How do I calculate Wire Loss in Electrical Wires

Wire Loss Tables for Solar Electric Systems
Includes 12, 24, and 120 volt charts.

This is a five percent table which means at these amperage ratings at the listed distances, 5% of the power would be lost to resistance. Five percent is normally acceptable in low voltage systems, but if you want a 2% figure, divide the given distances by 2.5. For a 10% loss multiply the distance by 2. For distances at 48 volts, double the 24 volt distances for a 5 percent loss figure. For 240 volt 5% loss, double the 120 volt distances. These distances include the NEC requirement for current over sizing of 25%.

Example: For a pump drawing 9 amperes at 24 volts, located 88 feet from the battery bank: look at the center table for 24 volts. In the far left column find the next number higher than 9 (which is 10) and follow that line across the table until you find a distance figure greater than 88. At the top of the column find the gauge of wire (#8) that should be used. This method insures that wire losses are kept to an acceptable level without spending too much money on extra-heavy cable. Using a heavier wire than indicated, however, will result in even higher efficiencies and we do sometimes invest in the next larger gauge. Wire can get expensive, and it may not be worth the money to get that last 1% if you have to go to a much larger wire size.

ALL DISTANCES ARE IN FEET

Do not use any wire sizes that might fall into the red zone - this would exceed the amperage rating of the wire and it may overheat and burn.

120 Volt AC or DC chart

24 Volt DC chart

12 Volt DC chart

These are one-way distances, measured from point A to point B. The out and back nature of electrical circuits has already been included. For PV arrays, figure the entire run, from the panels to the charge controller to the batteries

Cross reference of AWG (American Wire Gauge) sizes to metric (mm)