The insulating material for a cable should be

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Examoogle · Accepted Answer

Option D: All of the above

Explanation & Concepts:
An insulating material for a power cable must satisfy multiple functional requirements to ensure safety, reliability, and economic viability. These include electrical, mechanical, chemical, and thermal properties that prevent leakage current and withstand physical stress during installation and operation.

Working Principle: The insulation acts as a dielectric barrier to confine the electric field within the conductor. High dielectric strength ($E_d = \frac{V_{breakdown}}{d}$) prevents insulation puncture under high-voltage stress, while mechanical strength ensures the integrity of the cable against bending, tension, and crushing forces. Low cost is a practical engineering necessity to make large-scale power distribution infrastructure economically feasible.

Key Formulas: $E_d = \frac{V_b}{t}$ — Dielectric strength where $V_b$ is breakdown voltage and $t$ is insulation thickness; $I_{leakage} = \frac{V}{R_{ins}}$ — Leakage current through insulation, where $R_{ins}$ must be high

Key Points: Dielectric strength must exceed operating voltage with a safety factor.; Mechanical strength is vital for installation in conduits or underground burial.; Insulation must be chemically inert to moisture, acids, and alkalis.; High resistivity prevents hazardous current leakage.

Advantages: High dielectric strength prevents short circuits; Mechanical durability prevents physical failure; Cost efficiency enables widespread electrical grids

Disadvantages: High dielectric materials can sometimes be expensive; Extreme mechanical strength often correlates with high cable weight/stiffness

Applications: Underground distribution cables; High-tension transmission lines; Domestic house wiring

Additional Info: Materials used include XLPE (Cross-linked Polyethylene), PVC, and PILC (Paper Insulated Lead Covered).. Option B is technically correct but incomplete, as a material that is high-strength but too costly or mechanically brittle would fail to be a practical cable insulation.

Answer: D is correct — The insulating material must balance electrical performance, mechanical robustness, and economic feasibility.

Exam Tip: Always evaluate cable insulation properties in terms of the 'Triad' of engineering: Performance (Electrical), Durability (Mechanical), and Viability (Economic).

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Option A: Low cost

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Option B: High dielectric strength

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Option C: High mechanical strength

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