Had to replace some old ballasts in a school this week, dating from the 60s,along with a few tombstones,etc,installed the the regular,or so we thought 120-277 50/60Hz ballasts,no go,however,if we connected them phase to phase,about 425v,slightly high,ok,although buzzing a bit,but when we hooked a 3phase variac at home to test,and set the voltage to about 340v they worked quite well,which would be about 600v phase to phase.Where in the world do they use that voltage,South America or the Middle East,perhaps?