Understanding Cable Components and Protection

This question asks about the specific component within an electrical cable that provides protection against mechanical injury. Cables are made up of various layers, each serving a distinct purpose to ensure reliable and safe transmission of electrical energy.

Functions of Cable Components

Let's look at the functions of the components listed in the options to understand which one offers mechanical protection:

• Insulation: This layer surrounds the conductor(s) and prevents the flow of current from the conductor to the surrounding environment or other conductors. Its primary function is electrical isolation, not mechanical strength.
• Bedding: This is a layer typically found between the armouring and the insulated cores. It provides a cushion and a smooth surface for the armouring, preventing damage to the insulation from the armouring wires or tapes. It offers some minor mechanical support but its main role is preparatory for the armouring layer.
• Armouring: This layer consists of galvanized steel wire or steel tape wrapped around the bedding. Its specific purpose is to protect the cable from mechanical damage such as impacts, crushing, or tensile stress during installation and operation, especially in direct burial or harsh environments.
• Sheath (or Outer Sheath/Jacket): This is the outermost layer of the cable. It provides overall protection against moisture, chemicals, UV radiation, and other environmental factors. While it offers some degree of mechanical protection, its primary role is environmental sealing and providing a tough outer skin, less so than the dedicated armouring layer.

Identifying the Mechanical Protection Layer

Based on the functions described, the component specifically designed to withstand external physical forces and protect the internal parts of the cable from mechanical injury is the armouring.

Therefore, the component that protects a cable against mechanical injury is the armouring.

Revision Table: Cable Component Functions

Additional Information on Cable Construction

Understanding the typical construction of a power cable helps clarify the role of each part. A common power cable might have the following layers from inside out:

• Conductor(s) (e.g., copper or aluminum wires)
• Insulation (e.g., PVC, XLPE)
• Bedding (e.g., PVC, serving as a filler/separator)
• Armouring (e.g., Steel Wire Armour - SWA, or Steel Tape Armour - STA)
• Outer Sheath/Jacket (e.g., PVC, LSF)

The presence and type of bedding and armouring depend on the cable's application and the environment it will be installed in. Cables for indoor use in protected conduits might not have armouring, while outdoor direct burial cables almost always will.