I am creating a sub panel which will contain 20, 20 AMP circuits to provide power for 20, 1,000 watt, 120v stage lights. My calculations suggest that the light loads, which are constant, will require`20KW. 20KW at 120V means that I will be drawing 160 AMPS. My question is this: At the main panel, is it proper to feed the sub panel off of a double pole breaker that is rated for 80 AMPS? I came up with that by considering that 80 amps at 240v will be providing the equivalent wattage as 160amps 120v will need. Is this the correct way of looking at it?
If your loads are evenly spread across two legs, i don't see any problem on using 80A double-pole breaker, just size wires properly. You'll have two 80A legs. But using 100A breaker on main panel will be better (it'll allow you to load the legs not perfectly even)