Dropping Volts

Dear Swami,
How do you find the cross sectional area of a cable? In the book, "Electricity for Entertainment Electricians & Technicians," there is a formula in Appendix 4 to calculate voltage drop. It says, VD = (2KIL)/(#ACM), where K = the specific resistance of copper [12.9 at 75 degrees C (116 degrees F) or 11 at 32 degrees C (90 degrees F); I = current in amps; L = the length of the cable in feet; # = the number of conductors per phase; and ACM = the area of the cross section of the cable in circular mils. Where can I find the area of the cross section of the cable?

Dropping Volts in Downtown Detroit

Dear Dropping,
Congratulations for having gotten that far in the book! If you are wondering about how to calculate voltage drop then you probably already know how important it is to keep your volts up and your amps down. As Bob Dylan once said, "The answer my friend, is blowing in the wind," if by "wind" he meant in the wire gauge charts. There are lots of places to find this information, including Wikipedia. You can also use Ohm's law to calculate voltage drop (V = I x R) if you know the current and the resistance of the wire. Remember to double the length because the current has to flow to the load and back again.

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