GB2354374A

GB2354374A - Cable joint insert block with insulation displacement contacts

Info

Publication number: GB2354374A
Application number: GB9921001A
Authority: GB
Inventors: David Malcolm Goodwin
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-09-07
Filing date: 1999-09-07
Publication date: 2001-03-21
Anticipated expiration: 2019-09-07
Also published as: GB2354118B; GB9921002D0; GB2354118A; GB2354374B; GB9921001D0

Abstract

An electric cable joint for a multiconductor main cable comprises an insulating block 2,3 inserted between unstripped insulated conductors 6 of the cable. The block 2,3 has opposite convex outer surfaces with grooves 5 around its periphery for accommodating the conductors 6. Conductive elongate members 8 are mounted within the block 2,3 and extend generally parallel to the convex surfaces; the elongate members may have bores 9 in an end to form or be connected to a socket. Bores 10 in the block 2,3 extend from the grooves 5 to the elongate members 8; there is more than one bore 10 for each groove 5 and each conductive member 8. Mounted in the bores 10 are insulation piercing contacts 11 which cooperate with other insulation piercing contacts 18 in a clamping channel member 13 to provide electrical communication between the insulated conductor 6 of the cable and the longitudinal conductors 8 mounted in the block 2,3. The insert block can be formed as a single piece (fig 3) or as two separate parts 2,3 with a core 1 of heavily-filled fire-resistant polymer.

Description

2354374 Electric Cable Joints, Methods of and Kits f or Making Them This

invention relates to joints for multi-conductor electric cables and more particularly to joints for making tapping connections to extract a relatively small amount of power (or a communication signal) without cutting and joining the main cable conductors. For avoidance of uncertainty, a %%multi -conductor" cable may be taken to have at least three conductors (in some cases counting an armour layer as a conductor). There is no definite upper limit to the number of conductors, but the invention is likely to be used mainly for numbers of conductors ranging from three to about ten, but most frequently from three to six.

The invention is principally concerned with joints for cables in which the conductors are neither so small and flexible that any of the conductors can be readily taken to any desired place in the joint area for connection (like telephone or lighting circuit cables) nor so large as to be essentially self-supporting (like large "distribution" cables). Thus the invention will usually be applied to joints for main cables with a current rating of tens or hundreds of amp6res.

one major application of the invention is in making prefabricated cabling systems with factory-fitted connection points at pre-arranged positions, for use in providing power for lighting and small appliances (such as tools) on construction sites and in other circumstances (e.g. railway tunnels) requiring temporary installations and/or temporary connections to the system.

Such systems are currently made by a labour- intensive process in which, after the insulated conductors of the main cable are exposed, they (or at least those to which connections are required) are locally stripped of insulation to permit connection of short lengths of flexible insulated conductor, for instance by soldering or by crimped connections, after which the connection has to be insulated 2 with tape or otherwise; then the other end of each flexible insulated conductor is connected to the appropriate terminal of a socket or other "two-part" connector and the assembly enclosed in a body of insulating material, with or without an 5 enclosure.

In accordance with one aspect of the invention, an electric cable joint for a multiconductor main cable comprises:

an insulating block inserted between unstripped conductors of the said cable, the said block having opposite convex surfaces each with a plurality of grooves in some or all of which the said insulated conductors are accommodated; conductive elongate members mounted within the said block, each extending generally parallel to the said convex surfaces and forming or connected to an accessible contact element (such as a pin or a socket) at one of its ends; bores in the said block, each such bore extending from one of the said grooves to one of the said elongate members and there being more than one such bore for each groove, extending to a different elongate member and more than one such bore for each elongate member, extending from different grooves; and insulation-piercing contacts in some but not all of the said bores each providing a connection from an insulated conductor laid in the groove from which the bore extends to the elongate member to which it extends.

The invention includes a method of making a an electric cable joint for a multiconductor main cable comprising:

exposing the insulated conductors of the main cable but not stripping insulation from them; providing an insulating block having opposite convex surfaces each with a plurality of grooves, conductive elongate members mounted within it, each extending generally parallel to the said convex surfaces and forming or connected 3 to an accessible contact element at one of its ends, bores in the block, each such bore extending from one of the said grooves to one of the said elongate members and there being more than one such bore for each groove, extending to a different elongate member and more than one such bore for each elongate member, extending from different grooves; inserting insulation-piercing contacts in at a least two but not all of the said bores, each extending from a different one of the said grooves to a different elongate member; and placing the insulated conductors of the main cable in respective ones of the said grooves including the grooves from which the insulation- piercing contact blades extend.

It also includes a kit for making such a joint.

Ideally there would be a bore for every possible combination of groove and elongate member, but (as the sequence of the cable conductors will normally be fixed and only the starting point unpredictable) it is sufficient and convenient to arrange the elongate members on a pitch circle and provide bores for connections from each elongate member only to the grooves on the adjacent side of the insulating block.

It will be apparent that the installer of the joint will first determine in which of the grooves respective conductors can suitably and conveniently be inserted, and then insert the insulation-piercing contacts accordingly to make the required connections.

In some cases, every conductor of the cable may be connected to a respective elongate member, but in many cases only selected conductors need to be connected (e.g. one phase conductor and neutral in a three-phase four-wire or "star" system, two of the three phases in a three-phase three-wire or "delta" system, or one line conductor and the corresponding neutral in a double-circuit single- phase system); if there is any elongate member to which no connection is made, it is redundant and can optionally be 4 removed and discarded.

The contacts for connecting the cable conductors to the elongate members may be of any kind appropriate to the design electrical load. For loads up to the order of 20 amp&res at least, we prefer a type of connector that we believe to be novel (and which is the subject of a separate patent application filed simultanously with this application). This comprises a channel member having two generally parallel limbs with aligned apertures through which the elongate member may pass, a first insulation-piercing element mounted to the base of the channel member (for example by a screw thread) for movement towards an insulated conductor placed between the limbs of the channel member and a second insulation-piercing element positioned between the elongate member and an insulated conductor so placed. In the present context, the second insulation-piercing element will be positioned as defined by location in one of the bores of the insulating body, and additional bores are preferably provided to locate the limbs of the channel member individually.

Preferably both of the insulation-piercing elements and the channel member are all conductive, so providing duplicate current paths for maximum security and minimum contact resistance. Alternatively the channel member and/or the first insulation-piercing element might be insulating (or insulated) to facilitate testing by ensuring continuity failure if the second insulation-piercing element is inadvertently omitted.

For communications or light-current applications, blade contact of the type in which the insulation-piercing part is bifurcated and the legs of the resulting fork unsymmetrically bevelled so that contact pressure is aided by torsional deflection of the legs can be used.

For cables at the smaller end of the range for which the invention is appropriate, the conductors of the cable can be parted by hand without difficulty, but especially for larger sizes it may be desirable to use a tool which grips the cable on both sides of the part where the insulated conductors have been removed and relatively rotates the sides in the direction tending to cancel the lay of the cable conductors (assuming the cable is of a kind with conductors all helically laid in the same direction) and/or urges the ends towards one another.

The prefered form of connector described serves also to retain the insulated conductors in the grooves of the insulating body. With other forms of connection, they may need to be retained, either just by maintaining tension in the cable, or by using an appropriate clamping member.

When the main cable has metallic armour (or sheath) of any kind and/or an annular earth conductor, this will need to be connected from one side of the joint to the other, and in some other cases a tensile connection will be needed across the joint. Either or both of these functions can be fulfilled by suitable clamps mounted on a base-plate on which the insulating block may also be mounted to form a rigid assembly. Another possibility is for clamps on the cut-back cable ends to be connected by a number of rods, with or without mounting the insulating block on them. Other arrangements are of course possible, including in particular arrangements in which a length of insulated conductor is used to make the elctrical connection and is laid in one of the grooves of the insulating block and otherwise treated like the incsulated conductors of the cable, with or without using a separate tensile member.

The assembly described may be enclosed in any convenient way suited to its intended use environment, for instance in a rubber or thermoplastic moulding, in a shell filled with a casting resin, or by a wrap-round heat-shrink enclosure. An earth screen may be provided if required.

The invention will be further described, by way of example, with reference to the accompanying drawings in 6 which: Figure I is a diagrammatic view showing key parts of one form of cable joint ready for assembly; Figure 2 is a similar diagrammatic view on a larger scale and 5 seen from a different direction; and Figure 3 is a view corresponding to Figure 1 and showing a modified design.

In the preferred form shown in Figure 1, the joint comprises an insulating block assembled from three parts, namely a core 1 and two identical outer parts 2, 3. This has two objects: first, to simplify the moulding of a fairly complex shape, and second to allow the use of two different materials; specifically, it allows the selection of a heavily-filled polymer with relatively good fire-survival properties for the core and one with good precis ion-moulding and electrical properties for the outer parts. The core 1 has fins 4 providing interlock against separation except by sliding in the vertical direction (references to the vertical refer only to the orientation seen in the drawings) and positioned to resist movement of metallic parts towards one another even if the outer parts are melted or pyrolised.

The outer parts 2, 3 when assembled with the core form a generally cylindrical body with external grooves 5 (of which three are shown) so that the whole resembles a triple pulley wheel. Each groove can accomodate two conductors of the main cable to be tapped, on opposite sides of the block; for clarity only one of these (referenced 6) is shown. The outer parts also provide bores 7 which are vertical and receive elongate members 8 in the form of brass contact tubes designed to receive pins in sockets 9 in their upper ends. These are, in the preferred design, arranged uniformly around a pitch circle and are externally identical, but one is prefereably formed with a larger socket 9 than the others to "polarise" the connector and usually to act as earth (or ground) contact. This may be placed in any of the bores 7 on 7 the side of the block to which the corresponding (earth) conductor of the cable is applied. From each of the bores 7. three radial bores 10 extend, one to each of the grooves 5, and an insulation-piercing element 11 is placed in a selected one of these (exceptionally more than one of them, for instance if neutral - to- earth bonding is desired at the joint). There are also auxiliary, rectangular radial bores 12 for reception of brass channel members 13 in corresponding positions. These channel members have aligned apertures 14 in their limbs 15 into which the corresponding elongate member 8 is inserted (obviously after the limbs 14 have been inserted into the bores 12) and threaded apertures 16 in their bases 17 for reception of insulation- piercing screws 18.

The electrical connections will be better understood by reference to Figure 2, in which the insulating blocks are omitted and the metal parts shown partly assembled. The screw 18 constitutes the "first" insulation-piercing element as described above and the element 11 the "second"; on tightening the screw, both of these elements are driven through the insulation of the cable conductor 6 to make effective electrical contact with it, and at the same time the element 11 and the apertured limbs of the channel member 13 are brought into pressure contact with the elongate member 8, ensuring sound electrical contact and also securing the parts mechanically together.

The element 11 (and/or the screw 18) may be pointed as shown in the main drawings, or may have an annular sharp edge as shown at lla.

Figure 2 also shows diagrammatically how one of the pins 19 of a plug 20 may be inserted in the socket 9 in the top of elongate member 8.

Returning now to Figure 1, a socket-top moulding 21 may be clamped to the top of the assembly by a central screw passing through a bore 22 in the core 1 and co-operating with a plain base-plate (not shown) to clamp the parts together.

8 This moulding may receive any appropriate type of plug and may be formed with ribs, grooves or other polarising formations to facilatate correct insertion of the plug, in line with normal practice in this regard. A preferred form of plug is the subject of another application filed simultaneously with this application.

The alternative design of Figure 3 is substantially identical except that the core and outer parts of the insulating block are replaced by a onepiece moulded block.

9

Claims

CLAIMS I An electric cable joint for a multiconductor main cable

comprising: an insulating block inserted between unstripped conductors of the said cable, the said block having opposite convex surfaces each with a plurality of grooves in some or all of which the said insulated conductors are accommodated; conductive elongate members mounted within the said block, each extending generally parallel to the said convex surfaces and forming or connected to an accessible contact element (such as a pin or a socket) at one of its ends; bores in the said block, each such bore extending from one of the said grooves to one of the said elongate members and there being more than one such bore for each groove, extending to a different elongate member and more than one such bore for each elongate member, extending from different grooves; and insulation- piercing contacts in some but not all of the said bores each providing a connection from an insulated conductor laid in the groove from which the bore extends to the elongate member to which it extends.

2 An electric cable joint as claimed in calim 1 in which the elongate members are positioned on a pitch circle and bores for connections extend from each elongate member only to the grooves on the adjacent side of the insulating block.

3 An electric cable joint as claimed in claim 1 or claim 2 in which the contacts for connecting the cable conductors to the elongate members each comprises a channel member having two generally parallel limbs with aligned apertures through which the elongate member passes, a first insulation- piercing element mounted to the base of the channel member for movement towards an insulated conductor placed between the limbs of the channel member and a second insulation-piercing element positioned between the elongate member and an insulated conductor so placed, the second insulation-piercing element being located in one of the bores of the insulating body.

4 An electric cable joint as claimed in claim 3 in which additional bores are provided to locate the limbs of the channel member individually.

An electric cable joint as claimed in claim 3 or claim 4 in which both of the insulation-piercing elements and the channel member are all conductive.

6 An electric cable joint as claimed in claim 3 or claim 4 in which the channel member and/or the first insulation piercing element are insulating or insulated.

7 A electric cable joint substantially as described with reference to Figures 1 and 2 or Figures 2 and 3.

8 A method of making a an electric cable joint for a multiconductor main cable comprising: exposing the insulated conductors of the main cable but not stripping insulation from them; providing an insulating block having opposite convex surfaces each with a plurality of grooves, conductive elongate members mounted within it, each extending generally parallel to the said convex surfaces and forming or connected to an accessible contact element at one of its ends, bores in the block, each such bore extending from one of the said grooves to one of the said elongate members and there being more than one such bore for each groove, extending to a different elongate member and more than one such bore for each elongate member, extending from different grooves; inserting insulation-piercing contacts in at a least two but not all of the said bores, each extending from a different one of the said grooves to a different elongate member; and placing the insulated conductors of the main cable in respective ones of the said grooves including the grooves from which the insulation-piercing contacts extend.

9 A method as claimed in claim I comprising connecting the cable conductors to the elongate members by a connector I I comprising a channel member having two generally parallel limbs with aligned apertures through which the elongate member is passed, a first insulation-piercing element mounted to the base of the channel member for movement towards an insulated conductor placed between the limbs of the channel member and a second insulation-piercing element positioned as defined in a bore of the insulating block between the elongate member and the insulated conductor. 10 A method as claimed in claim 9 comprising using an insulating block with additional bores to locate the limbs of the channel member individually.

11 A method as claimed in claim 9 or claim 10 comprising using a connector in which both of the insulation-piercing elements and the channel member are all conductive.

12 A method as claimed in claim 9 or claim 10 comprising using a connector in which the channel member and/or the first insulation- piercing element are insulating or insulated. 13 A method as claimed in any one of claims 8-12 comprising using a tool which grips the cable on both sides of the part where the insulated conductors have been removed and relatively rotates the sides in the direction tending to cancel the lay of the cable conductors and/or urges the ends towards one another.

14 A method of making a cable joint substantially as described with reference to the drawings.

A cable-jointing kit comprising an insulating block to be inserted between unstripped conductors of the said cable, the said block having opposite convex surfaces each with a plurality of grooves in some or all of which the said insulated conductors are accommodated; conductive elongate members mounted or for mounting within the said block, each extending generally parallel to the said convex surfaces and forming or connected to an accessible contact element at one of its ends; 12 bores in the said block, each such bore extending from one of the said grooves to one of the said elongate members and there being more than one such bore for each groove, extending to a different elongate member and more than one such bore for each elongate member, extending from different grooves; and insulation-piercing contacts for insertion in some of the said bores so as to provide a connection from an insulated conductor laid in the groove from which the bore extends to the elongate member to which it extends. 16 A kit as claimed in claim 15 in which the elongate members are positioned on a pitch circle and bores for connections extend from each elongate member only to the grooves on the adjacent side of the insulating block.

17 A kit as claimed in claim 15 or claim 16 in which the contacts for connecting the cable conductors to the elongate members each comprises a channel member having two generally parallel limbs with aligned apertures through which the elongate member may pass, a first insulation-piercing element mounted to the base of the channel member for movement towards an insulated conductor placed between the limbs of the channel member and a second insulation-piercing element to be positioned between the elongate member and an insulated conductor so placed, the second insulationpiercing element being to be located in one of the bores of the insulating body. 18 A kit as clamed in claim 17 in which additional bores are provided to locate the limbs of the channel member individually.

19 A kit as claimed in claim 17 or claim 18 in which both of the insulation-piercing elements and the channel member are all conductive. 20 A kit as claimed in claim 17 or claim 18 in which the channel member and/or the first insulation-piercing element are insulating or insulated.

13 21 A kit substantially as described with reference to Figures 1 and 2 or Figures 2 and 3.