Ground resistance should be designed such that

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grounding resistance should be as low as possible

Explanation: Ground resistance refers to the opposition offered by the earth electrode and the surrounding soil to the flow of fault current. It is designed to be as low as possible to ensure that during a fault condition, the potential rise of the equipment remains within safe limits and the protective devices operate effectively.

Working Principle: When a fault occurs in an electrical system, the fault current seeks a path back to the source or to the ground. According to Ohm's Law $V = I 	imes R$, if the ground resistance $R$ is kept extremely low, the voltage rise $V$ at the point of the fault remains minimal, preventing dangerous step and touch potentials. A low resistance path ensures the circuit protective device (like a MCB or fuse) detects a high magnitude current quickly, resulting in rapid fault clearance.

Key Formulas: $V_g = I_f 	imes R_g$ — Voltage rise at the ground electrode during fault current $I_f$ and ground resistance $R_g$; $R_g = ho \frac{L}{A}$ — Approximate resistance of an earth conductor where $ho$ is soil resistivity

Key Points: Lower ground resistance ensures effective operation of protective relays.; Reduces the risk of electric shock by limiting potential gradients during fault conditions.; Soil resistivity significantly impacts the overall grounding resistance.; International standards like IEEE 80 or IEC 60364 define acceptable ground resistance levels.

Advantages: Minimizes step and touch potential risks; Ensures faster operation of overcurrent protection devices; Provides a stable reference potential for electronic systems

Disadvantages: Achieving very low resistance in dry or rocky soil is expensive and difficult; Requires periodic maintenance and testing to verify integrity

Applications: Industrial power distribution systems; Lightning protection systems; Data centers and telecommunication grounding

Additional Info: A standard goal for many small substations or residential systems is resistance less than 5 Ω.. Option B is incorrect because high resistance limits fault current, preventing circuit breakers from tripping and keeping the faulted equipment energized at a dangerous potential.. Option C is theoretically ideal but practically impossible as soil resistivity cannot be zero.

Answer: A is correct — A low ground resistance is essential to minimize dangerous voltage rises during fault conditions and to ensure prompt operation of circuit protection devices.

Exam Tip: Always remember that in grounding, 'lower is better' for safety, while in insulation, 'higher is better' for preventing leakage current.

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