Heat Shrink Kit

A Heat Shrink Kit is a collection of heat‑shrinkable tubing and associated components specifically selected for use in airfield ground lighting (AGL) cable jointing, termination, and repair applications. The kit typically includes a range of tubing diameters and colours, as well as adhesive liners, end caps, and sometimes a heat gun (or instructions for its use).

Heat‑shrink tubing is a polymer tube that shrinks radially (and often longitudinally) when heated, forming a tight, protective layer over cables, joints, and connectors. Dual‑wall tubing with an internal adhesive liner provides a watertight seal, making it ideal for buried and submerged AGL installations. The kit is designed to meet the demanding performance requirements of airfield environments, including resistance to moisture, temperature extremes, UV exposure, and mechanical stress.

A heat shrink kit exists to restore, at a joint or termination, the same level of insulation and moisture protection the cable had straight from the factory, since a splice is only as reliable as its weakest point of coverage. The dual-wall design with an internal adhesive liner is what makes this possible below ground: as the outer wall shrinks and the liner melts and flows around the conductor and any surface irregularities, the result is a continuous seal rather than a wrap that simply sits on top of the joint. Without that seal, moisture ingress at a buried termination is one of the more common and hardest-to-diagnose causes of intermittent circuit faults on an AGL system, since the fault can appear and disappear with soil moisture conditions long after installation.

The heat shrink kit is used across the airfield for a variety of cable and connector applications, including:

• Cable Splicing: Insulating and sealing joints in primary and secondary AGL cables, both underground and in pits.
• Connector Termination: Providing stress relief and moisture sealing at the cable entry points of L‑823 connectors and other terminations.
• Fixture Wiring: Protecting and insulating connections inside light fixtures, junction boxes, and signs.
• Repair and Maintenance: Quick, reliable insulation repair of damaged cable insulation in the field.
• Colour Coding: Using different colour tubing to identify cable phases, circuits, or function (e.g., primary vs. secondary).

The kit is suitable for use with both copper and aluminium conductors, and the tubing is compatible with common cable insulations such as XLPE, PVC, and EPR. It is designed for installation by trained personnel using a standard heat gun or gas torch with a suitable diffuser.

The kit is applied at the location of a cable splice or termination — a below-grade joint pit, a handhole, a junction box, or inside a light fixture base — with the tubing selected to suit the diameter of the completed splice before any of it is heated. Work is generally carried out in dry conditions or with the joint temporarily shielded from moisture, since the adhesive liner needs a clean, dry surface to bond and seal properly. The tubing is positioned to fully overlap the joint and a reasonable length of the original cable insulation on each side, then shrunk evenly from the centre outward using a heat gun or gas torch, so the adhesive flows around the joint's irregular profile rather than leaving voids. Once shrunk, the joint is generally allowed to cool before being placed in its final position — in a splice enclosure, buried trench, or junction box — so the sealed section isn't flexed or stressed while the adhesive is still warm and pliable.

Heat‑shrink tubing works by applying heat to cause the polymer material to shrink and conform tightly to the underlying cable or joint. The kit provides the necessary components and facilitates the following functions:

• Electrical Insulation: The tubing provides a high‑dielectric‑strength insulating layer over conductors, joints, and terminations, preventing short circuits and leakage.
• Moisture Sealing: Dual‑wall tubing with an internal hot‑melt adhesive liner melts and flows during heating, creating a watertight seal that prevents moisture ingress—critical for buried and pit installations.
• Mechanical Protection: The shrunk tubing provides a tough, abrasion‑resistant layer that protects against mechanical damage, vibration, and environmental stress.
• Strain Relief: The tight fit of the tubing provides strain relief at cable entries, preventing conductor fatigue and breakage.
• Colour Identification: Coloured tubing allows for easy identification of circuit phase, function, or cable type, aiding in maintenance and troubleshooting.

The typical installation process involves selecting the correct tubing size (pre‑shrink diameter must be larger than the cable, and the final diameter must be smaller), sliding it over the cable or joint, applying heat evenly with a heat gun until the tubing shrinks and the adhesive flows, and allowing it to cool to form a permanent seal.

Heat-shrink tubing carries no current at all — it is insulation, not conductor — so it has no direct place in the ALCMS/CCR control chain and no way to signal its own condition to the series circuit. Its function is to protect the loop's insulation resistance at the joint or termination it covers, and it is that insulation resistance, not the tubing itself, that the wider system depends on. A failed or poorly formed shrink seal does not present as a loop current or voltage anomaly on the CCR in the way a broken conductor would; instead it slowly admits moisture into the joint beneath it, which degrades insulation resistance over time and can eventually manifest as a nuisance earth-fault trip or increased leakage current, well after the original installation. Because the CCR's real-time loop monitoring is built around current and voltage rather than insulation resistance, a compromised heat-shrink seal is normally only caught through scheduled offline insulation resistance testing (megger testing) of the loop, not through anything the ALCMS reports during normal operation.

The core component of the kit, the heat‑shrink tubing itself, is manufactured as a dual‑wall extrusion: an outer wall of radiation cross‑linked polyolefin (or PVDF/elastomeric compound for higher‑temperature duty) that is expanded to several times its finished diameter during manufacture and "remembers" its smaller original size once reheated, and an inner wall of thermoplastic adhesive that remains solid at ambient temperature but melts and flows once the outer wall shrinks around it. When a heat gun or torch is applied on installation, the outer wall contracts radially (and to a lesser extent longitudinally) to conform tightly to the cable, connector, or joint underneath, while the melted inner adhesive is forced into any surface irregularities and bonds to the substrate, producing a continuous watertight seal rather than a simple mechanical wrap. The kit is supplied as a range of tubing diameters and pre‑cut lengths to match different cable and joint sizes, together with matching heat‑shrink end caps for sealing spare cores, and is packaged with basic application instructions since correct, even heating is what determines whether the finished seal performs to specification.