Control Cabinet Structure; Design And Assembly Of The Cabinet; Earthing Of Control Cabinet Components; Breakdowns In The Control Cabinet Wall - Siemens SIROTEC Planning Manual

5 Control Cabinet Structure

5.1 Design and assembly of the cabinet

5.1.1

Earthing of control cabinet components

The following measures improve the shielding effect of a control cabinet:
·
Connect all metallic parts of the control cabinet flat and with good conduction
between each other.
·
Cabinet covers as side plates, rear panels, roof and bottom plates should be
contacted with a sufficiently small distance.
·
Side, rear panel, assembly and roof plates must be connected extensively to
the cabinet framework.
·
The mounting angle for the component holders must have a large surface-area
metal-metal-connection to the cabinet framework.
·
All screw connections on painted and anodized metal parts must either be
executed by means of special contact discs or the insulating protective layers
between the parts must be removed before assembly.
·
If protective layers are extensively removed for a good metal-to-metal
connection, then long-term corrosion protection (e. g. contact grease) must be
ensured by taking additional measures.
·
The material of the parts to be connected including the connection elements
(screws, toothed washers, rivets, etc.) should lie close together in the
electrochemical voltage series.
5.1.2

Breakdowns in the control cabinet wall

The shielding effect of the control cabinet is impaired by the attachment of
ventiducts, installation of inspection windows and operating devices.
! Warning
If an opening in the control cabinet wall reaches the size of the half wavelength of
the interference signal, then the shielding effect is practically neutralized, since
the breakdown can act as an antenna.
Example: Interference signal = 500 MHz
© Siemens AG, 2004. All rights reserved
EMC Installation Guideline – Planning Guide (EMV) – 03.2004 Edition
Interference signal = 1000 MHz Þ
Þ
½ wavelength = 30 cm
½ wavelength = 15 cm
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