Guidelines for the Planning and Installation of the Product
S5-95F
3.4.3
Shielding of Cables and Lines
Shielding is a method of attenuating magnetic, electrical or electromagnetic interference fields.
Interference currents on cable shields are passed to ground via the shield bar which is electrically
connected to the housing. A low-impedance connection to the protective conductor is particularly
important so that these interference currents themselves do not become an interference source.
Where possible, only use lines with a braided shield. The coverage density of the shield should be
more than 80 %. Avoid lines with a foil shield because the foil can be very easily damaged by tensile
strain and compression during fitting; this results in reduced effectiveness of the shield.
As a rule, line shields should always be connected at both ends. This is the only way to achieve a
good degree of interference suppression in the higher frequency region.
Only in exceptional cases should the shield be connected at one end only, as this only achieves
attenuation of the low frequencies. Single-ended shield connection may be more advantageous
when:
•
an equipotential bonding conductor cannot be laid;
•
analog signals (of a few mV or mA) are to be transmitted;
•
foil (static) shields are used.
With data lines for serial communication, always use metal or metallized connectors. Secure the
shield of the data line to the connector case. Do not connect the shield to PIN 1 of the connector.
For stationary operation, it is advisable to fully strip the insulation from the shielded cable and
connect it to the shield/protective conductor bar.
Note
In the event of potential differences between ground points, a circulating current may
flow through the shield connected at both ends. In this case, install an additional
equipotential bonding conductor (see section 3.4.2).
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EWA 4NEB 812 6210-02
