Wire Size for 400 Feet Run
What wire size do you need for a 400 ft run? See the complete wire gauge chart for 15A–200A circuits at 400 ft, keeping voltage drop under 3%. Very long run. For high-amp loads, consider stepping up voltage (480V) to reduce conductor size and voltage drop.
Wire Size Chart for 400 Feet Run (Copper, 3% Max VD)
| Amps | 120V Wire | VD% | 240V Wire | VD% |
|---|---|---|---|---|
| 15A | 4 AWG | 2.5% | 6 AWG | 2.0% |
| 20A | 3 AWG | 2.6% | 6 AWG | 2.6% |
| 30A | 1 AWG | 2.5% | 4 AWG | 2.5% |
| 40A | 1/0 AWG | 2.6% | 3 AWG | 2.6% |
| 50A | 2/0 AWG | 2.6% | 2 AWG | 2.6% |
| 60A | 3/0 AWG | 2.5% | 1 AWG | 2.5% |
| 80A | 4/0 AWG | 2.6% | 1/0 AWG | 2.6% |
| 100A | 4/0 AWG | 3.3% | 2/0 AWG | 2.6% |
| 150A | 4/0 AWG | 4.9% | 4/0 AWG | 2.5% |
| 200A | 4/0 AWG | 6.5% | 4/0 AWG | 3.3% |
Based on copper conductors, 75°C rating, 400 ft one-way distance, 3% max voltage drop. Use our Voltage Drop Calculator for exact calculations.
Why Distance Matters for Wire Sizing
At 400 ft, conductor resistance becomes significant. Per NEC 210.19 (FPN No. 4), total voltage drop should not exceed 5% for branch circuits (3% recommended for the branch circuit alone). Very long run. For high-amp loads, consider stepping up voltage (480V) to reduce conductor size and voltage drop.
The voltage drop formula: VD% = (2 × L × I × R) / (CMA × V) × 100 where L is one-way distance in feet, I is current in amps, R is conductor resistivity (10.37 for copper), CMA is wire area in circular mils, and V is voltage.
Cost Considerations
For 400 ft runs at high amperage, wire cost becomes significant. At this distance, consider installing a sub-panel at the destination — it may be cheaper to run one large feeder than multiple oversized branch circuits.
Disclaimer: Reference only. Verify with a licensed electrician. Ambient temperature derating and conduit fill may require further upsizing.