# Fronius Symo 20.0-3 480 (Delta - Wye Transformer), Neutral Wire



## jay_the_gemini (Feb 13, 2018)

Hi Everyone,

Ok, I will try to be concise here. I am PV Designer who has been tasked with creating a 3 line diagram for my client, an electrician. 

The design calls for using a Fronius Symo 20.0-3 480 inverter, then sending that into a 480 Delta > 208 Y Transformer, then a line side tap via a 208V Fused Disconnect. All seems straightforward. 

However, after careful review of the inverter itself, it absolutely requires the Neutral. There is no way to disable neutral sensing, and there is even a supplemental technical publication from Fronius stating that for the Symo series specifically, they require a Neutral for voltage reference. 

Back to my main concern here. By its very nature, the 480 Delta side of this transformer will have no neutral, yet the 208 Y side will. The neutral on the 208 Y will already be “spoken for” as it is going back to the 208Y panel board. Which begs the question, where on earth does the Neutral from the Inverter output go???

I have come to my own conclusion.

a. This design is straight up inherently flawed, and the 480 Delta > 208 Y is not applicable here. I did some research, and found a 480 Y to 208 Y transformer. This seems to be a very RARE transformer, and does not have much info about it available at all.

Does anyone have experience with this particular inverter, or if not that inverter verbatim, the greater scenario of trying to land a Inverter that requires a Neutral onto a 480 Delta > 208 Y transformer?

Really would appreciate any advice on this situation...

Thanks everyone.


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## telsa (May 22, 2015)

One thread is sufficient.

This is the kind of query that ought to go to the manufacturer.

Their tech desk is as lonely as a Maytag repairman.

They'll have the canned solution right at their fingertips.

You must know that.


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## RePhase277 (Feb 5, 2008)

jay_the_gemini said:


> Hi Everyone,
> 
> Ok, I will try to be concise here. I am PV Designer who has been tasked with creating a 3 line diagram for my client, an electrician.
> 
> ...


We have discussed this in a similar thread where solar inverters needed the wye point in a transformer stepping up from 480 to 600 V. Turns out it is needed on the primary side, and you're right about the rarity of wye-wye transformers. 

One solution, less than ideal, would be to use two transformers, a wye-delta feeding a delta-wye.


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