5.4 Shields for Cables in Buildings

Cables shall be run near the equipotential bonding lines. These are parts of the steel construction, reinforced walls, cable supporting structures, cable trays or other electrically conductive parts which are connected to the equipotential bonding system at least at both ends. In principle, shielded cables should be used (Figure 5.4 a). This applies for electronic or data cables as well as for higher voltage levels. Pair-twisted signal cables are to be preferred. For related lines of one signalling circuit a twisted pair each is to be used, so that the incoupled transverse voltage on cable runs must be neglected. The limitation of the incoupled series voltage determines the protection measures.

Figure 5.4 a: Connection of cable screens to a local equipotential bonding bar

To lessen surges by overcoupling, power and signalling cables must be consequently separated, if possible by using cable supporting structures which are included in the equipotential bonding (Figures 5.4 b and c). Different separations are needed depending on the cable parallel running length. Thus:

Figure 5.4 b: Cable support constructions

Figure 5.4 c: Line screen out of continuous metal cable racks and metal coverings with pipe bends removed (Source H. Neuhaus)

Also in existing systems it may become necessary to shield the cable routes (subsequently). For this purpose a...