12 AWG Free-Air Ampacity
12 AWG in free air (single conductor, not in raceway): copper 40A at 90°C, 35A at 75°C. Free-air values are higher than in-raceway (Table 310.16) because heat dissipates more freely.
Cu 90°C40A
Cu 75°C35A
Cu 60°C30A
Free air vs in-raceway
| 60°C | 75°C | 90°C | |
|---|---|---|---|
| Free air (310.17) | 30A | 35A | 40A |
| In raceway (310.16) | -A | 25A | 30A |
| Al free air | 25A | 30A | 35A |
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.
Requirements vary by state. NEC edition, licensing, permits, and GFCI rules differ by jurisdiction. Check your state or pick it below for personalized info across WireRef.
Important: For reference only. Not a substitute for a licensed electrician. Electrical work can cause serious injury, death, fire, or property damage if performed incorrectly. Always hire a licensed electrician for electrical work, especially for service upgrades, panel work, and 240V circuits. Values are derived from NFPA 70 (NEC) for educational purposes. Always verify against your locally adopted NEC edition and amendments - local jurisdictions may enforce stricter requirements. WireRef provides reference information only and is not responsible for work performed based on this content. NEC® is a registered trademark of the National Fire Protection Association. Free NEC access via NFPA · OSHA Electrical Safety · Terms of use.
NEC 2023 references verified April 2026