Electrical protection of integrated wiring system

Integrated wiring system is a part of intelligent building, compared with the traditional cabling, its main features are compatibility, openness, flexibility, reliability, advanced and economical, it can make voice, data, image equipment and exchange equipment and other information management system connected, also can make these devices and external communication network connection. It can be said that the integrated wiring system is like an intelligent building of a highway, with this information superhighway, what the application system, have become very simple. The purpose of the integrated wiring electrical protection is to reduce the damage of electrical fault to cabling and related hardware, and to avoid the damage of terminal equipment or devices, and to ensure the normal operation of the system.

First, electrical protection
When an outdoor cable enters a building, it usually passes through a transfer into the room at the entrance, and the electrical protection equipment should be installed at the transfer point, so as to avoid causing damage to the user's equipment due to the cable being struck by lightning or contact with the power line.

Electrical protection is mainly divided into over voltage protection and overcurrent protection, these protective devices are usually installed in the building entrance of the special room or wall.

The Overvoltage protection of integrated wiring can choose gas discharge tube protector or solid state protector, the gas discharge tube protector uses disconnection or discharge clearance to limit the voltage between conductor and ground. The discharge gap is formed by two metal columns which are sealed in the ceramic housing and filled with inert gas, when the potential difference between two electrodes exceeds the AC 250V or the Lightning surge voltage exceeds 700V, the gas discharge tube appears an arc, which provides a conductive pathway between the conductor and the ground electrode.

The solid-state protector is suitable for the lower breakdown voltage (60~90v), and it cannot have ringing voltage in the circuit. It uses electronic circuits to vent excessive harmful voltages to the ground without affecting the transmission quality of the cables. Solid State Protector is an electronic switch, which can stabilize voltage clamp before the breakdown voltage is reached, and once the breakdown voltage is exceeded, it will introduce the overvoltage, and the solid state protector provides the best protection for the integrated wiring. ---http://bianceng.cn (computer science)

Besides the Overvoltage protection, the integrated wiring system also adopts overcurrent protection. The Overcurrent protector is connected in a line, and the line is cut off when the line has been streamed. In order to maintain the convenience, the Overcurrent protection generally uses the protector which has the automatic recovery function.

Second, shielding effect
Electromagnetic interference and radiation is the problem of the whole application system, the interference caused by the integrated cabling is only part of it, and the radiation energy and the voltage and frequency of the signal sent. The shielding is used to ensure the transmission performance of the integrated cabling channel in a disturbed environment. It includes two parts, that is to reduce the power of the cable itself outward radiation and improve the cable's ability to resist external electromagnetic interference.

The overall performance of the integrated wiring depends on the weakest cable and connection hardware in the application system and the connection process, the weakest link in the integrated wiring is the wiring frame and the connecting parts of the cable and the information socket and the plug. When the shielding layer of the shielding cable cracks in the installation process, it also constitutes the weak link of the shielding channel. In order to eliminate the electromagnetic interference, in addition to the requirements of the shielding layer without intermittent point, also requires the overall transmission channel must reach 360 ° total shielding, this requirement, for a point-to-point connection channel, it is difficult to achieve, because of the information in the socket, jumper, etc. it is difficult to do full screen, plus shielding layer of corrosion, oxidative damage and other factors , therefore, no channel can really do the whole screen. At the same time, shielded cable shielding layer of low frequency magnetic shielding effect is poor, can not resist such as motor and other equipment produced low-frequency interference. Therefore, the use of shielded cable can not completely eliminate electromagnetic interference.

Theoretically speaking, in order to reduce the outside world, shielding measures can be used to shield both electrostatic shielding and magnetic shielding. The principle of shielding is that the shielding layer after grounding to the interference current through the shielding layer short-circuit into the ground. Therefore, shielding the proper grounding is very important, otherwise not only can not reduce interference, but will make interference increase. Because when the site is not properly arranged and the grounding resistance is too large, when the grounding potential is unbalanced, it will cause the grounding noise, that is, the potential difference is generated at some two points in the transmission channel, thus causing the interference current on the metal shielding layer, then the shielding layer itself forms a maximum interference source, which results in a far less performance than the unshielded transmission channel. Therefore, in order to ensure the screen effect, the shielding layer must be properly and reliably grounded.

In practical applications, in order to minimize interference, in addition to maintaining the integrity of the shielding layer, the shielding layer of reliable grounding, but also pay attention to the working environment of transmission channels, away from the power lines, transformers or motor room and other interference sources. When the comprehensive wiring environment is extremely bad, the electromagnetic interference is strong, the information transmission rate is high, may use the optical cable directly, satisfies the electromagnetic compatibility the demand.

Third, the system grounding
Integrated cabling and related hardware grounding is an important means to improve reliability, restrain noise and ensure safety of application system. Therefore, designers, construction personnel in the wiring design and construction, must be all equipment, especially the application system equipment grounding requirements for careful study, to understand the grounding requirements and the relationship between all kinds of ground. If the grounding system is not handled properly, it will affect the stability of the system equipment, cause trouble, and even burn the system equipment, endanger the operation personnel life safety. Integrated wiring system computer room and equipment grounding, according to different functions are divided into DC work grounding, AC work grounding, protection of grounding, lightning protective grounding, anti-static connection and shielding grounding.

AC Work grounding, safety protection grounding, DC work grounding, lightning protection grounding and other four kinds of grounding should adopt a group of grounding devices. Grounding system is based on the grounding of the current easy to flow as the target, but also can reduce the potential changes caused by interference, so the smaller the grounding resistance is better. Therefore, the determination of the resistance value of the common grounding system should be based on the minimum value.

When the grounding device is set up by the Lightning protection grounding, the same set of grounding devices should be used for AC, DC and protection earthing. In order to prevent lightning voltage from attacking the integrated wiring and connecting equipment, it is necessary to keep a safe distance between the Lightning protection device and other grounding body, but this requirement is difficult to realize in engineering design. For example, multi-storey building lightning-proof grounding generally uses the main rib of the building and base floor as grounding wire and grounding body, can not meet the safety distance between the other grounding requirements, may produce counterattack, at this time, can only be the building of a variety of metal and incoming pipe strictly grounded, and all grounding devices must be shared, and many places to connect, So that the lightning protection devices and adjacent metal objects as much as possible to prevent lightning counterattack phenomenon, to ensure the safety of integrated wiring and system equipment.

In accordance with the requirements of national norms, grounding devices should be set up in the floor wiring or two-level exchanges between the building entrance area and high-rise buildings. The shielding layer of the integrated wiring cable must be connected to the grounding device in the entrance area of the building, and the shielding layer of the main cable shall be connected to the grounding device between the wiring and the exchange, and the shielding layer of the main cable should be kept continuously. The grounding of the wiring should be welded with multiple copper wires and grounding busbar, then the grounding device will be introduced. Non-shielded cable should be laid in metal pipe or metal wire groove, the metal groove tube should be connected reliably, keep electrical connection, and lead to the grounding main line. At the same time, wiring racks and other equipment grounding should be connected with the grounding device, can not be connected in tandem.

In short, the electrical protection of the integrated cabling system plays an important role in the safe and reliable operation of the system. Only careful design, careful construction, can make the electrical protection system to meet the specifications and equipment requirements, to ensure the general wiring system normal work.