Electrical ,what voltage to use
I don't know why this question is here as it's not a DIY process, but I'll answer anyway.

Three phase power (208/120 or 480/277) is divided by the square root of 3 and by the higher voltage. The square root of 3 is used because of the adjustment between phases.

Single phase power is completely different, and easier. You just divide by the higher voltage, 240. This is because 120 is not the voltage on the panel; 120 is simply a subdivision because of the neutral.