ABB S800 I/O User Manual page 49

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The interference suppression for external signals, are normally directly grounded to
chassis and/or plant ground. The plant ground potential must be stable and well
defined, even in the event of a low ground fault caused by high voltage equipment
or a lightning strike.
Each I/O module's grounding spring connects to the metallic DIN-rail which serves
as the module electronics ground conductor between the inter-connected devices.
This is to ensure a good ground connection both for the internal logic and for the
EMI immunity and RF emission of the modules. The DIN mounting rail must have
a good bond to the PE of the cabinet.
If S800 I/O-modules are configured as two or more groups interconnected with
extension cables, special care should be taken to ensure that the DIN-rails of all
groups have a good connection to ground. If the DIN-rails are mounted on a
common metal sheet, no extra means need be taken except to make sure that each
rail has a reliable low ohmic path to the metal plate. Protective earth connection can
be made at a single point on the common metal plate.
3BSE 020 923R101
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