Aerial optical and electric cable assembly

It is disclosed a cable assembly comprising a common figure-8 outer jacket comprising a first lobe and a second lobe, wherein the first lobe surrounds an electric core with a relevant first extruded inner sheath housing a strength member; and the second lobe surrounds an optical core with a relevant second extruded inner sheath.

BACKGROUND

The present invention relates to the field of cables. In particular the present invention relates to a cable assembly comprising both a number of optical conductors and a number of electric conductors. The cable assembly of the present invention is adapted to be used as drop cable in FTTH (Fiber To The Home) aerial applications for single buildings (for instance a house) or multiple dwelling units.

PRIOR ART

GB 2 230 106 A discloses a composite electric and optical aerial cable especially suitable for use as a drop cable for extending between an aerial electric and optical cable installation and a building. It is of a figure-of-eight transverse cross-section and has, in one lobe of the cable, at least one flexible reinforcing element and insulated electric conductors and, in the other lobe of the cable, an optical fibre element. In one lobe there are embedded electrically insulated elongate electric conductors and electrically insulated elongate metal reinforcing elements twisted together. The insulated electric conductors and the insulated reinforcing elements are bound together by a helically lapped plastics tape. The optical fibre element may consist of a plastics tube which is separately formed with respect to the lobe and in which optical fibres are loosely housed or it may comprise at least one tightly buffered optical fibre embedded in the lobe.

U.S. Pat. No. 5,740,295 discloses a composite drop cable comprising a dielectric optical drop cable and a copper cable containing twisted copper wire pairs enclosed within a metallic core tube and encased within a polyvinylchloride (PVC) jacket. The two cables are encased in a jacket or sheath of, for example, low density polyethylene and the entire assembly forms the composite cable. The dielectric fiber drop cable comprises a core tube of a polymeric material containing fibers. A plurality of dielectric strength members, are disposed around the circumference of the core tube. The assembly is then encapsulated in a jacket of insulating material.

SUMMARY OF THE INVENTION

In some circumstances it is convenient to separate composite electric and optical aerial cables into an electric cable and into an optical cable. The separation can be useful, for instance, when the electric cable enters a building through a certain duct or opening while the optical cable enters the building through a different duct or opening, or when the electric cable and the optical cable follow different paths from a certain position on, in order to reach relevant users.

To this purpose, it is convenient to obtain two self-standing cables from the original composite electric and optical aerial cable. The two self-standing cables should conveniently have a substantially circular cross-section with a relatively small diameter. Such two characteristics allow inserting each self-standing cable in tubes, possibly already existing in the building, which may be of a rather small diameter and at least partially occupied by other cables.

The Applicant has noticed that the prior art composite electric and optical aerial cables, such as the one of GB 2 230 106 A, are unsuitable for obtaining self-standing optical and electric cables having the above characteristics. As a matter of fact, these cables have an outer jacket not configured for being removed, and in case the web connecting the two lobes is cut in order to part electric and optical cables, it can leave residues on both the first and second lobe. These web residues make the cross-section and outer surface of the separated lobes irregular and the cable installation may be difficult, for example in case one of the cables becomes blocked in a duct or narrow passage.

In the above, the Applicant has tackled the problem of providing an aerial optical-copper cable assembly which is lightweight and with a rather reduced cross-section, adapted to be easily divided into an independent optical cable and an electric cable suitable to be separately routed and deployed in an effortless manner.

The Applicant has found a cable assembly comprising an optical core and an electric core each provided with an independent extruded sheath surrounded by a removable a common figure-8 outer jacket.

By “common figure-8 outer jacket” it is meant a jacket having portions surrounding the optical core and the electric core respectively, connected by a web portion.

Once the common figure-8 outer jacket has been removed, each of the optical core and electric core, with the relevant extruded inner sheath, forms a two self-standing cable having its own sheath with a thickness suitable for protecting the cable itself during the deployment and having a substantially circular cross-section, free of projecting parts deriving from the cable assembly partition.

As the common figure-of-8 outer jacket can be fully removed, the resulting two self-standing cables have a reduced diameter while maintaining a suitable mechanical resistance. Both the characteristics render them adapted to be laid in existing ducts, possibly following a tortuous path.

According to a first aspect, the present invention provides a cable assembly comprising a common figure-8 outer jacket comprising a first lobe and a second lobe, wherein the first lobe surrounds a first extruded inner sheath housing an electric core and a strength member; and the second lobe surrounds a second extruded inner sheath housing an optical core.

Advantageously, the common figure-8 outer jacket embeds a rip-cord, preferably a rip-cord per each first and second lobe. Preferably, the rip-cord of the first lobe and the rip-cord of the second lobe are embedded into the common figure-8 outer jacket at diametrically opposed positions.

The first and second extruded inner sheaths preferably have a thickness of at least 0.2 mm.

In the cable assembly of the invention the common outer jacket can comprise a web connecting the first lobe and a second lobe.

The common outer jacket preferably has a thickness of at least 0.5 mm.

Preferably, the strength member is an electrically non-conductive metallic strength member.

The electric core can comprise power or telecommunication conductors or both. Example of telecommunication conductor is a copper pair or quad.

Advantageously, the first extruded inner sheath of the electric core houses two strength members, preferably positioned at diametrically opposed positions.

Preferably, a strength member is laid parallel to the first lobe longitudinal axis.

The optical core comprises at least one optical fibre (an optical glass waveguide surrounded by a curable polymeric coating), advantageously a plurality of optical fibres.

The optical core can further comprise dielectric elements for the protection of the optical fibre or fibres, such as water blocking material, fillers, tubes and the like.

DESCRIPTION OF EXAMPLES

FIG. 1is a cross-sectional view of a cable assembly according to an embodiment of the present invention. The cable assembly is generally designed by reference number100.

Cable assembly100is an optical and electrical cable assembly and it comprises an optical core21and an electrical core11. More specifically, cable assembly100is adapted for use as an aerial drop cable in FTTH applications.

In the present description and claims:the term “radial” is used to indicate a direction perpendicular to a reference longitudinal axis of the cable;the expressions “radially inner” and “radially outer” are used to indicate a position along a radial direction with respect to the above-mentioned longitudinal axis;a size along the radial direction is termed “thickness”;the terms “conductive”, “insulated” are used to mean “electrically conductive and “electrically insulated” respectively, unless otherwise specified;the term “electrically conductive” indicates a material, e.g. copper or aluminium, having an electrical resistivity lower than 10×10−8Ohm·m; preferably lower than 8×10−8Ohm·m; more preferably lower than 5×10−8Ohm·m.

For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term “about”. Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

The cable assembly100comprises a common figure-8 outer jacket30having a first lobe10and a second lobe20.

First lobe10of the common figure-8 outer jacket30surrounds a first inner sheath15housing an electric core11. The first inner sheath15is an extruded sheath made, for instance, of polyethylene, such as low density polyethylene (LDPE) or medium density polyethylene (MDPE) suitable to fulfil the requirement of BS EN 50290-2-23-2013. In embodiments, the first inner sheath15can have a thickness of from 0.3 mm to 0.6 mm. In one preferred embodiment, the thickness of the first inner sheath15is 0.4 mm.

In embodiments, the outer diameter of the first inner sheath15is of from 4.0 to 6.0 mm. For example, the outer diameter of the first inner sheath15is of about 5.0 mm.

In the depicted embodiment, the first inner sheath15houses an electric core11comprising three power conductors12and one copper pair13.

Preferably, each of the power conductors12comprises an electrically conductive core and an electrically insulating layer therearound. The electrically conductive cores can be made of copper or aluminium, preferably of copper.

The power conductors12are, typically, for low voltage application, i.e. suitable for transport current up to a voltage of less than about 1 kV.

The power conductors can be, for example, solid annealed bare copper of 0.5/0.9 mm fulfilling the requirement of the standard IEC 60228-2004 3rded.

Copper pair13or quad is suitable for data transport. Each copper pair13or quad comprises a twisted pair or quad of telecommunication conductors13a, each comprising a copper wire covered by an electrical insulation layer made of polymeric material, for example polyethylene. The copper pairs or quads are stranded together and optionally wrapped by a tape16made of polymeric material, for example polypropylene.

It should be remarked that the number of power conductors and copper pairs may vary from the number shown inFIG. 1.

In case a plurality of power conductors12and/or copper pairs13are provided in the electric core11, such conductors12and/or pairs13are profitably twisted together.

The power conductors and/or copper pairs can be wrapped together by a polymeric tape, for example of polyester. Such polymeric tape is in radially inner position with respect to the first inner sheath.

The first inner sheath15further houses members14. The strength members14can be made of a non-metallic material or of an electrically non-conductive metallic material. An example of suitable non-metallic material is glass reinforced polymer. An example of suitable electrically non-conductive metallic material is steel or metal coated steel. Strength members in non-conductive metallic material are preferred, optionally coated with a polymeric material.

Preferably, the strength members14are provided in positions which are substantially radially opposed one to the other.

As the strength members are not embedded in the cable jacket, i.e. in the common figure-8 outer jacket, the cable will exhibit a reduced and more uniform flexibility. Also, as the strength members are not embedded in the cable jacket they are more easily accessible and this is important especially when the strength members are made of metallic material as they have to be earthed in case of short circuit test.

When an aerial cable comprises metallic strength members such as steel strength members, the cable could be requested to withstand a short circuit test, for example at 15 kV, where the metal strength members are earthed and the voltage is applied to the outside of the cable. In order to withstand this short circuit test a minimum of 0.75 mm of dielectric polymer (such as polyethylene) should be radially around the metallic strength members. In known cables where the metallic strength members are embedded in the cable jacket such a requirement implies increasing the jacket thickness and, accordingly, the cable dimensions.

In the cable assembly of the invention, as the metallic strength members are provided within the first inner extruded sheath there is more than 0.75 mm radial of dielectric polymer around the strength members. Accordingly, the radial thickness of the common figure-8 outer jacket does not have to be as high as in known cables thus making it easier to strip the jacket from the cable for releasing the electric and/or telecommunication self-standing cable.

In one embodiment strength members14may comprise one element of 3×0.41 mm brass coated steel strings, the element being coated with polyvinylchloride (PVC) to an overall diameter of 1.4 mm. In another embodiment, strength members14may comprise three elements of 3×0.25 mm brass coated steel strings; the element being coated with PVC to an overall diameter of 1.0 mm.

During deployment, the common figure-8 outer jacket is removed and the first inner extruded sheath housing the electric core and the strength member/s becomes a self-standing electric and/or telecommunication cable.

Second lobe20of the common figure-8 outer jacket30surrounds a second inner extruded sheath25housing an optical core21. Optical core21comprises one or more optical fibers22.

The second inner extruded sheath25is made, for instance, of polyethylene, such as low density polyethylene (LDPE) or medium density polyethylene (MDPE) suitable to fulfil the requirement of standard BS EN 50290-2-23-2013. In embodiments, the second inner sheath25can have a thickness of from 0.2 mm to 0.8 mm. In one preferred embodiment, the thickness of the second inner sheath25is 0.4 mm.

For example, the optical core (and the resulting self-standing optical cable) may comprise up to 24 optical fibers in loose configuration; 2, 4, 6, 8 or 12 optical fibers in EPFU (Enhanced Performance Fibre Unit) format for blown fibre applications; up to four tubes (modules or micromodules) each in turn containing 12 optical fibers; or up to two optical fibers each coated by yarns (for example, aramid yarns) surrounded by a polymeric protective jacket (patchcord format).

A water blocking material can be provided into radial internal position with respect to the second inner sheath25to prevent water or moisture to damage the optical fibers22. The water blocking material can be in form of yarn, tape or gel.

The outer diameter of the second inner sheath25can be of from 2.0 to 3.0 mm. For example, the outer diameter of the second inner sheath25is 2.2 mm.

During deployment, the common figure-8 outer jacket is removed and the second inner extruded sheath housing the optical core becomes a self-standing optical cable.

As said above, the cable assembly100of the present invention comprises an outer common jacket30. Outer common sheath30is provided radially outer the first inner sheath15and radially outer the second inner sheath25. The outer common jacket30is substantially in a shape of “8” with a web33connecting a first lobe10which is radially external to the first inner sheath15and a second lobe20which is radially external to the second inner sheath25.

Outer common jacket30may comprise, or may essentially consist of, a polyethylene. Preferably, outer common jacket30comprises, or essentially consists of, high density polyethylene (HDPE), preferably having a flexural modulus of 800-1400 MPa and a tensile Strain at Break (50 mm/min) of 900-1.500%. The HDPE polymer suitable for the outer common jacket of the present cable advantageously have an Environmental Stress Crack Resistance at 50° C. greater than 5000 h measured according to IEC 60811-4-1:2004.

Outer common jacket30can have a thickness of from 0.5 mm to 1.0 mm. For example, outer common jacket30has a thickness of 0.9-1.0 mm.

In the cable assembly of the invention, the outer common jacket should adhere to the underlying first and second inner sheaths in a sufficient manner to ensure a suitable mechanical congruence during operation, but should also be readily detachable from said sheaths to free the self-standing cables. To this end, the outer common jacket can be extruded over the first and second inner sheaths when the latters are already cooled down and/or carrying the extrusion under controlled temperature and pressure conditions known to the skilled ones. Alternatively, first and second inner sheaths can be spread with an anti-friction agent like chalk before the outer common jacket extrusion.

At least one ripcord32can be embedded within the thickness of the outer common jacket30. Preferably, two ripcords32are provided. The ripcords32are preferably arranged substantially opposed one to the other along the plane A-A′.

Preferably, the ripcords32are made of aramid, nylon or the like.

The cable assembly of the present invention can have small dimensions. For example, the assembly100can have a maximum radial width on the plane B-B′ of 6.8 mm (across the first lobe10; the width across the second lobe20can be of 4.0 mm) and a maximum radial width on the plane A-A′ 12.3 mm.