Earthing & LPS,
explained properly

Earth resistance is one part of a grounding system's electrical performance. Lower resistance can reduce voltage rise at the grounding point, but protective-device operation also depends on the complete fault loop, conductor impedance, system grounding arrangement and protection settings. Touch and step voltage performance likewise requires system-level assessment. That is why a test reading should be interpreted alongside the installation design and the equipment it protects.

The two methods you'll encounter

Fall-of-potential (3-point) testing is a common field method for earth resistance measurement. The test setup and distances should be selected for the electrode/system and available site space. Two temporary spike electrodes are driven into the soil at increasing distances from the system under test, current is injected, and the resulting potential is measured to plot a resistance curve. Where that curve flattens (the "true" resistance, not skewed by the spikes' own resistance areas overlapping) is your reading. It needs space — a suitable straight-line test area based on the electrode/system and chosen method — which is the main reason it's not always practical on a cramped urban site.

Clamp-on (loop) testing doesn't need spike electrodes at all — a clamp meter induces a signal and measures the loop resistance through the earth return path, using the utility neutral or other parallel earth paths as the return. It's fast and needs no digging or space, which is why it's the go-to for routine AMC checks on existing systems. Its limitation: it needs a genuine parallel return path to work at all, so it's not valid for isolated or newly-installed single electrodes with no other bonded path.

What counts as a "good" reading

IS 3043 doesn't set one universal pass/fail number — the acceptable value depends on the fault current your system needs to clear safely, which depends on transformer size, protective device ratings, and soil conditions. Acceptance or design targets are project-specific. They depend on the electrical system, fault conditions, protection coordination, soil characteristics, equipment requirements and applicable project or authority specifications. The honest answer to "what should my reading be" is: it depends on your transformer's fault current and your protective device coordination — which is exactly what a proper design calculation (not just a rule-of-thumb number) is for.

Curious what your own numbers would look like? Our rod resistance and soil resistivity calculators use the same working formulas referenced here.

These two standards get confused constantly because both end in "earthing rods driven into soil" — but they solve different problems.

IS 3043 — Code of Practice for Earthing

This is the Bureau of Indian Standards code covering how electrical installations should be earthed: neutral earthing, equipment (body) earthing, electrode types and spacing, soil resistivity measurement, conductor sizing based on fault current, and acceptable resistance values. Its job is electrical safety during normal operation and electrical faults — making sure a short circuit or insulation failure sends current safely to earth instead of through someone touching an appliance body.

IEC 62305 — Protection Against Lightning

This is the international standard (adopted in India as the IS/IEC 62305 series) covering protection of structures against a direct or nearby lightning strike — a completely different threat with far higher energy and much faster rise time than an electrical fault. The current 2024 edition is published in four parts: general principles and risk assessment, risk management, physical damage to structures (this is where the rolling sphere method for positioning air terminals comes from), and protection of electrical/electronic systems inside the structure (surge protection). Where IS 3043 asks "will this fault current find a safe path," IEC 62305 asks "will this building survive a direct strike, and will the strike's surge destroy the equipment inside."

How the two standards are coordinated

A factory with a lightning protection system still needs electrical earthing appropriate to the installation. Where an LPS and electrical earthing are both present, their earth-termination and bonding arrangements should be coordinated in the project design rather than treated as unrelated systems. The final arrangement depends on the building, electrical system, lightning-risk assessment and applicable project requirements.

See how we reference both together on our Standards page.

Earth resistance isn't a fixed, one-time number — it drifts with soil moisture, temperature, corrosion of the buried electrode, and physical disturbance near the pit (new construction, cabling work, landscaping). A system that measured 3 Ω at commissioning can read very differently two years later without anyone having touched it.

General guidance

• Periodic testing should follow the installation risk, manufacturer/project requirements, operating conditions and applicable inspection or maintenance program. Annual testing may be appropriate for many assets, but it is not a universal rule.
• Pre-monsoon testing is worth doing separately in high-rainfall regions — resistance can look artificially good in wet soil and spike once the ground dries out, so a single annual reading taken right after monsoon can be misleadingly optimistic.
• After any major fault event or lightning strike, the system that just did its job absorbing that energy should be re-tested — high fault currents and strikes can degrade connections and electrode contact even when nothing looks visibly damaged.
• Critical and high-corrosivity-soil installations — such as substations, data centres, telecom towers, or sites with aggressive soil — may justify more frequent testing than a general maintenance cycle.

Testing identifies whether further inspection or maintenance is needed; it does not itself repair a degraded system. See our maintenance service for the scheduled approach.

A degraded earthing system rarely announces itself clearly — it tends to show up as a collection of small, easy-to-dismiss annoyances rather than one obvious failure. Worth paying attention to:

Electrical symptoms

Frequent nuisance tripping of ELCBs/RCDs, especially ones that didn't used to trip, can indicate rising earth resistance forcing leakage current to find alternate, unstable paths. Mild shocks or a "tingling" sensation from touching equipment bodies — washing machines, motor casings, metal railings near electrical rooms — is a genuine warning sign, not something to get used to. Flickering or unstable readings on sensitive equipment, particularly after a nearby fault elsewhere in the building, can point to a shared or degraded earth reference.

Physical symptoms

Visible corrosion or green/white deposits at the earth pit connection, particularly on GI strip (which corrodes faster than copper-bonded conductor), is a direct sign of a weakening connection. A dry, cracked earth pit — especially in summer, when soil moisture drops — is worth checking with a resistance test rather than assuming it's fine because "it was fine last year." Physical damage to any visible conductor, strap, or test link — from construction work, vehicle movement, or simple age — breaks continuity even if the buried electrode itself is intact.

The pattern that matters most

Any one of these in isolation might be nothing. Two or more together, or any of them appearing on a system that hasn't been tested in over a year, is worth an actual resistance measurement rather than a guess. Get in touch if any of this sounds familiar.