Conductor Material, Insulation Material, Shielding, Types of Stranding and Filling Materials
The requirements for the conductor material of bare or metal-coated soft electrolytic copper are specified in DIN VDE 0295. The base is formed by an oxygenic copper wire according to DIN 40500 part 4, defined by the abbreviation E-CU 58 F21 with a conductivity of at least 58.0 m/ ohms mm2 at a temperature of 20°C. Apart from twisted fine and extra fine copper strands also tinsel conductors according to DIN 47104 can be used at high bending stress. Here fine-wire threads and core threads of chemical fibers are combined into a highly flexible tinsel conductor.
For sheathing and insulating of cables and lines thermoplastic plastics and thermoplastic elastomers are used. In combination with the geometric dimensions of the inner- and outer conductors the dielectric is responsible for the transmission characteristics (attenuation, impedance) and has to minimize capacitive interference exerting on or coming from the conductor. Consisting of suitable materials the outer sheath is a protection against weather influences, media and process materials and so guarantees a long cable life.
By this we mean a cover of highly conductive material protecting a single core, a core group or all cores of a line. The shielding has to protect conductors against the penetration of electric fields or avoid the outlet of any electrical disturbance out of a line.
The shielding supports electromagnetic compatibility (EMV) and so reduces electromagnetic diffusions on signal lines or on electrical equipment. On the other hand the shielding also reduces diffusions coming from the cable or from the electrical equipment on the environment. In our cable manufacture we mostly use braided shielding and coiled shielding of bare and tinned copper wires, but we also use shielding sheathed with conductive foils. Foil shielding is more efficient at high frequencies, braided shielding however at low frequencies. Foil shielding and braided shielding can also be laid in layers alternately.
Types of Stranding
The individual elements of lines and cables are coiled in parallel around a central element. These elements are either single wire conductors or cores or core groups. Depending on the requirements the stranding of the elements is made with different lay lengths. According to the number of elements this is done in concentric layers placed one above the other.
For cable construction we always choose the best layer structure of the stranding elements to get cables as round as possible. Empty spaces in the layer structure are filled with filling elements. Without stranding conductors arranged in parallel next to each other would be deformed during bending – the outer conductors would be extended, the inner ones would be compressed.
By this we mean non-conductive elements consisting of insulating material (dummy core) or textile for filling of gaps in the composite braid structure.