Belden HIRSCHMANN OZD Modbus Plus G12 Manuel page 40

3 Start-Up
Standard recommendations for the arrangement of
devices and cables:
EN 50174–2 contains recommendations for arran-
ging devices and cables which are aimed at redu-
cing mutual interference to a minimum.
Using bus line shields:
It is important to observe the following when
shielding bus lines:
- Use only fully shielded Modbus Plus bus 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).
Shield connections
Fig. 6: Securing shielded lines using cable clamps and tube
clips (schematic diagram)
38
- 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 groun-
ding 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.
Always observe the following points when installing bus
line shielding:
Secure the shield braid using metal cable clamps.
The clamps must fully enclose the shield and make
good contact (see Fig. 6).
Only connect the Modbus Plus bus 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!
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.
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 con-
tact points are unsuitable.
Shield clamps/contact points should not be used
as strain relief devices. Contact with the shield bus
could otherwise deteriorate or break completely.
3.1 Installation guidelines
Version 04 07/2014