Maximum Wire Length (feet) for Car Wiring (1)

For example: You wish to run a wire to the rear of the car, approximately 20 feet, to power a 100 Watt light. The 100 Watt light will draw about (100 Watts divided by 12 Volts equals) 8 or 9 Amps. Pick 10 Amps to be safe and go down to 22 (feet... the first number greater than 20). You'll need a wire of size at least 16 gauge. I would probably use 14 gauge.

(1) Maximum recommended wire lengths are based on a 1/2 volt maximum voltage drop over the length of the wire. If you want to determine lengths based on different drop, simply multiply the table value by the appropriate factor (for example, if you want the values for a 1 volt drop, multiply the table value by 2).
(2) If you want the lengths for 6 volt or 24 volt systems, multiply the listed amperage by 0.5 for 6 volt or 2 for 24 volt and then select the wire length from the table.
"nr" means wire size is not recommended at selected current. To be safe, always pick one wire size larger (smaller numerical AWG number) than you need for the specified wire length at the required current level.