Installation Guide for Cold Shrink Ends 

Introduction: Why installation of cold shrink cable termination requires special precision

Installationcable terminationis a critical step in creating a reliable power supply system. An error at this stage can lead to insulation breakdown, short circuit and long equipment downtime. Unlike heat-shrinkable counterparts, cold shrink technology does not require the use of open flames or gas burners, which makes it preferable for work in fire hazardous areas, tunnels and rooms with limited ventilation. However, the absence of thermal effects imposes its own requirements: mechanical preparation of the surface and compliance with the geometry of the installation play a decisive role here.

In our practice, we have repeatedly encountered situations where the failure of a cable line occurred not because of the quality of the coupling itself, but because of violations during its installation. For example, one of our clients in Siberia experienced a series of breakdowns at a 10 kV substation in winter. The investigation found that the installers did not properly clean the semiconductive layer of the cable before installing the stress control tube. Graphite microparticles created local high-intensity fields, which led to partial discharges and eventual destruction of the insulation. This case highlights that cold shrink technology is less forgiving of preparation errors than heat shrink, but provides a more consistent result when instructions are strictly followed.

This manual has been developed based on almost twenty years of company experienceShijiazhuang Hist Electric Co.,Ltd. We have been manufacturing cable accessories since 2004, and our engineers have accumulated an extensive knowledge base on the behavior of silicone rubber in various climate conditions. Here we'll go through every installation step in detail, from tool preparation to final inspection, so you can get the job done right the first time.

Preparatory phase: Tools and environmental conditions

The success of installation depends 80% on preparation. Before opening the coupling package, you must ensure that you have all the necessary tools and that the environmental conditions are appropriate. Working on your knees or with an unsuitable tool will inevitably lead to defects.

Required set of tools

For quality installationcable terminationyou will need the following basic set:

• Cable knife or stripper:For careful removal of the outer shell, armor tape and internal insulation. The blade must be sharp so as not to damage the wires and screen.
• Sandpaper (P120–P240 grit):Necessary for cleaning the insulation surface and creating roughness for better adhesion of sealants. Do not use paper that is too rough to avoid leaving deep scratches.
• Lint-free wipes and solvent:Use isopropyl alcohol or a special cleaner to degrease surfaces. Cotton wool leaves fibers that can become puncture centers, so it is prohibited.
• Measuring tape and marker:For precise marking of cutting dimensions. An error of 5 mm can result in incorrect positioning of the stress control element.
• Torque wrench or torque screwdriver:For tightening bolted connections of lugs to the torque recommended by the manufacturer.
• Silicone grease (optional):Sometimes required to ease the tension of cold-shrinkable tubing on large diameter cables, although most modern couplings are factory coated.

Environmental requirements

Cold shrinkage is less temperature sensitive than heat shrinkage, but extreme conditions will still affect the process. The optimum temperature for installation is from -10°C to +40°C. At temperatures below -10°C, silicone rubber becomes less elastic, increasing the risk of damage to the tube when stretched. If work is carried out outside in frosty weather, it is recommended to first keep the coupling set in a warm room for at least 24 hours.

Humidity also plays a role. Although silicone is hydrophobic, moisture or dirt cannot get between the layers of insulation. During rain, snow or fog, installation should be carried out under a canopy or in a special tent. Dust is the main enemy of high-voltage insulation. Each dust particle can create a microscopic air gap, which at high voltage will lead to corona.

Expert advice:Before starting work, always check the integrity of the coupling packaging. If the vacuum seal is broken, the silicone tubes could lose their elastic properties or become dirty. BShijiazhuang Hist Electric Co.,LtdWe use multi-layer vacuum packaging, which maintains the sterility of components even during long-term storage in open warehouses, but verification remains a mandatory step.

Step-by-step instructions for installing a cold shrink end sleeve

Below is a detailed sequence of steps for installing a single-core medium voltage (6-35 kV) termination. For three-core cables, the procedure is repeated for each phase, taking into account the observance of interphase distances.

1. Cable preparation and removal of external coverings

   Cut the cable perpendicular to its axis. An uneven cut will make subsequent installation of the O-rings difficult and may result in misalignment. Remove the outer polymer shell to the length specified in the instructions for the specific coupling model (usually 700–900 mm from the cut). Be extremely careful not to damage the metal screen (copper tape or wire). If the cable has armor, remove it, leaving enough margin for grounding. Clean the insulation surface from any remaining semiconducting layer if it protrudes beyond the edge of the screen. Important: do not make cuts on the main core insulation. Even microdamage can become a source of development of a breakdown tree.

2. Screen cutting and grounding installation

   Carefully cut and remove the semiconducting screen to the estimated length. The boundary between the screen and the insulation must be smooth and clean. Use a special tape to smooth the transition step, if this is provided for by the coupling design. This is a critical point: the abrupt transition creates a concentration of the electric field. Then install the grounding conductor. For cables with a copper screen, use a spring clamp or solder (if technology allows), ensuring reliable electrical contact. Check the contact resistance with an ohmmeter - it should be minimal. In productsHist ElectricPre-installed grounding elements are often used to simplify this step, but control of the quality of the connection remains with the installer.

3. Stripping and sanding insulation

   This is the most time-consuming, but most important stage. Take sandpaper and thoroughly sand the surface of the main core insulation in the area where the stress control tube will be installed. Your goal is to remove all traces of semiconductive material and create a uniform roughness. After cleaning, thoroughly clean the surface with a lint-free cloth soaked in alcohol. Move from the middle of the insulation to the edge to avoid bringing dirt back in. The surface must be absolutely dry and clean.Common mistake:installers touch the cleaned surface with their hands. Fatty fingerprints impair adhesion and dielectric properties. Use clean nitrile gloves after this step.

4. Installation of a stress-control tube (Cold Shrink Tube)

   The stress control tube is the heartcable termination. It equalizes the electric field in the area where the screen ends. The tube is supplied on a plastic spiral frame (core). Align the bottom edge of the tube with the edge of the cable's semiconductive shield. Make sure that the markings on the tube match the markings on the cable. Slowly pull the plastic frame down. The tube will compress the cable with a constant force. Do not pull too hard as you may dislodge the tube. After removing the frame, ensure that the tube fits snugly around the insulation and is not wrinkled. If the tube has become dislodged, it is almost impossible to correct it - the component will need to be replaced.

5. Mounting the coupling body and protective tube

   An outer insulating casing is installed on top of the stress control tube. It is also made using cold shrink technology. The process is similar: align, pull out the frame. The housing provides mechanical protection and additional insulation, and also seals the interface. Pay attention to the orientation of the flare (skirt) of the coupling. It should face down to prevent moisture from getting inside. Some models use a single tube for low voltage (1 kV) cables, combining the functions of insulation and sealing. For medium voltage the structure is multilayer. CompanyShijiazhuang Hist Electricproduces tubes from high-quality silicone rubber, which maintains elasticity from -50°C to +200°C, which guarantees long-term tightness even with thermal expansion of the cable.

6. Installing the Contact Tip

   Strip the insulation from the end of the core to a length equal to the depth of the lug hole plus 5 mm. Clean the core metal to a shine. Insert the core into the ferrule. Tighten the bolts using a torque wrench, observing the tightening torque specified in the tip data sheet. Over-tightening can strip the thread or deform the tip; under-tightening will lead to overheating of the contact. After installation, place an insulating sleeve or heat shrink tubing over the ferrule-core connection to prevent moisture ingress and corrosion. If a bolt end is used, ensure that the head of the bolt does not protrude beyond the coupling insulation dimensions.

7. Final sealing and fixation

   Check all O-rings. At the bottom of the coupling, where it connects to the outer sheath of the cable, there is usually a sealing tape or ring. Make sure it is pressed tightly. Some designs require additional wrapping with self-vulcanizing tape for complete waterproofing. Secure the coupling to the cable using banding tapes, if provided for in the design, to remove the mechanical load from the contact point. Visually inspect the entire structure: there should be no visible gaps, folds or damage to the silicone.

Typical installation errors and methods for preventing them

Even experienced electricians sometimes make mistakes that reduce their service life.cable termination. We will analyze the most common of them, based on an analysis of complaints received by our technical support.

1. Damage to insulation when removing screen

Using a dull knife or applying excessive pressure when cutting the semiconductive layer often causes cuts in the main insulation. These cuts may not be visible to the naked eye, but under voltage they become channels for the propagation of partial discharges.

Solution:Use specialized strippers that have a cutting depth limiter. If you must use a knife, hold it at a 45-degree angle and control the depth of penetration of the blade visually and tactilely.

2. Insufficient surface cleaning

Residues of semiconducting material or dust on the insulation surface under the stress control tube create conductive bridges. This leads to local overheating and breakdown.

Solution:Spend more time cleaning than seems necessary. Use the “white cloth” method: wipe the insulation until the cloth comes out perfectly clean. Change napkins more often.

3. Displacement of the stress control tube

If the tube is installed offset from the edge of the screen, the field leveling area will not be where it should be. Some of the high voltage will be on the unprotected insulation, and part of the shield will remain unshielded properly.

Solution:Carefully mark the cable before installation. Use a laser level or a straight edge to mark a clear boundary line. When pulling the frame, hold the tube steady with your other hand to compensate for friction.

4. Ignoring temperature conditions

Installation in severe frost without heating the coupling causes the silicone to lose its elasticity. When pulling on the cable, the tube may crack or fail to provide the required crimping pressure.

Solution:Always keep couplings warm before installation in winter. If the cable is cold, it is also advisable to warm it up with a hair dryer (at a low temperature, carefully) or let it rest in a warm room.

Technical advantages of cold-shrinkable couplings from Shijiazhuang Hist Electric Co., Ltd.

The choice of cable accessory manufacturer determines the reliability of the entire power system.Shijiazhuang Hist Electric Co.,Ltd, based in Hebei Province, China, combines deep engineering expertise and state-of-the-art manufacturing facilities. Founded in 2004, the company specializes in solutions for medium and high voltage networks, includingcable terminationscold and heat shrink.

The key difference between our products is the quality of raw materials. We use imported premium silicone rubber, which undergoes strict incoming inspection in our own electrical laboratory. This laboratory, one of the largest in Northern China, is capable of testing at voltages up to 1000 kV. This means that every batch of couplings is tested to ensure compliance with international safety standards such as IEC 60502 and GOST.

Our production base includes specialized silicone processing workshops, where strict air purity control is maintained. This is critical to prevent air bubbles from being incorporated into the rubber structure, which could become insulation defects. In addition, the presence of three specialized warehouses and developed logistics allows us to ensure stable delivery times to the CIS countries, the Middle East and Africa.

The company's engineering team, including 7 doctors and candidates of science, is constantly improving the design of couplings. For example, our latest developments in the field of stress-control elements reduce the electric field strength by 15% compared to standard solutions, which significantly increases the service life of the product in conditions of frequent switching overvoltages. We offer not just a product, but a comprehensive solution: from selecting the type of coupling for a specific cable to consultations on installation in difficult climatic conditions.

Quality control and acceptance testing

After installation is completed, it is necessary to carry out visual and instrumental inspection. Do not connect the cable to the network until you are sure of the quality of work.

Visual inspection

• Check for mechanical damage to the silicone coating (cuts, punctures).
• Make sure that all tubes fit snugly, without gaps or folds.
• Check the correct phasing and markings.
• Make sure that the grounding is connected securely and insulated at the points of contact with the phases.

Electrical tests

According to the standards (PUE, IEC 60502-4), after installing the end couplings, the following tests should be carried out:

1. Insulation resistance measurement:It is carried out with a megohmmeter at a voltage of 2500 V or 5000 V (depending on the voltage class of the cable). The resistance must comply with the standards (usually at least 1000 MOhm for cables up to 10 kV, but the exact values ​​depend on the length and type of cable).
2. DC high voltage test:For 6–10 kV cables, a voltage of 24–36 kV is applied for 5–15 minutes. There should be no breakdowns.
3. Ground continuity check:Measuring the resistance of the grounding device.

If the tests are successful, the cable is ready for commissioning. Document test results for future maintenance.

Frequently Asked Questions

Can cold shrink sleeve be reused?

No. Cold-shrinkable tubing is irreversibly deformed after being removed from the plastic frame and installed on the cable. Trying to remove them will cause the silicone to rupture. The coupling is intended for one-time use. If an installation error is made, a new kit must be used.

What is the main difference between cold shrinkage and heat shrinkage?

The main difference is in the fixation method and the requirements for installation conditions. Cold shrink uses silicone shape memory and tension without requiring heat. It is safer (no open flame), faster and allows you to work in gassy environments. Heat shrink is cheaper, but requires careful warming up, which is risky in strong winds or near flammable materials. For critical objects and difficult conditions, we recommend cold shrinkage.

What is the service life of cold shrink end sleeves?

With proper installation and operation under normal conditions, the service life of high-quality silicone couplings is at least 30 years. ProductsShijiazhuang Hist Electric Co.,Ltddesigned for a long service life due to the resistance of silicone to ultraviolet radiation, ozone and temperature changes. However, in aggressive chemical environments, service life may be reduced, which requires individual selection of materials.

What to do if the handset is not completely seated on the cable?

If after removing the frame there are gaps or folds, this is an installation defect. Trying to “straighten” the tube with your hands will not work, since the crimping force has already been distributed. The only correct action is to cut off the defective coupling and install a new one. Operation of such a line is unacceptable.

Conclusion

Installationcable terminationCold shrinkage is a process that requires discipline, purity and precision. Refusal to use open fire simplifies the procedure, but increases the requirements for the quality of surface preparation and positioning of elements. By following the instructions above, you will minimize the risk of accidents and ensure uninterrupted operation of your power system for decades.

Remember that the quality of the coupling and the quality of the installation are equally important. Choosing a trusted manufacturer such asShijiazhuang Hist Electric Co.,Ltd, gives you confidence that the material will withstand operating loads. Our products undergo multi-level control in the laboratory with test voltages up to 1000 kV, which confirms their reliability.

To receive technical advice, select couplings for your cable type, or place an order, contact our specialists. We provide full support at all stages - from design to commissioning.

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