275 Amp Wire Size at 400 Feet (208V Three-Phase (US Commercial Wye))
Complete conductor sizing, Ohm's law voltage drop, $I^2R$ line power loss, and circuit breaker specification for a 275 A load over a 400 ft (121.9 m) one-way run.
Copper Wire (≤3% Drop)400 kcmil202.7 mm² · Drop: 2.95%
Aluminum Wire (≤3% Drop)750 kcmilDrop: 5.39V (2.59%)
Voltage at Load End201.9 VLoss: 6.13 V (2920.3 W)
Power & Breaker (125%)99.07 kW350A Breaker Recommended
All AWG & kcmil Wire Gauges for 275 Amps at 400 Feet (208V)
| 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 | 597.47 V (287.25%) | 0.0 V | 985.55 V (473.82%) | 284585.0 W | Drop/Amp High |
| 12 AWG | 3.31 mm² | 20 A | 375.45 V (180.51%) | 0.0 V | 619.32 V (297.75%) | 178832.9 W | Drop/Amp High |
| 10 AWG | 5.26 mm² | 30 A | 236.26 V (113.59%) | 0.0 V | 389.72 V (187.37%) | 112535.5 W | Drop/Amp High |
| 8 AWG | 8.37 mm² | 50 A | 148.48 V (71.38%) | 59.5 V | 244.92 V (117.75%) | 70721.2 W | Drop/Amp High |
| 6 AWG | 13.3 mm² | 65 A | 93.44 V (44.92%) | 114.6 V | 154.13 V (74.1%) | 44506.5 W | Drop/Amp High |
| 4 AWG | 21.15 mm² | 85 A | 58.76 V (28.25%) | 149.2 V | 96.92 V (46.6%) | 27987.6 W | Drop/Amp High |
| 3 AWG | 26.67 mm² | 100 A | 46.6 V (22.4%) | 161.4 V | 76.86 V (36.95%) | 22194.9 W | Drop/Amp High |
| 2 AWG | 33.62 mm² | 115 A | 36.96 V (17.77%) | 171.0 V | 60.97 V (29.31%) | 17606.7 W | Drop/Amp High |
| 1 AWG | 42.41 mm² | 130 A | 29.3 V (14.09%) | 178.7 V | 48.34 V (23.24%) | 13957.5 W | Drop/Amp High |
| 1/0 AWG | 53.49 mm² | 150 A | 23.23 V (11.17%) | 184.8 V | 38.32 V (18.42%) | 11066.3 W | Drop/Amp High |
| 2/0 AWG | 67.43 mm² | 175 A | 18.43 V (8.86%) | 189.6 V | 30.4 V (14.62%) | 8778.5 W | Drop/Amp High |
| 3/0 AWG | 85.01 mm² | 200 A | 14.62 V (7.03%) | 193.4 V | 24.11 V (11.59%) | 6963.1 W | Drop/Amp High |
| 4/0 AWG | 107.2 mm² | 230 A | 11.59 V (5.57%) | 196.4 V | 19.12 V (9.19%) | 5521.8 W | Drop/Amp High |
| 250 kcmil | 126.7 mm² | 255 A | 9.81 V (4.72%) | 198.2 V | 16.18 V (7.78%) | 4672.0 W | Drop/Amp High |
| 300 kcmil | 152.0 mm² | 285 A | 8.18 V (3.93%) | 199.8 V | 13.49 V (6.48%) | 3894.3 W | ~ ≤5% |
| 350 kcmil | 177.3 mm² | 310 A | 7.01 V (3.37%) | 201.0 V | 11.56 V (5.56%) | 3338.6 W | ~ ≤5% |
| 400 kcmil | 202.7 mm² | 335 A | 6.13 V (2.95%) | 201.9 V | 10.11 V (4.86%) | 2920.3 W | ✓ PASS (≤3%) |
| 500 kcmil | 253.4 mm² | 380 A | 4.9 V (2.36%) | 203.1 V | 8.09 V (3.89%) | 2336.0 W | ✓ PASS (≤3%) |
| 600 kcmil | 304.0 mm² | 420 A | 4.09 V (1.97%) | 203.9 V | 6.74 V (3.24%) | 1947.2 W | ✓ PASS (≤3%) |
| 750 kcmil | 380.0 mm² | 475 A | 3.27 V (1.57%) | 204.7 V | 5.39 V (2.59%) | 1557.7 W | ✓ PASS (≤3%) |
| 1000 kcmil | 506.7 mm² | 545 A | 2.45 V (1.18%) | 205.5 V | 4.05 V (1.95%) | 1168.2 W | ✓ PASS (≤3%) |
Frequently Asked Engineering Questions
What size copper wire do I need for 275 amps at 400 feet (208V)?
To stay within the NEC recommended 3% maximum voltage drop for a 275A load over 400 feet one-way at 208V (3-Phase), you need 400 kcmil copper wire. This produces a voltage drop of 6.13V (2.95%) and delivers 201.9V at the load.
What size aluminum wire is required for 275 amps at 400 feet?
Using aluminum conductors (75°C rating), you should use 750 kcmil to maintain voltage drop at 5.39V (2.59%).
What breaker size is needed for a 275A continuous load?
Under NEC 210.20(A), continuous loads require a circuit breaker rated at 125% of the continuous current (275A × 1.25 = 343.8A), which corresponds to a standard 350A circuit breaker.
Compare Other Distances & Amperages
275 Amp Wire Size by Distance (208V)
275A at 20 ft (208V)275A at 30 ft (208V)275A at 40 ft (208V)275A at 50 ft (208V)275A at 60 ft (208V)275A at 75 ft (208V)275A at 80 ft (208V)275A at 100 ft (208V)275A at 120 ft (208V)275A at 125 ft (208V)275A at 150 ft (208V)275A at 175 ft (208V)