just as the OP has stated.
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If the low voltage were the intended primary side, wouldn't they ordinarily be marked as "H1, H2, H3, H0?

I agree that it may be designed to be reverse fed.
 
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