How to Install a Heat Shrink Cable Termination
2026-06-30 16:40Heat shrink cable terminations are one of the most widely used methods for terminating medium‑voltage cables. They offer a reliable, cost‑effective solution when properly installed. However, their success depends heavily on the installer's skill and attention to detail. Unlike cold‑shrink terminations, which rely on pre‑expanded elastomers, heat shrink terminations require the application of heat – typically from a propane torch or hot air gun – to shrink the tubing and activate the adhesive lining. This article provides a step‑by‑step guide to installing a heat shrink cable termination, highlighting the critical steps and common pitfalls.
1. Before You Start: Preparation and Safety
Proper preparation is the foundation of a successful termination. Rushing this stage is the most common cause of failure.
Read the manufacturer's instructions – Every heat shrink kit is different. Read the instructions thoroughly before starting. Note the stripping dimensions, temperature settings, and shrink times.
Gather your tools – You will need:
A heat source (propane torch with a flame‑spreader nozzle, or a hot air gun with adjustable temperature).
Cable stripping tools (ring cutter, longitudinal cutter, and insulation stripper).
Cleaning materials (manufacturer‑supplied wipes, abrasive cloths).
Crimping tools and dies for the connector.
A measuring tape or ruler.
(Optional) An infrared thermometer to check surface temperature.
Prepare the work area – Ensure the area is clean, dry, and well‑lit. Protect the work from wind (which can cool the heat shrink) and dust. Position the cable so you can work comfortably around its circumference.
Safety first – Wear safety glasses, heat‑resistant gloves, and appropriate clothing. Ensure adequate ventilation if working indoors.
2. Preparing the Cable: Stripping to Dimensions
The most critical step – and the one most often done incorrectly – is preparing the cable ends to the exact dimensions specified by the manufacturer.
Strip the outer jacket – Using a ring cutter, score the jacket at the specified distance from the end. Be careful not to cut into the metallic shield or insulation beneath. Remove the jacket.
Remove the metallic shield – If the cable has a copper tape or wire shield, cut it at the specified distance. For a corrugated aluminium or lead sheath, use a specialised cutter.
Strip the semi‑conductive layer – The semi‑conductor (screen) must be removed to expose the insulation. Score it with a knife, taking care not to nick the insulation, then peel it off.
Remove the insulation – Strip the insulation to expose the conductor to the specified length for the connector.
Create a smooth transition – At the point where the semi‑conductor ends, create a smooth, tapered transition by sanding or scraping. This is essential for stress control.
Clean thoroughly – Wipe the exposed insulation with the manufacturer‑supplied cleaning wipes. Remove all carbon residues, dust, and grease. Do not touch the cleaned surface afterwards.
Always measure twice. A small error in stripping dimensions can misalign the stress control tube, leading to partial discharge and eventual failure.
3. Installing the Conductor Connector
The connector (lug or pin) must be securely crimped onto the conductor.
Select the correct connector – Ensure it matches the conductor material (copper or aluminium) and size.
Slide the connector over the conductor – For stranded conductors, ensure no strands are splayed or missing.
Crimp using the correct die and pressure – Follow the connector manufacturer's crimping chart. Use the specified die size and apply the recommended number of crimps.
Inspect the crimp – The crimp should be symmetrical, with no sharp edges or cracks. The connector should be firmly attached with no movement.
Clean again – Wipe the connector and adjacent conductor to remove any metal filings or grease.
4. Positioning the Heat Shrink Components
Heat shrink termination kits include a series of tubes and components, each designed for a specific location on the termination.
Stress control tube – This is the most critical component. It must be positioned so that it covers the semi‑conductor cut‑back and extends a precise distance onto the exposed insulation. The manufacturer's instructions will specify the exact positioning.
Main insulation tube – This tube is larger and covers the stress control tube, extending down over the cable jacket.
Weather sheds (for outdoor terminations) – These are the disc‑shaped skirts that provide creepage distance. They slide over the main tube at specified positions.
Sealing sleeves – Smaller tubes that seal the cable jacket entry and the conductor exit.
Slide all components onto the cable in the correct order before shrinking any of them. Once a tube is shrunk, you cannot move it, and you cannot slide other components past it.
5. Applying the Heat: The Critical Operation
Heating is where skill matters most. Too little heat, and the tube does not fully shrink or the adhesive does not flow. Too much heat, and the tube can char, melt, or lose its properties.
Start from the centre – For each tube, apply heat from the centre outward, moving the flame or hot air in a circular motion.
Maintain the correct temperature – For polyolefin heat shrink, the recommended temperature is typically 120–140°C. Use an infrared thermometer to check the tube surface temperature.
Watch for adhesive flow – Most heat shrink tubes have an adhesive lining. When the tube shrinks, adhesive should appear as a bead at the ends. This indicates a good seal.
Work systematically – Shrink the stress control tube first, then the main insulation tube, then the sealing sleeves, and finally the weather sheds.
Avoid overheating – If the tube turns brown or black, it has overheated. This weakens the insulation. Overheating can also damage the cable insulation beneath.
Allow cooling – After shrinking, allow the components to cool undisturbed. Do not move or stress the termination until it has cooled to ambient temperature.
6. Sealing the Cable Jacket Entry
The seal between the cable jacket and the termination is critical to prevent moisture ingress.
Most heat shrink terminations include a mastic sealing sleeve or adhesive‑lined tube that covers the transition from the termination body to the cable jacket.
When heated, the adhesive melts and flows into the cable jacket's surface irregularities, creating a watertight seal.
Ensure the cable jacket is clean and abraded (as specified) to give the adhesive a good surface to bond to.
7. Installing Weather Sheds (Outdoor Terminations)
For outdoor terminations, weather sheds (also called skirts) must be installed.
They are usually slid over the main insulation tube before it is shrunk, or they may be separate components that are shrunk on afterwards.
Position them at the specified distances from the conductor and from each other. The spacing is designed to provide the required creepage distance and dry arcing distance.
Ensure they are oriented correctly – the large diameter should point downwards to shed water.
8. Connecting the Ground
The cable shield must be connected to the ground through the termination.
In many heat shrink terminations, a ground braid or wire is attached to the shield before the termination is applied.
This braid is then connected to the equipment's ground point or to a separate ground lug on the termination.
Ensure the ground connection has low resistance and is mechanically secure.
9. Final Inspection and Testing
After installation, the termination must be inspected and tested before energisation.
Visual inspection:
All tubes should be fully shrunk with no wrinkles or gaps.
The adhesive should be visible at the ends of the tubes.
Weather sheds should be correctly positioned and oriented.
There should be no signs of burning, charring, or melting.
Electrical testing:
Insulation resistance – typically measured with a 1 kV or 5 kV megger.
High‑voltage withstand (AC or DC) – at the specified test voltage for the cable's rating.
Partial discharge measurement – to confirm the absence of voids.
Only after passing these tests should the cable be energised.
10. Common Mistakes and How to Avoid Them
| Mistake | Consequence | Prevention |
|---|---|---|
| Incorrect stripping dimensions | Stress control misaligned; PD risk | Measure twice; follow instructions. |
| Contamination on insulation | PD initiation | Clean thoroughly; avoid touching. |
| Uneven heating | Incomplete shrinkage or charring | Rotate heat source; check temperature. |
| Overheating | Insulation damage; brittleness | Use temperature control; don't overheat. |
| Forgetting a component | Cannot be corrected after shrinking | Lay out all parts before starting. |
| Not allowing cooling | Disturbed seal | Wait until cool before handling. |
| Inadequate cleaning of cable jacket | Poor adhesive bond; water ingress | Abrade and clean the jacket surface. |
Heat shrink cable terminations are a reliable, field‑proven technology, but they demand respect and precision. The installation process is a sequence of carefully measured and executed steps – from stripping the cable to the final shrink. Each step affects the termination's long‑term performance. By following the manufacturer's instructions, using the correct tools, and paying attention to the details, an installer can produce a termination that will perform reliably for decades. In the world of cable accessories, there is no substitute for skill, and heat shrink installations are where that skill is most clearly demonstrated.