The diagram in Figure 14–9 shows a wye–wyeconnected transformer bank having a threephase, fourwire, 2400/4160V input and a threephase, fourwire, 1/8V output On the highvoltage input side, the neutral wire is connected to the common point Top that's an open wyeopen delta bank you have in your diagram Now there is also another configuration to what I posted utilizing two pots on a 1/8 or 277/480 service but it can only be done with a 4 external secondary bushing transformer (167kva) I have a diagram of it stashed away somewhere _____However, many jurisdictions forbid more than one class for a premises' service, and the choice may come down to 1/240 splitphase, 8 singlephase or threephase (delta), 1/8 threephase (wye), or 277/480 threephase (wye) (or 347/600 threephase (wye) in Canada) See also Transformer;
3 Phase Transformer Connections
