GB2224892A - Electric plug with safety catch - Google Patents

Abstract

A safety plug (1) has a pivoted catch (6) mounted in the earth pin (4) and releasable by a push button (7). The catch engages behind a complementary part of the socket. In an alternative embodiment the catch comprises a body of elastomeric material carried by the earth pin and adapted to be compressed by a manually operable plunger. The invention may also be applied to a socket cover. <IMAGE>

Description

IMPROVED ELECTRIC PLUG THIS INVENTION relates to an electrical plug and socket assembly.

It is commonplace in domestic and like environments to provide a connectable electrical supply using a plug with three pins, each rectangular in cross-section, fitting into a complementary socket. Usually one pin is longer than the other two, and represents an emergency earth connection whereby the electricity supply is connected to earth in the event of malfunction.

Electrical plugs of this nature are typically held in their sockets by being gripped between resilient leafs of metal acting e.g. on opposite faces of the rectangular cross-section of each pin. Because of this it not infrequently happens that the plug falls out.

Possibly, the leaf spring contacts within the socket become weak with age and use, or the plug can be mechanically knocked and dislodged from the socket, or the plug can be tampered with or removed from the socket, for example by a child.

All of these are inconvenient and dangerous outcomes. The present invention sets out to provide a plug for a plug/socket assembly which possesses a mechanically interengaging safety catch on at least one of the pins.

In one aspect the invention consists in an electrical plug or socket cover having a displaceable catch associated with a terminal pin, the catch being capable of engagement with the socket upon assembly therewith, and of disengagement from the socket upon manipulation of a member movable in relation to the body of the plug or socket cover Preferably, a retractable catch is provided upon the earth pin. It can project upward or downward or it can project to either side. Possibly, it could project from both the top and bottom or from both sides.

In another embodiment a catch is constituted by a body of elastomeric material located to be selectively deformable to a catching configuration or releasable to a configuration permitting plug or socket cover withdrawal. For example, an elastomeric insert may be incorporated within an open slot of a terminal pin (preferably the earth) so as to protrude therefrom, as a catch, when subject to pressure in the pin direction.

The slot can be open top and bottom or on both sides for such protrusion. Pressure may be exerted thereon by a longitudinal movable plunger housed within the plug, slidable by a cammed latch to permit selective catching or release from within the socket.

In yet another embodiment, more suitable for a socket cover than a plug, a socket-fitting pin carries a catch at an inner location; extends back through the plug to expose a manipulable end; and is pivoted intermediate its ends: so that the pin can adopt either a first lower tilted position or a second tilted position, thus selectively positioning the catch to permit or prevent withdrawal. Typically, such a pin will be electrically non-conductive.

While the invention as defined above relates to a plug or socket cover in itself it also extends to a plug/socket assembly incorporating such a plug The invention will be further described in the accompanying drawing in which: Figure 1 shows in three-quarters view an embodiment of safety plug in accordance with the invention, and Figure 2 shows a vertical median section through the plug, indicating diagrammatically the release mechanism.

Figure 3 shows in three quarters view a further embodiment of a safety plug in accordance with the invention, Figure 4 shows a vertical median section through the plug of Figure 3, located in its socket indicating diagrammatically the release mechanism of this further embodiment, Figure 5 shows a back view of the plug of Figure 3, Figure 6 shows a section through an embodiment of safety socket cover modified in accordance with the invention, Figure 7 shows a front view of Figure 6.

Figure 8 shows another embodiment of cover in section.

The plug shown diagrammatically in Figure 1 is a well known article of commerce, comprising a housing 1 which encloses the various connecting members for the wires entering as flex 2, and which carries pins 3a, 3b and 4 to extendforward from a flat inner plug face.

Typically, the plug may be assembled or disassembled by means of a screw member 5.

In the embodiment shown, two additional features are incorporated in accordance with the present invention.

Thus, there is a movable safety catch 6 shown towards one end of the uppermost (earth) connection 4. Secondly.

a release button 7 is provided at the top of the plug.

The vertical median section shown in Figure 2 will make clear the mode of operation of the equipment. The safety catch 6 is in fact part of a metal strip 8 extending along within the connector 3, and connected by its vertically upstanding end 9 beneath to the underside of a release mechanism 7. In use, as the plug is pushed in it pushes past a complementary section of the socket, so that the safety catch clicks up and prevent unauthorised removal of.or accidental dropping out of. the plug from the socket.

If it is desired to extract the plug the button 7 is depressed whereby the catch 6 and the plug can be withdrawn.

The man skilled in the art will realise that very many different modifications may be made within the broad scope of the invention, and that the example shown in the drawing is only one embodiment of many possible embodiments . For instance, the safety catch can be positioned further back nearer the face of the plug so that it catches just behind a face member of the socket.

If desired the safety catch can project from one or both side faces of the plug, with consequential alterations to the shape of the plug to incorporate release buttons at one or both sides. If desired, the catch can be placed upon the undersurface of the earth connection pin.

It is however less desired to place the catch upon other connecting elements since in use these conduct electricity and it is desirable to leave then unconnected to any mechanically operating member.

While the arrangement shown involves the use of a catch at the end of a metal strip, so that depression of the metal strip takes the catch out of engagement, other forms of mechanical interengagement are possible. Thus, angled linkages which manipulate the catch, or a pull button which straightens a metal strip otherwise deformed into a catching member can also be envisaged.

One valuable variant embodiment is shown in Figures 3, 4 and 5. For convenience, the same reference numerals as before are used wherever possible. Thus, connector pins 3a and 3b, and earth pin 4 protrude from the front face of a plug 1 which is held together by central screw 5.

In the embodiment shown, however, the earth terminal pin 4 is provided with side walls 8 defining a through slot, open towards the rear of the pin, in its rearward part. This through slot contains a suitably dimensioned elastomeric element 9. Within the plug, and as shown in more detail in Figure 4, there is a horizontal plunger member 10 such that, when the plunger member is moved forwardly it compresses the rubber element. The rubber element 9 is constrained at each side and at its outer face, so that when compressed it rises above and below the through slot defined between walls 8. In other words, the element 9 provides a swollen portion which mechanically interengages with the inner face of a socket shown at 11 and prevents the plug from being removed.

Movement of plunger 10 is effected by a latch 12, which has a camming surface at 12a and a stem 12b. When stem 12b is pressed into recess 13 at the back of the plug then the camming surface forces plunger 10 forwardly to cause the rubber element 9 to enlarge and prevent subsequent retraction. Conversely, when the stem 12 is raised, as shown in Figure 4, the elastic element 9 can regain its former shape and the plug can be withdrawn.

Figures 6 and 7 show a different variant of the invention, applied to a socket cover rather than the plug. A socket cover is a more or less flat body of polymer having three pins protruding from its face, of a spacing such as to fit within the holes of a socket.

Typically, these pins do not protrude as far into the socket as normal electrical connector terminals. The purpose of a socket cover is to provide security against unintentional penetration of the socket by any element capable of providing an electric shock or of splashes of water, etc.

In practice, socket covers, while somewhat difficult to remove, can be prised off by a diligent child. The embodiment of the present invention shown in Figures 6 and 7 therefore provides, upon a socket member 14, a socket cover 15 of, for example, generally circular periphery. From the socket cover three pins protrude.

Only two of these are shown, pin 16 being shown from th side and pin 17 in section and typically they are made of non-conductive material. When the socket cover 15 is placed over the socket 14 the three pins penetrate at least to some extent into the available spaces in the socket and the socket is held against casual removal.

The invention as shown envisages the pin 17 should carry a shoulder 17a which as shown interferes with the top part of the relevant socket recess at 17b to prevent removal. The pin 17 is also journalled at 18 so that it is capable of movement as shown by arrow A when a sliding movement of the serrated thumb plate 19 in its slot 20 takes place . As can be see from Figure 6, therefore, once the socket cover 15 is in place as shown it cannot be removed (since shoulder 17a encounters the surface 17b) until the thumb plate 19 is pushed upwardly to the upper end of its slot 20 thereby tilting the whole pin 17 and allowing it to be removed from the relevant slot in the socket.

The man skilled in the art will appreciate that the mechanism shown can, per se, be utilised for electric plugs as well as socket covers. It is believed, however, that in viewof safety regulations the mechanism shown is preferably utilised with the essentially polymeric and non-conductive pins of socket covers rather than with metallic electrically conductive pins of electrical plugs.

Figure 8 shows diagrammatically a section through a further embodiment of safety socket cover, with earth pin 801, terminal pins 802, and a recess 803 accommodating a thumb catch 804. When the cover is in place, shoulder 801a lodges behind the socket lid 805.

For release, the catch 804 is pushed upwards to pivot pin 801 about pivot 806.

Claims (8)

CLAIMS:

1. An electrical plug or socket cover having a displaceable catch associated with a terminal pin, the catch being capable of engagement with the socket upon assembly therewith, and of disengagement from the socket upon manipulation of a member movable in relation to the body of the plug or socket cover

2. An electrical plug, or socket cover, as claimed in claim 1 in which a retractable catch is provided on the earth pin.

3. An electrical plug or socket cover as claimed in claim 2 in which the retractable catch projects upwards.

4. An electrical plug or socket cover as claimed in claim 1 in which the catch constituted by a body of elastomeric material located to be selectively deformable to a catching configuration or releasable to a configuration permitting plug or socket cover withdrawal.

5. An electrical plub, or socket cover, as claimed in claim 3 in which an elastomeric insert incorporated within an open slot of a terminal pin (preferably the earth) so as to protrude therefrom, as a catch, when subject to pressure in the pin direction.

6. An electrical plug, or socket cover, as claimed in claim 4 comprising, as a means for exerting pressure in the pin direction a longitudinal movable plunger housed within the plug, slidable by a cammed latch to permit selective catching or release from within the socket.

7. An electrical plug, or socket cover1 as claimed in claim 1 in which a socket-fitting pin carries a catch at an inner location; extends back through the plug to expose a manipulable end; and is pivoted intermediate its ends: so that the pin can adopt either a first lower tilted position or a second tilted position, thus selectively positioning the catch to permit or prevent withdrawal.

8. A plug/socket, or cover/socket, assembly incorporating an electrical plug, or socket cover, as claimed in any one preceding claim.