Earth wire or ground wire is made of

Question

Examoogle · Accepted Answer

galvanized steel

Explanation: An earth wire or ground wire is primarily made of galvanized steel to provide mechanical strength and resistance to corrosion in outdoor or underground environments. It serves as a low-impedance path to ground for fault currents, ensuring the safety of personnel and equipment.

Working Principle: The principle of earthing relies on providing a path with impedance $Z_e$ significantly lower than the impedance of the human body. When an insulation failure occurs, the fault current flows through the galvanized steel wire to the ground, triggering protective devices like an MCB or ELCB to disconnect the supply. The galvanization process (zinc coating) prevents oxidation of the steel, ensuring the continuity of the protection circuit over time.

Key Formulas: $R = \rho \frac{l}{A}$ — Resistance of the conductor depends on resistivity, length, and cross-sectional area.; $I_{f} = \frac{V}{Z}$ — Fault current magnitude determined by system voltage and path impedance.

Key Points: Galvanization involves coating iron or steel with a protective layer of zinc.; Steel provides high tensile strength, which is crucial for overhead lines and external grounding electrodes.; Earth wires are sized based on the maximum potential fault current they must carry.; The resistivity of steel is higher than copper, so earth wires often have a larger cross-section.

Advantages: High mechanical strength and durability; Cost-effective compared to copper for large-scale installations; Excellent resistance to environmental corrosion due to zinc coating

Disadvantages: Higher electrical resistance compared to copper; Susceptible to slow oxidation if the galvanized coating is scratched or damaged

Applications: Electrical grounding systems for residential and commercial buildings; Overhead transmission line shielding wires; Grounding electrodes for distribution substations

Additional Info: Galvanized steel is standardized for earth electrodes due to its longevity in corrosive soil conditions.. Option A (Copper) is highly conductive but significantly more expensive and susceptible to theft in utility applications.. Option C (Iron) oxidizes quickly (rusts) when exposed to moisture, making it unsuitable without galvanization.

Answer: D is correct — Galvanized steel is used for earthing wires to provide the necessary combination of mechanical durability and corrosion resistance.

Exam Tip: In exams, always distinguish between a 'conductor' for transmission (usually ACSR - Aluminium Conductor Steel Reinforced) and an 'earth wire' for protection, where mechanical strength and corrosion resistance are prioritized over conductivity.

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