Greg,
I dug out an old LV lighting book. There was a formula for landscape lighting that I used to use. it was:
Total Watts X Cable Length
--------------------------
Cable Constant
The above formula equals the voltage drop
Lets see if this comes out. The cable constant was depending on size of cable.
The different wires sizes. All copper UL listed for landscape lighting. i.e. #18 = 1380, #16= 220, #14=3500, #12=7500, and #10=11920
So a circuit 80 foot long with 6 lights of 25 watt each: 6 X 25 = 150 total watts X 80' run = 27000
So 27000 using #18 ga wire at 1380 = 19.56 voltage drop OR
27000 using #10 ga wire at 11920 = 2.265 voltage drop
All of these calcs. would be at 12 volt. You can also up the voltage a wee bit if needed.
Last edited by harold endean; 02/24/13 01:36 PM. Reason: Couldn't get the formula to look right
