Electrical Resistivity of Aluminium at 20 °C

Aluminium conducts about 61 % as well as copper by volume but is only 30 % as dense, so per kilogram it is roughly twice as good a conductor: the reason every overhead transmission line and most large service entrances are aluminium. Sizing rule of thumb: to match a copper conductor's ampacity you go up about two AWG sizes. The trade constant for voltage drop is K = 21.2 Ω·cmil/ft against copper's 12.9.

The failure mode is the connection, not the conductor. Aluminium forms a tough insulating oxide the instant it is exposed, it creeps under the sustained pressure of a screw terminal, and its expansion coefficient differs from that of the brass or copper hardware clamping it. Cycle that joint and contact pressure decays, resistance climbs and the terminal overheats: the mechanism behind the 1960s-70s aluminium branch-circuit fires and the reason for AL/CU-rated devices, antioxidant compound, correct torque and periodic retorque. The wire is fine; the interface is what needs engineering.