Signalling instead of switching – Residual current monitoring in earthed systems

In TN systems, the star point of the feeding transformers is connected to earth through a low impedance and the exposed conductive parts of the electrical installation are connected to the protective earth (PE) of the system. In TT systems, the star point is also connected to earth through a low impedance but the exposed conductive parts of the electrical installation are earthed independently from the system earthing.

Continuous monitoring

Periodic testing and monitoring of electrical installations and equipment is time-consuming and expensive. Here, continuous residual current monitoring for earthed power supplies (TN/TT systems) offers a time and cost-saving alternative. With this method, the electrical installation is continuously monitored for residual currents or fault currents as required by the relevant standards. For this purpose, earthed installations (TN-S systems) are equipped with a selective system for residual current monitoring (RCM).

Since the residual current is an image of the insulation resistance, residual current monitoring systems (RCMS) can continuously detect a selective insulation deterioration in stationary electrical installations. This deterioration leads to a measurable change in the residual current of the installation, which may result in critical changes in the system. RCMS not only detect fault currents in the development phase, overloading of N conductors are also indicated at an early stage.This significantly reduces the risk of fire. The operator is conveniently informed by an alarm message, e.g. via e-mail.


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