The MEN (Multiple Earthed Neutral) system of earthing is an arrangement that uses the network neutral conductor as the conductive path for installation earth fault currents. These fault currents need to be large enough to cause the protective devices (such as circuit breakers or fuses) to operate. For example, when an ACTIVE to EARTH fault occurs, the fault path is the low impedance circuit via the MEN link, to the source of supply (eg. distribution transformer or generator – see diagram below).
In the diagram, the NEUTRAL conductor of the electrical distribution system provides the low impedance return path for the fault current (we call it the “earth fault current” because it goes to the earthed frame of a faulty appliance or piece of equipment).
If the MEN link was not in place, the return fault current path would be from E2 to E1 via the ground. The impedance of the ground is generally much higher than the MEN/NEUTRAL 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 does not operate, a life-threatening voltage may remain on the metallic enclosure of the appliance or equipment.
The installation of the MEN link is therefore crucial to the safety of an electrical installation. How to Make the MEN Connection
The MEN connection is a link between the main EARTH bar (or earth terminal/connection) and the main NEUTRAL bar and should be made at the main switchboard. The MEN link needs to comply with Clause 5.6 of the Wiring Rules.
Where to Make the MEN Connection
Generally, the MEN connection needs to be made at the main switchboard. Where a switchboard is installed at a separate installation (ie. outbuildings and detached portions of an installation), particular attention must be given to the method of earthing and the MEN connection (refer to Clause 5.6.6 of the Wiring Rules).
Once the installation has been tested, the MEN connection needs to be rechecked as a “last task” item. There have been several electrocutions and many serious electrical accidents where the MEN link was missing, and subsequent faults occurred in the installation.
