Why People Are Confused About Earthing Ohms
Values such as 0.5 Ω, 1 Ω, 2 Ω, 5 Ω and 10 Ω appear in project specifications, consultant requirements, utility practices and equipment instructions. Confusion begins when a project-specific target is repeated as a universal law for every transformer, DG set, panel, CNC machine, building or lightning protection system.
The correct assessment depends on earthing function, system voltage, fault current, clearing time, soil resistivity, electrode geometry, protective-device operation, touch voltage, step voltage, bonding, material quality and applicable project requirements.
Is Less Than 1 Ohm Mandatory Everywhere?
No single resistance value can safely be applied to every installation. IS 3043:2018 treats earthing as a complete system involving source earthing, protective conductors, bonding, electrodes, fault current, automatic disconnection, inspection and testing. IEEE substation-grounding practice evaluates grid current, Ground Potential Rise, mesh voltage, touch voltage, step voltage and fault duration.
Important interpretation
A low resistance target may be compulsory under a tender, consultant, utility, OEM or project specification. It should be respected. But compliance with one number does not replace complete safety analysis.
Earth Resistance Depends Strongly on Soil Resistivity
Soil composition, geological layers, moisture, temperature, salts, corrosion, electrode depth, spacing and seasonal conditions can change the result. Two identical electrodes at different sites may produce very different values.
Favourable soil
Moist, naturally conductive soil may give comparatively low resistance with a modest electrode system.
High-resistivity soil
Dry or rocky soil may require deeper electrodes, wider spacing, horizontal conductors, a ring or an engineered grid.
What Should Be Done When the Desired Resistance Is Not Achieved?
Simply adding more pits may waste money. Two electrodes do not automatically reduce resistance by exactly half because their resistance areas can interact.
What IEEE Grounding Principles Teach Us
Ground Potential Rise depends on current entering the grid and grid resistance. Human safety also depends on grid geometry, surface layer, soil model, fault duration and exposure path.
Touch voltage
Potential difference between grounded equipment touched by a person and the ground at the feet.
Step voltage
Potential difference between two points on the ground separated approximately by a person’s step.
A low measured resistance can still be unsafe if bonding is poor, clearing is slow, conductors are undersized or touch and step voltages are excessive.
Low Resistance Does Not Prove Good-Quality Earthing
Material quality is equally important. An electrode may initially show less than 1 Ω because of favourable moisture, temporary treatment, seasonal conditions or parallel metallic paths. That reading does not prove adequate pipe thickness, genuine size, copper purity, copper-bonding thickness, galvanization, terminal strength or joint quality.
Substandard material can fail even when the initial ohm value looks excellent.
Thin-wall pipe, undersized diameter, low-purity copper, poor coating, insufficient zinc, weak welding, thin terminals and undersized conductors can corrode, crack, perforate, overheat or lose continuity.
Material parameters that must be verified
Earthing Requirements Across Major Sectors
The same design and acceptance value should not be blindly applied everywhere.
The Correct Engineering Procedure
Final Conclusion
“Every earth must always be below 1 ohm” is an oversimplification. Low resistance can be desirable and contractually required, but it cannot alone prove safety or product quality.
SN Engineering — Application-Oriented Earthing Solutions
Share equipment type, voltage, fault current, location, soil-resistivity result, desired performance and BOQ for technical evaluation.
WhatsApp Technical EnquiryCall +91 9990645119View Chemical Earthing RangeDisclaimer: This educational page does not reproduce any copyrighted standard and is not a substitute for the official BIS/IEEE publication, approved project documents or qualified engineering judgement. Exact clause/page references must be verified against the official edition used for the project.