It is my understanding that the high leg was used a lot in rural areas so farms could could have three phase but not effect the homes were most electric ranges, water heaters, pumps were only rated for 240v and would not run on 208v. I'm not sure if it was designed this way or just a convenient side effect.
I'm pretty sure the 208-N connection has never been legal to USE in that coonection. But the 240 A-B, B-C, and C-B connection is just fine for the items listed.... The 208 is a byproduct of one and a 1/2 transformer windings - making it difficult to provid OCP for, and unstable due varying loads.
It is also my understanding that the split phase was only as a conveinence to provide for 120 lighting and general outlets in many industrial situations where only the delta would be provided otherwise. I assume it may also be the case for rural farming areas too???
While 208 WYE is very easy to reconnect for 208/120, and very friendly to 120 loads it is not the greatest for industrial motors - and a delta would be preffered for 3 phase loads. And you can still get a very 120 frindly edison circuit out of it too. The BEST of BOTH worlds... Back when the demand for 120 was much less in those areas.
And breaking up a delta transmission lines into single split-phased transformers is easier, making more remote single phased areas easier in an shared Residential/Industrial area.
