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/°C | 23 × 10⁻⁶/°C | 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)
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
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.