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1 CMD contactor monitoring relays
1.1 Application of the CMD
24
CMD(24VDC), CMDTD
08/23 MN121001ZU-DE/EN
Eaton.com
1 CMD contactor monitoring relays
1.1 Application of the CMD
In the event of an emergency in safety-related electrical control circuits, the
hazardous plant section is shut down from the main power supply by means
of contactors
a
Emergency stop (stopping in the event of an emergency) in
accordance with IEC/EN 60204-1.
For Category 3 control systems in compliance with EN/ISO 13849, the
connection of two contactors in series is recommended. This technique can
be replaced using one contactor and the CMD contactor monitoring device
connected to the backup circuit-breaker/motor-protective circuit-breaker in
the plant.
The contactors must be provided with an auxiliary NC contact that operates
as a mirror contact in accordance with IEC/EN 60947-4-1 Annex F.
The contactors also require an additional auxiliary NO contact.
The motor-protective circuit-breakers/circuit-breakers are provided with an
undervoltage release.
In the event of a hazard the contactor is disconnected via an upstream safety
PLC or a safety relay by means of an enable contact. The CMD compares the
control voltage of the contactor with the status of the main contacts.
The status of the main contacts is monitored via an auxiliary NC contact that
acts as a mirror contact in accordance with IEC/EN 60947-4-1 Annex F.
If the contactor is welded, the status of the main contacts does not
correspond to the status of the control voltage. The undervoltage release of
the backup circuit-breaker is tripped via an internal relay in the CMD.
This disconnects the outgoer. The undervoltage release prevents the welded
contactor from be switched on again.
The CMD contactor monitoring device is approved by the BG ETEM in
combination with Eaton contactors and circuit-breakers (
“System overview”, page 25). It is also provided with a CE declaration of
conformity and an EU type testing certificate.
Summary of Contents for CMD(24VDC)
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