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Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Which of the following protects cable against mechanical injury?
bedding
sheath
Armouring
none of above
Armouring
Quick Summary: Armouring is a layer of galvanized steel wire or steel tape provided over the bedding in an underground cable. Its primary function is to provide mechanical strength and protect the cable from physical damage, such as puncture, impact, or crushing forces during installation or service.
Armouring is a layer of galvanized steel wire or steel tape provided over the bedding in an underground cable. Its primary function is to provide mechanical strength and protect the cable from physical damage, such as puncture, impact, or crushing forces during installation or service.
Fmech∝Asteel — Mechanical resistance is proportional to the cross-sectional area and material properties of the armouring steel.
The armour layer is applied helically around the cable bedding. Being metallic, it acts as a robust shell that absorbs mechanical stresses. By distributing external loads and preventing sharp objects from penetrating the internal insulation layers (like the core insulation or the sheath), it significantly increases the longevity and reliability of power cables.
Armouring is usually made of galvanized steel wire or tape.
It is placed over the bedding to prevent it from direct pressure.
It also provides an easy path for fault current if the cable is damaged, aiding in fault detection.
Essential for buried cables or areas prone to heavy movement.
Protects against heavy mechanical stresses.
Provides longitudinal strength to the cable.
Assists in protecting the cable sheath from abrasion.
Increases the overall weight of the cable.
Makes the cable less flexible and harder to install in conduits.
Increases the material and manufacturing cost.
Directly buried underground power cables.
Industrial environments with heavy machinery traffic.
Cables subjected to high tension during installation.
Bedding (Option A) is made of fibrous material to protect the metallic sheath from corrosion and mechanical injury from the armour.
Sheath (Option B) is primarily used to prevent the ingress of moisture into the insulation, rather than mechanical impact protection.
C is correct — Armouring consists of metallic wires or tapes that physically shield the cable core from crushing, piercing, or other external mechanical forces.
Always remember the order of cable layers from core to outer: Conductor -> Insulation -> Metallic Sheath -> Bedding -> Armouring -> Serving.