VD for length

[Tulsa Electrician]

Here is what it would look like during a test with scratch paper per NEC table 8 for exact K.

I used #10, 7 strand uncoated copper from the example above.
See why 1.24*1.05 is easier for R2

Then find K for 90c
1.24*1.05= 1.302
1.302*10380=13514.76
13514.76/1000= 13.51476 for exact K

 

[FranklinMade]

Here is what it would look like during a test with scratch paper per NEC table 8 for exact K.

I used #10, 7 strand uncoated copper from the example above.
See why 1.24*1.05 is easier for R2

Then find K for 90c
1.24*1.05= 1.302
1.302*10380=13514.76
13514.76/1000= 13.51476 for exact K

Thank you. I really appreciated your time!

 

[Tulsa Electrician]

Your welcome.

 

[Carultch]

Resistance/ ohms per…..

The K-factor is the resistivity of the metal. It has the units Ohm-kcmil/kft. In SI units, it would Ohm-meters, but to reflect the units we use in practice, it is translated to ohm-kcmil/kft, or ohm-kcmil/km.

The dash in the units means units are multiplied, instead of divided (i.e. per). This means, to cancel out the kcmil, you divide by cross-sectional area in kcmil.

This constant doesn't account for AC-specific factors, like the skin effect or inductance, so it is only strictly valid for DC. For wires smaller than 1/0, these factors are negligible.

 

[Geber]

The K-factor is the resistivity of the metal. It has the units Ohm-kcmil/kft. In SI units, it would Ohm-meters, but to reflect the units we use in practice, it is translated to ohm-kcmil/kft, or ohm-kcmil/km.

Since I come from the electronics field, rather than the electrical trade, I was mystified by K. Thanks to Carultch for explaining. In physics books the symbol used is ρ which is Greek small letter rho. Obviously that isn't very convenient when using a keyboard. Nit-picking: Ohm is the scientist and ohm is the unit for resistance.