I believe if the sub panel in an outbuilding has more than six slots
it also needs a main disconnect - either a main switch or (more
commonly) a main breaker

A main breaker is required in a detached structure if there are more than
six breakers in the panel.

If the subpanel is in the same building as the main panel, I believe the
breaker in the main panel qualifies as the disconnect even if you have more
than six breakers in the subpanel.

Regardless, I prefer having a main breaker in a panel. If there's an
electrical issue, or you want to make changes, you can just kill the whole
panel instead of trying to figure out which circuit you're on. It's also
safer working in a panel when you can kill the main breaker and disconnect
all power from the panel.

When I built my pump house back in 1991, I thought the electrical inspector
said the limit was four breakers max without a main. Either he was wrong or
the codes have changed. In any case, I have a small panel in the pumphouse
that connect directly to the meter (not a subpanel). It has a double-pole
breaker for the pump, and a couple small breakers for lights and outlets.
There's no way to cut power to the panel if I need to replace a breaker or
something. I've done work in the live panel, but it's not something I would
recommend. If you slip with a screwdriver or something you have NO
overcurrent protection.

Anthony Watson
www.watsondiy.com
www.mountainsoftware.com