[HayZee518]

the downlead for a 200 amp service is 4/0-3 seu aluminum. there is no way in heck a 4/0 wire is going to fit a 100 amp breaker. a way you can get around this is to install a trough at the bottom or top of the two service entrance panels with its own 100 amp breaker. the #2 feeders to the panels are then spliced to the 4/0 cables. because the main cable is aluminum an oxidant MUST be used and split bolt connectors al and cu rated and torqued to manufacturer specs. You then tape up the splices.