What is the resistance for 1000 feet of # 8 wire at 75 degrees Fahrenheit ? And what section of the NEC?

2 Comments

1. tinkertailorcandlestickmaker says:

   July 5, 2009 at 5:26 am

   Well, while the previous answer looks good, you did ask about the NEC, while my copy is pretty old, I imaging things do stay in the same sections between editions. The "conductor properties" table is in Chapter 9, "table and examples", you might have tried looking in section 310, where the ampacity tables are, but resistance is in chapter 9.

   Are you sure you want the resistance at 75° F? Since the NEC tables are at 75°C and you did mention the NEC, I’m wondering if maybe you really want deg.C? If you do want deg.F the previous answer did explain how to make the a correction for temperature.
   DC resistance @75°C bare copper wire, #8 solid. 0.786Ω / 1000/ft; #8, 7strand, 0.778Ω
   I’m a little surprised there is a difference in DC resistance between solid and stranded, I though they had equal effective area, since the outside dia. of stranded is larger, but that is what is in the book
2. pmi says:

   July 5, 2009 at 5:26 am

   What wire, copper or aluminium
   For copper wire:
   #8 (AWG) has a resistivity of 0.67Ω/1000 at 68 °F
   So for 1000ft the resistance will be 0.67Ω
   For resistance calculation at 75°F we’ll use the formula
   R = R(T0) (1+α ΔT) with temperatures in degrees celcuis
   The coefficient of resistance α of copper is 0.0039

   Thus calculations obtain, R = 0.68Ω.

   Remember, the temperatures are in Degrees Celcius