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Installing and Preparing the C7
2.6
Setup Guidelines for Interference-Proof Installation
Introduction
2
Use and
Installation of
Interference-Proof
Cables
Interference-Proof
Hardware Setup
Cabinet Setup
2-16
An automation system must be shielded to prevent interference.
When a system is poorly grounded or not shielded, low-frequency and
high-frequency interference signals can penetrate the internal bus of the PLC
and cause malfunctions.
Interference signals can also be caused when relays or contactors switch
(very rapid changes in current or voltage; high-frequency interference
signals) or when two parts of a system have different grounding potentials
(low-frequency signals).
Use only shielded cables for all data lines, analog signal lines, and
connections to universal inputs.
Ground cable shields on both sides.
The standard cables specified in the ST80.1 and ST70 catalogs meet these
requirements.
Screw down or lock all plug connections.
Do not install data lines or signal lines parallel to power lines. Use a
separate cable duct located at least 50 cm from power lines.
The basis of trouble-free operation is the hardware setup of the control
system. Any interference signals resulting from the process should be kept
away from the hardware setup where possible.
Devices which could bring in interference signals from outside should be
installed at the bottom of the cabinet. Place the grounding rail directly at the
cabinet entrance so that cables which could be carrying interference signals
can be placed directly on the grounding potential. Place all shielded lines
with their shielding here. With double-shielded signal lines, place only the
outer shield on the grounding potential.
Install long signal lines along the cabinet walls. Setting up the cabinet in
accordance with EMC guidelines is an important factor in the reduction of
interference. All grounding connections in the cabinet must have large cable
cross-sections and be laid over a large surface.
Insulate analog devices in the switching cabinet and ground them to a single
point in the cabinet using copper tape.
Always use equivalent metals for the materials. Never use aluminum (danger
of oxidation).
Connect all doors and metal parts (sides, back and cover) of the cabinet at
least three times to the cabinet frame (short, paint-free, large-area
connections).
C7-626 / C7-626 DP Control Systems
C79000-G7076-C626-01
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