For a standard 100-amp circuit using aluminum wire, you need 1 AWG if your terminations are rated for 75°C (the modern standard), or 1/0 AWG if any termination in the circuit is limited to 60°C. Aluminum is lighter and significantly cheaper than copper, making it the default choice for 100-amp feeder runs to subpanels, EV chargers, and workshop outbuildings. However, because aluminum has a higher coefficient of thermal expansion and lower conductivity than copper, strict adherence to the NFPA 70: National Electrical Code (NEC) ampacity tables and torque specifications is non-negotiable to prevent lug overheating and fire hazards.
The 100 Amp Aluminum Wire Size Chart (NEC Table 310.16)
How to read this table: This chart extracts the Aluminum (or Copper-Clad Aluminum) rows from NEC Table 310.16. The three temperature columns (60°C, 75°C, 90°C) represent the insulation rating of the wire and the temperature limit of the equipment terminations. Most modern THHN/THWN-2 wire is 90°C rated, but you must use the column that matches the lowest temperature rating of any connected lug, breaker, or busbar. The 90°C column is strictly used as a starting point for calculating derating factors, never for the final termination ampacity.
| Wire Size (AWG/kcmil) | 60°C Column (140°F) | 75°C Column (167°F) | 90°C Column (194°F) |
|---|---|---|---|
| 4 AWG | 55A | 65A | 75A |
| 3 AWG | 65A | 75A | 85A |
| 2 AWG | 75A | 90A | 100A |
| 1 AWG | 85A | 100A | 115A |
| 1/0 AWG | 100A | 120A | 135A |
| 2/0 AWG | 115A | 135A | 150A |
Which Temperature Column Applies to Your Installation?
The most common mistake DIYers make when reading a 100 amp aluminum wire size chart is defaulting to the 90°C column because the wire jacket (like THHN) is printed with "90°C Dry / 75°C Wet". This is a code violation. NEC 110.14(C) dictates the "weakest link" rule: your final ampacity is limited by the lowest temperature rating of any termination in the circuit.
- The 60°C Column: Apply this if you are connecting to older equipment (pre-1990s panels), specific legacy disconnect switches, or if the manufacturer's documentation explicitly limits lugs to 60°C. If this applies, 1 AWG is insufficient; you must use 1/0 AWG.
- The 75°C Column: This is the modern standard. Virtually all contemporary residential load centers (Square D QO/Homeline, Eaton BR, Siemens) and 100-amp molded-case breakers feature 75°C rated lugs. Under this column, 1 AWG aluminum is perfectly legal and safe for 100 amps.
- The 90°C Column: You cannot terminate a 100A breaker with wire sized solely on the 90°C column. This column exists exclusively to give you a higher baseline ampacity before applying ambient temperature or conduit bundling derating factors.
How Derating Factors Modify Your Base Wire Size
The ampacities in the chart above assume two ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a single raceway. When your installation deviates from these baselines, you must apply derating factors from NEC 310.15.
Example: Bundling in Conduit
Imagine you are pulling four current-carrying conductors (e.g., two hots, a neutral, and a switched leg for a multi-wire setup) through a single PVC conduit to a detached garage. NEC Table 310.15(C)(1) requires an 80% adjustment factor for 4-6 conductors.
- Start with the 90°C column for 1 AWG THHN aluminum: 115A.
- Multiply by the 80% bundling derating factor: 115A × 0.80 = 92A.
- Because 92A is less than your 100A breaker rating, 1 AWG is now legally undersized.
- You must upsize to 1/0 AWG (90°C rating of 135A × 0.80 = 108A), which safely clears the 100A threshold.
Similarly, if your conduit runs across a hot attic space where ambient temperatures reach 110°F (43°C), you must apply a temperature correction factor (0.82 for the 90°C column) before checking your final ampacity. Consult EC&M National Electrical Code Resources for comprehensive derating matrices.
What This Table Cannot Tell You: Voltage Drop & Local Code
An ampacity chart only tells you the maximum current a wire can carry before its insulation melts. It does not account for voltage drop, which is the loss of electrical pressure over distance due to the inherent resistance of the aluminum.
For a 100-amp, 240V feeder run to a subpanel located 150 feet away, 1 AWG aluminum will experience roughly a 4.5% voltage drop at full load. While the NEC only strictly mandates voltage drop calculations for specific high-sensitivity equipment, industry best practice (and many local AHJs) limits feeder voltage drop to 3%. To maintain a 3% drop or less over 150 feet at 100 amps, you must upsize from 1 AWG to 1/0 AWG or even 2/0 AWG. Always run your specific distance through a voltage drop calculator before purchasing wire.
Furthermore, this chart represents NEC-style guidance. Your local Authority Having Jurisdiction (AHJ) or municipal inspector may have local amendments that require larger minimum feeder sizes for specific outbuildings or mandate copper-only for certain 100A applications. Always verify with your local building department.
Frequently Asked Questions About 100 Amp Aluminum Wire
Can I use 2 AWG aluminum wire for a 100 amp subpanel?
No. In the 75°C column, 2 AWG aluminum is only rated for 90 amps. While 2 AWG copper is rated for 115 amps (and is often used for 100A circuits), confusing copper and aluminum ampacities is a frequent and dangerous error. For a 100-amp breaker, the minimum aluminum size is 1 AWG, provided your terminations are 75°C rated.
What size aluminum wire do I need for a 100 amp service 200 feet away?
At 200 feet, voltage drop becomes the governing factor, not just thermal ampacity. To keep voltage drop under the recommended 3% for a 240V, 100-amp load over 200 feet, you should use 2/0 AWG aluminum. While 1/0 AWG might technically keep you just under 4% drop, upsizing to 2/0 AWG ensures heavy loads (like starting a well pump or running a welder) won't cause noticeable dimming or equipment stress at the subpanel.
Why does my 100 amp breaker require 1/0 AWG aluminum instead of 1 AWG?
If your breaker or panel manufacturer specifies 1/0 AWG for a 100A circuit, it is usually because the specific lug design on that breaker is only rated for 60°C, or the breaker requires a minimum wire size to physically fit and clamp securely in the lug barrel. Always read the wiring diagram printed on the breaker label; the manufacturer's listed instructions override general NEC table assumptions per NEC 110.3(B).
