Beyond conductivity, the differences in other critical technical characteristics between copper and aluminum are so significant (density being one glaring example) that their application domains have always been quite distinct. There has been little change in this regard, nor is it likely to change.

The only truly novel development in recent years has been the introduction of cast copper.

There are copper busbars, aluminum busbars and copper busbars made from aluminum.

In electrical engineering, there are actually only three, now four, areas where aluminum and copper compete in the same sub-markets:

Practical applications of copper and aluminum in electrical engineering - Areas where both metals are viable options are rare.

Medium Voltage Cables

Here, the decision is between lesser evils: a larger cable cross-section or heavier cable weight? Generally, aluminum cables are much cheaper. However, it's still worth noting that copper cables offer greater ductility and are less susceptible to electrical contact issues, thus offering a higher safety margin compared to their aluminum counterparts. Due to their smaller cross-section, copper cables are also easier to install, as the stiffness of a cable depends on the square of its cross-sectional area, thus on the fourth power of its diameter!

Very small stranded copper cables are also available, whereas stranded aluminum cables are only available for nominal cross-sectional areas of at least 10 square millimeters, still being quite thick compared to copper cables of equivalent size. For technical reasons, so-called "fine stranding" and "extra-fine stranding" conductors are only made of copper.

Therefore, the best aluminum conductors are much harder than the best copper conductors, a difference that sometimes leads to some quite expensive mishaps. Theoretically, aluminum conductors might be cheaper to purchase, but this does not take into account the additional costs and labor involved in installing less flexible aluminum cables.

Underground cables used at the Dietlikon Power Station - A compromise solution combining the technical characteristics of copper with the price of aluminum.

Recently, a combined copper-aluminum cable emerged as a compromise solution and was used by the Dietlikon Power Company in Switzerland for underground cables in low voltage distribution networks.

Representatives of the Dietlikon plant introduced the product and basic concept after being invited to attend the DKE Committee 712 meeting on "Safety of information technology equipment, including equipotential bonding and grounding" (DKE: German Commission for Electrical, Electronic & Information Technologies).

Dietlikon Power Company is known as the first distribution network operator to systematically convert its distribution network to a five-wire TN-S system—of course, this work is only done during maintenance, network extension, and new installations.

In this new type of cable, phase conductors have the same cross-sectional area as the neutral conductor, aiding in achieving a symmetric cable structure. Phase conductors are made of aluminum, while the neutral conductor of the same diameter is made of copper, enabling it to carry a larger current, thus making the cable more suited to address today’s often-discussed issue of harmonic pollution.

In this case, the protective earth conductor is configured as a surrounding copper wire screen, offering higher symmetry and EMC compared to the traditional fifth conductor.

Transformers 

The issue of winding space in transformers is not as critical as in motors, which is why aluminum can at least be considered. Indeed, the main leakage path, i.e., the gap between the high voltage and low voltage windings, must be of a certain size for three reasons: insulation, limiting short-circuit currents, and cooling.

However, if power losses and all other important operational data (e.g., short-circuit voltage) remain at the same level as those of an equivalent transformer with copper windings, the transformer with aluminum windings will be larger (after all, when we say two transformers are equivalent, this is what we mean). However, the overall weight of a slightly larger transformer with aluminum windings will be somewhat lower.

The difference in manufacturing costs almost cancels out, and in the view of many respected manufacturing companies, the choice of conductor material is primarily a question of corporate philosophy.

Double Copper Busbars

In this application, space requirements weigh even less in the decision-making process, but are still a factor. Secondly, the application is characterized by the use of a large amount of conductive material and a small amount of insulating material in a confined space. This highlights the difference in material prices.

Third, the large number of electrical connections in such a small volume means that the issues associated with connections in aluminum are more pronounced in these applications. When all these aspects are considered, we reach a deadlock, and the choice of material almost becomes philosophical. However, it's important to ensure that price and cost are not confused. If price is the main criterion for selection, aluminum is generally more favored. However, if all costs (including operational costs) are considered, it often turns out that aluminum could learn a thing or two from copper.

Copper also appears to have a better appearance, as some of the available aluminum busbars are copper-plated—not to improve electrical contact (since drilling, punching, and tightening would damage the copper coating anyway) but purely for aesthetic reasons.

The undisputed domain of aluminum is overhead high-voltage cables, where space requirements are not important, but weight plays a crucial role. The lower strength of aluminum means that the conductor cables need to be reinforced with a steel core, but this does not change the fact that the cables can be produced at a low cost, and both materials can be easily magnetically separated upon disposal.

Both aluminum and copper oxidize when exposed to the atmosphere. The oxides, chlorides, or sulfides of base metals are much more conductive to copper than to aluminum. For low-resistance aluminum joints, the aluminum bar conductors must be plated to minimize oxidation as much as possible. Concern about aluminum oxidation away from the joint is not an issue and can protect the conductor from further corrosion in most environments. Aluminum busbar conductors rely on the plating layer to ensure the integrity of the electrical connection.

Aluminum and copper conductors are usually silver or tin-plated. Generally, it is not recommended to bolt uncoated aluminum to copper busbars. Most Al to Cu connections are achieved by plating the aluminum with tin or using special bimetallic clamps designed to inhibit galvanic corrosion between the dissimilar metals. This is an essential consideration in the design and maintenance of electrical systems to prevent corrosion-related failures.

In summary, while both aluminum and copper have their respective strengths and weaknesses, the choice between the two often comes down to specific application requirements, cost considerations, and even corporate philosophy. Aluminum is favored for its lower cost and light weight, making it ideal for applications where these factors are critical, such as overhead high-voltage cables. Copper, on the other hand, is preferred for its superior conductivity, ductility, and resistance to corrosion, which makes it suitable for applications requiring high reliability and minimal maintenance, such as in certain types of cables and busbars.

Innovations like the combined copper-aluminum cable introduced by the Dietlikon Power Company demonstrate the ongoing efforts to leverage the benefits of both metals to meet the evolving needs of the electrical engineering field. These developments reflect a nuanced understanding of material science and engineering, aiming to optimize performance and cost-effectiveness in electrical infrastructure.