Lightweight, special processing: Aluminium cable lugs and connectors

  • The advantage of aluminium conductors: low weight and comparatively simple handling.
  • There are four different types of aluminium conductor, some of which require special processing methods.
  • Contact grease in aluminium connectors improves the contact properties and achieves a faultless electrical connection.

While special cable lugs provide perfect connections even under harsh conditions, certain circumstances do call for especially lightweight material. Aluminium cable lugs are set apart by their low weight. Aluminium, though, requires much more careful processing than copper: bear in mind that aluminium is less conductive.

Aluminium is being used in an increasing number of sectors. In energy distribution, for instance. Due to the low weight, ductility and the resultant simple handling of cables, distribution system operators are using aluminium cables with increasing regularity - in ring mains for municipal supplies, for example.

Aluminium compression cable lugs with tube dimensions to DIN 46329 and aluminium connectors with tube dimensions corresponding to DIN 46267 Part 2 are a good choice for processing aluminium conductors. All standard aluminium compression cable lugs and connectors with a tube are compatible with single and multi-stranded round and sector-shaped conductors to DIN EN 60228 and with aluminium conductor cables to DIN EN 50182. Compression cable lugs and connectors are not designed for fine and superfine stranded conductors, as these conductor types are not standardised.

A constant material thickness, exact diameter and a precise fit turn aluminium connectors into stable and safe connectors.

Aluminium compression cable lugs are produced with a barrier in accordance with DIN 46329 – allowing even oil-impregnated and paper-insulated cable to be processed without any oil leakage.

However, there are also simpler variants, which are produced from one tube and hence have no barrier. The quality of the connection is the same in both cases. The tube dimensions, however, are based on DIN 46329. The same crimping dies, therefore, can always be used.


Aluminium conductors at a glance

Aluminium conductors are offered in four different variants, some of which call for special processing methods: 

 

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

 

The abbreviations along with other information can be found on the connectors and cable lugs. These show which aluminium conductor is suitable for which connector or cable lug.

The markings on the aluminium compression cable lugs generally correspond to those found on copper cable lugs. For example: »KL22 12-120 rm/ sm 150 re/se« 

 

  • KL: Manufacturer code (in this case Klauke)
  • 22: Tool code
  • 12: Metric bolt dimensions of the connecting bolt bore (in this case M12 bolt)
  • 120: Conductor cross-section in mm² (rm/sm)
  • rm/sm: For multi-stranded round conductors and multi-stranded pre-rounded sector-shaped conductors
  • 150: Conductor cross-section in mm² (re/se)
  • re/se: For single-stranded round conductors and single-stranded pre-rounded sector-shaped conductors

 

You may have noticed that the nominal cross-section of the se and re conductors are always one unit higher than the nominal cross-section of the sm and rm conductors. The reason is quite simple: single-stranded conductors take up less volume than multi-stranded conductors. To obtain a reliable connection, we recommend hexagonal crimping dies to DIN 48083 Part 4 or the indent crimping tool EKM60ID for processing of compression cable lugs. For aluminium, there are special crimping dies which, with a crimping width of 7mm, are 2mm wider than the crimping dies for copper connectors. The larger crimping widths create a larger contact surface, which compensates for the low conductivity of aluminium.


Contact grease for aluminium connectors

Commercially-available connectors for aluminium conductors are supplied with a special contact grease. During the crimping process, this destroys the non-conductive oxide layer of the aluminium, which forms on the surface after just a short time. The grease improves contact properties. The grease also prevents re-oxidisation of the contact points. The result is a faultless electrical connection. Most cable lugs are sealed with a plastic plug, which prevents the contact grease from drying out or running out and extends the shelf life of the grease.

Contact grease for aluminium connectors consists of corundum, a sand-like mineral set apart by its high wear and corrosion resistance even at high temperatures. During the crimping process, an emery effect wears and destroys the oxide layer. The grease also improves the sliding friction between conductor and sleeve. With multi-stranded conductors, the grease is distributed during the crimping process between the single strands and seals them – thereby preventing the ingress of oxygen and moisture.

Another huge advantage is that aluminium compression connectors with contact grease can withstand higher current loads than if no contact grease is added. We therefore recommend the use of cable lugs and connectors with contact grease – play it safe with a high cable conductor utilisation.


Step by step: the processing of aluminium compression cable lugs and connectors

Aluminium has special properties and a precise processing procedure is therefore a must. Ideally, proceed as follows to make a clean connection:

  1. Remove the insulation from the aluminium conductor.
  2. Carefully treat the bright end of the conductor with a blade or wire brush for example, to coarsely remove the oxide layer and produce a clean contact surface. Make absolutely sure that that no metal traces remain on the conductor after cleaning, as this could lead to contact corrosion.
  3. Insert the conductor into the cable lug or connector to the full insertion length of the sleeve. The contact grease will flow out to the side, thereby creating an air seal which prevents reoxidisation.
  4. You can now make the hexagonal or indent crimp using the suitable tool. Before the actual crimping process, a single or multi-stranded sector-shaped conductor must be pre-rounded using a suitable round crimping die.
  5. Finally remove the discharged contact grease.

 

Aluminium cable lugs have alternative markings for narrow and wide crimps. The advantage of the wide variant is that the number of crimps required is halved. However, note that a correspondingly powerful crimping tool should be used.

With sector-shaped conductors, you can use Klauke prerounded dies. Unlike with copper conductors, sleeves cannot be used with multi-stranded sector-shaped conductors.