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A very common design technique for Buildings with 4 Wire Deltas, was to use 1 Phase 3 Wire Panelboards - fed with Lines "A", "C" and the Center Tapped Neutral, where only 1 Phase loads were used (like in Office spaces and such), and using 3 Phase Panelboards - fed with Lines "A, B & C" only - no Grounded Conductor (Neutral), where only L-L and 3 Phase loads were used (like in the warehouse shop area or for HVAC equipment).

Scott, I just did this exact setup in a major restaurant remodel, where the service is open Delta. We have a 125a 3ph panel for the two RTU's (HVAC) and a 200a 1ph panel for everything else.

The original plans called for a new 208/120Y system with two 3ph panels, but I bumped heads with the engineer and we redesigned the service. Saved my customer $5-6K in new transformer costs.

Larry Fine
Fine Electric Co.
fineelectricco.com