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I checked the inverter technical data and it says the inverter is compatible with grounded WYE http://files.sma.de/dl/7418/STP-US_MV_Trafo-TI-en-12.pdf https://files.engineering.com/getfile.aspx?folder=f77d1a51-9d8b-4c5a-8827-9b1507265ae3&file=Capture.JPG

Bill, I agree Yn doesn't tell me if the neutral is grounded or not. We will have grounded neutral at the service entrance. AHJ is adopting NEC 2017 although it is outside US. Luckily it is not my local AHJ [bigsmile]

prc, I have to check with the inverter manufacturer on that but you cannot have ungrounded neutral to the 480/277v serving the building.

Bill This is new installation so there is no transformer to replace. I agree I have to check with utility about the preferred primary configuration but I suspect I'll get an answer or the correct answer. Thanks

Thanks all for your responses. Bill, we are coordinating with utility during the design phase. The utility wants us to provide the transformer and my question and concerns about the transformer. My inverters have that feature. My question is about the configuration of the transformer. I see...

PRC, this is office building and the transformer I'm asking about is the one tied to the utility to step-down service to the building to 480/277v. Most of the time the building will draw excess power needed by loads from utility. in some cases solar will backfeed to utility. I don't think I want...

Thanks all for your input. Mike thanks for sharing Based on the website I'll go with delta_grounded wye

So I'm thinking in my case in lieu of using delta (utility side) to grounded wye (building side), is to use grounded wye to grounded wye

I'm not aware of any similar setup over there.

Apologies I should have made clear. This is not GSU setup. The PV system is mainly to reduce dependence on utility. We will still draw current from utility during peak loads but during light loads, we will backfeed to utility. We are not storing the extra energy produced.

The project is outside the US. The utility is asking to comply with NEC 2017 and IEEE standards. The utility is not providing the transformer and asking to be customer provided. Typically we specify delta-wye padmounted transformer but I'm not sure how it will react during backfeeding.

What about if the pad-mounted transformer is owner provided and not by the utility? are there specific requirements for the transformer?

I have a PV grid-tied system at 480/277volt tied to the service entrance switchgear. The secondary of the pad mounted transformer will be 480/277volt solidly grounded system. What configuration the transformer needs to be at the primary? what concerns I have to worry about when backfeeding?