Laying of optical cable: norms, methods and rules of installation

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Optical Cable Installation: Rules, Methods, Installation and Standards

The installation of optical cable is a critical stage of network construction that determines its throughput and service life. Glass fiber requires careful handling, compliance with bending radii and environmental conditions. This article brings together current standards, technologies for different environments and practical recommendations for installation. The full list of factory‑manufactured versions is presented in the optical cable section.

1. Regulatory Framework and General Rules

The installation of fiber‑optic communication lines is regulated by a set of documents: SP 134.13330.2012 “Communication Systems of Real Estate Objects”, PUE (Chapters 2.3, 2.4), RD 45.120‑2000. The standards set the burial depth, distances to engineering utilities, requirements for closures and fire safety. The manufacturer’s installation instructions contain details for the specific cable type. Before starting work, the design and working documentation must be studied, which reflects the routes, the number of fibers and the types of splice closures. Any deviation from the design requires approval. For cost estimates, the GESN collections for the installation of communication equipment are used, which take into account the costs of payout, tensioning, closure installation and connection.

2. Types of Installation and Application Conditions

The installation method is chosen based on the line purpose and the environment. Several main options are distinguished:

• for outdoor installation – overhead, in the ground, in cable ducts, underwater;
• for indoor installation – inside buildings, in trays, cable channels;
• for direct burial – armoured models resistant to crushing;
• for installation in cable ducts – with a reinforced polyethylene sheath;
• for indoor installation – non‑combustible LSZH compositions;
• for vertical installation – with additional fastening and a lightweight construction.

Each type imposes its own requirements on bending radius, installation temperature and protection. An in‑depth description of fiber types and their characteristics is given in the material details about optical cable. External installations are often performed with an armoured conductor, and outdoor installation of a self‑supporting optical cable makes it possible to dispense with an additional messenger wire. For indoor installation, fire safety certificates are mandatory, especially in places of mass assembly of people.

3. Preparation for Installation: Tools and Conditions

The installation kit includes a wide list of devices:

• payout rollers with a polymer coating, a drum jack;
• a winch with a dynamometer controlling the pulling force;
• an optical fusion splicer or mechanical connectors;
• an OTDR reflectometer for measuring fiber parameters;
• a standard set of tools: a stripper for removing the sheath, scissors, a crimper for connectors, side cutters;
• a closure entry kit including sealing rings and heat‑shrinkable tubes;
• cross‑connect equipment and adapters.

The installation temperature of the optical cable is standardised by the manufacturer. For a polyethylene sheath, the lower limit is –15 °C, for LSZH – 0 °C. At lower values, the cable is kept warm for at least 12 hours. The installation conditions inside a building must exclude direct exposure to sunlight, aggressive media and mechanical damage. The bending radius during installation is maintained at not less than 20 cable diameters, and after completion of work – not less than 10 diameters. Violation of this requirement leads to an increase in attenuation and microcracks. When laying multi‑module constructions in trays, group laying is permitted, but overlaps and sharp edges that can deform the sheath should be avoided.

4. Underground and Trench Installation

Underground installation is the most common method for trunk and intrazonal lines. The depth of laying optical cable in a trench must be not less than 0.6 m for armoured cable and up to 1.2 m in zones of crossing with roads and squares. The bottom is covered with a sand bed 10–15 cm thick, the cable is laid in a snake pattern without tension, then it is covered with the same layer of sand, soil and warning tape. In rocky and frozen soils, additional protection is provided – concrete slabs or an HDPE pipe.

The installation of an armoured optical cable with steel tape or wires makes it possible to dispense with a pipe on straight sections, but near crossings with other utilities a pipe is mandatory. For laying underground lines in cramped conditions, horizontal directional drilling is used, which reduces the volume of earthworks and allows obstacles to be bypassed. When crossing power cables, a clear distance of at least 0.5 m is maintained; during parallel laying, the low‑current optical lines are located above the power ones. After laying, reflectometric measurements are mandatory to check the integrity of the fibers.

5. Installation in Cable Ducts and Pipes

In cities and on industrial sites, optical cable is pulled into free channels of asbestos‑cement or polyethylene pipes. The installation of fiber‑optic cables in cable ducts requires preliminary cleaning of the channel and the use of a water‑based lubricant that does not destroy the sheath. As a rule, one pipe accommodates one cable; laying of up to five or six optical conductors in one free channel is permitted. The pulling force is monitored with a dynamometer – it must not exceed the rated values, usually 100–150 kgf. Exceeding the force threatens elongation of the fibers and an increase in attenuation.

Installation in an HDPE pipe is used for protection against aggressive soil, water and rodents. The pipe is laid with a slope for condensate drainage, and its internal diameter is chosen so that the cable occupies no more than 40 % of the cross‑section. For pulling, a steel wire or a fiberglass rod with a pulling stocking that evenly compresses the sheath is used. After pulling, the ends of the pipe are sealed to prevent the ingress of dirt and water. At the points of building entry, the pipe must protrude above the ground by at least 30 cm, and its mouth is sealed with heat‑shrink.

6. Aerial Installation on Poles

Aerial installation of optical cable is cheaper than underground and does not require earthworks. It is carried out on existing poles of power lines, contact networks or lighting columns. For this, a self‑supporting optical cable is manufactured, in which a strength member is embedded – a fiberglass rod or aramid yarns. The installation of a self‑supporting cable is carried out with payout over rollers and tensioning to a specified sag. Fastening to the poles is carried out with anchor and supporting clamps, with anchor clamps placed on terminal and angle poles.

Installation on poles requires compliance with clearances: the distance from the lowest point of the conductor to the ground must be not less than 4 m for communication lines in populated areas and 5 m above a carriageway. When suspending on high‑voltage poles, all‑dielectric versions are used that are insensitive to induced currents. Overhead communication installation is often combined with the suspension of telephone cables, maintaining a distance of 0.5 m. At building entries, a drip loop must be made, and the cable itself is protected by a corrugated tube or a metal conduit to a height of up to 2.5 m from the ground.

7. Indoor Installation and Building Entry

For indoor installation in premises, optical cable with an LSZH sheath that does not propagate combustion is used. Installation inside buildings is carried out in trays, boxes, cable channels, as well as on open structures. When installed in trays, the cable is fixed with ties at intervals of 1–1.5 m. In vertical risers, it is additionally fastened every 50–70 cm to exclude slipping. Laying of multi‑module constructions in trays permits group installation, but overlaps and sharp edges capable of deforming the sheath should be avoided.

The entry of an optical cable into a building is made through an embedded sleeve or an opening that is sealed after pulling. The closure entry kit includes sealing rings, a heat‑shrinkable tube and fasteners. The cable entry is protected from rain by making a downward bend – a drip loop. Inside the building, an optical distribution frame is mounted on the floor distribution board. The installation of an optical distribution frame includes the installation of adapters, the connection of patch cords and the splicing of fibers with pigtails. The subscriber connection scheme is built from the lead‑in cable through an outlet and a patch cord to the ONT terminal device, which converts the optical signal into an electrical one for a TV or a router.

8. Joint Installation and Fiber Splicing

The joining of factory lengths of optical cable is performed using closures. Splice closures can be butt and through‑type, for multi‑module and single cables. The closure installation process includes sheath stripping, removal of the hydrophobic filler, cleaning the fibers from buffer coatings and their splicing. Splicing is carried out with an automatic fusion splicer that aligns the fibers by the core with an accuracy of up to 0.01 µm and performs thermal splicing. The splice point is protected by a heat‑shrinkable splice protector and placed in the splice tray of the closure. After placing all spliced fibers, the closure is sealed with heat‑shrink or a mechanical lock, providing IP68 protection.

For branches, mechanical connectors and SC, LC connectors are used. Connection to a TV or a router is made through an ONT optical terminal that converts the optical signal into an electrical one. The connection scheme includes a lead‑in cable, an outlet, a patch cord and a terminal device. All equipment must be certified and comply with the standards for attenuation and back reflections.

9. GESN and Cost Estimate Standards

The cost of work on laying a fiber‑optic cable is calculated according to GESN installation 81‑02‑10‑2020 and GESNm 81‑03‑10‑2020. The standards take into account payout, tensioning, closure installation, and connection to distribution frames. Direct costs consist of labour intensity and the cost of materials, including the entry kit and the installation set. For aerial suspension, separate rates are applied, for underground laying – rates for earthworks. When compiling estimates, transport costs and climatic coefficients must be taken into account.

10. Common Mistakes and Quality Control

The following miscalculations are most often made during the installation of fiber‑optic lines: excessive tension during pulling, violation of the bending radius at turns, poor‑quality sealing of closures, failure to observe the temperature regime when laying in frost, lack of cable reserve in closures. After completion of installation, reflectometric measurements are carried out, checking the integrity of the fibers and the attenuation on each factory length. The test report is attached to the cable line passport. The frequency of operational monitoring is once a year, and on critical sections – once every six months. Only strict adherence to the technology guarantees a long service life of the optical network.

11. Conclusion

Proper installation of optical cable is the key to high throughput and durability of the network. Compliance with depth standards, temperature restrictions, bending radii, as well as high‑quality installation of closures and distribution frames make it possible to avoid signal losses and failures. To select the required type and fiber type, refer to the catalogues and technical manuals of the manufacturers.

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