Which voltage drop formula to use?

[chriskthx]

I'm curious which voltage drop formula you all use for standard roadway lighting or other circuits. I have come across three and all offer slightly different results (based on the complexity of the formula). My local resources show to use #1 as the default formula, however I have seen #2 and #3 used elsewhere.

1) The simple VD = 2 x K x I x D/CM

2) The IEEE Formula http://www.dolphins-software.com/voltageDrop.htm

3) The NEC Formula found in table 9.

 

[G._S._Ohm]

I'm curious which voltage drop formula you all use for standard roadway lighting or other circuits. I have come across three and all offer slightly different results (based on the complexity of the formula). My local resources show to use #1 as the default formula, however I have seen #2 and #3 used elsewhere.

1) The simple VD = 2 x K x I x D/CM

2) The IEEE Formula http://www.dolphins-software.com/voltageDrop.htm

3) The NEC Formula found in table 9.

Run results for all three formulas for conductors you normally use. If they all agree within some percent, probably 5%, use the simplest formula.

BTW, I've heard that skin effect @ 60 Hz is negligible for conductors smaller than #2 and dielectric heating is negligible for less than 2 kV.