Voltage Drop
3.18V (2.65%)
Ampacity
25A
Max Dist
57 ft
Voltage Drop
2.65%
3.18V of 120V ✔ Within 3% limit
Ampacity
25A
Max Distance
57 ft
Power Loss
63.52W
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Inputs
Result
12 AWG copper resistance = 1.588 ohm/1000ft. Drop = 20 × 1.588 × 100/1000 = 3.18V. Percent = 3.18/120 = 2.65%.
Inputs
Result
10 AWG copper resistance = 0.999 ohm/1000ft. Drop = 30 × 0.999 × 80/1000 = 2.4V. Percent = 2.4/240 = 1.0%.
NEC recommends no more than 3% voltage drop for branch circuits and 5% total for feeder + branch combined. At 120V, 3% = 3.6V drop. Longer wire runs need thicker gauge to stay within limits.
| Voltage | 3% Drop | 5% Drop | Impact |
|---|---|---|---|
| 12V DC | 0.36V | 0.6V | LED dimming, motor slowdown |
| 120V AC | 3.6V | 6V | Lights dim, motors run hot |
| 240V AC | 7.2V | 12V | Reduced appliance efficiency |
12 AWG copper wire handles 20 amps at 75°C rating per NEC Table 310.16. For runs over 50 feet at 120V, consider upsizing to 10 AWG to keep voltage drop under 3%. Aluminum wire requires one gauge larger than copper.
At 20A and 120V, 12 AWG copper can run about 50 feet one-way before hitting 3% voltage drop. At 10A, it can go about 100 feet. Lower current or higher voltage extends the safe distance.
Aluminum has 61% the conductivity of copper and requires one gauge size larger for the same ampacity. A 20A copper circuit uses 12 AWG while aluminum needs 10 AWG. Aluminum is cheaper but requires special connectors.
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Last Updated: Mar 19, 2026
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