User manual
Earthingandshielding | Earthing of shielded cables
243Manual u-remote1432790000/03/02.2014
In practice, the shield is still often twisted and connected
to a terminal point. There is very high attenuation (voltage
drop) on these connections, especially for high-frequency
interference. Therefore, this type of shielding should not be
used, even for short cable lengths. The shielding of the cable
is practically negated and can, at best, be helpful for low-
frequency interference. We recommend that there is a large
amount of surface contact with the braided shield of the
cable.
There are generally four distinct types of coupling:
– Galvanic coupling
– Capacitive coupling
– Inductive coupling
– Radiation coupling
These types of interference usually occur mixed together, but
they can be categorised as follows:
– Electromagnetic fields
– Ripple voltage (50Hz)
– Lightning
– Interference pulses (current, voltage)
– Transient surge voltages
– Radio interference
– ESD (electrostatic discharge)
– Burst
– Mains feedback
Another area of concern as regards shield
contact is the “ow” within the conductor. Tem-
perature changes caused by the current lead
to changes in the conductor cross-section. A
rigid contact can therefore only be partially
effective. A self-adjusting contact is what is
really required. Weidmüller's clamping bracket
products (KLBÜ series) provide the perfect so-
lution to meet this challenge.
Useofaclampingbracket