TN-S-/TT system
Signalling instead of switching – Residual current monitoring in earthed systems
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.
Why residual current monitoring?
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.
