voltage drop calc - help

[EIT231]

hey there and thanks in advance -

I found this article

http://ecmweb.com/mag/electric_basics_calculating_voltage/

and this problem: (480v branch ckt - uncoated copper)
Determine wire size Run a stranded copper wire 200 ft at 20A.
you can use the following method. To complete the numerator, multiply as follows: 1.73 x 212.9 ohms x 200 ft x 20A = 89371.2 Dividing the 89371.2 by the acceptable voltage drop of 14.4V gives you 6207 circular mils.

Where is the 212.9 Ohms from?

thanks

 

[deltawhy]

guessing from the info you provided the 212.9 ohms is the impedance of the line in ohms/ft.

 

[magoo2]

Sounds like an awful high impedance for 1 ft of wire!

 

[EIT231]

thanks -
it is a typo -

2 x .866 x 12.9 (k for cu) x 200ft x 20A = 89371

89371/14.4 (VD branch ckt - .03 x 480) = 6206cm

thanks folks