500 kcmil Free-Air Ampacity
500 kcmil in free air (single conductor, not in raceway): copper 700A at 90°C, 620A at 75°C. Free-air values are higher than in-raceway (Table 310.16) because heat dissipates more freely.
Cu 90°C700A
Cu 75°C620A
Free air vs in-raceway
| 75°C | 90°C | |
|---|---|---|
| Free air (310.17) | 620A | 700A |
| In raceway (310.16) | -A | 430A |
| Al free air | 485A | 545A |
When to use free-air ratings
Table 310.17 applies when conductors are run in free air - not enclosed in conduit or cable tray with covers. Common scenarios for kcmil conductors include overhead service drops, open cable tray, and messenger-supported wiring.
For conductors in conduit or cable, use the in-raceway values from Table 310.16.
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NEC 2023 references verified April 2026