Just following up on Paul's mentioning of the 4 wire Delta's KVA ratings per Transformer:

On Open Delta setups (two Transformers), the one used for 1Ø 3W service is typically no less than 150% larger than the "Kicker" Transformer. Normally it's 250% larger.
Example:
25 KVA Open Delta 4 wire setup.
Main Transformer = 20 KVA, Kicker = 10 KVA.

3Ø 3W Open Deltas normally use equal size pots on both sides.

For a 3Ø 4W Closed Delta (three Transformers), the "Center" pot (used for 1Ø 3W service) is typically 150% larger than one of the "Outer" pots.
Example:
45 KVA Closed 4 wire Delta:
Center pot = 25 KVA, Outer pots (2) = 10 KVA each.

These are rough guesstimates, just for discussion purposes only.

Scott35

BTW: Great job by all that replied in this thread! Very impressive knowledge base here!
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Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!