Howdy,
The Essex Electro A427 load bank fully test 120v 1 ph, 120/240 1ph, 120/208 3ph, 240/416 3ph
Trust me, on 120/240 1ph, each switch puts a load equally over each wire. The fans are drawn off one side, so when I take a amp per leg reading, one side might be 40 amps and the other side is 40.3
120/208 3ph is the same thing. A 12kw switched load is just that. Each leg will have the same load, except one which will be slightly higher due to the fans on that line.
I have had my MEP-803A loaded with the 12kw switch and 3kw switch and half way with the variable switch. With a 67.4 amps per leg. I figure it is around a 17kw resistive load.
Actually that loading is in this thread back at
post #20 here. Towards the end I pan down to the clamp meter sitting at 67.4 amps