What are the reasons for the increase in earthing resistance?

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Examoogle · Accepted Answer

Option D: All of above

Explanation & Concepts:
The resistance of an earthing system depends on soil resistivity, electrode dimensions, and the integrity of the connection. Factors such as loose joints, corrosion, and low soil moisture directly increase the overall contact resistance between the earth electrode and the surrounding soil.

Working Principle: The earth electrode resistance is governed by the formula $R = \frac{\rho}{2\pi L} \ln(\frac{4L}{d})$. Soil moisture acts as an electrolyte; as it decreases, resistivity ($\rho$) rises significantly. Furthermore, corrosion and loose connections create high-resistance gaps (contact resistance) at the junctions, impeding the dissipation of fault currents.

Key Formulas: $R = \frac{\rho}{2\pi L} \ln(\frac{4L}{d})$ — Simplified electrode resistance formula showing direct proportionality to soil resistivity $\rho$.

Key Points: Moisture in soil is essential for conductivity; dry soil is an insulator.; Corrosion increases the junction impedance, leading to local heating and higher potential rise during faults.; Loose connections prevent reliable current flow, increasing the voltage drop at the terminal.; Standard Indian earthing resistance (IS 3043) is generally recommended to be low (e.g.,

Advantages: Lower resistance ensures faster tripping of protective devices.; Proper grounding protects personnel from step and touch voltages.

Disadvantages: High earth resistance leads to 'floating' potentials during fault conditions.; Insufficient moisture levels require frequent chemical treatments or watering.

Applications: Electrical Substations; Transmission lines; Industrial machinery grounding; Residential distribution panels

Additional Info: The resistance of an earth electrode is primarily determined by the soil resistivity in the immediate vicinity of the rod.. Chemical treatments (like salt and charcoal) are often used in dry regions to reduce soil resistivity.

Answer: D is correct — Loose connections, corrosion, and low soil moisture are all critical physical factors that lead to an undesirable increase in the total earthing resistance.

Exam Tip: In exams, if an option is 'All of above' in maintenance questions, check if all factors contribute to the degradation of the system; usually, physical environmental factors and mechanical integrity are both culprits.

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Option A: Loose connection

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Option B: Corrosion between connections

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Option C: Low moisture in the soil

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