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Automotive Electrical Wiring
 
 

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

Wire Gauge
AWG
Current Load in Amps @ 12 Volts DC (2)
1A 2A 4A 6A 8A 10A 12A 15A 20A 50A 100A 200A
20 106 53 26 17 13 nr nr nr nr nr nr nr
18 150 75 37 25 18 15 12 nr nr nr nr nr
16 224 112 56 37 28 22 18 14 nr nr nr nr
14 362 181 90 60 45 36 30 24 18 nr nr nr
12 572 286 143 95 71 57 47 38 28 nr nr nr
10 908 454 227 151 113 90 75 60 45 nr nr nr
8 1452 726 363 241 181 145 120 96 72 29 nr nr
6 2342 1171 585 390 292 234 194 155 117 46 23 nr
4 3702 1851 925 616 462 370 307 246 185 74 37 nr
2 6060 3030 1515 1009 757 606 503 403 303 121 60 30
1 7692 3846 1923 1280 961 769 638 511 384 153 76 38
0 9708 4854 2427 1616 1213 970 805 645 485 194 97 48
000 - - - - - - 1296 1039 781 312 156 78

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.