How far can you run 8 AWG wire?

At 20 A on a 120 V single-phase circuit, 8 AWG copper stays under 3% voltage drop for about 115 ft one-way. At 240 V the same load reaches roughly 230 ft, because allowable drop scales with system voltage.

What is the voltage drop of 8 AWG wire per 100 feet?

About 3.13 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 8 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.

8 AWG Voltage Drop — Max Run Length by Load

Voltage drop for 8 AWG copper and aluminium: at 20 A on 120 V single phase the 3% limit is reached at about 115 ft one-way. Full table by load, voltage and distance.

Quick answer

8 AWG copper reaches 3% voltage drop at about 115 ft one-way carrying 20 A on a 120 V single-phase circuit. At 100 ft the same load drops 3.13 V (2.6%), calculated as VD = 2 × K × I × L / cmil with K = 12.9 for copper and 16,510 circular mils.

3% limit @ 20 A, 120 V

115ft

3% limit @ 20 A, 240 V

230ft

Drop @ 100 ft, 20 A

3.13V

Ω / 1000 ft (Cu)

0.6282

Maximum one-way run length at 3% drop

Copper 8 AWG. Aluminium distances are roughly 62% of these figures.

Load	120 V 1Ø	240 V 1Ø	208 V 3Ø	480 V 3Ø
5 A	460 ft	921 ft	922 ft	2,128 ft
10 A	230 ft	460 ft	461 ft	1,064 ft
15 A	153 ft	307 ft	307 ft	709 ft
20 A	115 ft	230 ft	230 ft	532 ft
25 A	92 ft	184 ft	184 ft	425 ft
30 A	76 ft	153 ft	153 ft	354 ft
40 A	57 ft	115 ft	115 ft	266 ft
50 A	46 ft	92 ft	92 ft	212 ft
60 A	38 ft	76 ft	76 ft	177 ft
80 A	28 ft	57 ft	57 ft	133 ft
100 A	23 ft	46 ft	46 ft	106 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	0.33%	0.49%	0.65%	0.98%
50 ft	0.65%	0.98%	1.3%	1.95%
75 ft	0.98%	1.47%	1.95%	2.93%
100 ft	1.3%	1.95%	2.6%	3.91%
150 ft	1.95%	2.93%	3.91%	5.86%
200 ft	2.6%	3.91%	5.21%	7.81%
300 ft	3.91%	5.86%	7.81%	11.72%

Percent drop, 120 V single phase, copper.

Published standard

Frequently asked

How far can you run 8 AWG wire?: At 20 A on a 120 V single-phase circuit, 8 AWG copper stays under 3% voltage drop for about 115 ft one-way. At 240 V the same load reaches roughly 230 ft, because allowable drop scales with system voltage.
What is the voltage drop of 8 AWG wire per 100 feet?: About 3.13 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 8 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.

8 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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