Aluminium and copper: making the connection

  • The combination of aluminium and copper is problematic.
  • High-quality Al/Cu compression cable lugs are suitable for connecting aluminium conductors to copper.
  • Contact grease with aluminium connectors improves the contact properties.
  • Aluminium/copper connectors are required for a professional connection between aluminium and copper conductors.

We will now concentrate on the connection between aluminium and copper, which is not exactly simple. As already mentioned, aluminium is now used quite often, but not always by itself. Since copper has been the material of choice for decades and is still being used, reliably connecting the two materials presents a problem. In practice, electrical engineers are facing this challenge with increasing regularity.

The connection between aluminium and copper is required more often than would appear at first glance. As an example, this is required when an industrial area has an aluminium ring main, but the supply to the adjacent operations is via copper conductors. In transformer stations too, there are times when aluminium conductors have to be connected to copper rails.

Electrical engineers face the problem that aluminium and copper cannot be readily connected to each other. For a lasting, reliable connection, you should therefore use special Al/Cu copper cable lugs and connectors.

Aluminium/Copper: a special connection

In practical use, aluminium appears to be resistant against corrosion. However, aluminium is a highly-reactive and readily-oxidising material. The material’s durability is down to a resistant oxide layer, which forms on its surface in the presence of atmospheric oxygen – also known as self-passivation.

If an electrically-conductive liquid such as condensate reaches an aluminium and copper connection, an electrochemical reaction occurs and causes contact element formation. 

The potential differences caused by the electrochemical series play a key role in this process. The contact element is formed by the copper electrodes (anode), the electrolytes (water) and the aluminium electrodes (cathode).

The voltage generated as a result is short-circuited by the contact between copper and aluminium. As a result of the current flow, the aluminium deposits or decomposes. This process is visible as a blooming oxidation spot and starts when even the smallest copper particles come into contact with the aluminium – specifically, as a permanent reaction, since copper does not decompose. An electrical connection increases the transition resistance, which can lead to a temperature rise and a fire in the worst case.

When joining copper and aluminium, therefore, you should prevent the influx of moisture at the junction of the two materials at all costs. In rooms where condensate forms, the point of contact between copper and aluminium must therefore be protected by means of special processing methods.

The use of Al/Cu copper cable lugs and connectors is the most important step here. These have no so-called creepage path where the conductive fluid produced by the oxidation process can accumulate. As a result, Al/Cu compression cable lugs and connectors are also especially suited to use in offshore wind farms. Tin-plated aluminium cable lugs can also be used. This solution should be used only in rooms that are constantly dry, since even minor damage to the tin layer can initiate contact corrosion.

Al/Co compression cable lugs

Compression cable lugs developed specifically for connecting aluminium conductors and copper rail consist in the crimping area of electrolytic aluminium (E-Al) and an attached screw-on palm to EN 13600.

Aluminium Conductors at a Glance

According to DIN EN 60228, there are four different variants of aluminium conductors, some of which call for special processing methods. Available conductors are: 


  • Single-stranded round conductors, class 1 (re)
  • Single-stranded sector-shaped conductors, class 1 (se)
  • Multi-stranded round conductors, class 2 (rm)
  • Multi-stranded sector-shaped conductors, class 2 (sm)


The abbreviations along with other information can be found at the markings on the Al/Cu compression cable lugs. This tells you which aluminium conductor is suitable for the respective cable lug.

Stamping »8 KL16 50 rm 70 se« stands for 


  • 8: Metric bolt dimension of the bore for the connecting bolt (in this case M8 bolt)
  • KL: Manufacturer code (in this case Klauke)
  • 16: Tool code
  • 50 rm/sm: Nominal conductor cross-section in mm² for use with a round or sector-shaped multi-stranded conductor
  • 70 re/se: Nominal conductor cross-section in mm² for use with a round or sector-shaped single-stranded conductor


For crimping Al/Cu compression cable lugs, we recommend the use of hexagonal crimping dies to DIN 48083 Part 4 or EKM60ID.

Incidentally, Klauke aluminium crimping dies are silver-coloured, copper dies are golden yellow – so they are very easy to differentiate.

Al/Co connectors: reliably joined

For a reliable connection of aluminium and copper conductors, Klauke offers reducing connectors.

Reducing connectors are often used for grid reconstruction, more precisely to produce stress-relieved connections between aluminium conductors to DIN EN 60228 and copper conductors to DIN EN 60228. The connectors are produced from two components: aluminium (E-Al) and copper parts (to EN 13600). As a rule the aluminium side has a larger diameter, since the low conductivity is compensated by the correspondingly high nominal cross-section.

As with compression cable lugs, the aluminium side of the connector also contains contact grease, which is prevented from running out and drying out by a protective cap.

When processing Al/Cu compression connectors, follow to the corresponding processing instructions for copper and aluminium to obtain reliable results.

When using compression connectors underground, be sure to protect the joints from moisture. Ideally, use a cast resin joint. The joint permanently protects the connections from moisture, dust and the penetration of foreign bodies.

Finally, an important note on cable lugs and compression connectors made from aluminium and copper: do not expose these products to any bending stresses, as this could cause the contact point of the two materials to break. Use in the overhead line sector is therefore not possible.

Klauke's product range

> Al/Co connectors