Configuring   
4.6 Distribution of modules to several racks 
  S7-300, CPU 31xC and CPU 31x: Installation 
4-8  Operating Instructions, Edition 08/2004, A5E00105492-05 
4.6  Distribution of modules to several racks 
Exceptions 
With CPU 312 and CPU 312C, only a single-row configuration on a rack is possible. 
Using interface modules 
If you are planning an assembly in multiple racks, then you will need interface modules (IM). 
Interface modules route the backplane bus of an S7-300 to the next rack.  
The CPU is always located on rack 0. 
Table 4-4  Interface modules - Overview 
Properties  Two or more rows  Cost-effective 2-row configuration 
Send IM in rack 0  IM 360  
 order no..: 6ES7 360-3AA01-0AA0 
IM 365  
 order no..: 6ES7 365-0AB00-0AA0 
Receiver IM in racks 1 to 3  IM 361  
 order no..: 6ES7 361-3CA01-0AA0 
IM 365 (hard-wired to send IM 365) 
Maximum number of expansion 
modules 
 3   1 
Length of connecting cables   1 m (6ES7 368-3BB01-0AA0) 
  2.5 m (6ES7 368-3BC51-0AA0) 
  5 m (6ES7 368-3BF01-0AA0) 
  10 m (6ES7 368-3CB01-0AA0) 
 1 m (hard-wired) 
Remarks  -  Rack 1 can only receive signal modules; 
the accumulated current load is limited to 
1.2 A, whereby the maximum for rack 1 is 
0.8 A 
These restrictions do not apply to operation 
with interface modules IM 360/IM 361