WO1983002531A1

WO1983002531A1 - Electrical coupling device

Info

Publication number: WO1983002531A1
Application number: PCT/GB1982/000005
Authority: WO
Inventors: Derek Hayes
Original assignee: Derek Hayes
Priority date: 1982-01-12
Filing date: 1982-01-12
Publication date: 1983-07-21
Also published as: EP0098262A1

Abstract

An electrical coupling device, for example a 3-pin electric plug, for effecting electrical connection between at least one electrically-conducting member of the coupling device, for example contact pins (2, 3 and 4), and the electrically-conducting material of at least one insulated electrical conductor, for example the insulated conductors (7, 8, 9) of an insulated cable (6). The coupling device is of the kind described in U.S. Patent No. 4, 148, 540 and shown in Figures 1 and 2, which comprises an electrically-insulating part 1 supporting said electrically-conducting members (2, 3, 4) metallic, conductor-piercing members (17, 18, 19) mounted on the insulating part 1 and electrically connected to said electrically-conducting members (2, 3, 4) respectively, pairs of conductor-locating jaws (10a, 10b, 11a, 11b and 12a, 12b) for the reception of the insulated conductors (7, 8, 9) respectively, which are to be pierced by the piercing members (17, 18, 19) respectively, for the purpose of effecting electrical connection between the piercing members and the electrically-conducting material of the conductors, and jaw-receiving members (20, 21, 22) associated with the piercing members (17, 18, 19) respectively, for guiding the pairs of jaws onto the respective piercing members and for preventing any substantial separation of the jaws as the insulated conductors are pierced by the piercing members. According to the invention, in a coupling device of this kind, each of the jaws, such as the jaws (28, 29) shown in Figure 6, comprises at least one metallic member (31) which, in use of the coupling device, at least partially displaces the electrically-insulating material (32) of the insulated conductor (7), whereby enhanced contact pressure between the conductor-piercing member (17b) (see Figure 7) and the pierced conductor (7) is achieved by the metallic members (31) bearing substantially directly on the electrically-conducting material of the insulated conductor (7).

Description

Electrical coupling; device

Technical Field

This invention relates to an electrical coupling device, and in particular, but not exclusively, it relates to a 3-pin, 13 amp fused nlug. Background Art

In my United States Patent c. , 1^8,5^0 there is described and claimed an electrical coupling device com¬ prising a body portion having an electrically-insulating part with a recess in its surface, and electrically-conduc-^" tive 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^' therefrom, and conductor-locating means comprising a pair of cooperating jaws movable relative to "each other and having first mutu¬ ally 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 the jaws is advanced into said recess, the outer surfaces of said pair of jaws and said opposed sur¬ faces 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

In U.S. Patent No. 4,148, 54-0 embodiments of the coupling device are described in which the conductor-locatin means comprises a pair of jaws which are hinged together, which pair of jaws is inserted into its associated recess either with its hinged end first (for example as described with -reference to Figures 7 and 8a. - 8c_) or with the end of the pair of jaws remote from its hinged end first. Further- more, in U.S. Patent No. 4,14.8,54.0 it has been proposed to employ a pair of jaws of metallic material as the conductor- locating means (as described with reference to Figure 17).

In the aforementioned embodiments of the coupling device of U.S. Patent No. 4,148,540, adequate contact pressure between each conductor and the metallic piercing means by which it is penetrated, is obtained for all normal uses of the coupling device. However, if the coupling device is mis-used by being made to carry a much higher current than the rated current for the conductor, the insulated conductor may become overheated, leading to deterioration of the insulating material.

The present invention aims to provide an electrical coupling device which has a greater ability to tolerate mis use of the kind just referred to. Disclosure of the Invention

According to one aspect of the present invention, in a electrical coupling device of the kind comprising an elec- trically-insulating part, a metallic, conductor-piercing member mounted on said insulating part, a pair of conductor- locating jaws for the reception of an insulated conductor to be pierced by said piercing member, and a jaw-receiving member associated with said piercing member for guiding the pair of jaws onto the piercing member and arranged to pre¬ vent any substantial separation of the jaws as the con¬ ductor is pierced by the piercing member, each of said jaws comprises at least one metallic member which, in use of the coupling device, at least partially displaces the insulating material of the conductor, whereby enhanced contact pressure between the conductor-piercing member and the pierced conductor is achieved by said at least one metallic member bearing substantially directly on the con¬ ducting material of the insulated conductor. The jaw-receiving member may be arranged, as in the case of the recess described in I..S. Patent No. 4,148,540, to exert a camming action on the pair of jaws to urge the jaws towards one another as they are advanced into the aw-receiving member. In this case, displacement of the insulating material of the conductor may take place at least partly due to the camming action of the jaw-receiving member, although some displacement of the insulating materia may take place at the time of inserting the conductor betwg the two jaws prior to advancement of the jaws into the jaw- receiving member.

Alternatively, the jaw-receiving member may be dimen¬ sioned so that it can receive the pair of jaws, with the insulated conductor located between the jaws, without exerting any camming action on the jaws, and simply pre¬ vents any substantial separation of the jaws as the conduc¬ tor is pierced by the piercing member. In this case, dis¬ placement of the insulating material of the conductor may take place entirely during insertion of the conductor between the two jaws prior to advancement of the jaws into the jaw-receiving member. However, even in this case, slight expansion of the conductive portion of the insulated conductor, due to the penetration of the conductor by the piercing member, may result in further displacement of insulating material from the conductor by said metallic ^• members.

Preferably, said at least one metallic member of each jaw is positioned so that, when the two jaws are inserted into the awrreceiying member, said metallic member- of one jaw is disposed opposite said metallic member of the other ^• jaw and said piercing member is located either in the region between these two opposed metallic- members or closely adjacent to said region. Said jaws may be formed entirely of metallic material, for example stamped from metallic sheet material, said at least one metallic member then being formed as a projection, for example a rib, formed integrally with the conductor- locating surface of the jaw. In this case it is convenient for the two jaws to be joined together to form a substan¬ tially U-shaped cradle for the reception of the insulated conductor, which cradle may be entered into the jaw- receiving member either with the open end or the closed end of the cradle first. At least in the latter case, the closed end of the cradle is provided with one or more apertures for the passage of the conductor-piercing member when the jaws are advanced into the jaw-receiving member.

In one embodiment of the U-shaped cradle just referred - I - to, the confronting surfaces of the two limbs of the cradle, which limbs form the two jaws of the cradle, are each provided with a pair of spaced-apart, inwardly-projecting ribs disposed substantially at right angles to the closed end of the cradle, each of these ribs forming one of said metallic members. When the cradle is stamped from metallic sheet material, these ribs may be stamped in the limbs at the time of forming the cradle.

In another embodiment of the coupling device in .accord ance with the invention, ^•each of said jaws may be made partly of plastics material which is clipped or otherwise secured to a metallic insert which provides said at least one metallic member. Again, in this embodiment, the two jaws may be hinged together, the hinge being formed in the metallic insert and/or in the plastics material.

In the wiring-up of the .embodiment of a coupling device in accordance with the invention in which the jaw-receiving member is arranged to urge the jaws towards one another as they are advanced into the aw-receiving member, it is anticipated that it will require^" a somewhat larger force to press the pair of aws into the aw-receiving member than is required in the case of a coupling device in accordance with U.S. Patent No. 4,148,540. The reason for this is that, in addition to effecting the piercing of the insulated conductor by the piercing member, the force required to press the pair of jaws into the jaw-receiving member also has to effect at least some displacement of insulation from the .conductor. The insertion of the pair of jaws into the jaw-receiving member may therefore be more easily performed using power assistance in a factory than in the home. Furthermore, withdrawal of the jaws from the jaw-receiving member may be more difficult than in the case of the jaws described in U.S. Patent No. 4,148,540. For these reasons, it is at present thought that this embodiment of the present invention may find its main appli¬ cation in the field of factory-assembled, non-rewirable coupling devices in which, after the pair of jaws has been inserted into the jaw-receiving member, a cover is perman- ently secured to, or moulded over, the electrically-insulat¬ ing part of the coupling device.

According to another aspect of the invention, in an electric plug of the kind comprising an electrically-insu- 5 lating contact-carrying portion, at least one metallic con¬ tact pin carried by and extending from said contact- carrying portion, a metallic conductor-piercing member electrically connected to said pin, a pair of conductor- locating jaws for the reception of an insulated conductor 10 which s to be electrically connected to said pin, and. a jaw-receiving member associated^' ith said piercing member for guiding the pair of jaws onto the piercing member and arranged to prevent any substantial separation of the jaws as the conductor is pierced by the piercing member, each 15 of said jaws comprises at least one metallic member which, in use Qf the plug, at least partially displaces the insulating material of the conductor, whereby enhanced contact pressure between the conductor-piercing member and the pierced conductor is achieved by said at least one 20 metallic member bearing substantially directly on the con¬ ducting material of the insulated conductor.

Whilst an electric plug in accordance with this last- mentioned aspect of the invention may have a single contact pin or two contact pins-, the main interest of this aspect ■^■5 of the invention lies in the field of 3-pin plugs, in partic¬ ular 3-pin, 13 amp fused plugs. Brief Description of Drawings

The invention will now be described, by way of example, with reference to the accompanying drawings, in which 0 Figure 1 is an exploded perspective view of the base and conductor-locating jaws of a known 3-pin, 13 amp fused electric plug,

Figure 2 is a perspective view of the pins and fuse of the plug shown partly in Figure 1, 5 Figure 3 is a perspective view of an alternative form of a pair of conductor-locating jaws for use in the plug of Figures 1 and 2,

Figure is a perspective view of the pair of jaws Figure 3 with one jaw partly broken away to reveal the inner construction,

Figure 5 is a sectional view, taken on the line V-V of Figure 4, through one of the jaws, Figure 6 is a sectional end view of the pair of jaws of Figures 3-5 with an insulated conductor between the jaws,

Figure 7 is a sectional view showing a first stage of entering the pair of jaws of Figures 3 - 6 into the jaw- 0 receiving member of an electric plug,

Figure 8 is a view similar to Figure 7, but showing the pair of jaws fully inserted into the jaw-receiving member,

Figure 9 is a sectional view taken on the line IX-IX of Figure 8, 5 Figure 10 is a view similar to Figure 7 but showing an alternative way of inserting the pair of jaws,

Figure 11 is a partly sectioned end view of a metallic insert forming part of another pair of conductor-locating jaws for use in the plug of Figures 1 and 2, 0 - Figures 12 and 13 are sectional views taken on the lines XII-XII and XIII-XIII, respectively, of Figure 11,

Figure 14, is a sectional view, taken on the line XIV-XIV of Figure 15, of a pair of jaws comprising the insert of Figures 11 to 13, the pair of jaws being shown ? partly inserted into one of the recesses of the plug of Figures 1 and 2,

Figure 15 is a sectional view taken on the line XV-XV of Figure 14, and

Figure 16 is aperspective view of a further pair of conductor-locating jaws for use in the plug of Figures 1 and 2. Modes for carrying out the Invention

Figure 1 shows part of a 13-amp, 3 pin electric plug of the kind shown in Figures 3 and 4 of U.S. Patent No. 4,148,540 but adapted to receive conductor-locating jaws of the general kind shown in Figures 7 and 8a. - 8c_ of that

Specification. The plug illustrated comprises a base 1 moulded from electrically-insulating material and carrying neutral, live and earth pins 2, 3 and 4, respectively, which are shown in more detail in Figure 2.

The numeral 5 designates a 3-core insulated electric cable with outer insulation 6 removed from one end thereof to reveal insulated neutral, live and earth wires 7, 8 and 9, respectively. The insulated wires 7, 8 and 9 are rec¬ eived between pairs of jaws 10a, 10b_, 11a, llb_ and 12a., 12b_, respectively, the wires being inserted into conductor- locating slots 13, 14 and 15, respectively, defined by rec¬ esses of substantially semicircular cross-section provided in confronting portions of the jaws 10a, 10b_, 11a, llb_ and 12a.,.12b_, respectively. The jaws, of each pair are hinged together at their lower ends (as viewed in Figure 1), there being two apertures 10_c, llc_, 12c_ through the hinged ends of the respective pairs of jaws.

Metallic insulation-piercing means, generally desig- ^■ nated by the reference numerals 17, 18 and 19, are located .in recesses 20, 21 and^' 22, respectively, provided in the upper portion of the base 1. Each of these insulation- piercing means comprises a pair of co-planar blades 17a,- 17b_, 18a., lδb_ and 19a., 19b_, respectively (see Figure 2). The piercing means 17 and 19 are electrically and physically connected to the pins 2 and 4, respectively. The piercing means 18 is formed from a metallic strip which is bent, at its end remote from the blades 18a, l8b_, into the shape of a clip 23. Another metallic strip 24, bent into the shape of a clip 25, is electrically and physically connected to the pin 3. The clips 23 and 25 receive a fuse 26 to com- plete an electrical circuit from the pin 3 to the blades. 18a, 18b.

Electrical contact between the pins 2, 3 and 4 and the insulated wires 7, 8 and 9, respectively, is made by press¬ ing the pairs of jaws 10a, 10b, 11a, llb_ and 12a, 12b_ into the recesses 20, 21 and 22, respectively, so that the blades 17a, 17b, 18a, l8b and 19a., 19b pass through the apertures 10c_, ll and 12c_, respectively, and enter between and are guided by their respective pairs of jaws 10a, 10b, lla, llb_ and 12at, 12b_. As the pairs of jaws are pressed into the recesses in this way, the pairs of blades 17a., 17b_, l8a, 18b and 19a, lQb_ piπrce the insulation of the wires 7, 8 and 9, respectively, as indicated for the wire 8 in Figure 2, and make electrical contact with the conducting parts of these wires. When the wires 7, 8 and 9 have been pierced in this way, a cover (not shown) is secured over the base 1. An electric plug of the same general kind as that shown in Figures 1 and 2 is illustrated and described in page 7 of the "Electrical Review" Vol. 204 No. 12 dated the 23rd March 1979, but in that version of the plug the recesses 20, 21 and 22 are differently positioned in the base 1.

In these known electric plugs, the pairs of jaws 10a, 10b_, lla, llb_ and 12a, 12b_ are made of synthetic resin material and adequate contact pressure between the conductiv portions of the conductors 7, 8 and 9 and the blades 17a, 17b_, Iδa_^, l8b_ and 19a., 19b_, respectively,, is achieved for all normal usages of the plugs. However, as previously mentioned, severe mis-use of the plug can result in deterior ation of. the insulating sheath of the conductors, and also of the jaws themselves.

Figures 3 to 5 show a pair of jaws of metallic material, for example brass,^' for use in place of the pairs of jaws employed in the plug of Figures 1 and 2. This pair of jaws is in the- form of a U-shaped cradle, generally designated by the reference numeral 27, the limbs 28., 29 of which constitute the two jaws of the pair. There are two through- holes 30 in the closed end of the cradle and each of the limbs 28, 29 has a pair of spaced-apart ribs 31 formed on its inwardly-facing surface.

Figure 6 shows the cradle 27 with an insulated conduc¬ tor 7 inserted between the limbs 28, 29, resulting in the free ends of these limbs being forced slightly apart and the ribs 31 penetrating partly into the insulation 32 of the conductor 1. In the case of a factory-assembled, non- rewirable plug, it may be preferred to hold the cradle in a clamp, so that the limbs 28, 29 cannot separate from one another, and then to force the conductor 7 between the limbs__ to ensure at least partial removal of insulation from the conductor by the ribs 31 before insertion of the cradle int the recess. In this case, a chute may be arranged to guide the- conductor into the clamped cradle, and this chute may be provided with projections to initiate removal of insulation from the conductor prior to its entry into the cradle.

Figure 7 shows the cradle 27, with an insulated con¬ ductor 7 between its limbs, being entered into the recess 20 of the base 1 of the plug of Figures 1 and 2. Figure 8 shows the cradle 27_.and the conductor 7 fully inserted into the recess -20, the conductor-piercing blade 17b_ having passed through the conductor. As. the cradle is pushed into the position shown in Figure 8, the side walls of the recess 20 urge the limbs 28, 29 of the cradle closer together so that the ribs 31 penetrate further into the insulation 32 of the conductor, as shown more clearly in Figure 9, in the immediate vicinity of the regions where the blades 17a, 17b_ penetrate the ^'conductor. As a result, enhanced contact pressure is obtained between the conductive portion of the ^'conductor 7 and the piercing blades 17a, 17b_ by the ribs 31 on the limbs 28, 29 exerting a compressi e force on the con¬ ductive portion of the conductor either directly or through only a very thin residual layer of insulating material. Since the ribs 31 are required to displace insulation from the conductor 7, it may be necessary to force the cradle 27 into the recess 20 using a power-operated press. If the recess 20 is shallower^' than shown, so ^"that the tips of the blades 17a., 17b_ are substantially level with the plane of the open top of the recess, it may be necessary to guide the cradle 27 as it is entered into the recess 20, to ensure that the blades 17a, 17b_ pass centrally through the conductor 7. Such guidance may be provided by a jig 33, show in chain lines in Figure 7, temporarily positioned over the recess. When the cradle 27 is fully inserted into the recess 20 the piercing blades 17a, 17b. will then pass through the holes 30 and can be bent over against the closed end of the cradle to assist in securing the cradle in recess.

Figure 10 shows how the cradle 27 may be inserted into the recess 20 with its closed end first. In this case the piercing blades 17a, 17b_ pass through and may be guided by 5 the holes 30 in the cradle before penetrating the conductor 7.

Once the cradle 27 has been fully inserted into the recess 20, it may be difficult to remove it again without the use of special tools. It is therefore anticipated i^ that the cradle 27. will find its main application in the field of non-rewirable plugs. Consequently, when cradles 27 are used ih the recesses 20 - 22 of the plug of Figures 1 and 2 a cover (not shown) may be moulded over, or secured permanently to, the base 1 to cover the open ends of the 5 recesses.

However, if the cradle 27 is employed in a rewirable plug-, it is possible to make provision to facilitate removal of the cradle from the recess 20. For example, the ^'recess 20 may -be provided with a groove as described with reference 0 to Figure 14 of U.S. Patent No. 4,148,540 to enable a screw-driver to be used to prise the cradle from the recess.

In use of the jaws described above with reference to Figures 3 - 10, it will be appreciated that deterioration of the insulation of the conductor 7 will have virtually no 5 adverse effect on the clamping pressure between the ribs 31 and the conductive portion of the conductor.

In a modified embodiment of the cradle 27 described above with reference to Figures 3 to 10, the cradle is dimensioned so that there is substantially no urging 0 together of its limbs 28, 29 by the side walls of the recess 20 when the cradle is inserted into the recess. In this case, displacement of insulating material from the con¬ ductor 7 is effected only during insertion of the conductor 7 into the cradle, prior to insertion of the cradle into the recess.

Figures 11 to 13 show a metallic insert forming part of another pair of jaws for use in place of the pairs of jaws employed in the plug of Figures 1 and 2. This metallic insert is again in the form of a substantially U-shaped cradle, stamped from metallic sheet material, which is gener ally designated by the numeral 35. This cradle comprises two limbs 36, 37 joined by a web 38, each of the limbs 36, 37 being of channel section, as seen in Figure 12 for the limb 36. The limb 36 comprises a pair of spaced-apart arms

39, joined h a web 40, and the limb 37 comprises a pair of spaced-apart arms 41 joined by a web 42. In the edge of each of the arms 39 lying remote from the web 40 there is a substantially semicircular recess 3. In the corres¬ ponding edge of each of the arms 4l there is a similar recess 44. In the relaxed state f the cradle 35, the two limbs 36,- 37 diverge from one another in the direction away from the web 38, as shown in Figure 11. The metallic cradle 35 forms an insert in a pair of jaw portions 45₃ 46 of plastics material, which are hinged to one another by hinge portions 47 moulded integrally with the two jaws. Each of the jaw portions 45, 46 has a conductor-locating slot of substantially semicircular cross-section in its inwardly-facing surface, the slot

48 of the jaw portion 45 being seen in Figure 15- Figure 14 shows the pair of jaw portions 45, 46 assembled on the metallic cradle 35 and partly inserted into the .recess 20 in the base 1, the jaw portions, having been squeezed to- gether, against the bias of the web 38 of the cradle 35, with the insulated conductor 7 lying in the conductor-locating slots of the jaw portions and in the recesses 43 and 44 of the cradle 35.

When the pair of jaws consisting of the jaw portions 45, 46 and the cradle 35 is pushed down into the recess 20 (Figure 1), the piercing blades 17a, 17b_ pass through holes 49, 50 formed in the hinged end of the jaws between the hinge portions 47 and the metallic web 38 of the cradle 35. The blades 17_a, 17b then penetrate the conductor 7 in regions between opposed arms 39 and 40 of the cradle 35. The cradle recesses 4^*3 and 44 are dimensioned so that their surfaces are forced into the insulation 32 of the con¬ ductor 7 as the pair of jaws is forced into the recess 20.

P Consequently, when the pair of jaws is fully inserted into the recess 20, the surface of the recesses 43 and 44 bear on the conductive portion of the conductor 7 either directl or through a thin residual layer of the insulation 32. The arms 39 and 41 may be provided with slits 51 which give the arms a degree of resilience, which has the additional advantage that the pair of jaws can accommodate conductors of different sizes.

In use -of the jaws described above with reference to Figures 11 to 15, it will be appreciated that deterioration of the insulation 32 of the conductor 7 and deterioration of the plastics material of-the jaw portions 5₃ 46 will have no adverse effect on the clamping pressure on the conductive portion of the conductor 7, since the conductive portion of the conductor will remain firmly held in the recesses 43, 44 of the cradle- 35. The jaw portions 45, 46 serve the purposes of locating the cradle 35 relative to the piercing blades 17i, 17b, of providing an electrically insulating shroud or. the cradle 35, o complementing the conductor-locating recess 43, 44 of the cradle, and of providing convenient handling means for squeezing the limbs of the cradle 35_.together and pressing the jaws down into the recess 20.

Although not shown in Figures 11 to 15, it is a simple matter, in the case of a rewirable plug, to provide the cradle 35 with lugs ^'which cooperate with grooves in side walls of the recess 20 to prevent complete withdrawal of the pair of jaws from the recess after initial insertion. These lugs and grooves are arranged so that, in a partially withdrawn position of the jaws, the two jaws separate to facilitate the insertion of the conductor 7 between the jaws. The jaw portions 45, 46 or the cradle 35 can be pro¬ vided with recesses for engagement by a screw-driver for partially withdrawing the jaws from the recess 20. Figure 16 shows a further pair of jaws for use in place of the pairs of jaws employed in the plug of Figures 1 and 2. This pair of jaws is made entirely of metallic material and comprises two spaced-apart U-shaped cradles 52, 53 joined by a common web 54. The cradle 52 comprises two spaced- apart L-shaped arms 55 joined to the web 54, and the cradle 53 comprises two shaped-apart L-shaped arms 56 joined to the web 54. Confronting edges of the limbs 57 of the arms 55 are provided with substantially semicircular conductor- locating recesses 58, and the corresponding edges of the limbs 59 of the arms 56 are provided with similar conductor- locating recesses 60. The web 4 is provided with holes 61 for the passage of the conductor-piercing blades 17a., 17b_ (Figure 2) when the pair σf jaws is inserted into the recess 20 (Figure 1).

In use of the pair of jaws shown in Figure 16, the. edges of the recesses 58, 59 bite into the insulation of the conductor located in the recesses so that these edges bear against the conductive portion of the conductor either directly or through a very thin residual layer of insulation.

The pair of jaws shown in Figure 16 is particularly suitable for use in non-rewirable plugs. The limbs 57 and 59 may be. provided with slits (not shown), similar to the slits 51 in Figure 11, to give these limbs a degree of resilience. -

Although in the embodiments of the invention described above, the pairs of jaws are inserted into a recess in a base of electrically-insulating material, it will be appre.c- iated that the jaws may be .received in other forms of jaw- receiving members, for example metallic ones physically and electrically connected to the pins 2 and 4 and the fuse clip 23.

Again, although the invention has been illustrated in connection with 3-pin plugs, it will be appreciated that the jaws described with reference to Figures 3 to 16 may be employed in other forms of electrical coupling devices, for example devices- such as those described with reference to Figures 11 and 13a, 13b of U.S. Patent No. 4,148,540.

Claims

1. An electrical coupling device for effecting electr cal connection between an electrically-conducting member (2, 3, 4) of the coupling device and the electrically- conducting material of an insulated electrical conductor (7, 8, 9), said coupling device comprising an electrically- insulating part (1) supporting said electrically-conducting member (2, 3, 4), a metallic, conductor-piercing member (17, 18, 19) mounted on said insulating part (1) and elec¬ trically connected to said electrically-conducting member (2, 3, 4), a pair of conductor-locating jaws (28, 29; 45, 46; 55, 56) for reception of an insulated conductor (7, 8, 9) which is to be pierced by said piercing member (17, 18, 19) for the purpose of effecting electrical connec tion between said piercing member and the electrically- conducting material of said insulated conductor, and a- - jaw-receiving member (20, 21, 22) associated with said piercing member (17, 18, 19) for guiding said pair of jaws (28, 29; 45, 46; 55, 56) onto said piercing member and for preventing any substantial separation of the jaws of said pair of jaws as said conductor is pierced by said piercing member, characterised in that each of said jaws (28, 29; 45, 46; 55, 56) comprises at least one metallic member (31; 39, 41; 58, 59) which, in use of the coupling device, at least partially displaces the electrically- insulating material (32) of said conductor (7, 8, 9), whereby enhanced contact pressure between said conductor- piercing member (17, 18, 19) and the pierced conductor (7, 8, 9) is achieved by said at least one metallic member (31; 39, 41; 58, 59) bearing substantially directly on said electrically-conducting material of said conductor (7, 8, 9).

2. An electrical coupling device in the form of an electric plug having at least one contact pin (2, 3, 4) which, in use of the plug, is electrically connected to the electrically-conducting material of an insulated electrical conductor (7, 8, 9), said plug comprising an electrically-insulating part (1) carrying said contact pin (2, 3, 4), a metallic, conductor-piercing member (17, 18, 19) mounted on said insulating part (1) and electricall connected to said pin (2, 3, 4), a pair of conductor-locatin jaws (28, 29; 45, 46; 55, 56) for the reception of an insulated conductor (7, 8, 9) which is to be pierced by said piercing member (17, 18, 19) for the purpose of effect ing electrical connection between said piercing member and the electrically-conducting material of said insulated conductor, and a jaw-receiving member (20, 21, 22) assoc¬ iated with said piercing member (17, 18, 19) for guiding the pair of jaws (28, 29; 45, 46; 55, 56) onto said piercin member and for preventing any substantial separation of the jaws of said, pair of jaws as said conductor is pierced by said piercing member, characterised in that each of said jaws (28, 29; 45, 46; 55, 56) comprises at least one metallic member (31; 39, 41; 58, 59) which, in use of the plug, at least partially displaces the electrically- insulating material (32) of said conductor (7, 8, 9), whereby enhanced contact pressure between said conductor- piercing member (17, 18, 19) and the pierced conductor (7, 8, 9) is achieved by said at least one metallic member (31; 39, 41; 58, 59) bearing substantially directly on said electrically-conducting material of said conductor (7, 8, 9).

3. An electrical coupling device according to claim 1 or 2, characterised in that said jaw-receiving member (20, 21, 22) exerts a camming action on said pair of jaws (28, 29; 45, 46; 55, 56) to urge the jaws toward one another as they are received in said jaw-receiving member.

4. An electrical coupling device according to claim 1 or 2, characterised in that said jaw-receiving member (20, 21, 22) is dimensioned to receive said pair of jaws (28,29; 45,46; 55, 56), with said insulated conductor

(7, 8, 9) located between the jaws, without causing any substantial movement of said jaws toward one another^^REΛ OMPI

5. An electrical coupling device according to any of the preceding claims, characterised in that said at least one metallic member (31; 39, 41; 58, 59) of each of said jaws (28, 29; 45, 46; 55, 56) is positioned so that, when said jaws are received in said jaw-receiving member (20, 21, 22), said at least one metallic member (31; 39; 58, 59) of one jaw (28; 45; 55, 56) is disposed opposite said at least one metallic member (31; 41; 58, 59) of the other jaw (29; 46; 55, 56) and said piercing member (17, 18, 19) is located in the region between these two opposed metallic members.

6. An electrical coupling device according to any of the preceding claims, characterised in that each of said jaws (28, 29; 55, 56) is formed entirely of metallic material and said at least one metallic member (31; 58, 59) is formed as a projection formed integrally with the conductor-locating surface of the jaw.

7. An electrical coupling device acco.rding to claim

6, characterised in that the jaws (28, 29; 55, 56) of said pair of jaws are joined together to form a substantiall U-shaped cradle (27; 52, 53).

8. An electrical coupling device according to claim

7, characterised in that the closed end of said U-shaped cradle (27; 52, 53) has at least one aperture (30; 61) therethrough for the passage of said conductor-piercing member (17, 18, 19) when said jaws are received in said jaw-receiving member.

9. An electrical coupling device according to claim 7 or 8, characterised in that the confronting surfaces of the two limbs of said U-shaped cradle (27; 52, 53) are each provided with a pair of spaced-apart, inwardly- projecting ribs (31; 58, 59) disposed substantially at right angles to the closed end of said U-shaped cradle.

10. An electrical coupling device according to any of claims 1 to 5, characterised in that each of said jaws (45, 46) is made partly of plastics material which is secured to a metallic insert (35) which provides said at least one metallic member.

11. An electrical coupling device according to claim 10, characterised in that said jaws (45, 46) are hinged together.-

12. An electrical coupling device according to claim 2 or any of claims 3 to 11 when dependent on claim 2, characterised in that said conductor-piercing member (17, 18, 19) is formed integrally with said contact pin (2, 3, 4).

13. An electrical coupling device according to any of the preceding claims, characterised in that said jaw- receiving member is formed by a recess (20-, 21, 22) in said electrically-insulating part (1), and said conductor- piercing member (17, 18, 19) is disposed in said recess.