S7-400H setup options 
  3.3 The S7–400H basic system 
S7-400H 
System Manual, 03/2012, A5E00267695-11 
35 
Synchronization modules   
The synchronization modules are used to link the two CPUs. They are installed in the CPUs 
and interconnected by means of fiber-optic cables. 
There are two types of synchronization modules: one for distances up to 10 meters, and one 
for distances up to 10 km between the CPUs.  
A fault-tolerant system requires 4 synchronization modules of the same type. For more 
information on synchronization modules, refer to section Synchronization modules for 
S7-400H (Page 341
). 
Fiber-optic cable   
The fiber-optic cables are used to interconnect the synchronization modules for the 
redundant link between the two CPUs. They interconnect the upper and lower 
synchronization modules in pairs. 
You will find the specifications of fiber-optic cables suitable for use in an S7-400H in 
section Selecting fiber-optic cables (Page 349).