iwire ---
I just do electrial engineering. I am not responsible for the tables, the assumptions used in making the tables, or the errors in the tables.
One assumption that the tables make is that there is enough power from the service to allow all the circuits to draw their rated amps.
On a 200amp/220volt service, 4 50amp/220volt circuits draw a total of 200amps (average or 50), 8 50amp/220volt circuits draw a total of 200amps (average of 25).
The service derates the conductors. So if you pull either the 4 or 8 circuits through a single hole in the joists you will get about the same temperature rise.
I could do an example using 20amp circuits, but that requires actual math.
