What Size Wire for 30 Amps?
NEC Table 310.16 wire sizing for a 30-amp circuit — copper and aluminum, with the continuous-load and voltage-drop adjustments that change the answer.
Calculations are built on the 2023 National Electrical Code (NEC) and cross-checked against the published code tables. How we verify. Last reviewed June 2026.
Ampacity 30A. Continuous loads (125%): 8.
Ampacity 40A. Continuous loads (125%): 8.
A 30A circuit is protected by a 30A breaker (NEC 240.6). The sizes above use the 75°C column of NEC Table 310.16.
Check your termination rating. Per NEC 110.14(C)(1), equipment rated 100A or less — or marked for 14 AWG through 1 AWG conductors — must be sized to the 60°C column unless its terminals are listed/marked for 75°C (most modern breakers are). When that applies the answer can be one size larger.
When the 30 Amp Answer Changes
Long runs (voltage drop)
Over distance, voltage drop can force a larger wire than ampacity alone. At 240V, 10 AWG copper drops about 1.5% at 50 ft, 3.0% at 100 ft, and 4.5% at 150 ft. NEC informational notes recommend (not mandate) ≤3% on a branch circuit and ≤5% combined feeder + branch.
Continuous loads (125%)
Loads that run 3+ hours (EV charging, electric heat) must be sized at 125%. That moves a 30A circuit to 8 copper / 8 aluminum.
Common 30 Amp Circuits
- Electric clothes dryers
- Window/through-wall AC units
- 30A RV outlets (TT-30)
- Water heaters
NEC Table 310.16 Ampacity Reference
Raw Table 310.16 ampacities (copper & aluminum, 60/75/90°C). Sizes whose usable 75°C ampacity meets 30A are highlighted. The 90°C column is only the basis for derating — terminations cap most installs at 60°C or 75°C.
| Size (AWG/kcmil) | Cu 60°C | Cu 75°C | Cu 90°C | Al 75°C | Al 90°C |
|---|---|---|---|---|---|
| 14* | 15 | 20 | 25 | — | — |
| 12* | 20 | 25 | 30 | 20 | 25 |
| 10* | 30 | 35 | 40 | 30 | 35 |
| 8 | 40 | 50 | 55 | 40 | 45 |
| 6 | 55 | 65 | 75 | 50 | 55 |
| 4 | 70 | 85 | 95 | 65 | 75 |
| 3 | 85 | 100 | 110 | 75 | 85 |
| 2 | 95 | 115 | 130 | 90 | 100 |
| 1 | 110 | 130 | 150 | 100 | 115 |
| 1/0 | 125 | 150 | 170 | 120 | 135 |
| 2/0 | 145 | 175 | 195 | 135 | 150 |
| 3/0 | 165 | 200 | 225 | 155 | 175 |
| 4/0 | 195 | 230 | 260 | 180 | 205 |
| 250 kcmil | 215 | 255 | 290 | 205 | 230 |
| 300 kcmil | 240 | 285 | 320 | 230 | 260 |
| 350 kcmil | 260 | 310 | 350 | 250 | 280 |
| 400 kcmil | 280 | 335 | 380 | 270 | 305 |
| 500 kcmil | 320 | 380 | 430 | 310 | 350 |
| 600 kcmil | 350 | 420 | 475 | 340 | 385 |
| 700 kcmil | 385 | 460 | 520 | 375 | 425 |
| 750 kcmil | 400 | 475 | 535 | 385 | 435 |
* 14, 12 and 10 AWG carry the tabulated ampacity but NEC 240.4(D) caps their overcurrent protection at 15A, 20A and 30A (copper) — so they cannot serve a higher-rated circuit even though the table value is larger.
Adjust for your exact run
Open the calculator pre-filled with 30A at 240V to add distance, temperature, and conductor count.