# 480V Delta vs 480V Y



## amptech

I have a situation with some new machinery coming to a factory. The engineers say the equipment needs 480V Y but it doesn't need a neutral. Presently the plant only has a 1200A 120/240 3Ø delta service. We were going to set a 112.5kva 240V delta primary/480V Y secondary transformer to take care of this new equipment. The trouble is finding a 480V Y secondary tranny. Everything is 480V Delta. Most transformers above 1 kva are listed to be wired in reverse so we have looked at that too. No luck finding a 480V Y primary/240V Delta secondary. My question is, if the equipment doesn't require a neutral how would it discern 480 Y from 480 Delta? I thought I saw a thread dealing with this a few days ago but I can't sem to find it. Can anyone shed some light on this? Thanks.


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## RePhase277

You will just have to tap the secondary that way. If you are using a transformer that comes from the factory with a 480 V delta primary and a 120/208 V Y secondary, backwards, then you need to retap it to what you need.

P.S. And the equipment will not be able to tell whether it is getting delta or Y connected 480. But the Y would be required for equipment grounding purposes. Without it, there would be no place to ground the frame.


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## frenchelectrican

Most case you can able get the transfomer run in reverse however there is a item or two you need to be address here .,

You will need to adjust the tap after you power up to get the correct voltage rating.

as far for grounding make sure you bond it properly otherwise you may get unstable voltage if not taken care of it.

Merci,Marc


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## micromind

Quite likely the requirement for the 480 wye connection has to do with the MOVs used in VFDs. If this is true, and the equipment is connected to a 480 delta system, the MOVs will likely blow up, whether the delta is floating or grounded B. 

If a delta system is installed, it can be easily made into a wye by means of a grounding transformer. You can make your own from 3 small (100VA is plenty) single phase transformers with 480 volt primaries, and any secondary voltage. Just connect the primaries in a wye, and ground the center of the wye. Make sure the 480 delta transformer is not grounded on the 480 side. This set-up will create a grounded wye, but the load must be 3 phase 3 wire, no neutral. 

If you want to go a step further, you can easily make a ground fault detector from this set-up. Simply connect the secondaries of the single phase transformers in a delta, and leave one corner open. Connect a relay coil across the open corner. Connect the contact of the relay to trip the feeder breaker. 

Here's how it works; Say the single phase transformers are 480 primary, and 120 secondary. Under normal conditions very little voltage will appear across the open corner (and the relay coil). If one of the 480 volt power legs becomes grounded, 120 volts will appear across the open corner. This will energize the relay coil, and trip the feeder breaker. 

I've done several of these where an existing drive isolation transformer was delta-delta, and the new drive needed a wye connection. 

Rob


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## MDShunk

The last time I bumped into this (printing presses), my choices were to have one wound and wait 6 weeks, buy a tested used transformer that had a 480 wye secondary (Romac) or buy three single phase transformers and make up my own bank. I bought used.


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## patriot1

I posted this in "watch for the high leg" thread, maybe this is what you saw....

"
I believe that the high leg panel should be for equipment use only, ie..a/c, motor, lighting, xfmrs...etc..strickly 3 phase or 1 phase items that would not "see" the "wild", "freak", "high" leg until it went to ground. There is a local church that has 120/208 and connected 3 single phase xfmrs so they could have a high leg to operate their a/c's more economically."


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## John

amptech said:


> I have a situation with some new machinery coming to a factory. The engineers say the equipment needs 480V Y but it doesn't need a neutral. Presently the plant only has a 1200A 120/240 3Ø delta service. We were going to set a 112.5kva 240V delta primary/480V Y secondary transformer to take care of this new equipment. The trouble is finding a 480V Y secondary tranny. Everything is 480V Delta. Most transformers above 1 kva are listed to be wired in reverse so we have looked at that too. No luck finding a 480V Y primary/240V Delta secondary. My question is, if the equipment doesn't require a neutral how would it discern 480 Y from 480 Delta? I thought I saw a thread dealing with this a few days ago but I can't sem to find it. Can anyone shed some light on this? Thanks.


Will this work? :whistling2:

View attachment 1094


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## j johnson

Is the equitment from the Eu.
If it is the ground is used as neutral!


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## Ernesto J Delgadillo

My line voltage is unvalance every so often to ground. for example. We take a reading between ground and line voltage and L1 to ground is 120, L2 to ground is 380 and L3 to ground 500 volts. but then it goes normal. 277 to ground. my secondary is Y connection.


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## Nildogg

amptech said:


> I have a situation with some new machinery coming to a factory. The engineers say the equipment needs 480V Y but it doesn't need a neutral. Presently the plant only has a 1200A 120/240 3Ø delta service. We were going to set a 112.5kva 240V delta primary/480V Y secondary transformer to take care of this new equipment. The trouble is finding a 480V Y secondary tranny. Everything is 480V Delta. Most transformers above 1 kva are listed to be wired in reverse so we have looked at that too. No luck finding a 480V Y primary/240V Delta secondary. My question is, if the equipment doesn't require a neutral how would it discern 480 Y from 480 Delta? I thought I saw a thread dealing with this a few days ago but I can't sem to find it. Can anyone shed some light on this? Thanks.[/quote


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## reddog552

. And the equipment will not be able to tell whether it is getting delta or Y connected 480. But the Y would be required for equipment grounding purposes. Without it, there would be no place to ground the frame.[/quote]
I DISSAGREE WITH THIS u can have a EGC on a Delta secondary.


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## BILLY 101

The best way to create 480 volt Y would be to use the primary of the incoming service and install the appropriate transformer.
If that is not possible use (3)-single phase 37 kva transformers 277 volt primary / 120-240 volt secondary. 
Of course the 277 volt will be used as the secondary connected is Y configuation. The 240 volt will be used as the primary connected in a delta configuration.
Such as a Hammond cat. # MF37037FE.

Bill


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## Skipp

This thread is a year old. I'm sure the OP has figured it out by now.


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## sparky312

*480 delta 240 delta transformer trips ground*

I am using a 480v delta to 240v delta backwards to get 480v for a motor from a 120/208 highleg panel. From the panel I have 120 to ground for the A and B phase and 211 to ground on the B phase.
I wired the 3 legs of the LV side to X1 X2 and X3 with nothing connected to X4.
Load side (480) connected to H1 H2 and H3.
When I turned the beaker on it tripped.
Any ideas ??


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