How far can you run 3 AWG wire?

At 20 A on a 120 V single-phase circuit, 3 AWG copper stays under 3% voltage drop for about 367 ft one-way. At 240 V the same load reaches roughly 734 ft, because allowable drop scales with system voltage.

What is the voltage drop of 3 AWG wire per 100 feet?

About 0.98 V at 20 A on 120 V single phase, using VD = 2 × K × I × L / cmil with K = 12.9 for copper.

Is 3% voltage drop a code requirement?

It is a recommendation, not a mandatory limit, in most adopted codes: roughly 3% on the branch circuit and 5% total including the feeder. Some local amendments and specifications do make it enforceable, so check what applies to your job.

Does aluminium change the 3 AWG numbers?

Yes. Aluminium uses K = 21.2 instead of 12.9, so drop is about 64% higher for the same size and run, and allowable distance falls by roughly the same proportion.

3 AWG Voltage Drop — Max Run Length by Load

Voltage drop for 3 AWG copper and aluminium: at 20 A on 120 V single phase the 3% limit is reached at about 367 ft one-way. Full table by load, voltage and distance.

Quick answer

3 AWG copper reaches 3% voltage drop at about 367 ft one-way carrying 20 A on a 120 V single-phase circuit. At 100 ft the same load drops 0.98 V (0.82%), calculated as VD = 2 × K × I × L / cmil with K = 12.9 for copper and 52,635 circular mils.

3% limit @ 20 A, 120 V

367ft

3% limit @ 20 A, 240 V

734ft

Drop @ 100 ft, 20 A

0.98V

Ω / 1000 ft (Cu)

0.1970

Maximum one-way run length at 3% drop

Copper 3 AWG. Aluminium distances are roughly 62% of these figures.

Load	120 V 1Ø	240 V 1Ø	208 V 3Ø	480 V 3Ø
5 A	1,468 ft	2,937 ft	2,940 ft	6,784 ft
10 A	734 ft	1,468 ft	1,470 ft	3,392 ft
15 A	489 ft	979 ft	980 ft	2,261 ft
20 A	367 ft	734 ft	735 ft	1,696 ft
25 A	293 ft	587 ft	588 ft	1,356 ft
30 A	244 ft	489 ft	490 ft	1,130 ft
40 A	183 ft	367 ft	367 ft	848 ft
50 A	146 ft	293 ft	294 ft	678 ft
60 A	122 ft	244 ft	245 ft	565 ft
80 A	91 ft	183 ft	183 ft	424 ft
100 A	73 ft	146 ft	147 ft	339 ft

Source & method: Derived from VD = 2 × K × I × L / cmil (1.732 × K × I × L / cmil for three phase), solved for L at 3% of nominal voltage. Run your exact circuit.

Voltage drop by distance at common loads

Distance	10 A	15 A	20 A	30 A
25 ft	0.1%	0.15%	0.2%	0.31%
50 ft	0.2%	0.31%	0.41%	0.61%
75 ft	0.31%	0.46%	0.61%	0.92%
100 ft	0.41%	0.61%	0.82%	1.23%
150 ft	0.61%	0.92%	1.23%	1.84%
200 ft	0.82%	1.23%	1.63%	2.45%
300 ft	1.23%	1.84%	2.45%	3.68%

Percent drop, 120 V single phase, copper.

Published standard

Frequently asked

How far can you run 3 AWG wire?: At 20 A on a 120 V single-phase circuit, 3 AWG copper stays under 3% voltage drop for about 367 ft one-way. At 240 V the same load reaches roughly 734 ft, because allowable drop scales with system voltage.
What is the voltage drop of 3 AWG wire per 100 feet?: About 0.98 V at 20 A on 120 V single phase, using VD = 2 × K × I × L / cmil with K = 12.9 for copper.
Is 3% voltage drop a code requirement?: It is a recommendation, not a mandatory limit, in most adopted codes: roughly 3% on the branch circuit and 5% total including the feeder. Some local amendments and specifications do make it enforceable, so check what applies to your job.
Does aluminium change the 3 AWG numbers?: Yes. Aluminium uses K = 21.2 instead of 12.9, so drop is about 64% higher for the same size and run, and allowable distance falls by roughly the same proportion.

3 AWG Voltage Drop — Max Run Length by Load

Maximum one-way run length at 3% drop

Voltage drop by distance at common loads

Frequently asked

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