600 kcmil Free-Air Ampacity
600 kcmil in free air (single conductor, not in raceway): copper 780A at 90°C, 690A at 75°C. Free-air values are higher than in-raceway (Table 310.16) because heat dissipates more freely.
Cu 90°C780A
Cu 75°C690A
Free air vs in-raceway
| 75°C | 90°C | |
|---|---|---|
| Free air (310.17) | 690A | 780A |
| In raceway (310.16) | -A | 475A |
| Al free air | 545A | 615A |
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