Appendix
A.2 Protection against electromagnetic interference
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05
A-5
A.2.2 Five basic rules for securing EMC
A.2.2.1 1. Basic rule for ensuring EMC
If you comply with theses five basic rules ...
you can ensure EMC in many cases!
Rule 1: Large area grounding contact
When you install the automation equipment, make sure that the surfaces of inactive metal
parts are properly bonded to chassis ground.
• Bond all passive metal parts to chassis ground, ensuring large area and low-impedance
contact.
• When using screw connections on varnished or anodized metal parts, support contact
with special contact washers or remove the protective insulating finish on the points of
contact.
• Wherever possible, avoid the use of aluminum parts for ground bonding. Aluminum
oxidizes very easily and is therefore less suitable for ground bonding.
• Create a central connection between chassis ground and the equipotential
grounded/protective conductor system.
A.2.2.2 2. Basic rule for ensuring EMC
Rule 2: Proper cable routing
Always ensure proper cable routing when wiring your system.
• Sort your wiring system into groups (high-voltage/power supply/signal/data cables).
• Always route high-voltage, signal or data cables through separated ducts or in separate
bundles.
• Install the signal and data cables as close as possible to grounded surfaces (e.g.
supporting beans, metal rails, steel cabinet walls ).
See also
Cable routing inside buildings (Page A-16)
Outdoor routing of cables (Page A-18)
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