Electrical Math
from Ryan Cole
Wire gauge Ohms per 1000ft
20 10
22 16
24 25
28 65
The TIA-568 spec which defines Cat5 (cat 3 as well) specifies that either one shall be no more than 9.38 ohms per 100 meters. Our testing of name brand Cat 5 says more like seven ohms per 100 meters, so 3 ohms per hundred feet is safe and conservative. — Scott Carter
Ohms Law
E = IR (Volts = Amps x Resistance)
We'll say 22 Gauge wire at 250 Ft under a 1 Amp load
22 Gauge @ 250 Ft = 4 Ohms
E = 1 x 4 or E = 4 Volts
So basically you should expect 4 Volts consumed leaving you 8 volts at the AP end.
Let's do another situation:
28 Gauge over 50 ft at 2 amps
28 Guage @ 50 ft = 3 Ohms
E = 2 x 3 or E = 6 Volts
So in this case you dissipate half your volts. Could be bad, or if I calculate correctly, possibly worse.
6 Volts x 2 Amps = 12 Watts dissipated over the wire
12 Watts / 50 Ft = .24 Watts per foot
I would not expect that to start a fire outright, but you could use it to keep your pipes from freezing in the winter.
Using 2 pairs as you did in the example will halve the voltage drop--good idea.