| MONITOR | 1/2016 ractical Page B Expertise 49 2/2018 | MONITOR | Practical implementation of the central earthing point Ideally, however, the entire installation should be set up in the TN-S system from the transformer so that only a single, so-called central earthing point is installed. Such a design fully avoids the undesired interference currents referred to above. Maximum electromagnetic compatibility is also guaranteed for operating the electrical installation. The design also offers a further, decisive advantage: a special current transformer can be used at the central earthing point to monitor the electrical installation’s entire leakage and residual currents. All leakage current from the installation flows through this measuring point. Abrupt changes in the measured leakage current indicate a new PE-N bridge, a PE-N reversal or a low-impedance earth fault. Using a residual current monitor with a history mem- ory is worthwhile here. The device's data logger and alarm messages can be used to accurately track when significant changes in current occur via the CEP. In practice, this information can also be used to deduct the cause (e.g. maintenance work on compo- nents in the installation) and narrow down the fault location. Dipl.-Wirtsch.-Ing. Michael Faust Bender Academy This guarantees that the TN-S system remains "clean" throughout the entire service life of the installation and that no unwanted connections are created be- tween the neutral conductor and earth (e.g. due to maintenance work or faults during installation and expansion). Recommended structure in the TN-C-S system with monitored central earthing point a) Do not earth transformer neutral point directly b) Central earthing point of the main distribution board with monitoring a) b) N L3 L2 L1 PE Installation Exposed conductive part Exposed conductive part Data line Power source