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Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
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In a cable immediately above metallic sheath ___________________ is provided.
earthing connection
bedding
armouring
none of above
bedding
In an underground cable construction, the bedding layer is placed directly over the metallic sheath. Its primary purpose is to protect the metallic sheath from corrosion and from mechanical injury due to the pressure of the armouring.
In an underground cable construction, the bedding layer is placed directly over the metallic sheath. Its primary purpose is to protect the metallic sheath from corrosion and from mechanical injury due to the pressure of the armouring.
TmechтАЛтИЭFarmouringтАЛ тАФ Indicates that armouring provides mechanical protection, necessitating a buffer (bedding) to protect the sheath underneath.
The metallic sheath (usually lead) is soft and vulnerable. When steel tape or wire armouring is applied for mechanical strength, the rough surface and high pressure of the armouring can damage or puncture the sheath. Bedding, typically composed of fibrous materials like jute or hessian, provides a cushioning effect and acts as a buffer layer to ensure longevity.
Metallic sheath protects the insulation from moisture and chemicals.
Bedding consists of fibrous materials such as jute or hessian impregnated with a preservative compound.
Armouring protects the cable from mechanical damage (sharp objects, soil stress).
Serving is the final outer layer protecting the armouring from atmospheric corrosion.
Prevents electrolytic corrosion of the metallic sheath.
Acts as a protective cushion against mechanical stress from armouring.
Increases the overall diameter and weight of the cable.
Jute-based bedding is susceptible to rot if the outer serving is damaged.
High voltage underground power cables.
Submarine cable construction where structural integrity is vital.
The metallic sheath is typically made of lead or aluminium.
The sequence of layers from core to surface is: Conductor, Insulation, Metallic Sheath, Bedding, Armouring, Serving.
Option A is incorrect because earthing is a safety feature applied externally; Option C is the layer applied above the bedding.
B is correct тАФ Bedding is the layer provided immediately above the metallic sheath to protect it from mechanical injury caused by the armouring.
Always remember the order of cable layers (Core-Insulation-Sheath-Bedding-Armouring-Serving) using the mnemonic: CIS-BAS.