Voltage Drop Calculator
Voltage drop across a wire run from gauge, current, and distance, against NEC's 3%/5% guidance.
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About the Voltage Drop Calculator
Calculates the voltage drop across a wire run from the wire's gauge (AWG), current, and one-way distance, using real NEC Chapter 9 Table 8 copper-conductor resistance values — flagged against the NEC's commonly cited 3%/5% voltage-drop recommendations.
- Select the wire gauge (AWG) and circuit type (DC/single-phase, or three-phase).
- Enter the current and one-way distance.
- Enter the source voltage.
- Read the voltage drop, percentage drop, and voltage reaching the load.
12 AWG copper wire carrying 15A over a 50ft one-way DC/single-phase run at 120V: a voltage drop of about 2.97V (2.48%).
| AWG | Ω / 1000 ft |
|---|---|
| 6 | 0.491 |
| 8 | 0.778 |
| 10 | 1.24 |
| 12 | 1.98 |
| 14 | 3.14 |
Uses NEC Chapter 9, Table 8 resistance values for uncoated copper at 75°C. The 3%/5% thresholds (NEC 210.19(A) Informational Note) are recommendations, not a mandatory NEC requirement in most jurisdictions. Consult a licensed electrician for any real installation.
- • Three-phase circuits have lower voltage drop than single-phase for the same current/distance/gauge.
- • Doubling the distance or current doubles the voltage drop — both scale linearly.
- • The 3%/5% thresholds are recommendations for efficiency, not safety limits.
- VoltageLab — NEC Chapter 9 Table 8 Explained — accessed 2026-08-30