When strength is weakness

Low current networks— an integral part of the engineering equipment of a modern home. Without them, high-quality communication is impossible, television, radio, home automation do not work, computers remote from each other do not function. What are low-voltage networks and what are their capabilities in apartment buildings?

wire services

Few of us think about what is the purpose of wires and cables, no one knows who and when transferred from one roof to another, pulled into underground sewers.

We will talk about low-voltage networks that provide cable television, wired radio, telephony and the Internet, fire and security alarm systems, automated energy metering, local computer networks, and intercoms in residential buildings. Since there is no monopoly on commercial activities related to the provision of services by wire to the consumer, various organizations create their own low-voltage networks, pulling wires and cables both over the air and underground. The laying of underground communications is much more expensive and in the conditions of the city is not always possible. Therefore, wires of low-voltage networks are often hung on power line poles and transferred from house to house. This is also done when laying the main fiber-optic communication cables, through which signals are transmitted in the form of light pulses. If it is impossible to stretch the wires to the object by air or underground, the signals are transmitted using radio channels.

The equipment of «smart home» systems, multi-rooms, home cinemas is mounted in cabinets placed in specially designated rooms. ATthey maintain the specified humidity and temperature. In practice, the situation is as follows: a telephone cable with several dozen pairs of wires is introduced into each entrance (according to the number of subscribers eligible for connection, plus a reserve), wires of a city radio center (there is no limit for connecting subscribers to them), a cable for broadcasting TV programs. ATnew buildings, by agreement with the residents, a fiber optic cable can be introduced to ensure the operation of high-speed Internet, IP-telephony and special types of communication (there is also no limit for connecting subscribers). If there is a television or other antenna for collective use on the roof, local input is carried out from it to the house. Antenna cables for individual use are introduced into the apartments through the windows. Today, a local low-voltage intercom network at the entrance— not at all a curiosity even in regional centers.

Entering the building through the attic or basement, low-voltage wires and cables are brought into a riser specially allocated for this purpose, which is two or more inch steel pipes, and stretch to distribution points. These items take the form of mounting panels or cross-countries, which, in turn, are placed in floor or wall cabinets and racks. ATin residential buildings built according to the projects of the 20th century, in interfloor input-distribution devices (electrical panels) for distribution points of low-voltage networks, as a rule, a special section is allocated. ATmodern buildings equipped with energy-saving automation are equipped with separate panels for this purpose. Despite the fact that the voltage in low-voltage networks is 12-24In, and the currents flowing in them are measured in milliamps, wires, cables and low-current equipment are part of the electrical installation of a house and apartment. They are included in the common potential equalization system and grounded according to the rules for electrical installations.

Now the relevance of low-voltage networks has increased dramatically, since the mayor’s offices of large cities have adopted a number of promising programs for the creation of automated accounting systems for energy resources and urban Intranet networks. The transmission of signals in them is carried out mainly by wires. Thus, in Korolev, near Moscow, the efforts of a specialized municipal organization and its dealer have practically completed the commissioning of the city’s Intranet network. Its subscribers enjoy free Internet access to local information resources, make appointments with doctors, pay bills andt.More and more citizens are installing security and video surveillance systems in their apartments, receiving information via the Internet about the state of affairs in their homes in the absence of owners.

Which organizations have the right to install low-voltage networks in houses, what are their rights and obligations, what responsibility do they bear to the customer and the administration in charge of the house? Traditionally, the rights to carry out this kind of work are held by city communication centers (they are in charge of telephony and wired radio broadcasting) and municipal enterprises that ensure the operation of television antennas and cable television networks. These organizations have licenses from the Ministry of Communications to carry out work in the field of low-voltage communications. The performance of work is preceded by the conclusion of an agreement with a private person, if it is a telephone or a radio point in an apartment, or with a legal entity (ZHEU, DEZ or other operating organization), if this is the installation of a common house cable network. ATThe contract outlines the rights and obligations of the parties, stipulates penalties. ATIn the course of the reform of housing and communal services, various commercial enterprises also received the right to such activities. They also have federal licenses for the installation of low-voltage communications. These organizations are engaged in the installation of leased Internet lines and cable (including fiber-optic) television in homes, the installation of video surveillance systems and intercoms in apartments and entrances, and the implementation of special types of communication. Their relationship with the customer is also legally formalized by the contract.

Obenefits of structuring

The day is not far off when the disparate low-voltage networks of apartment buildings will be combined into structured cabling systems (SCS), as is done in modern offices. What is SCS? It is a universal building/campus telecommunications infrastructure designed to transmit all types of signals, including voice, data and video. SCS may also not function in the entire building, but only on a separate floor or even in an apartment.

SCS is built in such a way that through each interface (connection point to the system) you can enter any of the interconnected networks. For example, to receive a video film, a TV program from the network, or to talk on the phone. At the same time, two lines are sufficient at the workplace. Toone, as a rule, connect a computer and TV, to the second— telephone. Cables are laid from workplaces to distribution points (shields in which switching devices are located). Distribution points are connected by trunk lines, and they are already connected to the main network cable entering the house.

ATCompared with separate information and telephone networks, SCS has a number of advantages. Firstly, the system is universal: you can connect a phone, a TV, and a computer to one cable. Secondly, it is an open system. It makes it possible to use any standard network equipment from various manufacturers and allows the simultaneous use of several different types of network protocols (rules and procedures for transmitting information signals). This is important because the protocols of automatic devices from different manufacturers are not always compatible. Whatever electronic device you buy, it will work on the network. Thirdly, SCS has a wider range of data rates: from 100 Kbps for voice applications to 10000 Mbps for information applications. In practice, this means saving money that we pay for the telephone and for the Internet at a per-time rate.

With all the advantages of SCS, it has a significant drawback: it is still expensive. So, for the normal operation of the network, it is necessary to lay in it a reserve for subsequent development. These are additional cells in cross-connects for connecting wires and cables, and signal amplifiers used when building cable lines, and cables with higher characteristics to ensure the operation of more devices, and much more. So far, this pleasure costs 3-4 times more than the installation of individual low-voltage networks.

Towhat to connect, where to insert?

Although there are not enough regulatory documents on low-voltage networks in our country, «the tree of life is lushly green.» Experts are guided by any documentation. Both in domestic and foreign practice of laying telephone cables and installing subscriber wiring, installers of low-voltage networks follow the rules, which are not much different in foreign and domestic manuals. According to OSTN-600-93, the distance between the telephone cable and parallel insulated wires of lighting or power wiring should be at least 25mm. This requirement is true for networks that transmit analog signals (traditional telephone, radio, television). Since digitized signals are used in Internet telephony, network interference does not significantly affect their transmission. Therefore, the distance between the Internet lines and electrical wiring may be less.

It is forbidden to run low-current wires and cables into the electrical wiring riser, since if unbalanced electric currents occur in the power or lighting wiring, they may enter low-voltage networks. BUTthis is already fraught with damage to expensive equipment. When crossing cables of greater capacity should be adjacent to the wall, and less— go around them from above or below (in a strobe). You can determine the capacity of the cables by looking at the wiring diagram, where their brand is indicated. Cables laid outside the building under drainpipes, fire escapes and windows should be protected from mechanical damage by metal plates. Junction boxes must be placed on the wall at a distance of at least 300mm from the ceiling. Do not install junction boxes above doors, openings and windows.

The route of telephone subscriber wiring laid in an open or hidden way (from the junction box to the telephone set) must meet the following requirements:

be the shortest and straightest;

take into account the location of electrical, radio broadcasting and other wiring in the premises and intersect with them as little as possible;

inside buildings, if the wiring is open, pass along the walls at a height of 2.3-3m from the floor and more than 50mm from the ceiling; if hidden, then through the channels of embedded devices at any convenient height.

Wiring to the terminal device should be carried out with a solid wire, splicing is not allowed. Telephone wires running in the same direction must be laid in parallel, close to each other. When a telephone cable is introduced into the house from a rack on the roof or from a pole, it is necessary to install a subscriber protective device (AZU) in close proximity to the place of entry into the house (usually in the attic), which must be grounded.

A wired broadcasting network (its presence in houses is mandatory according to the rules of the Ministry of Emergencies), as a rule, is carried out by hidden wiring (in partitions, walls, ceilings). ATIf the cables and wires of the telephone network and wire broadcasting are laid in a common box, a distance must be observed between them in order to exclude the influence of radio transmissions on telephone conversations. This distance must be at least 50mm with line length 70m, 15mm at length 10m.

As for cables for working with equipment designed for high-speed information transfer (digital television, Internet, IP-telephony), they can also be laid within the apartment in both hidden and open ways. Hidden wiring in this case is carried out in PVC sleeves under the raised floor and in the floor screed, behind suspended and hemmed ceilings, along the walls in strobes. Low-voltage sockets with two or more telecommunications sockets in such cases are mounted in floor boxes and on walls. Open laying of low-voltage networks in cable channels in dwellings is usually not practiced, but can be done if the apartment owners do not mind the appearance of office design elements in their interiors. For any type of installation between cables and sockets of the electrical wiring and low-voltage cables and sockets, a distance must be maintained that complies with the standards.

To protect the equipment from the action of unbalanced network currents and atmospheric discharges, the electric lines of low-current television and video surveillance systems must be grounded. Such a requirement is contained in the American standard J-STD-607-A 2002d. «Joint Standard. Requirements for Grounding and Electrical Connections of Telecommunications Systems in Commercial Buildings.» Grounding bars are insulated copper conductors with a cross section of up to 95mm² (depending on length). They connect the metal enclosures of distribution point equipment to the ground line. Connections can be made permanently (screws, bolts), as well as by isothermal welding. If for some reason grounding is not possible, the wires are shielded and the shield is grounded.

How much do installation services for low-voltage networks in apartment buildings cost? Let’s just say it’s fun— not cheap. The fact is that the user pays not only for installation work, he financially participates in laying the cable to the house, as well as in the depreciation of the basic equipment. Therefore, depending on the level of telephone penetration in the area, the commercial cost of connecting a telephone in the Moscow Region ranges from $400 to $1200. Leased Internet line costs $100 and more, the installation of an apartment intercom costs the same. Installation of security systems, video surveillance, audio and video systems is estimated depending on the complexity of the work, the number of equipment and the volume of premises. Fork is from $500 to $5000 or more. SCS installation costs an average of $30 per line, including its testing and certification (excluding switching and other equipment). The line is understood as a piece of cable from any distribution point to the socket or to the connecting socket. Totwo cables are run to the workplace.

The communication culture of modern society is growing. Andpeople who for some reason do not fully use modern technical means of communication run the risk of being outside the civilized world at one «perfect» moment.

The editors would like to thank the companies CASCADE PLUS, ECOLAN TECH, INTERNETDOM, ARCHITECTURAL ELECTRONICS for their help in preparing the material.

• Source: Ideas for Your Home Magazine#85