Wiring the S7-400
4-11
S7-400 and M7-400 Programmable Controllers, Installation Manual
C79000-G7076-C424-01
4.7 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.
Reference potential M
Frame element terminal
Chassis ground terminal
RC network
M
Jumper
removed
10 MΩ6.8 nF
Figure 4-3 An S7-400 Configured with Ungrounded Reference Potential
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