Bob,
Your worst case condition is that you will draw less than 2 amps (actually
1.7A) if you use 200 watts of lighting. The formula is watts divided by
voltage = amps. The rated ampacity of 14 AWG wire is 15A. In the National
Electric Code, the ampacity of 14 AWG wire is actually higher than 15A, but
a footnote in the NEC limits the overcurrent protection to 15A.
Your voltage drop over 300 feet will be minimal (about 2%) so the increased
current draw because of the decreased voltage will be insignificant. You
could safety use the lights and also use a trickle charger or any other low
current device and still not have any problems. one advantage is that the
light bulbs will last longer because of the slightly reduced voltage. You
couldn't use a welder or a high current motor. You really should have no
problems with decreased voltage if you limit your usage to 500 watts. Your
loss will only be about 6 volts. The decreased ampacity caused by resistive
heating of the wire will be negligible.
One word of caution is that you need to use underground wiring and any
splices must be made inside an approved waterproof box.
You could look at low voltage lighting in the lamp post along with a
photoelectric switch. Your overall cost might be less.
Good luck,
Jim Seippel
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