Correctly connecting al and cu

Aluminium and copper: how to connect them

  • Combining aluminium and copper is problematic.
  • High-quality Al/Cu compression cable lugs are perfect for coupling aluminium conductors with copper elements.
  • A compound in the aluminium connecting material improves the contact properties.
  • Aluminium-copper connectors are necessary for the skilled connection of aluminium and copper conductors.

We want to focus on the not-so-simple task of connecting aluminium and copper. As previously mentioned, aluminium is used quite often, but not always on its own. As copper has been the material of choice for decades, and continues to be used, there are problems in safely connecting both materials. In practice, electrical engineers are faced with this challenge more and more often.

Connecting aluminium and copper is required more often than you might think. For example, it is necessary if an aluminium ring conductor is located in an industrial area, but the adjacent plants are supplied via copper conductors. Even in transformer stations, aluminium conductors need to be connected to copper bars.

Electrical engineers are confronted with the problem that aluminium and copper are not easily connected. For a durable and secure connection, special Al/Cu cable lugs and connectors should be used.

Aluminium/copper: a special connection
Aluminium has proven itself to be corrosion-resistant in practical situations. However, aluminium is generally an extremely reactive material that oxidises quickly. The durability of the material is down to a resistant oxide layer that is formed on its surface when atmospheric oxygen is applied – a process also known as self passivation.

If an electrically conductive liquid, such as condensation, comes into contact with an aluminium and copper connection, this results in an electrochemical reaction and the subsequent formation of contact elements. The difference in potential by means of the electrochemical series plays a key role in this process. The contact element is formed by the copper electrode (anode), the electrolyte (water) and the aluminium electrode (cathode).

The voltage generated as a result is shorted by the contact between copper and aluminium. The aluminium is deposited and/or corroded in line with the current flow that is generated. This process is visible as a vibrant oxidation mark and is applied to even the very smallest copper particles on the aluminium – with this being a permanent reaction as the copper does not therefore corrode. If there is an electrical connection, the consequence is an increase in the contact resistance, which can result in a temperature rise and, in the worst case scenario, a fire.

When combining copper and aluminium, it is therefore essential than you aim to prevent moisture from getting into the junction between both materials under any circumstances. In spaces where condensation builds up, you will therefore need to protect the contact point between copper and aluminium by way of special processing methods.

Use of aluminium/copper cable lugs and connectors is the most important step here. These items do not have any so-called creepage distances in which conductive liquid that is ultimately responsible for kicking off the oxidation process can accumulate. As a result, aluminium/copper compression cable lugs and connectors are also particularly suitable for use in offshore wind turbines. There is also the option to use tin plated aluminium cable lugs. This solution should only be used in spaces that are kept constantly dry, as even small amounts of damage to the tin layer are enough to start the contact corrosion process.
Al/Cu compression cable lugs
Compression cable lugs which are developed for the special connection of aluminium conductors and copper bars are made of electrolytic aluminium (E-Al), and feature an attached copper mounting bracket according to EN 13600.

Aluminium conductors at a glance

Pursuant to DIN 60228, four different types of aluminium conductors are available – some of which require special processing methods. The following conductor types are available:
  • single-stranded round conductors, class 1 (re)
  • single-stranded sector shaped conductors, class 1 (se)
  • multi-stranded round shaped conductors, class 2 (rm)
  • multi-stranded sector shaped conductors, class 2 (sm)

The abbreviations and other information can be found among the markings on the Al/Cu compression cable lugs. This will help you to determine which cable lug is best for which aluminium connector.

The markings »8 KL16 50 rm 70 se« mean

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

For crimping Al/Cu compression cable lugs, we recommend using a hexagonal crimping die, according to DIN 48083 Part 4, or EKM60ID. Incidentally, Klauke aluminium inserts are silver, whereas copper inserts are gold/yellow. It is therefore very easy to tell them apart.

From the Klauke product range:

> Compression cable lugs - Al/Cu

> Bi-metallic washers

Al/Cu connectors: securely joined
Klauke offers reduction connectors to ensure that aluminium and copper are securely joined.

Reduction connectors are often used in network repairs – more specifically in the production of non-tension connections for aluminium conductors in accordance with DIN EN 60228, and copper conductors in accordance with DIN EN 60228. The connectors are made of two components: aluminium parts (E-Al) and copper parts (pursuant to EN 13600). The aluminium side generally has a larger diameter, because the lower conductivity is compensated by a correspondingly higher nominal cross-section.

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

To ensure safe results when processing the Al/Cu compression joints, follow the relevant copper and aluminium processing specifications.

When using compression connectors underground, make sure that the joints are protected from moisture. It is best if you use a cast resin joint. The joint permanently protects the connections from moisture, dust and the penetration of foreign bodies.

Lastly, an important note on aluminium and copper cable lugs and compression joints: Do not expose these products to bending stress, otherwise there is a risk of breakage at the contact point between the two materials. Use in the overhead line sector is therefore not possible.

From the Klauke product range:

> Al/Cu connectors