a yellow circle device around a copper busbar

Central earthing point (CEP)

Monitoring for EMC-compliant operation

Interference caused by multiple earthings in TN-S systems jeopardises smooth operation

In TN-S systems, the neutral conductor (N) and protective conductor (PE) are consistently separated from each other. The neutral conductor may only be connected to PE at one point, namely the central earthing point (CEP).

Multiple earthings of the neutral conductor (often referred to as PEN bridges) must be avoided at all costs, as this leads to stray or interference currents. These flow, for example, via the shielding of network cables or via conductive parts of the building structure (foundation earth electrode) or water and gas pipes via the equipotential bonding conductors and can lead to corrosion and EMC interference and impair the reliable operation of an electrical system.

Multiple earthings of the neutral conductor must be avoided at all costs, as this leads to stray or interference currents.

TN-S system with an impermissible PEN bridge

What causes multiple earthings?

Electrical systems in existing buildings in particular are often designed as TN-C systems. This means that PE and N conductors are not consistently separated. The DIN VDE 0100-444 standard recommends conversion to a TN-S system in order to prevent electromagnetic interference. However, multiple earthings cannot be completely ruled out after a conversion. In practice, it is often new equipment that has a PEN bridge ex works, or 4-core cables are used instead of 5-core cables due to cost-saving measures. In distant buildings, failure to comply with switch-off conditions may also require the use of an RCD or an additional earthing point.

Often, new equipment comes with a PEN bridge ex works, or 4-core cables are used instead of 5-core cables to save money.

Detect multiple earthings, measure stray currents

In order to detect multiple earthings and stray currents in a TN-S system and thus ensure a high level of electromagnetic compatibility (EMC), the central earthing point (CEP) should be permanently monitored. A current transformer at the CEP can be used to measure stray currents and physically induced leakage currents in the equipment. If a high current occurs at the PE with a frequency of 50 Hz, this may be an indication of multiple earthings in the TN-S system. By continuously monitoring currents at the CEP, the operator receives an initial indication and can evaluate their electrical system with regard to possible PEN bridges and increasing leakage currents.

A high current at the PE with a frequency of 50 Hz can be an indication of multiple earthings in the TN-S system. Permanent monitoring of currents at the CEP helps to assess the condition of the system

Example of permanent CEP monitoring

Schematic representation of TN-S system with multiple feeders in accordance with DIN VDE 0100-444 or IEC 60363-4-44 with CEP monitoring

A CEP monitoring system offers operators the ability to detect multiple earthings in their electrical systems and sudden increases in leakage currents 24/7. Such a system also provides access to comprehensive differential current monitoring of stray currents, leakage currents and fault currents.

CEP monitoring of existing systems

Existing systems in particular must be checked and optimised for electromagnetic compatibility (EMC). During renovation or expansion work, permanent CEP monitoring is the basis for safe and reliable operation of the electrical system. Foldable current transformers with high measuring accuracy are available for retrofit measures. These can be easily integrated into existing systems and significantly reduce installation costs.