User's Manual

4 – 7
EMC Directives
D101583 0207 BL ident
4
Avoiding sources of interference
Avoid the installation of sources of interference which occur
primarily due to switched inductances.
Interference is generated primarily by relays, contactors, fluorescent
lamps in the switch cabinet and valves, and can be avoided by the
use of RC combinations, freewheel diodes etc. This also avoids
inductive interference in the cables which are laid parallel to the coil
cables.
Potential equalisation
If the system sections are subject to a different design and different
voltage levels result, potential differences can result between the
different sections of the system. Equalization currents then flow via
signal cables (potential equalization should not be confused with a
protective earth).
Therefore correctly implemented potential equalization is essential.
The following points should be observed:
 The potential equalization cable must have a sufficient cross-
section (min. 10 mm
2
).
 The distance between signal cables and the respective potential
equalization cable must be as small as possible.
 A stranded conductor must be used.
 If the potential equalization cables are connected to the central
potential equalization bars, the power components and the non-
power components must be combined.
Shielding the cable
Signal cables must be shielded in order to avoid coupled
interference. Even though the best shielding effect when laying the
cables is achieved by using steel ducts, the use of cables with
braided shields is usually sufficient. Decisive for the effect of the
shield in both cases is however the correct connection, as a non-
connected or incorrectly connected shield has no effect.