The size of your service is determined by the service entrance conductors,
and if you have a single service disconnect, it would correspond to the size
of the entrance conductors as well. The "drop" is generally owned by the
utility company and doesn't conform to NEC standards. When you have multiple
service disconnects, the amperage of the total of the disconnects is not
required to equal the ampacity of the entrance conductors. As John Grabowsky
said, you probably have a 100 amp service already, and may be able to just
replace the panel and update the grounding electrode system




"Big Giant Head" wrote in message
. 125.201...
On branch circuits the size of the wire and type of circuit determines the
breaker size but what determines the size of the main or combination of
mains? Can it be as large as the panel is rated for or must it match the
size of the utility's drop?

We have an old panel with two mains, one is a double 50A feeding the rest
of the panel. The other is a double 30A feeding the dryer outlet
directly.
The town now mandates 100A and I think homes get inspected when sold.
Rather than replace the whole panel I could replace main #1 with a double
70A (if available) OR maybe better would be to replace main #2 with a
double 50A (or higher) and have it feed a small subpanel in which I would
put a double 30A for the dryer and maybe throw in a few others as well.
That's within the rating of the main panel but not sure about the utility
drop.