400 Amp Wire Size at 120 Feet (12V DC (Solar / Automotive / Marine))
Complete conductor sizing, Ohm's law voltage drop, $I^2R$ line power loss, and circuit breaker specification for a 400 A load over a 120 ft (36.6 m) one-way run.
Copper Wire (≤3% Drop)4× 1000 kcmil (Parallel)506.7 mm² · Drop: 2.58%
Aluminum Wire (≤3% Drop)1000 kcmilDrop: 2.04V (16.99%)
Voltage at Load End11.7 VLoss: 0.31 V (123.6 W)
Power & Breaker (125%)4.8 kW500A Breaker Recommended
All AWG & kcmil Wire Gauges for 400 Amps at 120 Feet (12V)
| 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 | 301.05 V (2508.74%) | 0.0 V | 496.59 V (4138.25%) | 120419.4 W | Drop/Amp High |
| 12 AWG | 3.31 mm² | 20 A | 189.18 V (1576.49%) | 0.0 V | 312.06 V (2600.47%) | 75671.4 W | Drop/Amp High |
| 10 AWG | 5.26 mm² | 30 A | 119.05 V (992.05%) | 0.0 V | 196.37 V (1636.42%) | 47618.3 W | Drop/Amp High |
| 8 AWG | 8.37 mm² | 50 A | 74.81 V (623.44%) | 0.0 V | 123.41 V (1028.38%) | 29925.0 W | Drop/Amp High |
| 6 AWG | 13.3 mm² | 65 A | 47.08 V (392.34%) | 0.0 V | 77.66 V (647.18%) | 18832.5 W | Drop/Amp High |
| 4 AWG | 21.15 mm² | 85 A | 29.61 V (246.72%) | 0.0 V | 48.84 V (406.98%) | 11842.7 W | Drop/Amp High |
| 3 AWG | 26.67 mm² | 100 A | 23.48 V (195.66%) | 0.0 V | 38.73 V (322.74%) | 9391.5 W | Drop/Amp High |
| 2 AWG | 33.62 mm² | 115 A | 18.63 V (155.21%) | 0.0 V | 30.72 V (256.02%) | 7450.1 W | Drop/Amp High |
| 1 AWG | 42.41 mm² | 130 A | 14.76 V (123.04%) | 0.0 V | 24.36 V (202.96%) | 5906.0 W | Drop/Amp High |
| 1/0 AWG | 53.49 mm² | 150 A | 11.71 V (97.55%) | 0.3 V | 19.31 V (160.92%) | 4682.6 W | Drop/Amp High |
| 2/0 AWG | 67.43 mm² | 175 A | 9.29 V (77.39%) | 2.7 V | 15.32 V (127.65%) | 3714.6 W | Drop/Amp High |
| 3/0 AWG | 85.01 mm² | 200 A | 7.37 V (61.38%) | 4.6 V | 12.15 V (101.25%) | 2946.4 W | Drop/Amp High |
| 4/0 AWG | 107.2 mm² | 230 A | 5.84 V (48.68%) | 6.2 V | 9.64 V (80.29%) | 2336.5 W | Drop/Amp High |
| 250 kcmil | 126.7 mm² | 255 A | 4.94 V (41.19%) | 7.1 V | 8.15 V (67.94%) | 1976.9 W | Drop/Amp High |
| 300 kcmil | 152.0 mm² | 285 A | 4.12 V (34.33%) | 7.9 V | 6.8 V (56.63%) | 1647.8 W | Drop/Amp High |
| 350 kcmil | 177.3 mm² | 310 A | 3.53 V (29.43%) | 8.5 V | 5.83 V (48.55%) | 1412.7 W | Drop/Amp High |
| 400 kcmil | 202.7 mm² | 335 A | 3.09 V (25.74%) | 8.9 V | 5.1 V (42.46%) | 1235.7 W | Drop/Amp High |
| 500 kcmil | 253.4 mm² | 380 A | 2.47 V (20.59%) | 9.5 V | 4.08 V (33.97%) | 988.4 W | Drop/Amp High |
| 600 kcmil | 304.0 mm² | 420 A | 2.06 V (17.17%) | 9.9 V | 3.4 V (28.31%) | 823.9 W | Drop/Amp High |
| 750 kcmil | 380.0 mm² | 475 A | 1.65 V (13.73%) | 10.4 V | 2.72 V (22.65%) | 659.1 W | Drop/Amp High |
| 1000 kcmil | 506.7 mm² | 545 A | 1.24 V (10.3%) | 10.8 V | 2.04 V (16.99%) | 494.3 W | Drop/Amp High |
Frequently Asked Engineering Questions
What size copper wire do I need for 400 amps at 120 feet (12V)?
To stay within the NEC recommended 3% maximum voltage drop for a 400A load over 120 feet one-way at 12V (DC), you need 4× 1000 kcmil (Parallel) copper wire. This produces a voltage drop of 0.31V (2.58%) and delivers 11.7V at the load.
What size aluminum wire is required for 400 amps at 120 feet?
Using aluminum conductors (75°C rating), you should use 1000 kcmil to maintain voltage drop at 2.04V (16.99%).
What breaker size is needed for a 400A continuous load?
Under NEC 210.20(A), continuous loads require a circuit breaker rated at 125% of the continuous current (400A × 1.25 = 500.0A), which corresponds to a standard 500A circuit breaker.
Compare Other Distances & Amperages
400 Amp Wire Size by Distance (12V)
400A at 20 ft (12V)400A at 30 ft (12V)400A at 40 ft (12V)400A at 50 ft (12V)400A at 60 ft (12V)400A at 75 ft (12V)400A at 80 ft (12V)400A at 100 ft (12V)400A at 125 ft (12V)400A at 150 ft (12V)400A at 175 ft (12V)