XLPE Cable Jointing Procedure: Step-by-Step Heat Shrink Joint Kit Installation Guide for Indian Engineers

Introduction: Why Correct XLPE Cable Jointing Procedure Matters

XLPE (cross-linked polyethylene) cables dominate India's underground power distribution network from 1.1kV to 33kV — and for good reason. XLPE cables are lighter, more flexible and thermally superior to the PILC cables they have replaced. But their performance advantage is entirely dependent on one critical factor: correctly installed cable accessories at every joint and termination.

Field statistics are consistent across utilities: over 70% of cable system failures occur at joints and terminations, not in the cable itself. The cable can run flawlessly for 30 years, but a poorly made joint may fail within months — due to moisture ingress, inadequate stress control, improperly prepared conductor contact surfaces, or incorrect application of heat shrink components.

This step-by-step XLPE cable jointing procedure guide covers the complete installation of a heat shrink straight-through joint kit for XLPE cables from 1.1kV to 33kV, as manufactured by VIKCHEM. It follows the requirements of IS 13573, the Indian Standard for cable jointing accessories, and reflects 38 years of field installation experience.

Tools and Materials Required

Before beginning any XLPE cable jointing procedure, assemble all tools and materials. Stopping mid-joint to locate missing equipment causes delays and introduces contamination risks.

Tools

• ●Cable stripper (rotary or adjustable blade — NOT a knife for XLPE insulation)
• ●Conductor shear or hydraulic crimping press with correct dies
• ●Semi-conductor screen scorer and remover
• ●Cable screen tape cutter
• ●Fine glass paper or abrasive roll (120 grit)
• ●Lint-free wiping cloths
• ●Propane torch or industrial heat gun (min. 2kW for joint applications)
• ●Heat-reflecting barrier sheet
• ●Steel tape measure and permanent marker
• ●Torque wrench (for mechanical connectors)

Materials (from VIKCHEM Heat Shrink Joint Kit)

• ●Crimped or mechanical connector appropriate for conductor size and material
• ●Stress control tube (one per conductor)
• ●Insulating tube (one per conductor, medium voltage)
• ●Screening tape or copper braid (for screen reinstatement)
• ●Mastic sealing tape
• ●Outer protective tubing
• ●Core identification sleeves (red, yellow, blue)
• ●Installation instruction sheet (follow kit-specific dimensions)

PPE

• ●Insulated gloves (rated for system voltage)
• ●Safety glasses or face shield
• ●Fire-retardant overalls
• ●Flame-resistant mat under work area

Pre-Installation Checks

1. Cable Drum Condition Check

Inspect both cable ends for:
• ●Physical damage to outer jacket
• ●Moisture at cut ends (check with megger — minimum 1000 MΩ insulation resistance before jointing)
• ●Correct cable type and voltage rating match between both drum ends

2. Kit Compatibility Verification

Confirm the joint kit is rated for:
• ●System voltage (1.1kV / 6.6kV / 11kV / 22kV / 33kV)
• ●Cable type: XLPE (not PILC — they use different kits)
• ●Conductor size and material (copper or aluminium) within kit range
• ●Number of cores (single-core, 3-core belted, 3-core screened)

3. Worksite Preparation

• ●Ensure joint pit is free of standing water
• ●Cover work area with plastic sheeting to prevent soil contamination
• ●Arrange lighting — adequate visibility is essential for screen preparation

Step-by-Step XLPE Cable Jointing Procedure

Step 1 — Cable End Preparation and Length Allowance

Straighten both cable ends for a minimum of 1.5 metres from the joint position. Never joint on a curved section — torsional stress at the joint degrades long-term performance.

Mark the cable with temporary identification tape if multiple cable ends are present in the joint pit — connecting the wrong phases is a common and costly error.

Allow a minimum of 800mm working length on each cable end beyond the final joint position. This allows for re-cuts if a preparation step is done incorrectly without having to move the joint position.

Step 2 — Outer Jacket (Sheath) Removal

Using the kit installation guide, mark the outer jacket removal length on both cable ends (typically 400–600mm for 11kV 3-core). Use a rotary cable stripper to cut through the jacket at the marked point — do NOT use a knife with a cutting motion that risks scoring the armour or screen beneath.

Score around the jacket circumferentially at the cut mark, then score longitudinally and peel back. On PVC-jacketed cables, gentle heating with a heat gun softens the jacket for cleaner removal.

Critical: Inspect the armour wires (if present) — they must be clean, undamaged and free of corrosion at the point where earth bonding connections will be made.

Step 3 — Armour Termination and Earthing

For armoured XLPE cables: 1. Fold back the armour wires over the outer jacket to the required length 2. Apply an armour clamp or earth bonding ferrule to secure the wires 3. Connect an earthing braid between both cable armour/screens — the screen must be continuous through the joint 4. Secure with armour clamp bolts to the specified torque (check kit instructions)

Armour earthing is non-negotiable on medium voltage cables. Un-earthed armour on a screened cable creates a dangerous touch voltage on the armour surface under fault conditions.

Step 4 — Core Separation and Identification

For 3-core cables, carefully separate the cores to the required length (typically 250–350mm for 11kV). Avoid sharp bends at the crotch — use a gentle sweeping separation.

Apply core identification sleeves immediately:

• ●Red: L1 (R phase)
• ●Yellow: L2 (Y phase)
• ●Blue: L3 (B phase)

Confirm phase identification matches between both cable ends before proceeding. A phase transposition error at this step will not be visible in subsequent steps and may only be discovered during energisation.

Step 5 — Metallic Screen Removal and Termination

On screened medium-voltage XLPE cables, the metallic screen (typically copper tape or wire screen) must be cut back to a precise dimension specified in the kit installation guide. This dimension is critical — it determines the electrical field distribution at the screen cut-back.

1. Mark the screen cut-back dimension on each core 2. Using the screen cutter tool, score around the screen at the mark — do NOT cut through to the semi-conducting screen beneath 3. Remove the cut screen section by unwinding copper tape or cutting the copper wire screen 4. Fold back the remaining screen neatly — it will be used later for screen reinstatement at the joint

Key warning: The cut edge of the copper screen must be smooth and burr-free. A rough or jagged screen edge concentrates electrical stress and can cause premature insulation failure. Smooth with fine file if needed.

Step 6 — Semi-Conducting Screen Removal

Beneath the metallic screen is a semi-conducting (semi-con) screen layer — a black extruded compound that bonds to the XLPE insulation. This layer must be removed from the conductor connection zone, leaving a clean transition.

1. Score around the semi-con at the specified dimension (from the kit guide) 2. Using the semi-con scorer, peel the semi-con back to the score line 3. The transition between remaining semi-con and XLPE insulation must be sharp and clean — not feathered or irregular 4. Clean the XLPE insulation surface with a dry lint-free cloth

Critical: Do not nick or score the XLPE insulation beneath the semi-con. Any cuts or scoring in the XLPE surface create stress concentration points that will lead to premature electrical failure.

Step 7 — XLPE Insulation Removal and Conductor Exposure

Remove the XLPE insulation from the conductor connection zone: 1. Mark the insulation removal length (from the kit guide — typically 50–70mm) 2. Using a rotary cable stripper set to XLPE insulation depth, cut at the mark 3. Slide the insulation section off the conductor 4. For aluminium conductors: the conductor surface must be cleaned with a wire brush immediately before crimping to remove the oxide layer — aluminium re-oxidises within minutes of exposure

Step 8 — Conductor Connection (Crimping or Mechanical Connector)

This is the highest-consequence step in the XLPE cable jointing procedure. A poor conductor connection is the most common cause of joint failure and fire.

Crimped Connections:

1. Select the correct crimp connector for conductor cross-section and material (Cu-Cu, Al-Al or Cu-Al bimetallic) 2. Insert both conductor ends fully into the connector barrel — both must reach the stop 3. Apply compression crimps using a hydraulic press at the positions marked on the connector 4. Remove all swarf (metal shavings) from around the crimp — swarf in the insulation zone causes failure 5. File or sand any sharp edges or protrusions on the connector to a smooth finish

Mechanical (Bolted) Connectors:

1. Clean conductor strands thoroughly 2. Apply joint compound (anti-oxidant) for aluminium conductors 3. Insert conductors and tighten bolts in the sequence given in the instruction, to the specified torque 4. Tighten shear-head bolts until heads shear — the mechanical contact is now complete 5. Remove all metal burrs from bolt stub ends

Step 9 — Stress Control Tube Application

The stress control tube (SCT) is the most critical heat shrink component in a medium voltage joint. It modifies the electric field at the screen cut-back, preventing the electrical stress concentration that would otherwise cause insulation breakdown.

1. Ensure the XLPE insulation surface is clean and dry — wipe with a lint-free cloth 2. Centre the stress control tube over the screen cut-back, extending onto the semi-con on one side and the XLPE on the other as specified in the kit guide 3. Apply heat evenly from the centre outward using a propane torch or heat gun 4. The tube must shrink smoothly with no lifting, blistering or wrinkles 5. Apply continuous heat until the mastic adhesive at the tube ends is visible flowing out — this confirms full bond

Heat application technique: Hold the flame or heat gun nozzle 75–100mm from the tube surface. Move in a slow, rotating motion around the circumference — never hold still. Overheating causes charring; underheating leaves air pockets.

Step 10 — Insulating Tube Application

The insulating tube restores XLPE insulation continuity over the connector and conductor connection zone.

1. The connector and any exposed conductor must be completely buried within the insulating tube 2. Centre the tube and heat from the centre outward 3. Confirm the tube has fully conformed to the connector contours — no bridging across the connector shoulders 4. Allow to cool for 2 minutes before touching or disturbing

Step 11 — Screen Reinstatement

The metallic screen must be continuous through the joint. Fold the copper tape or wire screen from both cable ends back over the insulating tube and lap them by minimum 50mm at the joint centre. Secure with self-amalgamating tape or copper braid as specified in the kit.

Apply mastic tape at both screen termination points — this seals against moisture ingress at the interface between the reinstated screen and the original cable screen.

Step 12 — Outer Protection — Core Identification and Outer Tube

1. Apply core identification heat shrink sleeves (red, yellow, blue) to each joint core 2. Apply the outer protection tubing over the full joint assembly, including the screen reinstatement 3. Heat from the centre outward until fully shrunk and mastic is flowing from both ends 4. This outer tube provides mechanical protection, environmental sealing and a degree of short-circuit withstand

Step 13 — Armour Reinstatement and Outer Jacket Restoration

For armoured cables: 1. Fold armour wires back over the joint 2. Apply armour glass cloth tape if required 3. Apply outer heat shrink jacket tube over the complete joint assembly 4. Ensure the jacket tube extends well onto the cable jacket on both sides (minimum 100mm overlap)

Step 14 — Post-Joint Testing

Before backfilling or energisation, test the completed joint:

• ●High voltage DC test (optional): DC 3U₀ (e.g. 26kV for 11kV system) for 15 minutes — confirms insulation integrity
• ●Insulation resistance test: Minimum 1000 MΩ between each conductor and earth
• ●Continuity test: Confirm phase identification is correct end-to-end
• ●Screen continuity test: Confirm screen resistance is within expected range for cable length

Do not backfill until all test results are satisfactory.

Common XLPE Cable Jointing Mistakes and How to Avoid Them

All VIKCHEM joint kits are supplied with step-by-step illustrated installation instructions. Contact VIKCHEM technical support for site-specific guidance on cable sizes, connector selection and test requirements.

Summary: Key Steps in XLPE Cable Jointing Procedure

1. Measure and mark all dimensions before cutting anything 2. Remove outer jacket, armour and metallic screen to exact dimensions 3. Remove semi-con cleanly — no scoring of XLPE beneath 4. Prepare conductor — clean aluminium oxide layer immediately before crimping 5. Crimp or bolt conductor connection — remove all swarf and burrs 6. Apply stress control tube centred on screen cut-back 7. Apply insulating tube over full connection zone 8. Reinstate screen and seal with mastic 9. Apply outer protection tube 10. Test before backfilling

Contact VIKCHEM for technical support, kit selection or to request a training session for your jointing crew.