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.
NEC 2023Every ampacity below is transcribed from the 2023 NEC (NFPA 70, 2023). The code is republished on a three-year cycle and adoption varies by jurisdiction - confirm against your locally adopted edition and your authority having jurisdiction (AHJ) before you build.
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
NEC 2023Every derated value in this table is transcribed from the 2023 NEC (NFPA 70, 2023). The code is republished on a three-year cycle and adoption varies by jurisdiction - confirm against your locally adopted edition and your authority having jurisdiction (AHJ) before you build.
| 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 |
NEC 2023Every property and drop figure below is transcribed from the 2023 NEC (NFPA 70, 2023). The code is republished on a three-year cycle and adoption varies by jurisdiction - confirm against your locally adopted edition and your authority having jurisdiction (AHJ) before you build.
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 |
FAQ
Frequently asked questions
How many amps can 12 AWG aluminum wire carry?
20 A at a 75°C termination rating under 2023 NEC Table 310.16, at the table's basis conditions of a 30°C ambient and no more than three current-carrying conductors. The 60°C column reads 15 A and the 90°C column 25 A, but terminations on breakers and equipment usually hold the practical answer to the 75°C column. Overcurrent protection for 12 AWG aluminum is separately capped at 15 A by the small-conductor rule.
What size breaker goes with 12 AWG aluminum wire?
15 A. The 75°C column of 2023 NEC Table 310.16 puts 12 AWG aluminum at 20 A, but the small-conductor rule (2023 NEC 240.4(D)) separately caps its overcurrent protection at 15 A, and 15 A is the largest standard rating at or below that ceiling. A hotter location or a fuller raceway derates the conductor and can push the breaker down; the derating table above shows how far.
Does 12 AWG aluminum ampacity change with heat or bundling?
Yes. The published 20 A assumes a 30°C ambient and at most three current-carrying conductors in the raceway or cable. At a 40°C ambient with seven current-carrying conductors, the same 12 AWG aluminum conductor is usable at 12.3 A after the 2023 NEC correction and adjustment factors. The derating table above covers more combinations.
How far can 12 AWG aluminum wire run before voltage drop is a problem?
Carrying its full 15 A on a 240 V single-phase circuit, the circular-mil estimate this page uses stays inside a 3% drop out to about 73 ft one way, and reads 1.01% at 25 ft. Lighter loads drop proportionally less. The 2023 NEC treats 3% as a recommendation for efficient operation, not a general requirement.
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 2023Transcribed from the 2023 NEC (NFPA 70, 2023). Confirm against your locally adopted edition and your authority having jurisdiction (AHJ).
Related