change: i think the 40a supply must match a 40a wire,and the subpanel
must have not 100a but a 40a breaker.
but first see:
http://www.selfhelpandmore.com/homew...rage/index.htm

http://www.faqs.org/faqs/electrical-wiring/part1/

Gary wrote:
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.

Thx
Gary