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Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
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Sheaths are used in cables to
Provide proper insulation
Provide mechanical strength
Prevent ingress of moisture
None of the above
Provide mechanical strength
In underground cable construction, the metallic sheath is primarily used to provide mechanical protection to the cable core. It prevents the ingress of moisture, chemicals, and gases into the insulation layers, which could otherwise degrade the dielectric strength over time.
In underground cable construction, the metallic sheath is primarily used to provide mechanical protection to the cable core. It prevents the ingress of moisture, chemicals, and gases into the insulation layers, which could otherwise degrade the dielectric strength over time.
RinsтАЛ=2╧АL╧БтАЛln(rRтАЛ) тАФ where the sheath ensures the insulation resistivity ╧Б remains stable by preventing moisture ingress.
The metallic sheath (typically made of lead or aluminum) acts as a continuous impermeable barrier surrounding the insulation. By enclosing the core, it creates a robust physical boundary that ensures the insulation remains dry and maintains its integrity despite external pressures or environmental mechanical stresses.
Metallic sheaths are primarily lead or aluminum.
They provide a continuous grounded path for capacitive leakage currents.
The sheath protects against mechanical damage during installation and operation.
Preventing moisture is critical because moisture reduces the breakdown voltage of paper insulation.
Protects insulation from water/moisture
Provides mechanical support and impact resistance
Acts as an electrostatic screen
Increases overall cable weight
Adds significant cost to the cable
Requires careful installation to avoid sheath currents
Underground transmission lines
Submarine power cables
High-voltage distribution networks
While the sheath provides mechanical strength, it is specifically designed as a moisture barrier to maintain the dielectric properties of the insulation.
Option C is technically a critical function of the sheath, but 'Mechanical Strength' is often emphasized in the context of resisting physical wear during burial.
B is correct тАФ The metallic sheath acts as a protective barrier that provides necessary mechanical strength and prevents the ingress of moisture.
Always remember the order of layers in a cable (from core to outside): Conductor, Insulation, Metallic Sheath, Bedding, Armouring, Serving. Mnemonic: 'C-I-M-B-A-S'.