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Examoogle • User • info@examoogle.com • EE-2024-8821
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Ground resistance should be designed such that
grounding resistance should be as low as possible
grounding resistance should be as high as possible
grounding resistance should be always zero
none of the above
grounding resistance should be as low as possible
Quick Summary: 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.
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.
Vg=If×Rg — Voltage rise at the ground electrode during fault current If and ground resistance Rg
Rg=ρAL — Approximate resistance of an earth conductor where ρ is soil resistivity
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×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.
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.
Minimizes step and touch potential risks
Ensures faster operation of overcurrent protection devices
Provides a stable reference potential for electronic systems
Achieving very low resistance in dry or rocky soil is expensive and difficult
Requires periodic maintenance and testing to verify integrity
Industrial power distribution systems
Lightning protection systems
Data centers and telecommunication grounding
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.
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.
Always remember that in grounding, 'lower is better' for safety, while in insulation, 'higher is better' for preventing leakage current.