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Short answer: a shock from an equipment body means the earth path has
failed, or current is flowing where it should not — broken earth continuity, high earth
electrode resistance, a loose or broken neutral putting voltage on the frame, insulation
breakdown inside the machine, or high-frequency leakage from a variable frequency drive. All
five are identifiable with standard tests, and none should be managed by telling operators to
wear rubber shoes.
Treat any report of a shock as a near-miss, not a nuisance. The same defect that produces a
tingle in dry weather produces a fatal contact when someone is standing in water.
| Cause | Typical Symptom | Test That Confirms It |
|---|---|---|
| Broken or missing earth continuity | One machine affected; earth wire loose, painted over or removed |
Earth continuity test from body back to the earth bar |
| High earth electrode resistance | Multiple machines affected; worse in dry season |
Earth resistance measurement at the electrode and grid |
| Loose or broken neutral | Voltage on bodies across a section; lights flickering, phase imbalance |
Neutral-to-earth voltage measurement; phase voltage check |
| Insulation failure inside equipment | One machine, often with heating or a smell; RCD trips |
Insulation resistance test on the motor or heater circuit |
| VFD or electronic leakage | Tingle rather than a sharp shock; RCD nuisance tripping |
Leakage current measurement with a suitable clamp meter |
An earth electrode installed to specification does not stay there. Electrodes and conductors
corrode, soil dries out and its resistivity rises through the summer, salt and charcoal
treatments deplete, joints at the earth bar loosen, and earth strips get painted during plant
shutdown maintenance. None of this is visible, and none of it is caught by inspection — only by
measurement. Indian practice for earthing design and testing is set out in IS 3043, and a
measured earth resistance record is a basic compliance document, not an optional extra.
A loose or broken neutral on a three-phase supply causes the neutral point to shift,
producing abnormal voltages across single-phase loads and voltage on equipment frames where
bonding is imperfect. The accompanying symptoms are usually visible elsewhere in the plant:
lights brightening or dimming in one section, single-phase equipment failing repeatedly, and
significant phase imbalance. Measuring neutral-to-earth voltage at the panel is a quick and
informative check.
Variable frequency drives, servo drives, UPS systems and switch-mode power supplies pass
small high-frequency currents to earth through their EMC filters by design. In a healthy
installation these flow harmlessly to earth. With a weak or broken earth path, they appear on
the equipment body as a tingling sensation and trip RCDs with no fault present. The remedy is a
proper low-impedance earth connection, correct cable gland and shield termination on screened
motor cables, and RCDs of the appropriate type — not the removal of the RCD, which is
unfortunately the most common field “solution”.
A durable correction is a designed and measured earthing system, not an extra rod driven
next to the machine: an earth grid sized for the site’s measured soil resistivity and fault
level, proper bonding of all metallic enclosures and structures, separate consideration for
equipment earth, neutral earth and clean earth for electronics, a documented test record with
values, and a periodic re-measurement schedule — because the value you measured last year is
not the value today.
VTPL designs, installs and tests earthing and lightning protection systems as part of
substation, industrial electrification and building electrification packages, following IS 3043
practice and CEA safety
regulations. With 33+ years of experience across 1,000+ projects in 19+ states, our teams carry
out earthing audits and rectification inside operating plants for clients in oil and gas,
steel, railways and infrastructure.
Because the earth path is not actually intact or is too high in resistance — a loose or
corroded connection, a painted earth strip, a depleted electrode — or because a neutral fault
or equipment insulation failure is placing voltage on the frame.
It depends on the installation type, fault level and the applicable specification, so it
should be taken from the design and the relevant standard rather than a universal figure — and
crucially, it must be measured and recorded, not assumed.
Periodically and seasonally, because soil resistivity rises in dry months and electrodes
corrode over time. Testing should also follow any modification, excavation or lightning event
near the installation.
Drives produce high-frequency leakage current to earth by design. With a sound earth
connection this is harmless; with a weak or broken one it can be felt as a tingle on equipment
bodies and can trip RCDs.
No. A mild shock in dry conditions indicates a defect that becomes far more dangerous in wet
conditions or with a different contact path. The equipment should be isolated and tested.
VTPL carries out earthing,
lightning protection and industrial electrification works across India. Need an earthing
audit? Talk to our engineering team →
