Electrical cables are used to connect two or more devices, enabling the transfer ofelectrical signals,power, or both from one device to the other. Physically, an electrical cable is an assembly consisting of one or more conductors with their own insulations and optional screens, individual coverings, assembly protection and protective covering.
One or more electrical cables and their correspondingconnectors may be formed into a cable assembly,[1] which is not necessarily suitable for connecting two devices but can be a partial product (e.g. to be soldered onto aprinted circuit board with a connector mounted to the housing). Cable assemblies can also take the form of acable tree orcable harness, used to connect many terminals together.
6 inch (15 cm) outside diameter, oil-cooled cables, traversing theGrand Coulee Dam throughout. An example of a heavy cable for power transmission.Fire test inSweden, showingfire rapidly spreading through the burning of cable insulation, a phenomenon of great importance for cables used in some installations.500,000circular mil (254 mm2) single-conductor power cable
Electrical cables are used to connect two or more devices, enabling the transfer of electrical signals or power from one device to the other. Long-distance communication takes place overundersea communication cables.Power cables are used for bulk transmission of alternating and direct current power, especially usinghigh-voltage cable. Electrical cables are extensively used inbuilding wiring for lighting, power and control circuits permanently installed in buildings. Since all the circuit conductors required can be installed in a cable at one time, installation labor is saved compared to certain other wiring methods.
Physically, an electrical cable is an assembly consisting of one or more conductors with their own insulations and optional screens, individual coverings, assembly protection and protective coverings. Electrical cables may be made more flexible by stranding the wires. In this process, smaller individual wires are twisted or braided together to produce larger wires that are more flexible than solid wires of similar size. Bunching small wires before concentric stranding adds the most flexibility.Copper wires in a cable may be bare, or they may be plated with a thin layer of another metal, most oftentin, but sometimesgold,silver or another material. Tin, gold, and silver are much less prone tooxidation than copper, which may lengthen wire life, and makessoldering easier.Tinning is also used to provide lubrication between strands. Tinning was used to help removal of rubber insulation. Tight lays during stranding makes the cable extensible (CBA – as in telephone handset cords).[further explanation needed]
In the 19th century and early 20th century, electrical cable was ofteninsulated using cloth,rubber or paper. Plastic materials are generally used today, except for high-reliability[clarification needed] power cables. The firstthermoplastic used wasgutta-percha (a naturallatex) which was found useful for underwater cables in the 19th century. The first, and still very common, man-made plastic used for cable insulation waspolyethylene. This was invented in 1930, but not available outside military use until afterWorld War 2 during which a telegraph cable using it was laid across the English Channel to support troops followingD-Day.[2]
Anycurrent-carrying conductor, including a cable, radiates anelectromagnetic field. Likewise, any conductor or cable will pick up energy from any existing electromagnetic field around it. These effects are often undesirable, in the first case amounting to unwanted transmission of energy which may adversely affect nearby equipment or other parts of the same piece of equipment; and in the second case, unwanted pickup ofnoise which may mask the desired signal being carried by the cable, or, if the cable is carryingpower supply or control voltages, pollute them to such an extent as to cause equipment malfunction.
The first solution to these problems is to keep cable lengths in buildings short since pick up and transmission are essentially proportional to the length of the cable. The second solution is to route cables away from trouble. Beyond this, there are particular cable designs that minimize electromagnetic pickup and transmission. Three of the principal design techniques areshielding,coaxial geometry, andtwisted-pair geometry.
Shielding makes use of the electrical principle of theFaraday cage. The cable is encased for its entire length in foil or wire mesh. All wires running inside this shielding layer will be to a large extent decoupled from externalelectrical fields, particularly if the shield is connected to a point of constant voltage, such asearth or ground. Simple shielding of this type is not greatly effective against low-frequencymagnetic fields, however - such as magnetic "hum" from a nearby powertransformer. A grounded shield on cables operating at 2.5 kV or more gathers leakage current and capacitive current, protecting people from electric shock and equalizing stress on the cable insulation.
Coaxial design helps to further reduce low-frequency magnetic transmission and pickup. In this design the foil or mesh shield has a circular cross section and the inner conductor is exactly at its center. This causes the voltages induced by a magnetic field between the shield and the core conductor to consist of two nearly equal magnitudes which cancel each other.
A twisted pair has two wires of a cable twisted around each other. This can be demonstrated by putting one end of a pair of wires in a hand drill and turning while maintaining moderate tension on the line. Where the interfering signal has a wavelength that is long compared to the pitch of the twisted pair, alternate lengths of wires develop opposing voltages, tending to cancel the effect of the interference.
Electrical cable jacket material is usually constructed of flexible plastic which will burn. The fire hazard of grouped cables can be significant.[3] Cables jacketing materials can be formulated to prevent fire spread[4](seeMineral-insulated copper-clad cable). Alternately, fire spread amongst combustible cables can be prevented by the application of fire retardant coatings directly on the cable exterior,[5] or the fire threat can be isolated by the installation of boxes constructed of noncombustible materials around the bulk cable installation.
Twin-lead – This type of cable is a flat two-wire line. It is commonly called a 300 Ω line because the line has an impedance of 300 Ω. It is often used as atransmission line between an antenna and a receiver (e.g., TV and radio). These cables are stranded to lower skin effects.
Twisted pair – Consists of two interwound insulated wires. It resembles a paired cable, except that the paired wires are twisted
CENELEC HD 361 is a ratified standard published by CENELEC, which relates to wire and cable marking type, whose goal is to harmonize cables.Deutsches Institut für Normung (DIN, VDE) has released a similar standard (DIN VDE 0292).
^Ash, Stewart, "The development of submarine cables", ch. 1 in, Burnett, Douglas R.; Beckman, Robert; Davenport, Tara M.,Submarine Cables: The Handbook of Law and Policy, Martinus Nijhoff Publishers, 2014ISBN9789004260320.
