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Which test are required to be performed to check the efficiency of the earthling installation.
Measurement of resistance of earth electrode
Measurement of resistance of earthing grid
and B
None of these
and B
Quick Summary: To ensure the safety and reliability of an electrical installation, the earth resistance must be periodically verified. This involves measuring the earth electrode's individual resistance and the combined resistance of the total earthing grid system to ensure they fall within safe, code-mandated limits.
To ensure the safety and reliability of an electrical installation, the earth resistance must be periodically verified. This involves measuring the earth electrode's individual resistance and the combined resistance of the total earthing grid system to ensure they fall within safe, code-mandated limits.
R=IV — Ohm's Law for calculating earth resistance
ρ=2πSR — Wenner's method formula for soil resistivity
The principle relies on the Fall-of-Potential method. By injecting a known current between the earth electrode and a remote current electrode, the potential drop is measured relative to a third voltage probe at varying distances. The ratio of voltage to current gives the resistance, defined by Ohm's Law as R=IV.
Lower earth resistance is critical for fast fault clearing during earth faults.
Earth electrodes must be tested periodically, typically annually, according to IS 3043.
The Fall-of-Potential method is the standard practice for validating ground systems.
Soil resistivity varies with moisture and temperature, affecting measured values.
Prevents dangerous potential rise on equipment chassis during faults.
Ensures protective relays operate correctly during ground fault conditions.
Testing can be complex in areas with limited space for auxiliary current probes.
Results can be skewed by buried metallic objects or stray currents.
Substation grounding systems
Lightning protection systems
Industrial plant earthing validation
The resistance of the earthing grid is often much lower than an individual electrode due to parallel conduction paths.
Option A focuses on local resistance, while Option B looks at the structural integrity of the entire network.
C is correct — Both the individual earth electrode resistance and the overall grid resistance are essential metrics to verify the safety and functional efficiency of an electrical earthing installation.
Always remember that earthing systems in large switchyards require grid measurements because the overall resistance is a complex parallel network, not just the sum of individual rod resistances.