350 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 350 A load over a 40 ft (12.2 m) one-way run.
Copper Wire (≤3% Drop)500 kcmil253.4 mm² · Drop: 0.3%
Aluminum Wire (≤3% Drop)750 kcmilDrop: 0.69V (0.33%)
Voltage at Load End207.4 VLoss: 0.62 V (378.4 W)
Power & Breaker (125%)126.09 kW450A Breaker Recommended
All AWG & kcmil Wire Gauges for 350 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 | 76.04 V (36.56%) | 132.0 V | 125.43 V (60.3%) | 46098.1 W | Drop/Amp High |
| 12 AWG | 3.31 mm² | 20 A | 47.78 V (22.97%) | 160.2 V | 78.82 V (37.9%) | 28968.0 W | Drop/Amp High |
| 10 AWG | 5.26 mm² | 30 A | 30.07 V (14.46%) | 177.9 V | 49.6 V (23.85%) | 18228.9 W | Drop/Amp High |
| 8 AWG | 8.37 mm² | 50 A | 18.9 V (9.09%) | 189.1 V | 31.17 V (14.99%) | 11455.7 W | Drop/Amp High |
| 6 AWG | 13.3 mm² | 65 A | 11.89 V (5.72%) | 196.1 V | 19.62 V (9.43%) | 7209.3 W | Drop/Amp High |
| 4 AWG | 21.15 mm² | 85 A | 7.48 V (3.6%) | 200.5 V | 12.34 V (5.93%) | 4533.5 W | Drop/Amp High |
| 3 AWG | 26.67 mm² | 100 A | 5.93 V (2.85%) | 202.1 V | 9.78 V (4.7%) | 3595.2 W | Drop/Amp High |
| 2 AWG | 33.62 mm² | 115 A | 4.7 V (2.26%) | 203.3 V | 7.76 V (3.73%) | 2852.0 W | Drop/Amp High |
| 1 AWG | 42.41 mm² | 130 A | 3.73 V (1.79%) | 204.3 V | 6.15 V (2.96%) | 2260.9 W | Drop/Amp High |
| 1/0 AWG | 53.49 mm² | 150 A | 2.96 V (1.42%) | 205.0 V | 4.88 V (2.34%) | 1792.6 W | Drop/Amp High |
| 2/0 AWG | 67.43 mm² | 175 A | 2.35 V (1.13%) | 205.7 V | 3.87 V (1.86%) | 1422.0 W | Drop/Amp High |
| 3/0 AWG | 85.01 mm² | 200 A | 1.86 V (0.89%) | 206.1 V | 3.07 V (1.48%) | 1127.9 W | Drop/Amp High |
| 4/0 AWG | 107.2 mm² | 230 A | 1.48 V (0.71%) | 206.5 V | 2.43 V (1.17%) | 894.4 W | Drop/Amp High |
| 250 kcmil | 126.7 mm² | 255 A | 1.25 V (0.6%) | 206.8 V | 2.06 V (0.99%) | 756.8 W | Drop/Amp High |
| 300 kcmil | 152.0 mm² | 285 A | 1.04 V (0.5%) | 207.0 V | 1.72 V (0.83%) | 630.8 W | Drop/Amp High |
| 350 kcmil | 177.3 mm² | 310 A | 0.89 V (0.43%) | 207.1 V | 1.47 V (0.71%) | 540.8 W | Drop/Amp High |
| 400 kcmil | 202.7 mm² | 335 A | 0.78 V (0.38%) | 207.2 V | 1.29 V (0.62%) | 473.0 W | Drop/Amp High |
| 500 kcmil | 253.4 mm² | 380 A | 0.62 V (0.3%) | 207.4 V | 1.03 V (0.5%) | 378.4 W | ✓ PASS (≤3%) |
| 600 kcmil | 304.0 mm² | 420 A | 0.52 V (0.25%) | 207.5 V | 0.86 V (0.41%) | 315.4 W | ✓ PASS (≤3%) |
| 750 kcmil | 380.0 mm² | 475 A | 0.42 V (0.2%) | 207.6 V | 0.69 V (0.33%) | 252.3 W | ✓ PASS (≤3%) |
| 1000 kcmil | 506.7 mm² | 545 A | 0.31 V (0.15%) | 207.7 V | 0.51 V (0.25%) | 189.2 W | ✓ PASS (≤3%) |
Frequently Asked Engineering Questions
What size copper wire do I need for 350 amps at 40 feet (208V)?
To stay within the NEC recommended 3% maximum voltage drop for a 350A load over 40 feet one-way at 208V (3-Phase), you need 500 kcmil copper wire. This produces a voltage drop of 0.62V (0.3%) and delivers 207.4V at the load.
What size aluminum wire is required for 350 amps at 40 feet?
Using aluminum conductors (75°C rating), you should use 750 kcmil to maintain voltage drop at 0.69V (0.33%).
What breaker size is needed for a 350A continuous load?
Under NEC 210.20(A), continuous loads require a circuit breaker rated at 125% of the continuous current (350A × 1.25 = 437.5A), which corresponds to a standard 450A circuit breaker.
Compare Other Distances & Amperages
350 Amp Wire Size by Distance (208V)
350A at 20 ft (208V)350A at 30 ft (208V)350A at 50 ft (208V)350A at 60 ft (208V)350A at 75 ft (208V)350A at 80 ft (208V)350A at 100 ft (208V)350A at 120 ft (208V)350A at 125 ft (208V)350A at 150 ft (208V)350A at 175 ft (208V)