PME (Protective multiple earthing) – an earthing arrangement, found
in TN-C-S systems, in which the supply neutral conductor is used to connect the earthing conductor of an installation with Earth.
TN system – a system having one or more points of the source of energy directly earthed, the exposed-conductive parts of the installation being connected to that point by protective conductors
TN-C-S – a system in which neutral and protective functions are combined in a single conductor in part of the system
TN-C – a system in which neutral and protective functions are combined in a single conductor throughout the system. Where: T – Terre (from the French, meaning ‘Earth’), N – Neutral, C – Combined and S – Separate.
On the low-voltage distribution network,
the earthing and neutral functions are combined in the same conductor of the supply cable; this is known as a PEN conductor and the distribution arrangement is TN-C, it should be noted that DNOs can refer to the PEN conductor as CNE (Combined neutral and earth). Along the length of the low-voltage distribution cable the PEN conductor is earthed, using earth electrodes at regular intervals. To supply the electrical installation, the neutral and earthing functions of the PEN conductor are separated out to create neutral and earth provisions.
The term ‘protective multiple earthing’ describes the method of earthing as
used on the low-voltage distribution network. On the underground/buried network, electrodes are used to earth the neutral conductor at regular intervals, usually 25-40m apart, hence the term ‘multiple earthing’. Where the low-voltage distribution network is overhead, earth electrodes are installed at transformers and at regular intervals at distribution poles.
