GB2079070A

GB2079070A - Electrical coupling device

Info

Publication number: GB2079070A
Application number: GB8020579A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-06-24
Filing date: 1980-06-24
Publication date: 1982-01-13
Also published as: GB2079070B

Abstract

The coupling device is of the kind described in British Patent Specification No. 1,559,789 and shown in Fig. 1 which comprises an electrically-insulating part 1 supporting metallic conductor-piercing members 17, 18, 19 which are electrically connected to electrically- conducting members 2, 3, 4, pairs of conductor-locating jaws 10a, 10b, 11a, 11b and 12a, 12b for the reception of the insulated conductors 7, 8, 9, which are to be pierced by the piercing members 17, 18, 19, and jaw-receiving members 20, 21, 22 associated with the piercing members 17, 18, 19, for guiding the pairs of jaws on 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 Fig. 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 Fig. 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. <IMAGE>

Description

SPECIFICATION Electrical coupling device This invention relates to an electrical coupling device, and in particular, but not exclusively, it relates to a 3-pin, 1 3 amp fused plug.

In my British Patent Specification No.

1,559,789 there is described and claimed an electrical coupling device comprising a body portion having an electrically-insulating part with a recess in its surface, and electricallyconductive 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 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 the 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.

In Specification No. 1,559,789 embodiments of the coupling device are described in which the conductor-locating 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. Furthermore, in Specification No.

1,559,789 it has been proposed to employ a pair of jaws of metallic material as the conductor-locating means (as described with reference to Fig. 17).

In the aforementioned embodiments of the coupling device of Specification No.

1,559,789, 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, and 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 misuse of the kind just referred to.

According to one aspect of the present invention, in an electrical coupling device of the kind comprising an electrically-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 prevent any substantial separation of the jaws as the conductor 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 conducting material of the insulated conductor.

The jaw-receiving member may be arranged, as in the case of the recess described in Specification No. 1,559,789, to exert a camming action on the pair of jaws to urge the jaws towards one another as they are advanced into the jaw-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 jawreceiving member, although some displacement of the insulating material may take place at the time of inserting the conductor between the two jaws prior to advancement of the jaws into the jaw-receiving member.

Alternatively, the jaw-receiving member may be dimensioned so that it can receive the pair of jaws, with the insulated conductor located between the jaws, without exerting any camming action on the jaw, and simply prevents any substantial separation of the jaws as the conductor is pierced by the piercing member. In this case, displacement 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, siight 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 jaw-receiving 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 metal lic 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 substantially Ushaped cradle for the reception of the insu lated 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 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 accordance 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 jawreceiving member, it is anticipated that it will require a somewhat larger force to press the pair of jaws into the jaw-receiving member than is required in the case of a coupling device in accordance with Specification No.

1,559,789. 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 jawreceiving member may be more difficult than in the case of the jaws described in Specification No. 1,559,789.For these reasons, it is at present thought that this embodiment of the present invention may find its main application in the field of factory-assembled, nonrewirable coupling devices in which, after the pair of jaws has been inserted into the jawreceiving member, a cover is permanently secured to, or moulded over, the electricallyinsulating part of the coupling device.

According to another aspect of the invention, in an electric plug of the kind comprising an electrically-insulating contact-carrying portion, at least one metallic contact 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 which is to be electrically connected to said pin, and a jaw-receiving member associated with 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 of said jaws comprises at least one metallic member which, in use of 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 metallic member bearing substantially directly on the conducting 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 of the invention lies in the field of 3-pin plugs, in particular 3-pin, 1 3 amp fused plugs.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is an exploded perspective view of the base and conductor-locating jaws of a known 3-pin, 1 3 amp fused electric plug, Figure 2 is a perspective view of the pins and fuse of the plug shown partly in Fig. 1, Figure 3 is a perspective view of an alternative form of a pair of conductor-locating jaws for use in the plug of Figs. 1 and 2, Figure 4 is a perspective view of the pair of jaws of Fig. 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 Fig. 4, through one of the jaws, Figure 6 is a sectional end view of the pair of jaws of Figs. 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 Figs. 3-6 into the jaw-receiving member of an electric plug, Figure 8 is a view similar to Fig. 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 Fig. 8, Figure 10 is a view similar to Fig. 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 Figs. 1 and 2, Figure 12 and 13 are sectional views taken on the lines XII-XII and XIll-XlIl, respectively, of Fig. 11, Figure 14, is a sectional view, taken on the line XIV-XIV of Fig. 15, of a pair of jaws comprising the insert of Figs. 11 to 13, the pair of jaws being shown partly inserted into one of the recesses of the plug of Figs. 1 and 2, Figure 15 is a sectional view taken on the line XV-XV of Fig. 14, and Figure 16 is a perspective view of a further pair of conductor-locating jaws for use in the plug of Figs. 1 and 2.

Fig. 1 shows part of a 13-amp, 3 pin electric plug of the kind shown in Figs. 3 and 4 of Specification No. 1,559,789 but adapted to receive conductor-locating jaws of the general kind shown in Figs. 7 and 8a-8c of that Specification. The plug illustrated comprises a base 1 moulded from electricallyinsulating material and carrying neutral, live and earth pins 2, 3 and 4, respectively, which are shown in more detail in Fig. 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 received between pairs of jaws 1 Oa, 1 Ob, 11 a, 11 band 12a, 12b, respectively, the wires being inserted into conductor-locating slots 13, 1 4 and 15, respectively, defined by recesses of substantially semicircular crosssection provided in confronting portions of the jaws 10a, 10b, 11a, 11band 12a, 12b, respectively. The jaws of each pair are hinged together at their lower ends (as viewed in Fig.

1), there being two apertures 10c, 11 C, 1 2c through the hinged ends of the respective pairs of jaws.

Metallic insulation-piercing means, generally designated 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 coplanar blades 17a, 17b, 18a, 18b and 19a, 19b, respectively (see Fig. 2). The piercing means 1 7 and 1 9 are electrically and physically connected to the pins 2 and 4, respectively. The piercing means 1 8 is formed from a metallic strip which is bent, at its end remote from the blades 18a, 18b, 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 complete 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 pressing the pairs of jaws 10a, 10b, 11a, 11band 12a, 12b into the recesses 20, 21 and 22, respectively, so that the blades 17a, 17b, 18a, and 18band 19a, 1 9b pass through the apertures 10c, 11 C and 12c, respectively, and enter between and are guided by their respective pairs of jaws 1 Oa, lOb, 11 a, 1 1 6 and 12a, ? 26.As the pairs of jaws are pressed into the recesses in this way, the pairs of blades 17a, 17b. 1 8a, 1 8b and 19a, 1 9b pierce the insulation of the wires 7, 8 and 9, respectively, as indicated for the wire 8 in Fig. 2, the 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 Figs. 1 and 2 is illustrated and described in page 7 of the "Electrical Review" Vol. 204 No. 1 2 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, 4 lea, 11band 12a, 12bare made of synthetic resin material and adequate contact pressure between the conductive portions of the conductors 7, 8 and 9 and the blades 17a, 17b, 18a, 18band 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 deterioration of the insulating sheath of the conductors, and also of the jaws themselves.

Figs. 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 Figs. 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.

Fig. 6 shows the cradle 27 with an insulated conductor 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 7. In the case of a factoryassembled, 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 into 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.

Fig. 7 shows the cradle 27, with an insu lated conductor 7 between its limbs, being entered into the recess 20 of the base 1 of the plug of Figs. 1 and 2. Fig. 8 shows the cradle 27 and the conductor 7 fully inserted into the recess 20, the conductor-piercing blade 1 7b having passed through the conductor. As the cradle is pushed into the position shown in Fig. 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 Fig. 9, in the immediate vicinity of the regions where the blades 17a, 1 7b penetrate the conductor.As a result, enhanced contact pressure is obtained between the conductive portion of the conductor 7 and the piercing blades 17a, 1 7b by the ribs 31 on the limbs 28, 29 exerting a compressive force on the conductive 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, 1 7b 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, 1 7b pass centrally through the conductor 7. Such guidance may be provided by a jig 33, shown in chain lines in Fig. 7, temporarily positioned over the recess. When the cradle 27 is fully inserted into the recess 20 the piercing blades 17a, 1 7b will then pass through the holes 30 and can be bent over againt the closed end of the cradle to assist in securing the cradle in the recess.

Fig. 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, 1 7b pass through and may be guided by 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 that the cradle 27 will find its main application in the field of non-rewirable plugs. Consequently, when cradles 27 are used in the recesses 20-22 of the plug of Figs. 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 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 to Fig. 1 4e of Specification No.

1,559,789 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 Figs. 3-10, it will be appreciated that deterioration of the insulation of the conductor 7 will have virtually no adverse effect on the clamping pressure between the ribs 31 and the conductive portion of the conductor.

In a modified embodiment of the cradle 275 described above with reference to Figs. 3 to 10, the cradle is dimensioned so that there is substantially no urging 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 conductor 7 is effected only during insertion of the conductor 7 into the cradle, prior to insertion of the cradle into the recess.

Figs. 11 to 1 3 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 Figs. 1 and 2. This metallic insert is again in the form of a substantially U-shaped cradle, stamped from metallic sheet material, which is generally 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 Fig. 1 2 for the limb 36. The limb 36 comprises a pair of spaced-apart arms 39, joined by a web 40, and the limb 37 comprises a pair of spacedapart 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 43. In the corresponding edge of each of the arms 41 there is a similar recess 44.In the relaxed state of the cradle 35, the two limbs 36, 37 diverge from one another in the direction away from the web 38, as shown in Fig. 11.

The metallic cradle 35 forms an insert in a pair of jaw portions 45, 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 Fig. 15. Fig. 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 together, against the bias of the web 38 of the cradle 35, with the insulated conductor 7 lying in the conductorlocating 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 (Fig. 1), the piercing blades 17a, 1 7b 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 17a, 1 7b then penetrate the conductor 7 in regions between opposed arms 39 and 40 of the cradle 35. The cradle recesses 43 and 44 are dimensioned so that their surfaces are forced into the insulation 32 of the conductor 7 as the pair of jaws is forced into the recess 20.

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 directly 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 Figs. 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 45, 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 17a, 17b, of providing an electrically insulating shroud for the cradle 35, of 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 Figs. 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 provided with recesses for engagement by a screw-driver for partially withdrawing the jaws from the recess 20.

Fig. 1 6 shows a further pair of jaws for use in place of the pairs of jaws employed in the plug of Figs. 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 54 is provided with holes 61 for the passage of the conductor-piercing blades 17a, 1 7b (Fig. 2) when the pair of jaws is inserted into the recess 20 (Fig. 1).

In use of the pair of jaws shown in Fig. 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 Fig. 1 6 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 Fig.

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 electricallyinsulating material, it will be appreciated 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 Figs. 3 to 1 6 may be employed in other forms of electrical coupling devices, for example devices such as those described with reference to Figs. 11 and 13a, 1 3b of Specification No. 1,559,789.

Claims

1. An electrical coupling device for effecting electrical connection between an electrically-conducting member of the coupling device and the electrically-conducting material of an insulated electrical conductor, said coupling device comprising an electrically-insulating part supporting said electrically-conducting member, a metallic, conductor-piercing member mounted on said insulating part and electrically connected to said electrically-conducting member, a pair of conductor-locating jaws for reception of an insulated conductor which is to be pierced by said piercing member for the purpose of effecting electrical connection between said piercing member and the electrically-conducting material of said insulated conductor, and a jaw-receiving member associated with said piercing member for guiding said pair of jaws 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, wherein each of said jaws comprises at least one metallic member which, in use of the coupling device, at least partially displaces the electrically-insulating material of said conductor, whereby enhanced contact pressure between said conductor-piercing member and the pierced conductor is achieved by said at least one metallic member bearing substantially directly on said electrically-conducting material of said conductor.

2. An electrical coupling device in the form of an electric plug having at least one contact pin which, in use of the plug, is electrically connected to the electrically-conducting material of an insulated electrical conductor, said plug comprising an electricallyinsulating part carrying said contact pin, a metallic, conductor-piercing member mounted on said insulating part and electrically connected to said pin, a pair of conductor-locating jaws for the reception of an insulated conductor which is to be pierced by said piercing member for the purpose of effecting electrical connection between said piercing member and the electrically-conducting material of said insulated conductor, and a jawreceiving member associated with said piercing member for guiding the pair of jaws onto said piercing member and for preventing any substantially separation of the jaws of said pair of jaws as said conductor is pierced by said piercing member, wherein each of said jaws comprises at least one metallic member which, in use of the plug, at least partially displaces the electrically-insulating material of said conductor, whereby enhanced contact pressure between said conductor-piercing member and the pierced conductor is achieved by said at least one metallic member bearing substantially directly on said electrically-conducting material of said conductor.

3. An electrical coupling device according to claim 1 or 2, wherein said jaw-receiving member exerts a camming action on said pair of jaws 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, wherein said jaw-receiving member is dimensioned to receive said pair of jaws, with said insulated conductor located between the jaws, without causing any substantially movement of said jaws toward one another.

5. An electrical coupling device according to any of the preceding claims, wherein said at least one metallic member of each of said jaws is positioned so that, when said jaws are received in said jaw-receiving member, said at least one metallic member of one jaw is disposed opposite said at least one metallic member of the other jaw and said piercing member is located in the region between these two opposed metallic members.

6. An electrical coupling device according to any of the preceding claims, wherein each of said jaws is formed entirely of metallic material and said at least one metallic member is formed as a projection formed integrally with the conductor-locating surface of the jaw.

7. An electrical coupling device according to claim 6, wherein the jaws of said pair of jaws are joined together to form a substantially U-shaped cradle.

8. An electrical coupling device according to claim 7, wherein the closed end of said Ushaped cradle has at last one aperture there-+ through for the passage of said conductorpiercing member when said jaws are received in said jaw-receiving member.

9. An electrical coupling device according to claim 7 or 8, wherein the confronting surfaces of the two limbs of said U-shaped cradle are each provided with a pair of spaced-apart, inwardly-projecting ribs 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, wherein each of said jaws is made partly of plastics material which is secured to a metallic insert which provides said at least one metallic member.

11. An electrical coupling device according to claim 10, wherein said jaws are hinged together.

12. An electrical coupling device according to claim 2 or any of claims 3 to tl when dependent on claim 2, wherein said conductor-piercing member is formed integrally with said contact pin.

13. An electrical coupling device according to any of the preceding claims, wherein said jaw-receiving member is formed by a recess in said electrically-insulating part, and said conductor-piercing member is disposed in said recess.

14. An electrical coupling device constructed and arranged substantially as herein described with reference to, and as illustrated in, Figs. 1 and 2 of the accompanying drawings as modified by Figs. 3 to 9, or Figs. 1 and 2 as modified by Figs. 3 to 5 and 10, or Figs. 1 and 2 as modified by Figs. 11 to 15, or Figs. 1 and 2 as modified by Fig. 16.