WO1995031018A1

WO1995031018A1 - Electrical coupling

Info

Publication number: WO1995031018A1
Application number: PCT/GB1995/001059
Authority: WO
Inventors: John Crawshaw Taylor
Original assignee: Strix Limited
Priority date: 1994-05-10
Filing date: 1995-05-10
Publication date: 1995-11-16
Also published as: AU2414895A; GB9421126D0

Abstract

An electrical coupling for an electrical appliance such as a kettle comprises an inlet (102) in the appliance and a connector (104) for engagement in the inlet. An earth pin (116) of the inlet has a tapered end (124) and grooves (122) behind the tapered end to receive latching portions (186, 188) of springs (182, 184). A spring (192) is loaded by the earth pin (116) as the pin (116) is introduced into the connector, the latching springs (182, 184) being deflected outwardly by the tapered portions (124) of the pin until the portions (186, 188) drop into the grooves (122) to latch the connector in position. To break the connection, the connector is moved away from the inlet either axially, or pivotally, whereupon the portions (186, 188) disengage from the grooves (122), to break the latch, allowing the connector to be ejected from the inlet by the spring (192).

Description

ELECTRICAL COUPLING

The present invention relates to electrical couplings and in particular to electrical couplings for domestic appliances such as kettles and hot water jugs. Typically such appliances comprise an appliance inlet housing a number of electrical contact pins in a predetermined configuration, power being supplied to the pins by a connector inserted into the inlet by hand and having a number of pin-receiving sockets arranged in the same configuration as the pins.

In existing couplings which meet IEC standards the contacts within the connector are formed as metallic sleeves into which the respective pins of the inlet are forced, the coupling being held together by the spring frictional force of the pin within the contact sleeve. Such an arrangement leads to an inconsistent engagement of the pins in the sleeves. If the sleeve is slightly too large, then the corresponding pin will not be held sufficiently tightly in the sleeve, reducing the contact force and causing arcing between the pin and sleeve which will eventually lead to destruction of the pin and sleeve. If, on the other hand the sleeve is too tight it will be difficult to insert the pins in the sleeve which again may cause arcing which will exacerbate the problem. Furthermore if the grip on the pin is very tight, then if the power lead extending from the connector is pulled then the appliance to which the connector is attached may also move. This is potentially very dangerous for example when the appliance is a kettle or hot water jug since it may contain boiling water which, if the appliance is tipped over may be spilt, possibly scalding a user of the appliance or a child who may inadvertently have pulled the cord. From a first broad aspect the invention provides an electrical coupling comprising first and second components each having respective electrical terminal means, spring disconnection means acting between the components to bias them apart, and latch means for holding the coupling closed, said latch means being automatically disconnectable upon the components being moved apart, whereupon said spring means ensures complete electrical disconnection of the two components. The spring means need not become operative until the latch is broken, and so from a second broader aspect, the invention also provides an electrical coupling comprising first and second components each having respective electrical terminal means, latch means for holding the coupling closed, said latch means being automatically disconnectable upon the components being moved apart, and spring ejection means operable to move said components apart after the latch means has disconnected to ensure complete electrical disconnection of the two components.

The first component may be an inlet in or for an appliance having line, neutral and earth terminals, for example pins, arranged in a predetermined configuration, and the other component may be a connector provided, or adapted to be provided on a power lead, for mating engagement with said inlet, and having terminals for engagement with the inlet terminals, for example having three sockets into which said pins may be inserted, and housing line, neutral and earth contacts which make electrical contact with said pins.

From a third aspect, the invention provides an electrical coupling comprising an inlet in or for an electrical appliance, and a connector provided, or adapted to be provided on a power lead, for mating engagement with said inlet, said inlet having line, neutral and earth pins arranged in a predetermined configuration, and said connector having three sockets arranged in a mating configuration and into which said pins may be inserted, and housing line, neutral and earth contacts which make electrical contact with said pins, characterised in that said coupling has latch means acting between the inlet and the connector to keep the coupling closed and a spring loaded ejection means acting so as to ensure breaking of the contact between the line and neutral pins and contacts as soon as the latch is broken. Thus in accordance with the invention the means for holding the connector in the inlet are separate from the line and neutral contacts themselves. This allows a more satisfactory electrical contact to be made within the coupling. Furthermore, the invention allows a positive disconnection of the connector from the inlet when the latch is broken to prevent arcing between the current carrying pins and contacts and to prevent one component dragging with it the other when they are moved apart. It would be possible to have the spring means act say between opposed faces of the respective components, but preferably the spring means acts on an end region, for example the end, of at least an earth terminal or pin of an inlet when it is inserted in the connector. Most preferably, however, it acts on the ends of all three pins. The spring means may comprise, for example, a shutter acting on the ends of one or more of the pins, but most preferably it comprises spring members acting on the ends of the respective pins. In a preferred embodiment, the line and neutral contacts within the connector are provided on the ends of the springs whereby they make electrical contact with the ends of the line and neutral pins of the inle . Such an arrangement has the advantage that the springs provide a contact force onto the ends of the springs, also contributing to the ejection force for the connector. Furthermore, since the contact is made on the end of the pins, the overall length of the pins can be reduced compared to the present arrangement where contact is made over a length of the pin within a sleeve. This has particular advantages as will be described later.

Preferably the contact carrying springs are low rate springs, so that the contact force remains generally constant as they are loaded, to give a predetermined acceptable contact force. The springs may be preloaded to give a desired contact force upon engagement. That force does not need to be great, since in the preferred embodiment, the major disconnection force for the coupling is provided by the other spring which, for example, acts on the end of the earth pin. As will be described below in further detail the spring could be provided by the latch means itself in that the latch spring may provide an ejection force when the latch is broken.

The earth contact may also be arranged to engage the end of the earth pin but in a preferred embodiment the earth contact is, instead, provided by or on a separate spring member which is biased against side surface of the earth pin. The arrangement of the earth pin and contact is preferably such that it will make first as the connector is inserted in the inlet and break last as the connector is withdrawn therefrom.

The size and configuration of inlets and their pins and of the corresponding connectors and their socket openings in couplings for electrical appliances such as kettles and hot water jugs is presently specified by standard 320 of the International Electrical Commission (320 IEC 1981) , the most relevant to these appliances being sheets C15 and C16 thereof. In the standard, the line and neutral pins are dimensioned with a cross- section of 4mm ± 0.1mm by 2mm ± 0.05mm ("the Standard dimensions"), and the centres spaced apart by 14mm ± 0.2mm. This effectively establishes a footprint for the pins, and preferably the line and neutral pins of the present invention fall within that footprint hereinafter termed the 'Standard Footprint'.

The pins may have the same centres as specified by the present standard, which allows existing controls to be easily adapted for use with the new connectors. However the pins may have a cross-sectional area and shape which differs from that of the present standard. Preferably they are less than the 'standard dimension' for example less than 3mm in diameter. For example they may be square, for example 2mm x 2mm. This has the advantage of reducing the overall height of the inlet and improving the electrical safety by reducing the size of the corresponding openings in the connector. If the pins are made smaller than the present standard, the corresponding connector may have smaller socket openings, thereby preventing the insertion of a standard socket into a non-standard inlet.

The earth pin may be in the position specified by the present standard, although both its size and its position may be changed, if desirable.

To prevent existing standard connectors being inserted in an inlet of a coupling in accordance with the invention, the inlet is preferably configured so as to interfere with the standard connector, for example by having its earth pin being in a non-standard position, or by the inlet or pin having a dimension which would interfere with a standard connector during insertion. Similarly, to prevent connectors of couplings in accordance with the invention being inserted in standard inlets, again the earth sockets could be in a non- standard position, or a dimension of the connector so as to interfere with the standard inlet. Preferably the respective profiles of the inlet and connector are asymmetrical in at least one plane, to allow for easy orientation before engagement.

The relative arrangement of the spring which acts on the earth pin and the earth pin is preferably such that the earth pin will start to load the spring before the line and neutral pins start to load their corresponding springs provided in the connector. This is an important preferred feature of the invention since it ensures that upon disengagement of the connector from the inlet, once the electrical connection between the line and neutral pins and their respective contacts is broken the spring means acting on the earth pin will continue to push the connector out of the inlet. For example the arrangement may be such that the line and neutral springs are preloaded by a movement of say only lmm whilst that of the earth pin is preloaded by a much greater distance, for example 4 or 5mm. Furthermore, the contacts are preferably arranged at a depth of over 6mm from the face of the connector which means that there will be at least 6mm of movement before contact is made therewith. This maximises the amount of movement which the earth pin may make so as to preload the ejection mechanism.

From a further broad aspect therefore, the invention provides an electrical coupling comprising a first component having line, neutral and earth pins and a second component having sockets for receiving said pins and housing corresponding line, neutral and earth contact means, and respective spring means acting on the said pins when they are inserted into said sockets in a direction to push the pins out of the sockets and thereby break the coupling, and latch means for holding the coupling closed against the force of the spring means, said latch means being disconnectable as the components are moved apart, the arrangement being such that the spring means acting on the earth pin is loaded by the earth pin as it is introduced into its socket before the spring means acting on the remaining pins are loaded by those pins.

From a yet further broad aspect the invention provides an electrical coupling in which an earth pin inserted axially into a corresponding socket engages with spring means within said socket, which spring means act to bias said pin in a direction opposite to the direction of engagement.

Turning now to the latch means which may be used with the invention, the latch means of the present invention is automatically disconnectable as the components of the electrical coupling are moved apart, so as to avoid the need for separate latch disabling means. This has the advantage that should the components be pulled apart unintentionally, they may separate automatically thereby preventing possible accidents. Magnetic latch means may be employed which break apart upon the application of a predetermined force. The magnetic latch means is preferably provided on opposing faces of the inlet and connector. Most preferably, magnetic means are provided on the base of the inlet, with corresponding metallic pole pieces only on the mating face of the connector. This has the advantage that magnetic materials will not be attracted to the connector. This*"-reduces the risk of small metallic objects being attracted into the sockets, and thereby inadvertently making electrical connection within the connector.

Preferably the magnet and pole pieces are 4mm wide to give 3mm clearance from the line and neutral pins. To obtain the necessary magnetic force within a small space it may be preferable to use a rare earth magnet of high efficiency.

However, rare earth magnets have the disadvantage of being expensive, and it is therefore preferred to use mechanical latch means.

Preferably the latch means comprises a detent which is held in the closed position of the latch by resilient latching means.

In a particularly preferred embodiment, the detent is provided on a terminal of the coupling means, preferably an earth pin, which engages latching spring means provided in a corresponding socket. Preferably the spring means comprises a leaf spring configured to engage with said detent in the closed latch position. Typically an end portion of the spring may be provided with a hook portion which engages in the detent on the pin.

The use of the earth pin to provide the latch means has the advantage that it is normally situated on the central vertical axis of the coupling, thereby providing a balanced latching force. Furthermore, the latch spring can act as the earth contact within the connector. Furthermore, by using a projecting pin of the coupling in the latch, the other part of the latch may be provided internally of, for example behind a front wall of the connector, thereby avoiding projecting latch means on the connector. Preferably the detent on the pin comprises a groove in which the spring means may engage, preferably extending fully across a surface of the pin.

Most preferably, the end portion of the pin is tapered so that as the pin is being introduced into its socket, the latch spring is resiliently deflected aside until such time as it engages the detent that is, in the arrangement described above, snaps into the groove.

The strength of the latch spring and the taper of the pin may be such that the latch spring itself provides the disconnection force once the latch is broken thereby obviating the need for a separate disconnection spring. Thus in broad terms, the latch means may in some embodiments constitute or form part of the spring disconnection ejection means. In embodiments where separate spring disconnection or ejection means are provided, the profiles of the interengaging detent and latch spring are such as to keep the coupling closed against the force of the spring ejection or disconnection means, but yet allow disconnection of the latch upon application of a predetermined higher force. The profiles of the detent means and latch means are preferably so designed to cam the two components together upon engagement, thereby effectively pulling a connector into an inlet.

Preferably detent means are provided on opposite faces of the pin, with corresponding opposed latch springs in the socket. This has the advantage of eliminating off-axis latching forces. In such an arrangement, the spring ejecting or disconnecting means may conveniently be located between the latch springs, so as to engage, and be loaded by, the end of the pin as the pin is inserted in the socket.

Preferably, the connector part of the coupling is a loose fit within the corresponding inlet, so that the connector may pivot relative to the inlet in selected planes whereby a pivotal movement of the two parts may result in, or assist in, breaking of the latch. The inlet may be tapered to accommodate such movement. This is an important feature since it will be appreciated that unintentional disconnection forces will very probably not be entirely axial, for example if a kettle power lead is pulled downwardly over the edge of a work surface by a child.

From a yet further broad aspect therefore the invention provides an electrical coupling comprising first and second components each having respective electrical terminal means, spring disconnection means arranged to act between the components, and latch means for holding the coupling closed, said latch means being breakable automatically upon the components being pivoted relative to one another, preferably about an axis generally transverse to the axis of the coupling, said spring disconnection means then acting to decouple electrically the two components. The spring disconnection means may act only once the latch has been broken, for example in the arrangement where latching springs from the disconnection springs. It is advantageous in this context to have the pins of the coupling as short as possible, since as they pivot, sufficient clearance must be provided within the corresponding sockets to accommodate such movement. The longer the pins, the greater will be the movement of their free ends, requiring more space. To keep the pins as short as possible therefore, the line and contacts within the connector are preferably spaced as near as possible to the front face of the connector, that is at substantially 6mm from that face. Also, by making the pins as short as possible, there is less chance of them projecting from an inlet, thereby preventing accidental damage to them during use of an appliance.

Preferably when the connector is engaged in the inlet the front face of the connector is positioned closely to and most preferably in contact with the base of the inlet, whereby when the connector is pivoted, a peripheral portion thereof will contact the inlet base, thereby providing a lever action which assists in the disconnection.

As mentioned above, it is advantageous to provide a coupling with a centrally disposed latch means. From a further broad aspect, therefore, the invention provides an electrical coupling having components movable apart by spring disconnection means, and latch means arranged generally centrally of said coupling and automatically disconnectable upon the components moving apart, to allow said spring disconnection means to disconnect said components. Where the coupling comprises earth, neutral and line pins, with the latch means comprising the earth pin, that pin may be arranged generally between the other pins. A central arrangement of the latch means also allows the coupling to be relatively compact.

The invention also extends to an inlet in or for an electrical appliance arranged and adapted for use in a coupling in accordance with the invention, to a connector arranged and adapted for use in a coupling in accordance with the invention, and to an electrical appliance comprising a coupling in accordance with the invention.

More particularly, the invention also provides an inlet in or for an electrical appliance comprising detent means for engagement with resilient latching means provided on a connector to be engaged in said inlet.

It further provides an electrical connector for insertion into an inlet of an electrical appliance, comprising resilient latching means for engaging detent means provided within said inlet.

It also provides a control, in or for an electrical appliance, having terminal means extending in use into an inlet of said appliance, said terminal means comprising detent means for engagement with resilient latching means provided on a connector to be engaged in said inlet.

The invention also extends to a control in or for an electrical appliance having a plurality of terminal pins extending therefrom, arranged and configured for engagement with a connector in accordance with the invention. Preferably a pin of the control, most preferably the earth pin, is provided with detent means, for example one or more notches, for engagement with a latch provided in said connector.

Two preferred embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Fig. 1 shows a perspective view of the front of an inlet of a first coupling in accordance with the present invention; Fig, 2 shows a perspective view of the inlet of Fig. 1;

Fig. 3 shows a perspective view of an engaged coupling in accordance with the present invention; Fig. 4 shows a part sectional view of Fig. 3;

Fig. 5 shows a connector of a coupling in accordance with the present invention with the top of the connector removed to reveal its internal components;

Fig. 6 shows a top view of Fig. 5; Fig. 7 shows the electrical contact parts of the coupling in accordance with the invention;

Fig. 8 shows the internal components of Fig. 5 in isolation;

Fig. 9 shows a second coupling according to the invention;

Fig. 10 shows the coupling of Fig. 9 with its parts uncoupled;

Fig. 11 shows an earth pin modified in accordance with the invention; Fig. 12 shows the connector part of Fig. 10 in exploded view;

Fig 13 shows a vertical section through the coupling of Fig 9;

Fig 14 shows a vertical section through the coupling of Fig 9, with the components disconnected from each other,- and

Fig. 15 shows an alternative form of latching and disconnection mechanism.

Referring now to Fig. 1, there is shown an inlet 2 of a coupling in accordance with a first embodiment of the invention. The inlet comprises a moulded plastics wall 4 upstanding from a plate 6 which could, for example, form a cover for the back of an appliance control. A line terminal pin, 8 a neutral terminal pin 10 and an earth terminal pin 12 extend into the inlet 2 from the plate 6. The pins are substantially identical, each having an end portion extending into the inlet 2 which measures 2mm x 2mm. The pins extend into the inlet 2 by the same amount such that their end faces lie in a common plane.

The pins retain the centre line configuration of a standard IEC connector, that is the centre of the line and neutral pins 8,10 are spaced apart by 14mm and the centre line of the earth pin 12 being displaced 4mm from the common centre line of the line and neutral pins 8, 10. The pins 8,10,12 may be insert moulded in the cover plate 6 or may extend through openings formed in the cover plate. For example the pins may extend rearwardly from a thermally sensitive control of an appliance such as a kettle or hot water jug. The inlet 2 has, in addition, a magnet assembly 14 of a magnetic latch for the coupling. This assembly comprises two 1mm thick steel keep plates 16,18 arranged on either side of a rare earth magnet 20. This assembly is insert moulded in the inlet such that the front faces of the keep plates 16,18, lie generally flat with the bottom surface 22 of the inlet. As will be seen the magnet 20 is arranged generally below the earth pin 12, in the sense of Fig. 1.

Turning now to Figs. 3 and 4, these show an assembled coupling in accordance with the invention. A connector 24 having a base part 26 and a cover part 28 extends into the inlet, the pins 8,10 and 12 in the inlet extending into correspondingly arranged sockets 30,32 and 34 in the front face 36 of the connector. As can be seen from Fig. 4, the wall 4 of the inlet 2 has two ribs, 38,40 formed on its upper and lower portions respectively. These ribs 38,40 are arranged to engage with the outer surface of the connector 24 such that it will allow the connector 24 to be inserted into the inlet 2 over a range of angles, thereby facilitating introduction of the connector into the inlet 2.

Turning now to Figs. 5 to 8, it will be seen that the connector 24 has a base part 26 which essentially houses the active components of the connector. The base part 26 is a moulded plastics component with chambers 38,40 and 42 for receiving contact assemblies of the connector. Chamber 38 of the base part houses a line contact assembly 44, chamber 40 a neutral contact assembly 46 and chamber 42 an earth contact assembly 48.

The line contact assembly comprises a serpentine spring 50 having a contact 52 rivetted to its front end and having its other end folded back and shaped to form a spade connector 54 for attachment to the line wire of a power cable entering the connector through a channel 56. The spade terminal portion 54 of the spring 50 is suitably located in the base part 26. The neutral contact assembly 46 similarly comprises a serpentine spring 58 having a contact 60 so mounted at one end thereof and a spade connector part 62 formed at the other end. This is similarly attached to a wire carrying the neutral side of the supply through the channel 56. As can be seen most clearly from Fig. 6, the contacts 60 lie substantially in the same plane and are arranged such that they lie at least 6mm behind the front face 36 of the base part 26, so as to conform to International standards. Furthermore, the openings 30, 32 and 34 are of a size such that a 3mm diameter test finger cannot be inserted therethrough.

The earth contact assembly comprises a generally U- shaped metallic strip 64. As for the spring members 58, 50 this may be formed of for example beryllium copper. One arm 66 of the member 64 has a raised end portion 68, the upper surface of which is intended to be contacted by a side surface of the earth pin 12 as the latter is inserted into the connector, the arm 66 deflecting downwardly to accommodate this movement. The U-shaped member 64 is formed with a spade connector portion 70 for connection to an earth wire of a lead extending through the channel 56. Again this contact is suitably located in the base portion 26.

As will be seen from Fig. 6, the contact forming part of the arm 66 extends substantially forward of the line and neutral contacts 52,60 which means that as the connector is inserted into the inlet the earth connection is made well in advance of the line and neutral connections.

Further associated with the earth contact assembly 48 is a target plate 72 which constitutes the other part of the magnetic latch for the coupling. This target plate is formed as one limb of an L-shape member 74 and is formed with the opening 34 to accommodate the earth pin 12. The L-shaped member is, for example of 1mm thickness, and the material of the plate 72 and the strength of the magnet 20 is such that preferably a latching force of between 300-500g is obtained when the connector 24 is inserted in the inlet 2.

The other limb 76 of the L-shape member 74 has an opening 78 which is arranged so as to lie under an opening 80 provided in the other limb 82 of the L-shaped contact member 64. The front face of the target plate 72 lies in the plane of the connector 36.

Arranged behind the target plate 72 is a spring mechanism 84 which comprises a cylindrical housing 86 housing a coil spring (not shown) . The cylinder 86 is aligned with the opening 34 such that the end of the coil spring engages on the end of the earth pin 12 as the pin 12 is inserted into the opening. The coil spring in its relaxed condition extends substantially to the contact forming portion 68 of the earth contact assembly 64 such that as the earth pin 12 enters the opening 34, the coil spring within the cylinder 86 begins to preload well in advance of the contact being made between the ends of the line and neutral pins 8,10 and the corresponding contacts 60,52.

The base part 26 of the connector 24 is closed by a cover part 28 which has means for locating in locating holes 88,90 in the base part 26 and also having a part which extends into the aligned openings 78,80.

Operation of the coupling in accordance with the invention will now be described. As the connector 24 is inserted into the inlet 2, the neutral, line and earth pins 8,10,12 enter the respective openings 32,34 and 30 in the connector 34. In view of the offset of the earth contact 68 from the line and neutral contacts 52, 60, the earth connection is made first. As the connector 34 is moved further into the inlet, the end of the earth pin 12 engages the coil spring within the cylinder 86 and begins to preload this spring member. As the connector moves further into the inlet, by about 6mm, eventually the line and neutral pins 8,10 engage with the contact 52,60. The length of the pins 8, 10 and the offset of the contacts 52,60 is such that the connector may only move for example approximately 1mm further before the front face 36 of the connector 24 engages with the bottom surface 22 of the inlet 2. In this condition, the target plate 72 of the connector lies opposite the magnet assembly 14 of the inlet, and the attraction between the target plate and the magnetic assembly is such as to keep the coupling closed. The coil spring within the cylinder 86 and the serpentine springs 50,58 of the contact assemblies together constitute a spring loaded ejection mechanism. The strengths of the springs are chosen such that in the assembled condition of the coupling the spring force is insufficient to overcome the magnetic attraction force, thereby ensuring the coupling will stay closed. The serpentine springs 50,58 of the line and neutral contact assemblies are only preloaded by a small extent which provides a sufficient contact force, but which does at least initially contribute to the ejection of the connector 24 when the magnetic latch is broken.

In this regard, when it is desired to disconnect the connector from the inlet a user merely pulls on the connector with sufficient force to overcome the magnetic latching force. Once the magnetic latching force is broken, the three springs act together over approximately 1mm travel of the connector to push the connector away from the inlet. After this movement the line and neutral contacts 52,60 assume their rest position as shown in Fig. 6, whereupon it is left to the coil spring in the cylinder 86 to complete the disconnection of the connector.

With reference to Figs. 9 to 14, a second embodiment of the invention is shown which incorporates a mechanical latch rather than a magnetic latch.

With reference to Figs. 9 and 10, an electrical coupling 100 comprises an inlet 102 and a connector 104 which engages in the inlet 102.

The inlet is shown here as part of a control unit 106 for a water heating appliance such as a kettle, and as can be seen from Fig. 10 comprises a base plate 108 and a circumferential wall 110 upstanding therefrom. A line terminal pin 112, a neutral terminal pin 114 and an earth terminal pin 116 extend through the base plate 108. The line and neutral pins 112, 114 are 2mm square in cross-section and mount or provide electrical contacts 118 on their ends. The pins 112, 114 are spaced apart by the standard spacing and thus arranged within the footprint specified by 320 IEC 1981. The earth pin 116 may be made of standard pin size, i.e. 4mm x 2mm section, although it may be of other dimensions if so desired.

The inlet 102 is provided with ribs 120 on its internal wall 4, which are chamfered to facilitate insertion of the connector 104 into the inlet 102 and also to allow the connector to pivot at least vertically in the inlet, as will be described further below. As can be seen from Figs. 10 and 11, the earth pin 118 is provided with opposed grooves 122 in its upper and lower surfaces for engagement with spring latches in the connector 104, and the end of the earth pin 116 is tapered to provide cam surfaces 124 to facilitate its engagement with the latches as will be described further below. With reference to Figs. 10 and 12 in particular, the connector 104 comprises two plastics mouldings 126, 128 which in use are, for example, snapped or welded together. Openings 127, 129 and 131 are provided on the front face 133 of the connector and are positioned to receive the pins 112, 114, 116. The lower moulding 126 acts to mount the various components within the connector, the upper moulding functioning essentially as a cap. The lower moulding has chambers 138, 140, 142 for receiving contact assemblies. Chamber 138 houses a line contact assembly 144, chamber 140 a neutral contact assembly 146 and chamber 142 an earth contact assembly 148.

The line contact assembly comprises a low rate Z- spring 150 having a contact 152 rivetted to its front end and having its other end shaped to form a crimp 154 for attachment to the line wire of a power cable entering the connector through a channel 156. The spring 150 is located in the moulding 126 by lugs 100 engaging in such a plastic moulding 126. The neutral contact assembly 146 similarly comprises a Z-spring 162 having a contact 164 mounted at one end thereof and a crimp part 166 formed at the other end. This is similarly attached to a wire carrying the neutral side of the supply through the channel 156.

The contacts 152, 164 are arranged such that at rest they project into holes 170, 172 provided through internal walls 174, 176 in the moulding 126. In this position, the portions of springs surrounding the contacts 152, 164 abut the walls 174, 176, to preload the springs, say to a force acting on the walls 174, 176 of about 25g per spring. The springs 150, 162 are low rate springs which means that they can be deflected easily without increasing substantially the end force exerted by the contacts.

The contacts lie substantially in the same plane and are arranged such that they lie at least 6mm and preferably substantially 6mm behind the front face 133 of the base part 126, so as to conform to International standards. Furthermore, the openings 127, 129 and 131 are of a size such that a 3mm diameter test finger cannot be inserted therethrough.

The earth contact assembly 148 comprises a double leaf spring member 180. The leaf spring member 180 has at one end a crimping portion 181 for crimping to the earth wire of a power lead and at its other end has two blades 182, 184 arranged opposite, and resiliently biased towards, one another. The ends of the blades are rolled over to produce hook portions 186, 188 which, upon full insertion of the earth pin 116 engage in the grooves 112 provided therein. The blades 182, 184 therefore not only provide an earth connection to the pin 116, but also forms latch springs for engagement with detents on the pin 116. By rolling the ends of the blades 182,184, a smooth engagement with the earth pin 116 is provided, thereby minimising wear of the pin 116, so maintaining the consistency of the electrical contact between the pin 116 and the blades 182,184. A spring ejector mechanism 190, comprising a coil spring 192 and a cap 194 is mounted within the leaf spring members 180. The coil spring 192 is chosen to have considerably higher spring force than the Z springs 150, 162 (for example 200g-250g in its loaded condition) , and at one end fits over a mounting spigot 196 provided on the leaf spring member 180. The other end of the coil spring 192 engages a spigot 193 (Fig 13) inside the cap 194. In its rest position, as shown in Fig 14, the cap 194 is urged against the hook portions 186, 188 of the latch springs 182, 184 by the coil spring 192, the hook portions 186, 188 being located substantially behind the front wall of the connector. When, as shown in Fig 13, the connector 104 is introduced into the inlet 102, the pins 112, 114, 116 enter the respective openings 127, 129, 131. The arrangement of the pins 112, 114, 116 and the corresponding socket contacts 152, 164, 180 is such that the earth pin 116 first makes electrical contact with the earth leaf spring member 180.

Upon further movement of the connector 104 into the inlet 102, the cam surfaces 124 of the earth pin 116 move apart the hook portions 186, 188 of the latch springs 182, 184 member 180, and at the same time the end of the earth pin 116 moves the cap 194 back against the force of the coil spring 192, thereby loading the coil spring 192. The movement of the earth pin 116 continues to the point at which the hook portions 186, 188 drop into the grooves 122 of the earth pin 116, thereby latching the coupling closed. The respective profiles of the hook portions 186,188 and the grooves 122 effectively pull the connector 104 fully into the inlet 102 when the latch closes.

The arrangement of the line and neutral pins 112, 114 and contacts 152, 164 may be such that electrical contact is not made between them until the earth pin 116 has been substantially fully introduced into its socket, preferably such that the contact is made just as or just before the hooks 186, 188 drop into the grooves 122. This means that it will not be possible to obtain a partial, arcing connection, since unless the connector 104 is substantially completely inserted, no electrical connection is made.

Since the Z springs 150, 162 are already pre-loaded against the walls 174, 176, when the contacts 152, 164 are pushed back by the pins 112, 114, a pre-determined contact force is generated, without the need for a substantial movement of the springs. Furthermore, since the springs are low rate, the movement generated by the pins will not significantly increase the contact force.

In the loaded condition, the total spring force generated by the coil spring 192 and the Z springs 150, 162 is insufficient to break the spring latch. Furthermore, the resilience of the latch springs 182, 184 is sufficient to retain the connector 104 in the inlet 102 generally horizontally. However, if a user pulls on the connector 104 with a predetermined axial force, the hooks 186, 188 will be cammed up the side of the grooves 122 to break the latch. Once the latch is broken, initially three springs 150, 162 and 192 will push the connector out of the inlet. The Z springs 150, 162, will only contribute to the disconnection force until such time as the line and electrical contacts are broken, whereafter the coil spring 192 alone pushes the connector 104 out to ensure that the electrical contacts are fully broken and the connector is fully ejected from the inlet.

Further, as can be seen in Fig 13, the connector 104 is a loose fit within the inlet 102, at least in the vertical plane so that it may pivot in the inlet to a limited extent, about an axis generally transverse to the common axis of the connector 104 and inlet 102. This is facilitated by the chamfering of the ribs 120. It will be apparent that should the end of the connector 104 remote from the inlet 102 be moved up or down, the connector 104 will pivot in the inlet 102 about one or other of the grooves 122 in the earth pin 118. The front face 133 of the connector 104 in the engaged condition is closely adjacent the base plate 108 of the inlet 102, so that as it pivots, one of the hook portions 186, 188 will be levered out of its corresponding groove 122 on the pin 118. As soon as one of the hook portions 186, 188 disengages, the latch is broken and the connector 104 is then disconnected from the inlet 102 by the spring ejection mechanism.

Due to this lever effect, a relatively low pivotal force need only be applied to assure a complete disconnection of the connector 104 from the inlet 104. Thus if a user accidentally pulls downwardly on a power lead attached to the connector, for example if a child pulls the lead of an appliance over the edge of a work surface, the connector will pivot downwardly in the inlet, the latch means be broken and the connector be ejected from the inlet, thereby preventing the appliance being pulled over the edge. In the embodiment shown, the connector 104 is also a loose fit in the inlet 102 in the horizontal plane. A similar leverage effect can be thus achieved in this plane also.

Whilst this embodiment is shown with a separate coil spring 192 to effect disconnection of the components, if the spring force of the latch springs 182, 184 is sufficiently high, this could be dispensed with. The action of the hook portions 186, 188 of the latch springs 182, 184 against the tapered cam surfaces 124 of the earth pin 118 would then act to effect the disconnection. Such an arrangement is shown schematically in Fig. 15 where latch springs 200,202 have opposed end portions 204 which, when the coupling components are disconnected, substantially touch. The spring force of the latch springs 200,202 is such that they will act on the tapered end 206 of the earth pin 208 to force the connector off the earth pin when the latch is broken. In any event, the latch springs 182,184 in the earlier described embodiment will contribute to the disconnection force.

The inlet 102 and connector 104 are configured and dimensioned so as to prevent a standard connector being inserted in the inlet and the connector being inserted in the standard inlet, by virtue of their non-standard profiles and by virtue of the openings in the connector 104 being too small to accept standard pins.

Claims

1. An electrical coupling comprising first and second components each having respective electrical terminal means, spring disconnection means acting between the components to bias them apart, and latch means for holding the coupling closed, said latch means being automatically disconnectable upon the components being moved apart, whereupon said spring means ensures complete electrical disconnection of the two components.

2. An electrical coupling comprising first and second components each having respective electrical terminal means, latch means for holding the coupling closed, said latch means being automatically disconnectable upon the components being moved apart, and spring ejection means operable to move said components apart after the latch means has disconnected to ensure complete electrical disconnection of the two components.

3. An electrical coupling comprising an inlet in or for an electrical appliance, and a connector provided, or adapted to be provided on a power lead, for mating engagement with said inlet, said inlet having line, neutral and earth pins arranged in a predetermined configuration, and said connector having three sockets arranged in a mating configuration and into which said pins may be inserted, and housing line, neutral and earth contacts which make electrical contact with said pins, characterised in that said coupling has latch means acting between the inlet and the connector to keep the coupling closed and a spring loaded ejection means acting so as to ensure breaking of the contact between the line and neutral pins and contacts as soon as the latch is broken.

4. An electrical coupling as claimed in any preceding claim wherein said spring means acts on an end of at least an earth pin or terminal of one component.

5. An electrical coupling as claimed in claim 3 or 4 wherein earth contact means engages a side surface of the earth pin.

6. An electrical coupling as claimed in claim 4 or 5 wherein the line and neutral contacts within the connector are provided on the ends of the springs whereby they make electrical contact with the ends of the line and neutral pins of the inlet.

7. An electrical coupling as claimed in claim 6 wherein the spring rate of the springs acting on the line and neutral pins is substantially lower than that of the spring means acting on the earth pin.

8. An electrical coupling comprising a first component having line, neutral and earth pins and a second component having sockets for receiving said pins and housing corresponding line, neutral and earth contact means, and respective spring means acting on the said pins when they are inserted into said sockets in a direction to push the pins out of the sockets and thereby break the coupling, and latch means for holding the coupling closed against the force of the spring means, said latch means being automatically disconnectable as the components are moved apart the arrangement being such that the spring means acting on the earth pin is loaded by the earth pin as it is introduced into its socket before the spring means acting on the remaining pins are loaded by those pins.

9. An electrical coupling as claimed in any of claims 3 to 8 wherein the positions and dimensions of the line and neutral pins fall within the standard footprint.

10. An electrical coupling as claimed in any preceding claim wherein said latch means is magnetic.

11. An electrical coupling as claimed in any of claims 1 to 9 wherein the latch means comprises a detent which is held in the closed position of the latch by resilient latching means.

12. An electrical coupling as claimed in claim 11 wherein said resilient latching means is arranged internally of a connector part of the coupling.

13. An electrical coupling as claimed in claim 11 or 12 wherein said detent is provided on an earth terminal or pin of the coupling.

14. An electrical coupling as claimed in claim 13 wherein said detent is formed on an earth pin or terminal to engage with corresponding latching spring means.

15. An electrical coupling as claimed in claim 14 wherein said latching spring means comprises a leaf spring.

16. An electrical coupling as claimed in claim 14 or 15 wherein said latching spring means acts as an earth contact.

17. An electrical coupling as claimed in any of claims 13 to 17 wherein said earth pin is situated substantially on a central vertical axis of the coupling.

18. An electrical coupling as claimed in any of claims 13 to 17 wherein the detent on the pin comprises a groove in which the spring means may engage.

19. An electrical coupling as claimed in any of claims 13 to 18 wherein the end portion of the pin is tapered so that as the pin is being introduced into socket, the latch spring is resiliently deflected aside until such time as it engages the detent.

20. An electrical coupling as claimed in any of claims 13 to 19 wherein the profiles of the detent and resilient latching means are such as to cam. the two components together upon engagement.

21. An electrical coupling as claimed in any of claims

13 to 19 wherein detent means are provided on opposite faces of the pin, with corresponding opposed latching spring means.

22. An electrical coupling as claimed in claim 21 wherein the spring ejecting or spring disconnecting means is located between the latching spring means.

23. An electrical coupling as claimed in any of claims

14 to 20 wherein said latching spring means constitutes or forms part of the spring disconnection or spring ejection means.

24. An electrical coupling comprising first and second components each having respective electrical terminal means, spring disconnection means arranged to act between the components, and latch means for holding the coupling closed, said latch means being breakable automatically upon the components being pivoted relative to one another, said spring disconnection means then acting to decouple electrically the two components.

25. An electrical coupling as claimed in claim 24 wherein line and neutral contact means are provided substantially 6mm behind a front face of a connector part of said coupling.

26. An electrical coupling having components movable apart by spring disconnection means, and latch means arranged generally centrally of said coupling and automatically disconnectable upon the components moving apart, to allow said spring disconnection means to disconnect said components.

27. An inlet in or for an electrical appliance comprising detent means for engagement with resilient latching means provided on a connector to be engaged in said inlet.

28. An inlet as claimed in claim 27 wherein said detent means are provided on an earth pin in said inlet.

29. An inlet as claimed in claim 28 wherein said earth pin has a tapered free end and opposed grooves formed behind said tapered end to receive said latching means.

30. A control, in or for an electrical appliance, having terminal means extending in use into an inlet of said appliance, said terminal means comprising detent means for engagement with resilient latching means provided on a connector to be engaged in said inlet.

31. A control as claimed in claim 30 wherein said detent means are provided on an earth pin in said inlet.

32. A control as claimed in claim 31 wherein said earth pin has a tapered free end and opposed grooves formed behind said tapered end to receive said latching means.

33. An inlet or control for an electrical appliance having earth, line and neutral terminal pins arranged within the standard footprint, but having cross- sectional dimensions smaller than the standard dimensions.

34. An electrical connector for insertion into an inlet of an electrical appliance, comprising resilient latching means for engaging detent means provided within said inlet.

35. An electrical connector as claimed in claim 34 wherein said resilient latching means are provided behind a front wall of the connector.

36. An electrical appliance comprising a coupling, an inlet or connector as claimed in any preceding claims.