Average K for Copper

[toastermaker]

Boss told me to use 10.8 as average K for Copper. I am not questioning him, I would however like to find info on the subject.

I thought I saw a reference to average K in the 1999 NEC Handbook that I am studying but now can't relocate that info in the book.
The other book I am studying says to use 12.9 as the average K for copper.

This doesnt make sense to me but I'll ask anyway, is a different K used depending on what is being solved?

Google has not produced for me yet. I may need to choose different search phrases. In the mean time if anyone would help I would much appreciate it.

Thank You,

[Roger]

Average K for copper is 12.9, I have no idea what a K of 10.8 would be good for other than to cause you to miss your test problems. You also need to know how to calcultate exact K of a copper wire for testing purposes.
K has many uses and is usfeul in several formulas to calculate voltage drop, load, distances, circular mil etc...

[toastermaker]

Thanks Roger,

I seriously was expecting my book to have been wrong. I have always considered my boss to be kind of a God of all things Electrical.
But then I don't have any experiance to base that on, I am just learning.

Thanks again,

[Wgoodrich]

Roger is correct. 12.9 for copper and 21.2 for aluminum is approximate K.

You use approximate k for example when you do a voltage drop calc and you don't yet know the wire size.

If you know the wire size then you use exact K. Exact k is calculated by using Table 8 in chapter 9 of hte nec. Formula is to find the resistance of 1000 ft of the wire size you are using paying attention whether solid or copper. Then multiply that by the circuilar mil of that certain wire then divide that answer by 1000 to find k per foot.

If you want to confirm for yourself go to table 8 of chapter 9 and calculate exact k of each wire size listed in that table then add all those answers of exact k together then divide that answer by the number of wire sizes. You should get the answer of 12.9 or close depending on the setting on your calculator. If you set your calculator on free mode and use all the numbers you will get exactly that answer. That would be approximate k.

Good Luck

Wg

[Ohm1]

How old is your Manager? I've noticed that some much older electricians do not like change, so they stick with the old rules. Watch your step on trying to change their old habits, because you want win.