How far can you run 4 AWG wire?

At 20 A on a 120 V single-phase circuit, 4 AWG copper stays under 3% voltage drop for about 291 ft one-way. At 240 V the same load reaches roughly 582 ft, because allowable drop scales with system voltage.

What is the voltage drop of 4 AWG wire per 100 feet?

About 1.24 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 4 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.

4 AWG Voltage Drop — Max Run Length by Load

Voltage drop for 4 AWG copper and aluminium: at 20 A on 120 V single phase the 3% limit is reached at about 291 ft one-way. Full table by load, voltage and distance.

Quick answer

4 AWG copper reaches 3% voltage drop at about 291 ft one-way carrying 20 A on a 120 V single-phase circuit. At 100 ft the same load drops 1.24 V (1.03%), calculated as VD = 2 × K × I × L / cmil with K = 12.9 for copper and 41,741 circular mils.

3% limit @ 20 A, 120 V

291ft

3% limit @ 20 A, 240 V

582ft

Drop @ 100 ft, 20 A

1.24V

Ω / 1000 ft (Cu)

0.2485

Maximum one-way run length at 3% drop

Copper 4 AWG. Aluminium distances are roughly 62% of these figures.

Load	120 V 1Ø	240 V 1Ø	208 V 3Ø	480 V 3Ø
5 A	1,164 ft	2,329 ft	2,331 ft	5,380 ft
10 A	582 ft	1,164 ft	1,165 ft	2,690 ft
15 A	388 ft	776 ft	777 ft	1,793 ft
20 A	291 ft	582 ft	582 ft	1,345 ft
25 A	232 ft	465 ft	466 ft	1,076 ft
30 A	194 ft	388 ft	388 ft	896 ft
40 A	145 ft	291 ft	291 ft	672 ft
50 A	116 ft	232 ft	233 ft	538 ft
60 A	97 ft	194 ft	194 ft	448 ft
80 A	72 ft	145 ft	145 ft	336 ft
100 A	58 ft	116 ft	116 ft	269 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	0.13%	0.19%	0.26%	0.39%
50 ft	0.26%	0.39%	0.52%	0.77%
75 ft	0.39%	0.58%	0.77%	1.16%
100 ft	0.52%	0.77%	1.03%	1.55%
150 ft	0.77%	1.16%	1.55%	2.32%
200 ft	1.03%	1.55%	2.06%	3.09%
300 ft	1.55%	2.32%	3.09%	4.64%

Percent drop, 120 V single phase, copper.

Published standard

Frequently asked

How far can you run 4 AWG wire?: At 20 A on a 120 V single-phase circuit, 4 AWG copper stays under 3% voltage drop for about 291 ft one-way. At 240 V the same load reaches roughly 582 ft, because allowable drop scales with system voltage.
What is the voltage drop of 4 AWG wire per 100 feet?: About 1.24 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 4 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.

4 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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