Crimping Copper & Aluminium Cables

Published 12 Nov 2018

Copper & Aluminium – Crimping CU-AL Cables

Copper & Aluminium – Crimping CU-AL Cables

  • uploaded by Chris Dodds - Thorne & Derrick Sales & Marketing Manager

Cable Crimps

Thorne & Derrick International, based in the UK, are leading suppliers of cable lugs and associated crimping tools for Low, Medium & High Voltage Cables and Power Systems – this series of articles by Klauke discusses the theory and practise of installing compression type cable lugs and connectors when jointing and terminating copper or aluminium cables at Low (LV), Medium (MV) or High (HV) voltages.

Klauke cable lugs and crimping tools are used by Jointers, Linesmen, Panel Builders and Electrical Engineers to install underground cables and overhead line conductors on power, transmission and distribution networks including LV MV & HV systems, 11kV-33kV.

➡ Download 2018 Klauke Cable Lugs catalogue and see the complete range of tools for cutting and crimping cables.

In this Article we cover the following:

  • Crimping copper and aluminium conductors integral to LV MV HV cables up to 33kV
  • Types of bi-metallic cable lugs for connecting aluminium cables to copper busbars
  • Aluminium conductors – 4 different types which require cable preparation for crimping
  • Connecting compound for aluminium connecting material to improve contact properties
  • Al/Cu connectors for a correct crimp connection of aluminium and copper conductors

Accurately Crimping

Copper & Aluminium Cables

Copper, due to its outstanding electrical conductivity properties, is always the first choice when selecting a conductor for an electrical connection.

A practicable alternative in many cases is aluminium particularly because of its low weight and easy application. In practice however the electrician can find it challenging to connect both these materials in a professional and electrically safe manner using crimping tools.

A copper-aluminium connection is used for instance in an industrial estate where local businesses use copper conductor power supply cables which are then fed off an aluminium ring main unit. But also in LV MV HV electrical substations it is necessary to connect aluminium conductors to copper busbars.

The main problem here is that connecting aluminium and copper is not straightforward – to ensure a safe and correct connection the use of special aluminium/ copper cable lugs and connectors is essential.

Incorrect Crimping Die

Use of an incorrect crimping die and/or an incorrect crimp will result in an over compression (right) or an under compression (left) and in the worst case in fire.

Infographic: Properties & Uses of Copper Materials For Electrical Applications 

Aluminium-Copper: A problematic connection

Generally aluminium is a reactive material that oxidises easily, but in practice it has proved to offer good corrosion resistance. This characteristic is due to a chemical reaction that takes place when in contact with atmospheric oxygen resulting in a very thin but also very resistant oxide layer being formed (oxide barrier).

When metals are connected to those with a higher electrical potential such as copper in the presences of an electrolyte (condensed water) will result in an electrochemical reaction taking place.

During this process the differences caused in electrochemical potential can have a significant impact. An electrical circuit is generated by the copper electrode (anode), the electrolyte (water) and the aluminium electrode (cathode).

The voltage generated in this copper and aluminium circuit “semi metallic” state results in a short circuit. As a result of the current generated the aluminium surface breaks down causing the metal to electrolytically decompose.

This destructive process is visible as a kind of blooming oxidation and begins already with the existence of tiny copper particles on the aluminium; this ongoing reaction itself does not cause the copper to corrode.

In an electrical connection however the resistance is increased leading to increased temperatures which then in the worst case lead to a fire. Therefore when connecting copper and aluminium it is important to ensure that no moisture can enter the connections.

In an environment where moisture is present the contact points between the copper and aluminium need to be protected by using accurate operating procedures.

AI/CU Cable Lugs

The construction of Al/Cu cable lugs prevents any gaps which would allow the accumulation of liquid to take place which would start the oxidation process.

Primarily this requires the use of aluminium/ copper cable lugs and connectors. Due to the design of these cable lugs areas where moisture could accumulate and where the oxidation process could start have been avoided. For this reason aluminium/copper cable lugs and connectors are specified for the use in offshore wind power stations.

Aluminium/copper compression cable lugs

Leading manufacturers of high quality compression cable lug such as Klauke or Cembre, for connecting aluminium connectors with copper bus bars consist of an electrolytic aluminium (E-Al) compression and are joined to a copper palm (to EN 13600).

Aluminium Conductor Professional Connection

A professional connection of an aluminium conductor with a copper busbar is done by means of an aluminium cable lug and a copper palm.

The available cross sections range from 16sqmm up to 400sqmm. The field of application covers in principle all non-tension connections of aluminium cables acc. to DIN 48201, Part 1, and aluminium ropes acc. to DIN 50182 (Conductors For Overhead Lines – Round Wire Concentric Lay Stranded Conductors).

Specifications and processing of aluminium/copper compression cable lugs are the same as those for pure aluminium versions. Quality products manufactured by market leaders such as Klauke feature a consistent material thickness, exact diameters and correct fit and are a prerequisite for ensuring high electrical safety standards are always met.

Like aluminium cable lugs conforming to DIN 46239, aluminium/copper compression cable lugs feature a barrier design allowing the use of oil soaked and paper insulated cables which prevents oil leakage.

Aluminium Cable Conductors At A Glance

Aluminium conductors are available in four different versions which require in some cases special processing.

These are:

  • round solid cable conductors (re)
  • sector solid cable conductors (se)
  • round stranded cable conductors (rm)
  • sector stranded cable conductors (sm)
Aluminium Conductors

Different types of aluminium conductors

These abbreviations will be found next to other markings on all Al/Cu compression cable lugs and identify which conductors will suit the appropriate cable lug.

Markings On Cable Lug

The markings on the cable lug provide information relating to the crimps, the manufacturer, cross section and allocation of cable.

Markings on the product provide the installer with essential information. Marking “16 KL25 150 rm/sm 185 re/se” stands for

  • 16: Metric bolt size for connecting bolt – size M16
  • KL: Manufacturer (in this case Klauke)
  • 25: Die code
  • 150: Cross section of conductor in sqmm
  • rm/sm: for round multi-stranded and sector stranded conductors
  • 185: Cross section of conductor in sqmm
  • re/se: for round single stranded solid and single sector solid conductors

The die code also needs special consideration. For an accurate and safe crimp the die reference should be the same as that shown on the cable lug. The die code can be seen on the die face as a mirror image so that after compression the die code is visible on the cable lug for final control and inspection.

For an accurate processing of Al/Cu cable lugs it is generally recommended to use hexagon crimping dies acc. to DIN 48083 Part 4. In order to ensure an accurate and professional crimp avoiding over or under compression is the use of appropriate crimping tools.

Poor crimps can result in an increase in joint resistance and temperatures that can lead to fires. To prevent such issues Klauke solely recommend using the manufacturers crimping tools to crimp their cable lugs.

For instance the special crimping dies for aluminium have a crimp width of 7mm, i.e. 2mm wider than the crimping dies for copper cable lugs and connectors. This, however, only applies to 60 kN crimping dies.

The reason for this is that cable crimping dies with a larger crimp width are able to connect a wider conductor surface area with the cable lugs and balance the poor conductivity of aluminium. To easily identify which die should be used, Klauke manufactures aluminium dies in a silver colour while dies for copper are yellow-gold coloured.

Connecting compound for aluminium connecting material

All cable lugs and connectors for aluminium conductors come with a special compound.

High Quality Aluminium Cable Lugs

High quality aluminium cable lugs come with a special compound which improves the contact properties and ensures a perfect electrical connection.

This aggravates the non-conductive oxide layer which is quickly formed on the surface of the cable lug – this compound improves the electrical contact properties of the cable crimped lug and enables a perfect electrical connection preventing further oxygen penetrating the contact joints where further oxidation could take place.

To maintain the functional capability of the compound all leading brand cable lugs are sealed with a plastic plug to prevent the compound from drying-out and leakage.

Al/Cu Connectors & Joints

For a correct connection of aluminium and copper conductors leading manufacturers such as Klauke offer reduction compression joints with a cross section range from 10sqmm up to 300sqmm.

Aluminium & Copper Conductors

Aluminium and copper conductors with different cross sections are being connected using reduction sleeves.

These products serve mainly the reconstruction of power lines, i.e. non-tension connections of aluminium conductors acc. to DIN EN 60228 resp. aluminium wires acc. to DIN EN 50182 with copper cables acc. to DIN 48201, part 1 and copper conductors acc. to DIN EN 60228.

These compression joints consist of interconnected aluminium (E-Al) and copper parts (acc. to EN 13600).

Normally the aluminium part of the cross section has a much larger diameter to compensate for the poor conductivity of aluminium.

Aluminium & Copper Conductor Diameter

Normally the aluminium section (right) has a larger diameter than the copper section (left) to equalize the poor conductivity of aluminium.

As with the cable lugs here too plastic plugs are used to prevent drying-out and leakage.

Important: The use of Al/Cu compression joints requires that the correct processing guidelines for copper and aluminium are observed.

Consequently the aluminium section needs to be crimped like an aluminium compression cable lug (see picture on the below).

Characteristically for Al/Cu compression joints are the different crimping marks which are 7mm on the aluminium section and 5mm on the copper section for crimping dies up to 60kN. The procedure for the copper section is absolutely identical as on copper compression cable lugs. The crimping marks on the product give detailed information as to origin and application of the Al/Cu compression joints.

The marking “KL14 50 rm/70 re/se” signifies:

  • KL: Manufacturer (in this case Klauke)
  • 14: Die code
  • 50: Cross section of designed conductor in sqmm
  • rm/sm: for round stranded and sector stranded conductors
  • 70: cross section of solid conductor in sqmm
  • re/se: for round solid and sector solid conductors

The marks on the copper section also indicate the correct procedure. The standard suggests crimping dies acc. to DIN Standard 48083 Part 1, 3 and 4 for solid, fine and fine stranded conductors; for braided round wires the standard refers to specifications of the manufacturer.

Generally Klauke recommends using hexagon crimping dies according to DIN 48083 Part 4 for processing the copper section of their compression joints.

Advice: When using crimp connections in the ground it should be strictly observed that the connecting joints should be protected against moisture. For this application Klauke recommends use of resin cable joints.

Ground cast-resin joints

When used in the ground cast-resin joints, such as Scotchcast, protect the connections against moisture. It is important to consider that the connection is not subject to bending to avoid the risk of fracture.

Should you require guidance or technical support to use the correct cable lug or connector using either compression or shearbolt technology please do not hesitate to call us.

Further Reading

Review other Blogs in this series of articles about Cable Lugs, Crimping Cables & Tools:

Cable Lugs – Crimping Applications & Standards

Copper Cable Lugs For Special Applications

Indent Crimping Of Cables – Benefits & Limitations

Cable Lugs & Crimps – Hexagonal v Indent Methods of Crimping

Cable Lugs & Crimping Using The Hexagonal Crimp Method

DIN Standard – Crimping & Compressing Aluminium Cable Lugs & Connectors

Electrically Driven Crimping Tools For High Volume Applications


LV MV HV Cable Accessories & Substation Electrical Equipment

Thorne & Derrick are Specialist Distributors of leading manufacturers of Cable Accessories, Jointing & Installation Equipment.

LV MV HV cable accessories used to joint, terminate, connect, cleat and gland power cables to air and gas insulated substations, transformers, switchgear and overhead line networks.

LV 600/1000V ◊ MV 11kV 33kV ◊ HV 66kV 132kV 

3M Pfisterer CONNEX Prysmian Nexans Euromold Elastimold Ellis Patents Furse CMP Cable Glands Cembre

Substation & Overhead Line Electrical Safety Equipment

Manufactured by CATU Electrical to enable the safe construction, maintenance and repair of underground cables and overhead lines network up to EHV (400kV).


Further Reading