NEC 310.16 conductor ampacity table
The NEC Table 310.16 allowable ampacities for insulated copper and aluminum conductors (not more than three current-carrying conductors in a raceway, 30 °C / 86 °F ambient), with the 310.15(B)(1) temperature-correction factors. These are the numbers Solar Scripto's engine uses to size every conductor.
Table 310.16 — allowable ampacity (A)
| Size | Cu 60°C | Cu 75°C | Cu 90°C | Al 60°C | Al 75°C | Al 90°C |
|---|---|---|---|---|---|---|
| 14 AWG | 15 | 20 | 25 | — | — | — |
| 12 AWG | 20 | 25 | 30 | 15 | 20 | 25 |
| 10 AWG | 30 | 35 | 40 | 25 | 30 | 35 |
| 8 AWG | 40 | 50 | 55 | 30 | 40 | 45 |
| 6 AWG | 55 | 65 | 75 | 40 | 50 | 55 |
| 4 AWG | 70 | 85 | 95 | 55 | 65 | 75 |
| 3 AWG | 85 | 100 | 110 | 65 | 75 | 85 |
| 2 AWG | 95 | 115 | 130 | 75 | 90 | 100 |
| 1 AWG | 110 | 130 | 150 | 85 | 100 | 115 |
| 1/0 | 125 | 150 | 170 | 100 | 120 | 135 |
| 2/0 | 145 | 175 | 195 | 115 | 135 | 150 |
| 3/0 | 165 | 200 | 225 | 130 | 155 | 175 |
| 4/0 | 195 | 230 | 260 | 150 | 180 | 205 |
| 250 kcmil | 215 | 255 | 290 | 170 | 205 | 230 |
| 300 kcmil | 240 | 285 | 320 | 195 | 230 | 255 |
| 350 kcmil | 260 | 310 | 350 | 210 | 250 | 280 |
| 400 kcmil | 280 | 335 | 380 | 225 | 270 | 305 |
| 500 kcmil | 320 | 380 | 430 | 260 | 310 | 350 |
Ambient temperature correction — Table 310.15(B)(1)
Multiply the base ampacity by the factor for the conductor's insulation column and the ambient temperature (base 30 °C):
| Ambient | 60°C factor | 75°C factor | 90°C factor |
|---|---|---|---|
| ≤ 10°C (50°F) | 1.29 | 1.2 | 1.15 |
| ≤ 15°C (59°F) | 1.22 | 1.15 | 1.12 |
| ≤ 20°C (68°F) | 1.15 | 1.11 | 1.08 |
| ≤ 25°C (77°F) | 1.08 | 1.05 | 1.04 |
| ≤ 30°C (86°F) | 1 | 1 | 1 |
| ≤ 35°C (95°F) | 0.91 | 0.94 | 0.96 |
| ≤ 40°C (104°F) | 0.82 | 0.88 | 0.91 |
| ≤ 45°C (113°F) | 0.71 | 0.82 | 0.87 |
| ≤ 50°C (122°F) | 0.58 | 0.75 | 0.82 |
| ≤ 55°C (131°F) | 0.41 | 0.67 | 0.76 |
| ≤ 60°C (140°F) | — | 0.58 | 0.71 |
| ≤ 65°C (149°F) | — | 0.47 | 0.65 |
| ≤ 70°C (158°F) | — | 0.33 | 0.58 |
More than three current-carrying conductors — 310.15(C)(1)
| Conductors | Adjustment |
|---|---|
| 4–6 | 80% |
| 7–9 | 70% |
| 10–20 | 50% |
| 21–30 | 45% |
| 31–40 | 40% |
| 41+ | 35% |
Worked example
A 10 AWG copper THWN-2 (90 °C) PV circuit on a hot roof (say 45 °C ambient, 4 conductors in conduit): base 90°C ampacity 40 A × 0.8 (fill) × 0.87 (temp) = 27.8 A after derating — then confirmed against the 75 °C termination limit of 35 A. Related: PV conductor & OCPD sizing (690.8).
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