Siemens SIMATIC S7-400 Hardware And Installation Manual page 248

Assembling and Installing Systems
2. Supporting Bars
Provide a large-area connection between supporting bars and the cabinet
housing (metal-to-metal connection).
3. Securing the Rack
There must be a large-area metal-to-metal connection between supporting bar
and rack.
4. Signal Lines
Use cable clamps on the protective ground bar or an additional shield bus for
large-area connection of the shield of signal lines.
5. Cable Clamp
The cable clamp must surround the braided shield over a large area and ensure
good quality contact.
6. Shield Bus
Provide a large-area connection between the shield bus and supporting bars
(metal-to-metal connection). The cable shields are connected to the shield bus.
7. Protective Ground Bar
Provide a large-area connection between the protective ground bar and the
supporting bars (metal-to-metal connection). Connect the protective ground bar
to the protective conductor system via a separate conductor (min. cross-section
10 mm).
8. Conductor to the Protective Conductor System (Grounding Point)
Provide a large-area connection between the conductor and the protective
conductor system (grounding point).
Example of Frame or Wall Mounting for EMC
If you operate your S7-400 in a low-interference environment in which the
permissible ambient conditions are complied with (see Reference Manual,
Chapter 1), you can mount your S7-400 in frames or on the wall.
Picked-up interference must be given a path to large metal surfaces. You should
therefore secure standard mounting channels, shield, and protective ground bars
to metal structural elements. For wall mounting in particular, installation on
reference potential surfaces made of sheet steel has proved advantageous.
Provide a shield bus for connecting the cable shields if you install shielded cables.
The shield bus can simultaneously serve as the protective ground bar.
Ensure the following for frame and wall mounting:
Use special contact washers with painted and anodized metal parts, or remove
the insulating protective layers.
Provide large-area, low-impedance metal-to-metal connections when securing
the shield/protective ground bar.
Cover the AC supply conductors in a shockproof arrangement.
A-8
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S7-400 and M7-400 Programmable Controllers, Installation Manual
C79000-G7076-C424-01