How does copper set the standard for electrical conductivity?

As the best electrical conductor among non-precious metals, 70% of copper is used for conductivity applications. How does copper set the standard for conductivity?

In 1913 (revised in 1925), the International Electrotechnical Commission (IEC) adopted the German standard for the electrical conductivity of copper. This International Annealed Copper Standard (IACS) has become the main reference for electrical conductivity, and the conductivity of copper and aluminium alloys are usually expressed in terms of IACS.

The IACS standard describes the properties for 100% IACS at 20°C:

• Volume resistivity: 1/58 = 0.017241 ohm-mm2/m
• Temperature coefficient of volume resistivity = 68e-6 ohm-mm2/m.K
• Density: 8,890 kg/m3
• Mass resistivity: 0.15328 ohm-gramme/m2
• Temperature coefficient of mass resistivity = 0.00393/K

Since the adoption of IEC 60028, copper processing technologies have improved and, as a result, routine production of high-conductivity copper can reach or exceed 101% IACS.

The conductivity of other metals can be expressed in IACS as well:

References

• IEC 60028:1925 - International standard of resistance for copper, available from https://webstore.iec.ch/publication/98 (checked October 28, 2021)
• White paper, electrical conductors, European Copper Institute, June 2019

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Last update: June 1, 2022