Electrical service panel - new construction - . My garage is nearer southern Cal edison therefore I would lkie to install a 400 amp service at the garage, I need 100 amps for the garage and 300 amps for the house. (house is an additional 100 feet from garage) How do I best accomplish this? Thank you! Wayne

Depending upon location just put the 400 amp in the house and install a 100 amp panel in the out building/garage.

Cheaper yet. Do a split. Use two 200 amp panels and pull 100 amps from one to the garage. Two 200 amp panels cheaper cost wise.

Mount your starting point outside that way you can come right off it to the garage. See your electrical contractor for details.