Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
  • H02G3/00—Installations of electric cables or lines or protective tubing therefor in or on buildings, equivalent structures or vehicles
  • H02G3/02—Details
  • H02G3/04—Protective tubing or conduits, e.g. cable ladders or cable troughs
  • H02G3/0462—Tubings, i.e. having a closed section
  • H02G3/0487—Tubings, i.e. having a closed section with a non-circular cross-section
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/46—Processes or apparatus adapted for installing or repairing optical fibres or optical cables
  • G02B6/48—Overhead installation
  • G02B6/483—Installation of aerial type
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/44—Mechanical structures for providing tensile strength and external protection for fibres, e.g. optical transmission cables
  • G02B6/4401—Optical cables
  • G02B6/4415—Cables for special applications
  • G02B6/4416—Heterogeneous cables

Definitions

• the invention relates to optical fibre drop cables for use in telecommunications systems and particularly, but not exclusively, to such cables for use in connecting between a customer's premises and a connection point common to a number of such customers.
• a final drop wire has typically comprised a number of insulated conducting wires contained in a sheath. More recently the development of optical fibres has made it desirable to replace the conducting wires in drop wires with optical fibres, since the latter can transmit significantly more data. However, it is also desirable that the drop wire should carry an electrical supply in order that a telephone connected to the drop wire can be used in emergency situations when the mains electrical supply to the premises in which the telephone is located has been interrupted. For this reason, it is desirable for a drop wire to include one or more optical fibres and a pair of insulated copper conductor wires.
• the applicant's application GB-A-2270992 discloses a cable containing separable electrical conductors and optical fibres.
• the cable comprises electrical power conductors for conveying mains voltage electrical supplies, a plurality of optical fibres and sheathing for the conductors and fibres.
• the sheathing is in the form of a figure of eight and defines two separate chambers; one for the electrical conductors and the other for the optical fibres.
• this cable is intended for underground routing and not for suspension installation. Furthermore, it is not suitable for conducting a relatively low voltage electrical supply for powering a telephone or otherwise as a final drop wire.
• An aspect of the invention relates to an optical fibre drop cable for suspension installation, said cable comprising sheathing having a first portion containing a strengthening arrangement for supporting the cable in a said suspension installation and a second portion separable from said first portion and containing a plurality of electrical conductors, said first portion defining at least one passage for optical fibres.
• Figure 1 is a schematic cross-section of an optical fibre drop cable comprising an optical fibre and electrical conductors
• Figure 2 is a schematic cross-section of an optical fibre drop cable containing a plurality of optical fibres and electrical conductors
• Figure 3 is a schematic cross-section of an optical fibre drop cable
• Figure 4 is a schematic representation of a drop cable installation including a cable as shown in Figure 1 , 2 or 3;
• FIG. 5 is an enlargement of the portion of Figure 4.
• Figure 6 is a schematic representation of a connecting box of the installation of Figure 4.
• Figure 7 shows a push-fit connector arrangement included in the connecting box.
• Figure 1 shows an optical fibre drop cable 10 containing a buffered optical fibre 11 and two insulated electrical conductors 12.
• the buffered optical fibre 11 comprises an optical fibre 13 and a plastics coating 14 that protects the surface of the fibre 13 from scratching and abrasion.
• the plastics coating may for example be a nylon coating and the fibre with coating will typically have a diameter of approximately 1 mm.
• the insulated conductors 12 comprise copper wires 16 encapsulated in a colour-coded electrical insulating coating 18, which may be of any suitable material as will be well known to those skilled in the art.
• the copper wires will have a diameter of approximately 0.4 mm and the outside diameter of the insulating coating will typically be approximately 1.2 mm
• One insulated conductor 12 is to serve as the live wire and the other as a neutral/earth wire in a circuit that will typically carry 9 to 12 volts for powering a telephone connected with the cable. It is to be understood that copper wires are given, only as an example and that any suitable conducting material, such as aluminium could be used
• the optical fibre 11 and electrical conductors 12 are housed in sheathing 19, which comprises a first portion 20 that contains the optical fibre 13 and a second portion 22 that is separable front the first portion and contains the electrical conductors 12.
• the optical fibre 11 is housed in a passage 23 defined by the first portion 20 with the wall defining the passage circumferentially engaging the optical fibre along the length of the fibre.
• the sheathing portions 20, 22 are substantially circular in cross- section and in side-by-side parallel relationship so as to define a shape approximating to a figure 8.
• a thickening, or web 24.
• the web houses a tear, or rip, cord
• the rip cord 26 which is offset with respect to a plane passing through the longitudinal axes of the first and second sheathing portions and runs along the cable substantially parallel to those axes.
• the rip cord 26 may be made of any material sufficiently strong to rip through the web 24 on application of a tear force so as to permit separation of the first and second sheathing portions.
• the sheathing 19 may be made of any suitable sheathing material such as polyethylene, MDPE, HDPE or nylon. Typically, the first portion 20 of the sheathing would have a diameter of approximately 8 mm and the combined height of the two sheathing portions would be approximately 12 mm.
• a strengthening arrangement is provided in the first portion 19 of the sheathing in the form of strengthening members 28 disposed adjacent the optical fibre 11.
• the strengthening members 28 are disposed in parallel spaced apart relationship, one on each side of the optical fibre 11 and encapsulated in the first portion 20 of the sheathing.
• the strengthening members are preferably disposed in a plane extending pe ⁇ endicular to a plane passing through the respective longitudinal axes of the sheathing portions 20, 22 and through the longitudinal axis of the first portion 20 of the sheathing.
• the strengthening members 28 have a substantially circular cross-section and extend generally parallel to the longitudinal axis the first portion 20 of the sheathing.
• the strengthening members are made of a dielectric material such as glass reinforced plastic (GRP), although glass yarns may be used with similar advantage.
• a dielectric material such as glass reinforced plastic (GRP)
• Other non-prefeoed materials include aramid fibres.
• dielectric materials are preferred, metallic strengthening elements may be used.
• GRP strengthening materials are a preferred material since the material has a similar coefficient of thermal expansion to optical fibres and thus changes in length of the strengthening members due to thermal effects, should not result in an increase in the forces transmitted to the optical fibre. Glass yarns offer a similar advantage.
• strengthening members made of an electrically non-conducting material such as GRP, glass yam or aramid fibres. If the strengthening members are made of an electrically conducting material such as a stranded steel, it is necessary to increase the diameter of the sheathing for electrical insulation pu ⁇ oses. When electrically nonconducting strengthening members are used, there is no requirement to maintain an increased thickness of sheathing in the first portion 20 of the sheathing in order to meet any voltage withstand requirement. Thus, the diameter of the first portion of the sheathing can be reduced, which reduces the effect of ice and wind loads on the cable. It is believed that by using electrically non-conducting strengthening members, the diameter of the first portion 19 of the sheathing can be reduced by up to 2 mm as compared with the case when the sheathing is required to provide electrical insulation.
• the optical fibre drop cable 40 shown in Figure 2 shows modifications which may be made to the optical drop fibre 10 singly or in combination.
• the first modification comprises the addition of two further strengthening members 28.
• the second modification comprises the provision of two optical fibres 11.
• the optical fibres 1 1 are loosely housed in a circular passage 44.
• the first portion 20 of the sheathing may be formed so as to define a single passage or separate passages encasing the optical fibres in the same way as in the optical fibre cable 10 in Figure 1.
• Figure 3 shows an optical fibre drop cable 60 that differs from the optical fibre drop cable 10 in that the optical fibre 11 is loosely housed in a hollow plastic tube 62 contained in a passage 63 defined by the first sheathing portion 20.
• This tube may contain more than one optical fibre although only one is shown in the drawing.
• a possible modification (not shown) to the optical fibre cable drop 60 shown in Figure 3 comprises omitting the optical fibre(s) 11 from the tube 62. In this case, one or more fibres 1 1 are blown into the tube after installation of the optical fibre drop cable.
• Optical fibres to be installed by blown fibre methods may, for example, take the form disclosed in EP-A-0345968, EP-A- 0521710 or EP-A-0646818 and may be introduced into the tube 62 by known blowing processes such as the process described in EP-A-0108590.
• the tube 62 may be made of polyethylene with a carbon loaded radially inner surface to increase conductivity, as disclosed in US4952021. Blown fibre installation has the advantage that optical fibre(s) are not subjected to stresses that arise during suspension of the cable.
• optical fibre drop cables 10, 40, 60 comprises replacing the strengthening members 28 with a strengthening arrangement in the form of a reinforcing sleeve contained in the first portion 20 of the sheathing.
• the sleeve would preferably be made of an electrically non-conducting material such as aramid fibres.
• the sleeve could be made of strands of a metallic element such as steel.
• the fibres or strands of such a sleeve would preferably be helically wound around the optical fibre(s) 11 and/or tube(s) 62 and electrical conductors 12 from two directions - a so-called SZ winding.
• FIG. 4 shows a drop installation 100 comprising any of the optical fibre drop cables 10, 40 and 60.
• the drop installation 100 includes a housing 101 containing a distribution arrangement for distributing connections to telecommunications lines that are to run to customer premises.
• the housing is fed from an exchange by means of a multifibre optical fibre cable 102 such as a known 48 fibre underground cable.
• a multifibre optical fibre cable 103 comprising sufficient fibres for connecting with ten telecommunications lines 104 (ten fibres for single fibre circuits or twenty fibres for twin fibre circuits), leads from the housing 101 to a connecting box, or manifold 105 of an adjacent pole 106.
• the reference numeral 103 indicates electrical conductors for conducting a voltage of 9 to 12 volts to the manifold.
• a telecommunications line 104 runs from the manifold 105 to customer premises such as a building 107. In the drawing, two telecommunications lines 104 are shown; one extending to the right of the manifold and leading to the building 107 and the other extending to the left of the manifold.
• the optical fibre cable 103 contains sufficient optical fibres to connect with ten telecommunications lines 104 and thus there may be ten separate telecommunications lines extending from the manifold 105.
• the telecommunications lines 104 each comprise a plurality of lengths of the optical fibre drop cable 10 connected end-to-end at respective connecting boxes 108 mounted on poles 106 and the building 107.
• the lengths of cable 10 are connected to the poles 106 by securing devices 1 10.
• securing devices 1 10 In the drawing, only two poles are shown, but in practice there will be as many poles as are required to support the cable en route between the manifold 105 and the customer premises. Typically the spacing between the poles is approximately 200 feet (61 metres), although it may be up to 100 metres.
• each securing device 110 comprises an elongate member 112 which is bent double to define two end portions 114, 116 that are helically wrapped around the first portion 20 of the sheathing in the same sense, and a bend, or loop, 118 that connects the end portions.
• the securing device 110 additionally comprises a tensile connecting member 120 having hooked end portions, one of which engages the loop 118 and the other of which engages a pole ring 122 fixed to the pole 106. The tensile
• connecting member 120 may include means (not shown) for adjusting the tension in the cable 10 between the securing devices on adjacent poles 106.
• the tensile connecting member may comprise two portions each having threading at their ends remote from the hooked end portions and interconnected by a nut such that rotation of the nut causes lengthening or shortening of the tensile connecting member.
• the second portion 22 containing the electrical conductors 12 is separated from the first portion 19. This separation is easily obtained by accessing the free end of the rip cord 26 at the adjacent end of the optical fibre cable 10 and using this to rip through the web 24 over a suitable distance.
• a break is shown in the separated portion of the first portion 19 of the sheathing simply to allow a better view of the loop 118 and the tensile connecting member 120.
• a connecting box 108 has a hollow interior 130, that can be accessed by removing a cover plate (not shown).
• An opening 132 for a cable 10 is provided at each side of the box to serve as an entry point for an end of a cable 10.
• pairs of openings may be provided for individually receiving the separated sheathing portions.
• the connecting boxes 108 are secured to the poles 106 by any suitable means, such as screws 133.
• Each box contains a push-fit connector arrangement, or device, 134 by means of which the ends of the cables 10 are secured within the box.
• the push-fit connector arrangement or device, 134
• Each push-fit connector 136 comprises a body 138 that defines a stepped through- passage 140.
• a gripping means 142 that comprises a ring having a plurality of circumferentially spaced apart radially and axially inwardly extending projections, or barbs is housed in a larger diameter portion 144 of the through- passage 140 at a position remote from the ends of the through-passage.
• the gripping means 142 is preferably made of metal, but may be made of a plastics material, and the barbs are able to deflect radially outwardly on insertion of an end of a sheathing portion 20, 22 into the through-passage 140
• a collet 146 may be provided to permit withdrawal of the sheathing portion should it become desirable to break the connection.
• the collet 146 has a cylindrical leading-end portion 148 which projects into the through-passage 140 and is engageable with the barbs on axial inward movement relative to the gripping means 142 to deflect the barbs radially outwardly to release the grip on the sheathing portion and permit its
• the separated first and second sheathing portions 20, 22 of the respective ends of the cables are fed through the openings 132 into the hollow interior of the connecting box 108.
• the sheathing and strengthening members 28 are cut back to expose the optical fibre 11 and insulated conductors 12 and then the ends of the sheathing portions are push- fitted into the respective push-fit connectors 136 until the cut end of the sheathing abuts a shoulder 150 defined by the through-passage 140.
• the ends of the first and second portions of the sheathing are secured in the push-fit connectors 136 by the barbs of the gripping means 142 and the exposed optical fibre 11 and insulated conductors 12 protrude from the inner ends 152 of the through-passages to a connection region 154 of the connecting box.
• the electrical conductors and optical fibres of the cable ends are connected by any suitable conventional means.
• the conductors 12 may be connected by stripping back the insulating coating 18 to expose the copper wires 16 and twisting the ends of the wires together.
• a terminal block in which the ends of the conducting wires are secured by means of screws may be used.
• the manifold 105 may be of similar construction to a connecting box 108.
• the manifold 105 would contain an additional opening through which the optical fibre cable 103 is fed and ten openings 132 to permit ten telecommunications lines 104 to feed from the manifold. The ends of the
• telecommunications lines 104 can be secured in the manifold 105 by means of push-fit connectors, such as the push-fit connectors 136 in the same way as in the connecting boxes 108, or by any other suitable means.
• push-fit connectors such as the push-fit connectors 136 in the same way as in the connecting boxes 108, or by any other suitable means.
• connections between the electrical conductors feeding into the manifold and the optical fibres of the optical fibre 103 may be made with the electrical conductors 12 and optical fibres 11 by any suitable conventional means.
• the lengths of optical fibre drop cable 10 suspended between the poles 106 are connected to the poles by the securing devices 1 10, which are secured to the cable at spaced apart positions remote from its ends.
• the tension in the cable suspended between the poles can be adjusted after suspension of the cable by means of the adjusting means of the tensile connecting members 120 if such means are provided .
• the end portions 10E ( Figure 5) of the first portion of the sheathing and its contents between the securing devices 110 and the connecting boxes 108 are untensioned.
• the helical winding of the ends 114, 116 of the elongate member 112 can be adapted such that it will grip the sheathing with a predetermined force so that the sheathing will slip when the tension in the cable 10 reaches or exceeds a predetermined level.
• the previously untensioned portions 10E will be tensioned and the connection points 136 are arranged such that the cable will be released, breaking the connection with the adjacent lengths of cable when the tension in the portion 10E reaches a second predetermined level which is no greater than the tension load that causes the slippage of the cable and is preferably substantially less.
• the tension load at which the elongate member 1 12 permits slippage of the cable is selected such that the cable will slip at a loading less than that required to break the cable. It is expected that the strength of the cable would be such that it would break under a load in the region of 2KN, that the elongate member 112 would be arranged to permit slippage of the cable under a load in the region of 1.2 to 1.5KN and the push-fit connectors would be arranged to permit the cable connections to break at a load in the region of 170N, although it is to be understood that these loads are given as examples and should not be taken as limiting.
• the ends 10E are described as being secured to the connecting box 106 by means of a push-fit arrangement. It will be appreciated that this arrangement whilst advantageous in terms of simplicity and ease of fitting, should not be taken as limiting.
• the ends 10E may be secured by any suitable means, such as a spring-loaded cable clamp that will provide sufficient security to hold the ends 10E in place and avoid any tensile load being transmitted to the joints between the optical fibres 11 and conductors 12 during normal operating conditions and at the same time reliably permit breakage of the connection at a tensile loading no greater than that required to cause slippage of the cable through the securing devices 110.
• the telecommunications line 104 is to be constructed using an optical fibre drop cable 60 as shown in Figure 3, with the optical fibre(s) being installed by blown fibre technique, it is necessary to provide a substantially gas-tight passage along which the optical fibres are to be blown.
• the first portion 20 of the sheathing is cut back such that when its end is push-fitted into a push-fit connector 136, the cut end of the plastics tube
• connection region 154 protrudes from the end 152 of the through-passage 140 into the connection region 154.
• the ends of the tubes 62 protruding into the connection region can then be interconnected to provide a gas-tight passage for the optical fibre(s) by means of a suitable length of tubing inserted therebetween.
• means defining a passage could be provided between the push- fit connection points 135 and arranged such that the ends of the tubes 62 can be inserted therein to provide a continuous air-tight passage for the optical fibre(s).
• optical fibre drop cables are described as being used in the drop installation 100, which provides for a controlled breakage of the telecommunications line, this is not essential and the cables could be used in any suitable conventional drop installation.
• the optical fibre drop cables 10, 40, 60 are installed in an arrangement such as the arrangement 100 that provides controlled breakage of the telecommunications line under a load less than that required to break the cable, it will be appreciated that such an arrangement is advantageous. This is because the loading which will cause the optical fibre drop cable to slip and the connection between adjacent ends to break can be chosen to be less than that required to break the cable, which is a useful safety feature in the event of a high vehicle driving into the telecommunications line 104 or a tree or other structure falling on it. Furthermore, since the connections between a length of the optical fibre drop cable and adjacent lengths in the line are broken in the event of such events, damage to the telecommunications line should be localised thereby reducing the time required for and cost of repair.
• the telecommunications line can be designed to break on application of a predetermined loading, the cable can be made significantly stronger than might otherwise be the case, thereby providing greater protection for the optical fibre(s) contained in the cable.
• the cable can be made stiffer and thus able to better withstand the effects of variable loading due to wind force and the settling of moisture or ice formation.
• the optical fibre drop cables of the embodiments are low fibre count cables intended to be used in aerial installations as a final drop wire. It is envisaged that such a low fibre count cable may comprise only one or two optical fibres. Furthermore, the electrical conductors are intended to carry only a low voltage, preferably in the region of 9 to 12 volts, and only two conductors are needed for this pu ⁇ ose.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Architecture (AREA)
• Civil Engineering (AREA)
• Structural Engineering (AREA)
• Light Guides In General And Applications Therefor (AREA)
• Cable Accessories (AREA)
• Insulated Conductors (AREA)
• Mechanical Coupling Of Light Guides (AREA)
• Communication Cables (AREA)

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• 2002
  • 2002-11-15 CN CN028229363A patent/CN1589417B/zh not_active Expired - Fee Related
  • 2002-11-15 CA CA2467513A patent/CA2467513C/en not_active Expired - Fee Related
  • 2002-11-15 JP JP2003546157A patent/JP2005510027A/ja active Pending
  • 2002-11-15 AU AU2002339166A patent/AU2002339166B2/en not_active Ceased
  • 2002-11-15 WO PCT/GB2002/005153 patent/WO2003044584A1/en not_active Ceased
  • 2002-11-15 BR BRPI0206428-6A patent/BRPI0206428B1/pt unknown
  • 2002-11-15 US US10/495,980 patent/US7106931B2/en not_active Expired - Lifetime
  • 2002-11-15 BR BR0206428-6A patent/BR0206428A/pt not_active IP Right Cessation
  • 2002-11-15 ES ES02777542T patent/ES2401082T3/es not_active Expired - Lifetime
  • 2002-11-15 EP EP02777542A patent/EP1446689B1/en not_active Expired - Lifetime

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