Twisted pair is correctly called. What is twisted pair

twisted pair It is used as a transmission medium in all modern network technologies, as well as in analog and digital telephony. The unification of passive network elements on twisted pair became the basis for the concept of building structured cable systems, independent of applications (network technologies). All twisted-pair networks (except the legacy LocalTalk) are based on a star-shaped physical topology, which, with the appropriate active equipment, can serve as the basis for any logical topology.

Twisted pair cables (TP cables), unlike coaxial cables, are symmetrical and are used for differential (balanced) signal transmission. A twisted pair of wires is significantly different in properties from a pair of the same straight wires running side by side parallel to each other. When twisted, it turns out that the conductors always run at a certain angle to each other, which reduces the capacitive and inductive coupling between them. In addition, a significant segment of such a cable for external fields turns out to be symmetrical (round), which reduces its sensitivity to interference and external radiation during the passage of the signal. The finer the twist pitch, the less crosstalk, but also the greater the linear attenuation of the cable, as well as the signal propagation time. The cable can have different designs; individual pairs can have a screen made of copper wire and/or foil. All cable pairs can also be enclosed in a common shield. For the first time in network technologies twisted pair was used in Token Ring networks - the so-called IBM STP Type 1 cable. It was (and is) an expensive and bulky cable, requiring the use of fairly large connectors. Currently, twisted pair cables are constantly being improved, mainly in the direction of increasing bandwidth. 100 MHz is already a common value for cable bandwidth; standards for cables with a bandwidth of up to 600 MHz are being developed.

A twisted pair wire consists of two twisted insulated conductors. This wire is used for cross-wires inside wiring closets or racks, but not for laying connections between rooms. The crossover wire can consist of one, two, three or even four twisted pairs. A cable differs from a wire by the presence of an external insulating stocking (jacket). This stocking mainly protects the wires (cable elements) from mechanical stress and moisture. The most common cables are those containing two or four twisted pairs. There are cables for big number pairs - 25 pairs or more. A cord is a piece of flexible (multi-core) cable of relatively short length. A typical example is a patch cord - a piece of multi-core 4-pair. cable 1-5 m long with modular 8-pin plugs (RJ-45) at the ends.

Twisted Pair Categories

The Category of a twisted pair cable determines the frequency range in which its use is effective (ACR has positive value). Currently, there are standard definitions for 7 cable categories (CAT1... CAT7). The categories are defined by the EIA/TIA 568A standard.

• CAT1- (frequency band 0.1 MHz) telephone cable, just one pair, known in Russia as "noodles". It was used previously in the USA, and the conductors were twisted together. Used only for voice or data transmission using a modem.
• CAT2- (frequency band 1 MHz) old type of cable, 2 pairs of conductors, supported data transmission at speeds up to 4 Mbit/s, used in Token Ring and ARCnet networks. Now sometimes found in telephone networks.
• CAT3- (16 MHz frequency band) 2-pair cable, used in the construction of 10BASE-T and Token Ring local networks, supports data transfer rates only up to 10 Mbit/s. Unlike the previous two, it meets the requirements of the IEEE 802.3 standard. Also still found in telephone networks.
• CAT4- (20 MHz frequency band) cable consists of 4 twisted pairs, used in token ring, 10BASE-T, 10BASE-T4 networks, data transfer speed does not exceed 16 Mbit/s, not currently used.
• CAT5- (frequency band 100 MHz) 4-pair cable, this is what is usually called a “twisted pair” cable, due to the high transmission speed, up to 100 Mbit/s when using 2 pairs and up to 1000 Mbit/s, when using 4 pairs, it is the most common network media used in computer networks still. When laying new networks, they use a slightly improved CAT5e cable (125 MHz frequency band), which better transmits high-frequency signals.
• CAT6- (frequency band 250 MHz) used in Fast Ethernet and Gigabit Ethernet networks, consists of 4 pairs of conductors and is capable of transmitting data at speeds up to 10,000 Mbit/s. Added to the standard in June 2002. There is a category CAT6a, in which the frequency of the transmitted signal is increased to 500 MHz.
• CAT7- data transfer rate 10000 Mbit/s, transmitted signal frequency up to 600-700 MHz. The cable of this category is shielded. Thanks to the double shield, the cable length can exceed 100 m.

Twisted pair cable types

In addition to the generally accepted designations of cables by category, there is also a classification of cables by type (Type), introduced by IBM.

Twisted pair can be either shielded or unshielded. The terminology of screen designs is ambiguous; the words braid (braid), shield and screen (screen, protection), foil (foil), tinned drain wire (tinned “drainage” wire running along the foil and slightly wrapping it around it) are used here.

Unshielded twisted pair(NVP) is better known by its abbreviation UTP(Unshielded Twisted Pair). If the cable is enclosed in a common shield, but the pairs do not have individual shields, but, according to the standard (ISO 11801), it also refers to unshielded twisted pairs and is designated UTP or S/UTP. This also includes SCTP (Screened Twisted Pair) or FTP (Foiled Twisted Pair) - a cable in which the twisted pairs are enclosed in a common shield made of foil, as well as SFTP (Shielded Foil Twisted Pair) - a cable in which the common shield consists of foil and braids.

Shielded twisted pair(EVP), aka STP(Shielded Twisted Pair), has many varieties, but each pair must have its own screen:

• STP with a designation of the form “Type xx” is a “classic” twisted pair cable introduced by IBM for TokenRing networks. Each pair of this cable is enclosed in a separate foil shield (except type 6A), both pairs are enclosed in a common braided wire shield, on the outside, all covered with an insulating stocking, impedance - 150 Ohms. The wire can be solid or stranded 22-26 AWG. Single-conductor 22 AWG cable can have a bandwidth of up to 300 MHz.
• STP category 5 is a general name for a cable with an impedance of 100 Ohms, having a separate shield for each pair, which can have different designs (foil, braid, a combination of both). Sometimes under the same name cable coming having only a general screen (AMP company),
• SSTP (Shielded-Screened Twisted Pair) category 7 - cable similar to PiMF.

Cables can have different impedance ratings. The EIA/TIA-568A standard defines two values ​​- 100 and 150 Ohms, IS01 1801 and EN 50173 standards also add 120 Ohms. Requirements for impedance accuracy in the operating frequency band are usually in the range of ±15% of the nominal. Note that UTP cable most often has an impedance of 100 ohms, while shielded STP cable originally only existed with an impedance of 150 ohms. Currently, there are types of shielded cable with both 100 and 120 ohm impedance. The terminal equipment is available in versions for both shielded (STP) and unshielded (UTP) twisted pair. With a cable that has at least one shield (STP, ScTP, FTP, PiMF), connectors are used to connect the shields and (not always) shielding. The impedance of the cable used must match the impedance of the equipment it connects, otherwise interference from the reflected signal may cause the connections to fail. This is especially critical for high frequencies (100 MHz and above).

The most widely used cables are those with a number of pairs of 2 and 4. There are also double designs - two cables of two or four pairs are enclosed in adjacent insulating stockings. STP+UTP cables can also be enclosed in a common stocking. Of the multi-pair ones, 25-pair ones are popular, as well as assemblies of 6 pieces of 4-pair ones. Cables with a large number of pairs (50, 100) are used only in telephony, since the production of multi-pair cables high categories- the task is very difficult. Each cable pair has its own twist pitch, different from its neighbors. This ensures a reduction in the mutual inductance and capacitance of the pairs of wires, and, consequently, a reduction in crosstalk. Since the wave characteristics of the pair (propagation speed, impedance, attenuation) depend on the twist pitch, the pairs in the cable are not identical. Each pair in a cable segment has its own “electrical length”, determined through the signal propagation time and the nominal (for a given cable) wave propagation speed. The “electrical length” of the pair will differ from the “mechanical” length measured with a tape measure. Sometimes a variable twist pitch is used for each pair - this equalizes the average parameters of the pairs while maintaining an acceptable level of crosstalk.

By gauge - conductor cross-section - cables are marked in accordance with the AWG (American Wire Gauge) standard. The main conductors used are 26 AWG (cross section 0.13 mm2, linear resistance 137 Ohm/km), 24 AWG (0.2-0.28 mm2, 60-88 Ohm/km) and 22 AWG (0.33-0, 44 mm2, 39-52 Ohm/km). However, the gauge of the conductor does not provide information about the thickness of the wire in insulation, which is very important when sealing the ends of the cable into modular plugs, and the outer diameter of the cable, from which the cross-section of the required cable channels can be calculated.

Conductors can be rigid single-core (solid) or flexible stranded (stranded or flex), usually consisting of 7 wires (7-strand). A cable with single-core wires has better and more stable characteristics. It is used mainly for stationary wiring (it is also cheaper than multi-core), which amounts to the largest part V cable lines. Multicore flexible cable is used to connect equipment (subscriber and telecommunications) with fixed wiring and patch cords.

Connecting equipment

The connecting equipment provides the ability to connect to cables, that is, it provides cable interfaces. For twisted pair, there is a wide range of connectors designed for both permanent and detachable connections of wires, cables and cords. Among permanent connectors, the most common types are S110, S66 and Krone connectors, which are industry standards. Among detachable connectors, the most popular are standardized modular connectors (RJ-11, RJ-45, etc.). To terminate, the insulation from the wires is not removed - it moves while the knives themselves seal the connector contacts. The procedure for terminating (terminating) wires into connectors of types S110, S66, Krone and similar using special impact tools is also called punch down, and blocks with these connectors are called PDS (Punch Down System).

The connecting equipment also includes various adapters that allow connecting different types of cable interfaces.

Modular connectors Modular Jack (sockets, sockets) and Modular Plug (plugs) are the most commonly used connectors for 1-, 2-, 3-, 4-pair cables of categories 3-6. Cable systems use 8- and 6-position connectors, better known as RJ-45 and RJ-11, respectively.

The designation RJ (Registered Jack) actually refers to a connector with a specific wiring layout and comes from telephony. Each of the connectors shown in the figure can be used with a different RJ number.

Modular RJ-45 plug

When installing a structured data cabling system, you should use 8-position connectors with the EIA/TIA-568A, abbreviated T568A, or EIA/TIA-568B, abbreviated T568B layout.

The disadvantage of all layouts is that at least one pair is not separated into adjacent contacts, but another pair is wedged inside it. This leads to an increase in crosstalk and signal reflection from inhomogeneity that occurs when the wires of these pairs are more untwisted. For this reason, the use of conventional modular connectors for categories above 6 is problematic. The most common modular connectors are Category 5 or 3; connectors of Category 5 and higher are also available for shielded wiring.

Modular sockets of category 5 and higher always have a corresponding designation; they differ markedly from sockets of the 3rd category in design and method of connecting wires. Here the socket itself is mounted on a printed circuit board, on which blade contacts (type S110, Krone or another design) are installed for terminating cable wires. The circuits are routed using printed conductors so that the wires of each pair are connected to adjacent contacts of the connector. In addition, the board contains reactive elements that match the impedance, made in printed form. Without these elements, on high-speed technologies (100 Mbit/s and above), problems associated with the reflection of signals from connectors are possible.

Modular socket

There are many options for the design and method of mounting sockets, which can be divided into fixed configurations and modular systems. Fixed-configuration sockets - wall-mounted with 1 or 2 identical sockets and blocks of 4, 6 or 8 sockets for patch panels - usually attached to printed circuit board on which they are mounted. To protect against dust, sockets with hinged covers or retractable spring-loaded curtains are used. For patch panels, the front-facing position of the socket (the plug enters from the front) is best suited. For workplace sockets, the socket can look both down and to the side (up is undesirable due to dust accumulation). Convenient in many cases corner sockets. There are many mounting options, and despite the external similarity of sockets from different manufacturers, they often do not fit “non-native” fittings, seemingly with the same dimensions.

Sealing of wires into sockets is carried out with a tool corresponding to the type of connector (S110, Krone), or using protective caps. There are designs of sockets that can be assembled without tools - the wires are laid out in a plastic cover, and when it is put on, they enter the contact knives.

Modular plugs different categories may not differ in appearance from each other, but have different designs. Category 5 plugs may have a separator that is placed on the wires before assembling and crimping the connector, which reduces the length of the unbraided part of the cable and makes it easier to lay out the wires. When installed (crimped), the contacts cut into the wires through the insulation. Plugs for single-core and multi-core cables differ in the shape of the contacts. Needle contacts are used for multi-core cable; the needles are stuck between the wire cores, ensuring a reliable connection. For single-core cable contacts are used that “embrace” the core on both sides. During crimping, the protrusion that secures the cable (the part that is still in the stocking) is also pressed in. The latch is used to snap the plug into the socket.

Twisted pair is a type of communication cable, which is presented in the form of a pair of conductors covered with insulation and twisted together with a certain pitch. Double conductors are combined into multi-pair wires, which are covered with a common protective sheath.

Depending on the twisting pitch of pairs, the number of double cores, material outer covering, type of insulation and shielding, determines the area of ​​use of the wire. Such wires are part of a structured cabling system, and therefore are widely used in telecommunications, video surveillance, and computer networks.

To build a local home or office network, an FTP cable 5e is most often used. If you decide to create your own local computer network in your apartment or for other reasons you need a twisted pair cable, then it’s worth figuring out what type you need to purchase.

Twisted pair shielding type

Shielding is the protection of conductors (or cores) from electromagnetic radiation that can affect transmitted data and speed.

There are several types of cable, depending on how the cores inside are shielded.

Unshielded UTP Wire

The cheapest type, limited in its use due to instability to crosstalk and EMI. Represents one or more pairs united by an outer shell.

Shielded FTP cable

It is more protected from EMR in that it has a common shield that covers all the wires with foil. It is the most popular type of cable and is used almost everywhere. It is slightly more expensive than UTP, but it ensures the integrity of the transmitted data.

Double Shielded STP Cable

This type uses double protection, that is, there is a common shield for all foil cores, plus a separate shield for each pair. One of the most reliable cables, several times more expensive than UTP and FTP, most often used in offices and production.

Many organizations use funny cable shielding markings. If you have to look twisted pair via the Internet and in markets, you may encounter the following symbols:

• F/UTP - twisted pair with common shield;
• U/UTP - completely screenless;
• SF/UTP - double shield pair;
• S/FTP - in it the overall screen is presented in the form of a copper braid, and the protection of each pair is made of foil.

As noted, the most common use case is an FTP cable, the price of which depends on the manufacturer, the shielding material used and the quality of the outer protective sheath.

Twisted pair by type of sheath used

Pairs of cores twisted together are connected into a single cable using an outer protective sheath. It is usually made of polyethylene or polyvinyl chloride. This polymer has excellent qualities resistance to most solvents, alkalis and oils, does not emit toxic fumes in the air and is not destroyed in temperature range from -15 to +66 degrees Celsius.

In its pure form, it has excellent ductility, therefore, so that the cable can be easily bitten or torn lengthwise if necessary, chalk is added to the polyvinyl chloride. When paired, they make an excellent material for making a protective shell.

Various additives can be added to the two main components, which provide required properties external part to the FTP cable. Based on them, the division of the shell into types, which are distinguished by color, was constructed.

Low smoke non-flammable shell

Orange - made of non-flammable polymer, has the highest fire safety rating. Marked LSZH (stands for Low Smoke Zero Halogen - low smoke emission, zero halogens).

For outdoor use

Black - it contains the same polymer, but it has an additional protective layer made of polyethylene, which is designed to protect the cable from external atmospheric influences, usually wires with such a sheath are used for laying on the street, in sewers or through the air.

For indoor installation

Gray is a common budget sheath, used for cables laid indoors. Quite fragile to break and break, which allows you to quickly break it in the right place.

There is always a marking on the shell indicating the type of shielding, manufacturer and category. Information is applied to the FTP cable every meter, for foreign ones it can be a foot. With its help you can easily measure desired length or find out the length of the laid lines by simple calculation.

As a rule, cables are flat and round; round ones are used in everyday life and in offices (not counting telephone noodles, which can be found less and less often). For its installation, boxes or cable channels are provided in the baseboards, and there are also semicircular fasteners that allow you to nail the cable to the wall without damaging it.

Cable categories by number of pairs and bandwidth

As already mentioned, there can be one twisted pair or several inside the cable. Depending on their number and bandwidth, FTP cable has different categories.

Legacy twisted pair cable categories

Cat1 - operating frequency 100 kilohertz, used for voice signal transmission, popularly called “telephone noodles”.

Cat2 - the used frequency is 1 megahertz, has the ability to transmit data up to 4 Mbit/s, contains 2 pairs of conductors, is currently not used anywhere.

Cat3 - operates at a frequency of 16 megahertz, maximum transmission speed up to 10 Mbit/s, contains 4 pairs, can be used in telephone and computer networks with a length of no more than 100 m.

Cat4 - used frequency band up to 20 megahertz, transmission speed up to 16 Mbit/s, contains 4 pairs and is not used anywhere at this moment.

Widely Used Twisted Pair Categories

Cat5e is the most popular FTP cable containing 4 pairs of conductors. Operates at a frequency of up to 125 megahertz, when using 2 pairs it provides a transfer speed of up to 100 Mbit/s, when using all pairs up to 1 Gbit/s per second.

Cat6 - operating frequency up to 250 megahertz, has 4 pairs of wires and, when all are used, provides speeds of up to 1 Gbit/s per second, at a distance of up to 50 meters it transmits up to 10 Gbit/s.

Rarely used promising categories

Cat6a - has an operating frequency of up to 500 megahertz and 4 pairs of wires, providing transmission speeds of up to 40 Gbit/s. Used to build high-speed lines.

Cat7 - four-pair cable, with operating frequency up to 700 megahertz, has a transmission speed of up to 50 Gbit/s.

Cat7a - 4 pairs, frequency up to 1200 megahertz, can provide speeds of up to 100 Gbit/s with a length of no more than 15 meters, and up to 10 Gbit/s when using all pairs.

How to choose the right twisted pair cable for home use

The most common cable is FTP category 5e twisted pair cable. It is used to lay local networks in offices and at home, and is used to connect computers to a router or hub. And, most likely, the cable that is installed in your apartment will be of the same category.

Some providers save on twisted pair cable and pass it on to their customers budget options no shielding at all. Unshielded twisted pair can be laid inside the apartment if it is possible to lay the network away from the wiring and hide it in a cable channel.

Based on the above, we can draw a conclusion. In order to choose the right twisted pair, you need to decide on:

• Required data transfer speed.

Most providers do not offer tariffs with speeds above 100 Mbit/s. However, if your equipment allows, you can build local network with speeds up to 1 Gbit/s per second.

• The need for cable shielding.

Laying the wire in the baseboard, away from electrical wiring, subwoofers and other devices that emit EMR, you can use UTP to save money. It is still recommended to use an FTP cable or at least an F/UTP cable.

• The installation location is where it takes place, outdoors or indoors.

If you're on the street, you'll have to buy a protected cable, which costs an order of magnitude more. For installation in an office, apartment or private house, it is enough to use a regular gray cable. Before installation in office space check fire safety requirements.

Having studied what twisted pair is and what types it comes in, you can easily choose the cable that is suitable specifically for your conditions. Do not forget that right choice FTP cable is only half the battle; you also need to learn how to crimp correctly and how many cores to use.

For these purposes, you can also invite a specialist who will come with necessary equipment, will crimp the cable and configure all computers. Or you can check how the pressure test was done on the wire that the provider brought into the apartment, and do it in the same way.

Quite often the question arises: what is twisted pair? - this is a type that uses insulated conductors twisted in pairs. This type of cable is used in the telecommunications industry and is an integral component of structured cabling systems ().

As has already become clear, the cable got its name from the use of twisted conductors in pairs, hence the twisted pair. What does this give in technical issue? Twisting is done specifically to reduce the impact of electromagnetic interference from external sources on the cores of the pair. And in cables of category 5+, the cores of each pair are twisted with different steps, to reduce interference from twisted pairs to each other.

Cable shielding is also used to protect against interference. And, in accordance with this, they are divided into two main types - shielded and unshielded. To understand what degree of shielding a cable has, you need to understand its markings.

Cable markings

When choosing a cable, you will definitely come across its special markings. One of the parts in this marking carries information about the shielding of the cable. For example: “FTP cat cable. 5e CCA” - let's figure out what the letters FTP mean in the name of this cable.

When marking cables, the following designations are used:

• TP (Twisted Pair)– type of twisting, twisted pair.
• U (Unshielded)– there is no protective screen.
• F (Foiled)– foil is used as a screen.
• S (Shielded)– a wire braid is used as a screen.

According to standard ISO/IEC 11801 to mark cables, a combination of these designations written in a certain order XX/YZZ is used. Where “XX” denotes the overall shield of the cable, “Y” denotes the shield of each pair, and “ZZ” marks the type of wire twist.

But in practice, confusion arises due to the fact that manufacturers often mark cables with only three letters. What is a twisted pair cable marked UTP or FFTP? Let's take a closer look.

Most common cables UTP(no shielding) and cables FTP(all pairs are enclosed in a common foil screen).

Twisted Pair Categories

There are currently seven categories of twisted pair cables in use. Their main difference is the cable bandwidth, which is a determining factor in the speed of information transfer and the ability to use special network technologies.

The following articles may be of interest to you:

IT outsourcing is one of the actively developing services in the field of information technologies. In European countries, outsourcing consistently occupies 50% of the market share of IT services. What is connected not only with highly appreciated various...

— installing RJ-45 connectors on a twisted pair, let’s figure it out, what is a twisted pair?

This is a cable that consists of one or more pairs copper conductors in colored insulation, twisted together. The entire bundle of wires is also twisted around a central axis and covered with a polymer sheath, sometimes with protective elements: metal braiding, Teflon or polyethylene coating.

twisted pair bundle

Twisting of conductors is additional protection from electromagnetic interference, as well as a method of strengthening the connection between the cores transmitting common differential signals.

To improve signal quality and reduce mutual interference, the number of turns in different cores is made unequal.

Types, devices and methods of twisted pair shielding

Having understood what a twisted pair is, let’s move on to studying its types and structure.

Types of cable according to the number of copper cores:

• Single-core(monolithic) - each wire consists of one solid wire, 0.3-0.6 mm thick or 20-26 AWG. Such cords break easily, so they are only suitable for laying inside wall panels and mounting boxes.
• Stranded— wires consist of bundles of very thin wires. This cord does not break when bent or twisted, and is used for movable connections between devices. Has more high level signal attenuation than single-core, so its maximum length should not exceed 100 m.

Multicore twisted pair

According to the shielding method - the presence of protection against electromagnetic interference:

• UTP (U/UTP)— unshielded twisted pair (without protection).
• FTP (F/UTP)- foil twisted pair - has one common foil sheath.
• STP (S/UTP)- shielded twisted pair - one common shield in the form of a metal braid.
• S/FTP (SF/UTP)— foil cable with an additional braided screen.
• U/FTP- cable with individual shielding of each twist with a foil sheath.
• S/FTP— separate shielding of each twist plus metal braiding.
• F/FTP— separate shielding for each twist plus a common foil shield for all cores
• SF/FTP— separate shielding of each twist plus a common shield of braid and foil.

Twisted pair SF/FTP

To make it clearer, here is a transcript letter code shielding:

• U— no screen;
• F- foil;
• S- braid.

By shell color and area of ​​application:

• • Black— for installation outdoors (the outside of such a cord is covered with a layer of polyethylene for corrosion resistance);

external twisted pair with steel cable

• • Grey— for installation indoors;

• • Orange with "LSZH" markings— non-flammable cord for installation in fire hazardous areas.

Twisted Pair for Fire Hazardous Areas

According to the shape of the cross section:

• Round- universal;
• Flat- for installation under wallpaper or carpet, such cords are more susceptible to interference than round ones.

Types of twisted pair

Today there are 7 categories of this type of cable and another one, the eighth, is still in development. In separate categories -5, 6 and 7, subcategories are distinguished, so their total number is 10. For ease of comparison, we have displayed them in the table.

There is no single standard for marking twisted pair cables - each manufacturer indicates on it what it considers necessary. Some of this data is not of practical importance, and you will find out what is important to pay attention to a little later.

Here is one example of standard cable markings:

Marking on UTP cable

The manufacturer's code and brand are usually indicated at the beginning. Further - Maximum temperature, at which operation is possible. Next comes the type of shielding, number of pairs, diameter of one conductor, category, certificates of conformity, length and year of manufacture.

In our example:

• Shell gray Accordingly, the cable is intended for indoor use.
• The alphanumeric designation that begins with “HTO-KEY E191267” is the manufacturer’s code.
• 75oC is the maximum temperature.
• UTP - this cable is unshielded.
• 4PR - 4 pairs of conductors.
• 24 AWG is the cross-sectional diameter of one wire (can also be specified in millimeters).
• ELT Verified - tested and meets the category standard.
• CAT5E - category 5e.
• EIA/TIA-568-B.2 - complies with the standard of the same name.
• The last numbers are the total cable length in feet and meters.
• Production date not specified.

The order of designations may be different, but any cable always indicates its category, shielding type and number of pairs. This data is important when purchasing, the rest is just for reference.

Conclusion

After reading this article, you have learned to understand the types and structure of twisted pair cables. Now it won’t be difficult for you to choose it yourself. Next you will learn a lot of useful things about.

To create communication networks, computer and communications, cables made according to special technology. Their veins are twisted together in pairs. Such products are called “twisted pair”. There are two main types of cables of this design: ftp and utp.

UTP (top) and shielded FTP (bottom)

Features of twisted pair

The main problem in protecting communication lines is their protection from interference. The signal amplitudes in the line are much smaller than those of the surrounding electrical equipment: in power cable lines, electric motors, household appliances, overhead power lines. Taking into account the degree of development of electrification, it is not difficult to imagine the amount of electromagnetic interference affecting communication cables along their entire route.

In addition, the conductors inside the cable itself interact with each other, creating mutual interference. When communication lines were made using the same technology as electrical ones (in the form air lines with wires on insulators), interference from neighboring conductors and high-voltage power lines was minimized by regularly changing the location of the line conductors relative to each other. This technical cunning called transposition.

Transposition using the example of a power line

The twisted pair in a modern cable is the same transposition, but made with high density. The veins are twisted together in pairs. This ensures minimal influence of individual pairs of cores on each other and increases protection from external interference.

However, the protective properties of twisted pair cables are nullified if the conditions for their installation are violated. The bending radius of such products is strictly limited and usually should not be less than eight diameters. If this is not taken into account, then geometric changes occur inside the cable, sometimes irreparable, worsening its noise immunity.

The bending radius of the twisted pair must be at least 8 cable diameters

Shielding of communication cables

However, twisting the wires does not always help to completely eliminate the influence of interference on the useful signal. In this case, the introduction of shielding shells into the design helps. Both individual pairs of cores and all cores inside the cable can be shielded. These methods are used both individually and jointly; in this case, each pair of cores is shielded and, additionally, all cores together.

However, this method of protection is effective only if the equipment housings connected by cable are grounded. Otherwise, the screen shells themselves become a source of interference, accumulating it along the entire path of the line.

Depending on the presence, absence and number of screens, a letter is added to the cable brand, meaning:

• U – no screen;
• S – general screen in the form of a metal braid;
• F – screen made of copper or aluminum foil or a metallized tape around the cores of each pair or all of them as a whole.

The full designation of the brand consists of the above letters written through a fraction. The numerator indicates the protection of individual cores, the denominator indicates the entire cable. Next, the letters “TP” are added, meaning “twisted pair”, translated as twisted pair.

For example, the designation U/FTP indicates that the cable does not have a protective shield for individual pairs of wires, but contains a common shielding sheath. There are also combinations of their two letters, for example “SF” - metal braid and foil are used together.

It must be taken into account that when using foil for shielding, its outer surface is covered with a layer of dielectric. Therefore, when connecting a screen, you only need to use it inner surface for contact connection.

If the screen is made of foil, then a metal wire of small cross-section runs parallel to it. It is necessary for better contact when connecting to grounding devices. It also eliminates possible breaks in the foil screen that occur in places of kinks, as if bridging the places of breaks.

Which cable is better: with or without screen?

When laying communication networks, which cable is better to use, utp or ftp? It would seem that the use of shielded cables solves all problems with noise immunity, while unshielded cables cope with the problem only partially.

Not so. Let us remember the ability of the screen to accumulate noise in the absence of grounding. If the equipment to which it is connected does not have a connection to a ground loop (or its own ground loop, which is mandatory for servers), then using ftp will only make the situation worse.

In addition, FTP cables are very sensitive to low-frequency interference, the level of which is at manufacturing enterprises quite high due to the presence of power electrical equipment. No matter how hard you try, it is still impossible to lay communication cables at a sufficient distance from existing power lines. And cable products passing through them always radiate interference around themselves. In addition, electric motors and induction elements also emit interference. Do not forget about impulse noise that occurs during the operation of switching devices.

Also, a utp cable, unlike ftp, has less attenuation of the useful signal. Which has a strong effect when the communication line is long.

Therefore, when deciding which cable to choose, unshielded or ftp, you need to focus on whether the equipment has the ability to connect the screen, the presence or absence of low-frequency interference and total length communication lines.

When choosing a cable, you need to pay attention to the material of its sheath. If it passes through open areas on the street, then it must be protected from exposure sun rays. For this purpose, the outer shell is made of polyethylene, usually black. But the polyethylene sheath, which protects the cable from sunlight, temperature fluctuations and precipitation, supports combustion. Therefore, they cannot be laid openly indoors.

For use inside buildings, the shell must not support combustion and not emit halogens (fluorine, chlorine, bromine or iodine). They are not only strong oxidizing agents, but also toxic to humans. Flame-retardant sheaths are indicated by adding the letters LS (low smoke) to the cable marking for imported products or “ng” for Russian products. Non-halogen-emitting products are additionally marked HF (halogen free).