Aluminium versus copper in variable frequency drive systems - Which one fits better?

Aluminium and copper in variable frequency drive systems: Which one is the right choice?

In variable frequency drive systems, electric conductors are key parts. Whether it is transformer winding, core of power cable, VFD internal busbars or stator and rotor winding of the main machine – all of them are made of electrically highly conductive material.
Which conductor is the right choice for the transformer, VFD or motor? Aluminium or copper?
We make a small dive into the subject in this blog post. And while our focus stays technical, we will also address the commercial and strategic dimension along with sustainability considerations.

Champions in electric conductivity

Measured by electric conductivity, the best conductors are:

1. Silver (Ag)

2. Copper (Cu)

3. Gold (Au)

4. Aluminium (Al)

Silver is the best electric conductor. Nevertheless, the price is much higher than copper and the relative difference in conductivity is just about 6%.

Gold is used for contacts in small electronics. Not because it is the best conductor (silver and copper have higher conductivity) but due to other valuable properties: no oxidation or corrosion, stable contact resistance, reliable performance in harsh environment or elasticity/deformation improving the contact area. Obviously, its very high price and scarcity prevent the use in power applications.

Copper offers almost the same conductivity as silver at a fraction of the cost. That makes copper the dominant metal in electrical wiring.

Aluminium ranks number 4. It is still an excellent conductor. Moreover, aluminium is light due to low density and on material price by far the most affordable metal.

Conductors used in power equipment

Based on previous paragraph, the key two electric conductors in power applications are aluminium and copper. We will look at both of them in detail.

Copper versus aluminium

Copper is a superior electric conductor with many excellent physical properties. Those make copper extremely popular in electrical engineering. Below we compare selected technical properties of aluminium. As some benefits of aluminium may be less known, we aim to highlight them. Nevertheless, it is not the intention to downgrade copper.

Mass

Aluminium is lighter than copper as it has much lower density. It allows to build equipment with lower weight.

Conductivity

Copper has higher conductivity for the same conductor cross section.

Thermal capacity

Aluminium has higher specific (relative) thermal capacity.

Heat capacity ratio

Aluminium has approx. 15% higher heat capacity –> better thermal stability during rapid heating, such as e.g. short circuit condition.

Heat losses

Windings made of aluminium can have approximately the same losses as copper windings (of course using larger cross section) and still having a commercial advantage.

Eddy losses

Aluminium has larger penetration depth meaning that skin effect is less prominent. Thus, eddy losses are lower and there is less risk of hot spots.

Thermal expansion

Aluminium has larger thermal expansion coefficient. That may be a little disadvantage in some cases but a particular benefit for dry type transformers (read further below).

Oxidation

Both copper and aluminium oxidize when exposed to outside air. The oxidation process of aluminium is much faster than copper. Moreover, the oxide layer has very high specific resistivity. Therefore, oxidation of the contact surfaces must be strictly avoided.

Voltage distribution

Aluminium windings have better (more equal) voltage distribution over the winding turns for base frequency as well as for impulse overvoltage. Aluminium reduces corona effect.

Sourcing

Aluminium price is more stable since the production of aluminium is roughly twice as large as the production of copper. In contrast, copper resources are more limited which pushes the market prices up.

Sustainability

Both metals are excellent from circularity perspective and can be recycled repeatedly (indefinite number of cycles). Production of aluminium is more energy intensive than copper. However, when using recycled aluminium the energy demand reduces dramatically. According to some studies, the energy savings go up to 95% (recycling compared to primary production) [2].

Conductors in drive system components

What conductor fits for transformer winding, VFD busbars or motor winding? What is common practice and where is future potential? How can aluminium increase your competitiveness? Which areas remain the domain of copper conductor? For the full content purchase our premium subscription or individual publications.

Summary

Copper and aluminum are both extensively used as winding materials for electric equipment. Depending on the application, one or the other conductor is a better fit.
Copper has higher relative conductivity allowing smaller volume and smaller dimensions, but is also heavier and more expensive. Copper is preferred in case the equipment shall have minimum volume (space restrictions) or higher mechanical strength is required (centrifugal forces acting on rotor windings).
Aluminum is lighter and its lower relative conductivity is compensated by larger cross-section. Although the volume is larger, the total weight is still lower compared to copper. Higher thermal capacity of aluminum is beneficial in overload or short circuit condition where lot of heat is dissipated within short time. Another advantage of aluminium is better voltage distribution at power frequency as well as impulse voltage.
The price of aluminium is significantly lower – about 8.8 times less per Ampere in September 2026 (it was “only” 6 times in 2014). On the equipment level the ratio is of course less. Still, aluminium typically leads to significantly lower equipment price.

References

[1] Electrical conductivity – The role of aluminium extrusions (whitepaper), Hydro, 2026
[2] Sustainability Assessment in Aluminum and Copper Industries, Nature index, available online, https://www.nature.com/nature-index/topics/l4/sustainability-assessment-in-aluminum-and-copper-industries
[3] A. Burdova, T. Vana: Cast resin transformers – Aluminium versus copper (original in Czech), Power-Energo s.r.o.
[4] Aluminum versus Copper Conductors – Application of Aluminum conductors in Bus Way systems for more sustainable Data Centers, Siemens Center of Competence Data Centers
[5] Power cable basics, MB Drive Services, November 2021, available online, https://mb-drive-services.com/power-cable-basics/
[6] What power connection is better: cable or busbar? MB Drive Services, December 2022, available online, https://mb-drive-services.com/what-power-connection-is-better-cable-or-busbar/

Aluminium versus copper in variable frequency drive systems – Which one fits better?

Published by admin on September 21, 2026September 21, 2026

Aluminium and copper in variable frequency drive systems: Which one is the right choice?

Champions in electric conductivity

Conductors used in power equipment

Copper versus aluminium