Wiring 
  6.2 Bonding the protective conductor to the mounting rail 
S7-300, CPU 31xC and CPU 31x: Installation 
Operating Instructions, Edition 08/2004, A5E00105492-05 
6-3 
 
6.2  Bonding the protective conductor to the mounting rail 
Requirements 
The mounting rail is fixed onto the mounting surface. 
Protective conductor Connecting 
Connect the rail with the protective conductor 
 using the M6 protective conductor bolt.  
Minimum cross-section of the protective conductor: 10 mm
2
 
The figure below shows how the protective conductor has to be bonded to the rail. 
 
 
 
Note 
Always make sure of a low-impedance contact between the protective conductor and the 
rail. You can achieve this by using a low-impedance cable, keeping it as short as possible 
and contacting it to a large surface.  
For example, an S7-300 mounted on a hinged frame must be connected to ground using a 
flexible grounding strap.