GB2342508A

GB2342508A - Gripping electrical cables

Info

Publication number: GB2342508A
Application number: GB9814812A
Authority: GB
Inventors: Richard Weatherley
Original assignee: R W DATA Ltd
Current assignee: R W DATA Ltd
Priority date: 1998-07-08
Filing date: 1998-07-08
Publication date: 2000-04-12
Anticipated expiration: 2018-07-08
Also published as: GB0212558D0; GB2372890A; GB9814812D0; GB2372890B; GB2342508B

Abstract

One method for gripping electrical cables comprises inserting a member 1 into the end of the cable sheath. The sheath can then be clamped between the arms 4 of the member and an external clamp, without putting pressure on the conductors, which run through longitudinal channels of the member. Another method uses a connector having a clamping member 14, 15. This is made as part of the connector (fig 7) but is broken off under pressure and latches into a new position. As the clamp is V-shaped it does not distort the cable as much as a flat clamp would. The methods can be used separately or together, and may be used in telecommunications connectors.

Description

GRIPPING OF ELECTRICAL CABLES This invention relates to the gripping of electrical cables, and more particularly relates to method and products for use in gripping an electrical cable adjacent the end thereof.

The term"electrical cable"used herein is to be construed broadly as covering a wide range of products which have one or more electrical conductors surrounded by one or more insulating covers. The invention is of particular utility in the context of cables used in telecommunications and data installations which comprise several pairs of individual insulated wires. Each pair of insulated wires is twisted together to form a so called"twisted pair"and the various twisted pairs are located within a common outer sheath. A typical cable of this type may consist of four twisted pairs within a single common sheath. It is to be understood, however, that the invention is not limited to such cables and indeed certain aspects of the invention may be generally applicable to a wide range of electrical cables having single or multi-strand conductors in various configurations, and of varying size and stiffness.

At the end of a cable, where it is connected to a plug or fixed appliance, it is often necessary to grip the cable to prevent strain being applied to the electrical connections. In the prior art, such gripping is often effected by compressing the cable between a fixed abutment and a movable clamping bar. The clamping bar is generally rigid or very stiff and the cable is compressed either by drawing the clamping bar towards the abutment by means of screws or the like, or by applying an external force to the clamping bar.

Such arrangement of the prior art have a number of disadvantages. In particular, in order to effect secure gripping of the cable a considerable compressive force must be applied. This compressive force will tend to distort the cable and disturb the natural internal arrangement of the conductors within the cable. This is in general undesirable, but is particular undesirable in the case of telecommunications or data cables where disturbing the internal arrangement of the conductors may increase the crosstalk therebetween.

According to one aspect of the present invention a method of gripping a cable which comprises a plurality of insulated conductors located within a cable sheath comprises: providing a support device comprising a plurality of longitudinally extending walls which are interconnected along the longitudinal centre of the device to provide a plurality of channels; inserting the support device into the cable sheath from the end thereof so as to position the support device with the walls thereof located at least partially within the cable sheath and the conductors of the cable located within the respective channels of the support device; and clamping the exterior of the cable by compressing it between an abutment and a clamping member to press the sheath into engagement with the arms of the support device.

In general, the support device will have a number of walls corresponding to the number of conductors or groups of conductors located within the cable. Thus, if the cable includes four twisted pairs of conductors the support device will have four walls so that one twisted pair may be located within each channel of the support device.

The effect of this arrangement is that the support device maintains the desired relative position of the conductors within the cable at the point of clamping, and at the same time limits the extent to which the cable is crushed during the clamping operation.

Accordingly, although a substantial clamping force may be applied to the exterior of the cable much of that clamping force is supporte internally of the cable by the support device and the conductors themselves are not subject to excessive compression.

Preferably, the walls of the support device are formed with a spiral twist so that the channels formed there between naturally follow the general line of the conductors within the cable. Such twisting of the walls of the support device assists the insertion of the support device into the cable sheath and further assists in maintaining the natural orientation of the conductors within the sheath.

In general, at the end of the cable the conductors must be separated from each other and connected to electrical terminas. In one preferred embodiment of the invention one end of the support device is formed with guide means for guiding the individual electrical conductors or pairs of electrical conductors to the desired location for connection to electrical terminals. To this end, the support device is formed integrally with a guide which provides passages for the individual conductors or groups of conductors within the cable. Such passages not only assist in presenting the individual conductors to the correct position for electrical termination, but also assist in maintaining a desired relative position of the conductors with a view to reducing to a minimum crosstalk induced between the conductors at the termination. In the case when the cable has groups of conductors, for example twisted pairs of conductors, the passages may initially receive all conductors of the group and made divide to provide individual passage for individual conductors.

In an alternative embodiment of the invention the support device performs purely a support and separations function and is accordingly sized to be inserted substantially completely within the cable sheath.

In accordance with the second aspect of the invention, which may be used in combination with or independently of the first aspect of the invention, a device for gripping a cable comprises a body which defines an aperture for passage of the cable to be gripped; an abutment surface defined by the body on one side of the aperture; and one or more clamping members for clamping the cable against the abutment surface; the clamping member being initially formed integrally with the body by a moulding process and in the as moulded condition being spaced from the abutment surface on the opposite side of the aperture thereto to allow passage of the cable through the aperture, the or each clamping member being movable, after insertion of a cable, from the as moulded position to a use position in which the cable is clamped between the abutment surface and the or each clamping member and the or each clamping member is locked in position by abutment of a latch surface on the clamping member with a latch surface defined on the body.

Preferably, two clamping members are provided symmetrically on either side of the longitudinal central plane of the aperture with the clamping surfaces of the clamping members generally parallel to the abutment surface in the as moulded configuration. After the cable has been inserted both clamping members are forced towards the abutment surface with a rotating action whereby one edge of each clamping member remains in substantially in its as moulded position relative to the remainder of the body whilst the opposite edge of the clamping member moves towards the abutment surface. Accordingly, in the in use configuration the clamping surfaces of the clamping members form a V and the cable is trapped between the V configuration of the clamping surfaces of the clamping members and the abutment surface. Preferably, the clamping members remain attached to the remainder of the body as they are moved into their use configuration.

The preferred embodiment of this aspect of the invention provides a clamping arrangement which is initially a unitary one-piece moulding of a suitable plastics material and which can be activated to clamp a cable by a simple rotation of the clamping members. Such rotation can readily be affected by a machine or hand tool.

The cable, as clamped, is compressed within a generally triangular space between the V-surface defined by the clamping members and the generally flat surface of the abutment surface. By clamping the cable within such a triangular space, rather than with the generally oblong space in prior art arrangements, effective gripping of the cable can be obtained without excessive distortion of the cable and accordingly the undesirable displacement of the conductors referred to above is avoided.

Whilst the second aspect of the invention is particularly useful when used in association with the first aspect of the invention, it will be appreciated that the two aspects of the invention are independently useful. An improved gripping arrangement can be obtained by using the first aspect of the invention in association with a conventional abutment/bar clamping system and, equally, a satisfactorily gripping may be obtained using the clamping device of the second aspect of the invention even if the support device of the first aspect is not used.

The invention will be better understood from the following description of preferred embodiments thereof, given by. way of example only, reference being hand to the accompanying drawings wherein Figure 1 illustrates schematically and in perspective view an embodiment of support device for use in the first aspect of the present invention ; Figure 2 is a side view of the device of Figure 1; Figure 3 is an end view of the device of Figure 1 ; Figure 4 is a perspective view of a plug incorporating a gripping device according to the second aspect of the present invention; Figure 5 is an end view of the plug of Figure 4; Figure 6 is a longitudinal cross-section of the plug of Figure 4; Figure 7 is a partial cross-sectional view on the line VII-VII of Figure 6 and Figure 8 is a perspective cross-sectional view illustrating the device of Figures 4-7 after it has been activated to clamp a cable in position.

Referring firstly to Figures 1-3 there is illustrated a support device 1 comprising a support portion 2 and a guide portion 3. The support portion 2 comprises four walls 4 which extend longitudinally of the support portion and join along the longitudinal axis of the support portion. Each adjacent pair of walls defines therebetween a channel 5. The walls 4, and accordingly the channels 5 are somewhat spirally twisted along the length of the support portion 4. The illustrated support device is intended to be used in connection with a cable having four twisted pairs of conductors. In such cables the twisted pairs are laid with each other in a slow spiral, and the spiral of the walls 4 is intended generally to match the spiral of the twisted pairs.

The guide portion 3 defines four passages 6 each of which, in use, receives one twisted pair of conductors. It will be appreciated that each channel 5 has associated therewith a passage 6 so that the conductors naturally pass from the channels 5 into the passages 6. The passages 6 ensure separation of the twisted pairs from each other and position the twisted pairs correct for subsequent termination.

In use, when it is desired to terminate a cable the cable is cut to length and the outer sheath is stripped a predetermined distance from the end of the cable so as to expose the twisted pairs within. The twisted pairs are separated from each other and the support device I is offered up to the cable with the somewhat tapered nose 7 leading. The twisted pairs are manipulated to lie within the channels 5 and the support device is pushed home with a slight twisting action until the support portion 2 is located substantially entirely within the sheath of the cable. The twisted pairs are laid within the passages 6. The cable may then be gripped by an appropriate clamping mechanism which clamps the cable between abutment surfaces. When such a clamping force is applied over the portion of the cable in which the support portion 2 is located crushing of the cable is prevented by the support portion, and the channels 5 maintain the twisted pairs in their correct position relative to each other. In effect, the outer sheath of the cable will be pushed into firm engagement with the abutment surfaces between which it is clamped and the edges of the walls 4 will be pushed into firm engagement with the interior surface of the cable sheath. The wall thickness and material from which the support device is constructed is selected to withstand significant crushing forces and accordingly although the outer sheath of the cable will be firmly gripped between the abutment surfaces little or no crushing of the conductors will occur.

It will be appreciated that in certain circumstances the guide portion may be dispensed with and a support device consisting substantially only of the support portion 2 may be used. Further, it will be appreciated that the size, shape and number of the walls 4 will be determined by the nature of the cable with which the device is to be used. Further, whether or not the walls twist in a spiral manner (as illustrated) and if so the angle at which twist occurs will be determined by the particular application of the support device.

If desired, the guide portion may incorporate additional guiding means so that each twisted pair may be split into its separate conductors and guided by the guiding means for easy termination.

Referring now to Figures 4-8 there is illustrated a body of a plug suitable for terminating a cable having four twisted pairs of conductors. The body incorporates a device for gripping a cable in accordance with an embodiment of the invention. The cable gripping arrangement embodied within the device of Figures 4-8 may be used in association with the support device of Figures 1-3 or independently thereof.

Referring now to Figures 4-7 the illustrated plug body is a unitary moulding of a suitable plastics material, for example polycarbonate. In use, the plug body is secured to the end of a cable and conductive pins are mounted on the plug body, connected to the conductors of the cable.

The body 10 defines an aperture 11 through which a cable is inserted. As will be clear from Figure 5, the aperture 11 leads to a series of passageways 12 each for receiving a conductor of a four twisted pair cable. The passageways 12 guide the conductors of the cable for connection to the terminas of the plug.

One side of the aperture 11 defines an abutment surface 13 against which the cable is, in use, clamped in order to grip the cable and prevent tension being applied to the conductors thereof. In order to clamp the cable against the abutment surface 13 the body is moulded with a pair of clamping members 14,15. In the as moulded condition of the plug (as illustrated in Figures 4-7) the clamping members 14,15 are an integral part of the plug body and each defines a clamping surface 16 which is generally parallel to and spaced from the abutment surface 13. Between the clamping members 14,15 is a central bridge portion 17 which is integral with both clamping members and with the remainder of the plug body.

After a cable has been inserted into the plug (optionally having been provided with the support device of Figures 1-3) the clamping members 14,15 are pressed inwardly of the body to sever the connections 18,19 between the clamping members and the remainder of the body at the outer edges of the clamping members. Continued inward force on the clamping members will cause them to rotate about the central bridge portion with the result that the clamping surfaces 16 will adopt a generally inverted V configuration (when the components are in the orientation illustrated in the drawings). After rotation of approximately 60 the apexes 20 of the clamping members will snap past the comer formed at the point where the connections 18-19 were severed. The geometry of the components is such that after the apexes 20 have snapped passed this shoulder reverse rotation of the clamping members will not be possible since a latch surface 21 formed by a portion of each clamping member immediately adjacent the apex 20 will engage a latch surface 22 formed by the upper wall of the aperture 11. Provided that the geometry of the plug body is matched that of the proposed cable the snapping of the apexes into position will correspond to the cable being locked in position. This configuration is illustrated in Figure 8. It will be noted that in this configuration the surfaces 16 of the clamping members 14,15 form a generally inverted V and that the cable 23 is trapped between these V-shaped clamping surfaces 16 and the generally flat abutment surface 13 of the plug body. It will be noted that in the use configuration of the plug as illustrated in Figure 8 the bridge portion 17 remains connected to the remainder of the body thereby controlling the position and orientation of the clamping members 14,15.

It will be readily apparent to those skilled in the art that the setting of the clamping device may readily be accomplished by a machine or hand tool.

As illustrated in Figure 8 the cable 23 has been fitted with a support device 24 generally in accordance with the arrangements shown in Figures 1-3. It is to be understood, however, that the clamping device described may be utilise without using the support device. In this context, it will be noted that although the support device assists in preventing crushing of the cable, the clamping configuration of the gripping arrangement illustrated in Figure 8 tends in any event to produce less crushing of the cable than conventional arrangements where the cable is clamped between a substantially flat abutment surface and a substantially flat clamping bar.

Claims

CLAIMS 1. A method of gripping a cable which comprises a plurality of insulated conductors located within a cable sheath, the method comprising: providing a support device comprising a plurality of longitudinally extending walls which are interconnected along the longitudinal centre of the device to provide a plurality of channels; inserting the support device into the cable sheath from the end thereof so as to position the support device with the walls thereof located at least partially within the cable sheath and the conductors of the cable located within the respective channels of the support device; and clamping the exterior of the cable by compressing it between an abutment and a clamping member to press the sheath into engagement with the arms of the support device.
2. A method of gripping a cable according to claim 1 wherein the support device has a number of walls corresponding to the number of conductors or groups of conductors located within the cable.
3. A method of gripping a cable according to claim lor claim 2 wherein the walls of the support device are formed with a spiral twist so that the channels formed there between naturally follow the general line of the conductors within the cable.
4. A method of gripping a cable according to any preceding claim wherein the support device is formed with guide means for guiding the individual electrical conductors or pairs of electrical conductors to the desired location for connection to electrical terminas.
5. A method of gripping a cable according to any preceding claim wherein the support device is formed integrally with a guide which provides passages for the individual conductors or groups of conductors within the cable.
6. A method of gripping a cable according to any of claims 1 to 4 wherein the support device is sized to be inserted substantially completely within the cable sheath.
7. A device for gripping a cable, the device comprising: a body which defines an aperture for passage of the cable to be gripped; an abutment surface defined by the body on one side of the aperture; and one or more clamping members for clamping the cable against the abutment surface; the clamping member being initially formed integrally with the body by a moulding process and in the as moulded condition being spaced from the abutment surface on the opposite side of the aperture thereto to allow passage of the cable through the aperture, the or each clamping member being movable, after insertion of a cable, from the as moulded position to a use position in which the cable is clamped between the abutment surface and the or each clamping member and the or each clamping member is locked in position by abutment of a latch surface on the clamping member with a latch surface defined on the body.
8. A device for gripping a cable according to claim 7 wherein two clamping members are provided symmetrically on either side of the longitudinal central plane of the aperture with the clamping surfaces of the clamping members generally parallel to the abutment surface in the as moulded configuration.
9. A device for gripping a cable according to claim 7 wherein the clamping arrangement is initially a unitary one-piece moulding of a suitable plastics material which can be activated to clamp a cable by a simple rotation of the clamping members.