GB1585094A

GB1585094A - Electrical sockets

Info

Publication number: GB1585094A
Application number: GB1990476A
Authority: GB
Original assignee: TENBY ELECT ACCESSORIES Ltd
Current assignee: TENBY ELECT ACCESSORIES Ltd
Priority date: 1977-05-13
Filing date: 1977-05-13
Publication date: 1981-02-25

Description

(54) ELECTRICAL SOCKETS We, TENBY ELECTRICAL ACCESSORIES LIMITED, a British Company, of 19 Warston Lane, Birmingham B18 6JG, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to electrical sockets of the kind comprising a face plate having at least a pair of spaced apertures through which in use, can be passed the pins of an electrical plug, contacts positioned to receive said pins and a housing for said contacts. Electrical sockets of this kind will hereinafter be referred to as "electrical sockets of the kind specified." It is well known to provide a safety device positioned between the apertures and the contacts and which prevents the contacts being touched by for example a small screwdriver, inserted through one of the apertures. in the past the movement of the safety device to allow the plug to be inserted has been effected by insertion of the earth-pin of the plug through a separate earth-pin aperture in the face plate. More recent developments have resulted in constructions in which the line and neutral pins of the plug when the plug is correctly presented to the socket, effect movement of the safety device to a position to allow the pins to engage with the contacts.

The present invention is concerned with the latter type of construction and has for its object to provide an electrical socket of the kind specified in a simple and convenient form.

According to the invention an electrical socket of the kind specified comprises a shutter member having a central limb and two arms forming a generally "T" configuration, said shutter member being positioned between said face plate and the contacts with the arms of the member positioned behind said apertures, a cam form on each of the said arms whereby in use when the correct plug is presented to the socket the pins will engage said cam forms to cause initial movement of said arms away from said apertures in the direction of movement of the pins, said member pivoting during the initial movement about an axis defined by an edge on the central limb of the member, further movement of the pins effecting lateral displacement of the member in a direction substantially at right angles to the movement of the pins thereby to allow the pins to engage with said contacts, resilient means acting on the member to oppose said initial movement and said lateral displacement and an elongated stop surface engageable by an abutment surface defied by the arms of the member, said stop surface being positioned to prevent lateral displacement of the member unless said abutment surface has been moved clear thereof during said initial movement, the arrangement being that if one arm only is moved away from the respective aperture, the member will rock but a portion of said abutment surface will engage with said stop surface thereby preventing said lateral displacement of the member.

One example of an electrical socket in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a sectional side elevation of a socket with the various parts in the rest position, Figure 2 is a view similar to Figure 1 but showing operation of the socket, Figures 3 and 4 show perspective views of a portion of the socket seen in Figures 1 and 2, Figure 5 shows a sectional view of the portion of the socket seen in Figures 3 and 4, Figure 6 shows an end view corresponding to Figure 2, Figure 7 shows a view similar to Figure 6 but demonstrating the movement of the parts when a screwdriver of the like is inserted through one aperture, Figures 8 and 9 correspond to Figures 1 and 2 and show a modification, Figure 10 is a perspective view of two parts of the socket of Figure 8 and Figure 11 is sectional view of parts of the socket seen in Figure 8.

With reference to the drawings the socket comprises a face plate 10 having a front face 11 and secured to the back of the face plate in any convenient manner is a housing 12. Formed in the face plate are a pair of spaced apertures 13 through which in use, can pass the pins 14 of an electrical plug shown at 15.

The housing 12 supports electrical contacts 16 which are themselves connected to terminal blocks 17 for electrical conductors. The contacts 16 are positioned in the housing behind the apertures 13 so that when the pins 14 of the plug are inserted through the apertures they will eventually engage the contacts 16 to establish an electrical connection.

Also provided is a shutter member 18 and as will be seen from Figures 3 and 4 the shutter member is of generally "T" configuration.

The shutter member 18 has arms 19, 20 and a central limb 21. The shutter member is disposed in a recess indicated at 22, formed in the face plate and closed by the housing 12. The upper surface of the shutter member i.e. that surface which lies immediately below the apertures, is flat but the lower and opposite surface of the member is inclined as best seen in Figures 1 and 5. Moreover, the end surface of the limb 21 remote from the arms 19, 20 is inclined so that a pivot edge indicated at 23 in Figures 3 and 5, is defined. The edge23 bears against a corner defined by the end wall of the recess 22 and the housing 12. This is best seen in Figure 1.

The upper surface of the shutter member is provided with a part cylindrical recess 24 and this accommodates a coiled compression spring 25. The compression spring bears against the end wall of the recess 24 and also against the end wall of the recess 22. The line of action of the spring 25 is off-set from the aforesaid pivot edge so that the effect of the spring is to urge the pivot edge towards the aforesaid corner and also to urge the upper surface into contact with the wall of the recess 22 which is defined in the face plate.

The wall in the face plate defines an elongated stop surface 26, this being defined by a step in the wall of the recess 22 which is defined by the face plate. The stop surface 26 extends parallel to the pin apertures and the arms 19, 20 define an abutment surface 27 for engagement with the stop surface. Because of the recess 24 the abutment surface 27 is interrupted but as will be seen when the operation is described, this does not affect the operation.

The arms 19, 20 lie below the apertures 13.

Moreover, the upper surfaces of the arms define cam forms 28 for engagement as will be described, by the pins 14 respectively of the plug.

The operation of the mechanism will now be described assuming initially that a plug 15 with the correct pins is presented to the socket. The pins 14 can initially pass through the apertures 13 and then move into engagement with the cam forms 28. Further movement of the pins effects initial displacement of the arms 19,20 towards the housing and during this movement the shutter member pivots about the pivot edge 23. Such initial movement moves the abutment surfaces 27 clear of the stop surface 26 and the movement is of course against the action of the spring 25. Continued movement of the pins will effect lateral displacement of the shutter member and the latter will slide in the recess again against the action of the spring 25.

This movement is illustrated in Figure 2 and such displacement then allows the pins 14 to engage with the contacts 16. Figure 6 illustrates in end view how the arms 19, 20 have been displaced equally thereby clearing the abutment surface 27 and the stop surface 26 and furthermore, it shows that during the lateral displacement the under surface of the member slides on a surface defined by the housing. When the plug is withdrawn from the socket then the shutter returns to the position shown in Figure 1.

Consider now the situation when a screwdriver or the like is inserted through one aperture only. As will be seen from Figure 7 the respective arm is depressed in the same way as occurs when the pins of the correct plug are engaged with the arms. However, the member 18 rocks as is shown in Figure 7 so that the abutment surface 27 is not moved clear of the stop surface 26. The aforesaid lateral displacement cannot therefore take place and therefore the contact 16 will not be exposed to the screwdriver. As will be seen from Figures 6 and 7 the under surfaces of the arms 19 and 20 slope upwardly and as best seen in Figure 7, the purpose of this is to ensure that pressure by means of the screwdriver on the shutter will not cause a lever action which might move the abutment surface 27 clear of the stop surface 26.

It will be appreciated that there are various standards relating to pin size and spacing and it is unfortunate that some of these standards are such that it is possible to insert through the apertures 13, the pins of plugs which are constructed with different standards in mind.

In the example shown in the drawings the pins are flat and the spacing and size of the pins corresponds to the line and neutral pins of the standard British type 13 amp socket.

It has been discovered that a plug manufactured according to a continental standard but having circular pins, can be passed through the apertures 13 and so could effect movement of the shutter member so as to expose the contact 16 for engagement by the pins.

This can be avoided by forming in the cam surfaces 28 blind circular section recesses indicated at 29. The effect of these recesses is that when the round pins are pushed through the apertures, they will enter the recesses 29 and whilst the aforementioned initial movement of the arms may take place the lateral displacement of the shutter member cannot take place because the pins in effect prevent the lateral movement. It is fortunate that the spacing of the pins of the plug manufactured in accordance with the continental standard, is such that the bridge between the apertures 13 is only slightly smaller than the distance between the pins.

In the modification shown in Figures 8, 9, 10 and 11 the socket is a conventional form of 13 amp socket with an earth contact 30 for engagement by an earth pin 31 on the plug. Additional protection can be afforded with a three pin plug if it is arranged that the shutter can only be moved if the three pins of the correct plug are inserted.

For this purpose the shutter member 18 is modified as shown at 18a in Figure 10, by the addition of a slot 32 in the end wall of the central limb of the member. The slot extends into the recess 24 of the spring 25 and accommodates the shank 34 of a hook member 35. The shank extends at one end from a wedge shaped body 36 and at its other end defines a catch in the form of a hook 37.

The spring 25 engages the body 36 of the hook member and imparts to the hook member a force such than in assembly, and by virtue of the wedge shape of the body 36 and as seen in Figure 8, the hook member is biased in an anticlockwise direction. The hook 37 engages with a catch surface 38 as seen in Figure 8. The hook 37 is engageable by the earth pin 31 to move the hook downwardly and also to a certain extent in a lateral direction against the action of the spring 25. When the hook is moved downwardly it is disengaged from the surface 38 so that the shutter member can then be displaced in a lateral direction after the initial downward movement as described earlier in this specification and as shown in Figure 9. If the hook member 35 is not moved by the earth pin then it will remain engaged with the surface 38 and will prevent the lateral displacement of the shutter member even if this has been moved through the initial movement. The shutter member cannot therefore be moved by a plug having only two pins. The rocking movement as described earlier, of the shutter member can still take place and so the shutter member cannot be moved by inserting a screwdriver or similar instrument through either the line or neutral apertures.

The hook member 35 during its movement by the earth pin 31 moves against the spring 25 and in so doing the force exerted by this spring is removed from the shutter member.

In order to prevent the possibility of the shutter member tilting in this situation a further spring 39 is provided which biases the shutter member about the pivot edge in the clockwise direction. The spring 39 is conveniently a coiled spring located within a bore in the housing and bears against the shutter member. During lateral displacement of the shutter member there is relative sliding movement between the end of the spring and the shutter member. When the correct three pin plug is inserted and the shutter member is moved correctly by the line and neutral pins the hook 37 is removed out of contact with the earth pin thereby minimising wear of the surface of the hook which engages the earth pin.

WHAT WE CLAIM IS: 1. An electrical socket of the kind specified comprising a shutter member having a central limb and two arms forming a generally "T" configuration, said shutter member being positioned between said face plate and the contacts with the arms of the member positioned behind said apertures, a cam form on each of said arms whereby in use when the correct plug is presented to the socket the pins will engage said cam forms to cause initial movement of said arms away from said apertures in the direction of movement of the pins, said member pivoting during the initial movement about an axis defined by an edge on the central limb of the member, further movement of the pins effecting lateral displacement of the member in a direction substantially at right angles to the movement of the pins thereby to allow the pins to engage with said contacts, resilient means acting on the member to oppose said initial movement and said lateral displacement and an elongated stop surface engage able by an abutment surface defined by the arms of the member, said stop surface being positioned to prevent lateral displacement of the member unless said abutment surface has been moved clear thereof during said initial movement, the arrangement being that if one arm only is moved away from the respective aperture, the member will rock but a portion of said abutment surface will engage with said stop surface thereby preventing said lateral displacement-of the member.

2. A socket according to Claim 1 in which said resilient means acts on said shutter member at a position offset from said edge.

3. A socket according to Claim 1 or Claim 2 in which said resilient means comprises a coiled compression spring the line of action of said spring being offset from said edge.

4. A socket according to claim 3 in which said spring is partly accommodated within a part cylindrical recess formed in the central limb of the shutter member, said spring at one end bearing against an end wall of the member and at its other end against a surface defined on the face plate.

5. A socket according to any one of the preceding claims in which said cam forms are as wide as the apertures in the face plate.

6. A socket according to Claim 5 including recesses in said cam forms, said recesses being positioned to receive the pins of a plug of a different type for which the socket is designed,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. take place because the pins in effect prevent the lateral movement. It is fortunate that the spacing of the pins of the plug manufactured in accordance with the continental standard, is such that the bridge between the apertures 13 is only slightly smaller than the distance between the pins. In the modification shown in Figures 8, 9, 10 and 11 the socket is a conventional form of 13 amp socket with an earth contact 30 for engagement by an earth pin 31 on the plug. Additional protection can be afforded with a three pin plug if it is arranged that the shutter can only be moved if the three pins of the correct plug are inserted. For this purpose the shutter member 18 is modified as shown at 18a in Figure 10, by the addition of a slot 32 in the end wall of the central limb of the member. The slot extends into the recess 24 of the spring 25 and accommodates the shank 34 of a hook member 35. The shank extends at one end from a wedge shaped body 36 and at its other end defines a catch in the form of a hook 37. The spring 25 engages the body 36 of the hook member and imparts to the hook member a force such than in assembly, and by virtue of the wedge shape of the body 36 and as seen in Figure 8, the hook member is biased in an anticlockwise direction. The hook 37 engages with a catch surface 38 as seen in Figure 8. The hook 37 is engageable by the earth pin 31 to move the hook downwardly and also to a certain extent in a lateral direction against the action of the spring 25. When the hook is moved downwardly it is disengaged from the surface 38 so that the shutter member can then be displaced in a lateral direction after the initial downward movement as described earlier in this specification and as shown in Figure 9. If the hook member 35 is not moved by the earth pin then it will remain engaged with the surface 38 and will prevent the lateral displacement of the shutter member even if this has been moved through the initial movement. The shutter member cannot therefore be moved by a plug having only two pins. The rocking movement as described earlier, of the shutter member can still take place and so the shutter member cannot be moved by inserting a screwdriver or similar instrument through either the line or neutral apertures. The hook member 35 during its movement by the earth pin 31 moves against the spring 25 and in so doing the force exerted by this spring is removed from the shutter member. In order to prevent the possibility of the shutter member tilting in this situation a further spring 39 is provided which biases the shutter member about the pivot edge in the clockwise direction. The spring 39 is conveniently a coiled spring located within a bore in the housing and bears against the shutter member. During lateral displacement of the shutter member there is relative sliding movement between the end of the spring and the shutter member. When the correct three pin plug is inserted and the shutter member is moved correctly by the line and neutral pins the hook 37 is removed out of contact with the earth pin thereby minimising wear of the surface of the hook which engages the earth pin. WHAT WE CLAIM IS:

1. An electrical socket of the kind specified comprising a shutter member having a central limb and two arms forming a generally "T" configuration, said shutter member being positioned between said face plate and the contacts with the arms of the member positioned behind said apertures, a cam form on each of said arms whereby in use when the correct plug is presented to the socket the pins will engage said cam forms to cause initial movement of said arms away from said apertures in the direction of movement of the pins, said member pivoting during the initial movement about an axis defined by an edge on the central limb of the member, further movement of the pins effecting lateral displacement of the member in a direction substantially at right angles to the movement of the pins thereby to allow the pins to engage with said contacts, resilient means acting on the member to oppose said initial movement and said lateral displacement and an elongated stop surface engage able by an abutment surface defined by the arms of the member, said stop surface being positioned to prevent lateral displacement of the member unless said abutment surface has been moved clear thereof during said initial movement, the arrangement being that if one arm only is moved away from the respective aperture, the member will rock but a portion of said abutment surface will engage with said stop surface thereby preventing said lateral displacement-of the member.

said pins when in said recesses acting to prevent movement of said shutter member.

7. A socket according to Claim 4 including a further aperture in said face plate to receive an earth pin of the plug.

8. A socket according to Claim 7 including a hook member carried on the shutter member, said hook member being adpated to engage with a catch surface to prevent movement of the shutter member unless the hook member is released from said catch surface by the earth pin.

9. A socket according to Claim 8 in which said hook member comprises a shank portion extending through a slot in said end wall, a hook portion and a wedge shaped body portion located in said part cylindrical recess, said body portion being urged into engagement with said end wall by said spring.

10. A socket according to Claim 9 in which insertion of said earth pin releases said hook member from said surface and engagement of line and neutral pins with said cam forms causes following said initial movement, lateral displacement of the shutter member, lateral displacement also being imparted to said hook member, whereby it is moved out of engagement with the earth pin.

11. A socket according to Claim 10 including further resilient means acting on said shutter member in a direction to oppose said initial movement.

12. A socket according to claim 11 including recesses formed in said cam forms, said recesses substantially as hereinbefore described with reference as Claim 6.

13. An electrical socket comprising the combination and parts substantially as hereinbefore described with reference to Figures 1-7 of the accompanying drawings.

14. An electrical socket comprising the combination and parts substantially as hereinbefore described with reference to Figures 8-11 of the accompanying drawings.