GB2160030A

GB2160030A - Sleeved plug pins

Info

Publication number: GB2160030A
Application number: GB08414165A
Authority: GB
Inventors: Derek Hayes
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-06-04
Filing date: 1984-06-04
Publication date: 1985-12-11
Also published as: GB8414156D0

Abstract

An electrically insulated region is provided on the surface of a hollow current-carrying pin 7 projecting from the base 20 of an electrical plug, by forming the pin so that it exhibits a recessed portion 2 in its peripheral surface which, in use of the plug, is adjacent to the base 20 and locating a strip 11 of electrically insulating material in the recessed portion 2. The strip 11 is formed with a lug 15 which is engageable in a hole passing through the wall of the recessed portion 2, whereby the strip 11 is held positively in the recessed portion 2 by hooking engagement of the lug 15 in said hole. The insulated region may be formed from two strips 11 each embracing half of the periphery of the pin, or from a single sleeve-like member provided with a longitudinal slit for ease of fitting. <IMAGE>

Description

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

Electrical plugs to which this invention relates have a base from one face of which one or more 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.

In my British Patent Application No. 2090077A there is described a method of forming a currentcarrying pin projecting from, or intended to project from, the base of a multi-pin electrical plug, which method comprises forming the pin so that it exhibits a waist portion which, in use of the plug, is adjacent to the base and locating a sleeve of electrically insulating material, or a plurality of sleeve parts of electrically insulating material, in the waist portion. The method is characterised by the step of securing the distal end of the sleeve, or the distal ends of the sleeve parts, in undercut regions on the pin in order positively to hold said distal end or ends in position around the waist portion.

The method described in the aforesaid Application is particularly suitable for use with solid current-carrying pins, in which it is a simple matter to provide said undercut regions. In application of the method to a hollow pin, it is difficult to provide adequate undercut regions at the distal end of said waist portion, without making the wall thickness of the hollow pin greater than is necessary purely from considerations of mechanical strength and current-carrying ability.

The present invention aims to provide an im proved method of providing an electrically insu lated region on the surface of a hollow current-car rying pin, and an improved form of electrical plug employing such a current-carrying pin.

According to one aspect of the invention, a method of providing an electrically insulated re gion on the surface of a hollow current-carrying pin projecting from, or intended to project from, the base of an electrical plug, comprising forming the pin so that it exhibits a recessed portion in its peripheral surface which, in use of the plug, is adjacent to the base and locating a strip of electrically insulating material in said recessed portion, is characterised by forming said strip with a lug which is engageable in a hole passing through the wall of said recessed portion of the pin, whereby said strip is held positively in said recessed portion by hooking engagement of said lug in said hole.

The lug may be formed intermediate the ends of the strip, but preferably it is formed at, or as close as possible to, the distal end of the strip, i.e. the end of the strip lying farthest from the base of the assembled plug. Preferably, the hooking engagement between the strip and the pin is such that, when the strip is held in the recessed portion, it is secured against any substantial movement in the longitudinal direction of the pin.

When the method of the invention is employed with a pin of circular cross-section, said recessed portion may extend partly around the circumference of the pin, for example half way round the pin. In this case said strip would be of arcuate cross-section so as to fit snugly into, and fill, the recessed portion, said lug being provided on the concave surface of the strip. Alternatively, said recessed portion may extend right round the circumference of a pin of circular cross-section, in which case a plurality, for example two, strips of arcuate cross-section may be fitted into the recessed portion, each strip having a lug on its concave surface which is received in hooking engagement with a respective hole through the wall of the recessed portion of the pin.

When the method of the invention is employed with a pin of rectangular cross-section, said recessed portion may extend across a first face of the pin and at least partly across two other faces of the pin which are joined to said first face. In this case, said strip would be of channel section, the lug being provided on the inner surface of the web of the channel section, preferably mid-way between the flanges of the channel section. Alternatively, said recessed portion may be formed in all four faces of the pin, in which case two channelsection strips may be fitted into the recessed portion, each strip having its lug on the inner surface of its web and the recessed portion of the pin having two holes for reception of the respective lugs.

When one, or two, channel section strips are fitted in the recessed portion, it is preferred that the flanges of the, or each, strip should "toe-in" slightly so as to improve the fit of the strip(s) in the recessed portion.

When the recessed portion of the pin extends all round the pin, whether the latter is of circular or rectangular cross-section, said strip may be in the form of a sleeve which is provided with a longitudinally-disposed split from end to end to facilitate assembly of the sleeve on the pin. In this case, the sleeve may be provided with one or more additional lugs and the pin would then be provided with at least one additional hole for reception of the additional lug or lugs.

When two strips are fitted into the recessed portion, whether the pin is of circular or rectangular cross-section, the two strips may be of substantially identical shape and arranged to overlap on opposite sides of the pin. Overlap of the two strips in this way increases the flashover distance between the inner and outer surfaces of the strips at the regions where they meet one another.

The, or each, strip may be assembled in the recessed portion of the hollow pin before the pin is fully inserted through the base of the plug, so that after full insertion of the pin in the base, the proximal end of the or each strip is embraced by the base, the base thereby serving to hold said proximal end or ends in position in said recessed portion.

If desired, the or each strip may also be secured in the recessed portion of the pin with an adhesive.

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

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 shows part of a sheet metal blank for employment in the manufacture, by the method according to the invention, of one embodiment of a hollow current-carrying pin for a 3-pin 13 amp electrical plug, Figure 2 is a plan of a current-carrying pin made from the blank of Figure 1, Figure 3 is a sectional view taken on the line 111- 111 of Figure 2, Figure 4 is an underside plan of a channel-section strip of electrically insulating material, Figure 5 is a sectional view taken on the line V-V of Figure 4, Figure 6 is a partly sectioned side view of the pin of Fibres 2 and 3 onto which the strip shown in Figures 4 and 5 has been fitted, Figure 7 is a sectional view taken on the line VII VII of Figure 6, Figures 8, 9 and 71 are views similar to Figure 7 of modified embodiments of hollow current-carry ing pins, and Figure 10 is an enlarged detail of part of Figure 9.

Figure 1 shows part of a substantially rectangu lar thin sheet metal blank 1, made for example of brass, from which a hollow current-carrying pin for a 3-pin 13 amp electrical plug is made by folding along the chain dotted lines a, b, c and d. Prior to the folding operation, a rectangular recessed por tion 2 is stamped into the blank 1, the long sides 3 and 4 of the recessed portion being parallel to the fold lines a-d, the side 3 being disposed midway between the fold lines a and b and the side 4 being disposed midway between the fold lines c and d. A rectangular hole 5 is formed through the floor of the recessed portion 2, this hole being midway between the sides 3 and 4 and extending up to the end 6 of the recessed portion 2. After folding of the blank 1, the resulting current-carrying pin 7 has the appearance shown in Figures 2 and 3.From these Figures it will be seen that the recessed portion 2 extends across one broad face 8 of the pin and approximately half way across the narrow faces 9 and 10 of the pin.

Figures 4 and 5 show a channel-section strip 11 of electrically insulating material, for example glass fibre reinforced nylon, having a web 12 and spaced-apart flanges 13 and 14 extending from opposite sides of the web 12. A lug 15 formed integrally with the web 12 is situated midway between the flanges 13, 14 and projects beyond the end 16 of the strip 11. The lug 15 has a width equal to the width of the hole 5 in the pin 7 and the part of the lug which is joined to the web 12 has a length equal to the length of the hole 5. The end 17 of the lug 15 is rounded, as can be seen in Figure 5. The web 12 and the flanges 13 and 14 have a thickness equal to the depth of the recessed portion 2 of the pin 7, and the strip 11 has a length slightly less than the length of the recessed portion 2, measured in the axial direction of the pin 7.The height of each of the flanges 13 and 14 is approximately half the width of the narrow faces 9 and 10 of the pin 7.

The strip 11 is fitted to the pin 7 as shown in Figures 6 and 7, by entering the free end of the lug 15 into the hole 5 and then laying the strip snugly into the recessed portion 2. This fitting of the strip to the pin is facilitated by the rounded end 17 of the lug and by the fact that the strip 11 is slightly shorter than the recessed portion 2. However, when the strip 11 has been fitted into the recessed portion 2, movement of the strip in the axial direction of the pin 7 is prevented by engagement of the rounded end 17 of the lug 15 against one end of the hole 5 and by engagement of the end 16 of the strip against the end 6 of the recessed portion 2.

The numeral 20 in Figure 6 designates part of the base of an electrical plug in which the pin is eventually mounted. From this Figure, it will be seen that the end 19 of the strip 11 enters, and is embraced by, the base 20. Thus, when the pin 7 is mounted in the base 20, the strip 11 is held positively in the recessed portion 2, the proximal end 19 of the strip being held by the base 20, and distal end 16 being held by the hooking engagement of the lug 15 in the hole 5.

In a typical example of a strip 11 for electrically insulating part of the surface of a pin 7 for a 3-pin 13 amp plug, the webs 12 and the flanges 13, 14 have a thickness of from 0.2 to 0.3 mm, the strip has a length of about 11 mm, and the portion of the strip which projects from the base 20 of the plug has a length of from 8 to 9.5 mm. The overall width of the strip 11 is the same as the width of the broad face 8 of the pin, i.e. from 6.22 to 6.48 mm. The two flanges 13 and 14 may incline inwardly towards one another in the direction of their free ends, for example so that the free ends of the flanges are from 1 to 2 mm closer together than the ends joined to the web 12, in the dismounted condition of the strip.When the strip is subsequently fitted into the recessed portion 2 of the pin 7, the flanges 13 and 14 are forced into parallelism, and this enhances the grip of the strip 11 on the pin 7.

By the method of the invention it is possible to provide an electrically insulated region in any desired position adjacent to the proximal end of a current-carrying pin mounted in the base of an electrical plug. The above description shows how it is possible to provide such a region which extends across one broad face and half way across two narrow faces of the pin. Figures 8 and 9 show two other possibilities. In Figure 8 the flanges 13 and 14 extend right across both narrow faces of the pin as well as across one broad face. In this case, the recessed portion 2 in the blank 1 of Figure 1 would extend from the fold line a to the fold line d. In Figure 9, two channel-section strips 11 are fitted in the recessed portion 2 of the pin 7 with the free ends of the flanges of both strips abutting one another midway across the narrow faces of the pin.

In this case, the recessed portion 2 of the blank 1 in Figure 1 would extend right across the width of the blank, and in addition to the hole 5, two further holes 5a (shown in chain dotted lines in Figure 1) would be provided at the side edges of the blank.

Each of the holes 5a would have a width equal to approximately half the width of the hole 5. In the Figure 9 embodiment, the free edges of the abutting flanges 13 and 14 of the two strips 11 may be chamfered at an angle of 45', as shown in Figure 10, in order to increase the length of the flashover path along the lines of abutment of the two strips.

Whilst the illustrated embodiments which have been described above show provision of the hole 5 in a broad face of the pin 7, the hole 5 may be formed in one of the narrow faces of the pin. The strip 11 could then be arranged to extend across one narrow face and partly or wholly across the two broad faces of the pin. In these cases, the recessed portion 2 in the blank 1 could be a single recessed portion extending from the side of the blank adjacent the fold line a to midway between the fold lines b and c, or two recessed portions 2 could be provided, one extending from the side of the blank 1 adjacent the fold line a to the fold line c and the other extending from the fold line d to the side of the blank adjacent the fold line d.

The above description has been limited to a discussion of hollow current-carrying pins of rectangular cross-section. The invention is not, however, limited to employment with such pins, but may be used with hollow pins of circular cross-section. Figure 11 shows how a strip 11a of electrically insulating material, having an arcuate cross-section, may be fitted into a recessed portion 2a of a pin 7a of circular cross-section. The strip 1 lea is fitted in the recessed portion 2a in exactly the same way as described above with reference to Figure 6 for the strip 11.

Claims

1. A method of providing an electrically insulated region on the surface of a hollow current-carrying pin projecting from, or intended to project from, the base of an electrical plug, comprising forming the pin so that it exhibits a recessed portion in its peripheral surface which, in use of the plug, is adjacent to the base and locating a strip of electrically insulating material in said recessed portion, characterised by forming said strip with a lug which is engageable in a hole passing through the wall of said recessed portion of the pin, whereby said strip is held positively in said recessed portion by hooking engagement of said lug in said hole.

2. A method according to claim 1, in which said lug is formed at, or as close as possible to, the end of the strip lying farthest from the base of the assembled plug.

3. A method according to claim 1 or 2, in which the hooking engagement between the strip and the pin is such that, when the strip is held in the recessed portion, it is secured against any substantial movement in the longitudinal direction of the pin.

4. A method according to any of the preceding claims when employed with a pin of circular crosssection, wherein said recessed portion extends partly around the circumference of the pin, and said strip is of arcuate cross-section so as to fit snugly into, and fill, the recessed portion, said lug being provided on the concave surface of the strip.

5. A method according to any of claims 1 to 4 when employed with a pin of circular cross-section, wherein said recessed portion extends right round the circumference of the pin, and a plurality of strips of arcuate cross-section are fitted into the recessed portion, each strip having a lug on its concave surface which is received in hooking engagement with a respective hole through the wall of the recessed portion.

6. A method according to any of claims 1 to 3 when employed with a pin of rectangular crosssection, in which said recessed portion extends across a first face of the pin and at least partly across two other faces of the pin which are joined to said first face.

7. A method according to claim 6, in which said strip is of channel section and said lug is provided on the inner surface of the web of the channel section.

8. A method according to any of claims 1 to 3 when employed with a pin of rectangular crosssection, in which said recessed portion is formed in all four faces of the pin and two strips of channel section are fitted into the recessed portion, each strip having its lug on the inner surface of its web and the recessed portion of the pin having two holes for the reception of the respective lugs.

9. A method according to claim 7 or 8, in which the flanges of the or each channel section strip toe in.

10. A method according to any of claims 1 to 3, in which said recessed portion extends all round the pin and said strip is in the form of a sleeve which is provided with a longitudinally-disposed split from end to end.

11. A method according to claim 10, in which said sleeve is provided with one or more additional lugs and the pin is provided with at least one additional hole for the reception of the additional lug or lugs.

12. A method according to any of claims 1 to 3, in which said recessed portion extends all around the pin and two strips of substantially identical shape are fitted into said recessed portion, the two strips overlapping one another on opposite sides of the pin.

13. A method according to any of the preceding claims, in which the or each strip is assembled in said recessed portion before the pin is fully inserted through the base of the plug, and in which, after full insertion of the pin in the base, an end of the or each strip is embraced by the base.

14. A method according to any of the preceding claims, in which the or each strip is also secured in said recessed portion with an adhesive.

15. A method of providing an electrically insulated region on the surface of a hollow current-carrying pin projecting from, or intended to project from, the base of an electrical plug, substantially as hereinbefore described with reference to the accompanying drawing.

16. A current-carrying pin of an electrical plug provided with an electrically insulated surface region by the method claimed in any of the preceding claims.

17. An electrical plug comprising at least one current-carrying pin as claimed in claim 16.