Hi all.
I recently had a question of what size buss bar for a 1200 amp load 1000 feet away.
Besides buss bar manufacturers sizing charts ,any one have any rule of thumb to size? I found no info in nec. I`ll spend some time in AE Handbook and see what I can come up with.

If you are looking for a quick rule like after a 100 ft you increase the wire size, that just doesn't work with buss bars. You have to depend on voltage drop formulas that will tell you the voltage drop. You can't just up size buss bars.

Somebody correct my if I am wrong...
Votage drop is pretty easy to calculate (the resistance meathod is more accurate.. but this is close) 2 x the length x amperage (load, not nominal amps) x constant (=12 for copper & 18 for aluminum) / (diveded by) cm of the wire (larger wire cm is the wire size). Size the wire for voltage drop; the bus bar 'length' is so short, you shoul be able to just use the standard rating for that amperage.