ÿWPCL ûÿ2BJ|xÐ ` ÐÐÌÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿH øÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÌÐÐ °°°è ÐÑ Âx„|ü@Ž ÑÐ Å°6Ø'°6Ø'Å ÐÓÓÃÃRecommendation L.10ÄÄ Ð € ÐÁàð#ÁOPTICAL FIBRE CABLES FOR DUCT, TUNNEL, AERIAL AND BURIED APPLICATIONƒ ÃÃIntroductionÄÄ Ð 8 ÐÁHÁWith the recent progress in optical fibre cable technology, optical fibres for telecommunication use have been applied to trunk and subscriber networks, indoor wiring and submarine sections. There are various kinds of installation, such as aerial, duct, cable tunnel, buried, on©premises and underwater. Thus, optical fibre cables are exposed to natural and man©made external factors. ÁHÁThere is a need to establish the mechanical and environmental characteristics of optical fibres which will satisfy operational requirements, and to advise on suitable testing methods. ÁHÁThis Recommendation advices on optical cables to be used in certain installation conditions. Cables for underwater and in©building applications require further study. 1.ÁHÁÃÃScopeÄÄ ÁHÁThis Recommendation: ÁHÁ©Âà  Ârefers to multi©mode graded index and single©mode optical fibre cables to be used for telecommunications networks, in duct, tunnel, buried and aerial installations;ÆÆ ÁHÁ©Âà  Âdeals with mechanical and environmental characteristics of the optical fibre cables concerned. The optical fibre dimensional and transmission characteristics, together with their test methods, should comply with Recommendations G.651 and G.652, which deal with multi©mode graded index and single©mode optical fibres respectively;ÆÆ ÁHÁ©Âà  Âdeals with fundamental considerations related to optical fibre cable from the mechanical and environmental points of view;ÆÆ ÁHÁ©Âà  Âacknowledges that some optical fibre cables may contain metallic elements, for which reference should be made to the Handbook "Outside plant technologies for public networks", and otherÆÆ ÁHÁÁ  ÁL©Series Recommendations; Ð Ð ÐÁHÁ©Âà  Âadvises that an optical fibre cable should be provided with cable end©sealing and protection during cable delivery and storage, as is common to metallic cables. If splicing components have been factory installed they should be adequately protected;ÆÆ ÁHÁ©Âà  Âadvises that pulling©devices can be fitted to the end of the cable if required.ÆÆ 2.ÁHÁÃÃCharacteristics of the optical fibres and cablesÄÄ 2.1ÁHÁÃÃMechanical characteristicsÄÄ 2.1.1ÁHÁÃÃFibre microbendingÄÄ ÁHÁSevere bending of an optical fibre involving local axial displacement of a few micrometres over short distances caused by localized lateral forces along its length is called microbending. This may be caused by manufacturing and installation strains and also dimensional variations of cable materials due to temperature changes during operation. ÁHÁMicrobending can cause an increase in optical loss. In order to reduce microbending loss, stress randomly applied to a fibre along its axis should be eliminated during incorporation into the cable, as well as during and after cable installation. 2.1.2ÁHÁÃÃFibre macrobendingÄÄ ÁHÁMacrobending is the resulting curvature of an optical fibre after cable manufacture and installation. ÁHÁMacrobending can cause an increase in optical loss. The optical loss increases if the bending radius is too small. 2.1.3ÂðHÂÃÃCable bendingÄÄÆÆ ÁHÁUnder dynamic conditions encountered during installation, the fibre is subjected to strain from both cable tension and bending. The strength elements in the cable and the installation bend radius must be selected to limit this combined dynamic strain. Any fibre bend radius remaining after cable installation shall be large enough to limit the macrobending loss or long©term strain limiting the lifetime of the fibre. 2.1.4ÁHÁÃÃTensile strengthÄÄ ÁHÁOptical fibre cable is subjected to short©term loading during manufacture and installation, and may be affected by continuous static loading and/or cyclic loading during operation (e.g. temperature variation). Especially in the case of aerial application, continuous loading during the full lifetime of the cable may be present. Fibre strain may be caused by tension, torsion and bending occurring in connection with cable installation and/or type of installation (e.g., aerial) and/or environmental conditions (e.g., wind, ice). ÁHÁExcessive cable tensile loading increases the optical loss and may cause increased residual strain in the fibre if the cable cannot relax. To avoid this, the maximum tensile strength determined by the cable construction, especially the design of the strength member, should not be exceeded. ÃÃNote 1ÄÄ © Where a cable is subjected to permanent loading during its operational life the fibre should preferably not experience additional strain. ÃÃNote 2ÄÄ © Aerial cable may be attached to a suspension wire. In this case, the strength member of the cable need only be designed to support the load during manufacture and installation. 2.1.5ÁHÁÃÃCrush and impactÄÄ ÁHÁThe cable may be subjected to crush and impact both during installation and operational life. ÁHÁThe crush and impact may increase the optical loss (permanently or for the time of application of the stress) and excessive stress may lead to fibre fracture. ÁHÁIn the case of self©supporting cylindrical aerial cables, the cable structure should be able to withstand the compression effects to prevent additional optical loss.Ô ñ,ÔŒ 2.1.6ÁHÁÃÃCable torsionÄÄ ÁHÁUnder dynamic conditions encountered during installation and operation, the cable may be subjected to torsion, resulting in the residual strain of the fibres and/or damage of the sheath. If this is the case the design of cable should allow a specified number of cable twists per unit length without an increase in fibre loss and/or damage to the sheath. 2.2ÁHÁÃÃEnvironmental conditionsÄÄ 2.2.1ÁHÁÃÃHydrogen gasÄÄ ÁHÁIn the presence of moisture and metallic elements, hydrogen gas may be generated. Hydrogen gas may diffuse into silica glass and increase optical loss. It is recommended that the hydrogen concentration in the cable, as a result of its component parts, should be low enough to ensure that the long©term effects on the increase of optical loss are acceptable. ÁHÁBy the use of dynamic gas pressurization, hydrogen absorbing materials, or careful selection and construction (moisture barrier sheath) or elimination of metallic components, the increase in optical loss can be maintained within acceptable limits. 2.2.2ÁHÁÃÃMoisture permeationÄÄ ÁHÁWhen moisture permeates the cable sheath and is present in the cable core, deterioration of the tensile strength of the fibre occurs and the time to static failure will be reduced. To ensure a satisfactory lifetime of the cable the long term strain level of the fibre must be limited. ÁHÁVarious materials can be used as barriers to reduce the rate of moisture permeation. Alternatively, filled metal©free cable constructions can be used. ÃÃNoteÄÄ © If required, minimum permeation is achieved by a longitudinal overlapped metallic foil. A continuous metallic barrier is effective to prevent moisture permeation. 2.2.3ÁHÁÃÃWater penetrationÄÄ ÁHÁIn the event of damage to the cable sheath or to a splice closure, longitudinal penetration of water in a cable core or between sheaths can occur. The penetration of water causes an effect similar to that of moisture. The longitudinal penetration of water should be minimized or, if possible, prevented. Techniques such as filling the cable core with a compound, providing discrete water blocks or water swellable tapes, or providing unfilled cable with dry©air pressurization, may be applied to prevent water penetration. ÁHÁWater in the cable may freeze and, under some conditions, can cause fibre crushing with a resultant increase in optical loss and possible fibre breakage. 2.2.4ÁHÁÃÃLightningÄÄ ÁHÁFibre cables containing metallic elements such as conventional copper pairs or a metal sheath, are susceptible to lightning strikes. ÁHÁTo prevent or minimize lightning damage, consideration should be given to Recommendation K.21 "Lightning protection of optical fibre cables". ÁHÁWhen a non©metallic cable is used, the cable should be filled and it should be protected against mechanical and thermal damage. 2.2.5ÁHÁÃÃBiotic damageÄÄ ÁHÁThe small size of an optical fibre cable makes it more vulnerable to rodent attack. Where rodents cannot be excluded, metallic protection should be provided. For further information reference should be made to Part IV©B, Chapter II of the Handbook "Outside plant technologies for public networks". 2.2.6ÁHÁÃÃVibrationÄÄ ÁHÁWhen optical fibre cables are installed on bridges they will be subject to relatively high amplitude vibrations of various low frequencies, depending on bridge construction and on the type of density of traffic. Cables should withstand these vibrations without failure or signal degradation. Care should be exercised, however, in the choice of installation method. ÁHÁUnderground optical fibre cable may be subject to vibrations from traffic, railways, pile©driving and blasting operations. Here again cables should withstand vibrations generated by these activities without degradation. ÁHÁA well established surveillance routine will identify activity in order to make a careful choice of route to minimize this type of problem. 2.2.7ÁHÁÃÃTemperature variationsÄÄ ÁHÁDuring their operational lifetime cables may be subjected to severe temperature variations. In these conditions the increase of attenuation of the fibres shall not exceed the specified limits. 2.2.8ÁHÁÃÃWindÄÄ ÁHÁFor optical fibre aerial cable, fibre strain may be caused by tension, torsion and vibration occurring in connection with wind pressure. Induced dynamic and residual strain in the fibre and may cause fibre breakage if the specified long©term strain limit of the fibre is exceeded. ÁHÁTo suppress any fibre strain induced by wind pressure, the strength member should be selected to limit this strain to safe levels, and the cable construction may mechanically decouple the fibre from the sheath to minimize the strain. Alternatively, to suppress fibre strain the cable may be lashed to a high strength support strand. ÁHÁIn aerial installations winds will cause vibrations and, in figure©of© eight and suspension wire installations, severe oscillations of the entire span of the cable may occur. Cables should be designed and/or installed to provide stability of the transmission characteristics in these situations. 2.2.9ÁHÁÃÃSnow and iceÄÄ ÁHÁFor optical fibre aerial cable, fibre strain may be caused by tension occurring in connection with snow loading and/or ice formation around the cable. Induced fibre strain may cause excess optical loss and may cause fibre breakage if the specified long©term strain limit of the fibre is exceeded. ÁHÁDynamic strain in the fibre may be induced by vibration caused by the action of snow and/or ice falling from the cable. This may cause fibre breakage. ÁHÁUnder the load of snow and/or ice, excessive fibre strain may easily beÔ ñ,Ô induced by wind pressure. ÁHÁTo suppress the fibre strain by snow loading and/or ice formation, the strength member should be selected to limit this strain to safe levels, and the cable profile may be selected to minimize snow loading. Alternatively, to suppress fibre strain the cable may be lashed to a high strength support strand. 2.2.10Á  ÁÃÃStrong electric fieldsÄÄ ÁHÁMetal©free aerial cables installed on high voltage power lines are susceptible to the influence of the electric field of these power lines which may lead to phenomena such as corona, arcing and tracking of the cable sheath. ÁHÁTo prevent damage, special cable sheath materials may have to be used depending on the level of electric field. 3.ÁHÁÃÃCable constructionÄÄ 3.1ÁHÁÃÃFibre coatingsÄÄ 3.1.1ÁHÁÃÃPrimary coatingÄÄ ÁHÁSilica fibre itself has an intrinsically high strength, but its strength is reduced by surface flaws. A primary coating must therefore be applied immediately after drawing the fibre to size. ÁHÁThe optical fibre should be proof©tested. In order to guarantee long© term reliability under service conditions, the proof©test strain may be specified, taking into account the permissible strain and required lifetime. ÁHÁIn order to prepare for splicing, it should be possible to remove the primary coating without damage to the fibre, and without the use of materials or methods considered to be hazardous or dangerous. ÁHÁThe composition of the primary coating, coloured if required, should be considered in relation to any requirements of local light©injection and detection equipment used in conjunction with fibre jointing methods. ÃÃNote 1ÄÄ © The coating should have a nominal diameter of 250 ÀÀm. ÃÃNote 2ÄÄ © The primary coated fibres should be proof tested with a strain equivalent to at least 0.5% for a duration of one second. The test method should be in accordance with IEC Publication 793©1. For aerial cable applications, taking into account large thermal changes and strong winds, a larger proof test strain may be necessary. ÃÃNote 3ÄÄ © Further study is required to advise on suitable testing methods for local light©injection and detection. 3.1.2ÁHÁÃÃSecondary protectionÄÄ ÁHÁSecondary protection of the fibre within the cable should be provided. ÃÃNote 1ÄÄ © Methods of secondary protection are described in the Handbook on the construction, installation, jointing and protection of optical fibre cables. Ð h ÐÃÃNote 2ÄÄ © When a tight secondary coating is used it may be difficult to use local light©injection and detection equipment associated with fibre jointing methods. ÃÃNote 3ÄÄ © To limit axial fibre stress, the mechanical coupling between fibre and cable should be minimized. 3.1.3ÁHÁÃÃFibre identificationÄÄ ÁHÁFibre should be easily identified by colour or position within the cable core. If a colouring method is used, the colours should be clearly distinguishable and have good colour©fast properties also in the presence of other materials, during the lifetime of the cable. 3.1.4ÁHÁÃÃSplicing propertiesÄÄ ÁHÁFurther study is required to advise on suitable testing methods for local light©injection and detection. 3.2 ÁHÁÃÃCable coreÄÄ ÁHÁThe make©up of the cable core, in particular the number of fibres, their method of protection and identification, the location of strength members and metallic wires or pairs, if required, should be clearly defined. 3.3ÁHÁÃÃStrength memberÄÄ ÁHÁThe cable should be designed with sufficient strength members to meet installation and service conditions so that the fibres are not subjected to excessive strain. ÁHÁThe strength member may be either metallic or non©metallic and may be located either in the cable core and/or in the sheath. ÁHÁFor example in the metal©free self supporting aerial cable the strength member may consist of a layer of aramid yarns located between the inner sheath and the outer sheath, or as a single glass fibre reinforced strand in a figure© of©eight construction. A knowledge of span, sag, wind and ice©loading is necessary to design such a cable. 3.4ÁHÁÃÃWater©blocking materialsÄÄ ÁHÁFilling a cable with water©blocking material is one means of protecting the fibres from water ingress. Any materials used should not be harmful to personnel. The materials in the cable should be compatible, one with the other, and in particular should not adversely affect the fibre performance, or any identification colours of the fibres. ÁHÁIn addition the material should be non©nutritive to fungus, electrically non©conductive, homogeneous and free from contamination. 3.5ÁHÁÃÃPneumatic ResistanceÄÄ ÁHÁIf the cable requires dry air pressurization during operation, the pneumatic resistance should be specified. ÃÃNoteÄÄ © It is intended that a cable can be pressurized only if it allows a flux of air which is in accordance with the criteria defined in Part III of the Handbook "Outside plant technologies for public networks". 3.6ÁHÁÃÃSheathÄÄ ÁHÁThe cable core should be covered with a sheath suitable for the relevant environmental and mechanical conditions associated with storage, installation and operation. The sheath may be of a composite construction and may include strength members.Ô ñ,ÔŒ ÁHÁSheath considerations of optical fibre cables are mostly those applied metallic conductor cables. Consideration should also be given to the amount of hydrogen generated from a metallic moisture barrier. The minimum acceptable thickness of the sheath should be stated, together with any maximum and minimum allowable overall diameter of the cable. ÃÃNote 1ÄÄ © One of the most common sheath materials is polyethylene. There may be however, some environmental conditions where it is necessary to minimize the flammability of a cable and limit the emission of fumes, smoke and corrosive products. Special materials should be used for the cable sheath in these situations. ÃÃNote 2ÄÄ © For directly buried cables installed in areas with chemically contaminated soils (acids, hydrocarbons, etc.) specially designed cable sheath combinations may be used. ÃÃNote 3ÄÄ © In the case of aerial cables the outer sheath should be resistant to the degradation due to ultraviolet radiation. 3.7ÁHÁÃÃArmourÄÄ ÁHÁWhere additional tensile strength or protection from external damage is required, armouring should be provided over the cable sheath. ÁHÁArmouring considerations of optical fibre cables are mostly those applied to metallic conductor cables. However, hydrogen generation due to corrosion must be considered. It should be remembered that the advantages of optical fibre cables, such as lightness and flexibility, will be reduced when armour is provided. ÁHÁArmouring for metal©free cables may consist of aramid yarns, glass fibre reinforced strands or strapping tape etc. 3.8ÁHÁÃÃIdentification of cableÄÄ ÁHÁIf a visual indentification is required to distinguish an optical fibre cable from a metallic cable, this can be done by visibly marking the sheath of the optical fibre cable. 4.ÁHÁÃÃTest methodsÄÄ 4.1ÁHÁÃÃTest methods for mechanical characteristicsÄÄ ÁHÁThis section advises appropriate tests and test methods for verifying the mechanical characteristics of optical fibre cables. ÃÃNoteÄÄ © The second edition (1987) of IEC Publication 794©1 is referred to throughout this section. 4.1.1ÁHÁÃÃTensile strengthÄÄ ÁHÁThis test method applies to optical fibre cables installed under all environmental conditions. ÁHÁMeasurements are made to examine the behaviour of the fibre attenuation as a function of the load on a cable during installation. ÁHÁThe test should be carried out in accordance with IEC Publication 794©1©E1. ÁHÁThe amount of mechanical decoupling of the fibre and cable can be determined by measuring the fibre elongation, with optical phase shift test equipment, together with the cable elongation. ÁHÁThis method may be non©destructive if the tension applied is within the operational values. 4.1.2ÁHÁÃÃBendingÄÄ ÁHÁThis test method applies to optical fibre cables installed under all environmental conditions. ÁHÁThe purpose of this test is to determine the ability of optical fibre cables to withstand bending around a pulley, simulated by a test mandrel. ÁHÁThis test should be carried out in accordance with IEC Publication 794©1©E11. 4.1.3ÁHÁÃÃBending under tension (flexing)ÄÄ ÁHÁThis test method applies to optical fibre cables installed under all environmental conditions. ÁHÁThis subject needs further study. 4.1.4ÁHÁÃÃCrushÄÄ ÁHÁThis test method applies to optical fibre cables installed under all environmental conditions. ÁHÁThis test should be carried out in accordance with IEC Publication 794©1©E3. 4.1.5ÁHÁÃÃSqueezing (abrasion)ÄÄ ÁHÁThis test method applies to optical fibre cables installed under all environmental conditions. ÁHÁThis subject needs further study, and is currently under consideration in IEC Publication 794©1©E2. 4.1.6 Á  ÁÃÃTorsionÄÄ ÁHÁThis test method applies to optical fibre cables installed under all environmental conditions. ÁHÁThis test should be carried out in accordance with IEC Publication 794©1©E7. 4.1.7ÁHÁÃÃImpactÄÄ ÁHÁThis test method applies to optical fibre cables installed under all environmental conditions. ÁHÁThis test should be carried out in accordance with IEC Publication 794©1©E4. 4.2ÁHÁÃÃTest methods for environmental characteristicsÄÄ ÁHÁThis section advises the appropriate tests and test methods for verifying the environmental characteristics of optical fibre cables. Ô ñ,ÔŒ4.2.1ÁHÁÃÃTemperature cyclingÄÄ ÁHÁThis test method applies to optical fibre cables installed under all environmental conditions. ÁHÁTesting is by temperature cycling to determine stability of attenuation of a cable at ambient temperature changes which may occur during storage, transportation and operation. ÁHÁThis test should be carried out in accordance with IEC Publication 794©1©F1. ÃÃNoteÄÄ © For aerial self©supporting cables the stability of the attenuation may be measured with a specified tension applied to the cable sample. 4.2.2ÁHÁÃÃLongitudinal water penetrationÄÄ ÁHÁThis test method applies to completely filled outdoor cables installed under all environmental conditions. ÁHÁThe intention is to check that all the interstices of a cable are continuously filled with compound to prevent water penetration within the cable. ÁHÁThis test should be carried out in accordance with IEC Publication 794©1©F5. 4.2.3ÁHÁÃÃMoisture barrierÄÄ ÁHÁThis test method applies to optical fibre cables installed under all environmental conditions. ÁHÁThis test applies to cables supplied with a longitudinal overlapped metallic foil. The moisture penetration can be tested according to the test method as described in Part I, Chapter III of the Handbook "Outside plant technologies in public networks". 4.2.4 Á  ÁÃÃFreezingÄÄ ÁHÁThis test method applies to optical fibre cables installed under all environmental conditions. ÁHÁThis subject needs further study and is currently under consideration in IEC Publication 794©1©F6. 4.2.5ÁHÁÃÃHydrogenÄÄ ÁHÁThis test method applies to optical fibre cables installed under all environmental conditions. ÁHÁA suitable short©duration test procedure needs to be determined for completed cable, so that the results of factory tests enable the long©term increase in fibre loss to be predicted. 4.2.6ÁHÁÃÃNuclear radiationÄÄ ÁHÁThis test method assesses the suitability of optical fibre cables to be exposed to nuclear radiation. ÁHÁThis subject needs further study and is currently under consideration in IEC Publication 794©1©F7. 4.2.7ÁHÁÃÃVibration (bridge and underground cables)ÄÄ ÁHÁThis test method assesses the suitability of optical fibre cables for bridge and underground application. ÁHÁThis subject needs further study. 4.2.8ÁHÁÃÃVibration (aerial cables)ÄÄ ÁHÁThis test method assesses the suitability of optical fibre cables for aerial application. ÁHÁThe subject needs further study. 4.2.9ÁHÁÃÃUltraviolet resistanceÄÄ ÁHÁThis text method applies to aerial optical fibre cable and assess the suitability of the cable sheath to withstand ultraviolet radiation. ÁHÁThis subject needs further study. 4.2.10Á  ÁÃÃSheath trackingÄÄ ÁHÁThis test applies to aerial optical fibre cables used on high voltage power lines. ÁHÁThis subject needs further study.