250 Amp Wire Size at 800 Feet (480V Three-Phase (US Heavy Industrial))
Complete conductor sizing, Ohm's law voltage drop, $I^2R$ line power loss, and circuit breaker specification for a 250 A load over a 800 ft (243.8 m) one-way run.
Copper Wire (≤3% Drop)350 kcmil177.3 mm² · Drop: 2.66%
Aluminum Wire (≤3% Drop)600 kcmilDrop: 12.26V (2.55%)
Voltage at Load End467.3 VLoss: 12.74 V (5518.4 W)
Power & Breaker (125%)207.85 kW350A Breaker Recommended
All AWG & kcmil Wire Gauges for 250 Amps at 800 Feet (480V)
| Wire Gauge | Metric Area | NEC 75°C Cu Ampacity | Copper Voltage Drop | Load Voltage | Aluminum Drop | Line Loss ($I^2R$) | NEC Status |
|---|---|---|---|---|---|---|---|
| 14 AWG | 2.08 mm² | 15 A | 1086.32 V (226.32%) | 0.0 V | 1791.91 V (373.32%) | 470388.5 W | Drop/Amp High |
| 12 AWG | 3.31 mm² | 20 A | 682.64 V (142.22%) | 0.0 V | 1126.04 V (234.59%) | 295591.5 W | Drop/Amp High |
| 10 AWG | 5.26 mm² | 30 A | 429.57 V (89.49%) | 50.4 V | 708.59 V (147.62%) | 186009.1 W | Drop/Amp High |
| 8 AWG | 8.37 mm² | 50 A | 269.96 V (56.24%) | 210.0 V | 445.3 V (92.77%) | 116894.6 W | Drop/Amp High |
| 6 AWG | 13.3 mm² | 65 A | 169.89 V (35.39%) | 310.1 V | 280.24 V (58.38%) | 73564.5 W | Drop/Amp High |
| 4 AWG | 21.15 mm² | 85 A | 106.83 V (22.26%) | 373.2 V | 176.23 V (36.71%) | 46260.4 W | Drop/Amp High |
| 3 AWG | 26.67 mm² | 100 A | 84.72 V (17.65%) | 395.3 V | 139.75 V (29.11%) | 36685.7 W | Drop/Amp High |
| 2 AWG | 33.62 mm² | 115 A | 67.21 V (14.0%) | 412.8 V | 110.86 V (23.1%) | 29102.0 W | Drop/Amp High |
| 1 AWG | 42.41 mm² | 130 A | 53.28 V (11.1%) | 426.7 V | 87.88 V (18.31%) | 23070.2 W | Drop/Amp High |
| 1/0 AWG | 53.49 mm² | 150 A | 42.24 V (8.8%) | 437.8 V | 69.68 V (14.52%) | 18291.4 W | Drop/Amp High |
| 2/0 AWG | 67.43 mm² | 175 A | 33.51 V (6.98%) | 446.5 V | 55.27 V (11.52%) | 14510.0 W | Drop/Amp High |
| 3/0 AWG | 85.01 mm² | 200 A | 26.58 V (5.54%) | 453.4 V | 43.84 V (9.13%) | 11509.3 W | Drop/Amp High |
| 4/0 AWG | 107.2 mm² | 230 A | 21.08 V (4.39%) | 458.9 V | 34.77 V (7.24%) | 9126.9 W | Drop/Amp High |
| 250 kcmil | 126.7 mm² | 255 A | 17.83 V (3.72%) | 462.2 V | 29.42 V (6.13%) | 7722.2 W | ~ ≤5% |
| 300 kcmil | 152.0 mm² | 285 A | 14.87 V (3.1%) | 465.1 V | 24.52 V (5.11%) | 6436.9 W | ~ ≤5% |
| 350 kcmil | 177.3 mm² | 310 A | 12.74 V (2.66%) | 467.3 V | 21.02 V (4.38%) | 5518.4 W | ✓ PASS (≤3%) |
| 400 kcmil | 202.7 mm² | 335 A | 11.15 V (2.32%) | 468.9 V | 18.39 V (3.83%) | 4826.9 W | ✓ PASS (≤3%) |
| 500 kcmil | 253.4 mm² | 380 A | 8.92 V (1.86%) | 471.1 V | 14.71 V (3.06%) | 3861.1 W | ✓ PASS (≤3%) |
| 600 kcmil | 304.0 mm² | 420 A | 7.43 V (1.55%) | 472.6 V | 12.26 V (2.55%) | 3218.4 W | ✓ PASS (≤3%) |
| 750 kcmil | 380.0 mm² | 475 A | 5.95 V (1.24%) | 474.1 V | 9.81 V (2.04%) | 2574.8 W | ✓ PASS (≤3%) |
| 1000 kcmil | 506.7 mm² | 545 A | 4.46 V (0.93%) | 475.5 V | 7.36 V (1.53%) | 1930.9 W | ✓ PASS (≤3%) |
Frequently Asked Engineering Questions
What size copper wire do I need for 250 amps at 800 feet (480V)?
To stay within the NEC recommended 3% maximum voltage drop for a 250A load over 800 feet one-way at 480V (3-Phase), you need 350 kcmil copper wire. This produces a voltage drop of 12.74V (2.66%) and delivers 467.3V at the load.
What size aluminum wire is required for 250 amps at 800 feet?
Using aluminum conductors (75°C rating), you should use 600 kcmil to maintain voltage drop at 12.26V (2.55%).
What breaker size is needed for a 250A continuous load?
Under NEC 210.20(A), continuous loads require a circuit breaker rated at 125% of the continuous current (250A × 1.25 = 312.5A), which corresponds to a standard 350A circuit breaker.
Compare Other Distances & Amperages
250 Amp Wire Size by Distance (480V)
250A at 20 ft (480V)250A at 30 ft (480V)250A at 40 ft (480V)250A at 50 ft (480V)250A at 60 ft (480V)250A at 75 ft (480V)250A at 80 ft (480V)250A at 100 ft (480V)250A at 120 ft (480V)250A at 125 ft (480V)250A at 150 ft (480V)250A at 175 ft (480V)