GB2104307A

GB2104307A - Improvements in electrical coupling devices

Info

Publication number: GB2104307A
Application number: GB08124114A
Authority: GB
Inventors: Derek Hayes
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-08-06
Filing date: 1981-08-06
Publication date: 1983-03-02

Abstract

An electrical coupling device comprises an electrically-insulating part 1a defining a recess 7, and electrically- conductive metallic piercing means 11 mounted in the recess 7 and extending generally in the direction of a pair of opposed sides of the recess. Associated with the recess 7 is a pair of cooperating, relatively movable jaws arranged to receive between them and locate an insulated electrical conductor when the jaws are urged towards one another, at least one end of the pair of jaws being configured to enter into the recess 7 and to allow entry of the piercing means 11 between the jaws and piercing of the conductor by the piercing means 11 when said one end of the jaws is advanced into the recess 7. The outer surfaces of the pair of jaws and said opposed surfaces of the recess 7 are configured to produce a camming action such that advancing the jaws into the recess 7 urges the jaws towards one another to locate the conductor at least during piercing of the conductor by the piercing means 11. The pair of cooperating jaws comprises a resilient metallic framework 22, 23 which provides a hinge connection 21 between the two jaws at said one end of the pair of jaws and comprises a pair of members 26, 27 which define mutually confronting surfaces for receiving and locating the conductor. The members 26, 27 are biased towards one another when the two jaws are urged together to locate the conductor 45 therebetween, and the framework 20 has two electrically-insulating parts 32, 33 secured thereto which form at least the ends of the respective jaws lying remote from said one end of the pair of jaws. The jaws may have portions 52 which retain the joint in the socket. <IMAGE>

Description

SPECIFICATION Improvements in electrical coupling devices This invention relates to an electrical coupling device of the kind comprising a body portion having an electrically insulating part with a recess in its surface, and electrically-conductive metallic piercing means mounted in said recess and extending generally in the direction of a pair of opposed sides of the recess but lateraily spaced therefrom, and conductor-locating means comprising a pair of cooperating jaws movable relative to each other and having first mutually confronting surfaces configured to receive between them and locate an insulated electrical conductor when said jaws are urged towards one another, at least one end of said pair of jaws being configured to enter into said recess and to allow entry of said piercing means between the jaws and piercing of said conductor by said piercing means when said one end of said jaws is advanced into said recess, the outer surfaces of said pair of jaws and said opposed surfaces of said recess being configured to produce a camming action such that advancing said jaws into said recess urges the jaws towards one another to locate said conductor at least during piercing of the conductor by the piercing means. An electrical coupling device of this kind is described in my British Patent Specification No. 1,559,789 (hereinafter called "the aforesaid Specification").

In an electrical coupling device of the kind referred to, the current-carrying capacity of the device is dependent on the achievement of good physical contact between the piercing means and the conductor, and in the coupling device described in the aforesaid Specification the accurate location of the conductor by the jaws during the conductor-piercing operation ensures that the area of contact between the piercing means and the conductor is a maximum. Furthermore, if the jaws are dimensioned so that the insulated conductor is gripped by the jaws, an enhanced contact pressure between the piercing means and the pierced conductor can be obtained for all normal usages of the coupling device.

However, it is possible for a person to misuse a coupling device of the kind referred to, by using it to carry a current in excess of the normal current rating of the conductor which has been pierced by the piercing means.

When mis-used in this way for an extended period of time, the pierced conductor can overheat and this can result in shrinkage of the insulation of the conductor and, if they are made of thermoplastics material, shrinkage of the jaws. Furthermore, ageing of the conductor can result in shrinkage of its insulation, and the thermoplastics material of the jaws may also shrink due to ageing. If the conductor is gripped and not just located by the jaws, all of these occurrences may result in reduction of the contact pressure between the piercing means and the conductor, giving rise to overheating of the conductor portion located within the jaws (due to the increased contact resistance) and the possibility of breakdown of the coupling device.

The present invention aims to provide an electrical coupling device of the kind referred to in which there is a considerably reduced risk of breakdown of the device in the way described above.

According to the invention, in an electrical coupling device of the kind referred to, the pair of cooperating jaws comprises a resilient metallic framework which serves as a hinge connection between the two jaws at said one end of the pair of jaws and comprises a pair of members which define said first mutually confronting surfaces, which members are biased towards one another when the two jaws are urged together to locate an insulated conductor therebetween, said framework having two electrically-insulating parts secured thereto which form at least the ends of the respective jaws lying remote from said one end of the pair of jaws.

Preferably, said framework is constructed from a single strip of resilient metallic material, for example phosphor bronze, and said electrically-insulating parts are made of a thermoplastic or thermosetting synthetic resin material.

In use of an electrical coupling device in accordance with the invention, the biasing of the two members of the metallic framework results in the insulated conductor being firmly held by the jaws, even if shrinkage of the insulation of the conductor, the electricallyinsulating parts of the jaws or the walls of the recess into which the jaws are inserted, due to mis-use or ageing, should occur. Furthermore, the metallic framework serves to conduct heat away from the region of the pierced conductor so that the risk of the conductor or the jaws overheating is considerably reduced.

Preferably, the part of the metallic framework which provides the hinge connection between the jaws is biased to urge the two jaws away from one another, so that when the pair of jaws is partially withdrawn from the recess, the ends of the jaws remote from said one end of the pair of jaws are urged apart to facilitate the entry of the insulated conductor between the jaws.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a plan of a part of one embodiment of a 3-pin, 1 3-amp plug in accordance with the invention, Figure 2 is a sectional view taken on the line ll-ll of Fig. 1, Figure 3 is an exploded perspective view, on an enlarged scale, of a pair of jaws of the plug of Figs. 1 and 2, Figure 4 is a view, on an enlarged scale, of part of Fig. 2, but showing the pair of jaws of Fig. 3 fully inserted into the recess, Figure 5 is a plan corresponding to Fig. 4, Figure 6 is a view similar to Fig. 4, but showing the pair of jaws partially withdrawn from the recess, and Figure 7 is an end view of a second embodiment of a pair of jaws for use in the plug of Figs. 1 and 2.

The plug shown partly in Figs. 1 and 2 has a base 1 with a first surface 2 from which the live, netural and earth pins 3, 4 and 5, respectively, of the plug project. The plug is of the kind described in the aforesaid Specification and has recesses 6, 7 and 8 opening into a second surface 9 of the base for the reception of pairs of conductor-locating jaws of a kind similar to those illustrated in, and described with reference to, Figs. 7 and 8a 8c of the aforesaid Specification. These jaws are not shown in Figs. 1 and 2, but will be described in detail hereinafter.

In each of the recesses 6, 7 and 8 of the base 1 of the plug there is a respective metallic insulation-piercing means 10, 11 and 1 2 for piercing the electrical insulation of, and making electrical contact with, the conductors which are pressed into the recesses 6, 7 and 8 using the conductor-locating jaws, all as described fully in the aforesaid Specification.

The piercing means 10 is electrically connected to the pin 3 by metallic strips 13, 14 and a fuse holder 15, the piercing means 11 is electrically connected to the pin 4 by a metallic strip 1 6 and the piercing means 1 2 is electrically connected directly to the pin 5.

The base 1 comprises upper and lower parts 1 a, 1 b, respectively, secured together with any suitable fastening means (not shown), e.g. screws or rivets, and the strips 13, 1 4 and 1 6 are conveniently located at the interface boundary between the parts 1 a, 1 b. The fuse holder 1 5 is conveniently sunk into a recess 1 7 in the surface 2 of the base 1, for example in the manner shown in Fig. 1 of the aforesaid Specification (see fuse 30 in recess 29).

A fourth recess 1 8 opening into the surface 9 of the base 1 serves to receive the jaws (not shown) of a cable grip.

A cover 1 9 (shown in chain lines in Fig. 2) is removably mountable on the base 1 to overlie the surface 9 of the latter.

Fig. 3 is a perspective view of a pair of jaws for insertion in any one of the recesses 6, 7 and 8, the parts in Fig. 3 being shown in the positions they adopt when the pair of jaws, in assembled condition, is fully inserted into the recess, as shown in Fig. 4 in which the pair of jaws is shown in the recess 7.

Referring to Fig. 3, the pair of jaws shown comprises a metallic framework generally designated by the numeral 20. The framework 20 is made from a strip of resilient metallic material, for example phosphor bronze, which is bent to provide a bottom piece 21, two side pieces 22, 23, two top pieces 24, 25 and two members 26, 27 depending downwardly from the top pieces 24, 25, respectively. Each of the top pieces 24, 25 has two holes 28 formed therein and along each of its edges each of these top pieces has a bent down tab 29. At its end remote from the top piece 24, 25 to which it is joined, each of the members 26, 27 is shaped to provide an inwardlyfacing channel 30 of approximately semicircular cross-section.When the two members 26, 27 are close together, as shown in Fig. 3, the two channels 30 define a hole 31 of approximately circular cross-section having its longitudinal axis disposed parallel to the bottom piece 21 and to the side pieces 22, 23.

Two electrically-insulating parts, generally designated by the numerals 32 and 33, made for example of a thermopiastics material such as nylon or a thermosetting material, are secured to the framework 20. Each of the parts 32, 33 is in the form of an inverted U, having spaced-apart limbs 34, 35 and 36, 37, respectively, these pairs of limbs being connected by bridging pieces 38, 39, respectively. The underside of the bridging piece 38 is formed with two projections 40 adapted to engage in the pair of holes 28 in the top piece 24 of the framework 20 and the confronting surfaces of the limbs 34 and 35 are provided with a respective recess, such as the recess 41 in the limb 34, for the reception of one of the tabs 29 of the top piece 24 of the framework 20. The confronting surfaces of the limbs 34 and 35 are also provided with respective projections, such as the projection 42 on limb 34.The part 33 is formed in the same way as the part 32 and has recesses similar to the recess 41 in the confronting surfaces of the limbs 36, 37 projections 42 on the confronting surfaces of the limbs 36, 37 and projections similar to the projections 40 on the underside of the bridging piece 39.

The parts 32 and 33 are mounted on the framework 20, as can be seen in Fig. 4, with the projections 40 engaged in the holes 28, with the tabs 29 engaged in the recesses 41 and with the projections 42 projecting into the framework 20 inside the side pieces 22, 23 and immediately above the bottom piece 21. The resulting assembly consists of a first jaw, formed by the items 22, 24, 26 and 32, a second jaw, formed by the items 23, 25, 27 and 33, and a hinge connection for the two jaws formed by the bottom piece 21.

The surfaces of the limbs 34 and 36 and 35 and 37 which confront one another when the two jaws are urged together (as shown in Figs. 3 and 4) have channels 43 extending across them, these channels being of approximately semicircular cross-section. When the two parts 32 and 33 are close together (as shown in Figs. 3 and 4) the channels 43 define two holes 44 of approximately circular cross-section, and when the parts 32, 33 have been mounted on the framework 20 the hole 31 of the latter is disposed between, and in axial alignment with, the two holes 44.

Fig. 4 shows the pair of jaws of Fig. 3 fully inserted into the recess 7 of the plug base shown in Figs. 1 and 2, with an insulated electrical conductor 45 located between the members 26, 27 of the jaws. The piercing means 11 has passed through a slot 46 in the bottom piece 21 of the framework 20 and has penetrated the conductor 45 which is firmly gripped by the members 26 and 27. The latter are biased towards one another so that, with no conductor 45 between them, their lower ends are urged into contact with one another, as shown in Fig. 3.The presence of the conductor 45 between the members 26, 27 forces the latter apart, with the result that the conductor is firmly gripped and will remain so if shrinkage of the conductor insulation, of the electrically-insulating parts 32, 33 of the jaws, or of the walls of the recess 7, occurs due to ageing or to over-heating of the coupling device. Furthermore the metallic framework helps to conduct heat away from the conductor 45, thus decreasing the risk of the jaws becoming over-heated.

Another advantage of using the metallic framework 20 in the pair of jaws is that the bottom piece 21 gives better guidance to the piercing means 11 compared with a hinge of plastics material. As a result of this, the conductor-locating slots 30 in the members 26, 27 can be positioned nearer to the hinged end of the pair of jaws than when a hinge of plastics material is used, leading to a more compact design.

In Fig. 1 it will be seen that the end faces of the recesses 7, 8 and 6 are provided with auxiliary recesses 47, 48 and 49, respectively. The provision of such auxiliary recesses has already been proposed in the aforesaid Specification (see the auxiliary recesses 23a, 24a in Fig. 3 of that Specification) for the purpose of accommodating the free ends of the insulated conductors located by the pairs of jaws inserted into the main recesses. In order to prevent access to the exposed ends of the insulated conductors received in the auxiliary recesses 47-49, the parts 32, 33 of the jaws may be provided with projections 50, 51, respectively, as shown in chain lines in Fig. 5, which close the upper ends of the auxiliary recesses when the jaws are fully inserted into their associated recesses.

Fig. 6 shows the pair of jaws partly withdrawn from the recess 7. The hinge connection formed by the bottom piece 21 of the framework 20 is biased so that the two jaws are urged apart in this partly withdrawn position, thus facilitating the positioning of an insulated conductor between the members .26, 27. The pair of jaws may be captive in the recess 7, and to this end tabs 52 are stamped out of the side pieces 22, 23 of the framework 20 (see Fig. 3), these tabs being received in slots 53 in the side walls 54, 55 of the recess 7. When the pair of jaws is first inserted into the recess 7, the tabs 52 will deflect upwardly at the entrance to the recess and then snap outwardly into the slots 53.

Alternatively, the part 1 a of the base in which the recess 7 is formed can be made in two portions separable at a horizontal plane desig nated by the line X-X in Fig. 6, the two portions being held together by any suitable fastening means (not shown), e.g. screws or rivets. The pair of jaws can then be inserted into the recess 7, from the lower end of the recess, before assembly together of the two portions of the base part 1 a In this embodi ment it may be convenient to inroduce the piercing means 11 into the recess 7 from a side of the latter at the plane of separation of the two portions of the base part 1 a, as shown in chain lines at 11 a. Parts of the strips 13, 14 and 16 (see Figs. 1 and 2) may be located in the same plane.

To facilitate withdrawal of the pair of jaws from the position shown in Fig. 4 to the position shown in Fig. 6, the side pieces 22, 23 of the framework 20 are provided with holes 56 (see Fig. 3) and the side walls 54, 55 of the recess 7 are provided with narrow slots 57. A thin rod, for example a small screw-driver 58 shown in chain lines in Fig.

4, introduced through one of the slots 57 into one of the holes 56, can then be used to lever the pair of jaws out of the recess 7.

The invention is not, of course, limited to the particular way in which the electrically insulating parts 32, 33 are secured to the metallic framework 20 in the embodiment of Figs. 1 to 6. Other, and possibly simpler, ways of effecting this securement will readily occur to those versed in the art.

Fig. 7 shows a modified pair of jaws suit able for employment in the recesses 6-8 of the coupling device of Figs. 1 and 2. This pair of jaws comprises a metallic framework con sisting of a strip of resilient material, for example phosphor bronze, bent to provide a bottom piece 60 and two upwardly-projecting members 61 and 62. The upper ends of the latter are shaped to provide conductor-locating slots 63 for the conductor 45, and the frame work is biased so that the two members are urged towards one another to grip the con ductor firmly. The bottom piece 60 is pro vided with a slot 64 for the passage there through of the piercing means of the associ ated recess, and the edges of this slot may be curved upwardly to facilitate entry of the piercing means into the pair of jaws. Jaws 65, 66 of electrically-insulating material, for example nylon, are secured to the members 61, 62 respectively. These jaws may, for example, be moulded directly onto the members 61, 62. This modified pair of jaws has the disadvantage, compared with the pair of jaws of Fig. 3, that bottom piece 60, which serves as the hinge connection for the jaws, always biases the jaws 65, 66 towards one another. It is therefore necessary to urge the jaws apart manually when it is desired to enter the insulation conductor 45 between them.

Claims

1. An electrical coupling device comprising a body portion having an electricallyinsulating part defining a recess, and electrically-conductive metallic piercing means mounted in said recess and extending generally in the direction of a pair of opposed sides of the recess but laterally spaced thereform, and conductor-locating means comprising a pair of cooperating jaws movable relative to each other and having first mutually confronting surfaces configured to receive between them and locate an insulated electrical conductor when said jaws are urged towards one another, at least one end of said pair of jaws being configured to enter into said recess and to allow entry of said piercing means between the jaws and piercing of said conductor by said piercing means when said one end of said jaws is advanced into said recess, the outer surfaces of said pair of jaws and said opposed surfaces of said recess being configured to produce a camming action such that advancing said jaws into said recess urges the jaws towards one another to locate said conductor at least during piercing of the conductor by the piercing means, characterised in that said pair of cooperating jaws comprises a resilient metallic framework which serves as a hinge connection between the two jaws at said one end of the pair of jaws and comprises a pair of members which define said first mutually confronting surfaces, which members are biased towards one another when the two jaws are urged together to locate an insulated conductor therebetween, said framework having two electrically-insulating parts secured thereto which form at least the ends of the respective jaws lying remote from said one end of the pair of jaws.

2. An electrical coupling device according to claim 1, wherein said framework is constructed from a single strip of resilient metallic material, and said electrically-insulating parts are made of a thermoplastic or thermosetting synthetic resin material.

3. An electrical coupling device according to claim 1 or claim 2, wherein the part of the metallic framework which provides the hinge connection between the jaws is biased to urge the two jaws away from one another, so that, when the pair of jaws is partially withdrawn from the recess, the ends of the jaws remote from said one end of the pair of jaws are urged apart to facilitate the entry of the insulated conductor between the jaws.

4. An electrical coupling device according to any of the preceding claims, comprising inter-engaging means in said recess and on said framework for preventing complete withdrawal of the pair of jaws from the recess after intitial entry of the jaws into the recess.

5. An electrical coupling device constructed and arranged substantially as herein described with reference to, and as illustrated in, Figs. 1 to 6, or Figs 1 to 6 as modified by Fig. 7, of the accompanying drawings.