Guys,
The 2008 NEC book say's on branch circuit's 600v or less you are allowed 3 percent voltage drop. That's 3.6 v on 120v system.
Formula for VD = 2K x L x I / cm
K= Resistance in ohms of one circular mil foot of conductor(12.9)
L= Length
I= Amps
cm=circular mils
If we plug in the info. 2x12.9=25.8 L=600 I=2.9 which comes up to 44892 If you divide that buy the circular mil of #10(10380)comes up to 4.32 . Slightly over the 3.6 allowed by code. if we plug in #8(cm 16510) we get 2.7 All that being said I personally I personally would run the #10 (close enough) But keep in mind if that pump ends up being inadequate you dont leave any room for upgrade. In that case use #8. Another option with the price of copper what it is would be to use aluminum.Which fi sized correctly and installed correctly would be fine. Bluegillerkiller is correct 120 or 240 makes no differance in the formula.
