Siemens Automation System S7-400 - Manual (Page 68)

Wiring the S7-400
4-8
Automation System S7-400 Hardware and 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.
Terminal Connection 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.
Frame element terminal
Chassis ground terminal
RC network
M
6.8 nF 10 MΩ
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.