Siemens Automation System S7-400 - Manual (Page 67)

Wiring the S7-400
4-7
Automation System S7-400 Hardware and Installation
A5E00850741-01
4.5 Assembling an S7-400 with Grounded Reference
Potential (M)
Application
You use an S7-400 with grounded reference potential in machines or industrial
plants.
Discharge of Interference Currents
When the S7-400 is configured with a grounded reference potential, any
interference currents are discharged to the chassis ground.
Terminal Connection Model
When delivered, the racks have a detachable metallic connection between the
internal reference potential M of the modules and the frame element of the racks.
Situated behind this connection is an RC network which is placed in the circuit for
the ungrounded configuration. This connection is located at the left edge of the
rack. The terminal for the chassis ground also has an electrical connection to the
frame element.
Shown in Figure 4-2 is an S7-400 configured with grounded reference potential. To
ground the reference potential M, you must connect the chassis ground terminal to
the chassis ground and you must not remove the jumper between reference
potential M and the frame element terminal on the rack.
Metallic connection
Frame element terminal
Chassis ground terminal
RC network
M
6.8 nF 10 MΩ
Detachable
jumper
Reference potential M
Figure 4-2 An S7-400 Configured with Grounded Reference Potential