Installation
30 Basic Supply Unit BUG 622, 623
5.94034.07a Baumüller Nürnberg GmbH
Shielding
y The screen is effective against magnetic fields when it is connected to ground at both ends.
With electrical fields, the screening is effective if the screen is connected to ground at one end.
Fields with high frequencies (depending on the cable length) are always electromagnetic. It doesn’t
matter it the field basically is electric or magnetic. Always apply the screen at both ends for fields with
high frequencies.
If you apply the screen to ground at both ends, the cable does not leave the screening ”system
housing”.
y If you connect cable screens to ground at both ends, the effect of earth loops (potential difference
on the ground system) cannot be excluded totally. However, these are very rare if you observe the
measures of the above chapters ”Cabling” and ”Grounding”.
The HF connection of a screen to ground can also be capacitive. This prevents low-frequent noise
caused by earth loops.
Screen cables passing through different EMC areas must not be separated at the terminals,
otherwise the screening would be reduced considerably. They should be led to the next module
without interruption.
The screen connection should be of low impedance and over a large surface. Cable tails with a
length of only 3 cm (1 cm wire = 10 nH) reduce the screening of up to 30 dB when noise occur in the
MHz range!
NOTE
The screen braid must have a coverage of at least 85%.
The following cables have a particularly high interference potential:
y Motor cable
y Cable to external regenerative resistors
y Cable between mains filter and converter
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