How far can you run 12 AWG wire?

At 20 A on a 120 V single-phase circuit, 12 AWG copper stays under 3% voltage drop for about 45 ft one-way. At 240 V the same load reaches roughly 91 ft, because allowable drop scales with system voltage.

What is the voltage drop of 12 AWG wire per 100 feet?

About 7.9 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 12 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.

12 AWG Voltage Drop — Max Run Length by Load

Voltage drop for 12 AWG copper and aluminium: at 20 A on 120 V single phase the 3% limit is reached at about 45 ft one-way. Full table by load, voltage and distance.

Quick answer

12 AWG copper reaches 3% voltage drop at about 45 ft one-way carrying 20 A on a 120 V single-phase circuit. At 100 ft the same load drops 7.9 V (6.58%), calculated as VD = 2 × K × I × L / cmil with K = 12.9 for copper and 6,530 circular mils.

3% limit @ 20 A, 120 V

45ft

3% limit @ 20 A, 240 V

91ft

Drop @ 100 ft, 20 A

7.9V

Ω / 1000 ft (Cu)

1.5882

Maximum one-way run length at 3% drop

Copper 12 AWG. Aluminium distances are roughly 62% of these figures.

Load	120 V 1Ø	240 V 1Ø	208 V 3Ø	480 V 3Ø
5 A	182 ft	364 ft	364 ft	841 ft
10 A	91 ft	182 ft	182 ft	420 ft
15 A	60 ft	121 ft	121 ft	280 ft
20 A	45 ft	91 ft	91 ft	210 ft
25 A	36 ft	72 ft	72 ft	168 ft
30 A	30 ft	60 ft	60 ft	140 ft
40 A	22 ft	45 ft	45 ft	105 ft
50 A	18 ft	36 ft	36 ft	84 ft
60 A	15 ft	30 ft	30 ft	70 ft
80 A	11 ft	22 ft	22 ft	52 ft
100 A	9 ft	18 ft	18 ft	42 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	0.82%	1.23%	1.65%	2.47%
50 ft	1.65%	2.47%	3.29%	4.94%
75 ft	2.47%	3.7%	4.94%	7.41%
100 ft	3.29%	4.94%	6.58%	9.88%
150 ft	4.94%	7.41%	9.88%	14.82%
200 ft	6.58%	9.88%	13.17%	19.75%
300 ft	9.88%	14.82%	19.75%	29.63%

Percent drop, 120 V single phase, copper.

Published standard

Frequently asked

How far can you run 12 AWG wire?: At 20 A on a 120 V single-phase circuit, 12 AWG copper stays under 3% voltage drop for about 45 ft one-way. At 240 V the same load reaches roughly 91 ft, because allowable drop scales with system voltage.
What is the voltage drop of 12 AWG wire per 100 feet?: About 7.9 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 12 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.

12 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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