How do you calculate what gauge wire you need to use over very long distance runs like 500 ft on 3 conductor solid copper wire at 1.5 amps and 120V formula or way to calculate for various lengths amps?

Answer 1

There are formulae, but it is much easier to simply use a "voltage drop calculator" (many interactive ones can be found online), plug in your values and increase your conductor size until the calculated voltage drop over the required distance, at 1.25 times the required load (80 percent design factor), does not exceed 5 percent (the allowed voltage drop in USA and Canadian electrical codes, other countries vary).

For instance, your example could use 14 AWG, giving you a 4.8 percent drop, or 12 AWG for a 3 percent drop (assuming copper). If you were to use aluminum, you would need the larger conductor.

Answer 2

To calculate the gauge of wire needed for a specific distance and amperage, you can use the voltage drop formula. For a 500 ft run at 1.5 amps and 120V, you would need a minimum of 16 gauge wire to keep the voltage drop below 3% which is typically acceptable for most applications. However, for longer distances or higher amperage, you may need to use a thicker wire gauge to minimize voltage drop.