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