In my experience the average 'installer' does not know how to figure this out and will either ignore it or tell people to increase the service size,
That is my problem with this, I do not know many electricians that do, or would do the calculations.
In some residential 200 amp panels, you may see 60 or seventy breakers that add up to 700 amps or more. The actual load may only be 100 or so amps.
Of course, but there is a main in the panel that will protect the service conductors if to to much load is added to this panel.
Don brought up this exception when I asked about a commercial service that was using 6 breakers that added up to about 3000 amps as the service disconnect.
My problem with this was the MLO switch gear these 6 breakers where installed in was only rated 1600 amps. The next OCPD up stream would be the high voltage cut outs feeding the transformer suppling this board.
I just find this odd.
Bob
