For one reason or another Section 230 has always given me trouble. I have never fully understood it and am looking for some clarification. I am wiring a detached garage and upgrading an existing 200A service to a 400A all-in-one. One main 200A breaker will supply the main house with the other 200A main supplying a 200A 40/42 space 3R subpanel at the detached garage. The problem I am having is that 42 spaces is not enough. With all the circuits in the garage I am still under on the load calcs but over on the breaker spaces. Can I feed an additional subpanel from my 200A subpanel?

Sure

That sounds like one busy garage! Is there going to be a workshop in there?

I speak, of course, from Maine, where many folks live in trailers, situated next to palatial garages.

Must be one really nice garage!!
Yes, you can add a sub-panel....or two if needed.

John

as others have said, yes you can.
can you tell use why or how a garage is using all 42 breakers spaces?
?? Just curious??

I want that garage...

...Might have to implode half the section for it though.

Ian A.

I am using a pretty big panel in my garage (SqD 20/40) and it is full with a couple tandems and a sub on for the spa.
If you start out with one of those 4 high/2 wide breakers to feed the house the slots start going away fast. I still agree 42 is a lot.

Can he use 310.15 (B)(6) for his garage feeder ampacity?

310.15 (B)(6) can be used if you are going from the garage to the house but not the other way.

It is one killer garage. He is a "Need for Speed" guy and moving part of his shop to his house. Everything seems to be small 220V and it really ate up my panel spaces. We put anything and everything you could think of this place. I am envious to say the least.

Why not just put feed through lugs on the garage panel and make it a two section 84 ckt panel? It would save the the 200A breaker in the main panel and the extra feeder too.