Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B7/00—Insulated conductors or cables characterised by their form
  • H01B7/38—Insulated conductors or cables characterised by their form with arrangements for facilitating removal of insulation
  • H01B7/385—Insulated conductors or cables characterised by their form with arrangements for facilitating removal of insulation comprising a rip cord or wire

Definitions

• This invention relates to electrical cables, in particular to cables that are provided with a screen, for example to prevent or reduce electromagnetic interference.
• Commonly employed screened cables include coaxial cables in which a single elongate electrical conductor is surrounded by a dielectric and a conductive screen.
• Other screened cables employ one or more insulated conductors, eg. in twisted pair configuration, the conductor or conductors being enclosed in a single common screen.
• the conventional method of terminating a cable with a braided screen comprises
• an electrical cable which comprises one or more elongate electrical conductors, a layer of insulation surrounding the or each electrical conductor, and a metal electrical shield surrounding the conductor or conductors and the insulation, the cable including a pull-thread that extends along the length of the cable under the shield so that the shield can be cut longitudinally by pulling the thread.
• Preferred jacket materials include polymers such as Polyolefins, eg. ethylene homopolymers and copolymers with alpha olefins, halogenated polymers, eg.
• tetrafluorethylene vinylidene fluoride, hexafluoropropylene and vinyl chloride homo or copolymers, especially ethylene/tetrafluoroethylene copolymer, polamides, polyesters, polyimides, polyether ketones, eg. polyarylether ketones, aromatic polyether imides and sulphones, silicones, alkene/vinyl acetate copolymers and the like.
• the polymers may be used alone or as blends with one another and may contain fillers, eg. silica and metal oxides, eg. treated and untreated metal oxide flame retardants such as hydrated alumina and titania.
• While the present invention is applicable to cables having only a single central conductor surrounded by a dielectric such as coaxial cables and single screened wires, it will more usually be applied to screened muliticonductor cables, eg. a screened twisted pair cables. It has hitherto been relatively difficult to cut back the screen of such cables in the case of flat filament braids, not only because it is difficult or impossible to cause the shield to bulge by pushing it toward the remainder of the shield but also because of the undulating surface of the cable caused by the helical geometry of the insulated conductors or wires.
• the pull thread In the case of multiconductor cables it is possible for the pull thread to be layed up in the cable in the manner of an additional wire so that when it is pulled it will cut through the shield and jacket in a helical path. This may not be particularly easy or convenient for an operator to perform manually, and so it is preferred for the pull thread to extend substantially axially along the cable in order that it may be pulled along the cable at a substantially uniform orientation.
• the invention may be employed with cables having a variety of screens although normally the screen will be in the form of a braid, and the invention is particularly suited to cables having braids formed from flat filaments.
• Such flat braids appear to be cut very easily by the thread and it is believed that this ease of cutting according to the present invention and the difficulty of stripping flat braided cables by the conventional method are, in fact, related:
• the braid filaments cannot easily slide over one another but tend to remain fixed when subjected to a force distorting the braid. In the conventional stripping method this prevents the braid being caused to bulge, and in the cable according to the invention this same tendency prevents any accommodation of the stress applied by the thread as it cuts through the filaments.
• the pull thread is preferably electrically insulating and more preferably formed from a polymer.
• the most preferred material is based on an aromatic polyamide for example as sold by Akzo under the trademark "Kevlar". It will normally be in the form of a relatively large number of monofilaments.
• the cable may be provided with more than one stripping thread.
• the cable may be provided with one thread under the shield and a second thread under the jacket but over the shield so that part of the shield can be exposed by stripping the jacket only.
• Figure 1 is a perspective view of a shielded twisted pair cable
• Figure 2 is a schematic side view of a cable at a number of stages during the stripping process of the invention.
• a screened twisted pair cable comprises a twisted pair of wires 1 and 2 each comprising a stranded tinned copper conductor 3 and a single wall or dual wall insulation 4, formed for example from polyethylene and/or polyvinylidine fluoride.
• a shield 5 is provided in the form of a braid of flattened tinned copper filaments followed by an extruded outer jacket 6 formed form an ethylene tetrafluoroethylene copolymer.
• a pull thread 7 formed from a number of monofilaments of an aromatic polyamide (sold under the trademark "Kevlar”) extends axially along the length of the cable underneath the cable jacket 6 and the shield 5.
• the pull thread 7 is simply pulled perpendicularly to the cable causing it to cut through both the shield 5 and the jacket 6 until the shield and jacket have been severed to the appropriate length.
• the shield may then be terminated in any appropriate manner.
• Figure 2 shows a number of side views of a screened twisted pair cable at various stages during the termination process.
• the cable comprises a pair of insulated conductors 1 and 2 enclosed by a braided shield 5 and a jacket 6.
• the cable has two pull-threads, one thread 7 located under the shield 5 and the second thread 8 located under the jacket 6 but over the shield.
• the threads 7 and 8 will normally have different colours or patterns in order to distinguish them.
• Thread 7 is then pulled in order to slit the jacket 6 and shield 5 to the point at which the shield 5 can be tidied up with a pair of snips to form the cable as shown in Figure 2b.
• the thread 8 is pulled back in order to slit the jacket 6 by the amount it is desired to expose the shield 5.
• the end of the jacket 6 can be torn off circumferentially and tidied by means of snips to form the cable as shown in Figure 2c.
• the excess lengths of pull-thread can be cut off at any convenient point.

Landscapes

• Insulated Conductors (AREA)
• Organic Insulating Materials (AREA)
• Communication Cables (AREA)
• Ignition Installations For Internal Combustion Engines (AREA)
• Inorganic Insulating Materials (AREA)
• Manufacturing Of Electric Cables (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Endoscopes (AREA)
• Removal Of Insulation Or Armoring From Wires Or Cables (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=10686982

Family Applications (1)

Country Status (13)

Cited By (1)

Families Citing this family (6)

Family Cites Families (4)

• 1990
  • 1990-12-13 GB GB909027110A patent/GB9027110D0/en active Pending
• 1991
  • 1991-12-03 CA CA002097595A patent/CA2097595C/en not_active Expired - Fee Related
  • 1991-12-03 EP EP91920674A patent/EP0561829B1/de not_active Expired - Lifetime
  • 1991-12-03 FI FI932679A patent/FI932679A0/fi unknown
  • 1991-12-03 DE DE69113812T patent/DE69113812T2/de not_active Expired - Fee Related
  • 1991-12-03 AT AT91920674T patent/ATE129092T1/de active
  • 1991-12-03 WO PCT/GB1991/002136 patent/WO1992010840A1/en not_active Ceased
  • 1991-12-03 AU AU89352/91A patent/AU8935291A/en not_active Abandoned
  • 1991-12-03 BR BR919107161A patent/BR9107161A/pt not_active IP Right Cessation
  • 1991-12-03 JP JP4500065A patent/JPH06503200A/ja not_active Withdrawn
  • 1991-12-12 IL IL10035191A patent/IL100351A/en not_active IP Right Cessation
• 1993
  • 1993-06-02 IE IE435691A patent/IE69361B1/en not_active IP Right Cessation
  • 1993-06-11 NO NO19932144A patent/NO310324B1/no not_active IP Right Cessation

Non-Patent Citations (1)

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