GB2171265A

GB2171265A - Electrical connection

Info

Publication number: GB2171265A
Application number: GB08603947A
Authority: GB
Inventors: Alexander Stewart
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-02-19
Filing date: 1986-02-18
Publication date: 1986-08-20
Also published as: GB8603947D0; GB2171265B; GB8504224D0

Abstract

The earth pin (11) of an electrical appliance (10) having male connections, such as a plug, adaptor or timer, has a slot (16) in which a locking element (17) is rotatable by a handle (24) so that a hook-shaped end (19) of the locking element may engage behind the face plate (13) of a socket in which the pin is inserted to prevent unintended removal of the appliance (10) from the socket. The arrangement is such that the usual safety shutter (14) of the socket is not interfered with, the hook (19) occupying the triangular space left by the depressed, chamfered shutter arm (14). In other embodiments the element (17) rotates with a shaft which may be controlled by an articulated link or is replaced by a locking element moving longitudinally of the earth pin either to extend transversely out of a slot or to expand by riding up cam surfaces of notches in the sides of the pin. Alternatively again, the locking element can be pressed out of its slot by a screw. <IMAGE>

Description

SPECIFICATION Electrical connection This invention relates to an electrical connection, and more particularly to means whereby an electrical appliance having male connecting elements or pins can be releasably held in position in a socket so as to prevent inadvertent removal.

It is known to provide an electrical supply socket incorporating a switch with means to grip one or more of the pins of an appliance, such as a plug, when inserted therein. This gripping means is controlled by the switch in such away as to resist the withdrawal of the appliance from the socket as long as the switch is in the "on" position.

This safety feature of old-fashioned mains supply sockets has been superseded in recent years by an alternative one. Most modern mains supply sockets have a shutter behind the face plate which is spring-biased to a position in which it blocks both the live and neutral openings. This prevents the insertion e.g. of a child's finger or a foreign body when the socket is empty. At the top of the shutter is a chamfer which is engaged by the earth pin when a plug or the like is inserted. Because the earth pin is longer that the other two it displaces the shutter out of the way of the live and neutral pins so that they can enter the socket.

The provision of a spring-biased shutter behind the face plate restricts the available room in the socket housing and it is not practicable to combine the two known safety features described.

On the other hand it is becoming increasingly important to prevent the unintentional full or partial displacement of an appliance out of a socket as sophisticated modern equipment becomes more widespread. The accidental disconnection of an electric clock with rotating hands is a nuisance but such a clock is quickly reset. Clocks which have a digital display are more laborious to reset and they are increasingly common in homes and offices on such equipment as video recorders and telephone monitors as well as the timers which control such equipment as central heating and immersion heaters.

Above all the increasing use of computers for data storage in home and office has introduced a new dimension to the problem. Interruption of mains supply when a computer is in use will cause the loss of data which, if retrievable at all, may represent hundreds of working hours of input. The most frequent cause of such an accident arises from the use of adaptors whereby two or more plugs can be connected to the same socket. Pulling one of the plugs out of the adaptor is likely to cause the adaptor pins to pull out of the mains supply socket with consequent unintentional loss of mains supply to the other plug or plugs.

An attempt to overcome this problem which would entail the replacement or modification of mains supply sockets is considered impractical.

Firstly the cost to consumers would be prohibitive and secondly the safety feature represented by the shutter should not be sacrificed as it is addressed to a quite different problem. Unless it is sacrificed, however, it is difficult to envisage a practicable mains supply socket modification which would fulfill the objects of the present invention.

Principally these objects are to provide means to effect the releasable locking of a piece of electrical equipment such as a plug, adaptor, timer or the like in a socket which relies on a modification not of the socket but of one of the male connections or pins.

The most suitable of these is, of course, the earth pin because alteration of either of the others could be dangerous either in exposing a live part exteriorly of the housing or giving rise to a short circuit within it.

Other objects of the invention are to achieve this in an economical way causing the least possible change to existing designs and as far as possible making use of existing features.

As used herein the expression "socket" does not mean exclusively a wall-mounted mains supply socket but includes the female connections of a second piece of equipment, such as an adaptor or timer, which in turn receives one or more plugs.

In accordance with one aspect of the present invention there is provided an elongated male connection or pin for an electrical appliance adapted for insertion in the appropriate opening in a socket face plate, the connection having one or more formations to receive or to engage a locking element which is displaceable relative to the connection transversely thereof between a retracted position and an operative position extending from the connection at a position therealong to engage the socket housing when the connection is fully inserted, the arrangement being such that in its operative position the locking element will restrain the unintended withdrawal of the connection from the socket but in its retracted position the locking element will not impede the movement of the connection in and out of the socket.

The connection may be in the form of an earth pin which has a slot opening transversely of the pin at a position which will be behind the socket face plate when the pin is fully inserted, means being provided to move the locking element in the slot between an inoperative position in which the locking element lies substantially wholly within the slot and an operative position in which a portion of the locking element extends out of said slot opening transversely of the pin to engage behind the socket face plate if the earth pin tends to retract from the socket. Said portion may be a hook-like free end portion of the locking element and the locking element may be rotatable in the slot about its other end.

Manually operable means accessible exteriorly of the housing of the appliance incorporating the earth pin is preferably adapted to exert a pressure on the locking element transversely of the earth pin such as to jam the earth pin in the socket opening. The manually operable means is preferably a screw engaging a screwzthreaded bore in the earth pin which opens to the slot therein art a position between said ends of the locking element. The outwardly presented face of said hook-like free end portion and the edge of the earth pin transversely opposite thereto are preferably formed with serrations to improve frictional engagement with opposite edges of the socket opening in which the earth pin is inserted.

Alternatively, said other end of the locking element may be pivotally mounted in the slot and there may extend angularly therefrom at the pivot point a lever integral with the locking element, the lever extending out of an upper opening of the slot to be accessible exteriorly of the housing of the appliance incorporating the earth pin for displacing the locking element between its operative and inoperative positions. An appliance incorporating the connection last described may have a housing formed with an opening positioned so that the free end of the lever will extend therefrom and may further comprise means spring-biasing the lever in one sense of rotation and releasable engagement means whereby the lever may be held against the action of said spring bias.

Alternatively, said other end of the locking element may be adapted for non-rotatable connection to a shaft extending transversely of and beyond the earth pin, means being provided to rotate the shaft so as to displace the free end portion of the locking element between its operative and inoperative positions. An appliance incorporating the connection last described preferably comprises a housing having formations to provide bearings for the shaft on one or both sides of the earth pin. One end of the shaft may pass out of the housing and may be provided with handle means whereby it may be rotated from a position external of the housing. Alternatively, the shaft may be cranked and its cranked portion may be articulated to a link which passes out of the housing through an opening therein whereby the link may be manipulated to rotate the shaft.

The appliance may further comprise means spring-biasing the shaft and locking element assembly in one sense of rotation and releasable engagement means for holding said assembly in a chosen angular position against the action of said spring bias.

In yet another embodiment of the invention the locking element may be resilient and may have a loop-like formation intermediate its ends which will project transversely of the earth pin from said slot opening when the locking element is in a first position retracted into the earth pin but which will engage one side of said slot opening and, by tending to straighten out, withdraw into the slot when the locking element is drawn axially out of the earth pin.

An appliance provided with the connection last described may have a housing in which there is rotatably but non-axially displaceably mounted a manually operable control means, and the end portion of the locking element which extends out of the earth pin may be connected via an anti-rotation device to a screw-threaded shank which is in screwthreaded engagement with the control means, the arrangement being such that by rotating the control means the locking element can be axially moved relative to the earth pin, thereby to effect the extension or retraction of the loop-like portion thereof.

In yet another embodiment of the invention the connection may be in the form of an earth pin which is cut away to receive the locking element and means may be provided to displace the locking element longitudinally of the earth pin, the locking element and cut away area of the earth pin having co-operating cam surfaces whereby when moved longitudinally of the earth pin the locking element is displaced transversely thereof.In this arrangement the locking element may comprise a U-shaped, resilient element having arms which tend to remain generally parallel and have claw-like formations at their free ends extending inwardly of the element and opposite sides of the earth pin may be cut away to provide recesses to receive said arms so that in the unstressed or inoperative position of the locking element the outer surfaces of its arms are generally co-extensive with the remainders of said earth pin sides, each said recess having an end face generally at right angles to the axis of the earth pin and a sloping or cam face extending from said end face toward the rear or inner end of the earth pin, the arrangement being such that when the locking element is drawn rearwardly off the earth pin the claw-like formations ride up the sloping faces of the recesses to expand the arms, thereby tending to jam them in a socket aperture in which the earth pin is inserted.

Aweb portion of the locking element connecting said arms thereof may be apertured and a screwthreaded shank may extend through said aperture to engage a screw-threaded bore in the earth pin, the shank being rotatably but non-axially displaceably connected to said web portion whereby rotation of the shank, and its consequent axial displacement relative to the earth pin, causes displacement of the locking element longitudinally of the earth pin.

Embodiments of the present invention will now be described by way of example with reference to the accompanying diagrammatic drawings, in which: Figures 1 and 2 partially illustrate a plug inserted in a wall mounted mains socket, Figure 1 being a sectional elevation taken generally on the line I-I of Figure 2, and Figure 2 being a perspective view of the earth pin unit in isolation, Figure 3 is a view similarto Figure 1 of a modified adaptor inserted in a wall mounted mains socket, Figures 4 and 5 illustrate the use of a modified earth pin of any chosen appliance, Figure 6 is a view similarto Figures 1,3 and 4 showing yet another modification primarily intended for adaptors where it is not desired to make an opening in the outwardly presented side of the housing, Figure 7 is a view similar to Figures 1,3,4 and 6, of another embodiment of the invention as applied to an adaptor, Figure 8 is a rear perspective view of the adaptor of Figure 7, and Figure 9 is a detail illustrating application of features similar to those of Figures 7 and 8 to the earth pin of a plug.

Referring first to Figures 1 and 2, the earth pin 11 of a plug 10 is shown inserted through the appropriate opening 12 of the face plate 13 of a wall mounted mains supply socket. The live and neutral pins of the socket 10 are not shown and neither are the corresponding openings in the plate 13, but these are blocked, when nothing is plugged into the socket, by a shutter an arm 14 of which has at its upper end a chamfer 15. With the live and neutral openings blocked by the shutter this chamfer 15 is aligned with the opening 12. The earth pin 11 is longer than the live and neutral pins and when the plug 10 is first pushed into the socket the pin 11 contacts and presses down the arm 14, unblocking the other openings of the socket for the entry of the other pins.

As so far described the assembly is conventional.

In accordance with the present invention, however, the pin 11 is formed with a slot 16 in which there is located a generally L-shaped locking element 17.

This is rotatable about an axis 18 in the slot between an operative or locking position in which it is shown in full lines in Figure 1, and an inoperative or retracted position in which it is shown in chain dotted lines in Figures 1 and 2. This rocking movement ofthe element 17 causes a hook-shaped end portion 19 thereof to move in and out of a lower opening 20 of the slot 16. Movement of the element 17 is controlled by an upper or "handle" portion 21 thereof which extends out of an upper, rearward opening 22 of the slot 16. This handle portion 21 also extends through a slot cut out of the upper portion of the plug housing so that it can be manipulated exteriorly of the plug 10.The free end of the handle portion 21 is received in a sleeve 24, and at its lower end this has a lateral projection (not shown) which can be inserted in a lateral branch (not shown) of the slot in the plug housing to hold the locking element 17 in the full-line, operative position. A compression spring 23 is located in a bore in the plug housing to bias the locking element 17 to the inoperative position shown in broken lines.

In use, with the locking element in the latter, retracted position the plug 10 is pushed, in the usual way, into the socket, displacing the shutter arm 14 downward as indicated by the arrow A in Figure 1.

With the plug fully inserted the sleeve 24 is moved forward toward the socket face plate 13 as indicated by the arrow B, compressing the spring 23, until it can be moved laterally to engage the branch in the slot in the plug housing. In so doing, the end 19 of the element 17 is extended out of the lower opening of the slot in the pin 11 to the full-line position shown, where it engages behind the face plate 13 of the socket in the triangular space vacated by the shutter arm 14. Unintentional removal ofthe plug 10 from the socket is thus prevented. When it is intended to remove the plug from the socket the sleeve 24 is moved laterally until the spring 23 is able to urge the handle 21 rearward, so displacing the locking element 17 to the inoperative position shown in dotted lines.With the "hook" 19 now fully retracted into the slot 16 in the pin 11 it is possible to remove the plug 10 from the socket and later to reinsert it.

As is clear from Figure 2 the terminal end portion 31 of the pin 11 is extended laterally at 60 so that an earth wire 61 can be connected in the usual way to the pin 11 by a screw 62 threaded into a cross bore.

It is to be noted in connection with all the described embodiments of the invention that no modification of existing wall mounted mains sockets is called for and that use is made of the very limited space available in sockets provided with a safety shutter. The embodiment of Figures 1 and 2 calls for a simple and feasible modification of a conventional plug.

Figure 3 diagrammatically illustrates the relevant parts of an adaptor 30 which on one face has live and neutral pins (not shown) and an earth pin 11 and on other faces a plurality of sockets so that more than one plug can receive mains supply from the wall mounted socket having, in common with that of Figures 1 and 2, a face plate 13 with earth opening 12 and shutter arm 14. The pins of the adaptor 30 are generally similar to those of the plug 10 of Figure 1, but in this case the slot 16 in the plug earth pin is replaced buy a longitudinal slot which opens to the terminal end 31 of the earth pin within the adaptor housing.This slot also opens downwardly at a suitable position along the length of the pin 11, and the edges 32 and 32A of the downward opening have the rounded configuration shown so as to have a camming effect on a loop 33 forming part of an otherwise straight spring locking element 34. This is located in the longitudinal slot in the earth pin 11 to be movable axially therealong and it extends out of the terminal end 31 of the earth pin 11 to engage the movable part 35 of an anti-rotation device 36 within the housing of the adaptor 30. A screw-threaded portion 37 of the part 35 is engaged by the internally screw-threaded, hollow portion 39 of a screw the head 40 of which is accessible outside the housing of the adaptor 30 so that it can be turned manually or by means of a suitable tool such as a screwdriver or a coin.By means known per se and not illustrated the screw having head 40 is rotatable in an opening 41 in the adaptor housing but is not axially displaceable.

Consequently rotation of the head 40 of the screw causes axial displacement of the part 35 together with the locking element 34. If moved to the left, as viewed, relative to the pin 11 the loop 33 of the locking element will bear against the edge 32 of the downward opening in the earth pin slot causing the loop to deform until it is fully retracted into the earth pin slot. Counter-rotation of the head 40 of the screw will subsequently draw the locking element 34 along the slot in the earth pin 11 until, by the inherent resilience of the locking element 34 its loop 33 resumes the shape shown and it extends out of the earth pin slot sufficiently to engage behind the face plate 13 in the triangular space vacated by the shutter arm 14. A compression coil spring 42 surrounds the locking element 34 and acts between the terminal end 31 of the earth pin and the part 35 of the anti-rotation device to take up any slack in the system.

In use the screw head 40 is rotated until the loop 33 is fully retracted into the earth pin 11,which can then be inserted in the wall mounted mains supply socket in the usual way. After insertion of the adaptor pins in the wall socket the head 40 is counter-rotated until the loop 33 reaches a limit position extending out of the earth pin by engaging the edge 32A of the downward opening. Withdrawal of the adaptor 30 from the wall socket will now be resisted by engagement of the loop 33 behind the face plate 13, and plugs (not shown) may be individually pushed into and pulled out of the adaptor 30 without dislodging the adaptor 30 from the mains supply socket.Of course, when it is intended to remove the adaptor 30 from the mains supply socket it is necessary to rotate the head 40 of the screw in the sense appropriate to retract the loop 33 back into the earth pin slot.

In the embodiment of Figures 4 and 5 an earth pin 11 (which may be that of a plug, adaptor1 timer or any other plug-in electrical appliance) is shown extending from the housing 50 of the appliance through the appropriate hole 12 in the face plate 13 of a wall mounted mains socket. The earth pin 11 is not hollow or slotted as in the embodiments previously described but instead notches 51 and 51A have been cut in its longitudinal edges at opposite positions suitably spaced from the terminal end 31 of the pin 11. These notices are shaped to accommodate the claw-like arms 52 and 52A of a U-shaped spring 53 shown separately in Figure 4. The web portion 54 of the spring 53, which bridges the terminal end 31 of the earth pin, has a central aperture through which passes a screw-threaded shank 55.Behind the screw-threaded free end portion 56 of the shank are fixed abutments 57 and 58 on opposite sides of the web 54 and the effect of these is to cause the spring 53 to travel with the shank 55 when this moves axially as a result of being rotated in a screw-threaded bore 59 in the terminal end 31 ofthe earth pin.

The arms 52 and 52A of the spring 53 tend always to resume the generally parallel position shown, but they can be splayed apart when their claw-like end portions ride up the sloping sides of the notches 51 and 51A as a result of displacement of the shank 55 away from the earth pin 11 when suitably rotated.

When the shank 55 is rotated in the other sense the spring 53 is pushed back so that its claw-like arms approach the earth pin 11 again, the ends of the notches 51 and 51A generally at right angles to the edges of the earth pin defining limit stops when the arms of the spring 53 are generally parallel and flush with the longitudinal edges of the earth pin.

In the latter position of the spring 53 the earth pin 11 can be freely moved into and out of the opening 12. If when the pin 11 is fully received in the socket the shank 55 is rotated to splay the arms 52 and 52A apart they will jam in the opening 12 and thus resist withdrawal of the pin 11 from the socket.

The end ofthe shank 55 remote from its screwthreaded end portion 56 is not shown as this may take a variety of chosen forms. It may simply terminate in a screw head which, like that of the adaptor 30 in Figure 2 may be accessible exteriorly of the housing 50.

The embodiment of Figure 6 is suitable for cases where it is preferable that the screw accessible outside the housing of the appliance should be located in a side surface 65 of the housing 70 of the appliance rather than in its outwardly-presented face 66.

In the embodiment of Figure 6 the earth pin 11 is cut away to provide a generally rectangular, downwardly opening recess 71 in which a locking element 72 is received. The locking element 72 is at one end 73 pivotally connected to the earth pin 11 and its other end portion 74 is generally U-shaped. A screw-threaded bore 75 penetrates the earth pin 11 so as to open to the recess 71 and in the assembled position of the earth pin 11 in the housing 70 is aligned with a bore 76 in the housing. The head 77 of a screw 78 is accessible outside the housing and, on rotation, manually or by means of a tool, causes the screw 78 either to bear down upon or to release the element 72.

The underside of the U-shaped portion 74 of the locking element 72 and the corresponding portion of the top surface of the pin 11 may be roughened or serrated to obtain better friction when engaging opposite sides of the socket opening 12.

In use the screw 78 is retracted into the bore 75 so that the earth pin 11 can be fully inserted into the socket opening 12. The screw 78 is now rotated to press the locking element 72 downward into contact with the bottom edge of the opening 12. This tends to raise the pin 11 until its upper surface jams against the upper edge of the opening 12.

It will be appreciated that if desired the locking element 72 may be spring-loaded to the inoperative position retracted within the slot 71. If made of spring material such as spring metal strip it is not essential that it is pivoted at 73 and it may simply be fixed to the pin 11 at this end.

The embodiment of the invention illustrated in Figures 7 and 8 resembles that of Figures 1 and 2 and like parts have like reference numerals. The earth pin 11 of an adaptor 80 projects therefrom to be inserted in the appropriate slot 12 of a wall socket 13 having a safety shutter 14. A hook 19 of an element 17 is movable into and out of the downward opening 20 of a slot 16 to release the pin 11 or engage behind the panel of the socket 13. In this case, however, the element 17 is not L-shaped but instead has at its inner end an opening 81 through which passes a shaft 82. The locking element 17 and the shaft 82 are relatively non-rotatable. This can, of course, be achieved in various ways. By way of example the aperture 81 is non-circular and the shaft 82 is similarly shaped where it passes through the aperture 81 although elsewhere it is of circular-section.

Bearings for opposite ends of the shaft 82 are provided by opposed recesses 83A, 83B in the housing 84 of the adaptor 80 and its removable front plate 85. One end of the shaft 82, extending out of the adaptor 80, is cranked to provide an integral handle 86 whereby the shaft, and with it the element 17, may be rotated.A compression spring 87 acts between the back of the front plate 85 of the adaptor and a radial arm or lug 88 integral with the shaft 82 to bias the element 17 to its inoperative position, in which the hook 19 is received into the slot 16so as notto oppose movement of the pin 11 into and out of the aperture 12 When the adaptor 80 has been inserted in the socket 13 the hook 19 may be moved to the operative, locking position, in which it is shown in full lines in Figure 7, by rotating the handle 86 in the direction of arrow B in Figure 8. The handle 86 may be held in the operative position, against the action of spring 87, by releasable engagement with a friction stop (not shown) or a suitable latch (not shown) on the exterior of the adaptor housing.

Figure 9 illustrates a modification of the embodiment of Figures 7 and 8 more suitable for a plug.

Here the shaft 82 is foreshortened and its bearings are provided not at opposite sides of the plug housing but by suitable trunnion-like formations (not shown) in the plug housing interior on opposite sides of the inner end of the earth pin 11. In this embodiment the shaft 82 is rotated to move the hook 19 to the operative or locking position by a link 89 which extends out of the plug housing (not shown) through an opening in the top of the cover of the plug housing to enable itto be grasped manually and moved up and down as indicated by the double arrow C. The link 89 is articulated at its lower end 90 to the web portion 91 of a U-shaped saddle piece 92 integral with the shaft 82 and straddling the rear or inner end of the earth pin 11.

It will be clear that by provision of the shaft 82, with or without a saddle piece 92, the point at which rotary motion is imparted to the element 17 is capable of wide variation to suit the available space within the interiors of different appliance interiors and to avoid the obstruction of external faces of the appliance.

It will also be apparent that instead of being spring-loaded to the inoperative position, as in the examples illustrated in Figures 1,2,7,8 and 9, any of the elements 17 could be spring-loaded or biased toward the operative position in which the hook portion 19 extends from the slot 16 transversely of the earth pin 11. The rounded leading edge of the hook portion 19 could be relied on to ride over the lower edge of the aperture 12 and lock behind the panel 13. Release mechanisms such as 24,86 and 89 would then be used only momentarily as a preliminary to withdrawing an appliance from a socket.

It will also be apparent that suitably positioned leaf springs or coil springs could be substituted for the springs 87 exemplified, and that for space-saving such alternative spring means should preferably be located within the slot 16 of the earth pin.

In a further modification of the embodiment of Figure 9 the saddle piece 92 may be L rather than U-shaped, so as to leave one side (such as 93) of the inner end of the earth pin 11 free for the provision of a lateral wire-engaging extension as shown in Figure 2, or it may bend away from the earth pin 11 so as to clear a wire engaging screw (not shown) entering a top or rear end face of the earth pin.

Claims

1. An elongated male connection or pin for an electrical appliance adapted for insertion in the appropriate opening in a socket face plate, the connection having one or more formations to receive orto engage a locking element which is displaceable relative to the connection transversely thereof between a retracted position and an operative position extending from the connection at a position therealong to engage the socket housing when the connection is fully inserted, the arrangement being such that in its operative position the locking element will restrain the unintended withdrawal of the connection from the socket but in its retracted position the locking element will not impede the movement of the connection in and out of the socket.

2. A connection as claimed in claim 1, in the form of an earth pin which has a slot opening transversely of the pin at a position which will be behind the socket face plate when the pin is fully inserted, means being provided to move the locking element in the slot between an inoperative position in which the locking element lies substantially wholly within the slot and an operative position in which a portion of the locking element extends out of said slot opening transversely of the pin to engage behind the socket face plate if the earth pin tends to retract from the socket.

3. A connection as claimed in claim 2, wherein said portion is a hook-like free end portion of the locking element and wherein the locking element is rotatable in the slot about its other end.

4. A connection as claimed in claim 3, wherein manually operable means accessible exteriorly of the housing of the appliance incorporating the earth pin is adapted to exert a pressure on the locking element transversely of the earth pin such as to jam the earth pin in the socket opening.

5. A connection as claimed in claim 4, wherein the manually operable means is a screw engaging a screw-threaded bore in the earth pin which opens to the slot therein at a position between said ends of the locking element.

6. A connection as claimed in any one of claims 3 to 5, wherein the outwardly-presented face of said hook-like free end portion and the edge of the earth pin transversely opposite thereto are formed with serrations to improve frictional engagement with opposite edges of the socket opening in which the earth pin is inserted.

7. A connection as claimed in claim 3, wherein said other end of the locking element is pivotally mounted in the slot and there extends angularly therefrom at the pivot point a lever integral with the locking element, the lever extending out of an upper opening of the slot to be accessible exteriorly of the housing of the appliance incorporating the earth pin for displacing the locking element between its operative and inoperative positions.

8. An appliance incorporating the connection claimed in claim 7, the appliance having a housing formed with an opening positioned so that the free end of the lever will extend therefrom and further comprising means spring-biasing the lever in one sense of rotation and releasable engagement means whereby the lever may be held against the action of said spring bias.

9. A connection as claimed in claim 3, wherein said other end of the locking element is adapted for non-rotatable connection to a shaft extending transversely of and beyond the earth pin, means being provided to rotate the shaft so as to displace the free end portion of the locking element between its operative and inoperative positions.

10. An appliance incorporating the connection claimed in claim 9, and comprising a housing having formations to provide bearings for the shaft on one or both sides of the earth pin.

11. An appliance as claimed in claim 10, wherein one end of the shaft passes out of the housing and is provided with handle means whereby it may be rotated from a position external of the housing.

12. An appliance as claimed in claim 10, wherein the shaft is cranked and its cranked portion is articulated to a link which passes out of the housing through an opening therein whereby the link may be manipulated to rotate the shaft.

13. An appliance as claimed in any one of claims 10 to 12, and further comprising means springbiasing the shaft and locking element assembly in one sense of rotation and releasable engagement means for holding said assembly in a chosen angular position against the action of said spring bias.

14. A connection as claimed in claim 2, wherein the locking element is resilient and has a loop-like formation intermediate its ends which will project transversely of the earth pin from said slot opening when the locking element is in a first position retracted into the earth pin but which will engage one side of said slot opening and, by tending to straighten out, withdraw into the slot when the locking element is drawn axially out of the earth pin.

15. An appliance provided with the connection claimed in claim 14, the appliance having a housing in which there is rotatably but non-axially displaceably mounted a manually operable control means, and wherein the end portion of the locking element which extends out of the earth pin is connected via an auto-rotation device to a screw-threaded shank which is in screw-threaded engagement with the control means, the arrangement being such that by rotating the control means the locking element can be axially moved relative to the earth pin, therey to effect the extension or retraction of the loop-like portion thereof.

16. A connection is claimed in claim 1, in the form of an earth pin which is cut away to receive the locking element and wherein means is provided to displace the locking element longitudinally of the earth pin, the locking element and cut away area of the earth pin having cooperating cam surfaces whereby when moved longitudinally of the earth pin the locking element is displaced transversely thereof.

17. A connection as claimed in claim 16, wherein the locking element comprises a U-shaped, resilient element having arms which tend to remain generally parallel and have claw-like formations at their free ends extending inwardly of the element and wherein opposite sides of the earth pin are cut away to provide recesses to receive said arms so that in the unstressed or inoperative position of the locking element the outer surfaces of its arms are generally co-extensive with the remainders of said earth pin sides, each said recess having an end face generally at right angles to the axis of the earth pin and a sloping or cam face extending from said end face toward the rear or inner end of the earth pin, the arrangement being such that when the locking element is drawn rearwardly off the earth pin the claw-like formations ride up the sloping faces of the recesses to expand the arms, thereby tending to jam them in a socket aperture in which the earth pin is inserted.

18. A connection as claimed in claim 17, wherein a web portion of the locking element connecting said arms thereof is apertured and a screw-threaded shank extends through said aperture to engage a screw-threaded bore in the earth pin, the shank being rotatably but non-axially displaceably connected to said web portion whereby rotation of the shank, and its consequent axial displacement relative to the earth pin, causes displacement of the locking element longitudinally of the earth pin.

19. An elongated male connection or pin for an electrical appliance adapted for insertion in the appropriate opening in a socketface platsubstantial- ly as described in the Description with reference to and as shown in Figures 1 and 2, Figure 3, Figures 4 and 5, Figure 6, Figures 7 and 8 or Figure 9 ofthe accompanying diagrammatic drawings.

20. An electrical appliance having a male connection or pin as claimed in claim 19.