Siemens S7-400 4.6 Assembling an S7-400 with Ungrounded Reference Potential (Ungrounded Configuration)

Wiring the S7-400
4-8 AutomationSystem S7-400 Hardwareand Installation
A5E00850741-01
4.6 Assembling an S7-400 with Ungrounded Reference
Potential (Ungrounded Configuration)
Application
In large installations, it may be necessary to configure the S7-400 with an
ungrounded reference potential, for example, for ground fault monitoring. This is
the case in the chemical industry or in power plants, for example.
Discharge of Interference Currents
With the S7-400 in an ungrounded configuration, any interference currents are
discharged to the chassis ground via an RC network integrated in the rack.
TerminalConnection Model
Shown in Figure 4-3 is an S7-400 configured with ungrounded reference potential.
In this case you must remove the jumper between reference potential M and the
frame element terminal on the rack. The reference potential M of the S7-400 is
then connected via the RC network to the chassis ground terminal. When you
connect this terminal to the chassis ground, RF interference currents will be
discharged and static charges will be avoided.
Frameelement terminal
Chassisground terminal
RC network
M
6.8nF 10MΩ
Detached
jumper
Reference potential M
Figure 4-3 An S7-400 Configured with Ungrounded Reference Potential
Power Supply Units
When using power supply units, ensure that the secondary winding is not
connected to the protective ground conductor.