An electrical insulator is a material whose internal electric charges do not flow freely. This contrasts with other materials and conductors, which conduct electric current more easily; the property that distinguishes an insulator is its resistivity. A perfect insulator does not exist, because insulators contain small numbers of mobile charges which can carry current. In addition, all insulators become electrically conductive when a sufficiently large voltage is applied that the electric field tears electrons away from the atoms; this is known as the breakdown voltage of an insulator. Some materials such as glass and Teflon, which have high resistivity, are good electrical insulators. A much larger class of materials though they may have lower bulk resistivity, are still good enough to prevent significant current from flowing at used voltages, thus are employed as insulation for electrical wiring and cables. Examples include rubber-like polymers and most plastics which can be thermoset or thermoplastic in nature.
Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves. An insulating material used in bulk to wrap electrical cables or other equipment is called insulation; the term insulator is used more to refer to insulating supports used to attach electric power distribution or transmission lines to utility poles and transmission towers. They support the weight of the suspended wires without allowing the current to flow through the tower to ground. Electrical insulation is the absence of electrical conduction. Electronic band theory says that a charge flows if states are available into which electrons can be excited; this allows electrons to gain energy and thereby move through a conductor such as a metal. If no such states are available, the material is an insulator. Most insulators have a large band gap; this occurs because the "valence" band containing the highest energy electrons is full, a large energy gap separates this band from the next band above it.
There is always some voltage. Once this voltage is exceeded the material ceases being an insulator, charge begins to pass through it. However, it is accompanied by physical or chemical changes that permanently degrade the material's insulating properties. Materials that lack electron conduction are insulators. For example, if a liquid or gas contains ions the ions can be made to flow as an electric current, the material is a conductor. Electrolytes and plasmas contain ions and act as conductors whether or not electron flow is involved; when subjected to a high enough voltage, insulators suffer from the phenomenon of electrical breakdown. When the electric field applied across an insulating substance exceeds in any location the threshold breakdown field for that substance, the insulator becomes a conductor, causing a large increase in current, an electric arc through the substance. Electrical breakdown occurs when the electric field in the material is strong enough to accelerate free charge carriers to a high enough velocity to knock electrons from atoms when they strike them, ionizing the atoms.
These freed electrons and ions are in turn accelerated and strike other atoms, creating more charge carriers, in a chain reaction. The insulator becomes filled with mobile charge carriers, its resistance drops to a low level. In a solid, the breakdown voltage is proportional to the band gap energy; when corona discharge occurs, the air in a region around a high-voltage conductor can break down and ionise without a catastrophic increase in current. However, if the region of air breakdown extends to another conductor at a different voltage it creates a conductive path between them, a large current flows through the air, creating an electric arc. A vacuum can suffer a sort of breakdown, but in this case the breakdown or vacuum arc involves charges ejected from the surface of metal electrodes rather than produced by the vacuum itself. In addition, all insulators become conductors at high temperatures as the thermal energy of the valence electrons is sufficient to put them in the conduction band.
In certain capacitors, shorts between electrodes formed due to dielectric breakdown can disappear when the applied electric field is reduced. A flexible coating of an insulator is applied to electric wire and cable, this is called insulated wire. Wires sometimes don't use an insulating coating, since a solid coating may be impractical. However, wires that touch each other produce cross connections, short circuits, fire hazards. In coaxial cable the center conductor must be supported in the middle of the hollow shield to prevent EM wave reflections. Wires that expose voltages higher than 60 V can cause human shock and electrocution hazards. Insulating coatings help to prevent all of these problems; some wires have a mechanical covering with no voltage rating—e.g.: service-drop, doorbell, thermostat wire. An insulated wire or cable has a maximum conductor temperature rating, it may not have an ampacity rating. In electronic systems, printed circuit boards are made from epoxy plastic and fibreglass.
Copper has been used in electrical wiring since the invention of the electromagnet and the telegraph in the 1820s. The invention of the telephone in 1876 created further demand for copper wire as an electrical conductor. Copper is the electrical conductor in many categories of electrical wiring. Copper wire is used in power generation, power transmission, power distribution, telecommunications, electronics circuitry, countless types of electrical equipment. Copper and its alloys are used to make electrical contacts. Electrical wiring in buildings is the most important market for the copper industry. Half of all copper mined is used to manufacture electrical wire and cable conductors. Electrical conductivity is a measure of; this is an essential property in electrical wiring systems. Copper has the highest electrical conductivity rating of all non-precious metals: the electrical resistivity of copper = 16.78 nΩ•m at 20 °C. Specially-pure Oxygen-Free Electronic copper is about 1% more conductive; the theory of metals in their solid state helps to explain the unusually high electrical conductivity of copper.
In a copper atom, the outermost 4s energy zone, or conduction band, is only half filled, so many electrons are able to carry electric current. When an electric field is applied to a copper wire, the conduction of electrons accelerates towards the electropositive end, thereby creating a current; these electrons encounter resistance to their passage by colliding with impurity atoms, lattice ions, imperfections. The average distance travelled between collisions, defined as the "mean free path", is inversely proportional to the resistivity of the metal. What is unique about copper is its long mean free path; this mean free path increases as copper is chilled. Because of its superior conductivity, annealed copper became the international standard to which all other electrical conductors are compared. In 1913, the International Electrotechnical Commission defined the conductivity of commercially pure copper in its International Annealed Copper Standard, as 100% IACS = 58.0 MS/m at 20 °C, decreasing by 0.393%/°C.
Because commercial purity has improved over the last century, copper conductors used in building wire slightly exceed the 100% IACS standard. The main grade of copper used for electrical applications is electrolytic-tough pitch copper; this copper is at least 99.90% pure and has an electrical conductivity of at least 101% IACS. ETP copper contains a small percentage of oxygen. If high conductivity copper needs to be welded or brazed or used in a reducing atmosphere oxygen-free copper may be used. Several electrically conductive metals are less dense than copper, but require larger cross sections to carry the same current and may not be usable when limited space is a major requirement. Aluminium has 61% of the conductivity of copper; the cross sectional area of an aluminium conductor must be 56% larger than copper for the same current carrying capability. The need to increase the thickness of aluminium wire restricts its use in several applications, such as in small motors and automobiles. In some applications such as aerial electric power transmission cables, copper is used.
Silver, a precious metal, is the only metal with a higher electrical conductivity than copper. The electrical conductivity of silver is 106% of that of annealed copper on the IACS scale, the electrical resistivity of silver = 15.9 nΩ•m at 20 °C. The high cost of silver combined with its low tensile strength limits its use to special applications, such as joint plating and sliding contact surfaces, plating for the conductors in high-quality coaxial cables used at frequencies above 30 MHz Tensile strength measures the force required to pull an object such as rope, wire, or a structural beam to the point where it breaks; the tensile strength of a material is the maximum amount of tensile stress it can take before breaking. Copper’s higher tensile strength compared to aluminium is another reason why copper is used extensively in the building industry. Copper’s high strength resists stretching, neck-down, creep and breaks, thereby prevents failures and service interruptions. Copper is much heavier than aluminum for conductors of equal current carrying capacity, so the high tensile strength is offset by its increased weight.
Ductility is a material's ability to deform under tensile stress. This is characterized by the material's ability to be stretched into a wire. Ductility is important in metalworking because materials that crack or break under stress cannot be hammered, rolled, or drawn. Copper has a higher ductility than alternate metal conductors with the exception of silver; because of copper’s high ductility, it is easy to draw down to diameters with close tolerances. The stronger a metal is, the less pliable it is; this is not the case with copper. A unique combination of high strength and high ductility makes copper ideal for wiring systems. At junction boxes and at terminations, for example, copper can be bent and pulled without stretching or breaking. Creep is the gradual deformation of a material from constant expansions and contractions under “load, no-load” conditions; this process has adverse effects on electrical systems: terminations can become loose, causing connections to heat up or create dangerous arcing.
Copper has excellent creep characteristics. For other met
A telephone, or phone, is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be heard directly. A telephone converts sound and most efficiently the human voice, into electronic signals that are transmitted via cables and other communication channels to another telephone which reproduces the sound to the receiving user. In 1876, Scottish emigrant Alexander Graham Bell was the first to be granted a United States patent for a device that produced intelligible replication of the human voice; this instrument was further developed by many others. The telephone was the first device in history that enabled people to talk directly with each other across large distances. Telephones became indispensable to businesses and households and are today some of the most used small appliances; the essential elements of a telephone are a microphone to speak into and an earphone which reproduces the voice in a distant location. In addition, most telephones contain a ringer to announce an incoming telephone call, a dial or keypad to enter a telephone number when initiating a call to another telephone.
The receiver and transmitter are built into a handset, held up to the ear and mouth during conversation. The dial may be located either on a base unit to which the handset is connected; the transmitter converts the sound waves to electrical signals which are sent through a telephone network to the receiving telephone, which converts the signals into audible sound in the receiver or sometimes a loudspeaker. Telephones are duplex devices; the first telephones were directly connected to each other from one customer's office or residence to another customer's location. Being impractical beyond just a few customers, these systems were replaced by manually operated centrally located switchboards; these exchanges were soon connected together forming an automated, worldwide public switched telephone network. For greater mobility, various radio systems were developed for transmission between mobile stations on ships and automobiles in the mid-20th century. Hand-held mobile phones were introduced for personal service starting in 1973.
In decades their analog cellular system evolved into digital networks with greater capability and lower cost. Convergence has given most modern cell phones capabilities far beyond simple voice conversation, they may be able to record spoken messages and receive text messages and display photographs or video, play music or games, surf the Internet, do road navigation or immerse the user in virtual reality. Since 1999, the trend for mobile phones is smartphones that integrate all mobile communication and computing needs. A traditional landline telephone system known as plain old telephone service carries both control and audio signals on the same twisted pair of insulated wires, the telephone line; the control and signaling equipment consists of three components, the ringer, the hookswitch, a dial. The ringer, or beeper, light or other device, alerts the user to incoming calls; the hookswitch signals to the central office that the user has picked up the handset to either answer a call or initiate a call.
A dial, if present, is used by the subscriber to transmit a telephone number to the central office when initiating a call. Until the 1960s dials used exclusively the rotary technology, replaced by dual-tone multi-frequency signaling with pushbutton telephones. A major expense of wire-line telephone service is the outside wire plant. Telephones transmit both the outgoing speech signals on a single pair of wires. A twisted pair line rejects electromagnetic interference and crosstalk better than a single wire or an untwisted pair; the strong outgoing speech signal from the microphone does not overpower the weaker incoming speaker signal with sidetone because a hybrid coil and other components compensate the imbalance. The junction box arrests lightning and adjusts the line's resistance to maximize the signal power for the line length. Telephones have similar adjustments for inside line lengths; the line voltages are negative compared to earth. Negative voltage attracts positive metal ions toward the wires.
The landline telephone contains a switchhook and an alerting device a ringer, that remains connected to the phone line whenever the phone is "on hook", other components which are connected when the phone is "off hook". The off-hook components include a transmitter, a receiver, other circuits for dialing and amplification. A calling party wishing to speak to another party will pick up the telephone's handset, thereby operating a lever which closes the switchhook, which powers the telephone by connecting the transmitter and related audio components to the line; the off-hook circuitry has a low resistance which causes a direct current, which comes down the line from the telephone exchange. The exchange detects this current, attaches a digit receiver circuit to the line, sends a dial tone to indicate readiness. On a modern push-button telephone, the caller presses the number keys to send the telephone number of the called party; the keys control a tone generator circuit. A rotary-dial telephone uses pulse
Plastic is material consisting of any of a wide range of synthetic or semi-synthetic organic compounds that are malleable and so can be molded into solid objects. Plasticity is the general property of all materials which can deform irreversibly without breaking but, in the class of moldable polymers, this occurs to such a degree that their actual name derives from this specific ability. Plastics are organic polymers of high molecular mass and contain other substances, they are synthetic, most derived from petrochemicals, however, an array of variants are made from renewable materials such as polylactic acid from corn or cellulosics from cotton linters. Due to their low cost, ease of manufacture and imperviousness to water, plastics are used in a multitude of products of different scale, including paper clips and spacecraft, they have prevailed over traditional materials, such as wood, stone and bone, metal and ceramic, in some products left to natural materials. In developed economies, about a third of plastic is used in packaging and the same in buildings in applications such as piping, plumbing or vinyl siding.
Other uses include automobiles and toys. In the developing world, the applications of plastic may differ—42% of India's consumption is used in packaging. Plastics have many uses in the medical field as well, with the introduction of polymer implants and other medical devices derived at least from plastic; the field of plastic surgery is not named for use of plastic materials, but rather the meaning of the word plasticity, with regard to the reshaping of flesh. The world's first synthetic plastic was bakelite, invented in New York in 1907 by Leo Baekeland who coined the term'plastics'. Many chemists have contributed to the materials science of plastics, including Nobel laureate Hermann Staudinger, called "the father of polymer chemistry" and Herman Mark, known as "the father of polymer physics"; the success and dominance of plastics starting in the early 20th century led to environmental concerns regarding its slow decomposition rate after being discarded as trash due to its composition of large molecules.
Toward the end of the century, one approach to this problem was met with wide efforts toward recycling. The word plastic derives from the Greek πλαστικός meaning "capable of being shaped or molded" and, in turn, from πλαστός meaning "molded"; the plasticity, or malleability, of the material during manufacture allows it to be cast, pressed, or extruded into a variety of shapes, such as: films, plates, bottles, amongst many others. The common noun plastic should not be confused with the technical adjective plastic; the adjective is applicable to any material which undergoes a plastic deformation, or permanent change of shape, when strained beyond a certain point. For example, aluminum, stamped or forged exhibits plasticity in this sense, but is not plastic in the common sense. By contrast, some plastics will, in their finished forms, break before deforming and therefore are not plastic in the technical sense. Most plastics contain organic polymers; the vast majority of these polymers are formed from chains of carbon atoms,'pure' or with the addition of: oxygen, nitrogen, or sulfur.
The chains comprise many repeat units, formed from monomers. Each polymer chain will have several thousand repeating units; the backbone is the part of the chain, on the "main path", linking together a large number of repeat units. To customize the properties of a plastic, different molecular groups "hang" from this backbone; these pendant units are "hung" on the monomers, before the monomers themselves are linked together to form the polymer chain. It is the structure of these side chains; the molecular structure of the repeating unit can be fine tuned to influence specific properties in the polymer. Plastics are classified by: the chemical structure of the polymer's backbone and side chains. Plastics can be classified by: the chemical process used in their synthesis, such as: condensation and cross-linking. Plastics can be classified by: their various physical properties, such as: hardness, tensile strength, resistance to heat and glass transition temperature, by their chemical properties, such as the organic chemistry of the polymer and its resistance and reaction to various chemical products and processes, such as: organic solvents and ionizing radiation.
In particular, most plastics will melt upon heating to a few hundred degrees celsius. Other classifications are based on qualities that are relevant for product design. Examples of such qualities and classes are: thermoplastics and thermosets, conductive polymers, biodegradable plastics and engineering plastics and other plastics with particular structures, such as elastomers. One important classification of plastics is by the permanence or impermanence of their form, or whether they are: thermoplastics or thermosetting polymers. Thermoplastics are the plastics that, when heated, do not undergo chemical change in their composition and so can be molded again and again. Examples include: polyethylene, polypropylene and polyvinyl chloride. Common thermoplastics range from 20,000 to 500,000 amu, while thermosets are assumed to have infinite molecular weight. Thermosets, or thermosetting polymers, can melt and take shape only once: after they have solidified, they stay solid. In the thermosetting process, a chemical reaction occurs, irreversible.
Sound recording and reproduction
Sound recording and reproduction is an electrical, electronic, or digital inscription and re-creation of sound waves, such as spoken voice, instrumental music, or sound effects. The two main classes of sound recording technology are analog digital recording. Acoustic analog recording is achieved by a microphone diaphragm that senses changes in atmospheric pressure caused by acoustic sound waves and records them as a mechanical representation of the sound waves on a medium such as a phonograph record. In magnetic tape recording, the sound waves vibrate the microphone diaphragm and are converted into a varying electric current, converted to a varying magnetic field by an electromagnet, which makes a representation of the sound as magnetized areas on a plastic tape with a magnetic coating on it. Analog sound reproduction is the reverse process, with a bigger loudspeaker diaphragm causing changes to atmospheric pressure to form acoustic sound waves. Digital recording and reproduction converts the analog sound signal picked up by the microphone to a digital form by the process of sampling.
This lets the audio data be transmitted by a wider variety of media. Digital recording stores audio as a series of binary numbers representing samples of the amplitude of the audio signal at equal time intervals, at a sample rate high enough to convey all sounds capable of being heard. A digital audio signal must be reconverted to analog form during playback before it is amplified and connected to a loudspeaker to produce sound. Prior to the development of sound recording, there were mechanical systems, such as wind-up music boxes and player pianos, for encoding and reproducing instrumental music. Long before sound was first recorded, music was recorded—first by written music notation also by mechanical devices. Automatic music reproduction traces back as far as the 9th century, when the Banū Mūsā brothers invented the earliest known mechanical musical instrument, in this case, a hydropowered organ that played interchangeable cylinders. According to Charles B. Fowler, this "...cylinder with raised pins on the surface remained the basic device to produce and reproduce music mechanically until the second half of the nineteenth century."
The Banū Mūsā brothers invented an automatic flute player, which appears to have been the first programmable machine. Carvings in the Rosslyn Chapel from the 1560s may represent an early attempt to record the Chladni patterns produced by sound in stone representations, although this theory has not been conclusively proved. In the 14th century, a mechanical bell-ringer controlled by a rotating cylinder was introduced in Flanders. Similar designs appeared in barrel organs, musical clocks, barrel pianos, music boxes. A music box is an automatic musical instrument that produces sounds by the use of a set of pins placed on a revolving cylinder or disc so as to pluck the tuned teeth of a steel comb; the fairground organ, developed in 1892, used a system of accordion-folded punched cardboard books. The player piano, first demonstrated in 1876, used a punched paper scroll that could store a long piece of music; the most sophisticated of the piano rolls were hand-played, meaning that the roll represented the actual performance of an individual, not just a transcription of the sheet music.
This technology to record a live performance onto a piano roll was not developed until 1904. Piano rolls were in continuous mass production from 1896 to 2008. A 1908 U. S. Supreme Court copyright case noted that, in 1902 alone, there were between 70,000 and 75,000 player pianos manufactured, between 1,000,000 and 1,500,000 piano rolls produced; the first device that could record actual sounds as they passed through the air was the phonautograph, patented in 1857 by Parisian inventor Édouard-Léon Scott de Martinville. The earliest known recordings of the human voice are phonautograph recordings, called phonautograms, made in 1857, they consist of sheets of paper with sound-wave-modulated white lines created by a vibrating stylus that cut through a coating of soot as the paper was passed under it. An 1860 phonautogram of Au Clair de la Lune, a French folk song, was played back as sound for the first time in 2008 by scanning it and using software to convert the undulating line, which graphically encoded the sound, into a corresponding digital audio file.
On April 30, 1877, French poet, humorous writer and inventor Charles Cros submitted a sealed envelope containing a letter to the Academy of Sciences in Paris explaining his proposed method, called the paleophone. Though no trace of a working paleophone was found, Cros is remembered as the earliest inventor of a sound recording and reproduction machine; the first practical sound recording and reproduction device was the mechanical phonograph cylinder, invented by Thomas Edison in 1877 and patented in 1878. The invention soon spread across the globe and over the next two decades the commercial recording and sale of sound recordings became a growing new international industry, with the most popular titles selling millions of units by the early 1900s; the development of mass-production techniques enabled cylinder recordings to become a major new consumer item in industrial countries and the cylinder was the main consumer format from the late 1880s until around 1910. The next major technical development was the invention of the gramophone record credited to Emile Berliner and patented in 1887, though others had demonstrated simi
A screw is a type of fastener, in some ways similar to a bolt made of metal, characterized by a helical ridge, known as a male thread. Screws are used to fasten materials by digging in and wedging into a material when turned, while the thread cuts grooves in the fastened material that may help pull fastened materials together and prevent pull-out. There are many screws for a variety of materials. A screw is a combination of simple machines—it is in essence an inclined plane wrapped around a central shaft, but the inclined plane comes to a sharp edge around the outside, which acts a wedge as it pushes into the fastened material, the shaft and helix form a wedge in the form of the point; some screw threads are designed to mate with a complementary thread, known as a female thread in the form of a nut, or object that has the internal thread formed into it. Other screw threads are designed to cut a helical groove in a softer material as the screw is inserted; the most common uses of screws are to hold objects together and to position objects.
A screw will have a head on one end that contains a specially formed shape that allows it to be turned, or driven, with a tool. Common tools for driving screws include wrenches; the head is larger than the body of the screw, which keeps the screw from being driven deeper than the length of the screw and to provide a bearing surface. There are exceptions; the cylindrical portion of the screw from the underside of the head to the tip is known as the shank. The distance between each thread is called the "pitch"; the majority of screws are tightened by clockwise rotation, termed a right-hand thread. If the fingers of the right hand are curled around a right-hand thread, it will move in the direction of the thumb when turned in the same direction as the fingers are curled. Screws with left-hand threads are used in exceptional cases, where loads would tend to loosen a right handed fastener, or when non-interchangeability with right-hand fasteners is required. For example, when the screw will be subject to counterclockwise torque, a left-hand-threaded screw would be an appropriate choice.
The left side pedal of a bicycle has a left-hand thread. More screw may mean any helical device, such as a clamp, a micrometer, a ship's propeller, or an Archimedes' screw water pump. There is no universally accepted distinction between a bolt. A simple distinction, true, although not always, is that a bolt passes through a substrate and takes a nut on the other side, whereas a screw takes no nut because it threads directly into the substrate. So, as a general rule, when buying a packet of "screws" nuts would not be expected to be included, but bolts are sold with matching nuts. Part of the confusion over this is due to regional or dialectical differences. Machinery's Handbook describes the distinction as follows: A bolt is an externally threaded fastener designed for insertion through holes in assembled parts, is intended to be tightened or released by torquing a nut. A screw is an externally threaded fastener capable of being inserted into holes in assembled parts, of mating with a preformed internal thread or forming its own thread, of being tightened or released by torquing the head.
An externally threaded fastener, prevented from being turned during assembly and which can be tightened or released only by torquing a nut is a bolt. An externally threaded fastener that has thread form which prohibits assembly with a nut having a straight thread of multiple pitch length is a screw; this distinction is consistent with ASME B18.2.1 and some dictionary definitions for bolt. The issue of what is a screw and what is a bolt is not resolved with Machinery's Handbook distinction, because of confounding terms, the ambiguous nature of some parts of the distinction, usage variations; some of these issues are discussed below: Early wood screws were made by hand, with a series of files and other cutting tools, these can be spotted by noting the irregular spacing and shape of the threads, as well as file marks remaining on the head of the screw and in the area between threads. Many of these screws had a blunt end lacking the sharp tapered point on nearly all modern wood screws. Lathes were used to manufacture wood screws, with the earliest patent being recorded in 1760 in England.
During the 1850s swaging tools were developed to provide a more consistent thread. Screws made with these tools have rounded valleys with rough threads; some wood screws were made with cutting dies as early as the late 1700s. Once screw turning machines were in common use, most commercially available wood screws were produced with this method; these cut wood screws are invariably tapered, when the tapered shank is not obvious, they can b
Category 5 cable
Category 5 cable referred to as Cat 5, is a twisted pair cable for computer networks. Since 2001, the variant in use is the Category 5e specification; the cable standard provides performance of up to 100 MHz and is suitable for most varieties of Ethernet over twisted pair up to 1000BASE-T. Cat 5 is used to carry other signals such as telephony and video; this cable is connected using punch-down blocks and modular connectors. Most Category 5 cables are unshielded, relying on the balanced line twisted pair design and differential signaling for noise rejection; the specification for category 5 cable was defined in ANSI/TIA/EIA-568-A, with clarification in TSB-95. These documents specify performance characteristics and test requirements for frequencies up to 100 MHz; the cable is available in both solid conductor forms. The stranded form is withstands more bending without breaking. Patch cables are stranded. Permanent wiring used in structured cabling is solid-core; the category and type of cable can be identified by the printing on the jacket.
Cable types, connector types and cabling topologies are defined by TIA/EIA-568-B. Nearly always, 8P8C modular connectors are used for connecting category 5 cable; the cable is terminated in either the T568B scheme. The two schemes work well and may be mixed in an installation so long as the same scheme is used on both ends of each cable; the category 5e specification improves upon the category 5 specification by revising and introducing new specifications to further mitigate the amount of crosstalk. The bandwidth and physical construction are the same between the two, most Cat 5 cables meet Cat 5e specifications, though they are not certified as such; the category 5 superseded by the category 5e specification. Category 5 cable is used in structured cabling for computer networks such as Ethernet over twisted pair; the cable standard provides performance of up to 100 MHz and is suitable for 10BASE-T, 100BASE-TX, 1000BASE-T. 10BASE-T and 100BASE-TX Ethernet connections require two wire pairs. 1000BASE-T Ethernet connections require four wire pairs.
Through the use of power over Ethernet, power can be carried over the cable in addition to Ethernet data. Cat 5 is used to carry other signals such as telephony and video. In some cases, multiple signals can be carried on a single cable; the USOC/RJ-61 wiring standard may be used in multi-line telephone connections. Various schemes exist for transporting both digital video over the cable. HDBaseT is one such scheme; the use of balanced lines helps preserve a high signal-to-noise ratio despite interference from both external sources and crosstalk from other pairs. Outer insulation is polyvinyl chloride or low smoke zero halogen. Most Category 5 cables can be bent at any radius exceeding four times the outside diameter of the cable; the maximum length for a cable segment is 100 m per TIA/EIA 568-5-A. If longer runs are required, the use of active hardware such as a repeater or switch is necessary; the specifications for 10BASE-T networking specify a 100-meter length between active devices. This allows for 90 meters of solid-core permanent wiring, two connectors and two stranded patch cables of 5 meters, one at each end.
Since 1995, solid-conductor UTP cables for backbone cabling is required to be no thicker than 22 American Wire Gauge and no thinner than 24 AWG, or 26 AWG for shorter-distance cabling. This standard has been retained with the 2009 revision of ANSI TIA/EIA 568. Although cable assemblies containing 4 pairs are common, category 5 is not limited to 4 pairs. Backbone applications involve using up to 100 pairs; the distance per twist is referred to as pitch. Each of the four pairs in a Cat 5 cable has differing precise pitch to minimize crosstalk between the pairs; the pitch of the twisted pairs is not specified in the standard. Measurements on one sample of Cat 5 cable yielded the following results. Since the pitch of the various colors is not specified in the standard, pitch can vary according to manufacturer and should be measured for the batch being used if cable is being used in non-Ethernet situation where pitch might be critical; some cables are "UV-rated" or "UV-stable" meaning they can be exposed to outdoor UV radiation without significant destruction.
Plenum-rated cables are slower to burn and produce less smoke than cables using a mantle of materials like PVC. Plenum-rated cables may be installed in plenum spaces. Shielded cables are useful for environments where proximity to RF equipment may introduce electromagnetic interference, can be used where eavesdropping likelihood should be minimized; the Category 6 specification improves upon the Category 5e specification by extending frequency response and further reducing crosstalk. The improved performance of Cat 6 provides 250 MHz bandwidth and supports 10GBASE-T for distances up to 55 meters. Category 6A cable supports 10GBASE-T for distances up to 100 meters. Both variants are backwards compatible with Category 5 and 5e cables