Can the steel wire armour of the ÖLFLEX® CLASSIC 100 SY also be used as EMC-compliant electromagnetic shielding resp. screening?
Although copper and steel are conductive metals, only copper (e.g. in the form of a braid) represents a suitable means of protecting a cable or wire from electromagnetic interference or shielding the environment from the interfering emissions originating from the cable itself. This not only depends on the electrical conductivity of the metal employed, but also on the braid density or the degree of coverage with which the cable is braided.
From all metals only pure silver offers marginally better conductive performance than copper. Although different qualities of iron/steel alloy exist, the conductivity of steel is generally six times lower than that of electrolyte copper. For this reason, a steel wire braid only ever protects a cable from external mechanical impact. To ensure optimised electromagnetic shielding, which also meets the requirements of the Electromagnetic Compatibility (EMC) directive, a sufficient level of copper braiding is required. As a minimum, a visual coverage level of 82-85% is required to achieve adequate screening protection. In the case of a steel wire braid used solely for mechanical protection, a visual coverage level of approx. 50% or less is standard. With a little practice, it is therefore quite easy to visually distinguish copper and steel wire braids by their degree of coverage. In addition, copper braids often have a slight reddish tinge (despite their tin plating), are somewhat softer than steel and are in comparison to steel non-magnetic.
However, even the densest, highest quality copper braid is rendered useless if it is not properly grounded! For safety reasons, steel wire braids should also be earthed when used in power networks. If the connected equipment develops a fault, this earthing prevents the transmission of dangerous voltages to the often exposed steel wire braid at the connecting points.