Cable: Wikis

  
  
  

Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.

Did you know ...


More interesting facts on Cable

Include this on your site/blog:

Encyclopedia

From Wikipedia, the free encyclopedia

6 inch (15 cm) outside diameter, oil-cooled cables, traversing the Grand Coulee Dam throughout. An example of a heavy cable for power transmission.
Fire test in Sweden, showing rapid fire spread through burning of cable jackets. Of great importance for cables used in installations.
500MCM 1C Power Cable Marking.

A cable is two or more wires running side by side and bonded, twisted or braided together to form a single assembly. In mechanics cables, otherwise known as wire ropes, are used for lifting, hauling and towing or conveying force through tension. In electrical engineering cables used to carry electric currents. An optical cable contains one or more optical fibers in a protective jacket that supports the fibers.

Electric cables discussed here are mainly meant for installation in buildings and industrial sites. For power transmission at distances greater than a few kilometres see high voltage cable, power cables and HVDC.

Contents

History

Ropes made of multiple strands of natural fibers such as hemp, sisal, manila, and cotton have been used for millennia for hoisting and hauling. By the 19th century, deepening of mines and construction of large ships increased demand for stronger cables. Invention of improved steelmaking techniques made high quality steel available at lower cost, and so wire ropes became common in mining and other industrial applications. By the middle of the 19th century, manufacture of large submarine telegraph cables was done using machiners similar to that used for manufacture of mechanical cables.

In the 19th century and early 20th century, electrical cable was often insulated using cloth, rubber and paper. Plastic materials are generally used today, except for high reliability power cables.

Electrical cables

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 often tin but sometimes gold, silver or some other material. Tin, gold, and silver are much less prone to oxidation than copper, which may lengthen wire life, and makes soldering easier. Tight lays during stranding makes the cable extensible (CBA - as in telephone handset cords).

Cables can be securely fastened and organized, such as by using cable trees with the aid of cable ties or cable lacing. Continuous-flex or flexible cables used in moving applications within cable carriers can be secured using strain relief devices or cable ties.

At high frequencies, current tends to run along the surface of the conductor and avoid the core. This is known as the skin effect. It may change the relative desirability of solid versus stranded wires.

Cables and electromagnetic fields

Coaxial cable.
Twisted pair.

Any current-carrying conductor, including a cable, radiates an electromagnetic 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 of noise which may mask the desired signal being carried by the cable, or, if the cable is carrying power 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 are shielding, coaxial geometry, and twisted-pair geometry.

Shielding makes use of the electrical principle of the Faraday 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 external electric fields, particularly if the shield is connected to a point of constant voltage, such as ground. Simple shielding of this type is not greatly effective against low-frequency magnetic fields, however - such as magnetic "hum" from a nearby power transformer.

Coaxial design helps to further reduce low-frequency magnetic transmission and pickup. In this design the foil or mesh shield is perfectly tubular - i.e. with a circular cross section - and the inner conductor (there can only be one) is situated 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.

The twisted pair is a simple expedient where two wires of a cable, rather than running parallel to each other, are twisted around each other, forming a pair of intertwined helices. This can be achieved by putting one end of the pair in a hand drill and turning while maintaining moderate tension on the line. Field cancellation between successive twists of the pair considerably reduces electromagnetic pickup and transmission.

Power-supply cables feeding sensitive electronic devices are sometimes fitted with a series-wired inductor called a choke which blocks high frequencies that may have been picked up by the cable, preventing them from passing into the device.

Fire protection

In building construction, electrical cable jacket material is a potential source of fuel for fires. To limit the spread of fire along cable jacketing, one may use cable coating materials or one may use cables with jacketing that is inherently fire retardant. The plastic covering on some metal clad cables may be stripped off at installation to reduce the fuel source for accidental fires. In Europe in particular, it is often customary to place inorganic wraps and boxes around cables in order to safeguard the adjacent areas from the potential fire threat associated with unprotected cable jacketing.

To provide fire protection to a cable, there are two methods:

A) Insulation material is deliberately added up with fire retardant materials

B) The copper conductor itself is covered with mineral insulation (MICC cables)

Electrical cable types

Basic cable types are as follows:

Shape

Construction

Based on construction and cable properties it can be sorted into the following:

Special

Market Information

  • Integer Research Ltd
  • International Cable Makers Federation
  • Wire Association International

Application

  • Wire rope (wire cable)
  • Audiovisual cable
  • Bicycle cable
  • Communications cable
  • Computer cable
  • Mechanical cable
  • Sensing cable [1]
  • Submersible cable

Further reading

  • R. M. Black, The History of Electric Wires and Cables, Peter Pergrinus, London 1983 ISBN 0 86341 001 4
  • BICC Cables Ltd, "Electric Cables Handbook", WileyBlackwell; London 3rd Edition edition 1997, ISBN 0 63204 075 0

See also

A 250V-16A electrical wire on a reel.

References

External links


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

CABLE (from Late Lat. capulum, a halter, from capere, to take hold of), a large rope or chain, used generally with ships, but often employed for other purposes; the term "cable" is also used by analogy in minor varieties of similar engineering or other attachments, and in the case of "electric cables" for the submarine wires (see Telegraph) by which telegraphic messages are transmitted.' The cable by which a ship rides at her anchor is now made of iron; prior to 1811 only hempen cables were supplied to ships of the British navy, a first-rate's complement on the East Indian station being eleven; the largest was 25 in. (equal to 21 in. iron cable) and weighed 6 tons. In 1811, iron cables were supplied to stationary ships; their superiority over hempen ones was manifest, as they were less liable to foul or to be cut by rocks, or to be injured by enemy's shot. Iron cables are also handier and cleaner, an offensive odour being exhaled from dirty hempen cables, when unbent and stowed inboard. The first patent for iron cables was by Phillip White in 1634; twisted links were suggested in 1813 by Captain Brown (who afterwards, in conjunction with Brown, Lenox & Co., planned the Brighton chain pier in 182 3); and studs were introduced in 1816. Hempen cables are not now supplied to ships, having been superseded by steel wire hawsers. The length of a hempen cable is 101 fathoms, and a cable's length, as a standard of measurement, usually placed on charts, is assumed to be 100 fathoms or 600 ft. The sizes, number and lengths of cables supplied to ships of the British navy are given in the official publication, the Ship's Establishment; cables for merchant ships are regulated by Lloyds, and are tested according to the Anchors and Chain Cables Act 1899.

In manufacturing chain cables, the bars are cut to the required length of link, at an angle for forming the welds and, after heating, are bent by machinery to the form of a link and welded by smiths, each link being inserted in the previous one before welding. Cables of less than 14 in. are welded at the crown, there not being sufficient room for a side weld; experience has shown that the latter method is preferable and it is employed in making larger sized cables. In 1898 steel studs were introduced instead of cast iron ones, the latter having a tendency to work loose, but the practice is not universal. After testing, the licensed tester must place on every five fathoms of cable a distinctive mark which also indicates the testing establishments; the stamp or die employed must be approved by the Board of Trade. The iron used in the construction, also the testing, of mooring chains and cables for the London Trinity House Corporation are subject to more stringent regulations.

Cables for the British navy and mercantile marine are supplied in 12-1/2 fathom and 15 fathom lengths respectively, connected together by "joining shackles," D (fig.1). Each length is (caption FIG. I. - Stud-link Chain.) "marked" by pieces of iron wire being twisted round the studs of the links; the wire is placed on the first studs on each side of the first shackle, on the second studs on each side of the second shackle, and so on; thus the number of lengths of cable out is clearly indicated. For instance, if the wire is on the sixth

(footnote)1 The word "cable" is a various reading for "camel" in the Biblical phrase, "it is easier for a camel to go through the eye of a needle" of Matt. xix. 24, Mark x. 25, and Luke xviii. 25, mentioned as early as Cyril of Alexandria (5th cent.); and it was adopted by Sir John Cheke and other 16th century and later English writers. The reading (Greed) for (Greek) is found in several late cursive MSS. Cheyne, in the Ency. Biblica, ascribes it to a nonSemitic scribe, and regards (Greek) as correct. (See under Camel.) 

studs on each side of the shackle, it indicates that six lengths or 75 fathoms of cable are out. In joining the lengths together, the round end of the shackle is placed towards the anchor. The end links of each length (C.C.) are made without studs, in order to take the shackle; but as studs increase the strength of a link, in a studless or open link the iron is of greater diameter. The next links (B.B.) have to be enlarged, in order to take the increased size of the links C.C. In the joining shackle (D), the pin is oval, its greater diameter being in the direction of the strain. The pin of a shackle, which attaches the cable to the anchor (called an "anchor shackle," to distinguish it from a joining shackle) projects and is secured by a forelock; but since any projection in a joining shackle would be liable to be injured when the cable is running out or when passing around a capstan, the pins are made as shown at D, and are secured by a small pin d. This small pin is kept from coming out by being made a little short, and lead pellets are driven in at either end to fill up the holes in the shackle, which are made with a groove, so that as the pellets are driven in they expand or dovetail, keeping the small pin in its place.' The cables are stowed in chain lockers, the inboard ends being secured by a "slip" (in the mercantile marine the cable is often shackled or lashed to the kelson); the slip prevents the cable's inner end from passing overboard, and also enables the cable to be "slipped," or let go, in case of necessity. In the British navy, swivel pieces are fitted in the first and last lengths of cable, to avoid and, if required, to take out turns in a cable, caused by a ship swinging round when at anchor. With a ship moored with two anchors, the cables are secured to a mooring swivel (fig. 2), which prevents a "foul hawse," i.e. the cables being entwined round each other. When mooring, unmooring, and as may be necessary, cables are temporarily secured by "slips" (caption) FIG. 2. - Mooring Swivel.

shackled to eye or ring bolts in the deck (see ANCHOR). The cable is hove up by either a capstan or windlass (see CAPSTAN) actuated by steam, electricity or manual power. Ships in the British navy usually ride by the compressor, the cable holder being used for checking the cable running out. When a ship has been given the necessary cable, the cable holder is eased up and the compressor "bowsed to"; in a heavy sea, a turn, or if necessary two turns, are taken round the "bitts," a strong iron structure placed between the hawse and navel ("deck") pipes. A single turn of cable is often taken round the bitts when anchoring in deep water. Small vessels of the mercantile marine ride by turns around the windlass; in larger or more modern vessels fitted with a steam windlass, the friction brakes take the strain, aided when required by the bitts, compressor or controller in bad weather. (J. W. D.)


<< George Washington Cable

Cable moulding >>


Simple English

A cable is made of many wires or optical fibers twisted together to make a larger wire. Each of these wires may be covered. Some cables contain both electrical wires and optical fibers. There are many kinds of cables, including coaxial cables which block out radio or magnetic interference from other wires or cables, by having one wire inside an insulated tube surrounded by a second wire, acting as a metal tube along the same axis.

Electrical cables are usually made of copper, because electricity moves well through copper, but it is not as expensive as silver or other better conductors. Cables are sometimes made of aluminium because it is cheaper than copper.

The word "cable" is also used as ellipsis, or a short form, for "cable TV". A cable car is a trolley which uses a cable wire above the track.

Other pages








Got something to say? Make a comment.
Your name
Your email address
Message