Which material is commonly used as insulation in underground cables?

• A. Jacket
• B. Metallic shield
• C. Insulation
• D. Conductor

Answer: (C)

The layer around the conductor that provides dielectric isolation and prevents current from leaking to the surrounding soil or other conductors is insulation. In underground cables, this insulation is designed to withstand moisture, soil chemicals, and temperature and to maintain a strong dielectric barrier between the conductive core and the outside environment. Materials used for this purpose are typically polymers like XLPE or PVC, chosen for their electrical strength and durability.

The jacket is the outer protective sheath that guards against mechanical damage and moisture; the metallic shield provides a grounded path and electromagnetic shielding; and the conductor is the metal core that carries the current. Insulation specifically serves to electrically separate the conductor from everything else, which is why it’s the material described as insulation.