I need to either replace my distribution box or add sub panel so that I can
use arcfault breakers. (my current panel does not have these available). I
am trying to decide if 100A is enough (and I won't need to change the
entrance conductors) or if I should upgrade to 200A for future upgrades.
In particular, I have done the load calculation per NEC 220 and come up with
75A. I want to reserve enough extra current for a future spa. When doing a
load calculation can I use all 100A rated on the panel or is there a
derating factor I must use? How high in the load calc can one go before a
larger service panel is indicated?