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S5-95F
3.3
Installation of Programmable Controllers for EMC
Measures for suppressing interference voltages are often applied only when the control system is
already operational and proper reception of a useful signal is impaired. The reason for such
interference is usually inadequate reference potentials caused by mistakes in equipment assembly.
Described in the following sections are:
•
Basic rules for grounding the inactive metal parts
•
Examples of cabinet assembly for EMC
•
Example of rack and wall mounting for EMC
3.3.1
Basic Rules for Assembling and Grounding the Inactive Metal Parts
Ensure wide-area chassis grounding of the inactive metal parts when mounting the equipment.
Properly implemented chassis grounding creates a uniform reference potential for the control
system, and reduces the effects of picked-up interference.
Chassis grounding is understood to mean the electrical connection of all inactive parts. The entirety
of all interconnected inactive parts is the chassis ground.
Inactive parts are conductive parts which are electrically isolated from active parts by basic
insulation, and can only develop a voltage in the event of a fault.
The chassis ground must not develop a dangerous touch voltage , even in the event of a fault.
The ground must therefore be connected to the protective ground conductor. To prevent ground
loops, locally separated ground elements such as cabinets, structural and machine parts, must
always be connected to the protective ground system in star configuration .
Ensure the following when chassis grounding:
•
Connect the inactive metal parts with the same degree of care as the active parts.
•
Ensure low-impedance metal-to-metal connections, e.g. with large-area good quality contact.
•
When you are incorporating painted or anodized metal parts in the grounding, these insulating
protective layers must be penetrated. Use special contact washers or remove the insulating
layer.
•
Protect the connection points from corrosion, e.g. with grease.
•
Movable grounded parts such as cabinet doors must be connected via flexible grounding strips.
The grounding strips should be short and have a large surface because the surface is decisive
in providing a path to ground for high-frequency interference.
EWA 4NEB 812 6210-02
Guidelines for the Planning and Installation of the Product
3-5
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