425 Amp Wire Size at 40 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 425 A load over a 40 ft (12.2 m) one-way run.
Copper Wire (≤3% Drop)750 kcmil380.0 mm² · Drop: 0.24%
Aluminum Wire (≤3% Drop)1000 kcmilDrop: 0.63V (0.3%)
Voltage at Load End207.5 VLoss: 0.51 V (372.1 W)
Power & Breaker (125%)153.11 kW600A Breaker Recommended
All AWG & kcmil Wire Gauges for 425 Amps at 40 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 | 92.34 V (44.39%) | 115.7 V | 152.31 V (73.23%) | 67971.1 W | Drop/Amp High |
| 12 AWG | 3.31 mm² | 20 A | 58.02 V (27.9%) | 150.0 V | 95.71 V (46.02%) | 42713.0 W | Drop/Amp High |
| 10 AWG | 5.26 mm² | 30 A | 36.51 V (17.55%) | 171.5 V | 60.23 V (28.96%) | 26878.3 W | Drop/Amp High |
| 8 AWG | 8.37 mm² | 50 A | 22.95 V (11.03%) | 185.1 V | 37.85 V (18.2%) | 16891.3 W | Drop/Amp High |
| 6 AWG | 13.3 mm² | 65 A | 14.44 V (6.94%) | 193.6 V | 23.82 V (11.45%) | 10630.1 W | Drop/Amp High |
| 4 AWG | 21.15 mm² | 85 A | 9.08 V (4.37%) | 198.9 V | 14.98 V (7.2%) | 6684.6 W | Drop/Amp High |
| 3 AWG | 26.67 mm² | 100 A | 7.2 V (3.46%) | 200.8 V | 11.88 V (5.71%) | 5301.1 W | Drop/Amp High |
| 2 AWG | 33.62 mm² | 115 A | 5.71 V (2.75%) | 202.3 V | 9.42 V (4.53%) | 4205.2 W | Drop/Amp High |
| 1 AWG | 42.41 mm² | 130 A | 4.53 V (2.18%) | 203.5 V | 7.47 V (3.59%) | 3333.6 W | Drop/Amp High |
| 1/0 AWG | 53.49 mm² | 150 A | 3.59 V (1.73%) | 204.4 V | 5.92 V (2.85%) | 2643.1 W | Drop/Amp High |
| 2/0 AWG | 67.43 mm² | 175 A | 2.85 V (1.37%) | 205.2 V | 4.7 V (2.26%) | 2096.7 W | Drop/Amp High |
| 3/0 AWG | 85.01 mm² | 200 A | 2.26 V (1.09%) | 205.7 V | 3.73 V (1.79%) | 1663.1 W | Drop/Amp High |
| 4/0 AWG | 107.2 mm² | 230 A | 1.79 V (0.86%) | 206.2 V | 2.96 V (1.42%) | 1318.8 W | Drop/Amp High |
| 250 kcmil | 126.7 mm² | 255 A | 1.52 V (0.73%) | 206.5 V | 2.5 V (1.2%) | 1115.9 W | Drop/Amp High |
| 300 kcmil | 152.0 mm² | 285 A | 1.26 V (0.61%) | 206.7 V | 2.08 V (1.0%) | 930.1 W | Drop/Amp High |
| 350 kcmil | 177.3 mm² | 310 A | 1.08 V (0.52%) | 206.9 V | 1.79 V (0.86%) | 797.4 W | Drop/Amp High |
| 400 kcmil | 202.7 mm² | 335 A | 0.95 V (0.46%) | 207.1 V | 1.56 V (0.75%) | 697.5 W | Drop/Amp High |
| 500 kcmil | 253.4 mm² | 380 A | 0.76 V (0.36%) | 207.2 V | 1.25 V (0.6%) | 557.9 W | Drop/Amp High |
| 600 kcmil | 304.0 mm² | 420 A | 0.63 V (0.3%) | 207.4 V | 1.04 V (0.5%) | 465.1 W | Drop/Amp High |
| 750 kcmil | 380.0 mm² | 475 A | 0.51 V (0.24%) | 207.5 V | 0.83 V (0.4%) | 372.1 W | ✓ PASS (≤3%) |
| 1000 kcmil | 506.7 mm² | 545 A | 0.38 V (0.18%) | 207.6 V | 0.63 V (0.3%) | 279.0 W | ✓ PASS (≤3%) |
Frequently Asked Engineering Questions
What size copper wire do I need for 425 amps at 40 feet (208V)?
To stay within the NEC recommended 3% maximum voltage drop for a 425A load over 40 feet one-way at 208V (3-Phase), you need 750 kcmil copper wire. This produces a voltage drop of 0.51V (0.24%) and delivers 207.5V at the load.
What size aluminum wire is required for 425 amps at 40 feet?
Using aluminum conductors (75°C rating), you should use 1000 kcmil to maintain voltage drop at 0.63V (0.3%).
What breaker size is needed for a 425A continuous load?
Under NEC 210.20(A), continuous loads require a circuit breaker rated at 125% of the continuous current (425A × 1.25 = 531.2A), which corresponds to a standard 600A circuit breaker.
Compare Other Distances & Amperages
425 Amp Wire Size by Distance (208V)
425A at 20 ft (208V)425A at 30 ft (208V)425A at 50 ft (208V)425A at 60 ft (208V)425A at 75 ft (208V)425A at 80 ft (208V)425A at 100 ft (208V)425A at 120 ft (208V)425A at 125 ft (208V)425A at 150 ft (208V)425A at 175 ft (208V)