4 Setting Up
4.1 Installation guidelines
20
Version 04 05/2014
Shield connections
Always observe the following points when installing bus
line shielding:
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Secure the shield braid using metal cable clamps.
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The clamps must fully enclose the shield and make
good contact (see Fig. 6).
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Only connect the lines via the copper braid shield,
and not via the aluminum foil shield. One side of the
foil shield is attached to a plastic film to increase its
tearing strength, and is therefore non-conductive!
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The shields of all cables which are routed into a
cabinet from the outside must be clamped at the
point of entry inside the cabinet and connected to the
cabinet ground with a large contact surface area.
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When removing the cable jackets, it is important to
ensure that the braid shield of the cables is not
damaged. Tin-plated or galvanically stabilized
surfaces are ideal for optimum contacting between
grounding elements. With zinc-plated surfaces,
suitable threaded connections must be provided for
the required contacts. Painted surfaces at the contact
points are unsuitable.
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Shield clamps /contact points should not be used as
strain relief devices. Contact with the shield bus could
otherwise deteriorate or break completely.
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Standard recommendations for the arrangement of
devices and cables:
EN 50174–2 contains recommendations for arranging
devices and cables which are aimed at reducing
mutual interference to a minimum.
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Using bus line shields:
It is important to observe the following when shielding
bus lines:
- Use only fully shielded lines. The shields of these
lines must be of sufficient thickness to satisfy the
legal requirements for interference radiated and
interference received.
- Always attach the shields at both ends of the bus
lines. The legal requirements vis-à-vis interference
radiated and interference received for your system
will only be satisfied if shields are connected at
both ends (CE symbol).
- Attach the shield for the bus line at the connector
plug housing or at the cable clamps provided.
- In the case of steady-state operation, it is advisable
to strip the shielded line entirely and connect it with
the shielding bus /protective conductor rail.
Note:
If differences in potential occur between the grounding
points, an inadmissibly high compensating current could
flow across the shielding connected at both ends. Never
eliminate this problem by removing the shielding from the
bus line!
The following solution is permissible:
Lay an additional equipotential bonding cable parallel to
the bus line. This additional cable will carry the shield
current.
Fig. 6: Securing shielded lines using cable clamps and tube
clips (schematic diagram)