The objective of earthing or grounding is

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Examoogle · Accepted Answer

to provide as low resistance possible to the ground

Explanation: The objective of earthing is to provide a low-impedance path to the ground for fault currents, ensuring the safety of equipment and personnel. By maintaining a low resistance path, the fault current flows to the earth instead of passing through human bodies or damaging insulation.

Working Principle: When a fault occurs (such as an insulation failure leading to a live chassis), the fault current seeks the path of least resistance. Since $R_{ground} \ll R_{human body}$, the majority of the current is diverted to the earth, triggering protective devices like MCBs, MCCBs, or ELCBs to isolate the faulty circuit.

Key Formulas: $I_{fault} = \frac{V_{phase}}{Z_{fault} + Z_{earth}}$ — Current division during a ground fault; $R_{earth} = \frac{\rho}{2\pi L} [\ln(\frac{4L}{d}) - 1]$ — Resistance of a rod electrode

Key Points: Earthing prevents the buildup of dangerous static charges on metallic surfaces.; It maintains the potential of non-current carrying parts at zero potential relative to the earth.; The IEEE standard typically recommends grounding resistance for power stations to be less than $0.5 \Omega$.

Advantages: Protects personnel from electric shocks.; Prevents fire hazards due to leakage currents.; Provides a stable reference potential for electronic circuits.

Disadvantages: Requires regular maintenance and periodic testing.; Susceptible to corrosion in high moisture environments.

Applications: Domestic wiring systems.; Industrial machinery grounding.; Substations and transformer neutral points.

Additional Info: Option B is incorrect because high resistance would limit the fault current, preventing protective devices from operating promptly, which creates a hazardous condition.. Earthing is mandated by the Indian Electricity Rules to ensure safe operation of electrical networks.

Answer: A is correct — Earthing provides a low-resistance path to the ground to ensure protective devices operate rapidly during a fault.

Exam Tip: In numerical problems, always remember that $Z_{earth}$ includes the electrode resistance and the soil resistivity, which varies seasonally.

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