Wire gauge vs. current

[Richard Wallace]

I'd make the decision based on resistance. 10 AWG wire is 0.001 Ohms per foot. 12 AWG is 0.0016 Ohms per foot. 14 AWG is 0.0025 Ohms per foot.

If you limit your motor currents to 25% of stall (3 x 27 / 0.25 ~= 20A) then a 10 AWG circuit will drop 0.02 Volts per foot, and dissipate 0.4 Watts per foot. By similar math the same circuit wired with 12 AWG would drop 0.032 Volts per foot and dissipate 0.64 Watts per foot; using 14 AWG you'd get 0.05 Volts per foot drop and 1 Watt per foot dissipation.

You need to assess how much voltage drop and dissipation is acceptable, and also how much overload (beyond 20 Amperes) is expected.

[edit]Sorry I mis-read the stall current information. Divide all my voltage drops by three, and dissipations by nine. Jim's recommendations below are good. I agree it would be nice to hear from Al, too.[/edit]