2
MRCDB423_D00396_00_M_XXEN/06.2020
MRCDB423
Since the values are measured with measuring current transformers, the MRCDB423 is almost independent of
the nominal voltage and the operating current of the monitored system.
The residual operating current I
Δn2
, the response delay t
on2
as well as the currently measured residual current
I
Δ
are shown on the standard display.
Information on factory settings
Page 9 provides a summary of all factory settings.
How to reset the MRCD to the factory settings is described on Page 8.
2. Safety instructions
Work activities on electrical installations
• Compliance with applicable regulations governing work on electrical installations, and with the regula-
tions derived from and associated with them, is mandatory. EN 50110 is of particular importance in this
regard.
• If the device is used outside the Federal Republic of Germany, the applicable local standards and regula-
tions must be complied with. The European standard EN 50110 can be used as a guide.
3. Function
3.1 Device features
• AC/DC sensitive MRCD type B in accordance with IEC 60947-2 annex M
• Operating characteristic type B in accordance with IEC 60755
• RMS value measurement of the residual current
• Alarm and prewarning indication via LEDs
• Alarm and prewarning output via relays (K1/K2)
• Measuring current transformer connection monitoring
• Fault memory
3.2 Functional description
After connecting the supply voltage U
s
, the start-up delay is active. During start-up delay "t", the device is in
alarm state, which means that the output relays K1 and K2 are open and thus the installation is switched off.
During start-up delay, changes on the measured residual currents do not influence the relays K1/K2. The resid-
ual current measurement is carried out via an external CTUB101-CTBC20(P)...210(P) measuring current trans-
former. The present measured value is indicated on the LC display. This allows changes to be detected, e.g.
when outgoing circuits are connected to the system.
If the set value of the prewarning I
Δn1
is exceeded, response delay t
on1
starts. After t
on1
has elapsed, the output
relay K1 switches and the prewarning LED lights up. The fault remains stored in the device: The output relay
K1 remains in alarm state and the prewarning LED lights until the reset button "R" is pressed or the supply volt-
age is interrupted. The residual current measurement continues to be carried out.
If the set residual operating current I
Δn2
is exceeded, response delay t
on2
starts.
After t
on2
has elapsed, output
relays K1 and K2 switch. Output relay K2 trips the circuit breaker, which disconnects the outgoing circuit to be
monitored. The prewarning and main alarm LEDs light up. The fault remains stored in the device: Both output
relays remain in alarm state and the LEDs light until the reset button "R" is pressed or the supply voltage is in-
Risk of electrocution due to electric shock!
Failure to carry out work on electrical installations properly and correctly
can put life and limb at risk!
Only skilled persons are permitted to carry out the work necessary to
install, commission and run a device or system.
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