Copper vs Aluminum Conductors
Aluminum carries roughly 78% of the current of copper at the same size, so it takes a larger conductor to do the same job — a trade that often still pays off on large feeders.
Ampacity at the same size
For a given conductor size, aluminum is rated lower than copper. The practical consequence is that a larger aluminum conductor is often needed to match the ampacity of a copper one.
Run both through the wire size calculator and compare before choosing — on long runs aluminum also loses more voltage per foot.
Terminations and installation
Aluminum has a history of termination problems, which is why terminations must be listed for the material and installed to the manufacturer's torque specification.
Modern AA-8000 series aluminum alloy has largely addressed the early failures, but the installation discipline is still essential.
Frequently asked
- Can I splice copper to aluminum?
- Only with connectors listed for the combination. A simple twist-on connector is not acceptable and is a common cause of failures.
- Why does the voltage drop calculator show more drop for aluminum?
- Because aluminum has higher resistivity, so K is larger (about 21.2 versus 12.9 ohm-cmil/ft). The same current and distance produces more drop.
- Is aluminum allowed for branch circuits?
- Larger aluminum conductors are common for feeders and services. Small aluminum branch-circuit conductors are restricted in many applications, so check the applicable rules.
Related calculators
Educational information only — not professional engineering advice. Reference table values are pending review; see the methodology page.