Originally Posted by Gigs
If you do this with service conductors, you need to be able to reach all the main breakers without walking, so the other panel has to be right next to it generally.
Can you explain this a bit better?
I know this is not a requirement, so I am wondering where it is you heard of this.
A feed-thru panel has lugs right off the main buss so the full amperage of the panel can be fed on to another panel. This eliminates the need for a feeder breaker that would be limited to typically 100 or 125A.
Say your main drop or underground came into your detached garage. Then on to the house. You could have a feed-thru panel in the garage that will have 6-8 circuits, and also allow the full 200A to continue on the the house without a sub-feed breaker. The main breaker serves this purpose.
The house, being a detached structure would still require a means of disconnect, so another main breaker panel would likely be used simply for convenience.