Electrical plug

Abstract

 An electrical plug which has a body (12) including walling bounding a central cavity with an entrance to the cavity through which, in use, an electrical lead passes. The body (12) also includes two or more, usually three, blocks (26, 28) each with a blind, threaded bore (42) therein. Passages (48, 50) lead from the cavity into the bores (42), the passages (48, 50) opening through the cylindrical walls of the bores. Discs (56) of electrically conductive metal are retained in the closed ends of the bores (42) by circumferential ribs (54) protruding inwardly from the bore walls. Plug pins (14, 18) are screwed into the bores (42) to grip the bared ends of the individual electrical wires, which ends enter the bores (42) through the passages (48, 50) between themselves and the discs (56). A cover is provided for closing the cavity.

Description

[0001] Electrical plugs conventionally comprise a body of insulating material from which project two or three brass pins. The body is generally in two parts which can be separated from one another to enable electrical wires to be connected to the pins.

[0002] Conventionally, the pins have cross bores therein into which the bared ends of the wires are inserted. Tapped bores intersect the wire receiving bores and small brass screws in the tapped bores clamp the bared wires in the cross bores.

[0003] Attachment of the bared wires to the pins is a somewhat tedious procedure partly due to the fact that the screws themselves are very small. Consequently, their screw driver slots are small and the screw driver which must be used is commensurately small. Additionally, it is possible for a bared wire to adopt a position in its bore which is off centre. In such circumstances the screw fails to grip the wire properly or, if the wire is made up of a number of fine filaments, only grips a few of the filaments. The electrical connection between the wire and the pins is thus poor, with a consequent increase in resistance and power loss, and furthermore detachment of the wire from the pin with consequent breaking of the circuit becomes more likely.

[0004] In British patent specification 637964 it is proposed that the plug pins should be threaded and screwed into threaded bores in metal blocks. The blocks are provided with transverse bores which intersect the threaded bores that receive the pins. When the plug pins are turned, the bared end of each wire is gripped between the end of the pin and the surface of the bore in the block. This plug suffers from some of the disadvantages of the plugs described above and which include small screws for clamping the bared electrical wires. The rotatable, threaded plug pins merely serve the same function as the small screws. The problems which arise in connection with the small screws ie failure to clamp the wires properly can also arise when the plug pins are used in the way described.

[0005] It is an object of the present invention to provide an electrical plug in which the bared electrical wires can be simply and reliably connected to the plug pins.

[0006] According to the present invention there is provided an electrical plug including a body comprising at least two blocks and walling bounding a main cavity which is open on one side, an entrance to said cavity through which an electrical lead can pass from externally of the body into the cavity, a blind, cylindrical bore in each of said blocks, a passage between each of said bores and said cavity, the passages opening into the bores through the cylindrical walls thereof and adjacent the closed ends thereof, and the bores being threaded, the threading being between said passages and the open ends of the bores, and an electrically conductive, externally threaded plug pin screwed into each of said bores.

[0007] To reduce the chances of the wires being pulled loose, the plug can include electrical lead clamps protruding towards one another from said walling, the clamps having their outer ends integral with said walling and the inner ends thereof defining an electrical lead receiving gap situated inwardly of said entrance, the clamps being flexible. To cause the clamps to flex throughout their lengths, they can each be in the form of a flat plate the thickness of which decreases from the outer end thereof to the inner end.

[0008] A metal disc is preferably provided at the closed end of each bore so that the bared wires are not pressed against the material forming the end walls of the bores. Each bore can have, between the passage which opens into it and the closed end thereof, an inwardly protruding, circumferentially extending rib, said discs being retained in the ends of the bores by said ribs.

[0009] The plug pins can each comprise a main cylindrical portion, an intermediate threaded section and a minor cylindrical portion, said main portion extending from one end of the pin to said threaded section and the minor portion extending from the other end of the pin to the threaded section, said minor portion being of smaller diameter than said main portion.

[0010] For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which :-Figure 1 is a pictorial view of an electrical plug;

Figure 2 is an underneath plan view of the plug of Figure 1 with the plug pins and a quick release bottom closure omitted;

Figure 3 is a longitudinal central section through the plug;

Figure 4 is a plan view of the quick- release bottom closure; and

Figure 5 is a section through the quick- release bottom closure.

[0011] Referring firstly to Figure 1, the electrical plug illustrated has been designated 10 and comprises an injection moulded body 12 from which three metal pins 14, 16 and 18 project. The body 12 is preferably of polycarbonate and the pins 14, 16 and 18 are brass. Externally, the body 12 is provided with a curved portion 20 opposite ends of which merge with the main part of the body 12.

[0012] The body 12 is moulded with a generally T-shaped central cavity 22 (Figures 2 and 3). The upright of the "T" runs from behind the pin 14 towards the rear end of the plug at which the electrical lead enters the plug, and the cross-bar of the "T" lies behind the pins 16 and 18.

[0013] Forwardly of the cavity 22 the body is moulded with a block 26 and on each side of the upright of the "T", where the upright joins the cross-bar of the "T", there are two further blocks 28 and 30. The cavity 22 is bounded by parallel side walls 32, by the blocks 28 and 30, by two skirts 34, and by a transverse rear wall 36. A further wall 38 forms the "floor" of the cavity 22 when the body 12 is inverted as shown in Figure 2, and forms the top of the cavity when the plug is as shown in Figures 1 and 3.

[0014] Generally triangular strengthening webs 40 lie outwardly of the side walls 32 and extend between the blocks 26, 28 and 26, 30 respectively.

[0015] The blocks 26, 28 and 30 are each formed with a blind, threaded bore. The bore of the block 26 is designated 42, the bore of the block 28 is designated 44, and the bore of the block 30 is designated 46. Near the closed end of each bore there is a passage which enters the bore and places the bore in communication with the cavity 22. In Figure 2 passages 48, 50 and 52 are shown leading from the cavity 22 into the bores 42, 44 and 46 respectively, and in Figure 3 only the passages 48 and 50 are visible. The threading of the bores 42, 44 and 46 extends from their open ends to adjacent the passages 48, 50 and 52.

[0016] Between the closed end of each bore and the passages 48, 50 and 52 there is in each bore a circumferentially extending inwardly protruding rib 54. Discs 56 are pressed into the bores 42, 44 and 46 so that they lie at the closed ends of the bores and are retained in place by the ribs 54.

[0017] The bores 42, 44 and 46 open through the flat face designated 58. As will be seen from Figure 3, the face 58 lies slightly below the lower edges of the skirts 34 and of the rear wall 36. The parallel side walls 32 are stepped so as to provide faces 60 which are above the face 58 (as viewed in Figure 3) and which lie in the same plane as the edges of the skirts 34 and rear wall 36. The faces 60 are discontinuous in that, adjacent the block 26, there are two projections 62 the lower faces of which (as viewed in Figure 3) lie in the same plane as the face 58.

[0018] The electrical lead enters the plug through an entrance generally designated 64. The entrance 64 is arch-like and passes through the rear wall 36. Inwardly of the entrance 64 there are two cable clamps 66, these being integral at their outer ends with the skirts 34 which form the end walls of the cross-bar of the T-shaped cavity 22. Each clamp 66 is of increasing thickness from the free end thereof to the end which is integral with the respective skirt 34. The cable clamps 66 are not integral with the wall 38, this permitting them to flex inwardly that is, away from the rear wall 36, when an electrical lead is inserted.

[0019] On each side of the entrance 64 there is a recess 65 in the outer face of the rear wall 36. Each recess 65 is bounded by an inclined upper face 67, a vertical face 69 and a horizontal face 71. The configuration is such as to leave a rearwardly extending projection 73 below each recess 65.

[0020] The quick release closure 68 shown in Figures 4 and 5 has a shape which matches that of the cavity 22. More specifically, the closure 68 is T-shaped in plan, Figure 4, and comprises an "upright" 70 and a "cross-bar" 72. The upright 70 terminates in a somewhat narrower portion 74 with which a cross pin 76 is integral. The pin 76 protrudes in each direction beyond the portion 74 and thereby provides two recesses 78. The recesses 78 are such that they can receive the projections 62.

[0021] Along the rear edge of the cross bar 72 of the T there are two protruding elements 80. The elements 80 are formed with enlarged heads 82, each head 82 being bounded by the rear face 84 of the element 80, by an inclined face 86 and by an undercut face 88. Between the face 88 and the adjacent face of the cross bar 72 there is a recess 90, the recesses 90 being dimensioned so as to be capable of receiving the projections 73. Each pin 14, 16 and 18 comprises a main cylindrical portion 92 one end of which is radiussed and across which there is a slot 94. Beyond the portions 92, the pins are each formed with a screw threaded section 96, and beyond the screw threaded section 96 there are short cylindrical portions 98. The portions 98 are of lesser diameter than either the portions 92 or the sections 96. Each pin is radiussed at 100 between the cylindrical wall of its portion 98 and its flat end surface 102.

[0022] To connect the plug 10 to an electrical lead a screw driver or the like is sucessivel^y inserted in the slots to rotate the pins 14, 16 and 18 so that the move away from the discs 56. Simultaneously, the cylindrical end portions 98 of the pins move to a position in which they are clear of the passages 48, 50 and 52. It will be understood that the pins do not have to be disconnected from the body 12 for this purpose.

[0023] The electrical lead is cut and the individual wires bared with the live and neutral wires somewhat shorter than the earth wire. The lead is then pressed and/or pulled through the gap between the cable clamps 66. The cable clamps 66, by virtue of their tapered shape, flex away from the wall 36 into a curved configuration and grip the lead to resist movement thereof out of the cavity should a pull be exerted thereon from externally of the plug. The bared ends of the wires are then inserted through the passages 48, 50 and 52 and the pins 14, 16 and 18 rotated so as to grip the bared ends of the wires between themselves and the discs 56. It will be understood that the end portions 98 of the pins 14, 16 and 18 are of smaller diameter than the bores 42, 46 and 44. This results in parts of the bared wire ends lying between the cylindrical portions 98 and the walls of the bores and the remainders lying gripped between the discs 56 and the surfaces 102.

[0024] The closure 68 is then connected to the body 12 by pressing the projecting ends of the cross pin 76 into the recesses between the projections 62 and the block 26. The projections 62 are received in the recesses 78 of the closure 68 and the edge portions of the upright 70 of the closure bear on the faces 60. As the closure 68 is pressed into position, the inclined faces 86 encounter the projections 73 and the elements 80 are deflected, as shown by the arrows A in Figure 5, so that the heads 82 clear the projections 73 and snap into the recesses 65 provided therefor above the projections 73. The angled ends of the cross bar 72 co-incide with the outer faces of the skirts 34 and the transverse edge of the cross bar 72 lies in the same plane as the outer face of the rear wall 36.

[0025] The closure 68 can only be removed from the body 12 by inserting a screw driver or other implement between the inclined faces 67 and 86 and twisting it to deflect the heads so that they are disengaged from the projections 73.

[0026] The closed ends of the bores 42, 44 and 66 can be coloured with the same colours used on the electrical wires before the discs 56 are inserted.

Claims

1. An electrical plug including a body comprising at least two blocks and walling bounding a main_cavity which is open on one side, and an entrance to said cavity through which an electrical lead can pass from externally of the body into the cavity, characterized in that there is a blind, cylindrical bore (42, 44, 46) in each of said blocks (26, 28, 30) and a passage (48, 50, 52) between each of said bores and said cavity (22), the passages (48, 50, 52) opening into the bores (26, 28, 30) through the cylindrical walls thereof and adjacent the closed ends thereof, and the bores (42, 44, 46) being threaded, the threading being between said passages and the open ends of the bores (42, 44, 46), and an electrically conductive, externally threaded plug pin (14, 16, 18) screwed into each of said bores.

2. An electrical plug according to claim 1, and characterized by three blocks arranged at the apices of a triangle.

3. An electrical plug according to claim 1 or 2 and characterized by electrical lead clamps (66) protruding towards one another from said walling (34), the clamps having their outer ends integral with said walling and the inner ends thereof defining an electrical lead receiving gap situated inwardly of said entrance (64), the clamps being flexible.

4. An electrical plug according to claim 3, characterized in that each clamp (66) is in the form of a flat plate the thickness of which decreases from the outer end thereof to the inner end.

5. An electrical plug according to any preceding claim and characterized by a metal disc (56) at the closed end of each bore (26, 28, 30).

6. An electrical plug according to claim 5, characterized in that each bore has, between the passage which opens into it and the closed end thereof, an inwardly protruding, circumferentially extending rib (54), said discs (56) being retained in the ends of the bores by said ribs.

7. An electrical plug according to any preceding claim characterized in that each pin (14, 16, 18) comprises a main cylindrical portion (92), an intermediate threaded section (96) and a minor cylindrical portion (98), said main portion (92) extending from one end of the pin to said threaded section (96) and the minor portion (98) extending from the other end of the pin to the threaded section, said minor portion (98) being of smaller diameter than said main portion (92).

8. An electrical plug according to any preceding claim in which there is a transverse slot (94) across one end of each pin.

9. An electrical plug according to any preceding claim and including a cover (68) for closing said cavity (22).

Drawing