But that is a different issue. There is nothing restricting having 2-6 service disconnects in a dwelling unit.
Wellllll. . . . First, I understand your point about the six disconnect rule still being valid as long as there isn't a split bus. I could have said it better in my first post that you reference in your post above, IF I had found the
Code citation while I was writing it. I missed this change in 408.36
Exception No. 1, which I believe happened first in the 2008 edition, and have just been learning about it myself.
As for restricting the number of disconnects. . . and also speaking directly to the OP question about OLD split bus panels, the
Code is silent about existing installations of old split bus panels. Old split bus panels, installed to the
Code in effect during their installation, are still acceptable by today's
NEC.
The "penny pinching thinking" that lead many to choose and install the old style split bus panels is where, in my opinion, today's practical restriction of the number of service disconnects comes from, not the
Code.
For NEW installations in average single family dwellings, where there is only a single service center housing the Service Disconnect, the Main Bonding Jumper and all the overcurrent protection for all the dwelling branch circuits, there is a
de facto restriction of the assembly that eliminates the possibility of a split bus and restricts the service disconnects to the included single main breaker because, with careful material purchasing, one can get the best price with a single main breaker service. Maybe that's not your experience, but it is mine.
Now, IF I could wire a new dwelling with only six branch circuits, I could install a single panel limited to six breaker positions and choose a main lugs only bus to land the service entrance conductors on, but, for any average single family dwelling I've been involved with, there are way more than six branch circuits.