The AC/DC sensitive RCMB104 residual current monitoring module is used in combination with a W15BS measuring current transformer and a type A RCD which has to be provided in the installation for fault current monitoring of AC charging systems for electric vehicles in which AC or DC fault currents can occur.
The residual current monitoring is carried out using externally connected measuring current transformers. Here, the r.m.s. value is determined by the DC component contained in the residual current and the AC component that is below the cut-off frequency.
Switching outputs indicate if the limits of IΔn = DC ≥ 6 mA and/or IΔn = RMS ≥ 30 mA are exceeded. The device test is initiated via an external control system (charge controller). After starting the self test via the digital input "Test", the device generates a test current. The level of the test current is designed so that when functioning correctly the threshold is exceeded triggering both alarm relays. Based on the system behaviour (residual current monitoring, load current switch), the charge controller detects whether the expected shutdown occurs. After successfully completing the device test, an offset measurement is carried out.
Prior to each charging process, it is necessary for the monitoring device to carry out a self test and an offset measurement. The check focuses on safety-relevant residual current monitoring. The charging process must be disabled. The function increases the safety of the charging process and prevents long-term drift of the residual current measurement.
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