Wires and cables.
The electric cables must ensure the greatest possible freedom for the flow of current between the source of electricity and the load, as well as between various electrical devices, included in electrical circuits.
One of the basic elements of the cable structure is a conductor, most often made of copper (marked with the symbol D.), aluminium (symbol A) or steel (symbol F) with a standardized cross-section and shape. There are single-wire and multi-wire conductors, so-called. links, resulting from the twisting of a number of wires (copper link symbol L, aluminum AL, steel FL). In some types of cables, the conductor is the only element of the cable, and then the conductors are called bare (not isolated).
The second element of the electric wire is insulation, which forms a layer of dielectric material, separating the individual elements of the duct. Electric wires are protected by various types of coatings, called, among others. clothing, metal jacket, wrap or fence.
According to the EPS classification, power cables can be divided into:
- bare wires,
- winding wires,
- power cables for permanent installation,
- cables for mobile and portable receivers.
Copper winding wires, less often aluminum, have complex insulation, which first layer, directly on the vein, creates enamel, and then the cotton cover, silk, paper or possibly PVC (drawing).
Drawing. Construction of winding wires: 1 - she was alive, 2 - enamel layer, 3 - cotton ruff, 4 - paper braid, 5 - polyethylene layer.
They are designed to make the windings of some transformers, machine rotors and must be highly susceptible to winding.
Permanent laying cables include: single-core with rubber or PVC insulation, multi-core, plug-in and cable, which, depending on the environment in which they will work, differ slightly in structure and properties.
Cables for mobile and portable receivers (the symbol S) they are used as housing cords (SM) with conductors insulated with rubber or PVC, protected by fibrous braid, or as multicore tire cables (O). They are resistant to winding and twisting, as well as vibration.
Cables, marked with the symbol K, are used to transmit electrical signals and consist of:
— one or more conductive conductors,
— insulating layer (paper saturated with insulating oil or rubber),
— protective layer (tight lead coating, external guards; drawing).
Drawing. Three-core cable in paper insulation: a) cable in armor made of steel strip, b) cable cross-section. 1 — aluminium or copper conductors, 2 — oil-saturated paper (phase insulation), 3 — jute filling, 4 — oil-saturated paper (core insulation), 5 — lead coating, 6 — paper tape, 7 — jute layer, 8 — steel strip armor, 9 — jute.
Cables, that transmit electricity, can be laid directly in the ground, in underground sewers, in water, outdoors and indoors. This is one of the main differences between the wires, and cables (wires can only be laid indoors). Another difference is the range of intensity values, in which they can work: the wires are intended for the lower values, cables, on the other hand, can carry the entire range of applied voltages.
Currently, optical fibers are becoming more and more popular. The fiber-optic information transmission system has very wide frequency bands and significant immunity to interference, from electromagnetic fields. Core (vein) optical fiber is made of glass fiber, and the mantle of glass, only with a lower refractive index.