750 kcmil Voltage Drop — Max Run Length by Load
Voltage drop for 750 kcmil copper and aluminium: at 20 A on 120 V single phase the 3% limit is reached at about 5232 ft one-way. Full table by load, voltage and distance.
Quick answer
750 kcmil copper reaches 3% voltage drop at about 5232 ft one-way carrying 20 A on a 120 V single-phase circuit. At 100 ft the same load drops 0.07 V (0.06%), calculated as VD = 2 × K × I × L / cmil with K = 12.9 for copper and 750,000 circular mils.
3% limit @ 20 A, 120 V
5232ft
3% limit @ 20 A, 240 V
10465ft
Drop @ 100 ft, 20 A
0.07V
Ω / 1000 ft (Cu)
0.0138
Maximum one-way run length at 3% drop
Copper 750 kcmil. Aluminium distances are roughly 62% of these figures.
| Load | 120 V 1Ø | 240 V 1Ø | 208 V 3Ø | 480 V 3Ø |
|---|---|---|---|---|
| 5 A | 20,930 ft | 41,860 ft | 41,892 ft | 96,675 ft |
| 10 A | 10,465 ft | 20,930 ft | 20,946 ft | 48,337 ft |
| 15 A | 6,976 ft | 13,953 ft | 13,964 ft | 32,225 ft |
| 20 A | 5,232 ft | 10,465 ft | 10,473 ft | 24,168 ft |
| 25 A | 4,186 ft | 8,372 ft | 8,378 ft | 19,335 ft |
| 30 A | 3,488 ft | 6,976 ft | 6,982 ft | 16,112 ft |
| 40 A | 2,616 ft | 5,232 ft | 5,236 ft | 12,084 ft |
| 50 A | 2,093 ft | 4,186 ft | 4,189 ft | 9,667 ft |
| 60 A | 1,744 ft | 3,488 ft | 3,491 ft | 8,056 ft |
| 80 A | 1,308 ft | 2,616 ft | 2,618 ft | 6,042 ft |
| 100 A | 1,046 ft | 2,093 ft | 2,094 ft | 4,833 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 | 0.01% | 0.01% | 0.01% | 0.02% |
| 50 ft | 0.01% | 0.02% | 0.03% | 0.04% |
| 75 ft | 0.02% | 0.03% | 0.04% | 0.06% |
| 100 ft | 0.03% | 0.04% | 0.06% | 0.09% |
| 150 ft | 0.04% | 0.06% | 0.09% | 0.13% |
| 200 ft | 0.06% | 0.09% | 0.11% | 0.17% |
| 300 ft | 0.09% | 0.13% | 0.17% | 0.26% |
Published standard — source: Voltage drop from the standard VD formula with trade K constants
Frequently asked
- How far can you run 750 kcmil wire?
- At 20 A on a 120 V single-phase circuit, 750 kcmil copper stays under 3% voltage drop for about 5232 ft one-way. At 240 V the same load reaches roughly 10465 ft, because allowable drop scales with system voltage.
- What is the voltage drop of 750 kcmil wire per 100 feet?
- About 0.07 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 750 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.
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