Bedding in Cable Manufacturing

Bedding is a protective layer applied over the laid-up cable cores and under the armour. It provides a smooth, cushioned surface for the armour and protects the inner cable components from mechanical damage.

What is Bedding?

In armoured cables, bedding is the layer placed between the inner sheath and the armour wires/tapes.

Cable Construction


Conductor
    ↓
Insulation
    ↓
Laid-up Cores
    ↓
Fillers
    ↓
Inner Sheath
    ↓
BEDDING
    ↓
Armour (SWA/STA)
    ↓
Outer Sheath

Functions of Bedding

1. Protection

Protects the inner sheath from damage caused by armour wires.

2. Cushioning Effect

Acts as a soft layer between the armour and cable core.

3. Smooth Surface

Provides an even surface for armour application.

4. Corrosion Protection

Helps isolate armour from the inner cable structure.

5. Shape Maintenance

Maintains the roundness and stability of the cable.

Bedding Materials

PVC Bedding

Most common
Good flexibility
Moisture resistant
Cost-effective

PE Bedding

Better moisture resistance
Used in special cables

Extruded Bedding

Applied by extrusion process
Uniform thickness

Taped Bedding

Applied using PVC or polymer tapes
Used in some control and instrumentation cables

Typical Bedding Thickness

The exact thickness depends on cable size and standards such as IEC and BS.

Cable Diameter	Typical Bedding Thickness
Up to 25 mm	0.8 – 1.2 mm
25 – 40 mm	1.2 – 1.5 mm
40 – 60 mm	1.5 – 2.0 mm
Above 60 mm	2.0 – 3.0 mm

Example

4 Core 25 mm² SWA Cable


Outer Sheath
██████████████████████

Steel Wire Armour
OOOOOOOOOOOOOOOOOOOOOO

PVC Bedding
======================

Inner Sheath
----------------------

4 Insulated Cores
( ●  ● )
( ●  ● )

Cable Cross-Section

Layer Identification


┌───────────────────────┐
│     Outer Sheath      │
├───────────────────────┤
│   Steel Wire Armour   │
├───────────────────────┤
│       BEDDING         │
├───────────────────────┤
│     Inner Sheath      │
├───────────────────────┤
│ Insulated Cable Cores │
└───────────────────────┘

Bedding Extrusion Process


Laid-up Core
      ↓
Inner Sheath
      ↓
PVC Bedding Extrusion
      ↓
Cooling Trough
      ↓
Armouring Machine
      ↓
Outer Sheath Extrusion

Advantages of Bedding

✔ Protects cable core

✔ Prevents armour damage to sheath

✔ Improves cable life

✔ Maintains cable roundness

✔ Enhances mechanical strength

✔ Provides smooth armouring surface

Conclusion

Bedding is a non-metallic protective layer applied between the inner sheath and armour of a cable. It cushions the cable core, protects against mechanical damage, and provides a smooth base for armour application. In most power cables, PVC bedding with a thickness of approximately 0.8 mm to 3.0 mm is commonly used depending on the cable diameter and applicable standards.

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