GB2469123A

GB2469123A - Socket with two shutters

Info

Publication number: GB2469123A
Application number: GB0905839A
Authority: GB
Inventors: Nik Baker; John Appleton
Original assignee: Hager Engineering Ltd
Current assignee: Hager Engineering Ltd
Priority date: 2009-04-03
Filing date: 2009-04-03
Publication date: 2010-10-06
Anticipated expiration: 2029-04-03
Also published as: GB0905839D0; GB2469123B

Abstract

A safety shield assembly for an electrical socket, for use with a 3-pin plug where the earth pin is longer than the live and neutral pins, has first and second shutters slidably mounted on a rear face of a socket front plate. The first shutter 7 is moveable by engagement with the earth pin from a first position blocking the earth aperture to a second position allowing the earth pin to engage with said earth contact through the earth aperture. The second shutter 8 is moveable by engagement with the live and neutral pins from a closed position to an open position when the first shutter is in the second position, but is locked in the closed position by the first shutter when the first shutter is in the first position, detents (24, 25, Fig 3) engaging in notches (26, 27, Fig 2) and stepped faces (12, 13, Fig 4, 29, Fig 3) preventing the shutter from moving backwards. The safety shield assembly provides a simple arrangement for preventing unsuitable plugs being used with a socket and for preventing the use of one or two probes to gain unsafe access to the live and neutral contacts of a socket.

Description

Safety Assembly and Socket

Introduction

The invention relates to a safety shutter assembly for an electrical socket, in particular a mains electrical socket arranged to mate with a three-pin electrical plug having live, neutral and earth pins, where the live and neutral pins are of substantially equal length and are 4mm or more shorter than the length of the earth pin. The invention in particular relates to such assemblies and sockets containing such assemblies, which are intended for use with three pin electrical plugs according toBS 1363 or BS 546.

Background

"BS 546" means the British Standard Specification for two-pole and earthing-pin plugs, socket-outlets and socket-outlet adaptors BS 546: 1950 published by the British Standards Institution on 16th March 1950, including Supplement No. 1(1960) published on 30th December 1960 and Supplement No. 2 (1987) published on 23rd December 1987, incorporating Amendment No. 1 issued in December 1953 and as amended by Amendment No. 2 published on 28th November 1961, Amendment Slips 3 and 4 published on 16th May 1969 and 29th July 1977 respectively, and Amendments No. 5, 6 and 7 published on 31st August 1982, 23rd December 1987 and 31st January 1989 respectively.

"BS 1363" means the British Standard Specification for 13 amp fused plugs and switched and unswitched socket-outlets BS 1363: 1984 published by the British Standards Institution on 31st August 1984, as amended by Amendments No. 1, 2, 3, 4, 5 and 6 published on 30th April 1985, 31St December 1985, 31St July 1987, 23rd December 1987, 30th June 1989 and 28th February 1990 respectively.

Plugs according to BS546 and BS1 363 have an earth pin which is longer than the live and neutral pins, and which is arranged to make earth or ground contact, by reaching the earth contact within a socket as the plug is engaged with a socket, prior to the live and neutral pins coming into contact with their respective electrical contacts within the socket.

Typically, such sockets are provided with a safety shutter, which is arranged to close apertures in the front plate of the socket such that the contacts are not accessible until a plug is inserted. The most usual safety shutter is in the form of a shutter, biased into a closed position by a spring and blocking entry to the earth, live and neutral contacts. A ramped or bevelled face, which is positioned in the earth aperture is arranged to engage with the earth pin as the plug is pushed into the socket. The longer earth pin, pushing against the ramped face, slides the shutter into an open position, uncovering the live and neutral apertures such that the shorter live and neutral pins can pass, unhindered, into the socket to mate with their respective contacts.

The problem with such an arrangement is that such a shutter is easily bypassed by the insertion of a probe, such as a pencil or screwdriver, into the earth aperture, to push against the ramped face and urge the shutter to a position where the live and neutral contacts are revealed. Such an easily bypassed shutter is undesirable, and there is a need to provide a shutter arrangement that is not bypassed in such a simple manner and which is of simple construction.

Summary of the Invention

It is one object of the present invention, amongst others, to provide a safety shutter assembly for a three pin socket which requires the earth pin to be inserted into the socket to engage prior to the live or neutral pins, preferably both the live and neutral pins, as for a plug engaging with the socket, in order for the shutter assembly to allow access to the live and neutral contacts by the pins.

A first aspect of the invention provides a safety shield assembly for an electrical socket, said electrical socket having earth, live and neutral contacts respectively adapted to engage with earth, live and neutral pins of a three-pin plug having the earth pin with a length greater than the live and neutral pins' length, the live and neutral pins having substantially the same length as each other, the safety shield assembly comprising a front plate for said socket having live, neutral and earth apertures extending through a front surface to a rear surface of the front plate, the apertures adapted to accept respectively said live neutral and earth pins of said plug, and first and second interengageable shutters slidably mounted in a housing on a rear surface of the front plate, wherein the first shutter is moveable by engagement with said earth pin from a first position blocking the earth aperture to a second position allowing said earth pin to engage with said earth contact through the earth aperture, wherein the second shutter is moveable by engagement with said live and neutral pins from a closed position shielding said live and neutral contacts from the live and neutral apertures to an open position allowing said live and neutral pins to engage with the live and neutral contacts through the live and neutral apertures when the first shutter is in the second position, and wherein the second shutter is locked in the closed position by the first shutter when the first shutter is in the first position.

A second aspect of the invention provides an electrical socket comprising a safety shield assembly according to the first aspect of the invention.

Detailed Description of the Invention

The features detailed below are applicable to both the first and to the second aspects of the invention.

Suitably, the length of the earth pin of the electrical socket for use with the invention is at least 3mm, preferably 4mm and more preferably 5mm greater than the length of the live and neutral pins.

The invention is particularly suitable for use with an electrical socket adapted to mate with an electrical plug according to the British Standard BS 1363 as detailed hereinbefore. For such a plug, the earth pin is about 5mm longer than the live and neutral pins.

Although the earth pin may be used to provide an electrical contact to earth or "ground", such electrical earthing or grounding through the earth pin of the plug is not essential, and the earth pin of the plug may be a non-conducting pin, for instance of a rigid, non-conducting polymer material rather than of a conducting metal. Usually, both the live and neutral pins will be electrically conductive, at least where they are adapted to mate with the electrical live and neutral contacts of a socket.

The second shutter is moveable by engagement with live and neutral pins from a closed position to an open position. Preferably, the second shutter is moveable only by engagement with both the live and neutral pins contemporaneously and is not moveable by engagement with only one the live and neutral pins. In other words, the second shutter is preferably arranged such that both the live and neutral pins must press against it at the same time in order for it to be moveable to the open position.

Hence, the second shutter is moveable by engagement with both the live and neutral pins contemporaneously but not by engagement with only one of the live or neutral pins. By "contemporaneously" it is meant that the live and neutral pins must engage with the second shutter at a common time, but simultaneous contacting with the shutter is not required, so long as both pins are engaging the shutter at a common time.

Typically, the first shutter of the safety shield assembly comprises a bevelled surface arranged to engage with the earth pin of the socket whereby engagement of the bevelled surface with the earth pin urges the first shutter in a first direction, from its first position (blocking the earth aperture of the front plate of the socket) to its second position such that the earth pin can pass through the earth aperture in the front plate to engage with the earth contact of the socket. Typically, the first shutter will comprise an opening adjacent the bevelled surface arranged to permit the earth pin

S

to pass though the opening to engage with the earth contact when the first shutter is in the second position.

The first direction will generally be a direction away from the second shutter and substantially parallel to the front surface of the front plate. The housing holding the first and second shutters, and allowing them to slide in the manner required by the invention, can be any suitable housing and may be unitarily formed as part of the rear surface of the front plate or may be attached thereto. The safety shield assembly may act as a replacement front plate for an existing socket or may be part of a purpose-built socket adapted to fit with the safety shield assembly.

Typically, the safety shield assembly will comprise a first resilient biasing means adapted to urge the first shutter towards the first position. This is so that when a plug is withdrawn from the socket, the first shutter is urged back to a position where it blocks the path between the earth contact inside the socket and the earth aperture in the front plate. However, with a conventional mounting arrangement, having the earth aperture vertically above the centre line between the live and neutral apertures, gravity may be used to urge the first shutter towards the first position.

Preferably, the safety shield assembly comprises a second resilient biasing means adapted to urge the second shutter towards the closed position. This is also to ensure that, when the plug is removed from the socket, the second shutter returns to the closed position, blocking the path from the live and neutral apertures in the front plate to the live and neutral contacts, within the socket, respectively. The second resilient means may suitably be a spring, arranged to engage with the earth pin of the plug whilst the earth pin is still extended through the earth aperture, in order to urge the second shutter towards the closed position. Once the plug has been completely removed from the socket, along with its earth pin, the spring no longer acts to bias the second shutter in place in the closed position. Instead, the second shutter is held locked in the closed position by the first shutter, which is in the first position once the plug has been removed from the socket.

The second shutter may comprise a first arm and a second arm, wherein, when the second shutter is in the closed position, distal ends of the first arm and the second arm block the live and neutral apertures respectively.

Preferably, the distal ends of the first and second arms are each provided with bevelled faces at their distal ends arranged to be contacted by said live and neutral pins, whereby the live and neutral pins of a plug entering the socket urge the second shutter in the first direction by pressing against the respective bevelled faces as the plug engages with the socket.

It is particularly preferred to provide first and second interlocking arrangements respectively between the distal ends of the first arm and second arms and the rear surface of the front plate, the first and second interlocking arrangements each having an engaged configuration preventing movement of the second shutter in the first direction when the second shutter is in the closed position and the first shutter is in the first position and arranged to be disengageable by the live and neutral pins as the plug enters the socket when the first shutter is in the second position.

Typically, the first and second arms are connected to a central body of the second shutter by resilient hinges biased to push the bevelled faces of the distal ends of the first and second arms towards the rear surface of the front plate when the second shutter is in the closed configuration whereby the first and second interlocking arrangements are held in the engaged configuration.

The first shutter may comprise a locking plate arranged and constructed to lock the first and second interlocking arrangements in the engaged configuration when the first shutter is in the first position, hence locking the second shutter in the closed position. The locking plate may comprise first and second stepped faces arranged to engage with corresponding stepped faces on rear sides of the first and second arms.

The interlocking arrangement, for example, may comprise a detent at the distal end of each first and second arm adapted to engage with a corresponding notch or groove in the rear surface of the front plate. This provides interlocking arrangements where the distal ends of both of the arms must first be pushed away from the rear face of the front place by each of the live and neutral pins entering the socket prior to being urged by said pins in the first direction.

A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows an exploded schematic view of a safety shield assembly according to a first embodiment of the invention viewed from the front, Figure 2 shows a rear perspective schematic view of the front plate of the first embodiment, Figure 3 shows a front perspective schematic view of the second shutter of the first embodiment, Figure 4 shows a front perspective schematic view of the first shutter of the first embodiment, Figure 5 shows a perspective schematic view of the operation of the safety shield assembly of the first embodiment, with the front plate shown as transparent, when a single pin is inserted into the earth aperture, Figure 6 shows a perspective schematic view of the operation of the safety shield assembly of the first embodiment, with the front plate shown as transparent, when a single pin is inserted into the neutral aperture, Figure 7 shows a perspective schematic view of the operation of the safety shield assembly of the first embodiment, with the front plate shown as transparent, when a two pins are inserted into the live and neutral apertures, Figure 8 shows a perspective schematic view of the operation of the safety shield assembly of the first embodiment, with the front plate shown as transparent, when a two pins are inserted into the earth and the neutral apertures, s Figures 9 and 10 show perspective schematic views of the operation of the of the safety shield assembly of first embodiment, with the front plate shown as transparent, when a sockets earth, live and neutral pins are correctly inserted into the earth live and neutral apertures of the assembly.

The first embodiment is for use with a system according to BS 1363. The live and neutral pins have a rectangular cross section 6.35 by 3.98 mm and are each 17.7 mm long with their centre lines are horizontally 11.1mm on either side of the symmetry plane of the plug. The earth pin is centred on the symmetry plane, is 22.7 mm long and has a cross section 7.93 by 3.98 mm. In other words, the earth pin is 5mm longer than the live and neutral pins.

Turning to figures 1 to 4, the safety shutter assembly has a front plate 1 with earth 2 live 3 and neutral 4 apertures passing through it from its front face 5 to its rear face 6.

First shutter 7 and second shutter 8 are constructed to inter-engage as shown in figure 1. The shutters are slidably mounted in a housing (not shown) mounted on the rear face 6 of the front plate 1 and allowing sliding movement of the shutters in the plane of first plate 1 forwards or backwards in the first direction (shown by arrow A).

The first shutter 7 has a first member 9 holding a bevelled surface 10, which closes the earth aperture when the first shutter 7 is in the first position. The member 9 is attached to a locking plate 11 carrying first 12 and second 13 stepped faces. A spring 30 mounted at the end of first member 9 acts as first resilient biasing means to urge the first shutter towards the first position by pressing against the housing (not shown).

The second shutter 8 has a central body 14 connected to a second member 15. The second member 15 is constructed to slidingly fit in the first member 9 of the first shutter 7 such that the first 7 and second 8 shutters can slide relative to each other, backwards or forwards, in the first direction A. First 16 and second 17 arms are attached to the central body 14 by narrow connections 20 and 21 adjacent to slots 22, 23. The second shutter 8 is formed unitarily from a resilient material (such as high density polyethylene or moulded nylon) such that the connections 20,21 act as resilient hinges allowing the arms 16,17 to be pushed away from the rear face 6 of the front plate 1, closing the slots 22, 23. The resilience of the second shutter 8 means that the arms 16, 17 are biased back to their starting position by the connections 20, 21.

Each arm 16, 17 has a bevelled face 18, 19 which closes the neutral 4 and live 3 apertures respectively of the front plate 1 when the second shutter 8 is in the closed position. Detents 24, 25 are provided on each arm 16, 7 and engage with notches 26, 27 in the rear face 6 of the front plate I when the second shutter 8 is in the closed position. The detents and notches provide interlocking arrangements between the second shutter 8 and the rear face 6 of front plate 1 when the second shutter 8 is in the closed position.

A second spring 28 located at the end of the second member 15 is positioned to bias the second shutter towards the closed position, acting as the second resilient biasing means, by pressing against the earth pin of a socket when a socket is inserted into the safety shutter assembly.

Each of the arms 16, 17 has a stepped face (29 for arm 17, not visible for arm 16) on its rear side which is arranged to engage with the corresponding stepped faces 12, 13 of the locking plate 11 of the first shutter 7 when the first shutter is in the first position and the second shutter is in the closed position.

The central body 14 of second shutter 8 is provided with ribs 40, 41 arranged to engage with grooves 42, 43 in the rear face 6 of front plate 1 when the shutters 7, 8 are located in the housing. The inter-engaging ridges and grooves ensure that the second shutter's movement is restricted to sliding forwards or backwards along the first direction A. At rest, as shown in figures 6 and 7, the first shutter 7 is in the first position and the second shutter 8 is in the closed position. Bevelled surface 10 of the first shutter closes the earth aperture 2 and bevelled faces 18 and 19 of the second shutter close the neutral 4 and live 3 apertures respectively. The stepped faces (not shown and 29) on the rear sides of the arms 16, 17 engage with the stepped faces 12, 13 on the locking plate 11 of the first shutter, holding the arms in their rest position with the detents 24, 25 locked into the notches 26, 27 in the rear face 6 of the front plate 1.

First spring 30 biases the first shutter 7 towards second shutter 8 holding the first shutter 7 in its first position pressed against the second shutter 8 in its closed position.

In operation, as shown in Figures 9 and 10, an electrical plug 31 is inserted into the safety shield assembly. The earth pin 32 is several mm longer than the live 33 and neutral 34 pins and so engages first with the bevelled surface 10 before the other pins 33, 34 engage with bevelled faces 19, 18. The earth pin 32 pushes against the bevelled surface 10 urging the first shutter 7 in the first direction A against the biasing force of the spring 30 and pushes the first shutter into the second position.

When the first shutter is in the second position with the earth pin 32 projecting through the earth aperture 2 and through the member 9, the locking plate 11 and stepped surfaces 12, 13 no longer press against the stepped faces (29, not shown) on the rear sides of arms 16, 17. This allows the live 33 and neutral 34 pins, pressing against bevelled faces 19 and 18 respectively, to push the arms 17, 16 away from the rear face 6 of the front plate 1, disengaging the detents 25, 24 from their respective notches 27, 26 and hence unlocking the second shutter 8. As the live 33 and neutral 34 pins progress through their respective apertures 3, 4,their pressing against the bevelled faces 19, 18 urges the second shutter, now free to slide, in the first direction A and towards the first shutter 7, which is now in the second position.

The live 33 and neutral 34 pins can thus push the second shutter 8 aside to its open position, permitting them to enter the socket through the safety shield assembly to engage with the live and neutral electrical contacts 35, 36.

As the socket 31 is removed, live 33 and neutral 34 pins are first withdrawn, allowing the second spring 28, pushing against the earth pin 32 (still in place against the spring 28 because of its greater length) to urge the second shutter back into the closed position. The resilient hinges 20, 21 will push the arms 16, 17 towards the rear face 6 of the front plate 1, causing the detents 24, 25 to interlockingly engage with the notches 26, 27. Then, as the plug 31 is withdrawn further, the earth pin 32 disengages from the earth aperture 2 allowing the first spring 30 to push the first shutter 7 back to the first position such that the locking plate 11 engages with the second shutter 8 and the stepped faces 12, 13 engage with the corresponding stepped faces in the rear sides of arms 16, 17, locking the second shutter in the closed configuration.

Figures 5 to 8 show how the safety shield assembly of the first embodiment prevents access to the live and neutral electrical contacts when only one or two pins are used in attempts to bypass the safety shield assembly.

For figure 5, although the insertion of a single pin 32 into the earth aperture 2 allows the earth contact to be accessed, pushing the first shutter 7 to the second position by pressing against the bevelled surface 10, the second shutter remains in the closed position, biased in place by the second spring 28 pressing against the pin 32.

For Figure 6, a single neutral pin 34 is shown pushed into the neutral aperture 4. The arm 16 cannot be pushed away fro the rear surface 6 of front plate 1 by the pin 34 because its rear side is locked in place by locking plate 11 of the first shutter 7, which is still in the first position. This means that detents 24 and 25 remain interlocked with notches 26, 27 and so the pressing of the pin 34 against bevelled face 18 cannot urge the second shutter into the open position. Thus the neutral pin 34 is prevented from passing through to the neutral contact 36.

For Figure 7, live 33 and neutral 34 pins are shown pushed simultaneously into the live 3 and neutral 4 apertures. The arms 16, 17 cannot be pushed away from the rear surface 6 of front plate 1 by the pins 34, 33 because their rear sides are each locked in place by locking plate 11 of the first shutter 7 which is still in the first position. This means that detents 24 and 25 remain interlocked with notches 26, 27 and so the pressing of the pins 33, 34 against bevelled faces 19, 18 cannot urge the second shutter into the open position. Thus the pins 33, 34 are prevented from passing through to the live 35 and neutral 36 contacts.

Turning to figure 8, this shows what happens when earth 32 and neutral 34 pins are pushed simultaneously into their respective apertures 2, 4 without the live pin 33.

Although the insertion of the earth pin 32 into the earth aperture 2 allows the earth contact to be accessed, pushing the first shutter 7 to the second position by pressing against the bevelled surface 10, the second shutter remains in the closed position, biased in place by the second spring 28 pressing against the pin 32. As the (shorter) neutral pin 34 presses against the bevelled face 18 of arm 16 of the second shutter 8, it will push the arm 16 away from the rear face 6 of the front plate 1, allowing the detent 24 to disengage from its respective notch 26. However, the detent 25 at the end of arm 17 of second shutter 8 will remain engaged and so prevents the neutral pin 34 from urging the second shutter 8 to its open position. The inter-engaging ribs 40, 41 and grooves 42, 43 help to ensure that the second shutter cannot be twisted out of place by pressure from the neutral pin 34 against bevelled face 18. Thus, the neutral pin 34 is prevented from coming into contact with the neutral contact 36.

It will be appreciated that numerous modifications to the above described embodiment may be made without departing from the scope of the invention as defined in the appended claims. For example, the locking plate may not include stepped faces or the second spring may be omitted, with the closure of the second shutter being effected by the first shutter pressing against it to return it to the closed position. For instance, the inter-engaging ribs and grooves may be omitted from the embodiment.

The described and illustrated embodiment is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be s protected. It should be understood that while the use of words such as "preferable", "preferably", "preferred" or "more preferred" in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and embodiments lacking such a feature may be contemplated as within the scope of the invention as defined in the appended claims. In relation to the claims, it is intended that when words such as "a," "an," "at least one," or "at least one portion" are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim. When the language "at least a portion" and/or "a portion" is used the item can include a portion and/or the entire item unless specifically stated to the contrary.

Claims

Claims 1. A safety shield assembly for an electrical socket, said electrical socket having earth, live and neutral contacts respectively adapted to engage with earth, live and neutral pins of a three-pin plug having the earth pin with a length greater than the live and neutral pins' length, the live and neutral pins having substantially the same length as each other, the safety shield assembly comprising a front plate for said socket having live, neutral and earth apertures extending through a front surface to a rear surface of the front plate, the apertures adapted to accept respectively said live neutral and earth pins of said plug, and first and second interengageable shutters slidably mounted in a housing on a rear surface of the front plate, wherein the first shutter is moveable by engagement with said earth pin from a first position blocking the earth aperture to a second position allowing said earth pin to engage with said earth contact through the earth aperture, wherein the second shutter is moveable by engagement with said live and neutral pins from a closed position shielding said live and neutral contacts from the live and neutral apertures to an open position allowing said live and neutral pins to engage with the live and neutral contacts through the live and neutral apertures when the first shutter is in the second position, and wherein the second shutter is locked in the closed position by the first shutter when the first shutter is in the first position.
2. A safety shield assembly according to claim 1 wherein the second shutter is rnoveable by engagement with both said live and neutral pins contemporaneously but not by engagement with only one of said live or neutral pins.
3. A safety shield assembly according to claim 1 or claim 2 wherein said electrical socket is a socket according to BS 1363.
4. A safety shield assembly according to any preceding claim wherein the first shutter comprises a bevelled surface arranged to engage with the earth pin whereby engagement of the bevelled surface with said earth pin urges the first shutter in a first direction, from the first position to the second position.
5. A safety shield assembly according to claim 4 wherein the first shutter comprises an opening adjacent the bevelled surface arranged to permit said earth pin to pass though the opening to engage with said earth contact when the first shutter is in the second position.
6. A safety shield assembly according to any preceding claim wherein the first direction is a direction away from the second shutter and substantially parallel to the front surface of the front plate.
7. A safety shield assembly according to any preceding claim wherein the safety shield assembly comprises a first resilient biasing means adapted to urge the first shutter towards the first position.
8. A safety shield assembly according to any preceding claim wherein the safety shield assembly comprises a second resilient biasing means adapted to urge the second shutter towards the closed position.
9. A safety shield assembly according to claim 8 wherein the second resilient means is a spring, arranged to engage with said earth pin when said earth pin is extended through the earth aperture, to urge the second shutter towards the closed position.
10. A safety shield assembly according to any preceding claim wherein the second shutter comprises a first arm and a second arm, wherein in the closed position, distal ends of the first arm and the second arm block the live and neutral apertures respectively.
11. A safety shield assembly according to claim 10 wherein the distal ends of the first and second arms are each provided with bevelled faces at their distal ends arranged to be contacted by said live and neutral pins, whereby said live and neutral pins urge the second shutter in the first direction by pressing against the respective bevelled faces as said plug engages with said socket.
12. A safety shield assembly according to claim 11 wherein first and second interlocking arrangements are provided respectively between the distal ends of the first arm and second arms and the rear surface of the front plate, having an engaged configuration preventing movement of the second shutter in the first direction when the second shutter is in the closed position and the first shutter is in the first position and arranged to be disengageable by said live and neutral pins when the first shutter is in the second position.
13. A safety shield assembly according to claim 12 wherein the first and second arms are connected to a central body of the second shutter by resilient hinges biased to push the bevelled faces of the distal ends of the first and second arms towards the rear surface of the front plate when the second shutter is in the closed configuration whereby the first and second interlocking arrangements are held in the engaged configuration.
14. A safety shield assembly according to claim 12 or claim 13 wherein the first shutter comprises a locking plate arranged and constructed to lock the first and second interlocking arrangements in the engaged configuration when the first shutter is in the first position.
15. A safety shield assembly according to claim 14 wherein the locking plate comprises first and second stepped faces arranged to engage with corresponding stepped faces on rear sides of the first and second arms.
16. A safety shield assembly according to claim 12 to 15 wherein the interlocking arrangement comprises a detent at the distal end of each first and second arm adapted to engage with a corresponding notch in the rear surface of the front plate.
17. An electrical socket comprising a safety shield assembly according to any preceding claims
I 8. A safety shield assembly or an electrical socket substantially as herein before described with reference to and as shown in the accompanying figures.