Square D has a listing of their series ratings in their Digest (pages 2-8 and 2-9).
In general you can not apply three devices in series and still have a series rated system. You may have to change each apartment to a main lug only style.
Is this a single 600A main breaker and meter feeding seperately mounted breakers which then feed the individual apartments? Or, is it a 600A main feeding a meter center with individual combination meter sockets for each circuit (Square D type MP or EZM) which then feed each apartment?
