The integrated wiring system is part of the intelligent building. Compared with the traditional wiring, its main features are compatibility, openness, flexibility, reliability, advancement and economy. It can make voice, data and image equipment and Switching devices are connected to other information management systems and can also connect these devices to external communication networks.
It can be said that the integrated wiring system is like a highway in a smart building. With this information highway, it is very simple to think about what application system. The purpose of integrated wiring electrical protection is to reduce the damage of the integrated wiring cable and related connection hardware caused by electrical failure, and at the same time avoid damage to the terminal equipment or components and ensure the normal operation of the system.
1. When the electrical lightning protection outdoor cable enters the building, it is usually transferred to the room through the entrance at the entrance. Electrical protection equipment should be installed at the transfer point. This can avoid the induced potential or the contact with the power line due to the lightning strike of the cable. Damage to user equipment. Dikai lightning protection
The electrical protection is mainly overvoltage protection (surge protection SPD), which is usually installed in a dedicated room or wall on the entrance of the building.
Overvoltage protection for integrated wiring may use a gas discharge tube protector or a solid state protector that uses a disconnect or discharge gap to limit the voltage between the conductor and ground. The discharge gap is formed by two metal posts sealed in a ceramic casing and filled with an inert gas. When the potential difference between the two electrodes exceeds 250V AC or the lightning surge voltage exceeds 700V, the gas discharge tube is arced. A conductive path is provided between the conductor and the ground electrode.
In addition to overvoltage protection, the integrated wiring system also uses overcurrent protection. The overcurrent protector is connected in series in the line, and when the line is overcurrent, the line is cut off. For the convenience of maintenance, Dikai lightning protection overcurrent protection generally uses a protector with automatic recovery function.
Second, the shielding effect
Electromagnetic interference and radiation are problems of the entire application system, and interference caused by integrated wiring cables is only part of it, and the radiant energy is related to the voltage and frequency of the transmitted signal. The shielded lightning protection is used to ensure the transmission performance of the integrated wiring channel in a disturbing environment. It consists of two parts, namely reducing the energy radiated by the cable itself and improving the cable's ability to withstand external electromagnetic interference.
The overall performance of the integrated wiring depends on the weakest cable and related connection hardware performance and connection process in the application system. In the integrated wiring, the weakest link is the contact part between the distribution frame and the cable connection part and the information socket and the plug. When the shielding layer of the shielded cable is cracked during the installation process, it also constitutes a weak link of the shielded passage. In order to eliminate electromagnetic interference, in addition to requiring the shielding layer to have no discontinuities, it is also required that the overall transmission channel must reach 360° full shielding. This requirement is difficult to achieve for a point-to-point connection channel because of the information socket. Jumpers, etc. are difficult to achieve full shielding, plus the corrosion of the shielding layer, oxidation damage and other factors, therefore, no channel can truly shield the whole process. At the same time, the shielding layer of the shielded cable has a poor shielding effect on the low frequency magnetic field and cannot withstand low frequency interference generated by equipment such as a motor. Therefore, the use of shielded cables can not completely eliminate electromagnetic interference.
In practical applications, in order to minimize the interference, in addition to maintaining the integrity of the shielding layer, the grounding lightning protection is reliable grounding to the shielding layer, and also pay attention to the working environment of the transmission channel, away from various interferences such as power lines, transformers or motor rooms. source. When the integrated wiring environment is extremely harsh, electromagnetic interference is strong, and the information transmission rate is high, the optical cable can be directly used to meet the requirements of electromagnetic compatibility.
Third, lightning protection grounding
Grounding of integrated wiring cables and related connection hardware is an important means to improve application system reliability, suppress noise, and ensure safety. Therefore, designers and construction personnel must carefully study the grounding requirements of all equipment, especially the application system equipment, before wiring design and construction, to understand the grounding requirements and the relationship between various types of ground lines. If the grounding system is not handled properly, it will affect the stability of the system equipment, cause malfunctions, and even burn system equipment, which will endanger the life of the operators. The grounding of the equipment room and equipment of the integrated wiring system is divided into DC working grounding, AC working grounding, safety protection grounding, lightning protection grounding, anti-static connection and shielding grounding according to different functions.
A set of grounding devices should be used for four groundings such as AC working grounding, safety protection grounding, DC working grounding, and lightning protection grounding. The grounding system is aimed at the easy flow of the grounding current, and can also reduce the interference caused by the potential change, so the smaller the grounding resistance, the better. Therefore, the resistance value of the common grounding system should be determined by the minimum value.
When the grounding device is separately set for lightning protection grounding, the same group of grounding devices should be used for AC, DC and safety protection grounding. In order to prevent the lightning strike voltage from countering the integrated wiring and connecting equipment, it is required to maintain a sufficient safety distance between the lightning protection device and other grounding bodies, but this requirement is difficult to achieve in engineering design. For example, the lightning protection grounding of multi-story buildings generally uses the main ribs of the building and the main ribs of the foundation floor as the grounding wire and the grounding body, which cannot meet the safety distance requirements with other grounding bodies, and may counterattack. At this time, only various buildings can be built. The metal body and the inlet and outlet pipes are strictly grounded, and all the grounding devices must be shared and connected in multiple places. The grounding lightning protection makes the lightning protection device and the adjacent metal objects have the same potential as possible to prevent lightning strikes and ensure integrated wiring. And the safety of system equipment.
According to the requirements of national regulations, grounding devices should be installed in the entrance area of ​​the building, the floor wiring closet of the high-rise building or the secondary exchange room. The shield of the integrated wiring lead-in cable must be connected to the grounding device in the entrance area of ​​the building. The shield of the trunk cable should be connected to the grounding device of the wiring closet or switch room by using multiple strands of copper wire larger than 4mm2, and the shield of the trunk cable. The layers must be continuous. The grounding of the wiring closet should be welded with a multi-strand copper wire and a grounding busbar before being led to the grounding device. Unshielded cables should be laid in metal pipes or wire troughs. The metal troughs should be connected reliably, kept in electrical communication, and routed to the grounding mains. At the same time, the grounding of equipment such as patch panels should be connected to the grounding device in parallel, and cannot be connected in series.
In short, the electrical protection of the integrated wiring system plays an important role in the safe and reliable operation of the system. Only careful design and careful construction can make the electrical protection system meet the specification requirements and equipment requirements, and ensure the normal operation of the integrated wiring system.
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