A question often asked of Certsure’s helpline is; “who is responsible for providing a means of earthing for an electrical installation”. In short, it is the consumer’s responsibility to ensure that the electrical installation is correctly earthed. This is because, in order to receive a supply of electricity, the consumer is required to have an installation meeting the safety requirements of Regulations 25(1) and 25(2) of The Electricity Safety, Quality and Continuity Regulations 2002 (ESQCR).
These requirements are to ensure that the installation is constructed, installed, protected and used (or arranged for use) so as to prevent, as far as is reasonably practicable, danger or interference with the distributor’s network or with supplies to others. Compliance with the requirements of BS 7671 is likely to give compliance with the safety requirements of Regulations 25(1) and 25(2).
In practice, it is the electrical installer, acting on behalf of the consumer, who ensures that the electrical installation is correctly earthed before it is put into service (or returned to service).
Distributor’s obligation to offer an earthing connection
When providing a new or replacement low voltage supply connection to an installation, a distributor has a general obligation under Regulation 24(4) of the ESQCR to make available for connection to the earthing conductor of the installation his PEN (combined neutral and protective) conductor or, if appropriate, the protective conductor of his network.
However, there is an exception to this obligation where this would be inappropriate for safety reasons, such as may be the case for a petrol ﬁlling station. Furthermore, a distributor is not permitted to make available his PEN conductor for connection to the earthing conductor of a caravan or boat, as this is prohibited by Regulation 9(4). To assist electrical installers, some distributors publish notes of guidance advising on situations where an earthing connection will not be made available.
A distributor is not obliged to make an earthing connection available for an existing installation where the supply connection is not being replaced, but may be willing to do so. Where a connection is provided by the distributor, the distributor is responsible for ensuring that this connection (that is, any earthing terminal provided by the distributorand the connection to the network) is installed and, so far as is reasonably practicable, maintained so as to prevent danger, and is suitable for the purpose.
(Regulation 24(1) of the ESQCR refers.)
Irrespective of the distributor’s responsibility, it is up to the electrical installer, acting on behalf of the consumer, to ensure that the earthing connection is suitable for the requirements of the electrical installation and that it is properly connected to the earthing conductor of the installation.
Basis for design
For either a new installation or an alteration or addition to an existing installation, it is important to establish at an early stage of the design whether or not a distributor’s earthing connection for the installation will be available at the service position.
For safety reasons, the effectiveness of any existing earthing connection should always be veriﬁed by inspection and by measurement of the external earth fault loop impedance (Ze). A safe method of measuring Ze is explained in the NICEIC publication; Inspection, Testing and Certiﬁcation.
For all installations, it is important to establish the type of earthing arrangement (TN-S, TN-C-S or TT – see Fig 1), and therefore how the earthing connection will be made to the earthing conductor of the installation. For example, in a TN-C-S system where protective multiple earthing (PME) is provided, the earthing conductor has to be connected to the supply PEN conductor, made available by the distributor.
Where NO earthing connection is available at the service position
Where no distributor’s earthing connection for the installation is available at the service position, and the distributor cannot or will not make one available, the installation will need to be connected with Earth by means of an electrically independent installation earth electrode (Regulation 5188.8.131.52 of BS 7671 refers).
In such circumstances, the requirements applicable to a TT system will have to be met. This will include the installation of RCDs in virtually all cases to provide for automatic disconnection of supply in the event of an earth fault. The RCDs are necessary due to the generally high value of external earth fault loop impedance (Ze) via the installation earth electrode, compared with that usually available in a TN system via an earthing connection provided by the distributor.
The types of earth electrode permitted by BS 7671 for an installation forming part of a TT system are listed in Regulation 542.2.3.
A metallic pipe used to supply a gas or a ﬂammable liquid must not be used as an earth electrode, and neither may a metallic pipe of a water utility supply. However, this does not preclude the bonding of such metalwork where required by Section 411 of BS 7671.
Other metallic water supply pipework (such as that attached to an underground well on private land) may be used as an earth electrode, provided precautions are taken against removal, and the pipework has been considered suitable for such a use.
‘Cable sheath’ earthing
Where ‘cable-sheath’ earthing is provided (TN-S system), the earthing connection to the distributor’s metallic cable sheath or armour is made by the distributor, generally prior to the electricity metering equipment being installed. However, there are occasions where such an earthing connection has not been made and no distributor’s earthing terminal is available for the installation.
Where this is the case, an electrical installer should not, under any circumstances, attempt to clamp, weld (or similar), or in any other way connect the consumer’s earthing conductor to the distributor’s metallic cable sheath or armour. The supply cable is the distributor’s property and the installer is not authorised to interfere with it.
Any attempt by the installer to make a connection to the metallic cable sheath or armour could result in creating an internal fault between the conductors of the cable or between the metallic sheath (or armour) and one or more internal conductors.
For other guidance and publications please see the ELECSA website. Information about the ELECSA Domestic Installers schemes, visit www.elecsa.co.uk