Siemens SIMATIC S7-400 Installation Manual page 69

Filtering the 24 VDC Supply
When you power the S7-400 from a battery with the ungrounded configuration, you
must provide interference suppression for the 24 VDC supply. Use a Siemens
power cable filter, such as the B84102-K40.
Insulation Monitoring
If a double fault could cause a hazardous state in the installation, you must provide
insulation monitoring.
Example of Ungrounded Operation
If you have configured an S7-400 with a local connection and you only wish to
ground the overall installation at the CR, you can operate the ERs in an
ungrounded configuration.
Note
If you connect an ER via a local connection with 5 V transfer, ungrounded
operation is mandatory for the ER.
Automation System S7-400 Hardware and Installation
A5E00850741-01
Wiring the S7-400
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