question about nec exam prep 20008

[warrenl]

question #18 under unit 1 practice questions gives a value of 12.90 ohms for the value of K. I'm sure it's obvious but I do not know how how to find that value, or I have forgotten please help.

 

[charlie b]

We have no way of knowing what book you are getting your practice questions from. A lot of companies publish practice exam books. So I cannot be sure what "K" means, in the context of that book. Can you be more specific?

Welcome to the forum.

 

[raider1]

Welcome to the forum.

If this question is in regards to voltage drop calculations then 12.9 is the resistance of 1000 circular mils of copper at 1000 feet.

This is a standard value (K) used for a copper conductor with many voltage drop formulas.

Also "K" for aluminum conductors is 21.2.

Hope this helps.

Chris

 

[chris kennedy]

Chapter 9 Table 8, ohm/kFT for 1000kcmil copper.

 

[raider1]

Chapter 9 Table 8, ohm/kFT for 1000kcmil copper.

Actually, that is ohms per 1000 feet for 1000 cmil copper not 1000kcmils.

Chris

 

[chris kennedy]

Actually, that is ohms per 1000 feet for 1000 cmil copper not 1000kcmils.

Chris

Yeah, well I use really, really big wire.:grin:

Actually 12.9 is ohms per 1000' of 1000cmil ? 1000.:roll:

 

[bob]

K varies with temperature. The 12.9 for CU and 21.2 for AL is at 65C. The value at 25C is 10.6 for CU and 17.4 for AL.

 

[raider1]

Good point Bob.

Chris