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Examoogle • User • info@examoogle.com • EE-2024-8821
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Where is the coil earthing used?
Substation
Factory
Distribution Poll
All of above
Distribution Poll
Quick Summary: Coil earthing is specifically designed for the grounding of overhead line distribution poles (typically wooden or RCC poles) where space and ground soil resistivity conditions make conventional pipe or plate earthing impractical. It consists of a long coil of G.I. wire buried in the ground at the base of the pole, providing an effective low-resistance path for fault currents.
Coil earthing is specifically designed for the grounding of overhead line distribution poles (typically wooden or RCC poles) where space and ground soil resistivity conditions make conventional pipe or plate earthing impractical. It consists of a long coil of G.I. wire buried in the ground at the base of the pole, providing an effective low-resistance path for fault currents.
R=2πLρln(d4L) — Simplified soil resistance relationship where ρ is soil resistivity, L is length, and d is diameter of conductor.
The coil, usually made of a long length of G.I. wire wound into a spiral, acts as an artificial earth electrode. When installed at the base of a pole, it increases the surface area of contact with the soil, thereby reducing the earth resistance (Re) at the base. This ensures that any leakage or fault current is safely dissipated into the ground, protecting both the structure and personnel.
Used primarily for distribution poles carrying low-voltage or medium-voltage lines.
Specifically employed where deep excavation for pipe earthing is difficult or restricted.
Effective in moist soil conditions for maintaining low earth resistance.
Requires a minimum depth of burial as per safety standards (e.g., 1.5 meters).
Cost-effective installation for individual poles.
Minimal space requirements compared to plate earthing.
Easy to maintain in rural and semi-urban distribution networks.
Ineffective in extremely dry or sandy soil with high resistivity.
Prone to corrosion over time if the G.I. quality is inferior.
Overhead distribution networks
Rural electrification poles
Street light pole grounding
The coil is usually made from 8 SWG or 6 SWG G.I. wire wound into a spiral of approximately 50-100 mm diameter.
Option A (Substation) typically uses heavy-duty grid or mat earthing, not coil earthing, due to higher fault current ratings.
Option B (Factory) generally requires plate or pipe earthing to meet stringent safety requirements for machinery and industrial grounding.
C is correct — Coil earthing is specifically utilized for providing grounding to overhead distribution poles where space and soil conditions limit conventional methods.
Always remember that in Indian standards (IS 3043), the choice of earthing method is determined by the fault current magnitude and soil resistivity; coil earthing is restricted to low-current, small-structure applications.