In plate earthing, rectangular or circular plates should present an area of at least _____ ft² to the soil.
A
2
B
1.5
C
3
D
4

Question

In plate earthing, rectangular or circular plates should present an area of at least _____ ft2 to the soil.

Examoogle · Accepted Answer

2

Explanation: According to IS 3043 (Code of Practice for Earthing), plate earthing systems must utilize a metallic plate with a minimum surface area of 2 square feet to ensure sufficiently low resistance to the earth. A larger surface area increases the contact interface with the soil, which helps in dissipating fault currents effectively.

Working Principle: The earthing plate provides a low-impedance path for leakage current to flow safely into the ground. By increasing the surface area, the contact resistance $R = \frac{\rho}{4r}$ (where $\rho$ is soil resistivity and $r$ is the radius of an equivalent circular plate) is reduced, thereby enhancing the dissipation of fault current through the surrounding moisture-retaining soil.

Key Formulas: $R \approx \frac{\rho}{4r}$ — Simplified resistance of an earth electrode, where $\rho$ is soil resistivity and $r$ is the radius

Key Points: Plate earthing is commonly used in power stations and substations.; Copper plates are preferred for their superior conductivity and corrosion resistance.; Minimum thickness for a copper plate is generally 3.15 mm.; The pit is usually filled with charcoal and salt layers to maintain soil moisture and improve conductivity.

Advantages: Provides a very low resistance path.; Highly durable for long-term industrial use.

Disadvantages: Requires significant excavation work compared to pipe earthing.; Higher initial cost due to material requirements.

Applications: Generating stations; Transmission line towers; Heavy industrial switchgears

Additional Info: The standard specification for GI plate earthing is a minimum of 6.30 mm thickness.. Option B (1.5), C (3), and D (4) are incorrect as they do not meet the mandated minimum threshold defined in the Indian Electricity standards for standard plate earthing configurations.

Answer: A is correct — The minimum area for a plate earth electrode is stipulated as 2 ft$^2$ by Indian Standards to ensure effective fault dissipation.

Exam Tip: Remember that while plate earthing is robust, pipe earthing is more economical for domestic installations, whereas plate earthing is mandatory for high-voltage power applications.

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