10 AWG THHN Aluminum Ampacity & Derating
Calculation Walkthrough
Per NEC 2023 Table 310.16, 10 AWG aluminum THHN (90°C column) = 35A 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 30A 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 10 AWG aluminum carrying 30A at 240V single-phase over a 100-foot one-way run: Vd = (2 × L × I × R) / 1000. The resistance per 1000 ft for 10 AWG aluminum at 75°C is used from NEC Chapter 9 Table 8. At 30A and 100 ft, the drop is 12.2V (5.1%). For longer runs or higher loads, use the voltage drop calculator with your specific distance and load.
Common Applications
10 AWG THHN aluminum at 30A has Table 310.16 ampacity for calculation work, but NEC 240.4(D) limits 10 AWG aluminum to a 25A overcurrent device. Do not use this conductor as the aluminum equivalent of 10 AWG copper on a 30A dryer, water-heater, or appliance circuit. For ordinary 30A branch circuits, use 10 AWG copper or upsize the aluminum conductor based on the load, wiring method, terminal listings, and local AHJ requirements. THHN in conduit can use the 90°C column as a starting point for derating calculations per Table 310.15(C)(1), but that does not override the 25A small-conductor breaker ceiling. Aluminum at small branch-circuit sizes is unusual; verify AL-rated equipment and torque requirements before installation.
NEC 2020 vs NEC 2023
Ampacity values for 10 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 |
|---|---|---|---|
| 10 AWG Aluminum TW | 60°C | 25A | Wet / underground |
| 10 AWG Aluminum THW | 75°C | 30A | Standard circuits |
| 10 AWG Aluminum THHN | 90°C | 35A | Derating start only |
| 10 AWG Aluminum free air | 75/90°C | 40A / 45A | Table 310.17 |
| 10 AWG Copper THHN | 75°C | 35A | Copper equivalent |
Frequently asked questions
What is the ampacity of 10 AWG Aluminum wire?
10 AWG THHN Aluminum has a base ampacity of 35A at 90°C per NEC 2023 Table 310.16. After applying the 110.14(C) termination temperature limit, the usable ampacity is 30A for most installations. This is the value you use for circuit sizing and breaker selection.
What size breaker do I need for 10 AWG aluminum wire?
Pair 10 AWG aluminum with a 25A breaker. The wire's usable ampacity of 30A must equal or exceed the breaker rating. For continuous loads (running 3+ hours), the load must not exceed 80% of the breaker rating (20A on a 25A breaker). See the full ampacity table for all wire sizes.
Can I use 10 AWG wire in conduit?
Yes. 10 AWG THHN is rated for conduit installations including EMT, PVC, and rigid metal conduit. The 35A 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 10 AWG aluminum wire?
The maximum distance depends on load and voltage. For 10 AWG aluminum at 30A 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 10 AWG Aluminum circuits
As an Amazon Associate we earn from qualifying purchases.
NEC 2023 references verified February 2026