
14 SGP 160-2,5/4/8P/16P
13.4 Radio interference suppression and shielding
Even when installing thyristor controllers, interference from the realm of radio interference
suppression and immunity must be reduced to a tolerable level (EC-EMC-guidelines). An inter-
ference suppression that has to be subsequently implemented in an already installed system
often causes high costs.
The use of interference suppression filters in the mains supply line or on the output alone does
not resolve these interference problems. These problems can only be solved by an appropriate
arrangement of the filter elements, and a proper implementation of the cabling and shielding.
However, whether the radio interference limit values are complied with can only be checked by
measurements.
13.5 Arrangement
The controller and the filter have to be mounted as close as
possible next to each other and must be earthed with a
large-surface contact. This is best done by means of a
mounting plate (figure 1). The varnish on the contact areas
of this mounting plate must be removed in advance. The
varnish on the contact areas of the controller or the filter
has to be removed too.
Some switchgear cabinet suppliers offer mounting plates
with conductive coating.
13.6 Shielding
To prevent the controller from radiating interfering energy to the environment, the controller
should be installed in a metal-enclosed housing (switchgear cubicle or switchbox); the following
cables must be shielded:
- Cable between mains filter and controller, if it is longer than 30cm.
- Control cables, if they are longer than 2m.
Cables for digital signal transmission must be connected on both ends to the earth potential.
Cables for highly impedant analog control signals (setpoint value) must only be earthed on one
side in order to avoid a 50Hz-hum.
The shield bondings must always be implemented with large-surface contact. (Figure 2a,2b).
Therefore bondings with sheath wire, via connector pins or wire connectors are not allowed
(Figure 2c).
SGP
unshielded
max. 30cm
filter
metal
mounting plate
shielded
motor cable
Figure 1
shield bonding for cable glands
housing conductive
(vamish removed)
e. g.,cable gland made of metal
with shield bonding option
housing conductive
(vamish removed)
e. g., shielding clamp for
cables from ø 3 - 8mm
conductive (vamish removed)
shield bonding an mounting plate
sheath wire
incorrect shield bonding
Figure 2a 2b 2c