Configuring 
  4.5 Arrangement of modules on a single rack 
S7-300, CPU 31xC and CPU 31x: Installation 
Operating Instructions, Edition 08/2004, A5E00105492-05 
4-7 
4.5  Arrangement of modules on a single rack 
Reasons for using one or multiple racks 
The number of racks you need will depend on your application.  
 
Reasons for using a single rack:  Reasons for distributing modules between 
several racks 
•  Compact, space-saving use of all your 
modules 
•  Local use of all modules 
•  Fewer signals to be processed 
•  More signals to be processed 
•  Insufficient number of slots 
 
 
Note 
If you opt for the installation on a single rack, insert a dummy module to the right of the CPU 
(order no.: 6ES7 370-0AA01-0AA0). This gives you the option of adding a second rack for 
your application, simply by replacing the dummy module with an interface module, and 
without having to reinstall and rewire the first rack. 
 
Rules: Layout of modules on a single module rack 
The following rules apply to module installations on a single rack: 
•  No more than eight modules (SM, FM, CP) may be installed to the right of the CPU. 
•  The accumulated power consumption of modules mounted on a rack may not exceed 
1.2 A on the S7-300 backplane bus. 
Reference 
For further information, refer to the technical data, for example, in the 
S7-300 Module 
Specifications Reference Manual 
or in the 
Reference Manual 
for your CPU
.
 
Example 
The figure below shows a layout with eight signal modules in an S7-300 assembly. 
CPU
PS
SM1
SM2
SM3
SM4
SM5
SM6
SM7
SM8