Local3Jr never more than 42 overcurrent devices in one enclosure (excluding the main)
But you can have as many breakers as you want connected to any service.
100 amp service go ahead and install ten 42 circuit sub panels and fill them up with breakers.
The only thing that matters is that the calculated load is less than the service size.
Say you are planing to wire a house in the 'normal' way with the code minimum circuits and the calculations show a 100 amp service will do the job.
Now the future homeowner says they want every receptacle, switch and appliance on it's own circuit.
To do this you will need a few sub panels and lots of breakers but the calculated load remains the same. The 100 amp service will still be fine.
Bob
