For the benefit of such applicants and as a reminder to contractors who are more familiar with the relevant requirements, this article provides guidance on sizing main bonding conductors where PME conditions apply.
NICEIC Approved Contractors and Domestic Installers should be aware that the requirements of BS 7671 for sizing the main equipotential bonding conductors of an installation where Protective Multiple Earthing (PME) conditions apply differ from those where such conditions do not apply. However, the NICEIC has found that some applicants wishing to register either as an Approved Contractor or as a Domestic Installer are not aware of this fact.
Main bonding conductors
The main bonding conductors of an installation are the conductors connecting extraneous-conductive-parts, such as metallic water service pipes, gas installation pipes and exposed metallic structural parts of the building, to the main earthing terminal of the installation, as required by Regulation 413-02-02.
Knowing whether or not PME conditions apply
In order to determine the minimum cross-sectional area (csa) required for the main bonding conductors of an installation, it is important to know whether or not PME conditions apply.
Protective Multiple Earthing is defined in Part 2 of BS 7671 as: “An earthing arrangement, found in TN-C-S systems, in which the supply neutral conductor is used to connect the earthing conductor of the installation with Earth in accordance with the Electricity Safety, Quality and Continuity Regulations 2002.”
The connection between the earthing conductor of the installation and the supply neutral conductor is made at a PME earthing terminal provided by the electricity distributor. The terminal is located either on the distributor’s fused cut-out or otherwise near the supply terminals and metering equipment for the installation. (Note: The supply neutral conductor is sometimes called a combined protective and neutral (PEN) conductor or a combined neutral and earth (CNE) conductor.)
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