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The material commonly used for sheaths of underground cables is
Lead
Rubber
Copper
Iron
Lead
Lead is the standard material used for the sheathing of underground cables to provide a moisture-proof barrier. It acts as an impermeable envelope that prevents the ingress of water and moisture into the insulation, which would otherwise lead to dielectric degradation.
Lead is the standard material used for the sheathing of underground cables to provide a moisture-proof barrier. It acts as an impermeable envelope that prevents the ingress of water and moisture into the insulation, which would otherwise lead to dielectric degradation.
RinsтАЛ=2╧АL╧БтАЛln(dDтАЛ) тАФ represents the insulation resistance, which must be protected by the sheath
Underground cables are buried in environments with varying soil moisture, chemicals, and mechanical stress. The lead sheath provides a high degree of corrosion resistance and is chemically inert to most soil conditions, maintaining the integrity of the insulating material (such as paper or XLPE) from environmental contamination.
Lead is highly resistant to chemical corrosion from soil and groundwater.
The sheath prevents moisture absorption, which is critical for impregnated paper insulation.
Lead is ductile, allowing the cable to be flexible during installation and thermal expansion.
Aluminum is now often used as a lightweight alternative to lead.
Impermeability to water and moisture
Excellent resistance to chemical corrosion
High flexibility and ductility
Heavy weight increases transportation and installation costs
High cost compared to modern synthetic materials
Susceptible to mechanical fatigue under vibration
High-voltage underground power transmission
Submarine power cables
Industrial environments with high moisture content
Modern cables often use PVC or polyethylene (PE) as moisture barriers instead of lead in low-voltage applications.
Option B (Rubber) is used as an insulating material, not a moisture-proof sheath.
Option C (Copper) and D (Iron) are not used for sheathing because they lack the required chemical inertness and flexibility for this specific purpose.
A is correct тАФ Lead is the most effective and traditional material used to protect underground cable insulation from moisture and chemical ingress.
Always remember that the 'sheath' is primarily for environmental protection, whereas 'armouring' is specifically added to provide mechanical protection against physical damage.