Re: Maximum amperage of circuits in service panel
If the service is 100-amps, then most likely the service entrance conductors are only rated for 100-amps. The 100-amps was originally calculated for the total demand load that the dwelling would draw.
To add a load as large as 50-amps will most likely require you to upgrade the service to handle the additional load. To be sure, calculate the total connected load of the existing system, apply the demand factors, and add in the new circuit loads. If you come out larger than about 24,000 volt-amps, you will need to increase the service size.
If you come in below 100-amp service load, the circuits can be added to the panel unless you exceed 42 circuits or the total amount of circuits allowed per the manufacturers specifications of the panel. You may also add a sub-panel off the service panel if desired.