In earthed systems (TN-S/TT systems) one point or several points of a system, an electrical installation or electrical equipment are connected to earth for the purpose of electrical safety.
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.
When residual current monitoring is used, residual and fault currents are signalled before the installation has to be disconnected in the event of a fault. This way, deteriorations of the insulation level are detected at an early stage and in a reliable way.
A comprehensive readiness for operation around the clock, constant competitive pressure and high cost pressure require the highest degree of electrical safety in the power supply of industrial, functional and residential buildings. With continuous monitoring of safety-relevant circuits for fault currents, residual currents and stray currents, incipient critical operating states are detected at an early stage. A potential risk of personal injury, fire damage and material damage as well as EMC interferences can thus be avoided.
By the use of residual current monitoring systems, a message is given to the user before the shutdown threshold of an RCD is reached.
RCMs (Residual Current Monitors) monitor residual currents in electrical installations, indicate the present value and signal when the response values are exceeded.
The devices are designed for signalling and/or switching. They comply with DIN EN 62020 (VDE 0663) “Electrical accessories – Residual current monitors for household and similar use (RCMs) (IEC 62020)”.