Siemens SIROTEC Planning Manual page 30

Control Cabinet Structure
Ventilation slots
If ventilation openings are integrated into the control cabinet, then offset boreholes
or HF grids are basically better than slots, since slots conduct high-frequency
signals into the interior of the control cabinet.
Many small boreholes are more favourable than few large boreholes.
Operating devices
When installing operating devices and control panels, pay particular attention to
good all-round contact with metallic assembly frames by tightening the fastening
elements with the torques indicated in the product documentation.
Bushings
The best way of ensuring the earthing of shields are bushings which have good all-
round contact with the shield and connect the housing (cabinet wall) with HF-
tightness. This measure also prevents the interference fields from arising in the
cabinet and being emitted outwards via the shielded line. For this reason, the
external shield at the cabinet inlet must be connected to the cabinet housing at all
shielded lines with an extensive and good conduction.
With coated cabinet housings (e.g. painted or powder-coated), the insulating
protective layer must be removed around the breakdown to ensure a perfect
contact with the bushing. Contact corrosion can be avoided by the selection of
suitable metals.
The connection of the shielding braid at the lead-through and/or at the plug should
be done in accordance with the assembly guidelines of the lead-through or plug
manufacturer. The correct connection of the shield is essential for the EMC quality
of the entire system.
EMC control cabinets from Siemens
The Siemens department A&D offers EMC executions of control cabinets. These
cabinets have a shield damping of approx. 60 dB, over a frequency range of
10 kHz to 1 GHz.
More detailed information on these EMC cabinets can be found in catalogue
NV 21.
Note
At this point, we would like to point out that the expenditure to increase the shield
effect of a cabinet at a later date far exceeds the purchase cost of a new EMC
cabinet.
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EMC Installation Guideline – Planning Guide (EMV) – 03.2004 Edition
© Siemens AG, 2004. All rights reserved