Grounded Systems

Residual current monitoring in grounded systems

In grounded systems, one or several points of a system, an electrical installation, or electrical equipment are connected to the ground for the purpose of electrical safety. Transformer neutral grounding is a common practice where the transformer's neutral is specifically connected to the ground for this purpose.

In ungrounded systems, the star point of the feeding transformers is connected to the ground through a low impedance. The exposed conductive parts of the electrical installation are connected to the protective earth (PE) of the system. In grounded systems, the star point is also connected to the ground through a low impedance but the exposed conductive parts of the electrical installation are grounded independently from the system grounding.

Why residual current monitoring?

When residual current monitoring is used, residual and fault currents are signaled 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. With continuous monitoring of safety-relevant circuits for fault currents, residual currents, and stray currents, critical operating states are detected at an early stage. A potential risk of personal injury, fire damage, and material damage can thus be avoided.

How does residual current monitoring work?

When using an RCM system, a message is given to the user before the shutdown threshold of an RCD is reached. RCMs monitor residual currents in electrical installations, indicating the present value and signal when the response values are exceeded.

RCMs differ in terms of type, frequency, and waveform of the currents that they are capable of detecting:

RCM series: Type A RCM in accordance with IEC 60755 for monitoring AC currents (42…2000 Hz) and pulsating DC fault currents.

RCMA, RCMB series: Type B RCM in accordance with IEC 60755 for monitoring AC currents, pulsating and smooth DC fault currents (0…2000 Hz).

RCMS series: Multi-channel type A and B RCM systems in accordance with IEC 60755 for monitoring AC currents, pulsating and smooth DC fault currents (0 (42)…2000 Hz).