modeltrainsparts posted:12 gauge is bloody overkill! That's what is used in 110 volt 15 amp house circuits - trains are running on 18 - 20 volts drawing maybe 8 amps max. Even 14 gauge is overkill. My around the wall layout in a 17 x 28 room is wired with nothing larger than 16 gauge wire and I've never had a current drop (even while running 3 trains of which 2 were 6 - 9 car passenger trains).
Not really. There's a big difference between 120V and 18V power distribution, specifically the amount of loss you can tolerate. Let's take your #16 wire as an example. The 1.67% voltage drop at 120 volts is pretty insignificant in the greater scheme of things. However, the 11.15% voltage drop at 18 volts is significant for a train layout. Note that this computation doesn't take into account ANY additional resistance of connections, track drops, conductivity between the rails and wheels/pickups, etc. I went with 25 feet, but odds are that there are runs larger than that in a 17 x 28 room, so the voltage drop would be even more significant.