Copper prices have made this question unavoidable: can I use aluminum instead? For big feeders and services, the answer is usually yes — with real savings. For branch circuits, copper remains the standard. Here's the full picture.
The Core Trade-Off
Aluminum conducts about 61% as well as copper, so an aluminum conductor must be roughly two gauge sizes larger to carry the same current. But aluminum is much cheaper per pound and weighs 30% as much as copper, so even after upsizing, aluminum wire typically costs 40–60% less than the copper equivalent for the same ampacity.
Equivalent Sizes at a Glance (75°C)
| Ampacity | Copper | Aluminum |
|---|---|---|
| 100 A | #3 AWG | #1 AWG |
| 125 A | #1 AWG | 2/0 AWG |
| 150 A | 1/0 AWG | 3/0 AWG |
| 200 A | 3/0 AWG | 250 MCM (4/0 for dwelling services per NEC 310.12) |
| 400 A | 500 MCM | 750 MCM |
What About the Aluminum Wiring Horror Stories?
They're real — and they're about a different product. The failures of the 1960s–70s involved small-gauge solid aluminum branch wiring (AA-1350 alloy) on devices never designed for it. Modern aluminum building wire uses AA-8000 series alloy (required by NEC 310.14), which behaves far better under thermal cycling, and it's used almost exclusively in large stranded feeder and service sizes with lugs listed for aluminum. Millions of services and feeders run on it without issue.
Doing Aluminum Right
- Use AL-rated terminations (AL9CU / dual-rated lugs) — standard on modern panels and breakers
- Apply oxide inhibitor on terminations where the manufacturer requires it
- Torque to spec — under- and over-torqued lugs cause most aluminum problems (true for copper too)
- Plan for diameter: upsized aluminum needs bigger conduit — check fill
Where Each Wins
| Application | Best choice | Why |
|---|---|---|
| Branch circuits (15–30 A) | Copper | Devices designed for copper; small sizes cheap anyway |
| Residential service (100–200 A) | Aluminum | Big savings, standard practice |
| Commercial feeders | Aluminum (usually) | Savings scale with size; verify lug ratings |
| Motor/equipment terminations with vibration | Copper | Better cold-flow behavior at stressed terminations |
| Long underground runs | Aluminum | Cost per foot dominates; voltage drop handled by upsizing |
Check Voltage Drop Both Ways
Aluminum's higher resistance means voltage drop bites sooner on long runs. Our wire size calculator handles both materials — enter your load and distance and compare.
We stock copper THHN, aluminum RHH/RHW-2/USE-2, and aluminum service entrance cable — all cut to length.
