EARTH PITS INSTALLATION
Some earth pits are installed at various locations throughout an electrical system for different applications such as transformer neutral, equipment body, lightning arrestors, and electronic equipment.
The practice adopted earlier was to keep all these earth pits electrically separated. We examined several reputable national and international standards, including IS3043, BS7430, IEC 61000-5-2, IEC 62305-3, and IEEE 142-2007. All the above standards have clearly advocated the need to interconnect all earth systems to achieve equipotential.
1) Interconnection of Transformer Neutral with the General Earth Grid
Transformer neutral should be solidly interconnected to the general earth grid as per IS3043, Clause 22.1.3 and 22.3.1. The standard has permitted and advocated the interlinking of the neutral earth pit with the general body earth, and mentions that the earlier practice of separate/isolated earth for transformer neutral needs to be revised to AVOID UNNECESSARY REDUNDANCY AND EXPENDITURE.
2) Interconnection of Lightning Arrestor Earth with General Earth Grid
IEC 62305-3 and BS7430 have clearly recommended that the lightning protection system earth should solidly bond to the general earth grid to avoid dangerous potential differences between two unconnected earth systems in case of a lightning current.
3) Inter-connection of Electronic Equipment Earthing with General Earth Grid
IEEE 142-2007 (Clause 5.5.3, Page 193) specifically states that a possible lack of understanding led to erroneous installation requirements using isolated earthings for electronic equipment. Analysis of various catastrophic incidents indicated that separation of grounds was responsible for very large voltages being impressed on electronic equipment components under thunderstorm conditions.
IEC 61000-5-2 (Clause 5.3.1) does not encourage the use of independent "ISOLATED" earth electrodes for computer and electrical systems. IEEE 1100-2003 (Clause 4.8.5.1) clearly mentions that electronic equipment should not use isolated grounds and details the benefits of connecting dedicated electronic earthing to the general earth grid.
Conclusion: All earth systems in a given electrical installation — neutral earth, lightning protection system earth, and electronic earth — should have their own dedicated earth pit/earth terminations. However, they should never be isolated from the general earth grid. These dedicated earth pits should be connected to the general earth grid to achieve equipotential, thereby avoiding catastrophic failures.
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