Bill,
On my 48v (nominal) system, I have 4 panels wired in series (25v each) and they typically give me about 90-100v total, which feeds into my charge controller. This charge controller steps the voltage down (and increases amps) to feed directly into my 48v battery bank.
So on my system I am running #8 wire straight through from the array to the DC disconnect which the charge controller connects to.
I'm guessing then that your solar panel(s) put out a total of 12v, and this feeds into a 12v charge controller - and that is why the large diameter wire - for less voltage loss? If so then get yourself a cheap busbar and put it inside your DC disconnect (you do have one don't you? code usually requires it!). This way the large diameter incoming wire can easily be adapted to what you have inside your house.
Dan Lenox