Buried on the IEEE C57.12 transformer standards are two variations for tapped-delta secondary terminal designations. If the highleg is across from grounded terminal X2, it is labeled X6. If the highleg is across from grounded terminal X3, it is labeled X4.

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If 120V is needed {say for controls} it would be grounded to form a separately derived system, although not a “:neutral” for the unsymmetrical phase-to-ground voltages. If the corresponding delta-tap terminal is grounded, highleg marking is in order for your and others’ safety.