How does copper compare to aluminium as a conductor for electricity?

Copper and aluminium are both extensively used as electrical conductors. How to compare a copper and an aluminium conductor? Cf the table below:

• Copper sets the standard for conductivity. Aluminium has about 60% of copper's conductivity, or copper is about 66% more conductive for electricity.
• Aluminium is 3.3 times lighter than copper.
• Hence, for the same current carrying capacity and the same efficiency (in ohmic regime):
  • The copper conductor will be 3.3/1.66 = 2 times heavier.
  • An equivalent aluminium conductor will be 1.66 larger in cross session, hence have 1.29 times the diameter., requiring more insulation, more steel, more oil, ... Or the copper conductor can save 22% (= 0.29/1.29) on materials surrounding the conductor.

In practice, conductor diameters are rarely available in 66% diameter increments and small differences in cable efficiency will be observed when comparing a copper conductor with a 1-size-up aluminium conductor. In addition, for power cables, other factors such as eddy currents and the proximity effect define a cable's efficiency. As for electrical machines such as motors and transformers, energy efficiency varies as a function of other design parameters besides conductor cross section.

Therefore, typical material savings in the range of 8-25% can be expected from the benefit of copper's compactness:

• Insulated cables: savings on the amount of insulation materials between 10 and 25%.
• Distribution transformers: 8-12% savings in steel when replacing the high-voltage winding with copper.
• Induction motors: 8-13% savings in steel when using a copper rotor induction motor.

References

• IEC 60228, Conductors of insulated cables
• Preparatory study for the review of Commission Regulation 548/2014 on ecodesign requirements for small, medium and large power transformers, July 2017, https://transformers.vito.be/sites/transformers.vito.be/files/attachments/ec_dg_growth_lot2_Transformer_Jul2017b.pdf - accessed June 23, 2022
• Francesco Parasiliti, Marco Villani, New induction motor designs with Aluminum and Copper rotor specially developed to reach the IE3 efficiency level, University of L'Aquila, Internal report, June 2012

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Last update: October 26, 2022