Five Basic Rules For Insuring Emc - Siemens SIMATIC S7-300 Hardware And Installation Manual

Appendix
11.2.2

Five basic rules for insuring EMC

If you conform with theses five basic rules ...
you can insure EMC in many cases!
Rule 1: Large-area grounding
When you install the automation equipment, make sure that surfaces of inactive
metal parts are well bonded to chassis ground (see the following sections).
• 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 is highly corrosive and is therefore less suitable for ground bonding.
• Create a central connection between chassis ground and the equipotential
busbar/protective conductor system.
Rule 2: Proper cable routing
Ensure proper cable routing when you wire your system (see the section below on
Indoor/outdoor cable routing).
• 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 ).
Rule 3: Mounting the cable shielding
Take care that all cable shielding is properly fastened (refer to the section on
Shielding of cables).
• Always use shielded data cable. Always connect both ends of the shielding to
ground on a large area.
• Analog cables must always be shielded. For the transmission of low-amplitude
signals it might prove to be more efficient to have only one side of the shielding
connected to ground.
• Directly behind the cable entry in the cabinet or enclosure, terminate the
shielding on a large area of the shielding/protective ground busbar and fasten it
with the help of a cable clamp. Then, route the cable to the module; however,
do not connect the shielding once again to ground in this place.
• Connections between the shielding/protective ground busbar and the
cabinet/enclosure must be of a low impedance.
• Always install shielded data cables in metal/metallized connector housings.
11-6
S7-300 Programmable Controller Hardware and Installation
A5E00105492-01