NEC Table 310.17 — Ampacity in Free Air
Single insulated conductors spaced apart in free air, 30°C (86°F) ambient. Formerly 310.15(B)(17).
Copper at 75°C in free air: 14 AWG 30 A · 12 AWG 35 A · 10 AWG 50 A · 8 AWG 70 A · 6 AWG 95 A · 4 AWG 125 A · 2 AWG 170 A · 1/0 230 A · 4/0 360 A · 500 kcmil 620 A.
| Copper | Aluminum or copper-clad aluminum | |||||
|---|---|---|---|---|---|---|
| Size | 60°C | 75°C | 90°C | 60°C | 75°C | 90°C |
| 18 AWG | — | — | 18 | — | — | — |
| 16 AWG | — | — | 24 | — | — | — |
| 14 AWG | 25 | 30 | 35 | — | — | — |
| 12 AWG | 30 | 35 | 40 | 25 | 30 | 35 |
| 10 AWG | 40 | 50 | 55 | 35 | 40 | 45 |
| 8 AWG | 60 | 70 | 80 | 45 | 55 | 60 |
| 6 AWG | 80 | 95 | 105 | 60 | 75 | 85 |
| 4 AWG | 105 | 125 | 140 | 80 | 100 | 115 |
| 3 AWG | 120 | 145 | 165 | 95 | 115 | 130 |
| 2 AWG | 140 | 170 | 190 | 110 | 135 | 150 |
| 1 AWG | 165 | 195 | 220 | 130 | 155 | 175 |
| 1/0 AWG | 195 | 230 | 260 | 150 | 180 | 205 |
| 2/0 AWG | 225 | 265 | 300 | 175 | 210 | 235 |
| 3/0 AWG | 260 | 310 | 350 | 200 | 240 | 270 |
| 4/0 AWG | 300 | 360 | 405 | 235 | 280 | 315 |
| 250 kcmil | 340 | 405 | 455 | 265 | 315 | 355 |
| 300 kcmil | 375 | 445 | 500 | 290 | 350 | 395 |
| 350 kcmil | 420 | 505 | 570 | 330 | 395 | 445 |
| 400 kcmil | 455 | 545 | 615 | 355 | 425 | 480 |
| 500 kcmil | 515 | 620 | 700 | 405 | 485 | 545 |
| 600 kcmil | 575 | 690 | 780 | 455 | 545 | 615 |
| 700 kcmil | 630 | 755 | 850 | 500 | 595 | 670 |
| 750 kcmil | 655 | 785 | 885 | 515 | 620 | 700 |
| 800 kcmil | 680 | 815 | 920 | 535 | 645 | 725 |
| 900 kcmil | 730 | 870 | 980 | 580 | 700 | 790 |
| 1000 kcmil | 780 | 935 | 1055 | 625 | 750 | 845 |
| 1250 kcmil | 890 | 1065 | 1200 | 710 | 855 | 965 |
| 1500 kcmil | 980 | 1175 | 1325 | 795 | 950 | 1070 |
| 1750 kcmil | 1070 | 1280 | 1445 | 875 | 1050 | 1185 |
| 2000 kcmil | 1155 | 1385 | 1560 | 960 | 1150 | 1295 |
| Column | Conductor types |
|---|---|
| 60°C (140°F) | TW, UF |
| 75°C (167°F) | RHW, THHW, THW, THWN, XHHW, USE, ZW |
| 90°C (194°F) | TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE-2, XHH, XHHW, XHHW-2, ZW-2 |
Frequently asked questions
When can I use Table 310.17 instead of 310.16?
Only for single insulated conductors installed in free air with space around them to shed heat — for example open wiring on insulators, some cable-tray installations and service drops. Wires in conduit, cable assemblies or direct burial use Table 310.16.
Why are free-air ampacities higher?
A conductor alone in moving air cools far better than three conductors sharing an enclosed raceway. 4/0 copper at 75°C is rated 360 A in free air against 230 A in conduit.
Do the bundle adjustment factors apply to Table 310.17?
No. The adjustment for more than three current-carrying conductors applies to conductors in a raceway or cable, not to spaced single conductors in free air. Ambient temperature correction still applies.
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