I concur with the others. 14 gauge is more than sufficient. I used 14 gauge for a bus on my last couple layouts and I am going down to 16 for the next one.
I used 14 gauge wire on my 22' x 42' layout and it works just fine.
Alton Junction
I will assume you mean in HO scale, and that all you will want the bus to carry is maybe 8 amps maximum. In that case, 14 gauge is ample. Your feeders can be as light as 22 gauge provided they are kept short, say 20-24" and under. Try for a pair of feeders every 6' of rails.
-Crandell
Leads are in now I'm starting the main buss layout 12 x 16, what size will carry. I have enough 14ga on hand is that too small.
NickyB