12 AWG XHHW-2 Aluminum Ampacity & Derating
Calculation Walkthrough
Per NEC 2023 Table 310.16, 12 AWG aluminum XHHW-2 (90°C column) = 25A base. Assumes ≤3 CCC at 30°C ambient.
At 30.0°C (86°F), factor = 1.0. No reduction. At 50°C attic: factor drops to ~0.82 for 90°C insulation.
≤3 CCC = factor 1.0. EGC + neutral (unbalanced) not counted per 310.15(E). Typical 240V circuit: 2 hots + N + G = 2 CCC.
Equipment termination governs the final ampacity. Circuits ≤100A: use 60°C column unless conductor + equipment both rated 75°C. Modern panels and breakers are listed for 75°C terminations, so the 75°C column value of 20A becomes the ceiling. The 90°C rating is only used as the starting point for temperature correction and bundling derating. After all adjustments, the result cannot exceed the termination column value. This is the single most commonly failed inspection item.
NEC recommends limiting voltage drop to 3% on branch circuits and 5% total (branch + feeder combined). For 12 AWG aluminum carrying 20A at 240V single-phase over a 100-foot one-way run: Vd = (2 × L × I × R) / 1000. The resistance per 1000 ft for 12 AWG aluminum at 75°C is used from NEC Chapter 9 Table 8. At 20A and 100 ft, the drop is 13.0V (5.4%). For longer runs or higher loads, use the voltage drop calculator with your specific distance and load.
Common Applications
12 AWG XHHW-2 aluminum at 20A covers 20A general-purpose and small-appliance circuits, making it the most commonly installed wire size in residential construction. Required for kitchen countertop circuits, bathroom receptacles, garage circuits, and laundry areas per NEC 210.11(C). Paired with a 20A breaker. In a typical home, 12 AWG Aluminum makes up more than half of all branch circuit wiring. XHHW-2 in conduit can use the 90°C column as a starting point for derating calculations per Table 310.15(C)(1). For dedicated 30A appliance circuits like dryers and water heaters, upsize to 10 AWG.
NEC 2020 vs NEC 2023
Ampacity values for 12 AWG aluminum are identical across NEC 2017, 2020, and 2023 editions. The only change affecting this conductor is the table renumbering from Table 310.15(B)(16) to Table 310.16 in the 2023 edition. This renumbering was part of a broader reorganization of Article 310 that also moved temperature correction factors from Table 310.15(B)(2)(a) to Table 310.15(B)(1) and bundling adjustment factors from Table 310.15(B)(3)(a) to Table 310.15(C)(1). When citing NEC references on permits or inspection reports, use the table numbers that match your state's adopted code year. States on NEC 2020 or earlier should cite Table 310.15(B)(16); states that have adopted NEC 2023 should cite Table 310.16.
Quick Reference
| Conductor | Temp | Amps | Use |
|---|---|---|---|
| 12 AWG Aluminum TW | 60°C | 15A | Wet / underground |
| 12 AWG Aluminum THW | 75°C | 20A | Standard circuits |
| 12 AWG Aluminum THHN | 90°C | 25A | Derating start only |
| 12 AWG Aluminum free air | 75/90°C | 30A / 35A | Table 310.17 |
| 12 AWG Copper THHN | 75°C | 25A | Copper equivalent |
Frequently asked questions
What is the ampacity of 12 AWG Aluminum wire?
12 AWG XHHW-2 Aluminum has a base ampacity of 25A at 90°C per NEC 2023 Table 310.16. After applying the 110.14(C) termination temperature limit, the usable ampacity is 20A for most installations. This is the value you use for circuit sizing and breaker selection.
What size breaker do I need for 12 AWG aluminum wire?
Pair 12 AWG aluminum with a 15A breaker. The wire's usable ampacity of 20A must equal or exceed the breaker rating. For continuous loads (running 3+ hours), the load must not exceed 80% of the breaker rating (12A on a 15A breaker). See the full ampacity table for all wire sizes.
Can I use 12 AWG wire in conduit?
Yes. 12 AWG XHHW-2 is rated for conduit installations including EMT, PVC, and rigid metal conduit. The 25A base ampacity applies in conduit with no more than 3 current-carrying conductors. If bundling more than 3 conductors, apply the bundling adjustment factors from NEC Table 310.15(C)(1).
How far can I run 12 AWG aluminum wire?
The maximum distance depends on load and voltage. For 12 AWG aluminum at 20A on a 240V circuit, use the voltage drop calculator with your specific distance. As a rule of thumb, keep voltage drop under 3% for branch circuits. Longer runs may require upsizing the conductor.
Common products for 12 AWG Aluminum circuits
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NEC 2023 references verified April 2026