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For parallel power production which side of transformer is primary/secondary?

Question asked by Scott Kupper on Jan 3, 2018
Latest reply on Jan 3, 2018 by Scott Kupper

We have an installation where we have 480V solar inverters feeding a panel, which feeds a 480 to 208 volt transformer, which then ties into the utility service. The only equipment on the 480V panel is solar inverters. I understand that we consider one side of the transformer, then the other, as the primary side when when selecting OCPD per 705.30(B). My questions is which side do we consider the "secondary" side, where the rules of 240.21(C) apply? 

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