"J. Clarke" writes:
Our "200 amp" service included a private transformer (long driveway)
that was only rated at 40 amps continuous.

40A continuous at what voltage?

It doesn't matter if I use one branch (120v) or both (240v). It still
causes the same heat and resistive losses in the transformer's coils.
But the transformer was officially rated at 10 KVa, the new one is 25
KVa. They normally assume a balanced (i.e. 240v) load, since houses
are supposed to be wired that way.

But given that I was drawing 123 amps at 240v, that's kinda an
irrelevent issue for me ;-)