Installation Of Programmable Controllers For Emc; Basic Rules For Assembling And Grounding The Inactive Metal Parts - Siemens S5-155U System Manual

3.2

Installation of Programmable Controllers for EMC

3.2.1
Basic Rules for Assembling
and Grounding the Inactive
Metal Parts
System Manual
C79000-B8576-C199-03

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
Ensure wide-area chassis grounding of the inactive metal parts when
mounting the equipment. Properly implemented 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.
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