(…under construction…)

Truth is, four-wire delta banks can have any size transformers, including one “zero-size” pot—that being only two transformers—a/k/a an “open delta” bank. See IEEE std C57.105-1978 §6/§8 or odds’n’sods from EPE overhead standards linked at http://6l6.net/bjarn/EPEdelta-loadg.DSO7.pdf (~1MB) for some sizing guidelines (that are not necessarily NEC-based.) A ‘shorthand’ sketch of delta and open-delta secondary interconnection…

[Linked Image from 6l6.net]

 

[This message has been edited by Bjarney (edited 04-04-2005).]