Wire Size for 125 Feet Run
What wire size do you need for a 125 ft run? See the complete wire gauge chart for 15A–200A circuits at 125 ft, keeping voltage drop under 3%. Long run typical for detached garages. Consider upsizing wire two gauges for high-amp circuits.
Wire Size Chart for 125 Feet Run (Copper, 3% Max VD)
| Amps | 120V Wire | VD% | 240V Wire | VD% |
|---|---|---|---|---|
| 15A | 8 AWG | 2.0% | 12 AWG | 2.5% |
| 20A | 8 AWG | 2.6% | 10 AWG | 2.1% |
| 30A | 6 AWG | 2.5% | 8 AWG | 2.0% |
| 40A | 4 AWG | 2.1% | 8 AWG | 2.6% |
| 50A | 4 AWG | 2.6% | 6 AWG | 2.1% |
| 60A | 3 AWG | 2.5% | 4 AWG | 1.6% |
| 80A | 2 AWG | 2.6% | 3 AWG | 1.6% |
| 100A | 1 AWG | 2.6% | 1 AWG | 1.3% |
| 150A | 3/0 AWG | 1.9% | 3/0 AWG | 1.0% |
| 200A | 4/0 AWG | 2.0% | 4/0 AWG | 1.0% |
Based on copper conductors, 75°C rating, 125 ft one-way distance, 3% max voltage drop. Use our Voltage Drop Calculator for exact calculations.
Why Distance Matters for Wire Sizing
At 125 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). Long run typical for detached garages. Consider upsizing wire two gauges for high-amp circuits.
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 125 ft runs at high amperage, wire cost becomes significant. Compare the cost of upsized wire against the energy savings from reduced voltage drop over the system lifetime.
Disclaimer: Reference only. Verify with a licensed electrician. Ambient temperature derating and conduit fill may require further upsizing.