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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Factors on which soil resistance depends
depth of electrode
moisture
NaCl
all of above
all of above
Quick Summary: Soil resistivity is a critical parameter for earthing design that depends on physical properties like soil composition, moisture content, temperature, and salt content. All factors mentioned—depth of the electrode, soil moisture, and presence of electrolytes like NaCl—significantly influence the total resistance path between the electrode and the earth.
Soil resistivity is a critical parameter for earthing design that depends on physical properties like soil composition, moisture content, temperature, and salt content. All factors mentioned—depth of the electrode, soil moisture, and presence of electrolytes like NaCl—significantly influence the total resistance path between the electrode and the earth.
R=2πLρ[ln(d4L)−1] — Resistance of a driven rod electrode in soil
The resistance of an earth electrode is given by R=2πLρ[ln(d4L)−1], where ρ is the soil resistivity. Moisture enhances ionic conduction, while NaCl acts as an electrolyte to further reduce resistivity. Increasing the depth (L) lowers the overall resistance by contacting a larger volume of soil and accessing more stable moisture levels at lower depths.
Moisture is the most influential factor; dry soil has extremely high resistivity.
Salt (NaCl) treatment is often used in artificial soil preparation to reduce resistivity in rocky or dry areas.
Greater electrode depth allows the rod to reach more consistent moisture levels and larger soil surface area.
Soil resistivity varies widely depending on soil type (e.g., clay vs. sand).
Provides a safe path for fault current dissipation
Stabilizes potential relative to the earth's mass
Seasonal variations (dry vs. wet seasons) can cause large fluctuations in resistance
Requires periodic maintenance and testing of the earthing system
Power distribution grounding
Lightning protection systems
Communication equipment shielding
Typical soil resistivity ranges from 10 Ω-m for swampy ground to over 1000 Ω-m for rocky soil.
Option A is correct because resistance decreases as contact length increases.
Option B is correct because water is a good conductor of ions.
Option C is correct because dissolved salts increase the ion concentration in the soil solution.
D is correct — The total resistance of an earthing electrode is dependent on the soil moisture, its chemical composition (like NaCl), and the physical installation parameters such as electrode depth.
Always remember that in soil resistivity problems, moisture and temperature are inversely proportional to resistance, while salt presence is a common method for ground improvement.