5Terminology#
5.1MEN (Multiple Earthed Neutral) system#
The MEN system has the neutral of the distribution system earthed at the source of supply, at regular intervals throughout the system and at each electrical installation connected to the system. If the MEN link was not in place during normal operation, the return fault current would be via ground. The impedance of the ground is generally much higher than the MEN/Protective Earth Neutral (PEN) conductor path. This would limit the magnitude of the fault current to a value which may be insufficient to cause the protective device to operate. If the protective device were not to operate, a life threatening voltage may remain on the metallic enclosure of the appliance or equipment.
5.2Protective and Functional Earthing#
The Protective Earthing (PE) conductor includes all earthing conductors (excluding the main earthing conductor and the functional earth) and is required to have sufficiently low resistance to permit adequate fault current to flow to earth and cause the protection device to operate. A Functional Earth (FE) is provided for the purpose of correct operation, rather than safety. Such functional earthing conductors are not required to be selected and installed to withstand fault currents or to be identified in the same manner as a protective earthing conductor. Note that a protective earth is always installed in addition to the functional earth.
