What size wire for 125 amps at 200 feet?
Short answer: For a 125 amp load 200 feet away (one way) at 240 V, use 1/0 AWG copper or 3/0 AWG aluminum in conduit with 75 °C terminations, which keeps voltage drop at 2.5% and 2.6%. In NM-B (Romex) cable it is 1/0 AWG copper. The breaker stays 125 A; the extra size is only for distance.
125 amps at 200 feet: wire size by type
| Wire type | Size by ampacity | Size for 200 ft (≤3% drop) | Voltage drop |
|---|---|---|---|
| Copper THHN/THWN-2 in conduit, 75 °C | 1 AWG | 1/0 AWG | 2.54% |
| Aluminum XHHW-2 in conduit, 75 °C | 2/0 AWG | 3/0 AWG | 2.63% |
| Copper NM-B (Romex) cable, 60 °C | 1/0 AWG | 1/0 AWG | 2.54% |
| Aluminum SER / NM-B cable, 60 °C | 3/0 AWG | 3/0 AWG | 2.63% |
That is one or more sizes above the 1 AWG that ampacity alone allows: at 200 ft the run, not the breaker, decides the gauge. NEC 250.122(B) then requires the equipment ground to be increased in proportion: start from 6 AWG copper for a 125 A breaker.
Voltage drop of each gauge over 200 ft
| Wire | Volts lost at 125 A | Drop at 125 A | Drop at 100 A (80%) |
|---|---|---|---|
| 1 AWG copper | 7.70 V | 3.21% | 2.57% |
| 1/0 AWG copper | 6.10 V | 2.54% | 2.03% |
| 2/0 AWG copper | 4.84 V | 2.01% | 1.61% |
| 3/0 AWG copper | 3.83 V | 1.60% | 1.28% |
| 4/0 AWG copper | 3.04 V | 1.27% | 1.01% |
voltage drop = 2 × length × resistance per 1,000 ft × amps ÷ 1,000
= 2 × 200 × R(1/0 AWG) × 125 ÷ 1,000 = 6.10 V
percent = 6.10 ÷ 240 × 100 = 2.54%
If the real load is the 80% continuous maximum (100 A, as with an EV charger on a 125 A breaker), copper in conduit can be 1 AWG. 3% is the NEC's recommendation for a branch circuit (Informational Note to 210.19), not a hard rule, but motors, compressors and chargers run better with it.
Same 125 A, other distances
50 ft · 75 ft · 100 ft · 150 ft. Minimum sizes with no distance correction: what size wire for a 125 amp breaker.
Other loads at 200 feet
30 A · 40 A · 50 A · 60 A · 100 A · 150 A · 200 A
Change the numbers in the calculator
Safety. A 125 A circuit or feeder over 200 ft needs a permit almost everywhere in the US. Buried runs have their own depth and conduit rules (NEC 300.5), and equipment nameplates override any general table.