A factory earthing system is not a pipe in the ground with a wire attached. For a three-phase industrial installation with motors, panels, a generator and a lightning arrester, IS 3043:2018 requires separate earth systems for different purposes, specific resistance limits for each, periodic testing with calibrated instruments, and documented records. Most MIDC factories in the Waluj and Shendra belt have been running for years without any of this having been checked since the initial installation.
This guide is written for factory owners and facility managers who want to understand what IS 3043 actually requires and what the common gaps look like in practice. It does not replace an on-site audit, but it gives you the context to ask the right questions.
Why earthing matters differently in a factory
In a house, the main risk from poor earthing is an electric shock from a faulty appliance. In a factory, the risks are compounded:
- Motors and machines have large metal frames. If the frame-to-earth connection is broken or high-resistance, a phase-to-earth fault in the motor puts dangerous voltage on the machine frame - every operator who touches it is at risk.
- Three-phase loads with unbalanced neutral current rely on a solid system earth for voltage stabilisation. A poor neutral earth leads to voltage fluctuations on single-phase loads and can drive increased motor stress.
- A lightning arrester with a shared or high-resistance earth is worse than no lightning arrester. When it discharges, it injects a pulse of energy into the common earth - everything connected to that earth gets the spike.
- RCCB protection operates by comparing current in the phase and neutral. If the earth path is high-resistance, a fault may not produce enough leakage current to trip the RCCB reliably.
The three earth systems a factory needs
IS 3043:2018 defines the principle of separate earth systems for different functions. For a typical factory:
1. Body / equipment earth
All motor frames, machine bodies, panel enclosures and metal cable trays should be bonded to a dedicated body earth bus, which connects to its own earth pit or pits. This is the earth that protects people from shock when a fault puts voltage on metal surfaces.
2. Neutral / system earth
The transformer secondary neutral (or the generator neutral) should have its own dedicated earth electrode. In a TN-S system this neutral earth is separate from the body earth all the way to the equipment. In older TN-C-S systems the combined PEN conductor is earthed at the main panel - this should still have its own electrode, not be shared with the body or lightning earth.
3. Lightning protection earth
If a lightning protection system (lightning arrester, surge diverter) is installed, its earth must be physically separate - IS 3043 and IEC 62305 both require minimum separation of at least 5 metres between the lightning earth electrode and other earth electrodes. This is routinely ignored in MIDC factories where all earths were connected to the same point during construction.
IS 3043 resistance requirements
The table below summarises the resistance limits from IS 3043:2018:
- Industrial earth pits (body and system earth): below 1 ohm.
- Residential installations: below 5 ohms (some authorities accept up to 8 ohms for a single earth pit with RCCB protection).
- Lightning protection earth: below 2 ohms for most structures.
- Generator earth (particularly important when running in island mode): below 1 ohm.
These numbers are not approximate targets - they are limits. An earth pit at 3 ohms in an industrial installation is a compliance failure and a safety issue, even if the wiring looks tidy and the panel is labeled.
How earth resistance is measured
Earth resistance is measured using the three-point (fall-of-potential) method with a calibrated earth resistance tester. Two auxiliary electrodes (current probe and potential probe) are driven into the ground at specified distances from the earth electrode being tested, and the meter injects a small AC test current to measure the resistance of the path to ground.
This is the only method recognised by IS 3043. A visual inspection of the earth pit does not give a resistance value. A continuity check with a multimeter from the equipment body to the earth bar tells you the bond is intact but says nothing about whether the earth electrode itself has a low enough resistance to the general mass of earth. You need both: continuity within the installation and a proper three-point measurement at the electrode.
Readings should be taken in dry soil conditions (not immediately after rain, when soil conductivity is artificially high). Measurements should be repeated six-monthly and after any significant change to the installation. Records should be kept.
Five mistakes we see in MIDC factory audits
- Single shared earth pit for everything - motor bodies, neutral, generator neutral and lightning arrester all bonded to the same electrode. Extremely common in units built in the early 2000s.
- Earth resistance never measured since installation - the pit was made during construction, it was accepted on visual inspection, and no calibrated tester has ever been used on it. Salt and charcoal in the pit have long since leached out.
- Earth wire corroded or undersized - the original earth wire may have been adequate at installation but has corroded at the pit junction or at the cable lug. Also common: the earth wire gauge is smaller than IS 3043 specifies for the connected circuit.
- Machine bodies not bonded - a new machine was added to the factory, connected for power, but no dedicated earth wire was run from the machine frame to the earth bus. The machine runs fine until there is an internal fault.
- Earth pit inaccessible or built over - the pit was installed during construction, then covered during subsequent civil work. No chamber cover, no access, no way to water or measure it.
What an earthing audit and remediation involves
A proper earthing audit starts with three-point measurements at every accessible earth electrode, continuity checks from all equipment bodies to the earth bus, and a visual inspection of earth wire sizes, routing, terminations and pit accessibility. The findings are compiled into a written report with IS 3043 compliance status.
Remediation depends on what the audit finds. Low-resistance issues where the pit is accessible can often be addressed by adding salt and charcoal and watering the pit. Resistance that does not improve needs a new electrode or a parallel earth pit. Isolated machine bodies need a dedicated earth conductor run back to the earth bus. Shared lightning arrester earths need to be separated physically.
We cover Waluj MIDC, Shendra MIDC and Chikalthana for industrial earthing work. Details of our industrial earthing service - including audit, remediation and IS 3043 measurement records - are on the service page. The Marathi guide on common earthing mistakes covers nine specific installation errors with IS 3043 references.
