# WYE to Delta transformer



## High End Power (Apr 23, 2016)

Hi everyone, I have commercial project and inverter out put is 480Y/277 but building power is 240Delta/120. We have to use transformer to convert, but I am not sure what to connect to X4 and H0, ground or neutral (I have X1,X2,X3,X4-H0,H1,H2,H3 terminals).On the label says "IF PRIMARY VOLTAGE IS WYE, THE NEUTRAL TERMINAL MUST NOT BE CONNECTED ANY WAY". I don't understand if it is taking for both side or only WYE side?


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## varmit (Apr 19, 2009)

Need more transformer data. Is this a wye to wye step up transformer or a transformer that is being reverse connected? Post a picture of the data plate if possible. 

I will assume that you are taking building power ( at 240 volt ) to the transformer for a 480/277 volt output to power a 480 volt inverter? If so, you would not connect the neutral on the 240 volt side. If the inverter ( VFD ?) does not require a neutral ( a rare case to need one) then do the normal grounding/ bonding of the load side neutral point of the transformer.


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## varmit (Apr 19, 2009)

Another scenario: If this "inverter" is the output from a solar system, then this 480 volt power would supply the transformer WITHOUT THE NEUTRAL FROM THE 480 SYSTEM CONNECTED. The neutral for the 240 volt side would be connected and bonded normally.

Your original post is not clear on what is supply and load.


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## High End Power (Apr 23, 2016)

Thanks for respond Varmit, I can figure it out how to send picture?
The system it for solar and power side witch is inverter in 480Y/277 and main panel is 240Delta/120.


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## don_resqcapt19 (Jul 18, 2010)

High End Power said:


> Thanks for respond Varmit, I can figure it out how to send picture?
> The system it for solar and power side witch is inverter in 480Y/277 and main panel is *240Delta/120*.


So you have a 3 phase, 4 wire, high leg system?


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## High End Power (Apr 23, 2016)

Yes don_resqcapt19. The building power is "3 phase, 4 wire, high leg". But my PV inverters supply 480Y/277, so in order to connection I have to transform "480Y/277" to "3 phase, 4 wire, high leg".


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## inetdog (Apr 13, 2016)

High End Power said:


> Yes don_resqcapt19. The building power is "3 phase, 4 wire, high leg". But my PV inverters supply 480Y/277, so in order to connection I have to transform "480Y/277" to "3 phase, 4 wire, high leg".


There is no need to connect to the neutral since the 120 will not be relevant. Just use a simple delta winding on the POCO side. 
(Assuming the high leg and therefore the delta is sized for the inverter power requirement. In some cases the high leg is from a much smaller transformer. In that case you might have to upgrade the service. Going to a single phase inverter on the A-C phase is probably not an option.)


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## KGN742003 (Apr 23, 2012)

You would connect your inverter power like a delta without a bond to the neutral. On the low side you will need a transformer with center tapped neutral on the bottom phase of that delta if you want 120 power. You would bond that neutal terminal to the gec (usually just to building steel). You can also make the bond in your first means of disconnect. one or the other not both.

What is the secondary side of this transformer feeding?


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## inetdog (Apr 13, 2016)

KGN742003 said:


> You would connect your inverter power like a delta without a bond to the neutral. On the low side you will need a transformer with center tapped neutral on the bottom phase of that delta if you want 120 power. You would bond that neutal terminal to the gec (usually just to building steel). You can also make the bond in your first means of disconnect. one or the other not both.
> 
> What is the secondary side of this transformer feeding?


I think the OP is referring to a grid tie inverter, not a standalone inverter. So it does not really matter what the building load is. The 120V loads will be supplied through the POCO transformer winding.
Connecting the inverter transformer to the neutral, like connecting the star point of a wye primary, can lead to excessive circulating currents.


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