Here is a simple formula for figuring out the voltage drop in a given current. You take the resistance per 1000 feet of wire and multiply it by the current. This equals the voltage loss.

(Figures from the Circ. 31, U.S. Bureau of Stds.)

Problem:

1,500 ft. of 18 gauge wire with a current draw of .3 Amps

Formula:

Ohms x (Wire Length/1000) x Current = Voltage Drop

Equation:

6.51 x (1500/1000) x .3 Amps

Simplified:

6.51 x 1.5 x .3 = 2.91 Volts

Solution:

2.91 Voltage Drop

As a rule of thumb, if you increase your wire length you must increase your wire gauge. Likewise, the lower your voltage, the larger your wire gauge must be. In any case, you should calculate the voltage loss and make your wire selection based on your findings.

*PLEASE NOTE THIS IS FOR REFERENCE ONLY. TPR MAKES NO CLAIM AS TO WHETHER THIS MEETS YOUR LOCAL ELECTRICAL CODE. THE FINAL DESIGN SHOULD BE COMPLETED BY A LICENSED ELECTRICAL ENGINEER.