Ampacity of #2 Aluminum Wire: NEC Chart, Breaker Sizing, and Derating

The Direct Answer: Ampacity of #2 Aluminum Wire

When sizing feeders or branch circuits, the ampacity of #2 aluminum wire depends entirely on the temperature rating of your equipment terminations, not just the wire insulation. Per NFPA 70 (NEC) Table 310.16, the base ampacities for #2 AWG aluminum are:

• 60°C Column: 75 Amps
• 75°C Column: 90 Amps
• 90°C Column: 100 Amps

NEC Table 310.16: #2 AWG Aluminum Ampacity Chart

To use this chart correctly, you must understand its columns. The temperature headings (60°C, 75°C, 90°C) refer to the weakest link in your circuit—usually the breaker lug or panel busbar—not the wire's insulation. Even if you pull THHN/THWN-2 wire (which has 90°C insulation), you are legally bound to the lower temperature column if your termination points are rated lower.

Below is the bookmark-friendly reference for #2 AWG aluminum, alongside adjacent sizes for quick comparison. All values assume copper-clad aluminum or pure aluminum, not more than three current-carrying conductors in a raceway, and an ambient temperature of 30°C (86°F).

Which Temperature Column Actually Applies to Your Install?

The rule governing this is NEC 110.14(C) - Termination Provisions. This section dictates that the ampacity of a conductor must be selected based on the lowest temperature rating of any connected termination, conductor, or device.

Here is how to determine your column in the field:

• The 60°C Column: Applies if you are connecting to older equipment (pre-1990s), equipment marked specifically for 60°C, or circuits rated 100A or less where the termination temperature is completely unmarked. (Note: Most modern breakers up to 100A are marked 75°C, overriding the unmarked default).
• The 75°C Column: This is your working column for almost all modern residential panels (Square D Homeline/QO, Eaton BR/CH, Siemens). If your breaker lug is stamped '75°C' or 'AL/CU 75°C', your #2 aluminum wire is capped at 90 amps.
• The 90°C Column: You can only use the 100A rating for overcurrent protection if every single termination point (breaker, lug, busbar, disconnect) is explicitly rated and marked for 90°C. This is exceptionally rare in standard residential subpanels.

Derating Factors: When 90 Amps Isn't 90 Amps

Base ampacity assumes ideal conditions: 30°C ambient temperature and no more than three current-carrying conductors (CCCs) in a conduit. When conditions change, you must apply adjustment factors per NEC Article 310.15.

The Golden Rule of Derating: You calculate derating using the 90°C column, but the final result cannot exceed the 75°C column limit for termination purposes.

Worked Example: Four Conductors in a Conduit

Imagine you are pulling two hots, a neutral, and a ground for a 240V subpanel feeder. If the neutral carries unbalanced current (e.g., multi-wire branch circuits or significant 120V loads in the subpanel), it counts as a CCC. That gives you 3 CCCs. But if you add a second circuit to that same conduit, you now have 4 or more CCCs, triggering NEC Table 310.15(C)(1) adjustment factors.

1. Start at 90°C: #2 Aluminum at 90°C = 100A.
2. Apply Adjustment: 4 to 6 CCCs requires an 80% multiplier.
3. Calculate: 100A × 0.80 = 80 Amps.
4. Check Termination Limit: Is 80A less than the 75°C limit (90A)? Yes.

Result: Your derated ampacity is now 80A. You must protect this #2 aluminum wire with an 80A breaker, not a 90A breaker.

What the Ampacity Table Cannot Tell You

NEC Table 310.16 only addresses thermal limits (preventing the wire insulation from melting). It completely ignores voltage drop and physical installation realities.

1. Voltage Drop (NEC 215.2 Informational Note)

While the NEC recommends keeping voltage drop under 3% for feeders, aluminum has higher resistance than copper. If your #2 aluminum feeder run exceeds 110 feet on a 240V circuit loaded to 90A, you will exceed a 3% voltage drop (7.2V). For runs over 120 feet, step up to #1 AWG or 1/0 AWG aluminum to maintain power quality, especially if the subpanel feeds sensitive electronics or motor loads.

2. Physical Lug Fitment and Torque

Ampacity charts don't tell you if the wire will physically fit into the breaker. Some older 90A breaker frames struggle to accept the physical diameter of stranded #2 AWG aluminum without flaring the strands. Always use a proper wire ferrule or ensure the strands are twisted tightly. Furthermore, NEC 110.14(D) requires you to torque the lug to the manufacturer's specification (typically 45 in-lbs for a 90A Square D breaker). Use a calibrated inch-pound torque screwdriver; aluminum creeps under pressure and loose lugs will arc and fail.

3. Local AHJ Amendments

Some municipalities ban aluminum branch wiring entirely or require specific anti-oxidant compounds (like Noalox) on all aluminum terminations, regardless of whether the wire is modern AA-8000 series alloy. Always check with your local inspector.

Final Decision Tree: Sizing Your Breaker for #2 Al

Use this decision matrix to finalize your overcurrent protection device (OCPD) selection for #2 aluminum wire.

Final Concrete Pick: If you are wiring a standard detached garage or shed subpanel under 100 feet away, buy #2 AWG XHHW-2 or THWN-2 aluminum, pair it with a 90A 2-pole breaker (e.g., Square D HOM290 or Eaton BR290), apply Noalox to the stripped strands, and torque the lugs exactly to the value printed on the breaker label.