Indent Crimping Of Cables – Benefits & Limitations

Published 11 Oct 2018

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

Thorne & Derrick International, based in the UK, are leading suppliers of cable crimp 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 for use with copper and aluminium conductors.

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:

W-crimp and indent crimp for different cross-sections
The permitted cable spectrum for indent crimping comprises both Class 2 multistranded copper conductors, as well as Class 5 and Class 6 fine and ultrafine-stranded types in accordance with VDE0295 up to a cross-section of 400sqmm
Klauke F cable lugs for ultrafine and fine-stranded conductors avoid fraying
Practical crimping method for small cross sections below 6sqmm and also in switch cabinet construction up to 1000V

Indent crimping

Well-tried yet reliable?

Benefits & Limitations: the oldest form of electrical connection, indent crimping has proven its worth in countless electrical cable termination applications. Yet for some time now, experts have been repeatedly asking the question: is indent crimping reliable?

Why this uncertainty?

Today, hexagonal crimping is considered to be the technical standard that has generally become established. But indent crimping is considered to be an acceptable and a reliable form of cable crimping that is preferred for switch cabinets of up to 1000V.

Indent crimping is still a reliable form of crimping cables, often used in the construction of switch cabinets up to 1000V.

Indent Crimping

Indent crimping is a purely manufacturer specific type of crimping.

In other words – the manufacturer must ensure that a standardised cable crimp can be produced using its components. Leading manufacturers demonstrate this through appropriate tests.

In tests to IEC 61238, for example, Klauke proved its crimping tools and cable lugs combined can be used to make connections of equivalent quality to a hexagonal crimp.

Warning: unlike hexagonal crimping, indent crimping is suitable only for processing copper. In terms of technology, indent crimping is set apart by its high degree of compaction.

The greater impact forces, however, cause high material stress. So it‘s important to remember that connections caused by indent crimping are always strain relieved.

Indent crimping allows multistranded, fine-stranded and ultrafine-stranded conductors to be permanently connected

The variants are W-crimp and indent crimp. There are two different versions of indent crimping in use:

the W-crimp for cross-sections from 0.5sqmm to 16sqmm
the indent crimp for cross-sections from 6sqmm to 400sqmm

Types Of Indent Crimp

The W-crimp is ideal for smaller cross- sections, since the material in the region of the two tips of the crimp insert is extremely highly compacted

Indent crimping is especially suitable for cross-sections from 6sqmm to 400sqmm

The W-crimp is preferred for smaller cross sections, since the material in the region of the two tips of the crimp insert is extremely highly compacted. Indent crimping is commonplace and generally accepted for processing small cross-sections, since the hexagon crimp is normally used only from cross-sections upwards of 6sqmm.

For multi-stranded, fine-stranded and ultrafinestranded copper conductors

The permitted cable spectrum for indent crimping comprises both Class 2 multistranded copper conductors, as well as Class 5 and Class 6 fine and ultrafine-stranded types in accordance with VDE0295 up to a cross section of 400sqmm.

Class 1 round single-stranded (rs) conductor (commonly known as solid conductor. Class 2 round multi-stranded (rm) conductor. Class 5 fine-stranded conductor 5 (commonly known as flexible conductor. Class 6 ultrafine-stranded conductor 6 (commonly known as highly-flexible conductor).

Conductor Types

In contrast to the hexagon crimp, thinned conductors can also be reliably crimped without transmission losses by means of indent crimping. The reason – thinned cables have in reality a smaller cross-section than is nominally specified – a specified cross-section of 50sqmm can in actual fact only be around 43smm, for example.

Thinned lines are produced from high-purity copper. Despite its smaller cross-section, this material has identical conductivity characteristics. The benefit to the manufacturer is the reduced material usage and the associated lower costs.

One of the key advantages of indent crimping is this versatility in the wide range of the conductor types to be processed. What’s more, all these conductor types can be indented simply and cost effectively using one tool. Klauke offers a mechanical crimping tool for indent crimp that covers a cross section range of 185sqmm to 400sqmm, for example.

The Klauke mechanical crimping tool K07 for indent crimps covers a crosssection from 185sqmm to 400sqmm

Generally speaking, only mechanical hand crimping pliers are used for indent crimping.

The cable crimping profiles to be used are based on the tube dimensions of cable lug and connector. But because indent crimping is not a standardised form of cable crimping, it is crucial that high-quality materials and crimping tools tested to IEC61238 from the same manufacturer are used.

A professional indent is obtained only from clean workmanship using a suitable tool and matching cable lug. That means the crimping tool must be correctly applied and the indent made up to the end stop of the tool. The same number of indents as for a hexagonal crimp is required. For example, a professional hexagonal crimp of a tubular cable lug with a cross-section of 240sqmm calls for four narrow crimps; an indent likewise requires four crimps.

Just like a hexagonal crimp, the indent crimp for a cable lug with 240sqmm cross section also requires four narrow crimps

With indent crimping too, the cross-section is stamped on the back of the cable crimp for checking. Important in all cases – to avoid under or over-crimping the use of a suitable and well-maintained crimping tool is a basic pre-requisite.

Incorrectly made cable crimps due to an incorrect tool setting for example can increase contact resistance which can in turn cause temperature rises and ultimately cable fires.

Indents made incorrectly due to unsuitable crimping tools, for example, can in the worst case cause a cable fire

Klauke recommends that its cable lugs are crimped using only Klauke tools – this is the only way the electrical engineer or cable jointer is guaranteed the use of matched cable lugs or connectors and tools, which are the prerequisite for a reliable connection.

Also important in this regard Klauke F or R cable lugs (Cu copper standard version) can be used for indent crimping.

F and R-series cable lugs can be used for indent crimping

Klauke F & r series cable lugs

Due to their design F cable lugs for fine stranded and ultrafine-stranded conductors avoid the problem of fraying as they are introduced into the cable lug. These tubular cable lugs have a larger internal tube diameter than standard cable lugs – they also have funnel-shaped widening to better guarantee cable entry into the lug.

F cable lugs have a larger tubular inside diameter than standard cable lugs; they also have a funnel shaped widening

Besides easier handling, this also provides advantages in terms of safety – cross-section tapering due to fraying is prevented and so the cable retains its full cross section.

The funnel-shaped widening of the F cable lugs prevents a cross-sectional tapering of the cable caused by fraying

Suitable for use with Klauke F series tubular cable lugs, various manufacturers also offer joints for conductor extensions or repair purposes. These also have funnel-shaped widening and an enlarged tube diameter. A central impression prevents the two cable ends being inserted unevenly.

Tubular Cable Lug – Commercially Available

In addition to DIN cable lugs, various manufacturers offer standard Klauke R-series tubular cable lugs. Due to their dimensions, these tubular cable lugs differ from DIN cable lugs – they are usually shorter than the DIN designs. But because they are governed by the same test standard this does not affect the durability of the electrical and mechanical connection.

The standard R series tubular cable lugs, which are shorter than DIN cable lugs, guarantee a durable connection when indent crimping is carried out correctly

Conclusion & outlook

Indent crimping remains a standardised and practical crimping method. For small cross sections below 6sqmm in any case and also in switch cabinet construction up to 1000V. If the recommendations given in this article are followed, any uncertainties about their reliability are unfounded.

There is no doubt, however, that the acceptance of indent crimping among experts is not quite what it once was with hexagonal crimping increasingly preferred and specified. It is therefore important to clarify with customers in advance as to whether they allow indent crimping in their technical facilities and plants. The arbor and 4-arbor crimp offer a similar degree of compaction to indent crimping.

These cable crimps even allow the production of gas-tight crimped connections. We will be explaining what is important to note about these types of crimp in a later issue.

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

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

Copper & Aluminium – Crimping CU-AL Cables

Electrically Driven Crimping Tools For High Volume Applications

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