The way most panels are designed, you wouldn't be able to use a 2-pole 30A breaker, as each pole would be on a different phase. (or phase shift if it was 240/120 1-phase). Now, a yoked double 1/2" breaker MIGHT be able to fit on a single phase, but I've only ever seen them designed such that it's impossible to do that.
Back to the paralleling transformers thing- I know I've seen paralleled transformers on separate breakers, but only in regards to UPS and generator power, and only ever in redundant configuration- EG, the two transformers were there in case of one failure, and they're never required to run parallel. Although when hooked up through a UPS, they *do* run in parallel, and from different breakers, plus typically an additional bypass run that is JUST the transformer. When switching to maint bypass when the UPS has failed into static bypass mode, there is a short period of time when two or more transformers are in parallel. But I suppose that's a completely different animal once you throw a UPS into the picture...
[This message has been edited by SteveFehr (edited 10-13-2006).]
