Copper vs Aluminum Conductor — Ampacity, Cost, Code
Aluminum is ~30% cheaper than copper but requires one trade size up to match ampacity.
Copper has higher conductivity, smaller cross-section per amp, and broader terminal compatibility. Aluminum is significantly cheaper (per pound and per foot at equal amp rating) but requires careful termination and larger conductors.
NEC ampacity comparison
From Table 310.16 (75°C terminations):
| Amp rating | Copper | Aluminum (AA-8000) |
|---|---|---|
| 30A | 10 AWG | 8 AWG |
| 40A | 8 AWG | 6 AWG |
| 50A | 6 AWG | 4 AWG |
| 60A | 6 AWG | 4 AWG |
| 100A | 3 AWG | 1 AWG |
| 125A | 2 AWG | 1/0 |
| 150A | 1 AWG | 2/0 |
| 175A | 1/0 | 3/0 |
| 200A | 2/0 | 4/0 |
Aluminum requires one to two trade sizes larger than copper for the same ampacity.
NEC 310.12 dwelling reduction
For one-family and two-family dwellings, NEC 310.12 permits smaller conductors for the main service-entrance and main feeder only:
| Service rating | Standard copper | Dwelling copper | Standard aluminum | Dwelling aluminum |
|---|---|---|---|---|
| 100A | 3 AWG | 4 AWG | 1 AWG | 2 AWG |
| 200A | 3/0 | 2/0 | 250 kcmil | 4/0 |
| 400A | 600 kcmil | 400 kcmil | 1000 kcmil | 600 kcmil |
This is the "83% rule" and applies only at the main service point — not downstream sub-panels.
Conduit fill
NEC Table 5 conductor areas are the same for copper and aluminum at the same gauge and insulation. Switching from copper to aluminum doesn't change the fill chart count at the same gauge — but you'll use a larger gauge for aluminum, which DOES change the fill.
Example: 100A service in 1-inch EMT:
| Material | Gauge | Area × 3 conductors | Fill % |
|---|---|---|---|
| Copper (4 AWG dwelling) | 4 AWG | 3 × 0.0824 = 0.247 in² | 28.6% |
| Aluminum (2 AWG dwelling) | 2 AWG | 3 × 0.1158 = 0.347 in² | 40.2% — fails by 0.2% |
The aluminum option pushes you over the 40% limit in 1-inch EMT — you'd need 1-1/4 inch.
Termination requirements (NEC 110.14)
- Copper-only devices: Most modern residential receptacles, switches, and breakers
- CO/ALR (copper-aluminum revised) devices: Permitted with aluminum 15A/20A branch wire — increasingly rare in new construction
- Listed for aluminum (CU-AL): Required for aluminum lugs in panels, transformers, and large connectors
- Anti-oxidant compound: Required on aluminum service-entrance and feeder terminations (NEC 110.14(A) Note)
Cost rough comparison
At 2026 prices (US retail, varies by region):
| Gauge | Copper THHN $/ft | Aluminum THHN $/ft |
|---|---|---|
| 12 AWG | $0.40 | n/a (rarely sold in branch sizes) |
| 6 AWG | $1.50 | $0.65 |
| 4 AWG | $2.40 | $1.10 |
| 1/0 | $5.50 | $2.40 |
| 4/0 | $11.00 | $4.80 |
Aluminum ~50–60% of copper price at equivalent gauge. After upsizing one trade size for ampacity equivalence, aluminum still saves 20–35%.
Quick reference
- Branches (15A / 20A): Copper. Aluminum branch wiring is effectively obsolete.
- Service entrance (100A, 200A, 400A): Aluminum is cost-effective, common in residential.
- Sub-panel feeders: Aluminum frequently used; verify breaker and lug listings.
- Long underground runs: Aluminum's weight savings matters; one trade size up offsets the cost difference.
- Fill chart for either: Same Table 5 area per gauge. Pick the right gauge for the right metal.