IE20060199A1 - Improvements in and relating to electrical plugs and sockets - Google Patents

Abstract

A plug and socket arrangement (1), the plug (2) engaging with the socket (3) by means of contacts (80) arranged about a centre of rotation (3C), the plug being arranged to interlock with the socket by relative rotation (3R) of the socket and plug about an axis (3A), the plug and socket having an interfitting arrangement so arranged to ensure the plug can only fit the socket in one particular way, the interfitting arrangement comprising an upstanding wall (4) form a frontplate (10) of the socket. A gap (138) is provided between the wall (4) and plug (2) in the fully engaged situation between the plug and the socket to provide a visual indication of plug engagement. <Figure 3>

Description

IMPROVEMENTS IN AND RELATING TO ELECTRICAL PLUGS AND SOCKETS The present invention relates to electrical plugs and sockets.

Electrical plugs and sockets are used to make disconnectable connections to electrical wiring installations. It is known to arrange the pin and socket clip configurations of plugs and the corresponding sockets to ensure that it is not possible to connect live conductors to a protective earth conductor, or to interchange live connections. It is also known to provide plugs and sockets with multiple poles or to provide sockets able to accept plugs with different pin configurations according to the appliance connected to the plug. It is known to provide chamfers on the entry to the socket openings provided to receive plug pins so as to provide a means of guiding the plug pins into engagement with the socket. However, with known arrangements it is particularly difficult to insert a plug into a socket in a correct orientation without being able to see what one is doing. This is a particular problem where, for example, the sockets are mounted high on a ceiling, or within a ceiling void and can only be accessed while standing on a step ladder. Hence a person wishing to make a connection, who in the interests of safety wishes to keep one hand on the safety handrail of the step ladder, needs to be able to easily insert a plug into a socket with the only other hand, locating the socket by touch, and able to thus discern the correct orientation of the plug so as to be able to successfully insert it into the socket.

According to the invention, there is provided a plug and socket arrangement, the plug engaging with the socket by means of contacts arranged about a centre of rotation, the plug being arranged to interlock with the socket by relative rotation of the socket and plug about an axis through the centre of rotation, the plug and socket having an interfitting arrangement so arranged to ensure the plug can only fit the socket in one particular way, the interfitting arrangement comprising an upstanding wall from the frontplate of the socket, the upstanding wall being asymmetrical about the centre of rotation, and the plug having a plug body, the body being asymmetrical about the OPEN TO PUBLIC INSPECTION INTCLfeil Ho 1ft \3/6<· IE 0 6 Ο 1 9 9 - 2 centre of rotation, such that a gap may be seen between the wall and the plug body when the plug is fully engaged.

A benefit of the plug and socket interlocking by relative rotation and being able to fit together in only one particular way, is that electrical safety may be enhanced by a secure polarised electrical connection, which is not disconnectable by a direct pull on a cable attached to the plug. A benefit of the upstanding wall is that incompatible plugs may be prevented from engaging with the socket.

In an embodiment preferably the interfitting arrangement further comprises a continuous upstanding wall.

A benefit of the upstanding wall being continuous is that it is easier for an installer to feel the outline of the wall of the socket, and so correctly orientate the plug to insert into the socket.

In an embodiment, preferably the upstanding wall of the interfitting arrangement comprises a boundary of a front face of the frontplate of the socket, the front face being recessed below a surrounding face of the socket A benefit of the front face being recessed below a surrounding face is that the location of a particular socket from a series of similar adjacent sockets is facilitated.

Preferably apertures are provided in the frontplate for access to socket contacts behind the frontplate, and more preferably the apertures are located within the wall.

A benefit of the apertures in the socket frontplate being located within the wall is that safety is enhanced as the wall prevents a metallic blade object from sliding between IE 0 6 0 1 9 9 the front face of the socket and the plug when inserted into the socket, and the blade contacting live plug pins.

Preferably the upstanding wall is asymmetrical about the centre of rotation.

Preferably the plug body is asymmetrical about the centre of rotation.

A benefit of the upstanding wall and the plug body being asymmetrical about the centre of rotation is that the plug and socket may be arranged so that the plug may only be inserted into the socket in one particular orientation. Hence, the interconnection of particular plug pins to particular corresponding socket clips is assured.

Preferably the plug body is arranged to fit within the upstanding wall, the fit being such that it permits relative partial rotation of the plug and socket.

A benefit of the fit being such as to permit relative partial rotation of the plug and socket when the plug is fitted to the socket, is that the relative partial rotation may be utilised to ensure positive electrical contact between the plug pins and corresponding socket clips.

Preferably the plug is provided with plug pins protruding from the plug body. More preferably the plug pins are partially arcuate. The partially arcuate shape being preferably formed as short arcs about the centre of rotation.

A benefit of the plug pins being partially arcuate, is that the strength of the pins is enhanced. A further benefit is that each of the socket apertures may be of a shape and size that closely conforms to the corresponding plug pin, hence safety may be improved by providing only a narrow aperture to access live socket clips. ΙΕ ο 6 Ο 1 9 9 Preferably the direction of insertion is perpendicular to a plane of a front face of the socket.

Preferably a cable outlet from the plug is co-axial with the axis through the centre of rotation.

Preferably a cable grip is provided to restrain a cable passing out of the cable outlet, the direction of the cable through the cable grip being at an angle of greater than 30 degrees to the axis through the centre of rotation. More preferably the said angle is substantially perpendicular to the axis.

A benefit of the cable grip being at an angle to the axis through the centre of rotation is that the cable grip may more easily and safely support a heavy load exerting an axial pull on the cable. A requirement of British Standard BS6972:1998 Including Amendment 1, is that such a plug and socket shall safely support a 5kg load on the cable. An embodiment of the invention safely meets this requirement.

Preferably the plug and socket are provided with further interlocking means arranged to mechanically interlock the plug and socket, independently of the plug pins and socket contacts.

A benefit of the mechanical interlock, is that the standards requirement mentioned above may be safely met without relying on the mechanical strength of current carrying parts.

Preferably the interlocking means further comprises a detent arranged to provide a positive engagement and disengagement of the interlocking means.

IE 0 6 0 ί 9 9 A benefit of the detents is that an installer may more easily feel when the plug is fully engaged with the socket.

Preferably the line and protective conductor plug pins are substantially the same.

A benefit of the line and protective plug pins being substantially the same is that savings in the cost of manufacturing may be achieved.

Preferably the plug and socket mouldings are arranged to optionally accommodate three line pins and sockets contacts respectively and one protective conductor pin and socket contact respectively.

A benefit of the plug and socket moulding being arranged to accommodate multiple line pins is that the functionality of the plug and socket may be enhanced.

Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:Figure 1 is a perspective view of a plug and socket of a first embodiment of the invention; Figure 2 is a perspective view of the plug and socket shown in Figure 1, the plug being partially inserted into the socket; Figure 3 is a perspective view of the plug and socket shown in Figure 1, the plug being fully inserted into the socket; Figure 4 is a view of the plug shown in Figure 1, showing the plug pins; IE 060 1 9 9 Figure 5 is a scrap sectioned diagrammatic view through a part of the socket shown in Figure 1, showing a socket clip, and a plug with a plug pin positioned ready for insertion into the socket.

Figure 6 is a perspective partially exploded view of the plug shown in Figure 1, with a plug cover part removed; and Figure 7 is a perspective view of a plug and socket of a second embodiment of the invention.

From Figure 1, a perspective view of a plug and socket arrangement 1 is shown, the plug 2 being shown disengaged from the socket 3. The socket has a engaging front face 10, having apertures 11, 12, 13 and 14 for providing access to socket clips 80 (not visible in Figure 1), the socket clips providing electrical supply contacts. The apertures 11,12,13 and 14 are arranged in a circular basis about a centre of rotation 1C, each aperture forming a short arc on a circle having a diameter 1D. The plug is arranged to engage with the socket clips by means of contact pins 111,112,113 and 114 which are also arranged in an at least circular basis on a circle having the same diameter 1D. The plug pins 111 to 114 are shaped with a upstanding blade 120 having a L shape 124 forming a hook 122.

From Figure 3, a perspective view of the plug 2 locked into the socket 3 it can be seen that the plug 2 is arranged to interlock with the socket 3 by relative rotation of the plug 2 in the direction of arrow 3R with respect to the socket 3 about an axis 3A. Hence, the axis 3A is at the centre of rotation the plug relative to the socket. The relative rotation in the direction of the arrow 3R is through an angle 2G. The angle is preferably greater than 5 degrees. The axis 3A lies along the direction of insertion of the plug into the socket and is perpendicular to a plane of the face 10 of the socket. ΙΕ ο 6 ο ί g g A wall 4 is provided surrounding the socket front face 10 arranged to provide an interfitting arrangement, so that the plug can only fit the socket in one particular way. To assist in this, the wall 4 is shaped with an internal profile 5 so as to conform to a peripheral profile 130 of an external shape 132 of the plug 2, when swept through the angle 2G.

The wall 4 is an upstanding protrusion above the front face 10 and a surrounding face 7 of the socket frontplate 15. Surrounding face 7 is bounded by an edge 8 of the socket. Screw holes 9 are provided for mounting the socket to a suitable mounting. Such a suitable mounting may be a conduit box.

Hence from Figure 2, showing the plug 2 inserted into the socket 3 by moving in the direction of arrow 1S, it may be seen that gap 134 and gap 136 are provided at the diagonally opposite corners 140 and 142 of the plug. Hence, the plug may only rotate in the direction or arrow 3R to ensure the plug pins 111 to 114 have fully engaged the respective socket clips 80. When fully engaged, as shown in Figure 3, it may be seen that a gap now exists at 138 and also at 139 (not visible in this Figure). The gaps 134 and 136 have now been closed. Hence, a visual indication is provided that the plug has been fully engaged with the socket.

On insertion into the socket 3, rear edges 121 (only one labelled for clarity) of each of the plug pins 111 to 114 abuts an edge 128 of each corresponding socket aperture.

As the plug 2 is rotated in the direction of arrow 3R, the plug pins 111 to 114 move angularly in the sockets, and the hooks 122 engage under the frontplate at 126, the rear edges 121 moving away from the edges 128. From Figure 5, a diagrammatic section through the socket frontplate 15 showing the aperture 13, with the edge 128 and the plug 2 positioned with rear edge 121 axially aligned with the edge 128 so that the plug may be inserted into the socket by moving in the direction of arrow 1S. The frontplate has a thickness 8T, and the hook 122 is spaced a distance 8S from an external surface 92 of the plug. The distance 8S being slightly greater than the IE 060 1 9 9 - 8 thickness 8T. Hence when the plug is inserted into the socket and partially rotated such that the plug pins are engaged with the socket clips, the external surface 92 closely abuts the front face 10 of the socket frontplate 15.

Hence the plug and socket are arranged to be able to fit together in only one particular way, so that electrical safety is enhanced by a secure polarised electrical connection, which is not disconnectable by a direct pull on a cable attached to the Plug.

To provide additional strength and security the plug and socket are provided with further interlocking means arranged to mechanically interlock the plug and socket, independently of the plug pins and socket contacts. The further interlocking means comprise protruding clips 150 and 152 which are provided with latching faces 154 and 156 respectively, which when the plug 2 is fitted to the socket 3, locate in apertures 158 and 160 (or when fitted to socket 700, apertures 758 and 760) respectively.

To provide further positive tactile feedback that the plug is fully inserted the interlocking means preferably further comprises a detent arranged to provide a positive engagement and disengagement of the interlocking means. The detent comprises a rounded protrusion 162 provided on the face 10 and positioned to locate within recess 164 when the plug is fully inserted into the socket having been rotated relative to the socket through the angle 3R.

In another alternative embodiment, not shown, the faces 154 and 156 are provided with latches which engage with latching features on an inside surface of the frontplate 15 at apertures 158 and 160 so as to provide the said further positive tactile feedback.

IE 06 0 19 9 - 9 The wall 4 has a top edge 6 which is a height 1H above the engaging front face 10. The blade 120 of each of the plug pins 111 to 114 has a height 4H. Preferably the height 1H is such that the height 1H plus the thickness 8T of a front wall 83 of the socket 3, is greater than the height 4H of the plug pins. Hence the upstanding protrusion of the wall 4 is such that an incompatible plug may be prevented from contacting the socket clips 80.

Hence variations of the profile 130 may be used to differentiate between plugs and sockets in an installation. By way of example in a lighting installation, a particular profile may be used for ordinary lighting off the mains, while another profile may be used only for emergency lighting, and yet another profile may be used only for safety low voltage lighting.

It should be noted that although a particular application for the plug and socket arrangement of the present invention is for use with lighting installations, it may also be of use in other applications.

From the figures it may be seen that the profile 130 is asymmetrical, and preferably that the upstanding wall is asymmetrical about the axis perpendicular to the direction of insertion of the plug into the socket. Hence, since the plug body is likewise asymmetrical about the said axis, the plug may only be inserted into the socket in a particular orientation as shown in Figures 2 and 3. This ensures that the polarity of the connections is maintained.

From Figure 7, a second embodiment 700 is shown to comprise the plug 2 and a panel socket 703. This embodiment is similar to the first in most respects, except that the interfitting arrangement comprises a wall 704, the wall 704 comprising a boundary between the surrounding surface 707 and a front face 710 of the panel socket, the front face 710 being recessed below a surrounding face 707 of the panel socket 703.

IE 0 6 Ο ί 9 9 - 10 From Figures 1 and 7 it can be seen that the apertures provided for access to socket contacts are located in the face portion 10, 710 of the socket frontplate 15, 715 within the wall 4, 704. A benefit of this is that safety is further enhanced since it is not possible to slide a rigid conductive member between the plug and socket either while it is being inserted or when it is inserted into the socket.

From Figures 1 and 7 a flexible cable outlet 170 from the plug 2 is co-axial with the axis 3A, 7A which passes through the centre of the circle on which the arcs of the apertures 11,12, 13,14 and 711, 712, 713, 714 lie. In the case of socket 3, the axis 3A is also a centre of the circular edge 8. Hence, in the case of socket 3, a circular cover 174 may be used to cover the plug and socket when the plug is inserted into the socket. The cover is provided with a hole 176 through which flexible cable 172 may pass, and may be arranged to locate on the edge 8 by means of a screw fitting arrangement or alternatively by means of a clip fitting arrangement.

From Figure 4 the plug 2 is shown provided with plug pins 111, 112, 113, 114 protruding from the plug body. The plug pins are formed as short arcs 4C about the perpendicular axis 3A at the centre of rotation 3C, the axis being along the said direction of insertion 1S, 7S. Hence, each of the plug pins is partially arcuate, being curved about the axis 3A. The arcuate form of each of the plug pins closely corresponding with the arcuate form of the respective apertures 11,12,13 and 14.

Figure 6 a perspective partially exploded view of the plug 2 shown in Figure 1, with a plug cover part 602 removed from a plug base 600 to show a cable grip 604 provided to restrain the flexible cable 172 passing out of the outlet 170. The cable grip 604 is clamped against the cable by means of a fixing, such as screws 605 and 605'. A direction 6C of the cable through the cable grip is at an angle 6A to the axis. In the embodiment of this Figure, it may be seen that the said angle 6A is substantially perpendicular to the axis 3A.

IE ο 6 Ο 1 3 9 - 11 The angle 6A is preferably greater than 30 degrees so as to provide enhanced strain relief to prevent strain on cable terminations 611, 612, 613, 614 arising from a force pulling on the cable in the direction of arrow 6F.

Channels 621, 622, 623, 624 are provided for access to the cable terminations 611, 612, 613, 614 respectively. The cover 602 is provided with blanking tabs 631, 632, 633, 634 which close off the channels when the cover is mounted to the base 600, so as to prevent inadvertent contact with live current carrying parts. A benefit of this arrangement is that the current carrying path of the plug pins and cable terminations may be kept short, and hence a dissipation of heat arising from a lower conductivity of material used for the plug pins may be minimised. Hence also component costs may be minimised.

In the embodiment shown the plug 2 and socket 3 mouldings are arranged to accommodate up to three line pins and sockets respectively and one protective conductor pin and socket respectively. Where only two line connections, live and neutral, are required, one of the plug pins and the corresponding socket may be omitted.

From Figures 4 and 6 it can be seen that the pins 111, 112,113, 114 which are the line and protective conductor plug pins are the same, since incorrect insertion of the plug into the socket is prevented by the arrangement of the wall 4 as described above. Hence, manufacturing costs are reduced.

In a further embodiment not shown, the plug pins and socket contacts are arranged in a circular basis having a substantially common centre, at least one plug pin and corresponding socket clip and aperture being arranged on a circle of a different diameter to another of the plug pins and its corresponding socket clip and aperture. This embodiment is similar in other respects to the embodiment described above with reference to the figures.

Claims (15)

1. A plug and socket arrangement, the plug engaging with the socket by means of contacts arranged about a centre of rotation, the plug being arranged to interlock with the socket by relative rotation of the socket and plug about an axis through the centre of rotation, the plug and socket having an interfitting arrangement so arranged to ensure the plug can only fit the socket in one particular way, the interfitting arrangement comprising an upstanding wall from a frontplate of the socket, the upstanding wall being asymmetrical about the centre of rotation, and the plug having a plug body, the body being asymmetrical about the centre of rotation, such that a gap may be seen between the wall and the plug body when the plug is fully engaged.

2. A plug and socket arrangement as claimed in claim 1 wherein the interfitting arrangement further comprises a continuous upstanding wall.

3. A plug and socket arrangement as claimed in claim 1 or 2 wherein the upstanding wall of the interfitting arrangement comprises a boundary of a front face of the frontplate of the socket, the front face being recessed below a surrounding face of the socket.

4. A plug and socket arrangement as claimed in claim 2 or 3, wherein apertures are provided in the frontplate for access to socket contacts, the apertures being located within the wall.

5. A plug and socket arrangement as claimed in any one or more of the preceding claims wherein the plug body is arranged to fit within the upstanding wall, the fit being such that it permits relative partial rotation of the plug and socket.

6. A plug and socket arrangement as claimed in any of the above claims wherein the plug is provided with plug pins protruding from the plug body. IE 06 0 1 9 9 - 13

7. A plug and socket arrangement as claimed in claim 6 wherein the plug pins are partially arcuate.

8. A plug and socket arrangement as claimed in any one or more of the preceding claims wherein the direction of insertion is perpendicular to the frontplate..

9. A plug and socket arrangement as claimed in any one or more of the preceding claims wherein a cable outlet from the plug is co-axial with the centre of rotation.

10. A plug and socket arrangement as claimed in any one or more of the preceding claims wherein a cable grip is provided to restrain a cable passing out of the cable outlet, the direction of the cable through the cable grip being at an angle of greater than 30 degrees to the axis through the centre of rotation.

11. A plug and socket arrangement as claimed in claim 12 wherein the said angle is substantially perpendicular to the axis.

12. A plug and socket arrangement as claimed in any one or more of the preceding claims wherein the plug and socket are provided with further interlocking means arranged to mechanically interlock the plug and socket on partial relative rotation about the centre of rotation.

13. A plug and socket arrangement as claimed in any one or more of the preceding claims wherein the line and protective conductor plug pins are substantially the same.

14. A plug and socket arrangement as claimed in any one or more of the preceding claims wherein the plug and socket mouldings are arranged to optionally - 14 ΙΕ θ 6 ο 1 9 9 accommodate two, or three line pins and socket contacts respectively and one protective conductor pin and socket contact respectively.

15. An electrical plug and socket, substantially as hereinbefore described and 5 with reference to the accompanying drawings.