By Peter Pollak, The Aluminum Association (Retired).
In 1914, the National Bureau of Standards and 14 copper wire manufacturers developed an electrical conductivity standard for copper.1 This International Annealed Copper Standard (IACS) enabled the development of uniform resistance tables that became the foundation for electrical engineering, codes, and standards. Back then, the possibility of another metal being used for electrification was not foreseen, so copper conductivity was assigned a value of 100%. However, this was only a measurement of volume conductivity. It completely ignored weight.
While the IACS was well intentioned and provided great utility for decades, significant changes have occurred during the last 110 years. As a result, the standard now needs to be revised. In particular, the IACS does not properly identify itself as a volume conductivity standard. The assignment of 100% for the conductivity for annealed copper is, therefore, being misinterpreted to mean that copper is the best electrical conductor. That was never the intent, as it originally was only meant to identify copper with sufficient conductivity to be used for electrical wire.
Since the development of the IACS, aluminum production has grown significantly and provides a viable alternative to copper. Aluminum has a number of benefits over copper, including higher volumes of production, lighter weight, and lower cost — all of which are not reflected in the current IACS standard.
Historical Context
In the early decades of the electrical industry (1884–1944), thousands of tons of copper were readily available, but only small amounts (ounces and pounds) of aluminum existed. Therefore, for the first 60 years of the electrical industry, only copper was available in sufficient quantity needed for electrification. There just was no other viable material. Therefore, the rapidly growing electrical industry was exclusively built with copper. As a result, copper became known as the “Metal of Electrification.”
During World War II, aluminum production began to grow significantly (Figure 1), largely due to its use in the production of airplanes during the war. After the war ended, aluminum began to be used in a wide variety of industries beyond just airplanes — ushering a new light metal age. This Age of Aluminum was first predicted by Nikola Tesla in 1900,2 who saw aluminum as the optimal material for electrical infrastructure.
By 1955, aluminum production exceeded that of copper. Today, aluminum is one of the world’s most utilized materials, second only to iron. It exceeds copper production by 300% on a weight basis and 900% by volume.3
Aluminum’s Conductivity
Based on the current standard, the volume conductivity of aluminum is 61% IACS. Thus, a larger cross-sectional area of aluminum (50%) is needed to provide the same electrical conductance as its copper equivalent.
However, aluminum is one-third the density of copper at an atomic level (Figure 2), which is not reflected in the IACS standard. The additional protons and neutrons in copper have no role in conductivity and only result in increased density. The lower density of aluminum allows for the material to achieve more conductivity per pound. As a result, the increased aluminum volume required to achieve the same volume conductivity as copper would result in only half the weight. Therefore, on a weight basis, aluminum has 200% the conductivity of copper.
Essentially, there are different ways of looking at conductivity. In 1900, before the IACS was created, Nikola Tesla recognized that the combination of aluminum’s relatively high conductivity and light weight resulted in an electrical material he believed to be superior to copper.2 At the time, he said that, in the future, copper would not be able to compete with aluminum — and aluminum would eventually annihilate copper’s use for electrification.
Value of Updating the IACS
The IACS volume conductivity standard currently misleads users to incorrectly view aluminum as being not as good of an electrical conductor as copper, while the reality is that when weight conductivity is considered, the opposite is true. Therefore, the IACS needs to be updated to include weight conductivity, so that, it can present a clear picture of both copper and aluminum’s capabilities (Table I). The revised standard with weight and volume conductivities could, for historical continuity, still retain copper’s conductivity at 100%.
Including weight conductivity within the IACS standard would also enable insight into the financial impact, as well. Currently, the price of copper is roughly $4 per pound, and aluminum is $1 per pound (Table II).4 Thus, $1 worth of aluminum provides the same electrical conductance as $8 worth of copper.
It is important to note that the price of metals varies daily with global supply and demand. The physical properties of metals, however, are constant—as they are defined by their atomic structures. Aluminum is seeing dramatic growth in both primary and secondary production, while copper production is experiencing supply challenges that could affect the electrical industry.5 Paying more for a pound of copper just results in greater weight and less conductance. Modern society can no longer afford to be confused and mislead by an outdated standard that hides electrical capability and value by omitting weight conductivity from the IACS.
Conclusion
The existing IACS needs to be updated to include weight conductivity. The revised standard should present both volume and weight conductivities, which will enable a more transparent picture of copper and aluminum capabilities from which the reader can then choose.
A global energy transformation involving electrification of transportation, integration of renewable energy sources, and other measures aimed at meeting net-zero carbon emissions by 2050 is underway. A revised IACS that includes both volume and weight conductivities could help to avoid projected copper shortages and strengthen the economics of the entire net-zero electrification endeavor. The world needs modern, up-to-date standards to successfully realize a sustainably electrified future.
References
- “International Annealed Copper Standard,” Wikipedia.
- “Tesla’s View on Uses of Aluminum,” Tesla Universe.
- Bhutada, Govind, “All the Metals We Mined in One Visualization,” Elements, October 4, 2021.
- Daily Metal Price, www.dailymetalprice.com.
- “The Future of Copper: Will the looming supply gap short-circuit the energy transition?,” S&P Global, July 2022.
Editor’s Note: This article first appeared in the June 2024 issue of Light Metal Age. To receive the current issue, please subscribe.