Overhead Optical Cable Construction Guidelines

In the communications industry, how to construct overhead optical cable is a problem that many front-line communications construction workers will encounter. If we can reduce failures and increase the service life of optical cables by carrying out communication optical cable construction in a standardized manner, it is worth understanding and learning for us telecommunications construction workers. To this end, overhead optical cable construction generally has the following eight steps.

Pole

1. Choose the type of pole

The basic pole height is 7m and the tip diameter is 150mm. In case of special sections, crossing obstacles or roads or railways, the pole height of 8m, 9m, etc. can be selected according to the actual terrain.

2. 7m basic pole hole depth

If the surface is stone, the depth needs to be 0.9m, and if the surface is other soil, the depth needs to be 1.2m.

3. Pole distance

The basic pole distance is 50m, which can be adjusted to 60m according to the terrain of mountainous areas. In some areas where the terrain is restricted, such as crossing a river, the pole distance should be handled as an overhead flying line. We will explain the handling method in detail in the later part of laying the suspension line.

4. Pole number

The design paragraph should be written as an independent unit. The last character should be 2.5m from the ground. The pole number should face the road, with black characters on a white background and Arabic numerals as the font.

5. Construction precaution

• The pole can be erected only after the hole depth is checked and qualified.
• The vertical deviation between the center line of the pole (middle pole) on the straight line and the center line of the route should be less than 5 cm, and the pole itself should be vertical; the root of the corner pole should be moved inward by half a pole root (10-15 cm), and after the tension wire is tightened, the pole tip should be tilted toward the outer corner by about one pole tip. The terminal pole body should be tilted toward the tension wire side by 10-20 cm.
• The root fixing devices such as the pole root chassis and chuck should meet the design requirements.
• The backfill should be compacted layer by layer, and the backfill of the urban solidified road surface should be flush with the road surface. The backfill in the suburbs should be 10-15 cm higher than the road surface.
• When the line crosses the 10KV power line, lightning arresters should be installed on both poles.

Install the Wire Pulling

1. The wire pulling procedure should meet the design requirements.

2. After checking that the anchor depth is qualified, the anchor can be buried and the guy wire installed. The actual unearthed length of the guy wire anchor is 30 to 60 mm.

3. The distance-to-height ratio of the guy wire should be 1, not less than 0.75. The distance-to-height ratio of the support pole should be 0.6, not less than 0.5.

4. The angle pole guy wire should be on the extension line of the inner angle bisector. The terminal guy wire should be on the center line of the line. If the angle depth is greater than 15m, two top guy wires should be installed on the corner pole.

5. A windproof guy wire (herringbone guy wire) is set for every 16 steps of the straight pole. An anti-icing guy wire (four-way guy wire) is set for every 32 poles. The downwind guy wire should be set 10-15cm above the suspension wire and serve as an auxiliary wire, and the side guy wire should be set 25-30cm below the suspension wire.

6. Wire pulling method: In this phase of the project, the upper handle of the wire pulling adopts the method of splinting and wrapping, and the middle handle adopts the method of wrapping. Please see the attached figure for the binding specifications.

7. For cables near high-voltage power facilities, grounding devices should be installed according to design requirements.

8. When it is impossible to bury anchor blocks in rocky areas, holes can be drilled in rocks (non-weathered rocks), 1:3 cement mortar can be poured into 1/2 of the hole, threaded steel handle anchors (at least 26mm in diameter and 0.5m in length) can be driven in and sealed and smoothed, with the steel handle at 90° to the wire direction.

Laying Down the Suspension Wire

Technical specification requirements:

1. When the first suspension wire is installed on the pole line, the suspension wire should be set on the left side of the forward direction (facing the B end). The suspension wire should be laid below the power line as much as possible.
2. The optical cable suspension wire is fixed to the pole with a suspension wire clamp and a three-eye single-slot clamp. The installation position of the suspension wire clamp should be no less than 50 cm from the top of the pole, and no less than 25 cm in special cases.
3. The termination of the suspension wire adopts the other winding method, and the continuation of the suspension wire adopts the “sleeve connection” method. The two ends of the sleeve are uniformly wrapped. If the overhead suspension wire is found to have jump strands, loose twisting and other damaged parts that damage the mechanical strength of the suspension wire, they should be cut off before continuation.
4. The verticality of the suspension wire should comply with the design requirements and should be equidistant from the ground. The slope change of the suspension wire should not exceed 5% of the pole distance. When it exceeds, an auxiliary device for the pitch angle should be installed; when the corner depth is greater than 5m, an inner or outer angle auxiliary device is required.
5. The base station is introduced by soft hanging wire, that is, the hanging wire is not tightened. Steel stranded wire or 4.0 iron wire is used according to the actual situation. The terminal uses the terminal pull and fixes it with the base station room to introduce the optical cable into the room.

Construction requirements:

1. Before going up the pole, check the firmness of the foot buckle, safety belt and the environment around the pole to avoid safety accidents.
2. When the optical cable line crosses the power line, it is necessary to contact the local electrician and take power suspension or other safety measures before the cable crossing construction can be carried out to ensure the personal safety of the power supply line and personnel. When crossing the road, warning signs must be set up at the corresponding locations to ensure the safety of construction workers.
3. In some areas where the terrain is restricted, such as crossing the river, the span is long, it should be treated as an overhead flying line.

When the pole distance is ≤120m, 7/2.2 steel strands are used.

When the pole distance is 121m-300m, long poles are used (top wires or three-way wires are set as auxiliary wires), 7/2.6 steel strands are used, and 7/3.0 steel strands are used for wires.

When the pole distance is 301m-500m, flying wires are used (main and auxiliary suspension wires are used), 7/2.2 steel strands are used for main suspension wires, 7/2.6 steel strands are used for auxiliary suspension wires, four-way wires are used for crossing poles, and three-way wires are set for adjacent poles. Square guy wire, cross pole as auxiliary wire (main and auxiliary wire), auxiliary wire terminates at adjacent pole, guy wire uses 7/3.0 steel strand.

When pole distance >500m, fly wire treatment (main and auxiliary wire), cross pole erects H pole, main wire uses 7/2.6 steel strand, auxiliary wire uses 7/3.0 steel strand, cross pole makes six guy wires, adjacent poles are set with three square guy wires, cross pole as auxiliary wire (main and auxiliary wire), auxiliary wire terminates at adjacent pole, guy wire uses 7/3.0 steel strand.

Lightning Protection Wire and Ground Wire

Requirements for setting up lightning protection grounding wires:

1. It is particularly required that terminal poles, lead-in poles and 5 poles in front of the bureau must be equipped with direct buried lightning protection grounding wires.
2. The discharge terminal, corner pole, crossing pole, branch pole, slope top pole and poles above 12m must be equipped with pull-wire lightning protection grounding wires, and the suspension wires are also grounded at the same time. The lightning protection wire is 10cm higher than the pole top.
3. The poles, pull wires and suspension wires crossing both ends of the high-voltage power line must be grounded. The overhead lines parallel to the power lines are grounded once every 200m.
4. Each pull line is connected to the ground with the help of a pull line and a lightning protection line is set here. The four-way pull line is directly connected to the ground with a ground rod. For all overhead lines, it is guaranteed to be grounded at least once every 1 kilometer.
5. Grounding of optical cables in the machine room: After the optical cable enters the machine room, the optical cable reinforcement core must be connected to the ODF frame lightning protection ground wire row, and the lightning protection ground must be connected to the outdoor ground wire row with a 16mm2 power cable.

Optical Cable Laying

1. The laid optical cables must be optical cables that have passed the optical cable single-reel inspection.

2. The optical cable hook uses a 25mm plastic support hook with a spacing of 50cm.

3. The overhead optical cable is reserved for one place for every 10 poles, with a reserved amount of 10 meters per place and a coil diameter of 60cm. 20 meters are reserved at each end of the inlet and outlet, and 8-10 meters are reserved for each pole before and after the junction box at the optical cable joint.

A “U”-shaped expansion bend is reserved for every 3 poles. The optical cable is protected by a 20cm long corrugated tube at the point where it contacts the pole.

The poles are tied with a single-strand leather wire for 50 to 80cm on both sides. The lowest point of the expansion bend is 25-30cm away from the suspension wire. Special sections (such as crossing rivers, bridges, etc.) are reserved according to actual conditions.

4. The upper part is protected by a steel pipe, requiring the ground part to be no less than 2.5m, the underground part to be no less than 0.5m, and the sub-pipe to extend at least 1m from the suspension wire and be treated with a drip bend. The sub-pipes are tied every 50cm.

5. A special protective sleeve is used to protect the intersection of overhead optical cables, power lines and other communication poles. The protective sleeve should extend at least 1m from the edge of the power line and be grounded.

6. Warning issues: Roadside poles should be painted red and white, roadside wires should be installed with reflective tubes, cross-road suspension wires should be installed with reflective plates (at least 4m) and billboards in the middle.

And other billboards should be set up at bridge crossings, obstacles, joints, densely populated areas, etc., and a warning sign should be set up every 5 poles on river crossing poles, joint poles, optical cable reserved poles, branch poles, and other sections. The side with words on the optical cable warning sign should face the road.

7. Identification issues: hang signboards (at the entrance station and ODF rack), identify the pigtails, and display the fiber sequence comparison table (fiber number, color spectrum, opposite station, opposite fiber number) on the panel.

Optical Cable Splicing

Optical cable splicing is a key link in the construction of communication line projects. The quality of splicing and installation will directly reflect the communication transmission performance and affect the final quality of the entire project.

1. Optical cable splicing and testing personnel must undergo special technical training before they can take up their posts.

2. Before splicing, check whether the specifications, end types, and fiber core distribution of the optical cable meet the requirements of the design documents. Optical cable splicing must be monitored synchronously with OTDR, and problems must be dealt with in a timely manner.

3. The packaging of the joint box must be strictly carried out in accordance with the process requirements provided by the supplier.

4. Place a splicing responsibility card in the joint device.

5. The loose tube at the end is required to be protected by a fiber heat shrink tube with a moderate length.

6. The fiber joint loss (two-way average) is ≤0.08dB/piece.

7. There are many sections connected from the optical cable joint box in this project. Therefore, when connecting the optical cable core, the original fiber core resources must be carefully verified and connected correctly to ensure communication safety.

Optical Cable Termination and Testing

Optical cable termination:

1. Sufficient reserved optical cables should be reserved according to regulations or design requirements. After the reserved optical cables are terminated, they should be coiled on the reserved bracket of the terminal pole. It is not allowed to be placed on the roof of the machine room or hung on the iron tower or terminal pole.

2. The optical cables in the machine room should be protected and tied according to the design requirements.

3. The connectors of the single-core optical fiber should be inserted into the optical distribution frame in the order of design requirements. The interface end of the optical distribution frame (distribution plate) that is not connected to the optical fiber should be covered with a plastic dust cap.

4. The curvature radius of the optical fiber in the rack should be greater than that specified in its manual.

5. At the termination of the optical fiber distribution frame (ODF), the metal components are led out with a copper core polyvinyl chloride sheathed cable and connected to the protective ground wire.

6. The direction and serial number of the optical fiber should be marked in a conspicuous place.

7. Optical cable test:
Test conditions: The entire section has been connected and the loss value of each joint has reached the index requirements, the fiber obstacle points have been handled, and the termination has been completed.

Average attenuation index of optical cable line: 1310nm is not more than 0.36dB/Km, 1550nm is not more than 0.22dB/Km.

Project Acceptance

1. After receiving the handover notice and completion documents, the construction unit (owner) should organize the branch construction department, maintenance department, supervision unit, construction unit, design unit, material suppliers, etc. to conduct an initial inspection of the project within seven days in accordance with the spirit of the relevant documents.

2. If any unqualified items are found during the initial inspection, the construction unit and manufacturer should immediately repair them until they are qualified, and the supervision unit should conduct re-inspection and supplementary inspection.

3. The construction unit should count the equipment, materials and materials in full according to the equipment and material attachment list and design drawings, and carry out the transfer and return of materials.

4. The acceptance team shall write the preliminary inspection report and engineering conclusions based on the preliminary inspection results and send a copy to the relevant units.

Summary and Suggestions

The above are eight aspects of the overhead optical cable construction specifications. Of course, there are still many details to pay attention to. This article can only cover some of the main points of the aerial optical cable construction.

As laying aerial optical cables is a low-cost, high-efficiency and reliable optical cable laying method, but it is also a highly technical job that requires construction personnel to have strong professional skills and practical experience. In order to ensure the quality of optical cable construction, it is recommended to strengthen the training and examination of relevant personnel on the basis of standardized construction, improve the management level of relevant practitioners, and build a more efficient and reliable optical cable communication network.

If you need to lay an aerial optical cable for long-distance network communication, please contact us to design and produce the most suitable optical cable for you according to the use environment and usage. If you encounter any difficulties in laying the overhead optical cable, you can also contact Bonelinks for timely technical support.