electric wire
In electrical engineering and information technology, a cable is generally referred to as a single-core or multi-core group of cores ( individual lines ) sheathed with insulating materials , which is used to transmit energy or information . Different plastics are usually used as insulating materials , which surround the wires used as conductors and insulate them from one another. Electrical conductors are usually made of copper , more rarely of aluminum or suitable metal alloys . Optical waveguides consist of plastic or quartz glass fibers, which is why we also speak of glass fiber cables in this context. Viewed three-dimensionally, the cable follows a mostly cylindrical or similar geometry and can contain additional layers of insulating material or metallic foils or braids for the purpose of electromagnetic shielding or as mechanical protection in the overall structure.
Distinguishing features
There are different definitions for the term cable depending on the field of application.
- For electrical energy conductors as a subset of the electrical line, there is only the global term cable and line systems with the IEV entry 826-15-01 . In detail, a distinction is made between installation lines and cables in the respective product standards in the VDE group 0200 (for cables in particular VDE 0266, VDE 0271 and VDE 0276-603 to -632). In general, however, the stipulation applies to cables as energy conductors that they "withstand higher mechanical stresses than cables and are laid in the ground" (→ underground cables ), regardless of whether they are single-core or multi-core energy conductors.
- The aerial cable , a term commonly used in wired telecommunications, is a self-supporting cable structure with sufficient support elements, which is intended for suspension on masts and similar devices without the aid of other supporting wires or conductors.
- The YMT cables, which are constructed in a similar way to aerial cables, for use as self-supporting cables in overhead line networks for energy supply and for house connections in rural areas, are referred to as insulated power cables or PVC sheathed cables with carrying cables and are not counted as cables. They are not suitable for laying freely in the ground; laying in water is permitted.
- In data, network, signal and audio technology and similar fields, the combination of several, mutually insulated conductors (veins) to form a permanently connected unit is generally regarded as a cable; Here this term is taken from the English-speaking area, which does not conceptually differentiate between the types of cable and wire (everything is cable ). The individual wires are mostly electrical conductors , but can also be optical conductors, for example .
- Overhead lines are electrical conductors without insulation - the surrounding air acts as an insulator. The wire- like conductors are not referred to as cables, although thick ropes are nautically referred to as cables.
construction
The cable structure must meet several requirements:
- Inexpensive to manufacture
- Stresses during installation (tensile strength, bending radius, etc.)
- Environmental and operating conditions (corrosion, temperature, traffic loads, etc.)
- Investment purpose (energy or information transmission, i.e. number of cores, conductor cross-section, etc.)
Number of conductors
The number of current-carrying or optical conductors (also called cores ) in the cable is the number of conductors or the number of cores. With multi-core cables, each individual core is always covered by its own insulator, the core insulation, while an outer jacket, the cable sheath, surrounds all the cores.
- In two-core cables for direct current , the core insulation colors are often red for plus (+) and black for minus (-).
- In power cables , a black or brown is outer conductor and a blue neutral conductor used. The colors brown and black are also used for device connection cables, although the assignment to neutral and external conductors is not given. A green-yellow protective conductor is added to protection class I power cables . This carries earth potential and serves to prevent dangerous touch voltages on conductive housing or control parts in the event of a fault by diverting them to earth.
- With three-phase current , two black and one brown outer conductor are used according to the old standard, and one brown, one black and one gray outer conductor according to the new standard. The neutral conductor can be omitted if the load is symmetrical or if a PEN conductor is used. In this case, one of the outer conductors is often blue if the system was built before 2004.
- In old buildings you can occasionally still find the wire colors that are no longer permitted for new installations according to the old standard (existing installations are protected as existing in Germany ). According to the old German standard, the following was until 1965: black was the outer conductor, gray could be a neutral conductor or PEN (previously referred to as a neutral conductor), red was the protective conductor (PE), but could also be a switched outer conductor. Blue could be an external conductor in the three-wire AC network (L1: black; L2: red; L3: blue; PEN: gray). In installations and industrial plants with mains voltage, the wire colors yellow and green may only be used if there is no risk of confusion with the protective conductor (green-yellow). Red insulated wires are only permitted for control signals that are galvanically isolated from the mains.
- High voltage cables are often single-core. However, there are also two-pole high-voltage cables for DC voltage. Three-core high-voltage cables for three-phase alternating current are also known as H cables . Sometimes two-pole cables are also operated single-pole by connecting them in parallel at their ends.
- Cables for EDP , signal transmission and communication technology can have two to several thousand wires, depending on the application. A distinction is also made according to the type of stranding (for example stranded in layers, stranded in pairs, star quad ). Signal cable cores are often surrounded by a screen in pairs or as a whole.
- Cables for low and high frequency signals are often coaxial cables .
- Fiber optic cables consist of a glass or plastic fiber and a relatively thick jacket that provides mechanical protection and (especially for high-power applications in laser material processing) a limitation of the bending radius.
Conductor material
Copper is used most often because of its very good electrical conductivity, followed by aluminum .
Although aluminum only has around 2/3 the electrical conductivity of copper, the specific weight of aluminum is only around 1/3 that of copper and it is cheaper. Thus, in all applications in which the space requirement for the aluminum conductors that are thicker (with the same current carrying capacity by a factor of 1.5) does not play a major role, but weight and costs play an important role, aluminum is the better choice over copper. This is also typical for overhead lines where the conductors are made of aluminum. Conductor ropes and field cables for field telephones also contain steel to improve tensile strength. Aluminum conductors are also used in electric vehicles to save mass.
The disadvantage of aluminum is contact corrosion, spontaneous oxide layers and thus increasing contact resistance at terminal points, poor solderability and lower flexural strength. Peugeot bicycles around 1970 were made with aluminum strands, which corroded heavily at the transitions to the clamped bronze contacts when wet. In the GDR, aluminum cables were common for house installation despite these problems , and attempts were made to improve them using so-called Alcu (copper-clad aluminum conductors). Today aluminum cables are no longer used in house installation, but they are used as underground cables with larger cross-sections in the low and medium voltage range. In air, aluminum forms an oxide layer that is promoted by heat and can therefore only be soldered with special fluxes and solders . The most reliable connection method is pressing and large-area screwing after brushing and greasing.
Silver has the highest electrical conductivity of all metals, but for cost reasons it is only used in special cases, e.g. B. for high frequency ( skin effect ) or with thermal stress, mostly only as a coating.
In special cases, superconductors are used which have to be cooled below their transition temperature by pumping coolant through separate channels in the cable. However, such cable connections are rare. The constant cooling is relevant to safety, as the cable would be immediately destroyed by the heat of electricity if the superconductivity breaks down.
In addition to copper wires, optical conductors ( glass fiber cables , fiber optic cables ) are also used in communication networks .
In the case of headphone cables and other highly stressed signal cables, fine-stranded copper strands are mixed with synthetic fibers with a high tensile strength (e.g. aramid ) to increase the cable's tensile strength. Cables for telephones, which are made by wrapping textile fibers with copper tape, have been around since the 1930s. They are suitable for high alternating bending stress, tensile strength, but low currents. A cable structure with enamelled copper wires is also common for similar purposes . Enamelled copper wire can be solderable because the enamel decomposes at the soldering temperature.
For high frequency, high-frequency stranded wire is used, the individual stranded wires of which are insulated with varnish. It is rather not used for cables.
Copper conductors (especially strands) can be tinned for corrosion protection.
In flexible applications and in automotive and plant construction, the cores of cables consist of stranded wires . In the case of particularly high mechanical stress from repeated bending (handheld devices, energy chains , event and stage technology), so-called finely stranded strands and braided stranding are used.
| metal | Relative conductivity (Copper = 100) |
Electrical resistance at 20 ° C (in Ω 10 −8 ) |
Resistance temperature coefficient (in α 10 −1 ) |
|---|---|---|---|
| silver | 106 | 1.626 | 0.0041 |
| Copper HC (annealed) | 100 | 1.724 | 0.0039 |
| Copper HC (hard drawn) | 97 | 1,777 | 0.0039 |
| tinned copper | 95-99 | 1.741-1.814 | 0.0039 |
| Aluminum EC (soft) | 61 | 2.803 | 0.0040 |
| Aluminum EC (½H – H) | 61 | 2.826 | 0.0040 |
| sodium | 35 | 4.926 | 0.0054 |
| Structural steel ( English mild steel ) | 12 | 13.8 | 0.0045 |
| lead | 8th | 21.4 | 0.0040 |
Identification of multi-core cables
There are several ways to mark the veins. Flexible control lines with cross-sections from 0.75 mm 2 often have numbers. Thinner control lines and telecommunication cables are indicated by colors. In the case of multi-core cables, there is the option of applying multicolored coding with longitudinal or transverse stripes to the respective core, with cross-striped coding also being able to vary in distance in order to designate different cores.
The following table shows the core identification for telecommunication cables according to DIN 47100 with color repetition from 45 cores.
| No. | colour | No. | colour | No. | colour | No. | colour | No. | colour | No. | colour | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | White | 11 | gray-pink | 21st | White blue | 31 | green Blue | 41 | grey black | 51 | blue | |||||
| 2 | brown | 12 | Red Blue | 22nd | brown-blue | 32 | yellow blue | 42 | pink-black | 52 | red | |||||
| 3 | green | 13 | white-green | 23 | White-red | 33 | green red | 43 | blue-black | 53 | black | |||||
| 4th | yellow | 14th | Brown Green | 24 | brown-red | 34 | yellow Red | 44 | Red Black | 54 | violet | |||||
| 5 | Gray | 15th | White yellow | 25th | White black | 35 | green-black | 45 | White | 55 | gray-pink | |||||
| 6th | pink | 16 | yellow-brown | 26th | Brown black | 36 | yellow black | 46 | brown | 56 | Red Blue | |||||
| 7th | blue | 17th | white-gray | 27 | gray-green | 37 | gray-blue | 47 | green | 57 | white-green | |||||
| 8th | red | 18th | gray-brown | 28 | yellow grey | 38 | pink-blue | 48 | yellow | 58 | Brown Green | |||||
| 9 | black | 19th | white-pink | 29 | pink-green | 39 | grey Red | 49 | Gray | 59 | White yellow | |||||
| 10 | violet | 20th | pink-brown | 30th | yellow-pink | 40 | pink | 50 | pink | 60 | yellow-brown | |||||
| 61 | white-gray |
Insulating materials
Insulating materials that can be used for cables must generally be plastic or elastic. Exceptions are the soaking oil for oil cables and ancient coaxial cables insulated with porcelain beads. The insulating materials must have a high specific electrical resistance and a high dielectric strength. Further parameters for signal cables are the lowest possible loss factor and low dispersion .
In the past, paper was often used for core insulation. In order to reduce the sensitivity to moisture and to increase the dielectric strength, the paper was soaked in oil or wax. Oil-paper cables (also called earth cables) are still in use today and in the high and medium voltage range are superior to cables insulated with PVC in terms of their service life and dielectric strength. However, the assembly costs are extremely high, which is why they are replaced by plastic cables with insulation made of cross-linked polyethylene (XLPE).
The most common insulation material used in power and signal cables today is polyvinyl chloride (PVC), followed by polyethylene (PE), rubber and polyurethane (PUR).
One way of increasing the operating temperature of PVC-insulated cables is electron beam crosslinking. However, PVC has a high dielectric loss factor, which is why it is often unsuitable as an insulation for signal cables, especially with high frequencies or great lengths. Broadband signal cables, high-frequency cables and telephone lines are therefore often insulated with PE.
For flexible cables that are subject to high thermal and mechanical loads, rubber is used as insulation and is tread-resistant on construction sites and in the garden.
Silicone cables are used for high, but also particularly low temperatures and high voltages . Since these are not very cut and pressure-resistant, silicone is sometimes connected with a glass fiber covering, for example on the supply lines for kitchen stove tops.
Of all plastics, polytetrafluoroethylene (PTFE) withstands the highest and lowest temperatures, also withstands almost all chemical attacks, but is more mechanically vulnerable. (E.g. in the engine area of aircraft).
Cables in electrical heating devices are now rarely covered with threaded ceramic beads (cylinder with axial bore and spherical cap-shaped cover surfaces, one concave , one convex or ceramic tube).
Length-elastic spiral cables for telephone receivers, microphones, electric guitars etc. are made to measure with straight end sections.
Sheath material
The cable sheath protects the cable from external influences and, if necessary, contains a shield. For a long time, lead was a frequently used material for sheathing paper-insulated cables. It is still used today in lead-sheathed cables (e.g. NYKY-J for low voltage or N2XS (F) K2Y for medium voltage) in refineries in order to protect the cables from damage by aromatics and hydrocarbons . In some cases, cables with an intermediate jacket made of polyamide or nylon are now used . In most cases, these cables are sheathed again with the flame-retardant PVC in order to obtain a flame-retardant effect. (Types e.g. 2XS (L) 2Y4YY for medium voltage or 2X (L) 2Y4YY for low voltage).
Today, in addition to PVC, plastics such as polyurethane or polyethylene are also used. Polyethylene is very inexpensive, but it is flammable. When exposed to fire, PVC generates poisonous gases such as hydrogen chloride and dioxins . This is why halogen-free , flame-retardant cables and lines are used in modern buildings with large numbers of people, such as train stations, airports, museums, congress halls and department stores . Rubber is used as a jacket for flexible, highly stressed cables. For signal transmission ( network cables for IT, control and audio cables), the cable sheaths are often provided with a shield made of metal foil or copper wire mesh in order to improve the cable's electromagnetic compatibility .
The power lines leading from frequency converters to the motors often have to be shielded in order to avoid radiated interference (see electromagnetic compatibility ).
Underground and submarine cables as well as overhead lines are provided with armouring (steel wire mesh, sheet steel) as protection and to increase their mechanical stability.
In order to detect damage to the jacket at an early stage, multi-core cables are filled with compressed air in communications technology and the internal pressure is monitored. In the case of power cables, an insulating protective gas (e.g. sulfur hexafluoride ) is used instead.
Fiber optic cables for high-power lasers are equipped with a fiber break monitor, which monitors the conductivity of a wire or a metal coating on the fiber.
For most purposes, cables are manufactured according to international standards , which often also define abbreviations for certain cable classes. See also harmonized type codes for cables .
Conditions of use
There are fixed cables in cable trenches, in plaster, in ducts, on cable racks and flexible cables for moving devices or systems. Further stress conditions of a cable essentially determine its construction:
- Laying on the seabed Submarine cables : strong reinforcement, tensile strength, longitudinally and transversely watertight
- Underground installation ( underground cable ): secure sheathing, possibly reinforcement, if necessary longitudinally and transversely watertight
- Above ground in outdoor areas: UV radiation stable jacket, tensile strength
- For mobile devices: fine or finely stranded cores, possibly rubber or silicone insulation
- Mechanical stress from edges: fabric, lacquer fabric, lacquer fiberglass fabric
- In fire-endangered rooms: halogen-free, flame-retardant insulation
- Influence of hydrocarbons: Oil-resistant materials
- High electrical or magnetic interference or susceptibility to interference: twisted wire pairs, single or double shielding
- High temperatures or heating: rubber, silicone rubber, PTFE
The temperature resistance of cables is specified in thermal classes (according to IEC 60085):
| Thermal class |
Limit temperature in ° C |
Insulating materials | Application examples |
|---|---|---|---|
| Y | 90 | PVC; PET; Natural rubber; Cotton; Paper products; Rayon | Lines and covers |
| A. | 105 | Synthetic rubber; Insulating oils; | Lines, windings, insulating hose |
| E. | 120 | Laminated paper impregnated with synthetic resin lacquers | Windings |
| B. | 130 | Unimpregnated and impregnated fiberglass products; Pressed parts with mineral fillers | Windings and pressed parts |
| F. | 155 | Glass fiber products impregnated with suitable resins (e.g. epoxy resin); Polyester lacquers | Windings |
| H | 180 | Glass fiber and mica products impregnated with silicone resins; synthetic rubber | heat-resistant cables and windings, covers, insulating tubes |
| C. | > 180 | Mica; Glass, porcelain and other ceramic materials; fiberglass and mica products impregnated with silicone resins; | Heat-resistant windings |
Intended use
Wiring harness
A harness is a device -, product- or system-specific summary of individual lines and cables, which is often already provided with connectors to a prefabricated composite. In automobiles there are cable harnesses with a weight of around 50 kg. Wire harnesses transmit both electrical power and signals.
Power cable
The amperage allowed for a cable depends on the following criteria:
- Temperature resistance of the insulation
- Cross-sectional area of the conductor
- Number of conductors
- Ambient temperature
- Laying type
- Number of cables in the same channel
- Operating voltage (because of the thickness of the insulation, which hinders heat dissipation)
Corresponding information can be found, for example, in EN 60204-1 : 2007-06 "Electrical equipment of machines - General requirements".
Radio frequency, signal and control cables
In the case of HF and signal cables, the impedance or the wave impedance as well as the dielectric quality or the dielectric loss factor of the insulation material also play a role.
In the case of LF cables, in addition to the effective resistance R '(Ohm / km), the capacitance C' (µF / km) is also of major importance. The cable capacitance of control cables has a value of approx. 0.3 µF / km.
Coaxial cables are mostly used for high frequency and broadband signal transmission (also for high transmission capacities) . In principle, these have no outwardly penetrating electric and magnetic field when the sheathed conductor is closed and the core is in the middle. Coaxial cables for high-frequency applications therefore have a dielectric that optimally supports the inner conductor with the lowest possible density. The low density required for low loss is often achieved using air or foam. On the outside, double shielding, consisting of braid and metal foil, is often applied. Such coaxial cables are very immune to interference. They usually have a wave impedance of Z = 50… 75 Ohm.
In the past, so-called ribbon cables (Z = 240 ohms) were also used for antenna cables . They consist of two symmetrically arranged cores connected by an insulating bar. These cables are more sensitive to interference due to the outward penetrating fields, but have less attenuation than coaxial cables when they are laid at a distance from parts of the building.
Multi-core, shielded or unshielded cables with cross-sections of 0.14 to 0.5 mm² are often used as signal lines or control lines, which are variable if the length of the cable (e.g. telephone receivers , keyboards , headphones, etc.) is used should, also as so-called. " Spiral cable " can be designed.
For the transmission of high data rates, e.g. For example, with USB cables, so-called twisted pair cables are used: One or more wire pairs are twisted together and, if necessary, also routed in separate shields.
Flat ribbon cables ("suspender cables ") consist of a large number of parallel cores and are used as signal lines in computers and electronic devices in particular. They can be connected inexpensively and reliably using insulation displacement technology.
There are also ribbon cables folded in round shielding sheaths, so that insulation displacement technology can also be used.
Examples
- Such cables are multi-core. The cores are twisted in pairs or in groups of four as "star quads" . In a star quad, the diagonally opposite wires are used as a pair. Telephone cables are usually buried on public land (roads). The picture shows the fanned out "test flower".
- Often found in computers. The connection is made using insulation displacement technology for all wires simultaneously.
- Shielded cables
- One or more insulated wires are surrounded by a conductive shield; After the respective isolation, one or (rarely) two further shielding conductors can be coiled or braided over it. The crosstalk (undesirable mutual influencing of actually independent signal channels) and the ability to intercept are thereby greatly reduced. Measuring lines with a grounded shield catch fewer interference signals from the environment. In residential construction, shielded installation cables / sheathed lines (NYM (ST) -J) are occasionally used to reduce electrosmog in living spaces.
- Cables with a concentric structure and a wave impedance adjusted by geometry and insulation material are used for the transmission of high-frequency signals such as from the antenna to VHF radios and televisions, with the outer conductor also acting as the shield for the inner conductor.
- Consists of twisted wire pairs. The twisting allows a similarly interference-free signal transmission as coaxial cable. In addition, twisted pair cables are usually also shielded.
Telephone cord fanned out
Ribbon cable
Coaxial cable
Twisted pair cable
Security-relevant installations
In the case of safety-relevant systems, such as safety lighting systems, fire alarm systems or alarm systems, the relevant requirements for fire in certain areas of cables and lines require integrated function maintenance for a specified period of time. Alarm systems here do not mean alarm systems in the sense of intrusion detection technology; as a rule, no functional maintenance is necessary for such systems. Rather, it concerns systems according to. DIN VDE 0828 or DIN VDE 0833-4, which use acoustic signals to warn people in the presence of dangers and prompt them to evacuate the building.
In Germany, this issue is regulated in DIN 4102 Part 12 and the state-specific implementation of the "Model Line Systems Guideline" MLAR . This means that the cabling (fastening material and cables) must remain functional for a specified time in the event of fire. During this time, the insulation resistance must not become so small that there is a flow of current between the conductors, nor can the resistance of the conductor increase so that the flow of current would be impeded. In other words, neither a short circuit nor an interruption must occur. These properties are achieved through a special structure of the line and special materials for the insulation. The cables can be recognized from the outside by their orange sheath (red sheath for fire alarm cables) as well as by repeated identifying imprints. Common times for the required functional integrity are 30 minutes, 60 minutes or 90 minutes (E30, E60, E90). If these lines catch fire after this period has expired, they also have a higher fire load than normal lines such as NYM or JY (St) Y.
In order to achieve effective functional maintenance, the cable routing system and the environment must be considered in addition to the cable. The different types of cable routing systems (cable tray, armored steel conduit , individual fastening) have in common that they must also withstand a fire for the corresponding duration.
Together with the management, they result in a so-called "tested pipeline system". Appropriately tested combinations are named by the manufacturer in test certificates. The installation environment must be designed in such a way that the cables and lines are not impaired or destroyed by parts that burst or fall during the fire.
Lead cable
In the past, cables were often sheathed with lead . In the case of underground cables, the lead sheath was additionally protected with tarred jute and, in some cases, a steel spiral. Jute and paper, which were mostly impregnated with wax , were also used as insulation material around the conductors . In order to process such veins, this insulation first had to be made supple, which was done by bathing in a bath made of liquid wax and required a lot of experience.
See also
- Three-phase line
- Cable break
- Structured cabling
- Pigtail
- Abbreviations in cable technology
- Type codes of cables
- Cable bridge
- Neutral conductor
literature
- Hans Schultke: ABC of electrical installation . 14th edition. EW Medien und Kongress GmbH, Frankfurt 2009, ISBN 978-3-8022-0969-7 .
- Wilhelm Rudolph: VDE series 39; "Introduction to DIN VDE 0100", electrical systems in buildings . 2nd Edition. VDE Verlag GmbH, Berlin - Offenbach 1999, ISBN 3-8007-1928-2 .
- Daniel Gethmann, Florian Sprenger: The ends of the cable. Small media history of transmission . 1st edition. Kadmos, Berlin 2015, ISBN 978-3-86599-205-5 .
Web links
- Cable cross-sections for house installations (PDF; 4.0 MB)
- "Das Kabelbuch" - information medium of the cable and electrical industry , kabelbranche.de
- IT cabling , at lanline.de
- All about the cable cross-section , at sengpielaudio.com
- Cable cross-sections according to DIN 57100 (PDF; 14 kB), at njumaen.de
- Control cable, cable capacity , at moeller-engineering.com (PDF, 319 KiB)
- Optical conductor
- Specifications and pictures of various fiber optic cables ( Memento from November 7, 2013 in the Internet Archive ), at ftth.ccm.ch
- Connector types for fiber optic cables ( Memento from April 2, 2015 in the Internet Archive ), at lwl-kabel.ch
- Cables and wires for digital control signals in lighting technology , at hbernstaedt.de
Individual evidence
- ↑ DIN VDE 0100-200: 2006-03, Section 826-15-01 Cable and line system , " Entire unit consisting of one or more insulated conductors, cables and lines or busbars, and their fastening means, and, if necessary, their mechanical protection"
- ↑ Cables and wires. (PDF; 657 kB) State Environment Agency North Rhine-Westphalia, accessed on August 21, 2013 : “Generally valid characteristics for differentiating between these two types of construction are not defined in the VDE regulations. In general, however, compared to lines, cables can withstand higher mechanical loads and may be laid underground. "
- ↑ Electrotechnical applications. Electric conductors. (No longer available online.) Deutsches Kupferinstitut e. V., archived from the original on December 2, 2013 ; Retrieved August 21, 2013 .
- ↑ Major Tesla order for a Viennese company ( Memento from March 21, 2017 in the Internet Archive ) orf.at, March 20, 2017, accessed March 21, 2017.
- ↑ http://www.vdi-nachrichten.com/Technik-Gesellschaft/Erstmals-supraleitendes-Kabel-im-Vreisenetz
- ^ GF Moore (Ed.): Electric Cables Handbook , 3rd Edition, Blackwell Science, 1997, ISBN 0-632-04075-0 , p. 33