"Gary" wrote in message
news:2Omhh.501373$R63.440567@pd7urf1no...
I want to connect a second electrical panel in my house. I am going to run
it from a 40 amp breaker in my main panel. The second panel I bought has a
100 amp main breaker in it. Is it code to keep that breaker in there? I
assume it is redundant and would only act as a switch if I wanted to do
some servicing in the 2nd panel.

You bought a main panel instead of a subpanel. That was a small mistake
since you are paying for a breaker you won't be using (but won't do any harm
either) and will have to buy a separate neutral bus.

Take it back and buy the right thing if you can. If not, you can use it,
but don't forget the neutral bus.
I just bought a real nice GE subpanel from Lowes for $30 with 4 breakers
thrown in. I wish my main panel was as nice. But I see you are up North...