The panel you are talking about has the “service disconnect as a component” The NEC, (National Electrical Code), says it has to be in a “readily accessible” location. It can be indoors but at the “nearest point of entrance of the service conductors”.
I have installed many and always assumed it was on the outside in an easily accessible location so that the fire dept. or other emergency response crew could find it and shut off the entire house quickly. This may be true, but is enforced by a stronger local code(that I never saw a reason to question).There could be different customary practices in other regions. Based on the builder’s convenience, cost and also safety concerns, the disconnect right below or above where SDG&E’s drop comes in are the best locations. Often times only the main disconnect is outside and a feeder is run to a sub panel in a closet or utility room.This is how condos are wired.
Usually in residential, the panel is a meter and disconnect combo panel, it is all so located with approval of the the utility. The builder works with a planner from the utility. They are nice to work with,IMO, but you do what they want or you won’t get a drop. You will more frequently, see different arrangements in commercial buildings.
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