FOUNDATION EARTH ELECTRODES TECHNICAL
Depth of understanding
By Bob Cairney I Eng MIET Technical Standards Adviser, SELECT
F
oundation earth electrodes (FEE) are being considered as a possible solution to prevent the potentially dangerous consequences of a break in an incoming supply protective earth
and neutral (PEN) conductor. FEE may be installed to provide an additional connection to earth to the PEN conductor of TN-C-S (PME) earthing systems provided by the distributor. In BS 7671 there is already a note to Regulation 411.4.2 which advises that for TN systems, an additional connection to Earth is an option that may be considered by the installation designer for these systems at the point of entry of the supply into the building. Regulation 411.4.2 requires that the neutral point of the power supply system shall be earthed and exposed- conductive-parts of the installation are connected by a protective conductor to the main earthing terminal of the installation, which is connected to the earthed point of the power supply. In protective multiple earthing (PME)
systems, the neutral and protective functions are combined in a single PEN conductor in part of the system, i.e. in the incoming low voltage distribution network cable. Thereafter, the functions are provided in separate conductors within the installation. If a break in a distributor’s PEN conductor occurs, this could result in
50 CABLEtalk OCTOBER/NOVEMBER 2019 Terminating the electrode
Working with the Ogilvie Group, DEHN UK and Megger Ltd, SELECT have been helping an IET working group investigate the benefits of foundation earth electrodes
danger to persons located within that installation due to the significant potential that can appear between exposed conductive parts of the electrical installation and the general mass of Earth.
In single phase installations this is caused by load current returning through the protective conductors of the installation to the general mass of Earth, rather than through the neutral conductor which is broken. In three- phase installations this is due to
Concrete is poured in at the Ogilvie Homes development
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