4/0 AWG Free-Air Ampacity
4/0 AWG in free air (single conductor, not in raceway): copper 405A at 90°C, 360A at 75°C. Free-air values are higher than in-raceway (Table 310.16) because heat dissipates more freely.
Cu 90°C405A
Cu 75°C360A
Cu 60°C300A
Free air vs in-raceway
| 60°C | 75°C | 90°C | |
|---|---|---|---|
| Free air (310.17) | 300A | 360A | 405A |
| In raceway (310.16) | -A | 230A | 260A |
| Al free air | 235A | 280A | 315A |
When to use free-air ratings
Table 310.17 applies when conductors are run in free air - not enclosed in conduit, cable tray with covers, or bundled together. Common scenarios include:
- Overhead service entrance conductors
- Open cable tray installations
- Messenger-supported wiring
- Single conductors spaced apart in open air
For the more common scenario of conductors in conduit or cable, use the in-raceway values from Table 310.16.
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NEC 2023 references verified April 2026