Electrical Properties Compared
| Property | Copper (Cu) | Aluminum (Al) | Al vs Cu |
|---|---|---|---|
| Resistivity (Ω | mm²/m at 20°C) | 0.0172 | 0.0282 | 64% higher |
| Conductivity (% IACS) | 100% | 61% | 39% lower |
| Density (g/cm³) | 8.96 | 2.70 | 70% lighter |
| Tensile strength (MPa) | 210 - 250 | 55 - 95 (AA-8000) | Lower |
| Thermal expansion coefficient | 17 × 10⁻⁶/CC | 23 × 10⁻⁶/CC | 35% more expansion |
Size Penalty: Aluminum Needs to Be Bigger
Because aluminum has lower conductivity, you must use a larger gauge to carry the same current. The standard rule: aluminum requires wire two AWG sizes larger than copper for equivalent ampacity.
- 100A circuit: 4 AWG copper → 2 AWG aluminum
- 200A service: 3/0 AWG copper → 250 kcmil aluminum
- 400A feeder: 500 kcmil copper → 700 kcmil aluminum
The larger conductor also means larger conduit - which partially offsets aluminum's cost savings and must be factored into total installed cost calculations.
Cost Analysis: Where Aluminum Wins
Aluminum is approximately 50 - 65% cheaper per pound than copper, and much lighter per unit of conductivity. For large feeders and service entrance conductors, the savings are substantial:
- 350 kcmil copper: ~$6.50/ft (current market)
- 500 kcmil aluminum (equivalent ampacity): ~$2.80/ft
- Savings on a 200 ft feeder: ~$740
For branch circuits (under 30A), copper's smaller size advantage in conduit and termination simplification typically makes it more economical despite higher material cost.
The Aluminum Problem: Terminations
Aluminum expands and contracts more than copper with temperature changes. Over cycles of heating and cooling, aluminum terminations can loosen - creating high-resistance connections that cause arcing and fires. This gave aluminum wiring a bad reputation in residential construction in the 1960s - 70s.
Modern solutions that make aluminum safe:
- AA-8000 series alloy conductors (NEC 310.14) - significantly better creep resistance than old 1350 alloy
- CO/ALR listed devices - receptacles and switches rated for both copper and aluminum
- Anti-oxidant compound (Noalox, Penetrox) - applied at all terminations to prevent oxidation layer formation
- Rated termination lugs - all lugs must be marked "AL" or "CU/AL" - copper-only lugs cannot be used
- Torque specifications - aluminum terminations have specific torque requirements; under-torque is as dangerous as over-torque
NEC Code Requirements for Aluminum
- NEC 310.14 - Aluminum conductors must be AA-8000 alloy for 8 AWG through 1000 kcmil
- NEC 110.14 - Termination equipment must be rated for the conductor material being used
- Aluminum prohibited for 10 AWG and smaller branch circuits in residential occupancies (many AHJs enforce this; not explicit in NEC but common local amendment)
Case Study: A 250 ft Feeder Run
A panel upgrade project needed a 200A feeder run 250 ft from the main service to a detached shop. Two options were priced:
- Copper option: 3/0 AWG copper, ~$11.80/ft installed material cost - total ~$2,950
- Aluminum option: 250 kcmil AA-8000 aluminum, ~$5.40/ft installed material cost - total ~$1,350
The aluminum option saved roughly $1,600 in conductor cost alone, even after accounting for the larger conduit needed. Both options were also checked for voltage drop at this distance using the standard formula - see our voltage drop calculation guide for the worked math. At 250 ft, both conductors stayed under the 3% recommended limit, but the larger aluminum CM area meant its voltage drop was actually slightly lower than the smaller copper conductor for the same load.
Don't Forget Ampacity Derating
Whichever metal you choose, the conductor's table ampacity still needs to be derated for ambient temperature and any bundling with other current-carrying conductors in the same raceway. Aluminum's larger required CM area for a given ampacity can actually help here, since the same percentage derating leaves more margin in absolute amps. See our NEC 310.15 derating guide for the full correction factor tables.
Where Each Metal Belongs
Use Copper When:
- Branch circuits in buildings (10 AWG and smaller)
- High-flex applications (cable carriers, pendant drops)
- High-temperature environments (silicone or mica cable)
- Marine, mining, or corrosive environments
- Control wiring and instrumentation
Use Aluminum When:
- Service entrance and utility feeders (2 AWG and larger)
- Long overhead power distribution runs (ACSR)
- Large motor feeders in industrial plants (350 kcmil+)
- Overhead transmission lines (virtually all are aluminum)
- Cost-sensitive large infrastructure projects
Frequently Asked Questions
Is aluminum wiring actually safe to use today?
Yes, when installed correctly with modern materials. The reputation problems came from 1960s-70s era 1350 alloy aluminum, which had poor creep resistance at terminations. Today's AA-8000 series alloy conductors, CO/ALR-listed devices, anti-oxidant compound, and correctly torqued AL-rated lugs eliminate the historical failure mode.
How much bigger does aluminum wire need to be than copper?
As a rule of thumb, two AWG sizes larger than copper for equivalent ampacity, because of aluminum's lower conductivity (61% IACS vs copper's 100%). A 100A circuit needs 4 AWG copper or 2 AWG aluminum; a 200A service needs 3/0 AWG copper or 250 kcmil aluminum.
Can copper and aluminum conductors be connected together?
Only through devices and connectors specifically listed for dissimilar metals, such as CO/ALR-rated devices or AL/CU dual-rated lugs, with anti-oxidant compound applied. Direct contact without a rated connector causes galvanic corrosion, a common cause of overheating at the joint.
Source Copper or Aluminum Cable Factory-Direct
Shanghai Unicorn manufactures both copper and aluminum conductor cables from our Shanghai factory. AA-8000 alloy aluminum conductors, UL/CSA listed, with anti-oxidant treatment available. Factory-direct pricing with volume discounts.