correct k factor for voltage drop

[nakulak]

I was taught to go to NEC tables, table 8, 1000kcmil and use the number for CU or AL from there (for 2005 that's 12.9 and 21.2) I often see people using the numbers from the older books (10.4), but then I see guys using other numbers and I have no idea where they are getting them from. Soooo...

what's the correct numbers to use (in a perfect world)?

 

[bob]

I was taught to go to NEC tables, table 8, 1000kcmil and use the number for CU or AL from there (for 2005 that's 12.9 and 21.2) I often see people using the numbers from the older books (10.4), but then I see guys using other numbers and I have no idea where they are getting them from. Soooo...

what's the correct numbers to use (in a perfect world)?

K varies with the temperature. At 20 C K = 10.5 , 10.6 at 25C and 12.9 at 75C.

R = K/A x 1000 where A = cross=sectional area in cmil.