Category: Safety & Compliance

Getting Shocks From Machine Bodies? What Your Earthing System Is Telling You

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. The Five Causes, and How Each Announces Itself 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 Why Earthing Degrades Without Anyone Noticing 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. The Neutral Problem Behind Many “Mystery” Shocks 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. The Modern Cause: Leakage From Drives and Electronics 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”. Immediate Actions When a Shock Is Reported Isolate and tag the equipment; do not leave it in service pending investigation Measure voltage between the body and a known good earth, and body to floor Test earth continuity from the body back to the earth bar and electrode Measure earth resistance of the local electrode and the grid Measure insulation resistance of the equipment circuit Measure leakage current on the feeder, especially where drives are present Check neutral integrity and phase balance at the feeding panel What a Permanent Fix Looks Like 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. Frequently Asked Questions Why do I get a shock from a machine body that is earthed? 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. What is an acceptable earth resistance value? 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. How often should earthing be tested? 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. Can a VFD cause shocks? 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. Is it safe to keep using equipment that gives a mild shock? 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 →