Cable cabling knowledge details

Optical fiber has been widely used in various transmission networks as a high-bandwidth and high-security transmission medium. Due to the high cost of cables and equipment, most of the fiber is used only for the network backbone, that is, the system wiring for the vertical backbone subsystem and the building group subsystem, to achieve the connection between buildings and between the floors.

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

The minimum allowable radius of curvature of the cable shall not be less than 20 times the outer diameter of the cable during construction, and shall not be less than 15 times the outer diameter of the cable. When the cable is laid, the traction force required to lay the cable shall not exceed 80% of the allowable tension of the cable, and the instantaneous maximum traction shall not exceed the allowable tension of the cable. The main traction force should be added to the reinforcing member of the optical cable, and the optical fiber cannot directly bear the tensile force.

Light wiring is usually divided into indoor wiring and outdoor wiring. We will analyze them in detail below.

First, optical cable classification and wiring knowledge

Indoor fiber optic cable is mainly used for laying horizontal subsystems and vertical trunk subsystems. The laying of the horizontal subsystem cable is very similar to that of the twisted pair, except that the cable has a lower tensile performance, so it should be more careful when pulling and the radius of curvature should be larger. The vertical trunk subsystem cable is used to connect the equipment room to the wiring closet of each floor, usually in the cable shaft or ascending room. In order to prevent sagging or slipping, the cable must be firmly fixed at the upper, lower and middle of the channel on each floor. In general, nylon cable ties or steel clips can be used for effective fixing. Finally, the linseed plugging material is also used to block and seal the gaps of all the slots and pipe holes through which the optical cables of each floor in the building pass, and fireproof measures such as adding fireproof materials should be taken to achieve the effects of moisture and fire prevention. When laying the optical cable, the appropriate length should be reserved according to the design requirements. Generally, the equipment should be reserved 5m-10m, and if necessary, it should be extended.

The laying of outdoor optical cables can be divided into many types depending on the environment. In long-distance trunk lines, urban dian relay, underwater and submarine communications, and local area networks, private networks, etc., the choice of fiber cabling is different. The main laying methods are overhead, direct burial, pipeline, underwater, indoor and so on.

1, overhead cable

Overhead optical cables are mostly used on electric 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 altitudes and are vulnerable to natural disasters such as typhoons, ice, floods, etc., and are also susceptible to external forces and weakened mechanical strength. Therefore, the failure rate of overhead optical cables is higher than that of direct-buried and pipeline-type optical fiber cables. There are two main methods of laying:

Suspension type: first fasten the pole with a hanging wire, then use the hook to suspend the cable on the hanging wire, and the load of the cable is carried by the hanging wire. Self-supporting: It adopts a self-supporting optical cable. The optical cable is in the shape of “8”, and the upper part is the self-supporting line. The load of the optical cable is carried by the self-supporting line.

2, direct buried optical cable

Direct buried cables are usually buried directly underground, which requires performance against external mechanical damage and corrosion resistance. Depending on the soil and environment, the depth of the cable buried in the ground is generally between 0.8 and 1.2 meters. At the time of laying, care must also be taken to keep the fiber strain within acceptable limits.

The laying of direct buried optical cable requires trenching. The standard of trenching is 1.2m for ordinary soil, 1.0m for semi-stone, 0.8m for quicksand, and 1.2m for crossing the iron and road. The bottom of the trench should be padded with 10cm fine soil or Sand, the width of the bottom of the ditch is generally 30CM. If two or more cables are to be laid, the cable should be spaced 5 CM apart. Steel pipes or pre-placed rigid plastic pipes shall be pre-buried on sections of the road surface where pressure is often applied. The laying optical cable shall be laid in an "S" shape when it encounters a special section such as slope, crossing iron or highway.

3, pipe cable

Pipe laying is generally in urban areas, and the environment is not as harsh as overhead cable and direct buried cable. Therefore, there is no special requirement for the cable sheath and no armoring is required. The length of the laying section and the position of the splicing point must be selected before laying the pipe. Mechanical bypass or manual traction can be used for laying. The traction of one traction should not exceed the allowable tension of the cable. The materials used for the production of pipes can be made of concrete, asbestos cement, steel pipes, plastic pipes, etc. according to geography.

The city standard tube hole size is generally ф90MM, which can accommodate 3 to 4 inch plastic sub-tubes. The 1-inch sub-tube is suitable for fiber optic cables with a diameter of less than 20 mm. When the sub-tube is laid, the distortion is easy to occur. When the twist pitch is within 10 meters, the friction between the cable and the inner wall of the sub-tube increases, which will bring certain difficulties to the laying of the cable. Therefore, the laying of the plastic sub-tube should be avoided. distortion. Pipeline cable laying should be through the entrance and exit route of the manhole, and the curve and the height difference of the pipe manhole should be timely arranged to reduce the friction of the cable and reduce the traction tension of the cable. The special tool “Nylon rod” should be selected in the cable traction tube, and the appropriate engineering and technical personnel can pull it. After the cable is pulled, the remaining cable in each hole is manually placed on the specified bracket. For future safety, it is generally protected by a hose or PE hose and fixed with a tie. The end of the cable should be hung on the wall of the manhole after the appropriate length of the coil, do not soak in the water.

4, underwater cable

Among these kinds of cable laying methods, the laying environment of the underwater cable is the most severe, so the techniques and measures for repairing the fault are also much more difficult. Generally, the underwater optical cable must be constructed with steel wire or steel tape. The structure of the protective layer should be considered comprehensively according to the hydrogeological conditions of the river. For example, in the case of stony soil and scouring seasonal riverbeds, the cable is subject to wear and tear, and it requires not only the thick steel wire to be armored, but also the double-layer armor. The method of construction should also be selected according to river width, water depth, flow rate, riverbed, flow rate, riverbed soil quality, etc.

Second, the fiber wiring tips and precautions

Regarding the problem of fiber signal attenuation, it is mainly divided into two aspects: intrinsic attenuation and extrinsic attenuation. The internal attenuation is determined by the material made of fiber, while the external attenuation is closely related to the construction process. So in terms of reducing the internal attenuation, we have to learn to choose the right fiber. For example, high-quality fiber provided by the Flying Speed ​​(FS) can minimize signal attenuation. Also, pay attention to different environments and choose different fibers. surface

The type of fiber selected for the three common environments:

1. If the transmission distance is within 2km, multimode fiber can be selected, and more than 2km can be used for relay or single mode fiber.

2. The fiber used in the building should pay attention to the characteristics of flame retardant, poison and smoke when selecting. Flame-retardant but smoke-free types are generally available in pipelines or forced ventilation; in exposed environments, flame retardant, non-toxic and smoke-free types should be used.

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

There are several basic requirements for fiber optic cabling:

1. The probe fiber is stored in the cable tray. The protective package is retained before installation and the cable tray is kept upright to prevent cable breakage and damage to the probe fiber. Always pay attention to the detection of fiber bending radius and tension limit during storage and transportation.

2. In the fiber-optic wiring process, the Φ0.9 fiber pull force is less than 4Kg; the Φ3 fiber pull force is less than 10Kg; the armored fiber pull force is less than 30Kg

3. When the fiber is placed on the spot, use the slender rod to horizontally pass through the center of the fiber winding disk, and rotate the wire to release the wire. It is forbidden to put the fiber winding disk on the ground and rotate the fiber from the disk.

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

5. The bending radius of the detecting fiber must be greater than 30mm. Do not wear or crush the detecting fiber when passing through the wall or through the pipe.

6. When multiple fibers pass through the same long metal or PVC pipe, ensure that the fiber passes through once and cannot pass through the fiber.

7. The detection fiber is prohibited from falling, strongly twisting, gravity impact, excessive force stretching, etc., to avoid detecting fiber core breakage.

8. The fiber type and specifications used in the project should meet the design requirements and requirements.

The following points should also be considered during the construction process:

1. Before performing fiber optic cabling, be sure to select a highly trained technician to perform fiber termination and maintenance. In addition, a complete set of design and construction drawings must be prepared for easy and reliable construction and future inspections.

2. Be careful not to subject the cable to heavy pressure during the wiring process. Carefully place the cable to avoid wear and strain on hard objects. In addition, the traction should not exceed the maximum laying tension.

3, the length of the deployment should not be too long (usually 2km, the wiring should start from the middle to the two sides).

4. In the process of laying the fiber, the influence of the curve should also be considered. Generally, the turn of the fiber should be greater than 20 times the diameter of the fiber itself.

5. If it is necessary to cross the wall and floor when wiring, be sure to add a plastic tube with a protective cover to the fiber, and fill the tube with a flame-retardant filler. A certain amount of plastic pipes can also be laid in advance in the building.

6. When the fiber is applied to the backbone network, at least 6-core fiber optic cable should be used in each floor wiring room. For advanced applications, 12-core fiber optic cable should be used as much as possible. This is considered in terms of application, backup and expansion.

7. The most important thing for a longer distance fiber installation is to choose a suitable path. The path that is not necessarily the shortest is ideal, and attention should be paid to the right to use the land, the possibility of erecting or burying.

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

Fiber optic cabling is the trend of the times and has gradually become the dominant building wiring medium. In the near future, fiber optics can save the cost of intermediate links by eliminating the need for wiring closets and active hardware, which can greatly reduce the cost of total cost, so it will also achieve fiber-to-desktop applications.