Siemens Simatic S7-300 CPU 31xC Series Installation And Operating Instructions Manual page 218

Appendix
A.2 Protection against electromagnetic interference
Observe the following for ground connection:
• In the same way as with active elements, exercise meticulous care to interconnect
• Always make sure that you have a low-impedance interconnection between metal
• The protective insulating finish on varnished or anodized metal elements must be pierced
• Protect your connecting elements against corrosion (e.g. with a suitable grease).
• Interconnect moving chassis ground elements (e.g. cabinet doors) with flexible ground
A-8
inactive metal elements.
elements (e.g. large and highly conductive contact surface).
or removed. Use special contact washers or completely remove the finish on the point of
contact.
straps. Always use short ground straps with a large surface (the surface is decisive for
the diversion of high-frequency currents).
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05