Heat Shrink Cable Joints & Cable Terminations | Manufacturers & Assemblers
uploaded by Chris Dodds - Thorne & Derrick Sales & Marketing Manager
Although modern cable manufacturing technologies evolve and develop the essential factors to consider when installing heat shrink type joints or terminations on medium/high voltage power cable systems remain essentially unchanged. Materials quality allied with installation by competent trained Jointers is the fundamental basis to ensure reliability, safety and operational service of MV HV cables, joints and terminations.
Here, from the archive we reproduce an important Technical Article by Norman Poulter – Norman was the Managing Director of Shrink Polymer Systems, the UK’s leading specialist manufacturer and assembler of MV HV cable joints and terminations for standard and non-standard cable applications up to 33kV.
Today, SPS’s Managing Director Richard Poulter continues to support the UK and overseas market with the competitive supply of MV HV heat shrink cable accessories for all cable voltages including 11kV/33kV and types such as XLPE, EPR, PILC and Triplex cables.
author Norman Poulter
Power cable installation throughout Europe and the UK until the early 1960s exclusively used impregnated paper for the primary insulation of the conductors for both single- and three-core MV-HV cables.
The UK adopted both aluminium and lead-sheathed cables with and without steel wire armouring (SWA); these are still in use today. In the very early days of paper-insulated cable terminations, dry-type systems were employed along with compound-filled end box designs and cast-iron boxes with hot pour bitumen for cable joints.
PILC SWA Paper-insulated Lead Covered & Steel Wire Armoured Cable
11kV PILC Cable
Cold shrink products such as push-on, pre-stretched tube and grease applied slip-on types also became popular in the 1960s and are still specified by specific electric authorities and utilities for terminating and jointing MV-HV cables.
In the early 1970s polymeric (XLPE) cable types began to emerge in Europe and the UK, mainly on three-core cables, while the USA employed the single-core cable concept at 10kV, 20kV and 35kV medium voltages.
The heat shrink concept began to be employed at this period by the utility companies and has now spread internationally as the preferred method of cable terminating and jointing.
There are many advantages of using heat shrink cable accessories and techniques, such as:
Figure 1 – Cable Box Air Insulated Termination
Cable Joint & Termination Kit Instructions
Shrink Polymer Systems also realised the importance of good cable jointing and terminating instructions. By using pictorial drawings with a minimum of text, non-English speaking countries can identify the important highlighted areas in an easily identified format.
Cable Terminations 11kV 33kV – Instruction Excerpt
Failures are nearly always attributed to poor cable preparation by the jointer and failure to observe the correct jointing procedures in the areas where the electric cable stresses are prudent, such as the semicon screen cut back.
Although the USA shares a language with the UK, there are many differences in the selection of words to describe various things. Below is a list of some UK terminology and the common equivalent used in the United States.
Terminations | Indoor or Outdoor
The major MV HV switchgear and transformer manufacturers have, for many years, designed dry-air filled cable boxes, resulting in a much greater demand for heat shrink-on terminations.
All heat shrink cable terminations and joints have to be tested to various international standards, and while cables prepared by experts in perfect laboratory conditions will undoubtedly meet these requirements under test, field experience shows that failures still occur at working voltage due to a variety of reasons.
Typical List Of Weakness Resulting In Failures
Of Heat Shrink Terminations
Figure 2
There are solutions and remedies to these weaknesses relating to MV HV cable accessories which will be described later in the article.
Many of the points discussed regarding cable terminations are also relevant to joints.
The object of the cable jointing exercise is to replace all the materials that were removed to joint the conductors and replace them in such a way as to replicate the cable as closely as possible to its original state.
There are many techniques used in conductor jointing from “sweating” the weak-back ferrule (normally associated with the original cast iron paper joints) to compression and the present popular “shear bolt” designs.
Connector jointing is a complex subject due to the variety of designs for copper and aluminium conductors in circular-solid, circular-stranded, and sector-shaped styles.
There is also the consideration of copper being jointed to aluminium, cables of unequal cross sectional area being jointed to themselves, and transition jointing where paper is being jointed to polymeric at medium or high voltages.
Figure 3 An 11kV 3 Core Heat Shrink Cable Joint
Let’s look at some of these designs.
Compression Connections – Crimps
There are a substantial number of manufacturers, such as Cembre, who specify suitability of their electrical connector design for voltages up to 33kV/36kV. Caution is needed if the body of the barrel is not smooth and does not have tapered ends.
Also, responsible MV HV connector manufacturers will be able to manufacture appropriate crimping tooling for their designs or confirm the compatibility of other cable tooling and die combination for their connectors. There are three types of crimping configurations currently in use: hexagonal, oval, and indent.
For instance, the Cembre HT131-C is the industry standard hydraulic crimping tool used by LV HV cable jointers to install copper type lugs and splices onto stranded cable conductors.
Oval and hexagonal crimping can leave sharp “ears” if incompatible tooling is used.
These “ears” must be filed smooth to avoid a highly stressed area which will be subjected to electrical discharge. Indent crimping will leave void holes which must be filled with high permittivity, stress relief tape.
Mechanical Connections – Shearbolts
Mechanical split type connectors are now very popular in the UK, as this design comes in two halves which are easy to apply to three-core cables at 11kV or 33kV where the cable conductors do not have to be bent. The heads shear-off at a given torque; therefore, no compression tooling or die combinations are necessary.
As this connector is “blocked,” it is also suitable for transition cable jointing for paper to plastic to stop the migration of the paper oils. There are several disadvantages of this type of connector, however. The ends of connector are non-tapered, resulting in high “step downs”, and the conductor insertion is non-centralised. (See figure 4.)
Figure 4 Mechanical Shearbolt Connector
These two conditions result in areas of high electrical stresses leading to probable discharge.
Shrink Polymer systems have now standardised on a shearbolt connector design where these critical areas of high stresses are removed by tapering the ends and centralising the conductor. (See figure 5.)
Figure 5 Mechanical Shearbolt Connector (Tapered)
Stress-Relieving Tapes
This type of stress relief tape generally has permittivity values between 7 and 13 (test method IEC 250). (See figure 6.) This does not necessarily mean that a value of 13 will perform better than a value of 7, as void filling characteristics are equally as important.
Figure 6 MV HV Connectors & Stree Relief Tape
Shrink Polymer Systems have a yellow stress control tape, reference number TS 31785Y, which possesses high tack, high stretch, and low viscosity void-filling qualities with a permittivity value of minimum 9. Whichever type of cable connector is selected, stress-relieving tape must be used in conjunction with heat shrinkable installations.
This is applied in a half width overlap with stretch by the cable jointer and must also be applied to any indents left by the tooling.
Gaps between end of primary insulation and connector must also be filled in.
Push-on molded components are also widely used, eliminating the need to fill voids and use stress tapes.
They rely on the Faraday Cage principle, in which conductive rubber-ribbed moldings are in contact with the connector. As the potential difference across the air is very low, discharge should not occur. Push- on molded components, joints and terminations have several disadvantages however.
On three-core cables the molded components prove to be very bulky and have no design features to eliminate moisture penetration unless used in conjunction with large diameter shells and resins. On large aluminium conductor sizes the ferrule could possibly be longer than the moulded component. The positioning over the ferrule is critical.
Stress Control Heat Shrink Tubing
Shrink Polymer Systems employ the heat shrinkable, high permittivity, and low resistivity stress control tubing which is shrunk onto the stress relief tape using heat applied by a jointers gas torch previously applied.
This has the effect of achieving a more uniform distribution of the field lines. This heat shrink tube extends over the ferrule or connector and onto the prepared screen cut-off points of the medium/high voltage power cable (See figure 2.)
Insulation Thickness
When designing cable jointing systems, the thickness of the insulation over the bare conductor (i.e. ferrule) should have a safety factor in excess of 15% of the original cable.
Shrink Polymer Systems employ a one-piece, combined dual wall (insulation / semiconductive) heat shrink tube of appropriate diameter to match this insulation at voltages to 11/12kV.
At 17.5kV, 24kV and 36kV additional heat shrink insulation tubes are added to meet these cable specifications.
The cable jointer must remember to shrink this material all around the heat shrink tube to avoid inconsistent wall thicknesses on full recovery.
Typical List of Weaknesses Resulting in Failures
The solutions and remedies to these weaknesses are described below.
Earthing Cable Terminations
Earthing must be provided to carry any circulating currents to core screens, metal sheaths and armour wires. It must also have the ability to carry fault current. On indoor MV HV cable terminations the use of tin plated copper, solder-blocked braids, metal canisters, armour support, clamps and a complete corrosion protection system should be employed.
Figure 7 Low Voltage Heat Shrink Cable Joint For Multicore Cables
Earthing Cable Joints
Connecting the earthing components across a heat shrink cable joint requires correctly choosing and fitting the components to take care of both circulating currents and the short circuit requirements.
The outer semiconducting layer of the core/connector insulation should be wrapped in a tin copper mesh bandage and connected to the cable earth at each end.
There are a great many variations and earthing complexities and such a wide variety of cable types to consider.
Once a cable type, size, and voltage are specified it should be left to the manufacturer to supply the correct type of earthing system to meet both the national and local standards.
Remedies & Solutions To Overcome Cable Termination Failures
Remedies & Solutions To Overcome Cable Joint Failures
Cable Jointing & Terminating Instructions
It is the responsibility of cable accessory manufacturers to supply easy-to-read, simplified, pictorial jointing instructions and to avoid heavy reading of text manuals.
This point cannot be overstated, as, in the writer’s opinion, far too many jointing instructions are not read or understood, resulting in the installer compromising on the areas of importance previously mentioned. This all too often results in that first failure.
Since 1985 Thorne & Derrick have been servicing the UK and Export market with Joints, Terminations & Connectors for LV MV HV cables and power systems – call us to discuss your requirements including specialist LV cable joints for high performance applications including hazardous areas, marine and offshore cables, fire resistance cables and low smoke zero halogen cables.
Key Product Categories: Duct Seals | Cable Cleats | Cable Glands | Electrical Safety | Arc Flash Protection | Cable Jointing Tools | Cable Pulling | Earthing | Feeder Pillars | Cable Joints LV | Joints & Terminations MV HV
HV Cable Joints & Cable Terminations | Heat Shrink | 6.6kV 11kV 33kV Cables
by Chris Dodds T&D - estimated reading time 5 minutes
33kV heat shrink cable joints are high voltage cable jointing kits complete with mechanical connectors or compression crimp connectors for cable jointing of polymeric (XLPE) insulated cables.
Polymeric insulated cables distributing high voltage electricity at 33kV can be used to joint cables with XLPE or EPR type insulation, armoured/unarmoured and with copper wire screen (BS7870) or copper tape screened cables (BS6622).
Heat shrink cable joints feature integrated stress control sleeves and torque controlled mechanical shearbolt connectors can be used to connect conductors (copper or aluminium) without resort to use of crimping tools or associated die sets.
Mechanical cable connectors are ideal for confined space cable jointing where there is restricted working space in manholes, cable vaults and underground trenches, especially on large cross sectional area conductors where hydraulic crimping heads coupled with foot pumps are required for conductor jointing. Bolted cable connections, such as Pfisterer SICON connectors, are installed directly onto the 33kV conductor using standard Allen keys. The bolt shears off smoothly and cleanly when tightened by the cable jointer.
Pfisterer Sicon – cable lugs and connectors with stepless shearbolts for use with cable joints and terminations on high voltage power cable systems
Primarily, a heat shrink cable joint provides electrical insulation, mechanical protection and stress control for high voltage power cables – integral also to the cable joint design is the requirement to prevent water ingress into the cables. Although initial risk assessments would include consideration of electrical water damage, such as cable flood damage, the requirement to deliver medium/high voltage power can necessitate cable exposure to potential flooding, condensation and water immersion. A robust cable joint is designed to withstand the deteriorative effects of water in both indoor or outdoor environments.
The cable joint kits include thick-wall heat shrink adhesive lined tubes to provide high performance water sealing, protection and corrosion resistance in above ground exposed or direct buried underground cable trenches – the outer protection heat shrink tubing (colour black) provides a moisture barrier to water ingress through the activation of an inner lining of adhesive which melts and flows upon the application of a heat source provided by the cable jointers gas torch.
Prior to installing the outer shrink tube the jointer should clean, de-grease and abrade the outer cable sheath of the 33kV cable – to achieve an even wall thickness the cable jointer should keep the flame moving and avoid scorch or burn damage to the heat shrink or cable.
The jointer will apply heat evenly to the centre of the cable joint – once the heat shrink tube is fully recovered (“shrunk”) the joint should be smooth, wrinkle-free and the heat activated sealant should be visible at the tube ends in contact with the cable sheath.
The tough and durable heat shrink provides reinstatement of cable sheath or jacket insulation and withstands trench backfill prior to energisation of the HV joint.
The 33kV joints are installed using normal procedures for heat shrink cable joints with clear installation instructions confirming precise cable stripping dimensions and marking measurements for sheath, semicon and insulation removal – joints are installed using the standard cable jointing tools depending upon cable construction.
Although not designed to be permanently submerged in water, 33kV cable joints use heat shrink tubes to prevent water ingress into high voltage cables whether buried underground or located onto cable containment in MV-HV substations.
Should you require any assistance with the selection or specification of MV-HV joints or terminations please do not hesitate to contact us.
Further reading:
The following Training Video shows the installation process for installing heat shrink joints to single core 33kV cable – this Video is for familiarisation purposes and not intended as a substitute for attending recognised industry training courses and achieving manufacturers competency. The Video produced by SPS with narration provides comprehensive guidance from the initial stripping and removal of the 33kV cable sheath to the final completion of the heat shrink joint.
More 33kV Products For High Voltage Cables ♦ 33kV Surge Arresters ♦ 33kV Fuses ♦ 33kV Lugs ♦ 33kV Portable Earthing ♦ 33kV Cable Terminations
LV ♦ MV ♦ HV
T&D distribute the most extensive range of LV, MV & HV Cable Jointing, Terminating, Installation & Cable Pulling Equipment – we service UK and international clients working on underground cables, overhead lines, substation earthing and electrical construction at LV, 11kV, 33kV and EHV transmission and distribution voltages.
LV – Low Voltage Cable Joints, Glands, Cleats, Lugs & Accessories (1000 Volts)
MV HV – Medium & High Voltage Cable Joints, Terminations & Connectors (11kV 33kV EHV)
Cable Laying – Underground Cable Covers, Ducting, Seals & Cable Pulling Equipment
T&D’s Power Blog covers: LV MV HV & EHV Transmission & Distribution, Substations, Switchgear, Cable Jointing & Termination, Cable Fault & Repair, Underground Cables
➡ Visit Power Blog.
Cable Joint Application Notes – the smooth profile LV heat shrink cable joints were specified to connect and splice single core shielded 185mm CSA cables powering test cells located in a cable trench. The 500KW battery simulator unit provides 1000V and 1000A up to 500KW which can be supplied to several test cells.
The cable joints were required to enable the relocation of the LV distribution unit by extending the existing low voltage cables by inline jointing.
Lapp Cable ÖLFLEX® joints are available to suit single core 10-300sqmm cable conductors.
Heat shrink cable joints are compatible with polymeric cables with XLPE or EPR insulation – specialist versions of the joint kit are available for zero halogen and fire resistant cables.
♦ Cable Joint Installation Instruction
Once the cable insulation has been removed and stripped and the conductors jointed using appropriate crimp connectors and crimping tools the inner heat shrink tube can be positioned onto the cable to be jointed overlapping equally at both sides – the joints were supplied with Cembre connectors. Earth continuity of wire braided or wire armoured cables is achieved across the cable joint using tinned copper mesh and earth braid secured using constant force roll springs.
Connectors – both crimped or mechanical shearbolt connectors are suitable for use with heat shrink cable joints. Where mechanical shearbolt connectors are used the inner heat shrink tube may need to be increased in size. Check with T&D.
Heat Shrink Cable Joint Kit Installation
Highly flexible, screened single core cable with PVC insulation and PVC sheath – certified for North America.
ÖLFLEX® FD 90 CY manufactured by Lapp Group is a screened single core power cable for use in low voltage power chains with UL/CSA AWM certification – EMC compliant copper screening. Flame retardant according to IEC 60332-1-2 & CSA FT1. High oil resistance. Low adhesive surface. 4000V test voltage.
Headquartered in Stuttgart, Germany, the Lapp Group is a leading supplier of integrated wire, cabling and connector products and solutions. Lapp Group manufactures and supply’s electrical and fibre optic cables, industrial plug-in and screw connectors, cabling solutions, automation technology and technical accessories. Lapp Group’s core markets are in the mechanical and plant engineering and electronics manufacturing sectors, with rapid market expansion in the renewable energy, mobility and life science industries.
Thorne & Derrick International can specify and supply standard and bespoke LV cable joints utilising heat shrink, cold shrink or resin cast type jointing kits.
Should you have a specific application for LV, MV, HV up to 33kV cable joints please contact us. For further information:
Published 21 Apr 2026
5 Common Cable Management Mistakes And How To Avoid Them Cable management is often overlooked but in industrial environments, it plays a critical role in safety, reliability and long-term performance. Loose, poorly routed or unprotected cables can quickly become...
Published 10 Apr 2026
Rethinking Cable Cleats for High-Density Data Centres Global demand for cloud computing, AI workloads and digital services is accelerating the construction of data centres at an unprecedented scale. Hyperscale facilities are now being developed across Europe, North America and...
