Voltage drop scenario
At 240 V single-phase, copper 10 AWG keeps a 20 amps load at about 2.02% drop over 100 feet — within the NEC 3% branch target. Adjust material, voltage, or phase below.
Voltage drop
—Enter a run to estimate voltage drop.
| Voltage drop | — |
|---|---|
| Percent drop | — |
| Voltage at load | — |
| Resistance used | — |
At 240 V single-phase over 100 feet, a 20 amps load needs copper 10 AWG to stay near 2.02% — inside the NEC 3% branch-circuit target. For comparison, copper 12 AWG would drop about 7.72 V (3.22%) on the same run.
This is a voltage-drop estimate only. The conductor must also meet ampacity, temperature derating, and overcurrent rules — use the larger of the voltage-drop size and the ampacity size. Aluminum of the same size drops more, so it usually needs to go up one or two sizes. Always confirm with a licensed electrician and your local code (AHJ).
Sized for voltage drop using NEC Ch.9 Table 8 (DC resistance).
For voltage drop at 240 V single-phase, copper 10 AWG keeps a 20 amps load near 2.02% over 100 feet, meeting the NEC 3% branch guidance. Ampacity, derating, and local code may require a different size — confirm with a licensed electrician.
On a baseline copper 12 AWG at 240 V single-phase, 20 amps over 100 feet drops about 7.72 V (3.22%). Larger conductors drop less; the calculator shows the exact figure for any size.
No. This page sizes for voltage drop only, using NEC Chapter 9 Table 8 DC resistance. The conductor must also satisfy ampacity, temperature derating, and overcurrent-protection rules. Use the larger of the voltage-drop size and the ampacity size, and verify with your local code (AHJ).
Estimate only, based on NEC Chapter 9 Table 8 DC resistance. Not a substitute for a licensed electrician or your local code (AHJ). Voltage-drop sizing does not replace ampacity, temperature derating, power factor, or continuous-load checks. Verify against the current NEC and local code before wiring. Based on NEC Ch.9 Table 8.