Ampacity by temperature rating
| Temperature rating | Ampacity | Typical insulation |
|---|---|---|
| 60°C | 15 A | — |
| 75°C | 20 A | THW |
| 90°C | 25 A | THHN / THWN-2, XHHW-2 |
Reference tables · Aluminum ampacity
2023 NEC · Table 310.16
12 AWG aluminum wire ampacity
At a 75°C termination rating, 12 AWG aluminum carries 20 A under the published table's basis conditions — 30°C ambient, no more than three current-carrying conductors. Overcurrent protection is separately capped at 15 A by the small-conductor rule.
What 12 AWG aluminum is used for
12 AWG aluminum is limited to 15 A by the small-conductor rule, which makes it an unusual choice for branch circuits. Aluminum is normally reserved for larger feeders where the cost saving is meaningful.
Note the gap between the table and the ceiling. The 90°C column reads 25 A, but a 12 AWG aluminum conductor cannot be protected above 15 A regardless — the small-conductor rule sets that ceiling independently of ampacity. The higher table value exists so the conductor has headroom to be derated from, not so it can be put on a larger breaker.
Terminations usually decide the practical answer. Breakers and equipment are typically listed for 60°C or 75°C, so even 90°C-rated insulation on this conductor is normally limited to the 20 A column at the terminals. Check the equipment's listing rather than assuming.
Derating
Ampacity in real conditions
| Ambient | 3 conductors | 4 conductors | 7 conductors | 10 conductors | 21 conductors |
|---|---|---|---|---|---|
| 20°C | 15 A | 15 A | 15 A | 11.1 A | 10 A |
| 30°C | 15 A | 15 A | 14 A | 10 A | 9 A |
| 40°C | 15 A | 14.1 A | 12.3 A | 8.8 A | 7.9 A |
| 50°C | 15 A | 12 A | 10.5 A | 7.5 A | 6.8 A |
Properties
| Circular mils | 6,530 |
|---|---|
| DC resistance | 3.25 Ω per 1000 ft |
| Ampacity at 75°C | 20 A |
| Overcurrent ceiling | 15 A (small-conductor rule) |
| Largest standard breaker | 15 A |
| Area, THHN / THWN-2 | 0.0133 in² |
| Area, XHHW-2 | 0.0181 in² |
| Area, THW | 0.026 in² |
Voltage drop over distance
Single-phase 240 V, carrying 15 A on 12 AWG aluminum.
| One-way distance | Drop | Within 3%? |
|---|---|---|
| 25 ft | 1.01% | Yes |
| 50 ft | 2.03% | Yes |
| 100 ft | 4.06% | No |
| 150 ft | 6.09% | No |
| 200 ft | 8.12% | No |
| 300 ft | 12.17% | No |
Source: NFPA 70, National Electrical Code, Table 310.16; NFPA 70, National Electrical Code, Table 310.15(B)(1)(1); NFPA 70, National Electrical Code, Table 310.15(C)(1); NFPA 70, National Electrical Code, Chapter 9, Table 8. Published by NFPA.NEC 2023
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