TWO PIECE SAFETY SHUTTER FOR THREE PIN PLUG SOCKET

Field of invention

The present invention relates to the fields of electrical sockets for a three pin plug, and more particularly to a two piece safety shutter assembly placed within the socket to provide terminal access to the Earth pin, Live and Neutral pins of the plug and the socket upon actuation.

Background of invention

Electrical socket generally have a socket outlet with a terminal contact member for providing electrical connectivity for the three pin plug and a front cover for guiding the three pin plug through the live, neutral and earth pin apertures. The front cover receives the plug through the apertures and provides respective terminal contact and connection with the contact member of the socket assembly. The contact member having live, neutral and earth terminals receiving the respective plug pins is disposed behind the front cover.

The socket assembly receives electrical supply and provides the received electrical supply to the plug pins for utilization when accessed through a standard plug.

Normally electrically insulated safety shutters are placed in between the contact member and the plug pin apertures of the socket outlet. Safety shutters are the parts of electrical socket outlets that shield the live and neutral contacts of the socket outlet from coming into accidental contact with a human being. These shutters are assembled within the sockets such that the terminal pins of the contact members are not accessible until a standard plug is inserted. Usually the shutter is arranged in a closed condition to bar access to the current carrying parts of the socket.

Safety shutters are usually provided as a safety unit to prevent the playful children to have accidental contact with the live and neutral pins of the socket. This is achieved by ensuring that even when a conducting part is pressed or probed into any of the apertures of the socket outlet which is provided for the entry of the plug pin, it is prevented from coming into contact with the current carrying parts of the socket outlet. The operation of the standard plug through the front cover apertures in the socket moves the shutter and provides access for the plug pins with the contact member of the socket outlet.

Further, safety shutters are mandatory in most of the countries, and the relevant standard agencies ensure that this safety feature is incorporated for certification of the socket outlet. Most shutters on three pin socket outlets are operated by earth pin of the plug, and some of the products also have shutters operated by live and neutral pins, similar to shutters seen in Europe and elsewhere. In both cases, safety is achieved by ensuring that the live parts cannot be accessed with a single pin.

The shutters are usually actuated when a plug is inserted into the socket outlet, but the problem with the existing shutter designs is that, the arrangement can be easily by-passed by the insertion of a probe, such as pencil or a screw driver into the earth aperture to push the shutter towards the open position where the live and neutral contacts are revealed.

Such an easy bypass is undesirable. Therefore there is need to provide a shutter arrangement for socket assembly that is not easily bypassed accidentally or in such a simple manner. In order to increase the safety level in accessing the socket outlet, three pin shutters are developed, which bars access to all three pin apertures and operates only when standard three pin plug introduced into the respective socket apertures. There are multiple designs available on three pin shutters, some of these are single piece construction, and others are sub-assemblies made of multiple parts to constitute a safety shutter.

The conventional arrangements of safety shutter in the electrical three pin plug socket assembly are analyzed with respect to the structural and functional arrangement of shutters in the socket assembly. The prior art documents having three pin shutters are discussed.

The EP0539093 Patent discloses an electrical socket having a shutter which closes the plug pin openings in the front wall of the socket to cover two of the contacts in the absence of the plug. A latch provided with the shutter at the earth pin area makes the shutter to move when operated by the plug earth pin and makes the contact between the plug terminal and the socket. The plug earth pin up on insertion acts on the ramped surface of the latch and makes the shutter to open and enable the terminal contact.

The GB2363917 Patent discuses about the safety improvements relating to electrical sockets, in which the expansion and contraction of the earth pin contact element releases and locks the shutter to make contact between the plug and socket elements. The earth pin contact element is adapted to undergo elastic deformation due to the introduction of the plug earth pin to break the contact between the earth contact element and the shutter and thereby allowing the shutter to move towards an open position and making contact between the plug pins and the socket elements.

The Patent document GB2374988 discuses about a safety shutter having retractable flaps which bars the access between the contact members of the plug and socket. The flaps include guide and retainers through which the flaps will undergo transition on each other to make access to the terminal pins of the socket. The operation of plug pins into the socket makes the flaps to retract and enable access between the contact members.

However, all these available conventional shutter arrangements fails to ensure required safety level in bypassing the socket outlet and contacting the current carrying parts. For instance, the system fails to ensure that the two pin plugs with alternate Earth system, like Schuko plugs, will not enter the three pin socket. Schuko plug, when introduced into socket outlets that are designed for three pin plugs, does not provide earthing for the equipment and suffers lower safety level to the user.

The conventional shutter arrangement also suffers in respect of shutter control mechanism which is difficult to achieve a precise control, and such arrangement will affect the safety level requirements and will result in an undesired effect. With respect to the various conventional safety shutter arrangements, and protection level requirement towards current carrying parts, it is necessary to have an improved safety shutter arrangement for the socket outlet which provides safe access and prevents unsafe access to the current carrying parts.

Moreover, it is necessary to provide a two piece safety shutter system in which one shutter moves with respect to the movement of the other shutter and safely allows engagement of the live and neutral pins in the electrical socket. For the above reasons, it is desirable to provide an improved two piece type safety shutter arrangement developed for controlled accessing of current carrying parts in the three pin socket, which is capable to address and overcome the above disadvantages of conventional sockets.
Object of the invention

The main object of the present invention is to provide an improved safety shutter arrangement for the three pin plug socket.

Another object of the invention is to provide a shutter assembly which provides access to the current carrying parts, only when all three pins of the plug are introduced into the socket apertures.

Another object of the present invention is to provide a shutter arrangement which prevents access to the current carrying parts when a single pin or less than three pins are operated into the socket outlet.

Another object of the present invention is to provide a shutter arrangement having a two piece construction such that one shutter moves with respect to the movement of another
shutter.

Further object of the invention is to provide an improved shutter arrangement that is economical and deliver increased level of safety in accessing the current carrying parts.

Summary of the invention:

The present invention which achieves the objectives relates to an electrical socket for a three pin plug having earthing pin lengthier than the live and neutral pins. The socket comprises a two piece safety shutter assembly placed within the socket, which provides access to the three pin plug only when all the three pins are operated and prevents access when less than three pins operated in the socket. The three pin electrical socket assembly comprises a front plate having apertures for receiving a three pin plug and a contact member adopted for providing terminal connectivity for the three pin plug. A two piece shutter assembly having a top shutter and a bottom shutter is transiently assembled with a spring load within the socket to normally prevent and to provide access to the plug pins with the contact member.

The top shutter has an inverted T shaped profile with a straight portion and flat portion, and the straight portion has a vertical flap which shuts the Earth pin and the flat portion has extended projections that actuate the bottom shutter. The vertical flap has beveled surface which slides downward when the earth pin of plug is inserted inside the socket.

The bottom shutter has horizontal flaps formed at the in-between portions of the corner and the center part of the bottom shutter. The bottom shutter receives the projections of the top shutter and gets actuated against the spring force and provides access to the live and neutral pins. The bottom shutter has blocking surfaces which are usually exposed at the Live and neutral pin contact points in the socket. The top shutter travels between the normally closed and intermediate position to prevent and to provide access to the earth pin. The bottom shutter moves with respect to the movement of the top shutter and allows engagement of the live and neutral pins in the socket. The spring makes the flaps to shut and retract and allows access between the contact members of the live and neutral pins.

The shutter assembly travel between the normally closed position, intermediate position and open position to provide and prevent access to the plug pins with said contact member. In the Normal/closed position, the live and neutral contacts of the socket are blocked by the blocking surface of the bottom shutter. Since the visible or accessible surface of the bottom Shutter is blocked, and it cannot be moved down, and thus the bottom shutter does not facilitate easy or accidentals opening of the shutter.

In operation, the earth pin of the plug makes first contact since it is longer than the Live and Neutral pins of the plug. The Earth Pin of the plug displaces both the top shutters and bottom shutter to the intermediate position. When the bottom shutter is displaced to the intermediate position, the entry chamfer for the Live and Neutral pins on the bottom shutter are exposed. This exposed chamfer facilitates to receive the Live and Neutral pins of the three pin plug.

After the intermediate position, the Live and Neutral pins of the plug start to make contact with the bottom shutter, and the contact for the live and neutral pins is made on the now exposed entry chamfer region. On further insertion of the plug, the bottom shutter is displaced to make by the Live and Neutral pin of the plug to make contact with the contacts of the three pin socket. The bottom Shutter has provisions to facilitate locking with the extended projections from the top shutter. The spring arrangement makes the shutter assembly to retract to its original closed position when the plug is removed from the socket outlet and thus prevents access to electrical contacts.

The shutter arrangement ensures safe electrical connection each time when the plug is connected to a socket outlet by having first earth connection and then lives and neutral connections, which makes the equipment earthed or grounded during insertion of the BS three pin plug.

The improved shutter arrangement prevents access to live and neutral contacts of the electrically connected socket outlet when anyone forcefully wants to operate the socket by inserting a single pin undesirably to Earth pin entry to move the shutter.

Also, The improved shutter arrangement prevents access to live and neutral contacts of the electrically connected socket outlet when anyone forcefully wants to operate the socket by inserting a single pin or two pins simultaneously to Live or/and neutral aperture of the Socket.

Brief description of drawings:

Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same.

FIG. 1 shows a three pin socket outlet having a two piece safety shutter assembly, in accordance with an exemplary embodiment of the present invention.

FIG. 2 shows the improved two piece safety shutter assembly with spring, in accordance to the present invention.

FIG. 3a shows the top shutter having vertical flap and extended projections, in accordance to the present invention.

FIG. 3b shows the bottom shutter having horizontal flaps and blocking surfaces, in accordance with an exemplary embodiment of the present invention.

Fig. 4 shows the Normal / closed position of the three pin socket with terminals blocked, in accordance to the present invention.

Fig. 5 shows the Earth Pin entered position in the three pin socket with Earth contact, in
accordance to the present invention

Fig. 6 shows the complete plug inserted position of the three pin socket with all terminals contacted, in accordance to the present invention.

Detailed description:

The present invention relates to a two piece safety shutter assembly placed within the socket to provide terminal access to the Earth pin, Live and Neutral pins of the plug and the socket upon actuation. The three pin plug has earthing pin lengthier than the live and neutral pins which conforms to the specified Standards specification and provides access to the three pin plug only when all the three pins are operated and prevents access when less than three pins operated in the standard electrical socket.

FIG. 1 shows a three pin socket outlet having a two piece safety shutter assembly, in accordance with an exemplary embodiment of the present invention. The three pin electrical socket (1) comprises a front plate (2) having apertures for receiving a three pin plug and a contact member (3) adopted for providing terminal connectivity for the three pin plug. A two piece shutter assembly having a top shutter (4) and a bottom shutter (5) is transiently assembled with a resilient member (6), for example, a spring member within the socket (1) to normally prevent and to provide access to the plug pins with the contact member.

The three pin actuated safety shutter according to the present invention will NOT operate even when two pins are introduced into any two of the three apertures on the socket outlet front plate (2), and needs a three -pin plug for operation, thus ensuring the safety in operation of the three pin plug socket (1). The top shutter (4) has an inverted T shaped profile with a straight portion (7) and flat portion (8), and the straight portion has a vertical flap (9) which shuts the Earth pin and the flat portion has extended projections (10) that actuate the bottom shutter (5). The vertical flap (9) is a beveled surface which slides downward when the earth pin of plug is inserted inside the standard electrical socket.

The bottom shutter (5) has horizontal flaps (11) formed at the in-between portions of the corner and the center part of the bottom shutter. The bottom shutter receives the projections (10) of the top shutter (4) and gets actuated against the spring force (6) and provides access to the live and neutral pins. The bottom shutter (5) has blocking surfaces (12) which are usually exposed at the Live and neutral pin contact points in the socket.

The top shutter (4) travels between the normally closed and intermediate position to prevent and to provide access to the earth pin. The bottom shutter (5) moves with respect to the movement of the top shutter (4) and allows engagement of the live and neutral pins in the socket. The spring (6) makes the flaps (9) and (11) to shut and to retract and allows access between the contact members of the live and neutral pins with the socket.

The shutter assembly travel between the normally closed position, intermediate position and open position to provide and prevent access to the plug pins with the contact member. In the Normal/closed position, the live and neutral contacts of the socket (1) are blocked by the blocking surface (12) of the bottom shutter. Since the visible or accessible surface of the bottom Shutter is blocked it cannot be moved down, and thus preventing the blocking surface (12) of the bottom shutter (5) from easy or accidentals opening of the bottom shutter in the socket.

FIG. 2 shows the improved two piece safety shutter assembly with spring, in accordance to the present invention. The top shutter (4) is placed in position to actuate the bottom shutter (5) through the projections (10) formed at the lower end of the top shutter. The bottom shutter has provisions to receive the projections (10) extending from the top shutter and get actuated upon activation of top shutter through the Earth pin. The top shutter (4) and the bottom shutter (5) is assembled and transiently accommodated inside the front plate (2) of the socket. The spring (6) is compressed while assembling the bottom shutter (5), and provides the energy for the shutter assembly to move back into original position after removal of the plug pin. The standard plug operation at the socket makes the vertical flap (9) and the horizontal flap (11) to have respective transient movement and enable access to the plug pin contact element (3) in the socket.

FIG. 3a shows the top shutter having vertical flap and extended projections, in accordance to the present invention. According to the invention, the top shutter (4) has an inverted T shaped profile with a straight portion (7) and flat portion (8). The straight portion (8) in the top shutter (4) has a vertical flap (9) formed in upright direction and arranged to shut the Earth pin. The vertical flap (9) is a beveled surface which slides downward when the earth pin of plug is inserted inside the standard electrical socket. The vertical flap portion in the front plate is in coordination with the top shutter (4) to receive the plug earth pin, such that the operation of plug earth pin makes the top shutter to move the top shutter downward and further to access the earth terminal of the contact member
formed in the socket. The flat portion (8) in the top shutter (4) is arranged to contact and drive the bottom shutter (5) through the extended projections (10) in the top shutter. The spring (6) is placed such that the bottom shutter (5) is drive downwards against the spring force. The vertical flap (9) of the top shutter (4) is constructed to prevent unwanted probing at the earth pin. This ensures that, in case of introduction of a probe or side pin entry at the earth pin aperture in the front plate of the socket (1), the top shutter (4) prevents the shutter opening in the front plate.

FIG. 3b shows the bottom shutter having horizontal flaps and blocking surfaces, in accordance with an exemplary embodiment of the present invention. The bottom shutter has horizontal flaps (11) formed at the in-between portions of the corner and the center part of the bottom shutter. The bottom shutter (5) has blocking surfaces (12) which are usually exposed at the Live and neutral pin contact points in the socket. The blocking surfaces (12) are formed below the horizontal flaps (11), such that horizontal flap is made invisible in the normal closed condition and thus preventing probing of Live and Neutral pins in the standard socket. The spring (6) makes the horizontal flap (11) to shut and to enable access between the contact members of the live and neutral pins with the socket.

The horizontal flap (11) in the bottom shutter is formed of sliding surfaces for making transient movement of the bottom shutter (5) when contacted by the Live and Neutral pins together and enables the three pin plug to contact the live and neutral terminals of the socket. The horizontal flaps (11) are formed on the top portion of the bottom shutter (5) at the in-between portions of the corner and the center part in the bottom shutter (5).

The sliding surfaces formed in the horizontal flap (11) slides to make the live and neutral pin contact members to contact and access to the three pin plug when operated.

Fig. 4 shows the Normal / closed position of the three pin socket with terminals blocked, in accordance to the present invention. In the three pin plug the Earth pin is made as comparatively longer than the live and neutral pins to use with the socket assembly, and this makes the earth pin to first contact the contact member (3) prior to the live and neutral pins coming into contact with their respective terminals in the socket. The live and neutral pins of the plug will then contact into the respective terminal parts of the socket. The spring (6) gets compressed while assembling the bottom shutter (5) to provide the energy for the shutter (5) to move back into original position after removal of the plug pin. The operation of standard plug into the socket by passing down the shutter through the front plate (2) will enable electrical connection between the plug and the standard socket.

The movement of shutter assembly up on introduction of the plug into the socket is described using the diagrams. In the normal closed position, the beveled surface of the vertical flap (9) appears in the Earth pin aperture and the blocking surfaces (12) appear in the Live and neutral pin apertures. The plug upon application into the socket, through the apertures on the front plate (2) of the socket, the earth pin of the three pin plug makes the first contact with the top shutter (4). The live and neutral pin of the plug are shorter than the earth pin, usually 3mm to 5mm and this makes the Earth pin to make the first contact with the socket. The actuation of the Earth pin makes the top shutter (4) to travel downward and to contact the Earth pin contact member in the socket.

Fig. 5 shows the Earth Pin entered position in the three pin socket with Earth contact, in accordance to the present invention. The Earth Pin of the plug displaces the top shutter (4) and makes the bottom shutter (5) to move to the intermediate position. When the bottom shutter (5) is displaced to the intermediate position, the angled surfaces in coordination with the Live and Neutral pins on the bottom shutter are exposed. These exposed angled surfaces facilitate to receive the Live and Neutral pins of the three pin plug. The further operation of the three pin plug makes the live and neutral pins to enter into the respective front plate apertures (2). The sliding surfaces in horizontal flaps (11) are come into contact with the live and neutral pins of the BS plug. In this intermediate
position, the angled surfaces formed at the top of the bottom shutter (5) facilitate introduction to the live or earth aperture of the front plate of the socket outlet.

Fig. 6 shows the complete plug inserted position of the three pin socket with all terminals contacted, in accordance to the present invention. In this final position, the plug has completely entered the socket outlet and all the pins of the plug are in contact with the respective contact parts of the socket. The plug has moved further down towards the sliding surfaces on the horizontal flap (11), and the live and neutral pins push the bottom shutter (5) further down. This makes the bottom shutter (5) downwards and make downward transition movement against the spring force (6).

After the intermediate position, the Live and Neutral pins of the plug start to make contact with the bottom shutter (5), and the contact for the live and neutral pins is made on the now exposed entry horizontal flap region. The further insertion of the plug, the bottom shutter (5) is displaced to make by the Live and Neutral pin of the plug to make contact with the contacts of the three pin socket. In this completely entered position, the plug pins have moved towards the level of the shutter assembly, and can now access the live, neutral and earth contacts in the contact member.

The spring arrangement (6) makes the shutter assembly to retract to its original closed position when the plug is removed from the socket outlet and thus prevents access to electrical contacts. When the three pin plug is removed, the sequence is reversed and the bottom shutter (5) and the top shutter (4) moves back into original normally closed position due to the shutter spring (6). In this way, the safety shutter assembly ensures that introduction of one or two pins will not be able to access the socket, and all three pins of the plug is needed to operate the shutter and access the current carrying contact member.

The shutter arrangement according to the present invention ensures safe electrical connection each time when the plug is connected to a socket outlet by having first earth
connection and then lives and neutral connections, which makes the equipment earthed or grounded during insertion of the BS three pin plug. The improved shutter arrangement prevents access to live and neutral contacts of the electrically connected socket outlet when anyone forcefully wants to operate the socket by inserting a single pin undesirably to Earth pin entry to move the shutter.

The present invention provides an improved three pin operated safety shutter with a simple and economical two part design, developed for constructional and functional requirements and ensuring required level of safety in accessing the current carrying parts and in bypassing through any probe or unsafe plug means in the socket outlet.

The spring loaded safety shutter will regains its original closed position with the socket front plate, and bars access to the contact member, when the three pin plug is removed from the socket assembly. The improved shutter arrangement according to the present invention prevents access to live and neutral contacts of the electrically connected socket outlet when anyone forcefully wants to operate the socket by inserting a single pin or two pins simultaneously to Live or/and neutral aperture of the Socket.
The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

Part Numbers:

Three pin electrical socket (1)

Front plate (2)

Electrical contact member (3)

Top shutter (4)

Bottom shutter (5)

Resilient member - Spring (6)

Straight portion (7)

Flat portion (8)

Vertical flap (9)

Extended projections (10)

Horizontal flaps (11)

Blocking surfaces (12)

We Claim:

1. A three pin electrical socket assembly comprises,

a front plate (2) having apertures for receiving a three pin plug and a contact member (3) adopted for providing terminal connectivity for said three pin plug; and

a shutter assembly having a top shutter (4) and a bottom shutter (5), transiently assembled with a resilient member (6) to normally prevent and to provide access to said plug pins with said contact member (3);

wherein said top shutter (4) has a straight portion (7) with vertical flap (9) which shuts the Earth pin and a blocking portion (8) which actuates the bottom shutter (5), said top shutter (4) and bottom shutter (5) travels between the normally closed position to intermediate position to provide access to the earth pin;

wherein said bottom shutter (5) has blocking surface (12) and horizontal flaps (11) formed at the in-between portions of the corner, wherein said bottom shutter (5) moves from the intermediate position to open position to provide access to the live and neutral pins.

2. The socket assembly as claimed in claim 1, wherein said top shutter (4) and bottom shutter (5) travels respectively between the normally closed position, intermediate position and open position to provide and prevent access to the plug pins with said contact member (3).

3. The socket assembly as claimed in claim 1, wherein said vertical flap (9) has beveled surfaces which slides downward when said earth pin of plug is inserted inside the socket.

4. The socket assembly as claimed in claim 1, wherein said top shutter (4) has extended projections (10) to actuate the bottom shutter (5).

5. The socket assembly as claimed in claim 1, wherein said bottom shutter (5) receives said projections (10) from the top shutter (4).

6. The socket assembly as claimed in claim 1, wherein said Earth Pin of the plug displaces both the top shutter (4) and bottom shutter (5) to the intermediate position.

7. The socket assembly as claimed in claim 1, wherein said top shutter (4) has an inverted T shaped profile with a straight portion (7) having vertical flap (9) and projections (10) on flat portion (8) connecting the bottom shutter (5).

8. The socket assembly as claimed in claim 1, wherein said bottom shutter (5) moves with respect to the movement of the top shutter (4) and allows engagement of the live and neutral pins in the socket.

9. The socket assembly as claimed in claim 1, wherein the bottom shutter (5) is displaced by the Live and Neutral pin of the plug to make contact with the contacts of the three pin socket.

10. The socket assembly as claimed in claim 1, wherein the bottom shutter (5) has blocking surfaces (12) which exposed at the normally closed position at the Live and neutral pin contact points in the socket.

11. The socket assembly as claimed in claim 1, wherein the resilient member (6) place the top shutter (4) and the bottom shutter (5) to retract to its original closed position when the plug is removed from the socket outlet.