[SteveSchemenauer]

I need to run Electric to Driveways lights that are nearly 450' from the switch.
I am concerned about Voltage Drop, and it's effect.

The lights in question will be CFL (Compact Fluorescent Lamps), the small 26 watt variety you see in hardware stores.

The 5 lamp-posts, (spaced along the driveway) have 4 lights each, thus the total expectage wattage is only 520 watts or about 4.3 amps (not much)

What is the smallest wire size I can use... and still get acceptable voltage for the lighting?
My starting voltage is 121V

With such a long run, I would prefer to us the lightest gage wire possible (direct burial)

I have heard answers from #4 copper to #12 wire.
How much voltage drop is on a 450' run of #12 wire... and would this adversely effect the use of CF Lamps?

[tkrussell]

If #12 is used, the total voltage drop would be 8.91 volts dropped, which is about 7.5%. The recommended maximum is 3%, or 3.6 volts.

Assuming 5 amp load at the end of the 450 foot run, as a hypothetical worst case scenario, at nominal 120 volts, and not exceed 3% voltage drop, I would recommend #8 copper.

The minimum size aluminum wire required to achieve the same result would be #1, which is not practical.

CF lamps can be sensitive to too much voltage drop.


I realize the load is not all at the end of the circuit, and more accurate result would be to calculate the Vd to each light, and subtract the remaining lights, but I would need to know the length of circuit to the first light, and then the distance between each light. This may help reduce the wire size to the first light, and then reduce wire size between each light because of the reduced load.