^^ Fail.
you derate your wire for branch circuit conductors @ 300' in normal ambient temps. (and that is actually shorter than the code requires)
temps have alot to do with voltage drop... more than you would think.
#12 will get you 20amps all day @ any distance within less than 350'
a thing to consider is that 20 amps of continuous duty will not run on #12....
continuous duty is any electrical load that is energized for a period greater than 6 hours.
since we flower @ 12/12, this is something to be seriously considered.
to find your
demand factor for a continuous duty cycle:
multiply your max power factor (the sum of ALL connected equipments' max wattage/amperage to the circuit) bt 120% to find your demand factor (amount of power that can be used)
example:
johnny wants to run 2 1000w hps in his flower cab in the garage.
he has 120v available.
he uses one oscillating fan, one timer.
2 x 1000w lamps
2 x 60w ballast draw (the ballasts concume a small amount of power, its expressed as heat)
1 x 45w fan
1 x 15w timer
____________
2180 watts @ 120v
(P= I x E, where P = watts, I = amperage, E= voltage)
2180 watts @ 120v = 18.16666 amps (this number, the sum of all your connected devices is also known as
max power factor)
18.16666 amps x 120% = 21.79999 amps
so for johnny to run his 2 1000w hps, he requires 21.79999 amps, which is greater than 20. his wire size should be #10 awg.............
you following me?
do you see how that by running equipment for longer than 6 hours at a time changes your electrical requirements?
pay attention, because this is one of the more common causes of grow related fires...
people add up all there wattage/amperage and then pick the closest size wire someone on an internet forumn tells them they need.
YOU need to learn the math for yourself... that way the only person to blame is you!