For a standard 200A residential service, the NEC mandates 4/0 AWG aluminum (per NEC 310.12). For a 100A subpanel feeder, use 1 AWG aluminum (rated exactly 100A at 75°C) or 1/0 AWG if you need margin for voltage drop. This aluminum wire sizing chart is based on the 2023 NEC Table 310.16. We will cover exactly which temperature column applies to your lugs, how to derate for conduit bundling, and provide a concrete decision tree so you can buy the right SER cable or THHN wire without a second trip to the electrical supply house.
How to Read the Aluminum Wire Sizing Chart
The most common mistake DIYers and junior apprentices make is reading the wrong temperature column. The NEC publishes ampacities across three main columns: 60°C, 75°C, and 90°C. Here is how to determine which column applies to your installation:
- The 75°C Column (Your Default): Almost all modern breakers (Square D, Eaton, Siemens) and panelboard lugs are rated for 75°C terminations. Unless your equipment is explicitly marked otherwise, this is the column that dictates your maximum breaker size.
- The 90°C Column (For Derating Only): Modern aluminum wire insulation (like THHN, THWN-2, and XHHW-2) is rated for 90°C. However, you cannot use this higher ampacity to size your breaker because the breaker lug will melt before the wire does. You only use the 90°C column as the starting baseline when calculating derating adjustments for conduit bundling or high ambient temperatures.
- The 60°C Column (Legacy/Small Circuits): Rarely used for aluminum feeders today, this applies to older equipment or specific small-gauge circuits where termination ratings are unknown.
The Complete Aluminum Wire Sizing Chart (NEC Table 310.16)
Below is the benchmark reference for aluminum conductors. We have highlighted the most queried feeder sizes for quick bookmarking. Source standard: NFPA 70 (2023 NEC) Table 310.16.
| AWG / kcmil | 60°C (Legacy) | 75°C (Termination Limit) | 90°C (Derating Base) |
|---|---|---|---|
| 8 AWG | 30A | 40A | 45A |
| 6 AWG | 40A | 50A | 60A |
| 4 AWG | 55A | 65A | 75A |
| 3 AWG | 65A | 75A | 85A |
| 2 AWG | 75A | 90A | 100A |
| 1 AWG (100A Feeder) | 85A | 100A | 115A |
| 1/0 AWG | 100A | 120A | 135A |
| 2/0 AWG | 115A | 135A | 150A |
| 3/0 AWG | 130A | 155A | 170A |
| 4/0 AWG (200A Service)* | 150A | 180A | 205A |
| 250 kcmil | 170A | 205A | 230A |
| 350 kcmil | 210A | 250A | 280A |
| 500 kcmil (400A Feeder) | 260A | 310A | 350A |
*NEC 310.12(A) Exception: While 4/0 AWG aluminum is rated 180A at 75°C, the code specifically permits it for 200A residential service entrance conductors.
Derating and Installation Adjustments
The base values above assume ideal conditions. When you bundle multiple current-carrying conductors in a single conduit or run them through hot environments, the wire cannot dissipate heat as effectively. This is where the 90°C column saves the day.
How derating modifies the base value: You start with the 90°C ampacity, multiply it by the NEC bundling adjustment factor (Table 310.15(C)(1)), and then compare that result to the 75°C termination limit. Your final breaker size cannot exceed the lower of these two numbers.
You are pulling four current-carrying 2 AWG aluminum THHN wires through a conduit in an attic that hits 110°F (43°C).
1. Base 90°C Ampacity: 100A.
2. Bundling Derating (4 conductors = 80%): 100A × 0.80 = 80A.
3. Temperature Correction (110°F = 0.87 multiplier): 80A × 0.87 = 69.6A.
4. Compare to 75°C Limit: The 75°C limit for 2 AWG is 90A. Since 69.6A is lower than 90A, your derated ampacity is 69.6A.
Result: You must size your breaker to 60A, or step up to 1 AWG aluminum wire to maintain a higher load capacity.
Decision Path: Picking Your Exact Aluminum Feeder Size
Use this decision tree to terminate your sizing process with a concrete purchase order. These recommendations assume standard residential 120/240V split-phase systems and standard 75°C rated lugs.
- IF you are wiring a 200A Main Residential Service Entrance → Buy 4/0 AWG (Use 4-4-4-6 SER cable or individual 4/0 THHN in conduit).
- IF you are wiring a 100A Subpanel and the run is under 75 feet → Buy 1 AWG (Use 1-1-1-3 SER cable).
- IF you are wiring a 100A Subpanel and the run is over 75 feet → Buy 1/0 AWG (Stepping up mitigates voltage drop over long distances).
- IF you are wiring a 60A EV Charger or Spa disconnect → Buy 4 AWG (Rated 65A at 75°C, perfectly matched for a 60A breaker).
- IF you are wiring a 400A commercial or large estate feeder → Buy 500 kcmil (Rated 310A at 75°C, but standard practice rounds up to 500 kcmil or parallel runs for 400A main lugs).
What This Chart Cannot Tell You
An ampacity chart is only half the engineering equation. Before you pull the wire, you must account for three physical realities that the NEC table ignores:
- Voltage Drop: The NEC ampacity tables do not enforce the recommended 3% voltage drop limit for branch circuits or feeders. If you are running a 100A aluminum feeder 150 feet to a detached workshop, 1 AWG will legally carry the current, but your 240V will drop to roughly 228V under full load, causing motors to overheat. Use the Southwire Voltage Drop Calculator to verify your distance, and step up one AWG size if drop exceeds 3%.
- Physical Lug Fitment: Aluminum wire has a larger physical diameter than copper for the same ampacity. A 500 kcmil aluminum wire will not physically fit into the lugs of a standard 100A or 200A breaker without a mechanical lug reducer. Always check the breaker datasheet for maximum wire termination sizes before buying large kcmil cable.
- Oxidation and Torque: Aluminum oxidizes rapidly when exposed to air, creating a resistive layer that causes heat buildup and fires. You must apply an anti-oxidant compound (like Noalox) to stripped aluminum conductors before terminating them. Furthermore, aluminum creeps under pressure; you must use a calibrated torque screwdriver or wrench to tighten lugs to the exact inch-pound specification printed on the breaker or panel label. Hand-tightening aluminum is a primary cause of panel fires.
Always verify your final wire and breaker selections with your local Authority Having Jurisdiction (AHJ), as local amendments to the NEC can dictate stricter sizing rules for specific municipalities.
