[0] Okay, technically 240V did not become official until around 1967, but the split-phase design was there from the beginning. They capped it at 240V to stop the creeping up that had been going on in the earlier part of the century. This is why you still have a lot of people (not all of them old enough to have been alive in 1967, oddly enough) that refer to 240V as 220.