I didn't think the O.P. was running modern units.
Please note some suggestions for lighter wire are sometimes being made by folks running mostly modern trains.
Kerrigan I have to ask. You have ten amps availible, or you draw ten amps across one line?
Modern can motor trains use way less amps. than a pre or postwar open frame motor type. A 90w transformer is barely enough for operating some bigger PW at all. I have had three engines that will pull 3-alps3.5a normally, peaking at 5.5a on a loaded start up(peak, not continuous). One 4-6-4 can't pull more than a few cars or it will stall on the 15v90w 1033. Give it 10-20 more watts and it flys well enough to jump.
Do the math for two of these PW trains running on the same rails (block control) and tell me you want to even touch the smaller gauge wire after an hour.... while I get the burn cream and a band aid for your finger. I didn't always use 12g. I didn't like how hot my wiring got with 16-20g
If I'm not mistaken, I think Tom T likely has the most long wire pull experience with wire length/ gauge/watt tables locked into memory, but the mininum size for length at x volts, x amps, info is an actual common standard, you'll find it all over if you seach for wiring tables. (note solid wire also needs a lesser gauge because of air gaps in stranded wire.)
