Copper vs Aluminum AWG Wire: Ampacity, Resistance & Thermal Expansion
Copper offers superior electrical conductivity and lower thermal expansion, while aluminum provides substantial weight and cost savings in heavy feeder and service entrance conductors, requiring approximately two AWG sizes larger to match copper ampacity.
Technical Comparison & Conversion Matrix
| AWG Gauge | Copper Ampacity (75C) | Aluminum Ampacity (75C) | Weight Ratio (Cu / Al) |
|---|---|---|---|
| #8 AWG | 50 Amps | 40 Amps | 3.29x heavier |
| #6 AWG | 65 Amps | 50 Amps | 3.29x heavier |
| #4 AWG | 85 Amps | 65 Amps | 3.29x heavier |
| #2 AWG | 115 Amps | 90 Amps | 3.29x heavier |
| #1/0 AWG | 150 Amps | 120 Amps | 3.29x heavier |
| #4/0 AWG | 230 Amps | 180 Amps | 3.29x heavier |
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Frequently Asked Questions
Why is aluminum wire banned for branch circuit wiring in residential homes?
Legacy 1960s-70s aluminum branch wiring caused fires due to galvanic corrosion and thermal expansion 'creep' at screw terminals. Modern AA-8000 series aluminum alloy is safe but restricted primarily to large service entrance feeders (#4 AWG and larger).
How do you size aluminum wire compared to copper?
As a rule of thumb under NEC 310.16 tables, aluminum wire must be sized approximately two AWG sizes larger (e.g. #2 AWG aluminum replaces #4 AWG copper) to achieve equivalent current-carrying ampacity.