cctalk Digest, Vol 88, Issue 2

[Jonathan Chapman]

> Why couldn't 120V be derived from either of the 240V phase and the
> grounded corner via a 2:1 transformer?

It can. That's often how, say, an Edison base decorative luminary is run when all other lighting is 277V (the ratios would of course be different). Otherwise someone invariably screws a 120V bulb into a socket providing 277V.

> I would wonder if it would be
> possible to ground the center tap on the secondary side of the 2:1
> transformer mentioned above or not.

Sure, that's one way of getting split phase 120/240V on a delta system. You've basically made high leg delta the hard way. You do also get to use a completely separate two busbar panel for your 120/240V loads, which prevents the "oops that empty breaker spots give 208V to ground" mistake.

A more common method of supplying significant small loads on a delta service is to use a delta:wye transformer and provide 120/208Y. This provides more even loading on the three-phase service, and also provides 120/208Y for, say, computers :P The center/star connection in the secondary is grounded at the transformer.

Thanks,
Jonathan