3/0 AWG Voltage Drop — Max Run Length by Load
Voltage drop for 3/0 AWG copper and aluminium: at 20 A on 120 V single phase the 3% limit is reached at about 1170 ft one-way. Full table by load, voltage and distance.
Quick answer
3/0 AWG copper reaches 3% voltage drop at about 1170 ft one-way carrying 20 A on a 120 V single-phase circuit. At 100 ft the same load drops 0.31 V (0.26%), calculated as VD = 2 × K × I × L / cmil with K = 12.9 for copper and 167,806 circular mils.
3% limit @ 20 A, 120 V
1170ft
3% limit @ 20 A, 240 V
2341ft
Drop @ 100 ft, 20 A
0.31V
Ω / 1000 ft (Cu)
0.0618
Maximum one-way run length at 3% drop
Copper 3/0 AWG. Aluminium distances are roughly 62% of these figures.
| Load | 120 V 1Ø | 240 V 1Ø | 208 V 3Ø | 480 V 3Ø |
|---|---|---|---|---|
| 5 A | 4,682 ft | 9,365 ft | 9,373 ft | 21,630 ft |
| 10 A | 2,341 ft | 4,682 ft | 4,686 ft | 10,815 ft |
| 15 A | 1,560 ft | 3,121 ft | 3,124 ft | 7,210 ft |
| 20 A | 1,170 ft | 2,341 ft | 2,343 ft | 5,407 ft |
| 25 A | 936 ft | 1,873 ft | 1,874 ft | 4,326 ft |
| 30 A | 780 ft | 1,560 ft | 1,562 ft | 3,605 ft |
| 40 A | 585 ft | 1,170 ft | 1,171 ft | 2,703 ft |
| 50 A | 468 ft | 936 ft | 937 ft | 2,163 ft |
| 60 A | 390 ft | 780 ft | 781 ft | 1,802 ft |
| 80 A | 292 ft | 585 ft | 585 ft | 1,351 ft |
| 100 A | 234 ft | 468 ft | 468 ft | 1,081 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 | 0.03% | 0.05% | 0.06% | 0.1% |
| 50 ft | 0.06% | 0.1% | 0.13% | 0.19% |
| 75 ft | 0.1% | 0.14% | 0.19% | 0.29% |
| 100 ft | 0.13% | 0.19% | 0.26% | 0.38% |
| 150 ft | 0.19% | 0.29% | 0.38% | 0.58% |
| 200 ft | 0.26% | 0.38% | 0.51% | 0.77% |
| 300 ft | 0.38% | 0.58% | 0.77% | 1.15% |
Published standard — source: Voltage drop from the standard VD formula with trade K constants
Frequently asked
- How far can you run 3/0 AWG wire?
- At 20 A on a 120 V single-phase circuit, 3/0 AWG copper stays under 3% voltage drop for about 1170 ft one-way. At 240 V the same load reaches roughly 2341 ft, because allowable drop scales with system voltage.
- What is the voltage drop of 3/0 AWG wire per 100 feet?
- About 0.31 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 3/0 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.
More on 3/0 AWG
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