The technical experts at NAPIT answer a contractor query related to the use of earth electrodes in the wake of Amendment 2.
Q. Do we have to install an additional earth electrode for all TN systems now Amendment 2 is in force?
Within BS 7671:2018+A2:2022, Regulation 411.4.2 provides requirements regarding the connection of exposed-conductive-parts of the installation to the main earth terminal of the installation. This is not a new requirement and has always been part of BS 7671 to provide a reliable connection to the earthing system.
The new wording within Regulation 411.4.2 is the final paragraph, where it introduces a recommendation that an additional connection to Earth by means of an earth electrode to the main earthing terminal. See Fig 1 for an example of an additional earth electrode.
The idea of adding an additional connection to Earth is to supplement the earthing system of the distributor in case of failure in the ageing network. This recommendation contradicts the advice given in Regulation 411.4.1, which advises that conditions external to the installation are the distributor’s responsibility.
The important word here is ‘recommendation’, as such, it is not a requirement, and there is no requirement to install an earth electrode for every TN system in a client’s premises.
Therefore, the answer would be no, you do not have to install an additional earth electrode. If you were to decide to follow the recommendation to install such an electrode, there are several things to consider:
● Type of earth electrode
● Location
● Connection and termination enclosure
● Verification of the resistance
● Identification
● Certification
The type of earth electrode will be selected in accordance with Regulation 542.2. Any location for an earth electrode must be selected taking into account any adjacent surface and buried service pipes or cables.
A ground scan of the prospective additional earth electrode location should be carried out to ensure there will be no damage to any other equipment buried in the ground. The earthing conductor connected to the earth electrode should be enclosed, protected from the effects of corrosion and securely terminated.
The same test requirements for confirming the resistance of the earth electrode should be carried out on the installation earth electrode and recorded on the electrical installation certificate.
Identification of the electrode termination shall be marked with the ‘Safety Electrical Earth Connection Do Not Remove’ label. Further identification at the main earth terminal should be provided to ensure the user and anyone working on the installation in future are aware of additional earth electrodes.
Within the electrical installation certificate, the details of the additional earth electrode should be recorded separately to the installation earth electrode as this refers to a TT system of earthing only.
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