Wire composition is also a factor. I don't know if you remember or not but, several years ago, some home builders decided to save money on electrical work in their new projects and used aluminum wires instead of copper. They didn't take into account that aluminum wasn't nearly as good of conductor as copper and, before all was said and done, several of the houses had burned down due to electrical failures. The sad part is that, even though the wires failed, the circuit breakers never tripped. The builders used the appropriate sized breakers for copper wires instead of using smaller breakers or larger wires. That is the very reason that the main power lines from the generators to the electronics bays on commercial jetliners use a spliced set up. A couple of feet on each end is copper. The ends are then spliced to aluminum wire of one or two sizes larger for the rest of the run to save weight but still be able to handle the electrical load.
You mentioned a couple of things that let you get away with 12 guage at 3000 watts:
1) You have cooling air flowing around the wires during the whole flight.
2) You're running 800 watts for most of the flight
3) You're using short wires
Cooling air definitely helps but its the other two that make the difference. 800 watts is less than half of the 1700 theoretical peak I mentioned above. The short wires make a big difference as well. Short wires mean less resistance, less resistance means less heat. If you were running a couple of feet of wire, you probably wouldn't get away with it but, as I said, I'm not a DC expert
Last edited by Hydro Junkie; 08-01-2020 at 07:38 AM.