Cable

As a sheathed cable with insulating materials on or multi-core composite is generally referred to by veins, which serves for the transmission of energy or information. When insulating materials are usually different plastics to use surrounding the land under conductor wires and insulate against each other. Electrical conductors are usually made of copper, less commonly made ​​of aluminum or other suitable metal alloys. Optical fiber made ​​of plastic or quartz fibers, which is why in this context, speaking of fiber optic cables. In mechanics, the cable follows a generally cylindrical or similar geometry and in the overall structure can also contain other mantle layers of insulating material or metallic foils, or braids for the purpose of electromagnetic shielding or for mechanical protection.

• 4.1 Power cables
• 4.2 High-frequency, signal and control cables

Distinguishing features

For the term cable is available depending on the application field different definitions.

• For electrical power conductors as a subset of the electrical line exists with the IEV 826-15-01 entry only global term " cable and pipe systems ." In detail, a distinction is made between installation conductors and cables in the product standards in the VDE 0200 group. As a general rule for cable as power conductors but the determination that this " withstand higher mechanical stresses " compared to lines and are suitable for free laying in earth (see also underground cables ), or may be installed as a submarine or underwater, and regardless of whether it is single-core or multi-core power conductors.

• When air cable, a standard in the cable telecommunications concept is a self-supporting cable design with sufficient support elements provided for the suspension on poles and similar devices without the assistance of other supporting wires or conductors.

• The similar to the aerial cables constructed YMT lines for use as a self-supporting cable in overhead line networks for energy supply and for house connections in rural areas are known as " Insulated power cables, PVC sheathed cable with suspension rope " and not the cables attributed (whether or not suitable for the free installation in earth).

• In the data, network, signal and audio technology and related services, the combination of several, mutually insulated conductors (wires ) is considered to be a firmly connected unit and cable in general. The individual wires are usually electrical conductors, but can be, for example, optical conductors.

• A special form represent overhead lines, where the electrical conductor has no solid insulation and the ambient air is used as an insulator. The cable -like strands of wire are not associated with the term cable.

Construction

The cable design must meet several requirements:

• Cost-effective production
• The stresses during installation ( tensile strength, bending radius, etc.)
• Environmental and operating conditions ( corrosion, temperature, traffic loads, etc. )
• The investment purpose ( energy or information transfer ie number of wires, wire size, etc.)

Number of Conductors

The number of current-carrying wires or stranded wires (also called leads ) in the cable is the number of cores. In multi-core cables is always every single vein of its own insulator, the conductor insulation, covered, while an outer sheath, the cable jacket, all the veins surrounding:

For two-wire cables for DC are the colors of the wire insulation often red for positive ( ) and black for negative (-), with AC voltage usually brown and blue, even if at pluggable power lines blue is not always the neutral conductor.

In power cables a green - yellow earth wire is carried for protection class I. This leads to ground potential and serves to prevent an error occurs dangerous touch voltages to the conductive housing or controls, in that they are discharged to earth. In addition, a black or brown the outer conductor and a neutral blue. When connecting cables, the colors are brown and black also common, although the assignment to neutral and phase conductors is not given.

For three-phase, two black and one brown, according to new standard, a brown, a black and a gray outer conductors are used to the old standard. The neutral conductor can be omitted if desired with symmetrical load or when using a PEN conductor. In this case, one of the outer conductor is often blue, provided that the plant was built before 2004.

In older buildings, one occasionally finds yet no longer permitted for new installations Wire colors according to the old standard (existing installations are in Germany under grandfathering ). According to the old German standard was to 1965: Black to the outer conductor, Gray was a neutral conductor or PEN (formerly referred to as zero -wire) be, Red was the protective earth ( PE), but could also be a switched outer conductor. Blue was in a three -wire AC power, an outer conductor be (L1: Black; L2: Red; L3: Blue; PEN: gray). In installations and industrial installations with line voltage, the wire colors yellow and green may only be used when there is no likelihood of confusion with the protective conductor (green- yellow). Red insulated wires are allowed only for control signals which are electrically isolated from the mains.

High voltage cables are often single core. However, there are also two-pole high-voltage cable for dc voltage. Three-core high-voltage cable for three-phase alternating current are also referred to as H cable. Sometimes even two-pole cable operated single-pole, where they are connected in parallel at their ends.

Cable for computer, signal transmission and communication equipment have cores depending on the application two to several thousand. In addition, according to the type of Adernverseilung distinguished (for example, stranded layers, twisted pair, star quad ). Signal cable wires are often in pairs or as a whole is surrounded by a shield.

Cables for low and high frequency signals are often coaxial cable.

Fiber-optic cables are made of a glass or plastic fiber and a relatively thick coat, mechanical protection and (especially for power applications of laser material processing ) to limit the effect of the bending radius.

Material of the wires

The most common copper is due to its excellent electrical conductivity used, followed by the light metal aluminum. Although aluminum has only about 2/3 of the electrical conductivity of copper. Therefore, with the same length and the same resistance requires a line of aluminum about 1.5 -fold larger cross section than a copper cable. However, the specific gravity of aluminum only about 1/3 of copper. Thus, in all applications where the space required for the thicker aluminum head no, but the weight plays an important role, aluminum to copper represents the better choice This is typical for overhead lines, where the conductors are made up on a steel core, aluminum.

Although silver has among the metals on the highest electrical conductivity, but is used for cost reasons only in special cases, such as in the field of high frequency technology, as a thin coating on a copper conductor. In special cases, superconductors are used, which have to be cooled below its critical temperature by the coolant is pumped through separate channels in the cable.

In communication networks, in addition to copper wires, optical fiber ( fiber optic cable, fiber optic cable ) may be used.

Identification of multi-core cables

There are several ways to characterize the veins. Flexible control cables with cross-sections from 0.75 mm2 often wear numbers. Thinner control cables and communication cables are identified by colors. In case of multicore cables is possible, a multi-color coding longitudinally or transversely striped on the respective wire to apply, with a striated coding also can vary in distance to denote different veins.

The following table lists the core identification for telecommunication cables according to DIN 47100 is shown with color repetition from 45 wires. Brevity, the color abbreviations are used in accordance with IEC 60757.

Material of conductor insulation

The wire insulation should have and must also overvoltage withstand the highest possible electrical resistivity. Often, they must also have a very low dielectric loss factor.

In the past often used for this paper is to reduce the moisture sensitivity and increase the dielectric strength, soaked to the paper with oil or wax. Oil-paper cable (also called ground wire ) are superior to PVC insulated cables in terms of their durability and dielectric strength still in use today and in the high and medium voltage range. However, the installation costs are extremely high, so they are replaced by plastic cable with an insulation of cross-linked polyethylene (XLPE ).

A common insulation materials of today's energy and signal cable is polyethylene (PE). One way to increase the operating temperature of PVC insulated cable, is the electron beam crosslinking. However, PVC has a high dielectric loss factor, and therefore it is not suitable as insulation for signal cables, in particular at high frequencies and large lengths of times. High signal cables, high-frequency cable and telephone lines are therefore often isolated with polyethylene (PE).

Cable for extremely high demands with PTFE ( Teflon) insulated (eg engine area in airplanes ). For flexible, thermally and mechanically highly stressed cable rubber is used as insulation. Silicone rubber is used at high temperatures and high voltages.

The veins consist of cables in flexible applications and in the automotive and engineering from stranded wire. With particularly high mechanical stress (hand tools, power chains, event and stage equipment ) called superfine strands and a special stranding be applied.

Sheath material

The cable jacket protects the cable against external influences and optionally containing a shield. Lead has long been a widely used material for wrapping paper-insulated cable. It is still used in bleigemantelten cables (eg NYKY -J for low voltage or N2XS (F) K2Y in medium voltage ) in the refining industry to protect the cables from damage due to aromatics, and hydrocarbons. Some said they were now used cable with an intermediate casing made ​​of polyamide or nylon. Mostly, these cables are again coated with the flame-retardant PVC to obtain a flame-retardant effect. ( Eg types 2XS (L ) 2Y4YY for medium voltage or 2X (L ) 2Y4YY for low voltage ).

Today, in addition to PVC are also plastics such as polyurethane or polyethylene used. Polyethylene is very cost effective, but will burn. PVC creates toxic gases such as hydrogen chloride and dioxins to fire. Therefore, in modern buildings come with large gatherings of people, such as in railway stations, airports, museums, conference halls and department stores, halogen- free, flame retardant cables and wires used. For flexible, heavy-duty rubber cable is used as a cloak. For signal transmission ( network cables for computer, control and audio cable ) the cable sheaths are often provided with a shielding made of metal foil or copper mesh to improve the electromagnetic compatibility of the cable.

The leading of frequency to the motors power lines must often be shielded to prevent noise radiation (see Electromagnetic Compatibility).

Underground and submarine and overhead lines with reinforcements ( steel wire mesh, steel plate) is provided as a protection and to increase their mechanical stability.

In order to detect damage to the casing at an early stage, multi-core cable to be filled with compressed air in the telecommunications and cable internal pressure is monitored automatically. Wherein power cables, an insulating protective gas is used instead (for example sulfur hexafluoride ) here.

Fiber optic cable for high power lasers are equipped with a fiber breakage monitoring, which monitors the conductivity of an entrained wire or a metal coating of the fiber.

For most applications cables are manufactured according to international standards, in many cases also define the keys for specific classes cable. See Harmonised type code of lines.

Stress conditions

Often the focus is on the creation of the cable (cable trays, pipes, power poles, cable trench, pipe chase, etc.). The laying of the cable itself is then to assemble these preparations moderate the smaller share.

The stress conditions of a cable essentially determine its construction, such as:

• Laying on the seabed submarine cables: strong reinforcement, tensile strength, longitudinal and transverse watertight
• Undergrounding ( underground cable ): secure shell, possibly reinforcing, possibly longitudinal and transverse watertight
• Aboveground outdoors: ultraviolet - stable sheath tensile strength,
• For movable equipment: fine or superfine wires, possibly rubber insulation eg Ölflex
• Mechanical stress by edges: Fabric, paint fabric, glass fiber fabric paint
• In fire-prone areas: halogen-free, flame-retardant insulation
• Influence of hydrocarbons: oil resistant materials
• Strong magnetic or electric interference or noise sensitivity: twisted pairs, single or double shield
• High temperatures or heating: rubber, silicone rubber, PTFE

The temperature resistance of cables is given in thermal classes (according to IEC 60085 ):

Purpose

Power cable

The permissible for a cable amperage depends on the following criteria:

• Temperature resistance of the insulation
• Cross-sectional area of the conductor
• Number of Conductors
• Ambient temperature
• Laying
• Accumulation of lines with the same cable path
• Operating voltage

Relevant information can be found for example in EN 60204-1:2007-06 "Electrical equipment of machines - General requirements ."

High-frequency, signal and control cables

With RF and signal cables, the impedance and the wave impedance and the dielectric quality and the dielectric loss factor of the insulation material plays a role.

In NF- cables, in addition to the effective resistance R '( Ohm / km ), the capacitance C' ( microfarads / km ) is essential. The cable capacity of control cables has a value of about 0.3 uF / km.

For high frequency and broadband signal transmission are most commonly used coaxial cable ( also for high transmission services). This basically have no immediate outward electric and magnetic field when the shell is closed and head is the soul in the middle. Coaxial cable for high -frequency use therefore have a dielectric which the inner conductor is supported with minimum optimal density. The required for low loss low density is often achieved by air units or foam. Outside is often a double shielding, consisting of mesh and metal foil applied. Such coaxial cables are very resistant to interference. They tend to have a characteristic impedance of Z = 50 ... 75 ohms.

It used to be used for aerial lines also called ribbon cables (Z = 240 ohms). They consist of two symmetrically arranged, with a Isolierstoffsteg wires connected. These cables are sensitive to interference due to the penetrating external fields, but have a lower attenuation of a coaxial cable when they are moved to a distance from parts of the building.

When signal lines or control lines are often multi-core, using shielded or unshielded cables with cross-sections from 0.14 to 0.5 mm ², which, if the length of the cable ( eg for telephone receivers, keyboards, headphones, etc.. ) Is variable, even than absorbed. " Spiral cable " can be performed.

For the transmission of high data rates, for example, of USB cable, so-called twisted-pair cables are used: One or more pairs are each twisted together and possibly also performed in separate shields.

Flat ribbon cable ( " cable harness " ) consist of a plurality of parallel adjacent cores, and are used particularly in computers and electronic devices as signal lines. They can be cost-effectively and reliably connected with IDC technology.

There are also folded in round Abschirmmänteln led ribbon cable to also use the IDC can.

Examples

• Telephone Cables

• Ribbon cable

• Coaxial cable

• Twisted -pair cable

Safety-relevant installations

In safety-related systems, such as emergency lighting systems, fire alarm systems or alarm systems require the relevant regulations in certain areas cables with functional integrity. Under alarm systems are here no alarm systems in terms of intrusion detection technology meant for such systems no integrity is usually necessary. Rather, it is to equipment acc. DIN VDE 0828, DIN VDE 0833-4, warn the people present by acoustic signaling of dangers and have them building evacuation.

In Germany, this state of affairs is 4102 part 12 and the federal state -specific implementation of the " pattern - line systems Directive" MLAR regulated in DIN. This means that the cabling (mounting hardware and cables ) must remain functional to fire for a specified time. During this time, neither the insulation resistance must be so small that there is a current flow between the conductors, nor may increase the resistance of the conductor, the current flow would be impeded. In other words, neither short nor interruption may occur. These properties are achieved by a special structure of the cable as well as specific materials for the insulation. The lines can be seen from the outside by their orange coat and by a characteristic repeated imprint. Common times for the required integrity are 30 minutes, 60 minutes or 90 minutes ( E30, E60, E90). Advised these lines after expiry of the period on fire, they have also a higher fire load than normal lines as NYM or JY ( St) Y on.

In order to achieve effective prevention function, next to the line and the wiring system and the environment is considered. The various forms of wiring systems ( cable tray, steel conduit, single attachment ) have in common is that they have to withstand a fire also for the corresponding period.

Together with the guidance they give a so-called " certified management system ." According to tested combinations are designated by the manufacturer in test certificates. The installation environment can be designed so that the cables and lines during exposure to fire destroyed not affected by bursting or falling parts or.