GB2486260A

GB2486260A - Stackable plug limiting number of plugs in stack

Info

Publication number: GB2486260A
Application number: GB1020908.8A
Authority: GB
Inventors: Andrew Daniel Merron
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-12-10
Filing date: 2010-12-10
Publication date: 2012-06-13
Also published as: GB201020908D0

Abstract

A stackable mains plug includes a set of plug pins, a socket face comprising a matching socket for transmitting power through the plug to another plug, and a mains power cable connection. The plug further comprises means to inhibit stacking of more than a predetermined number of said plugs one plugged into another as a safety feature. A movable pin 40, shorter than the depth of the plug, can go into an aperture 16 of a further plug, increasing the depth of the aperture on its own plug; as the plugs are stacked these move increasing far forward until part of the pin (see top of pin 40c) interferes with the shutter of the socket. Additionally, each stackable plug may further include a pair of fuses: a device fuse and a pass through fuse whereby the pass through fuse limits the current provided to subsequently stacked plugs.

Description

Power Adapter

FIELD OF THE INVENTION

The present invention relates to electrical plugs, in particular those for connecting electrical devices to mains power outlets.

BACKGROUND TO THE INVENTION

An increase in the use of electrical devices both in and out of the house means that more and more connections to mains power outlets are needed. This may be for powering an ac powered device or for charging a portable device such as a mobile phone. Conventional approaches use multi-way power adapters to increase the number of power outlets however this requires any devices already connected to the power outlet to be first disconnected so that the multi-way adapter can be inserted.

Accordingly there is therefore need for stackable plugs, which in addition to allowing one plug to be inserted into another, also considers physical and electric safety.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a stackable ac grid mains plug including a plug face bearing a set of plug pins, a socket face comprising a matching socket for transmitting power through the plug to another plug, and a mains power cable connection for connecting a power cable for an electrical device to the plug, wherein the plug further comprises means to inhibit stacking of more than a predetermined number of the plugs one plugged into another.

Inhibiting stacking of more than a predetermined number of plugs (each one plugged into another) provides a safety mechanism to mechanically limit the number of devices plugged into a wall socket. With each plug plugging into another (the first plugging into the wall socket) a limit is imposed to ensure the plugs are not put under undue mechanical stress from the accumulative weight of plugs extending out from the wall socket.

Preferably stacking is inhibited by use of a moveable protrusion on the plug face that engages with a corresponding recess on the socket face of a second plug. Movement of the protrusion into the plug releases a shutter obscuring one or more openings on the socket and so allows a further plug to be stacked. In typical embodiments the shutter is moved to reveal the openings on the socket by subsequent insertion of the further plug to be stacked -if the shutter is not released by movement of the protrusion then pins of the further stackable plug cannot be inserted. Inhibiting movement of the shutter may also prevent a conventional plug being inserted to prevent any additional connection.

Preferably movement of the protrusion into the plug moves a stop within the recess to reduce a depth of the stop in the recess by a lesser amount, thus, with the depth of the stop reducing on each subsequent stacked plug, each protrusion engages with a respectively deeper stop pushing the protrusion deeper into the corresponding recess.

Furthermore, preferably greater than a minimum degree of movement of the protrusion is required to release the shutter such that when more than the predetermined number of plugs are stacked movement of the protrusion is less than the minimum degree of movement required to release the shutter so that a further stackable plug cannot be inserted.

In some preferred embodiments of the stackable plug an internal part of the protrusion comprises a stop behind the recess such that when a protrusion from a subsequent stackable plug is inserted into the recess the movement of the protrusion is controlled by the position of the stop in the plug, furthermore the protrusion preferably has a cut-out of predetermined length into which said shutter is able to move to release the shutter to allow subsequent plugs to be stacked. The predetermined length used defines a predetermined number of stackable plugs that can be stacked one plugged into another, thus by varying the predetermined length the number of predetermined stackable plugs that can be stacked can be varied.

According to a further aspect of the invention there is provided a stackable electrical connector for connecting an electrical device to a power socket, the electrical connector comprising: a set of internal terminals for connecting a power cord of the electrical device to the stackable electrical connector; a plug portion for receiving power from a power socket, the plug portion comprising at least one electrical pin for insertion into a power socket or an upstream stackable electrical connector; a socket portion for providing power from the power socket via the stackable electrical connector, the socket portion comprising a socket capable of receiving a the at least one electrical pin of the plug portion of an downstream the stackable electrical connector, wherein the socket portion further comprises a shutter, wherein the shutter is moveable between a closed position in which an aperture of the socket is substantially covered to inhibit insertion of a the electrical pin and an open position in which the aperture is open; an engagement pin protruding from the stackable electrical connector to engage with a corresponding recess on a further said stackable electrical connector, wherein the engagement pin is moveable between an open position and a locking position to inhibit stacking of more than a predetermined number of the stackable electrical connectors one plugged into another, wherein in the open position the engagement pin enables the shutter to move between the closed position and the open position, and wherein in the locking position the engagement pin inhibits the shutter moving from the closed position to the open position; The position of the engagement pin determines if the shutter is inhibited from opening, i.e. the depth of the protrusion determines if the shutter is inhibited from opening or not and varies depending on the depth it moves into a further stacked connector (which may be upstream or downstream, but preferably upstream).

By virtue of inhibiting movement of the shutter, further conventional plugs are also inhibited from being added once a threshold on stacking has been reached.

More preferably the engagement pin is configured to move between the open position and a locking position when the stackable electrical connector is engaged with the upstream the stackable electrical connector, wherein movement to the locking position is dependent on a number of the upstream the stackable electrical connectors between the stackable electrical connector and the power socket such that when the total number of engaged stackable electrical connectors is greater than a threshold the engagement pin is in the locking position. The engagement pin moves into the respective recess of a connected stackable plug which contains a stop (which may be formed from the top of the respective engagement pin located if the connected stackable). By arranging each engagement pin to be shorter than the depth of the stackable plug when subsequent connectors are inserted, the depth of the engagement pin in each recess changes with each connector -this enables the engagement pin to be constructed to prevent further connectors being connected once a predetermined threshold has been reached.

The engagement pin may be configured to allow one or more stackable electrical connectors to be stacked. In some preferred embodiments the engagement pin is configured to move between the open position and the locking position (to prevent further connectors I conventional plugs being added) when two other stackable electrical connectors are between the stackable electrical connector and the power socket and thus providing a stacking threshold of three devices.

Preferably the engagement pin is further moveable to a second locking position such that when the stackable electrical connector is not connected to a mains outlet or to any other stackable electrical connector the shutter can be prevented from opening.

This prevents any objects being inserted into the connector which could be dangerous as a result of subsequent connector to a mains outlet. Preferably when the stackable electrical connector is connected to a mains outlet or another stackable electrical connector the engagement pin is arranged to move from the second locking position to the open position such that further stackable electrical connectors (or a conventional plug) can be inserted.

In some preferred embodiments the engagement pin and the shutter mechanically interact with each other -the pin and shutter each comprise a keyed member such that when the engagement pin is in the locking position a protruding element of the engagement pin keyed member abuts a protruding element of the shutter keyed member which prevents any subsequent movement of the shutter. The shutter cannot move from its closed position and prevents any further connectors being stacked.

Preferably the shutter is also biased closed, using a springed member for example.

When the engagement pin is in an open position a notched portion of the engagement pin keyed member means that it no longer abuts the shutter keyed member and so allows the shutter to open. Alternatively in a different preferred embodiment the noticed portion may be on the shutter keyed member. The open position may extend along multiple intervals of engagement pin keyed member so that a range of open positions exists. This allows the shutter to still open when the engagement across this range of open positions.

Preferably the engagement pin is arranged substantially perpendicular to the shutter so that the two interleave and abut to prevent further connectors being coupled. By doing so the engagement pin is preferably biased to protrude from the plug portion of the connector to engage with the recess in the upstream connector, but may alternatively protrude from the socket portion to engage with the recess in the downstream connector. Such biasing is preferably by use of a spring. Protruding from the socket portion to engage with the downstream connector is less desirable because a conventional plug may not securely engage with the stackable plug and leave live electric pins accessible if the conventional plug cannot be fully inserted due to the engagement pin interfering.

In preferred embodiments the stackable electrical connector further comprises a pass-through fuse connected between one of the at least one electrical pins and the socket portion. This limits the current provided to subsequent downstream connectors and thus provides electrical safety to prevent a current overload. In the UK for example, this would comprise a 13 Amp fuse. In addition to the pass through fuse the stackable electrical connector preferably further comprising a device fuse to limit current provided to the set of internal terminals and thus limits the current provided to the directly connected electrical device according to the safety requirements of that particular device.

In some embodiments a power cord is coupled to the set of internal terminals. In such an embodiment the plug may be sealed at manufacturing time (with the fuses still accessible) and provided on a newly purchased device (rather than retrofitting). In some alternative embodiments the connector integrates an ac to dc rectifier circuit such that dc power can be provided to an electrical device. Such a configuration is suited to dc power adapters used on devices such as mobile phone chargers for example, and more preferably in this situation the connector may further comprises a USB outlet to provide the dc power to the dc rails on the USB socket.

Preferably the electrical pins are arranged according to a three pin British Standard plug format comprising an earth electrical pin, a live electrical pin and a neutral electrical pin. The socket portion is thus arranged to receive such a pin configuration. In such an arrangement the earth pin pushes on the shutter to reveal the earth socket, and live and neutral sockets to allow insertion of the live and neutral pins.

According to a still further aspect of the invention there is provided a stackable electrical connector for connecting an electrical device to a power socket, the electrical connector comprising: a set of internal terminals for connecting a power cord of the electrical device to the stackable electrical connector; a plug portion for receiving power from a power socket, the plug portion comprising at least one electrical pin for insertion into a power socket or a second upstream the stackable electrical connector; a socket portion for providing power from the power socket via the stackable electrical connector, the socket portion comprising a socket capable of receiving a the at least one electrical pin of the plug portion of an downstream stackable electrical connector or a non-stackable electrical connector; and a pass-through fuse connected between one of the at least one electrical pins and the socket portion to limit current provided from the socket portion.

In some preferred embodiments the stackable electrical connector is arranged according to a three pin British Standard plug comprising an earth electrical pin, a live electrical pin and a neutral electrical pin. In such a configuration the pass through fuse is in the live path such that it connects the live electrical pin to the corresponding live socket and on to live electrical pin of subsequently connected stackable connectors or conventional plugs. In addition to the pass through fuse the connector preferably comprises a further fuse -a device fuse which connects from the downstream side of the pass through fuse to the live terminal connector to an electrical device. This allows a current limit to be set for the connected electrical device.

According to a further aspect of the invention there is provided a method of inhibiting a user from plugging a stackable plug into another stackable plug, each of the stackable plugs comprising a plug face bearing a set of plug pins, a socket face comprising a matching socket for transmitting power through the plug to another plug, a mains power cable connection for connecting a power cable for an electrical device to the plug, a shutter moveable from an closed position obscuring one or more openings on the socket face, and a moveable protrusion on the plug face, the method comprising: moving the moveable protrusion on the plug face to engage with a corresponding recess on the socket face of another the plug; moving a stop within a the recess of the stackable plug to reduce a depth of the stop in the recess by a lesser amount than in the corresponding recess such that when the depth of the stop in the stackable plug is reduced below a threshold the moveable protrusion in the stackable plug inhibits the shutter from moving from the closed position to inhibit a further stackable plug being stacked.

By virtue of inhibiting a further stackable plug being stacked, the effect is also to prevent any other conventional (non-stackable) plugs being added.

According to a still further aspect of the invention there is provided a stackable plug system, each stackable plug in the stackable plug system comprising a plug face bearing a set of plug pins, a socket face comprising a matching socket for transmitting power through the plug to another plug, a mains power cable connection for connecting a power cable for an electrical device to the plug, a shutter moveable from an closed position obscuring one or more openings on the socket face, and a moveable protrusion on the plug face, wherein the moveable protrusion on the plug face of each the stackable plug is moveable to engage with a corresponding recess on the socket face of another the plug; and wherein a stop within a the recess of each the stackable plug is moveable to reduce a depth of the stop in the recess by a lesser amount than in the corresponding recess such that when the depth of the stop in the stackable plug is reduced below a threshold the moveable protrusion in the stackable plug inhibits the shutter from moving from the closed position to inhibit a further stackable plug being stacked.

According to yet a further aspect of the invention there is provided a stackable ac electrical plug comprising: a female connector for receiving the male connector of a further stackable or non-stackable plug, wherein said female connector comprises at least two apertures; and a safety mechanism to limit the number of stackable plugs that can be stacked to a predetermined number, said mechanism comprising: a pin which protrudes at least partially out of the plug housing; and a shutter to obscure an aperture of the female connector; configured such that when the plug is inserted into a socket face, the pin is displaced into the plug and releases the shutter if the predetermined number of stackable plugs has not been reached.

According to yet a further aspect of the invention there is provided a method of limiting the number of stackable plugs that can be stacked, comprising: engaging the male connector of a first stackable plug as described above in the female connector of a socket face; displacing the pin of said plug into the plug housing; moving the surface within the aperture of said first plug to determine the depth of said aperture such that the shutter which obscures an aperture of the female connector is released if the predetermined number of stackable plugs has not been reached.

According to yet a further aspect of the invention there is provided a stackable plug system comprising: a means for engaging the male connector of a first stackable plug as described above in the female connector of a socket face; a means for displacing the pin of said plug into the plug housing; a means for moving the surface within the aperture of said first plug to determine the depth of said aperture such that the shutter which obscures an aperture of the female connector is released if the predetermined number of stackable plugs has not been reached.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will now be further described, by way of example only, with reference to the accompanying figures in which: Figure 1 shows a 3-dimensional representation of an embedment of the stackable electrical connector; Figure 2 shows the shutter mechanism within the stackable electrical connector; Figure 3 shows the engagement pin; Figure 4 shows the shutter mechanism of Figure 2 and engagement of Figure 3 arranged to enable movement of the shutter mechanism; Figure 5 shows the arrangement of three engagement pins when three respect stackable electrical connectors are connected.

Figure 6 shows a circuit diagram of the fusing arrangements according to an embodiment of the invention; Figure 7 shows a perspective view of the mechanical arrangement of the stackable electrical connection to integrate the fusing arrangement of Figure 6; Figure 8 shows an alternative perspective view of Figure 7; and Figure 9 shows a component of the embodiment show in Figure 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description downstream' refers to a stackable electrical connector I conventional plug located further away from a wall plug socket than the particular stackable electrical connector in question. Conversely, an upstream' stackable electrical connector is closer to the wall plug socket than the particular stackable electrical connector in question. Thus, in an arrangement of three stacked connectors arranged and coupled as wall plug socket -connector A -connector B -connector C', connectors B and C are downstream from connector A and the wall socket and connector B are upstream from connector C. Referring to Figure 1 this shows an embodiment of the stackable electrical connector arranged as a 13 amp mains plug suitable for the UK market. The embodiment described herein can be used to connect electrical appliances to a domestic electrical supply. It also allows safe connection of additional plugs without removal or disconnection from the electrical supply. The stackable electrical connector may be used as a direct replacement for a conventional plug and is compatible with existing UK format plugs, extension leads and extender blocks. Similarly, the stackable electrical connector, arranged to meet the standards in other countries, may accordingly be compatible with other forms of plug, leads and extender blocks.

The stackable electrical connector 10 in Figure 1 comprises a plug portion 12 having electrical pins 24 and 25 and a further pin 26 (not shown on the 3D projection in Figure 1) and a socket portion 14 comprising socket apertures 21, 22 and 23 arranged to receive a standard UK mains plug or a further stackable electrical connector. On the surface of the socket portion a further aperture 16 is provided to allow an engagement pin from a downstream stackable electrical connector to be inserted into a recess on the stackable plug.

Figure 2 shows a shutter plate 30 integrated into the stackable electrical connector 10 shown in Figure 1. The shutter comprises three elements 31, 32 and 33 which cover electrical terminals within the stackable electrical connect to prevent insertion of small objects (or child's fingers for example) and so provides a safety feature. The shutter is coupled to a spring within the stackable electrical connector to bias the shutter closed.

Generally speaking, such a slidable shutter is known within the art and is moved (slid) aside by the insertion of the longer earth pin which pushes against a chamfered edge although, as will be described further with reference to the embodiments described herein, the shutter has been modified to interact with an engagement pin/moveable protrusion to inhibit opening of the shutter. The shutter 30 comprises an additional keyed element 34 comprising a protrusion 35 extending laterally from the keyed stem of the shutter. This keyed element and protrusion are used to interact with an engagement pin to provide further mechanisms for enabling the shutter to slidably move to allow a subsequent stackable electrical connector or conventional plug to connect to the stackable electrical connector.

Figure 3 shows the engagement pin 40 used to interact with the shutter 30 to allow the shutter to slide to open and allow a further stackable electrical connector to be inserted or to prevent it opening and thus prevent a further stackable electrical connector (or a conventional plug) being inserted. In the embodiment shown herein the engagement pin is configured to allow three stackable electrical connectors to be stacked on one another (as shown in Figure 5). It will however be appreciated that alternative embodiments of the invention may vary the number of stackable electrical connector that may be stacked and this is merely an implementation feature. In the embodiments shown in Figure 5 the number of stackable electrical connectors is limited to three.

Limiting the number of stackable electrical connectors that can be stacked is a safety feature to ensure that the stackable electrical connectors, when in use, are not put under undue mechanical stress due to the accumulative weight of stackable electrical connectors extending out from a plug socket mounted vertically on the wall. Such accumulative weight could lead to live terminals becoming exposed as plugs and the cabling from devices attached to the plugs are put undue stress.

Returning now to Figure 3 the engagement pin 40 comprises a keyed element 44 which has a notched element 45. When integrated into the stackable electrical connector base member 42 of the engagement pin 40 extends out of the base of the plug portion of the stackable electrical connector to interact with a stop on an upstream electrical connector or a wall socket (or other power socket). Upwardly directed member 41 is used to provide a mounting point for a spring which in turn fits into a downwardly facing trough on the underside of socket portion face plate 14. The spring element biases the engagement pin 40 downwards so that by default the engagement pin protrudes from the base of plug portion 12.

Referring now to Figure 4 this shows the shutter 30 interacting with the engagement pin 40. In the arrangement shown in Figure 4 the notch 45 of the engagement pin overlaps the protruding element 35 of the shutter so that when a further stackable plug or a conventional mains plug is inserted into the socket portion the shutter is able to slide to allow a downstream stackable plug to be inserted into the stackable electrical connector.

Referring now to Figure 5 this shows three stackable electrical connectors (stackable plugs) stacked together and the positioning of the engagement pin within each stackable electrical connector at each location within the stack. The enclosure is shown to the side of the engagement pins and shutter mechanism in Figure 5. Stackable electrical connector SF1 is first inserted into a wall socket and as a result the engagement pin (which is biased to protrude from the base of the plug) is pushed fully into stackable electrical connector SF1 resulting in the notched portion of the keyed element aligning with the protrusion from the shutter -this allows the shutter portion to open and allow a subsequent stackable electrical connector, in this case SF2 to be connected. An electrical connection is made between the electrical pins to terminals in the corresponding socket apertures. When SF1 is plugged into a wall socket (or other power outlet) power is thus provided to SF2. Similarly, an earth connection is also made via the earth pin and socket. Considering SF2 now, the electrical connectors of SF2 are inserted into the socket of SF1 to provide an electrical connection through to SF2. The engagement pin (biased to protrude through the base proportion of the stackable electrical connector) now aligns with an engagement pin aperture on the socket faceplate of plug SF1 and thus extends partially into SF1 until it reaches a stop at the top of the engagement pin in SF1. In SP2 the notch portion of the engagement pin still aligns with the protrusion from the shutter and therefore still allows the shutter to open to make the electrical connectors within the socket accessible to subsequent (downstream) stackable electrical connector (or conventional plugs). SF3 (or a conventional plug) can then be connected to SF2 as the shutter is still able to slide and thus SF3 connects to SF2 to electrically connect the socket together. As with SF2 the engagement pin aligns with the corresponding engagement pin aperture on the surface of SF2 and so the engagement pin partially enters SF2. However, now in SF3, owing to each of the engagement pins being shorter than the depth of the stackable electrical connector, a different portion of the keyed member now aligns with the shutter protrusion.

A portion of the keyed element now abuts the protrusion from the shutter and stops any subsequent conventional plug or stackable connector from being connected as the shutter will no longer open.

The effect of stacking connectors is that the engagement pin (moveable protrusion) moves a stop within its recess to reduce a depth of the stop in the connector by a lesser amount than in the corresponding recess in a preceding (upstream) plug. The resulting effect is that the engagement pin subsequently moves position relative to its own plug depending on its position in the stack.

The engagement pin and shutter may also interact to prevent the shutter moving when the stackable electrical connector is not plugged into the wall. When the engagement pin extends to its maximum reach from the stackable electrical connector a protrusion from the shutter abuts a further portion of the keyed element on the engagement pin to prevent the shutter sliding to open.

It will be appreciated that the embodiments shown herein show an arrangement with a protrusion from the shutter and notches in the engagement pin. Alternative arrangements are possible, for example reversing this arrangement such that the engagement pin has protrusions and the shutter has corresponding notches. The embodiment described herein demonstrates an approach whereby the engagement pin is biased in the upstream direction to protrude from the base of the electrical connector.

This advantageously allows a conventional plug (not a stackable connector) to be inserted into the socket portion of the most downstream stackable electrical connector as there is no protrusion extending outwards from the stackable plug in the downstream direction. However, it will be appreciated that in alternative embodiments the direction of the engagement pin may be reversed so that it does protrude from the upper surface (from the socket side of the plug).

It will also be appreciated however that, depending on features including the physical construction of the stackable connectors, safety requirements and the particular use, that the limit, or threshold, at which the shutter locks to prevent further plugs being connected may be varied. In the embodiment shown for UK plugs, a limit of three has been shown, but this may be limited to two, four or five for example. For other types of connectors with different mechanical arrangements this may be even more.

Figure 6 shows a schematic of the fusing arrangement within the stackable electrical connector 10. This provides a further safety feature to ensure the current is limited through all of the stackable electrical connectors to prevent the current exceeding a predefined safety limit. In Figure 6 the schematic shows a fusing arrangement for a stackable 13 amp mains plug suitable for the UK market. The pass through fuse 50 connects from the live upstream electrical pin to the downstream live pin socket and limits the supply to the directly connected appliance and any additional stackable electrical connectors connected. As more and more stackable electrical connectors are connected each subsequently has a further pass through fuse in series with upstream stackable electrical connectors. Should the total maximum current is limited to (in this example) 13 amps regardless of how many stackable electrical connectors are connected in series. However it will be appreciated that if a downstream stackable electrical connector contains a smaller fuse then this fuse may blow first if the current drawn through this particular fuse exceeds the limit allowed by that particular fuse. The stackable electrical connector further comprises a conventional load/device fuse coupled from the downstream side 51 of the pass through fuse and connected between this downstream position and the live terminal that a power cord of an electrical device is connected to. This load fuse is of a conventional size appropriate to the electrical requirements of the electrical device.

Figures 7 and 8 show two projections of the internal arrangements of the stackable electrical plug encompassing the pass through fuse 50 and the load fuse 54. The load supply for the device is connected to connection point 52, the live electrical pin is connected to location 53 and the extreme live connection is connected to location 51.

Figure 9 shows the connection plate 51 used to couple the fuses to this downstream live connection point. This plate is inserted into the stackable plug enclosure to provide the connection between the downstream side of fuse 50, the downstream side of fuse 54 and the downstream socket.

The embodiments described herein show an example for a UK market style of 13 amp mains plug and may include a strain relief device which will prevent strain on the electrical terminals if the electrical cord connected to an appliance is pulled. It will be appreciated that the invention described herein can be adapted to be used on sockets for other regions throughout the world, and also for other conventional sockets which may not be ac mains sockets. Configurations may include an OEM moulded stackable electrical connector with an electrical cord attached for connection to an appliance or an aftermarket stackable electrical connector which will allow an electrical cord to be connected.

It is also possible to integrate an ac to dc rectifier into the stackable plug such that a dc outlet can be provided to an electrical device. Such an embodiment is particularly useful for the consumer market, for example for mobile phone power adaptors which may have a USB output or a conventional rounded dc plug outlet so that multiple stackable mobile phone chargers can be connected to a single plug socket at any point in time. In this configuration an OEM moulded stackable electrical connector may be provided with the USB socket replacing the cord outlet.

No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.

Claims

CLAIMS: 1. A stackable ac grid mains plug including a plug lace bearing a set of plug pins, a socket face comprising a matching socket for transmitting power through the plug to another plug, and a mains power cable connection for connecting a power cable for an electrical device to the plug, wherein the plug further comprises means to inhibit stacking of more than a predetermined number of said plugs one plugged into another.
2. A plug as claimed in claim 1 wherein said means comprises a moveable protrusion on said plug face to engage with a corresponding recess on said socket face of a second said plug, and wherein movement of said protrusion into said plug is configured to release a shutter obscuring one or more openings of said socket.
3. A plug as claimed in claim 2 wherein movement of said protrusion into said plug moves a stop within said recess to reduce a depth of said stop in said recess by a lesser amount, and wherein greater than a minimum degree of movement of said protrusion is required to release said shutter, such that when more than said predetermined number of plugs are stacked movement of said protrusion is less than said minimum degree of movement required to release said shutter.
4. A plug as claimed in claim 3 wherein an internal part of said protrusion comprises a stop behind said recess, and wherein said protrusion has a cut-out of predetermined length into which said shutter is able to move, wherein said predetermined length defines said predetermined number of stackable plugs.
5. A stackable electrical connector for connecting an electrical device to a power socket, the electrical connector comprising: a set of internal terminals for connecting a power cord of said electrical device to said stackable electrical connector; a plug portion for receiving power from a power socket, said plug portion comprising at least one electrical pin for insertion into a power socket or an upstream said stackable electrical connector; a socket portion for providing power from said power socket via said stackable electrical connector, said socket portion comprising a socket capable of receiving a said at least one electrical pin of said plug portion of an downstream said stackable electrical connector, wherein said socket portion further comprises a shutter, wherein said shutter is moveable between a closed position in which an aperture of said socket is substantially covered to inhibit insertion of a said electrical pin and an open position in which said aperture is open; and an engagement pin protruding from said stackable electrical connector to engage with a corresponding recess on a further said stackable electrical connector, wherein said engagement pin is moveable between an open position and a locking position to inhibit stacking of more than a predetermined number of said stackable electrical connectors one plugged into another, wherein in said open position said engagement pin enables said shutter to move between said closed position and said open position, and wherein in said locking position said engagement pin inhibits said shutter moving from said closed position to said open position.
6. A stackable electrical connector as claimed in claim 5, wherein said engagement pin is configured to move between said open position and said locking position when said stackable electrical connector is engaged with a said upstream said stackable electrical connector, wherein movement to said locking position is dependent on a number of said upstream said stackable electrical connectors between said stackable electrical connector and said power socket such that when the total number of engaged stackable electrical connectors is greater than a threshold said engagement pin is in said locking position.
7. A stackable electrical connector as claimed in claim 5 or claim 6, wherein said engagement pin is further moveable to a second locking position; wherein in said second locking position said engagement pin inhibits said shutter moving from said closed position to said open position; and wherein when said stackable electrical connector is not engaged with a said power socket or a said upstream said stackable electrical connector said engagement pin is biased to said second locking position.
8. A stackable electrical connector as claimed in claim 5, claim 6 or claim 7, wherein when said stackable electrical connector is engaged with a said power socket said engagement pin is arranged to move from said second locking position to said open position.
9. A stackable electrical connector as claimed in any one of claims 5 to 8, wherein said engagement pin and said shutter each comprise a keyed member such that when said engagement pin is in said locking position a protruding element of said engagement pin keyed member abuts a protruding element of said shutter keyed member said shutter to inhibit said shutter moving from said closed position to said open position.
10. A stackable electrical connector as claimed in claim 9, wherein when said engagement pin is in an open position a notched portion of said engagement pin keyed member is aligned with said protruding element of said shutter keyed member to allow said shutter to move from said closed position to said open position.
11. A stackable electrical connector as claimed in claim 9, wherein when said engagement pin is in an open position said protruding element of said engagement pin keyed member is aligned with a notched portion of said shutter keyed member to allow said shutter to move from said closed position to said open position.
12. A stackable electrical connector as claimed in any one of claims 5 to 11, wherein said engagement pin is arranged substantially perpendicular to said shutter.
13. A stackable electrical connector as claimed in any one of claims 5 to 12, wherein said engagement pin is biased to protrude from said plug portion to engage with said recess in said upstream said stackable electrical connector.
14. A stackable electrical connector as claimed in any one of claims 5 to 12, wherein said engagement pin is biased to protrude from said socket portion to engage with said recess in said downstream said stackable electrical connector.
15. A stackable electrical connector as claimed in claim 13 or 14 wherein said engagement pin is biasing using a spring.
16. A stackable electrical connector as claimed in any one of claims 5 to 15, further comprising a pass-through fuse connected between one of said at least one electrical pins and said socket portion to limit current provided from said socket portion.
17. A stackable electrical connector as claimed in any one of claims 5 to 16, further comprising a device fuse to limit current provided to said set of internal terminals.
18. A stackable electrical connector as claimed in any one of claims 5 to 17, wherein said shutter is biased closed.
19. A stackable electrical connector as claimed in any one of claims 5 to 18, further comprising a power cord coupled to said set of internal terminals.
20. A stackable electrical connector as claimed in any one of claims 5 to 18, further comprising an ac to dc rectifier circuit coupled to said set of internal terminals.
21. A stackable electrical connector as claimed in claim 20, further comprising a USB socket coupled to said dc rectifier circuit.
22. A stackable electrical connector as claimed in any one of claims 5 to 21, wherein said one or more electrical pins are arranged according to a three pin British Standard plug format comprising an earth electrical pin, a live electrical pin and a neutral electrical pin, and wherein said socket portion comprises three apertures arranged to receive a conventional 3-pin UK British Standard plug or a said downstream said stackable electrical connector comprising said one or more electrical pins arranged according to a three pin British Standard plug.
23. A stackable electrical connector as claimed in any one of claims 5 to 22, wherein said engagement pin is configured to move between said open position and said locking position when two other stackable electrical connectors are between said stackable electrical connector and said power socket.
24. A stackable electrical connector for connecting an electrical device to a power socket, the electrical connector comprising: a set of internal terminals for connecting a power cord of said electrical device to said stackable electrical connector; a plug portion for receiving power from a power socket, said plug portion comprising at least one electrical pin for insertion into a power socket or a second upstream said stackable electrical connector; a socket portion for providing power from said power socket via said stackable electrical connector, said socket portion comprising a socket capable of receiving a said at least one electrical pin of said plug portion of an downstream stackable electrical connector or a non-stackable electrical connector; and a pass-through fuse connected between one of said at least one electrical pins and said socket portion to limit current provided from said socket portion.
25. A stackable electrical connector as claimed in claim 24, wherein said one or more electrical pins are arranged according to a three pin British Standard plug format comprising an earth electrical pin, a live electrical pin and a neutral electrical pin; wherein said socket portion comprises three apertures arranged to receive a conventional 3-pin UK British Standard plug or a said downstream said stackable electrical connector comprising said one or more electrical pins arranged according to a three pin British Standard plug; and wherein said pass-through fuse is connected between said live electrical pin and a live electrical socket of said socket portion.
26. A stackable electrical connector as claimed in claim 24 or 25 further comprising a device fuse to limit current provided to said set of internal terminals.
27. A stackable electrical connector substantially as herein described with reference to one or more of the drawings.
28. A method of inhibiting a user from plugging a stackable plug into another stackable plug, each of said stackable plugs comprising a plug face bearing a set of plug pins, a socket face comprising a matching socket for transmitting power through the plug to another plug, a mains power cable connection for connecting a power cable for an electrical device to the plug, a shutter moveable from an closed position obscuring one or more openings on said socket face, and a moveable protrusion on said plug face, the method comprising: moving the moveable protrusion on said plug face to engage with a corresponding recess on said socket face of another said plug; moving a stop within a said recess of said stackable plug to reduce a depth of said stop in said recess by a lesser amount than in said corresponding recess such that when said depth of said stop in said stackable plug is reduced below a threshold said moveable protrusion in said stackable plug inhibits said shutter from moving from said closed position to inhibit a further stackable plug being stacked.
29. A stackable plug system, each stackable plug in said stackable plug system comprising a plug face bearing a set of plug pins, a socket face comprising a matching socket for transmitting power through the plug to another plug, a mains power cable connection for connecting a power cable for an electrical device to the plug, a shutter moveable from an closed position obscuring one or more openings on said socket face, and a moveable protrusion on said plug face, wherein the moveable protrusion on said plug face of each said stackable plug is moveable to engage with a corresponding recess on said socket face of another said plug; and wherein a stop within a said recess of each said stackable plug is moveable to reduce a depth of said stop in said recess by a lesser amount than in said corresponding recess such that when said depth of said stop in said stackable plug is reduced below a threshold said moveable protrusion in said stackable plug inhibits said shutter from moving from said closed position to inhibit a further stackable plug being stacked.
30. A stackable ac electrical plug comprising: a female connector for receiving the male connector of a further stackable or non-stackable plug, wherein said female connector comprises at least two apertures; and a safety mechanism to limit the number of stackable plugs that can be stacked to a predetermined number, said mechanism comprising: a pin which protrudes at least partially out of the plug housing; and a shutter to obscure an aperture of the female connector; configured such that when the plug is inserted into a socket face, the pin is displaced into the plug and releases the shutter if the predetermined number of stackable plugs has not been reached.
31. A plug according to claim 30, wherein the safety mechanism further comprises: an aperture in the plug housing which engages with said second pin of a second stackable plug, wherein the depth of said aperture is determined by the displacement of the first pin within the first plug, which provides a surface within the aperture to engage with said second pin.
32. A plug according to claim 31, wherein said surface within the aperture is provided by an internal part of said pin, and wherein the predetermined number of plugs that can be stacked is set by the displacement of the pin that is required to release said shutter, such that if the predetermined number of stackable plugs has been reached the shutter is not released on displacement of the pin.
33. A plug according to any one of claims 30 to 32, wherein said shutter comprises at least two fingers to obscure the apertures of the female connector, said shutter also comprising one or more portions for engagement with a cut-out of said internal portion of the pin, configured such that when said pin is displaced by the required amount to release the shutter, said shutter is released and engages with the internal portion of the pin, and wherein the required amount to release the shutter is set by the length of said cut-out of said internal portion of the pin.
34. A method of limiting the number of stackable plugs that can be stacked, comprising: engaging the male connector of a first stackable plug according to claims 30 and 31 in the female connector of a socket face; displacing the pin of said plug into the plug housing; moving the surface within the aperture of said first plug to determine the depth of said aperture such that the shutter which obscures an aperture of the female connector is released if the predetermined number of stackable plugs has not been reached.
35. A method according to claim 34, wherein said surface within the aperture is provided by an internal part of said pin, and wherein said method further comprises: engaging said shutter with a cut-out of said internal portion of the pin such that the shutter is released if the pin is displaced by an amount determined by the length of said cut-out of the internal portion of the pin.
36. A stackable plug system comprising: a means for engaging the male connector of a first stackable plug according to claims 30 and 31 in the female connector of a socket face; a means for displacing the pin of said plug into the plug housing; a means for moving the surface within the aperture of said first plug to determine the depth of said aperture such that the shutter which obscures an aperture of the female connector is released if the predetermined number of stackable plugs has not been reached.
37. A stackable plug system according to claim 36 wherein said surface within the aperture is provided by an internal part of said pin, and wherein said system method further comprises: a means for engaging said shutter with a cut-out of said internal portion of the pin such that the shutter is released if the pin is displaced by an amount determined by the length of said cut-out of the internal portion of the pin.