How far can you run 350 kcmil wire?

At 20 A on a 120 V single-phase circuit, 350 kcmil copper stays under 3% voltage drop for about 2441 ft one-way. At 240 V the same load reaches roughly 4883 ft, because allowable drop scales with system voltage.

What is the voltage drop of 350 kcmil wire per 100 feet?

About 0.15 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 350 kcmil 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.

350 kcmil Voltage Drop — Max Run Length by Load

Voltage drop for 350 kcmil copper and aluminium: at 20 A on 120 V single phase the 3% limit is reached at about 2441 ft one-way. Full table by load, voltage and distance.

Quick answer

350 kcmil copper reaches 3% voltage drop at about 2441 ft one-way carrying 20 A on a 120 V single-phase circuit. At 100 ft the same load drops 0.15 V (0.12%), calculated as VD = 2 × K × I × L / cmil with K = 12.9 for copper and 350,000 circular mils.

3% limit @ 20 A, 120 V

2441ft

3% limit @ 20 A, 240 V

4883ft

Drop @ 100 ft, 20 A

0.15V

Ω / 1000 ft (Cu)

0.0296

Maximum one-way run length at 3% drop

Copper 350 kcmil. Aluminium distances are roughly 62% of these figures.

Load	120 V 1Ø	240 V 1Ø	208 V 3Ø	480 V 3Ø
5 A	9,767 ft	19,534 ft	19,549 ft	45,115 ft
10 A	4,883 ft	9,767 ft	9,774 ft	22,557 ft
15 A	3,255 ft	6,511 ft	6,516 ft	15,038 ft
20 A	2,441 ft	4,883 ft	4,887 ft	11,278 ft
25 A	1,953 ft	3,906 ft	3,909 ft	9,023 ft
30 A	1,627 ft	3,255 ft	3,258 ft	7,519 ft
40 A	1,220 ft	2,441 ft	2,443 ft	5,639 ft
50 A	976 ft	1,953 ft	1,954 ft	4,511 ft
60 A	813 ft	1,627 ft	1,629 ft	3,759 ft
80 A	610 ft	1,220 ft	1,221 ft	2,819 ft
100 A	488 ft	976 ft	977 ft	2,255 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	0.02%	0.02%	0.03%	0.05%
50 ft	0.03%	0.05%	0.06%	0.09%
75 ft	0.05%	0.07%	0.09%	0.14%
100 ft	0.06%	0.09%	0.12%	0.18%
150 ft	0.09%	0.14%	0.18%	0.28%
200 ft	0.12%	0.18%	0.25%	0.37%
300 ft	0.18%	0.28%	0.37%	0.55%

Percent drop, 120 V single phase, copper.

Published standard

Frequently asked

How far can you run 350 kcmil wire?: At 20 A on a 120 V single-phase circuit, 350 kcmil copper stays under 3% voltage drop for about 2441 ft one-way. At 240 V the same load reaches roughly 4883 ft, because allowable drop scales with system voltage.
What is the voltage drop of 350 kcmil wire per 100 feet?: About 0.15 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 350 kcmil 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.

350 kcmil 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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