GB2090077A

GB2090077A - Multi-pin electrical plug

Info

Publication number: GB2090077A
Application number: GB8138072A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-12-17
Filing date: 1981-12-17
Publication date: 1982-06-30
Also published as: GB2090077B

Abstract

A method of providing an electrically insulating sleeve around a current-carrying pin 1 for projecting from the base 3 of a plug comprises forming the pin 1 with a waist portion 2 which, in use, is adjacent to the base 3, filling the waist portion 2 with an insulating sleeve comprising one or more sleeve parts 4a, 4b and securing the sleeve 4a, 4b in position around the waist portion. In one embodiment, shown, the sleeve parts 4a, 4b are applied to the waist portion 2 before the pin 1 is fully inserted through the base 3 of the plug, so that after full insertion of the pin in the base, proximal ends of the sleeve parts 4a, 4b are embraced by the base 3 and the distal ends 8a, 8b of the sleeve parts 4a, 4b locate in undercut regions 5 on the pin 1 so that both ends of each sleeve part are positively held in position around the waist portion 2. The sleeve may be heat shrunk into position, or adhesive or ultrasonic welding may be employed to secure the sleeve in position. <IMAGE>

Description

SPECIFICATION Multi-pin electrical plug This invention relates to a multi-pin electrical plug, and in particular, but not exclusively, to a 3pin, 13 amp electrical plug.

Electrical plugs to which this invention relates have a base from one face of which the contact pins project. In the case of a 3-pin, 13 amp electrical plug, one of these contact pins is an earth pin and the other two are current-carrying pins. In use of the electrical plug, it is inserted into an appropriate socket and should be pressed into the socket to the fullest extent possible leaving the said face of the base in contact with the outer face of the socket. In this correct position of the plug in the socket, no part of any of the contact pins is exposed and a safe connection between the plug and the socket is obtained. However, it is possible to insert the electrical plug partially in the socket so that one of the current-carrying pins is live but to leave a gap between the said face of the base and the said face of the socket.In this incorrect position of the electrical plug, there is the possibility for an inadvertent and possibly dangerous contact to be made with the exposed area of the live pin. Furthermore, it is possible for the fingers of a person, during insertion of the plug into, or its withdrawal from, the socket, inadvertently to touch the live pin.

To prevent inadvertent and possibly dangerous contact with the live pin in either of the ways mentioned above, it is known to electrically insulate regions of the current-carrying pins which are closest to the said face of the base and this invention relates to an improved method of electrically insulating said regions and to an improved form of electrical plug in which said regions are electrically insulated.

Prior proposals for achieving an electrical insulation of the said regions of the currentcarrying pins have included moulding an electrically insulating material in situ in grooves formed in the said pins to form a sleeve on the pins which is flush with the uninsulated distal end portions thereof. To put this prior proposal into practice, it is necessary separately to insert each grooved pin in a surrounding mould which tightly embraces regions of the pin on opposite ends of the groove and to inject a hardenable electrically insulating material into the mould so that it fills the said grooves and to retain the pins in the mould until the insulating material has hardened sufficiently to permit the mould to be removed from the pin.There are practical problems in performing this method and since the cost of the operation affects the unit cost of the electrical plug, and a low unit cost is a vital commercial consideration, there is a need for an alternative method of providing an electrically insulating sleeve on the said region of the current-carrying pins.

According to one aspect of the invention a method of providing an electrically insulated sleeve around a current carrying pin projecting from the base of a multi-pin electrical plug comprising forming the pin so that it exhibits a waist portion which, in use of the plug, is adjacent to the base and filling said waist portion with an electrically insulating material, is characterised in that said filling is effected by locating a sleeve or a plurality of sleeve parts in the waist portion and securing the sleeve or sleeve parts in position around the waist portion during said location or subsequent thereto.

In one embodiment of the method in accordance with the invention, two pre-shaped sleeve parts are provided which are locked around the waist portion by inter-engaging means provided on the sleeve parts and/or on the pin. The two sleeve parts may be applied to the waist portion before the pin is fully inserted through the base of the plug, so that after full insertion of the pin in the base, proximal ends of the sleeve parts are embraced by the base, the base thereby serving to hold the sleeve parts in position around the waist portion. Where this method is employed, the distal ends of the sleeve parts may locate in under-cut regions on the pin so that both ends of each sleeve part are positively held in position around the waist portion.

Where two pre-shaped sleeve parts are used to define the sleeve, the sleeve parts may be substantially identical and arranged to overlap each other on opposite sides of the pin.

Overlapping the sleeve parts in this way increases the flashover distance between the outer and inner surfaces of the sleeve at the regions where the sleeve parts meet one another.

In another embodiment of the method in accordance with the invention, a single sleeve is mounted in said waist portion. This sleeve may have an uninterrupted surface, in which case it is suitably shrunk around the waist portion by a heat treatment. Alternatively, the sleeve may have a longitudinally disposed split from end to end, in which case it can be secured around the waist portion by inter-engaging means on the faces of the sleeve which confront each other when the sleeve is located on said waist portion.

In addition to, or as an alternative to, the use of inter-engaging means on the sleeve or sleeve parts and/or on the pin, an adhesive or ultrasonic welding may be used to provide and/or increase the securement of the completed sleeve on the pin. Adhesive or ultrasonic welding can also be used at the region where confronting faces of the sleeve or sleeve parts meet to close any gap left there and further improve resistance to flashover.

A current-carrying pin of an electrical plug provided with an electrically insulating sleeve by the method of the invention constitutes a further feature of this invention as does an electrical plug having at least one current-carrying pin provided with such an insulated sleeve.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side elevation of a current-carrying pin provided with a waist portion for reception of a two-part pre-moulded sleeve, Figure 2 is a plan from above of the pin shown in Figure 1 after it has been sleeved by the -method of the invention, Figure 3 is a side elevation of the sleeved pin corresponding to Figure 2, Figure 4 is an eniarged section on the line IV--IV in Figure 2, Figure 5 is a schematic view illustrating the way in which the two sleeve parts shown in Figures 2, 3 and 4 are applied to the pin of Figure 1.

Figures 6, 7 and 8 are cross-sections corresponding to Figure 4 showing alternative forms of pre-shaped sleeves, Figure 9 is a plan of a further current-carrying pin showing the waist portion prepared for reception of a sleeve by the method of the invention, Figure 10 is a section on the line X-X of Figure 9 showing the pin of that Figure sleeved by the method of the invention, Figure 1 1 is a view similar to Figure 9 showing an alternative arrangement for locking the sleeve in place around the waist portion, Figure 12 is a section on the line XII-XIl of Figure 11 showing the sleeve parts in place, Figure 1 3 is a section through a sleeved current-carrying pin showing an alternative shaping of the waist portion and sleeve parts, and Figure 14 is an electrical plug which has been sleeved by the method of the invention.

Referring first to Figure 14, a 3-pin 13 amp plug is shown having a current-carrying pin 1 projecting from a base 3, a short region of the pin 1 adjacent to the base 3 being provided with an electrically insulating sleeve 4, the outer surfaces of which are flush with the surfaces of the distal end of the pin 1.

Figures 1-5 show in detail one method for providing the sleeve 4 around the pin 1, the dashed line 3a in Figure 1 illustrating the plane of the underside of the base 3 in the fully assembled plug. From Figure 1 it will be seen that the pin is provided with a waist portion 2 which is limited at its distal end on the two wide faces of the rectangular pin 1 by undercuts 5, and on the two narrow faces of the pin 1 by first shoulders 6. At its proximal end, a second shoulder 7 is provided on all four faces of the pin 1. Figures 2, 3 and 4 show the pin of Figure 1 after it has been sleeved with two pre-shaped sleeve parts 4a and 4b and Figure 5 shows schematically the way in which the sleeve parts are applied to the pin 1 prior to its insertion through the base 3.From Figures 3 and 5 it can be seen that each sleeve part 4a and 4b has a shaped tongue portion 8a, 8b, respectively which locates one under each undercut 5 to lock the distal ends of the sleeve parts to the pin 1 in overlapping relationship. As can be seen from the cross-section of Figure 4 (which has not been provided with section lines to avoid confusion) the sleeve parts 4a and 4b confront each other along the narrow faces of the pin 1 along oblique lines 9.

The proximal ends of the sleeve parts 4a and 4b are cut away at 1 Oa and 1 Ob, respectively, to clear the second shoulders 7 as the sleeve parts are pressed over the waist portion 2 to bring regions of these sleeve parts along the wide faces of the pin into abutment with the second shoulders 7. After the sleeve parts 4a and 4b have been closed around the waist portion, the pin 1 can be drawn through the base 3 in the direction of the arrow A in Figure 5 partially to draw the sleeve parts through the pin aperture in the base 3 and leave the proximal ends of the two sleeve parts retained within the pin aperture in the base 3.

Thus it will be seen that the distai ends of the two sleeve parts are locked to the pin by inter engagement of the tongues 8a and 8b in the undercuts 5 and the proximal ends of the sleeve parts are held around the waist portion by their engagement in the pin aperture of the base 3.

It will be appreciated that the sleeve parts 4a and 4b are identical and this is an advantage having regard to manufacturing costs of these parts and ease of assembly of the sleeved pin in the base 3. The meeting lines 9 need not be as shown in Figure 4 and these can be shaped to further increase the flash-over distance along any slight gap left between the sleeve parts 4a and 4b after they have been fitted in place.

Figures 6, 7 and 8 are sectional views corresponding to Figure 4 of alternative designs of pre-formed sleeves and again section lines have not been used in these Figures to avoid confusion.

Figure 6 shows a one-piece, longitudinally split sleeve which completely embraces the waist portion, the confronting edge faces of the sleeve being shaped to interlock in the region generally designated 11. To facilitate the interlocking in the region 11 , the contact pin can be relieved slightly, e.g. as shown at 1 a. Figure 7 shows an alternative form of two-part sleeve 4, the two parts in this case being designated 4dand 4e, these two parts interlocking at regions indicated by 1 2 and 1 3 in Figure 7. As in the embodiment of Figure 6, a slight relieving of the pin 1 may be provided at 1 a (and optionally also at 1 b) to facilitate the locking together of the two parts 4d and 4e.Figure 8 shows a futher arrangement using a one-piece, longitudinally split sleeve 4f, this arrangement being similar to that shown in Figure 6 but utilising a different form of interlock between the confronting faces of the sleeve 4f. Figure 9 shows an alternative form of waist portion 2 adapted to receive two sleeve parts 4g and 4h applied on opposite sides of the pin 1 and in this arrangement the locking of the sleeve parts into the waist portion is effected by providing blind holes 1 5 in the waist portion 2 and furnishing each sleeve part with pegs 1 6 which lock into these blind holes. As in the previously-discussed embodiments, the base 3 is employed to retain the proximal ends of the sleeve parts tightly around the waist portion.

Figure 11 and 12 show a further modification in which undercut grooves 1 7 are provided in the waist portion 2 and each sleeve part (designated 4i and 4j in Figure 12) is provided with a projection 1 8 which locks into the appropriate groove 17.

Figure 13 shows a still further arrangement for locking sleeve parts around the waist portion and in the arrangement illustrated in this Figure the narrow faces of the waist portion 2 are made concave so that the sleeve parts (here shown as 4k and 41) lock around the waist portion by virtue of thicker edge portions received in the concave recesses. Although in Figure 1 3 the recesses on opposite sides of the pin 1 have been shown with a generally V cross-section they can be formed by a curved recessing of opposite faces of the pin in the vicinity of the waist portion.

It is also possible to fit the sleeve in place by slipping a one-piece pre-shaped tube of electrically insulating material over the waist portion 2 of the pin 1 and then shrinking the preshaped tube down on to the waist portion by a suitable thermal treatment. This method is, of course, not preferred since it is difficult to ensure the desired coplanar relationship between the sleeve and the surfaces of the distal end of the plug after the shrinking operation.

Although the disclosure has so far concentrated on solid pins of rectangular cross-section, it will be appreciated that the method of the invention applies equally to hollow pins of rectangular crosssection and to solid or hollow pins having crosssectional shapes other than rectangular.

In the case of a 3-pin 13 amp plug, the overall length of the sleeve 4 measured from the plane 3a should not exceed 9.5 millimetres.

Claims

1. A method of providing an electrically insulating sleeve around a current-carrying pin projecting from, or intended to project from, the base of a multi-pin electrical plug comprising forming the pin so that it exhibits a waist portion which, in use of the plug, is adjacent to the base and filling said waist portion with an electrically insulating material, characterised in that said filling is effected by locating a sleeve or a plurality of sleeve parts in the waist portion and securing the sleeve or sleeve parts in position around the waist portion during said location or subsequent thereto.

2. A method according to claim 1, wherein two pre-shaped sleeve parts are located in the waist portion and are locked around the waist portion by inter-engaging means provided on the sleeve parts and/or on the pin.

3. A method according to claim 2, wherein the sleeve parts are applied to the waist portion before the pin is fully inserted through the base of the plug, so that after full insertion of the pin in the base, proximal ends of the sleeve parts are embraced by the base, the base thereby serving to hold the sleeve parts in position around the waist portion.

4. A method according to claim 3, wherein the distal ends of the sleeve parts locate in under-cut regions on the pin so that both ends of each sleeve part are positively held in position around the waist portion.

5. A method according to any of claims 2 to 4, wherein the sleeve parts used are substantially identical and are arranged to overlap each other on opposite sides of the pin.

6. A method according to claim 1, wherein a single sleeve with an uninterrupted surface is located in said waist portion and is shrunk around the waist portion by a heat treatment.

7. A method according to claim 1, wherein a single sleeve having a longitudinally disposed split from end to end is located in said waist portion, and the sleeve is secured around the waist portion by inter-engaging means on the faces of the sleeve which confront one another along said split.

8. A method according to claim 2 or 3, wherein the sleeve parts are secured to the waist portion by engagement of pegs on the sleeve parts in holes formed in the waist portion.

9. A method according to claim 2 or 3, wherein the sleeve parts are secured to the waist portion by engagement of projections on the sleeve parts in grooves in the waist portion.

10. A method according to claim 2 or 3, wherein the waist portion is formed with opposed concave surfaces and the sleeve parts are secured to the waist portion by engagement of thickened edge portions of the sleeve parts with said concave surfaces.

11. A method according to claim 1, wherein a single sleeve having a longitudinally disposed split from end to end is located in said waist portion, and the sleeve is secured around the waist portion by joining together the faces of the sleeve which confront each other along said split with an adhesive or by ultrasonic welding.

12. A method according to claim 7, wherein the faces of the sleeve which confront each other along said split are also joined together with an adhesive or by ultrasonic welding.

13. A method according to claim 1, wherein two pre-shaped sleeve parts are located in the waist portion and are secured around the waist of portion by joining together of confronting aces the two sleeve parts with an adhesive or by ultrasonic welding.

14. A method according to any of claims 2 to 5 or 8 to 10, wherein the faces of the sleeve parts which confront each other are also joined together with an adhesive or by ultrasonic welding.

1 5. A method according to claim 1, wherein the sleeve is or the sleeve parts are secured in the waist portion with an adhesive.

1 6. A method according to any of claims 2 to 14, wherein the sleeve is or the sleeve parts are also secured in the waist portion with an adhesive.

1 7. A method of providing an electrically insulating sleeve around a current-carrying pin of a multi-pin electrical plug, substantially as herein described with reference to Figures 1 to 5, Figure 6, Figure 7, Figure 8, Figures 9 and 10, Figures 11 and 12 or Figure 1 3 of the accompanying drawings.

18. A current-carrying pin of a multi-pin electrical plug when made by the method claimed in any of the preceding claims.

1 9. A multi-pin electrical plug comprising at least one current-carrying pin according to claim 18.