---
title: "Splicing techniques of HV cable"
subject: "Industrial Power Distribution and Illumination"
chapter: 3
key: "semester_6/industrial_power_distribution_and_illumination:hv-cable-splicing"
source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/hv-cable-splicing
site: BCT Engineering
---

# Splicing techniques of HV cable

Industrial Power Distribution and Illumination · Chapter 3: Power Carrying Devices

- Asked in: 2080 Chaitra, 1+3 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/hv-cable-splicing
- Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-3

## Question

Why Splicing cannot be avoided? Explain splicing techniques of an HV Cable.

## Short answer

Splicing is unavoidable because cable drums are limited, longer routes need joints, and repairs/ranching require them. HV splicing methods: heat-shrink, cold-shrink, pre-oulded, resin, taped. A heat-shrink joint steps: conductor crimped, stress-control tube, insulation, semicon tube, copper mesh screen, armour bond, outer sheath, then test.

## Answer

#### Why splicing cannot be avoided
Splicing (jointing) means joining two lengths of cable so that the joint is electrically and mechanically as good as the cable. It cannot be avoided because:
- Cables are made and transported on **drums of limited length** (a few hundred metres for HV cables), while routes are often longer.
- A damaged section after a **fault or digging accident** must be cut out and a new piece joined in.
- **Tee/branch joints** are needed to tap supply to new loads.
- Cable routes may need changes when roads and buildings are extended.

#### Splicing techniques of HV cable (e.g. 11 kV XLPE)
Common types of joints:
1. **Heat-shrink joint:** tubes of cross-linked polymer that shrink tightly when heated with a gas torch. Most common in Nepal and India.
2. **Cold-shrink joint:** pre-expanded silicone rubber tubes held on a removable core; they shrink when the core is pulled out. No flame needed.
3. **Pre-moulded (push-on) joint:** factory-made rubber body pushed over the prepared cable.
4. **Resin (cast) joint:** a mould is filled with epoxy or polyurethane resin.
5. **Taped joint:** layers of insulating and semiconducting tapes applied by hand (older method).

#### Steps for an 11 kV XLPE heat-shrink straight-through joint
```text
Layers built over each core joint (inside out):
 conductor + crimped ferrule
 stress-relief mastic over ferrule
 stress-control tube (over screen cut-back)
 insulating tube(s)
 semiconducting tube
 tinned copper mesh (screen continuity)
Over all three cores:
 armour bond (braid) + outer sheath tube
```
1. **Prepare cables:** check for moisture, overlap the ends, cut to length. Slide on the outer sheath tube and other tubes beforehand.
2. **Remove outer sheath, armour and inner sheath** to the dimensions given by the kit. Clamp the armour ends.
3. **Remove the copper tape screen and the semiconducting layer** back to the marked length, leaving a clean, smooth cut on the insulation.
4. **Remove insulation** from the conductor ends equal to half the ferrule length.
5. **Join conductors** with a mechanical or crimped (compression) connector/ferrule; file off any sharp edges.
6. **Fill voids** over the connector with stress-relief mastic.
7. **Stress control:** shrink a **stress-control tube** over the semicon cut-back to spread the electric field evenly; otherwise the field concentrates at the screen edge and causes breakdown.
8. **Insulation:** shrink one or more **insulating tubes** over the joint, then a **semiconducting tube** (or a dual-wall tube) over them.
9. **Screen continuity:** wrap **tinned copper mesh** over the joint and solder/clamp it to the copper screens of both cables.
10. **Repeat** for all three cores, then bind the cores together.
11. **Armour continuity and earth:** bridge the armour across the joint with a braided earth connector.
12. **Outer protection:** shrink the **outer heavy-wall sheath tube** (or a joint box) over the whole joint to keep out water and give mechanical strength.
13. **Test:** insulation resistance test and, for HV, an HV/VLF withstand test before energising.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which is a reason why cable splicing cannot be avoided?
   A. Cables come on drums of limited length and damaged sections must be cut out and replaced
   B. Splicing increases the current rating of the cable
   C. Cables cannot be bent without a joint
   D. XLPE insulation always needs a joint every 10 m
   Answer: A. Drum lengths are limited and faults, digging damage, tee branches and route changes all require joints. (Key point: Why splicing is unavoidable)

2. How does a cold-shrink joint differ from a heat-shrink joint?
   A. It uses a gas torch to shrink silicone tubes
   B. Pre-expanded silicone tubes on a removable core shrink when the core is pulled out, so no flame is needed
   C. It is filled with epoxy resin in a mould
   D. It is made of hand-applied insulating tapes
   Answer: B. Cold-shrink tubes are held expanded on a core and contract when it is removed; heat-shrink needs a torch. (Key point: Heat-shrink vs cold-shrink)

3. Why is a stress-control tube shrunk over the semiconducting cut-back in an 11 kV joint?
   A. To join the two conductors mechanically
   B. To keep water out of the joint
   C. To spread the electric field evenly, otherwise the field concentrates at the screen edge and causes breakdown
   D. To provide the earth path for the armour
   Answer: C. The screen cut-back creates a high-stress point; the stress-control tube grades the field. (Key point: Stress-control tube)

4. Which order is correct for building the joint over each core?
   A. Insulating tube, crimp ferrule, copper mesh, stress-control tube, semicon tube
   B. Outer sheath tube, ferrule, mastic, insulating tube, stress-control tube
   C. Copper mesh, ferrule, semicon tube, insulating tube, mastic
   D. Crimp ferrule, stress-relief mastic over ferrule, stress-control tube, insulating tube, semicon tube, copper mesh
   Answer: D. Layers are built from the conductor outward: ferrule, mastic, stress control, insulation, semicon, then screen mesh. (Key point: Joint sequence)

## Related in other subjects

- [Cable fault location techniques and Murray loop](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Acable-fault-techniques-murray) — Power System Analysis I, chapter 2
- [Locating phase-to-phase cable fault](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Aphase-to-phase-cable-fault) — Power System Analysis I, chapter 2