What is voltage drop per foot?

Voltage drop is caused by resistance. From the equation V=IR the voltage across that resistance can be calculated. For a uniform conductor the resistance is linear with the length R=kx where k is in ohms per foot. For a given current, the voltage drop V=Ikx so the voltage drop per foot is Ik. Voltage drop per foot can be measured, allowing a calculation of voltage drop for very long lengths of conductor such as power transmission lines. This is a reasonable approximation as long as the total voltage drop in transmission is small relative to the supply voltage. If the voltage drop is large, the current will be limited by the total resistance. This implies that long distance transmission lines should be high voltage, because 1 megawatt at 10,000 volts requires 100 amps, while at 100,000 volts it only requires 10 amps. The voltage drop per foot for the same conductor would be 10 times as large at 10 times the current, and the power loss (I*IR) would be 100 times as large.

For alternating current, inductance can be a factor; this implies that relatively low frequency would be preferred.