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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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Which factor is enriched in soil by using coal and salt?
Humidity
Fertility
Sodium
Chlorine
Humidity
Quick Summary: In electrical earthing systems, a mixture of coal (charcoal) and salt (NaCl) is added to the earth pit to reduce soil resistivity. Coal acts as a moisture-retaining agent, and salt acts as an electrolyte to improve conductivity, thereby ensuring lower overall earth resistance.
In electrical earthing systems, a mixture of coal (charcoal) and salt (NaCl) is added to the earth pit to reduce soil resistivity. Coal acts as a moisture-retaining agent, and salt acts as an electrolyte to improve conductivity, thereby ensuring lower overall earth resistance.
R=ρAL — Resistance of the electrode depends on soil resistivity ρ (L = length, A = cross-sectional area).
ρ∝Moisture×Ion Concentration1 — Inverse relationship between conductivity and moisture/salt levels.
The soil resistivity (ρ) depends on the moisture content and ionic concentration. Salt provides ions to facilitate current flow, while coal has high porosity and hygroscopic properties, which absorbs and retains moisture from the surrounding soil to maintain the required level of humidity in the earthing pit.
Salt increases the ionic concentration, significantly reducing the contact resistance between the electrode and the soil.
Coal prevents the rapid erosion of the earth electrode by controlling the chemical action and maintaining the water table level.
This mixture is primarily used in dry, rocky, or sandy soil where natural conductivity is insufficient.
Regular maintenance is required as salt is gradually leached away by rainwater.
Significantly decreases earth electrode resistance.
Ensures stable earthing performance even in dry seasons.
Extends the operational life of the earth electrode.
Salt increases the corrosive effect on the metal electrode (usually copper or GI).
Requires periodic replacement or re-salting due to drainage.
Earthing of electrical transmission and distribution substations.
Lightning arrester grounding systems.
Industrial machinery safety earthing.
Standard practice often involves using a ratio of 1:1 or 1:2 of salt to coal.
Option B (Fertility) is a biological term, while C and D are components of the salt (NaCl) that contribute to conductivity, but 'Humidity' is the broad property maintained for consistent resistance.
A is correct — The mixture of coal and salt is specifically used in earthing pits to maintain adequate soil moisture levels (humidity) and improve ionic conductivity, thereby reducing earth resistance.
Always remember that in power systems, grounding must have minimal resistance; any maintenance practice that retains moisture is critical for safety.