4.1 Installation guidelines
21
4 Setting Up
Version 04 05/2014
Laying cables inside of buildings
Laying cables within control cabinets
If a repeater is installed within a control cabinet, the cable
shield of the incoming bus cable should be electrically
connected to a grounding rail as close as possible to the
cable leadthrough using a shield grounding clamp or
similar The cable shield should continue within the cabi-
net to the fieldbus device and be connected there in
accordance with the manufacturer’s instructions.
Laying cables outside of control cabinets
PROFIBUS cables and cables for
- DC and AC voltages > 400 V (unscreened),
- areas with explosion hazard and
- Telephone cables
separate cable runs spaced at least 10 cm apart.
All cable ducts should be constructed of electrically
conducting material and connected to functional ground
at regular intervals. Bus cables should not be subject to
mechanical loads which exceed the manufacturer’s
specifications. If this cannot be avoided, additional
protective measures should be taken, e.g. by laying the
cables in a steel pipe or rugged metal duct. The pipe or
duct should then be grounded at regular intervals and
protected against corrosion.
Potential equalization and screening
The cable screen should be connected to ground at both
ends of the cable. The use of fiber optic cable is recom-
mended if problems are experienced with interference.
A low impedance potential equalization cable should be
used if this is not possible.
Situations where interference can present a problem
include:
- Plant which extends over a large area
- Power is fed to the plant from different power sources
- Networking extends over several buildings
If one of these situation apply, the following should be
observed when installing the potential equalization
system:
- The circuit through which interference signals flow must
be closed, and
- Each part of the plant must be electrically connected
to the potential equalization system/functional ground
at as many places as possible. Electrically conducting
pipes, parts of machines or supporting structures
should be integrated in the potential equalization
system. In order to ensure long-term reliability, appro-
priate measures should be undertaken to protect
against corrosion.
- The potential equalization cable must be protected
against corrosion.
- The cross-section of the potential equalization cable
should be chosen with regard to the maximum potential
equalization currents which can flow.
Special care should be taken when installing potential
equalization cables to maximize the interference immuni-
ty of the data cables. If possible, the potential equalizati-
on cable should be laid parallel to and as close as possi-
ble to the data cable (preferably in the same plastic pipe).
The cable screen should never be used for potential
equalization. The potential equalization cable should be
finely stranded to ensure that it is also effective at high
frequencies as a result of the large surface area.
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Fig. 6: Laying cables inside of buildings