Baumuller BUM 62, Operating Instructions Manual

Page: 31 / 74

Installation
Mono Power Unit BUM 62, 63, 64
31
Baumüller Nürnberg GmbH
5.94005.12
Screening
y The screen is effective against magnetic fields if it is connected to frame ground at both ends.
With electrical fields, the screen is effective when it is connected to frame ground at one end.
However, in the case of (electrical or magnetic) fields with high frequencies (depending on the length
of the line), you must always connect the screen at both ends due to the linkage (electro-magnetic
field).
Connecting the screen to frame ground at both ends ensures that the conductor does not leave the
screening "system housing".
y Frame-grounding of conductor screens on both sides does not entirely rule out the influence of earth
circuits (potential differences on the frame ground system). However, this is very rare if you carry out
the measures described in the previous sections entitled "Cabling" and "Grounding".
You can also make a capacitive RF connection of a screen to frame ground. This prevents low-fre-
quency interference due to earth circuits.
Screened cables that pass through different EMC areas must not be separated at terminals, since
screen damping would otherwise be considerably reduced. The cables should be routed to the next
module without interruption.
Make the screen connection low-impedance and over a wide surface area. Cable tails that are only
three centimetres long (1 cm of wire = 10 nH) reduce the screening effect in the megahertz range by
up to 30 dB!
NOTE
The screen braid must have a coverage of at least 85%.
The following cables have a particularly high interference potential:
– Motor cable
– Cable to external regenerative resistors
– Cable between mains filter and converter