Optical fiber cabling knowledge and precautions


For a long time, optical fiber, as a high-bandwidth and high-security transmission medium, has been widely used in major transmission networks. Due to the high cost of cables and equipment, optical fibers are mostly only used in the network backbone, that is, the system wiring applied to the vertical backbone subsystem and the building group subsystem to realize the connection between buildings and between floors. Let's take a brief look at the basics of fiber optic cabling.


Optical fiber cabling knowledge and precautions

Before carrying out fiber optic wiring, the requirements for fiber optic cable laying must be considered first. Generally, the optical cable should meet the following requirements:

The minimum allowable curvature radius of the optical cable shall not be less than 20 times the outer diameter of the optical cable during construction, and shall not be less than 15 times the outer diameter of the optical cable after construction. When laying the optical cable, it is required that the traction force of the optical cable should not exceed 80% of the allowable tension of the optical cable, and the instantaneous maximum traction force should not be greater than the allowable tension of the optical cable. The main pulling force should be applied to the strengthening member of the optical cable, and the optical fiber cannot bear the pulling force directly.


Fiber Optic Cabling

After understanding the basic requirements of optical fiber laying, the next step is to carry out optical fiber wiring. Light wiring is usually divided into indoor wiring and outdoor wiring, and we will analyze them in detail below.

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1. Optical cable classification and wiring knowledge

Indoor optical cables are mainly used in the laying of horizontal subsystems and vertical backbone subsystems. The laying of cables for the horizontal subsystem is very similar to twisted pair, except that due to the poorer tensile properties of the cables, more care should be taken when pulling and the radius of curvature is larger. The vertical backbone subsystem optical cable is used to connect the equipment room to the wiring room on each floor, and is generally installed in the cable shaft or the rising room.


In order to prevent sagging or slipping, the optical cable must be securely fastened at the top, bottom and middle of the channel on each floor. Usually, nylon ties or steel clips can be used for effective fixation. Finally, oil hemp plugging materials are also used to block and seal all the grooves and the gaps of the pipe holes through which the optical cables pass through each floor in the building, and fire prevention measures such as blocking fire-proof materials should be taken to achieve the effect of moisture and fire prevention. When laying the optical cable, an appropriate length should be reserved according to the design requirements. Generally, 5m-10m should be reserved at the equipment end. If there are special requirements, it should be appropriately extended.


The laying of outdoor optical cables can be divided into many types according to different environments. In environments such as long-distance trunk lines, local telephone relays, underwater and submarine communications, local area networks, and private networks, the selection methods of optical fiber wiring are different. The main laying methods include overhead, direct burial, pipeline, underwater, indoor, etc.


1. Aerial optical cable

Aerial optical cables are mostly used on utility poles. When laying overhead optical cables, the original overhead open line poles can be used, which can save construction costs and shorten the construction period. However, overhead optical cables are located at high places and are vulnerable to natural disasters such as typhoons, ice, floods, etc., as well as external forces and weakening of their own mechanical strength. Therefore, the failure rate of overhead optical cables is higher than that of directly buried and pipeline-type optical fibers. There are two main laying methods:


Hanging wire type: first fasten it on the pole with a hanging wire, and then hang the optical cable on the hanging wire with a hook, and the load of the optical cable is carried by the hanging wire. Self-supporting: A self-supporting optical cable is used. The optical cable is in an "8" shape, and the upper part is a self-supporting wire. The load of the optical cable is carried by the self-supporting wire.


2. Directly buried optical cable

Direct buried optical cable Direct buried optical cable is usually buried directly underground, which requires it to have the performance of resisting external mechanical damage and the performance of preventing soil corrosion. Depending on the soil quality and environment, the depth of the optical cable buried underground is generally between 0.8 meters and 1.2 meters. When laying, care must also be taken to keep fiber strain within allowable limits.


The laying of direct buried optical cables requires trenching. The trenching standards are generally 1.2 meters for ordinary soil, 1.0 meters for semi-stone, and 0.8 meters for quicksand, and 1.2 meters when crossing iron and highway. For sandy soil, the width of the ditch bottom is generally 30CM. When two or more optical cables are to be laid, a distance of 5CM should be maintained between the optical cables. Steel pipes or rigid plastic pipes should be pre-buried in the sections where the road surface is often under pressure. When laying the optical cable, it should be laid in an "S" shape when it encounters special sections such as slopes, crossing iron, and highways.


3. Pipeline cable

Pipe laying is generally in urban areas, where the environment is not as bad as overhead optical cables and direct-buried optical cables, so there are no special requirements for the sheath of optical cables, and no armoring is required. Before pipe laying, the length of the laying section and the position of the connection point must be selected. When laying, mechanical bypass or manual traction can be used. The pulling force of one pull should not exceed the allowable tension of the optical cable. The materials for making pipes can be selected from concrete, asbestos cement, steel pipes, plastic pipes, etc. according to geography.


The size of the urban standard pipe hole is generally ф90MM, which can accommodate 3 plastic sub-pipes of 3~4 inches. 1-inch tube is suitable for optical cable with diameter less than 20MM. It is easy to twist during the laying process of the sub-pipe. When the twist pitch is within 10 meters, the friction between the optical cable and the inner wall of the sub-pipe will increase, which will bring certain difficulties to the laying of the optical cable. Therefore, laying plastic sub-pipes should be avoided. distortion. When laying the optical cable in the pipeline, the entrance and exit routes of the manhole must be turned, and the curve and the height difference of the manhole in the pipeline should be equipped with a guiding device to reduce the friction of the optical cable and reduce the traction tension of the optical cable.


The special tool "nylon rod" should be used in the optical cable pulling sub-pipe, which can be pulled by appropriate engineering and technical personnel in a row. After the optical cable is pulled, the remaining cables in each manhole shall be manually placed on the specified bracket. For future safety, hoses or PE hoses are generally used for protection, and they are rolled and fixed with cable ties. The end of the optical cable should be hung on the wall of the manhole after leaving a suitable length of coil, and do not soak in water.


4. Underwater optical cable

Among these several optical cable laying methods, the laying environment of underwater optical cable is the most severe, so the technology and measures to repair the fault are also much more difficult. Generally, the underwater optical cable must be armored with steel wire or steel tape, and the structure of the sheath should be comprehensively considered according to the hydrogeological conditions of the river. For example, in the case of stony soil and seasonal riverbed with strong scour, the optical cable is subject to wear and high tension, not only thick steel wire is required for armoring, but even double-layer armoring is required. The construction method should also be selected according to the river width, water depth, flow velocity, river bed, flow velocity, and soil quality of the river bed.


Second, the skills and precautions of fiber optic wiring


Regarding the attenuation of optical fiber signals, it is mainly divided into two aspects: internal attenuation and external attenuation. Intrinsic attenuation is determined by the material the fiber is made of, while extrinsic attenuation is closely related to the construction process. So in terms of reducing intrinsic attenuation, we have to learn to choose the right fiber. For example, the high-quality fiber provided by Pheenet Finite can reduce the signal attenuation to a minimum. In addition, pay attention to the selection of different optical fibers for different environments. noodle


Fiber types used in three common environments:

1. If the transmission distance is less than 2km, you can choose multi-mode fiber. If it exceeds 2km, you can use relay or single-mode fiber.


2. When selecting optical fibers used in buildings, attention should be paid to their flame retardant, toxic and smoke characteristics. Generally, the type of flame retardant but smoke can be used in the pipeline or forced ventilation; if it is in an exposed environment, the type of flame retardant, non-toxic and smoke-free should be used.


3. When the outdoor optical cable is directly buried, the armored optical cable should be selected. When overhead, an optical fiber with a black plastic outer jacket with two or more reinforcing ribs can be used.


There are several basic requirements for fiber optic cabling:

1. The detection optical fiber is stored in the cable reel, and the protective packaging is reserved before installation, and the cable reel is kept upright to prevent the cable from falling and damaging the detection optical fiber. During storage and transportation, always pay attention to detecting the bending radius and tension limit of the optical fiber.


2. During the optical fiber wiring process, the tensile force of Φ0.9 fiber is less than 4Kg; the tensile force of Φ3 fiber is less than 10Kg; the tensile force of armored fiber is less than 30Kg


3. When on-site optical fiber payout, use a slender rod to pass through the center of the fiber winding reel horizontally, and rotate the reel to pay off. It is forbidden to put the optical fiber reel upright on the ground, and rotate the optical fiber from the reel to pay off.


4. The end of the optical fiber away from the temperature measuring host should be treated as follows: take the last 30 cm long Φ0.9 optical fiber (if there is a sheath or armor, remove it), and wrap the optical fiber in a small circle with a diameter of 1 cm for 10 turns.


5. The bending radius of the detection fiber must be greater than 30mm, and the detection fiber should not be severely worn or crushed when passing through walls or pipes.


6. When multiple optical fibers pass through the same long metal or PVC pipe, it is necessary to ensure that the optical fibers are passed through at one time, and the optical fibers cannot be passed through several times.


7. The detection fiber is prohibited from falling, vigorously twisting, gravitational impact, overstretching, etc., to avoid the detection of fiber core breakage.


8. The type and specification of the optical fiber used in the project should meet the design regulations and requirements.


The following points should also be considered during construction:


1. Before carrying out fiber optic wiring, be sure to select strictly trained technicians for fiber termination and maintenance. In addition, very complete design and construction drawings must be prepared for convenient and reliable construction and future inspections.


2. Be careful not to put the optical cable under heavy pressure during the wiring process, and place the optical cable carefully to prevent it from being worn and punctured by hard objects. Also, the traction force should not exceed the maximum lay tension.


3. The length of one laying should not be too long (usually 2km, when wiring, it should be pulled from the middle to both sides).


4. In the process of laying optical fibers, the influence of bends should also be considered. Generally, the turning of the fiber should be greater than 20 times the diameter of the fiber itself.


5. If the wiring needs to pass through walls and floors, be sure to add a protective plastic tube with a mouth guard to the optical fiber, and fill the tube with flame-retardant filler. A certain amount of plastic pipes can also be pre-laid in the building.


6. When the optical fiber is used in the backbone network, at least 6-core optical cable should be used in the wiring room of each floor, and 12-core optical cable should be used for advanced applications. This is considered from three aspects: application, backup and expansion.


7. The most important thing for long-distance optical fiber laying is to choose a suitable path. The shortest path is not necessarily the best, but also pay attention to the right to use the land, the possibility of erection or burial, etc.


8. When laying in mountainous areas and high-voltage power grid areas, pay attention to the reliable grounding of metal objects in the optical fiber. Generally, there are 3 grounding points per kilometer, or non-metallic optical fibers are used.


Fiber optic cabling is the general trend and has slowly become the dominant building cabling medium. In the near future, since the optical fiber can be equipped with no wiring room and active hardware, the cost of intermediate links can be saved, and the total cost can be greatly reduced, so the application of optical fiber to the desktop will also be realized. Finite focuses on the R&D and sales of optical fiber cabling products.


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