I assume that the voltages on 2ph were similar to the modern 3ph systems, depending on the equipment being serviced.
7-12.5 kV knocked down to 480, 460, 240, 230 208 etc. I think 600V was developed after 2ph went away.
I once heard that voltages have slowly increased to shrink the size of the wire, and therefore the size of motors and feeders. We have motors at work that have 230/480V wiring diagrams (delta/wye or parallel/series). The amperage is double for the lower voltage.
The first 600V motor I saw was a 10HP and it was about the size of a breadbox.
Does anyone have any pics of 5-20 HP motors in single phase? They must be huge.
