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(11) | EP 0 615 313 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Improvements in or relating to electrical sockets |
| (57) In an electrical socket, fins 53 to 55 projecting rearwards from a front wall of
the socket are received in slots 32, 58 and 31 when pins of a correct plug are correctly
inserted but, when a single pin is inserted, the shutter 15 is tilted laterally and
causes free end faces of tongues 66, 67 and 68 of the shutter to abut against the
fins 53, 54 and 55 to retain the shutter closed. In an alternative embodiment, the
shutter has to be displaced rearwardly to beyond stops on the front wall before it
can be cammed linearly upwardly to open it. |
[0002] In electrical sockets used for connecting various items of equipment, especially domestic appliances, it is necessary to obtain characteristics of safety in usage; above all it should be impossible to introduce any electrically conductive objects to beyond the socket openings for the plug pins, thus preventing accidents which could occur in practice.
[0003] There are various devices which are intended to prevent the introduction of conductive elements other than the corresponding electrical plug pins into the connection openings of sockets. For example, there are the conventional caps which are fitted into the openings of sockets and which have to be removed in order to fit the electrical plugs. Nevertheless, these caps present the traditional problems that in some cases they can easily be removed by small children and also they can fall out quite easily, so their efficacy is not guaranteed.
[0004] Also it is known, especially from British Patents Nos. 501,609; 545,743; 870,845; 1210359 and 1210360 that there are some devices in which a rotating safety element is incorporated in the socket, so that, when the plug pins are introduced, the rotating element is made to turn, thus freeing the socket openings. In this type of device, there is provided a torsion spring in addition to the electrical contact members of the socket.
[0005] There is also known from Spanish Utility Model No. 287,727 a safety device for sockets, in which the protection is intended to be obtained by means of a linearly displaceable shutter formed with cams whereby the shutter can be linearly opened by the actual pins of the plug when connection is made. Although this device has significant advantages in the simplicity of its construction and its operating efficiency, it may be possible to overcome the safety device by introducing a sharp object into one of the openings of the socket and forcing it hard against the relevant cam.
[0007] According to one aspect of the present invention, there is provided an electrical socket comprising a wall through which are formed openings for receiving electrical contact pins of an electrical plug, a shutter having a closed condition behind said openings and linearly movable from said closed condition to an open condition by pushing action of said pins inserted through said openings, and biassing means urging said shutter into said closed condition, characterised by preventing means preventing said shutter from being opened by insertion of only one of said contact pins.
[0008] Owing to this aspect of the invention, only appropriately dimensioned pins of an electrical plug or of an equivalent object appropriately inserted can open the shutter.
[0009] According to a second aspect of the present invention, there is provided an electrical socket, comprising a wall through which are formed openings for receiving electrical contact pins of an electrical plug, and a shutter having a closed condition behind said openings and linearly movable by the pushing action of the pins, against the action of biassing means, from said closed condition to an open condition, which shutter is guided by guide means in the shutter and in the housing of the socket, which guide means is disposed after the openings in the direction of movement of the shutter from its closed condition to its open condition, characterized in that said guide means guides the shutter throughout its displacement from its closed condition to its open condition.
[0010] Owing to this aspect of the invention, lateral tilting of the shutter, especially in the case of insertion of a single elongate member through one of the openings, to reveal a socket contact, is obstructed by the guide means.
[0011] According to a third aspect of the present invention, there is provided an electrical socket, comprising a wall through which are formed openings for receiving electrical contact pins of an electrical plug, a shutter having a closed condition behind said openings and movable by the pushing action of the pins, against the action of biassing means, from said closed condition to an open condition, and an arrangement of stop means to restrict the displacement of the shutter from its closed condition to deter the shutter from leaving a protection active condition, so that a rearward displacement of the shutter is necessary, in order to enable the shutter to by-pass the stop means and move to its open condition, characterised in that the stop means comprising ramp means which facilitates return of the shutter from its open condition to its closed condition.
[0012] Owing to this aspect of the invention, any risk of the shutter remaining in its open position once the plug pins have been removed is reduced.
[0013] According to a fourth aspect of the present invention, there is provided an electrical socket, comprising a wall through which are formed openings for receiving electrical contact pins of an electrical plug, and a shutter having a closed condition behind said openings and movable by the pushing action of the pins, against elastic action of internal contacting laminar means, from said closed condition to an open condition, characterised in that the laminar means continuously and elastically urges the shutter against the wall.
[0014] Owing to this aspect of the invention, the shutter is held firmly against the wall, so that significant force is required to displace the shutter rearwards relative to the wall.
[0015] According to a fifth aspect of the present invention, there is provided an electrical socket comprising a wall through which are formed two side-by-side openings for two side-by-side connecting pins of an electrical plug, and a shutter having a closed condition behind said openings and movable by the pushing action of the pins, against elastic action of two side-by-side internal contacting laminar units extending towards the two openings, characterised in that the foremost edges of the laminar units and their respective directly facing surface portions of the shutter are so arranged relative to each other as to permit limited transverse rocking of the shutter.
[0016] Owing to this aspect of the invention, a force applied to the shutter by an elongate member inserted through one of the openings tends to turn the shutter about the innermost end of the foremost edge of the associated laminar unit and thus urge an opposite end zone of the shutter firmly against the inside surface of the wall.
[0017] According to a sixth aspect of the present invention, there is provided an electrical socket comprising a housing including a wall through which are formed openings for receiving electrical contact pins of an electrical plug, and a shutter having a closed condition behind said openings and movable by the pushing action of the pins, against elastic action of internal contacting laminar units, from said closed condition to an open condition, characterised in that one or more resiliently arranged projections which serve to urge the shutter resiliently against the wall are arranged between the shutter and the housing.
[0018] Owing to this aspect of the invention, the shutter is urged more firmly against the inside surface of the wall.
[0019] According to a seventh aspect of the present invention, there is provided an electrical socket comprising a housing including a wall through which are formed openings for receiving electrical contact pins of an electrical plug, a shutter having a closed position behind said openings and linearly movable from said closed condition to an open condition by pushing action of said pins inserted through said openings, biassing means urging said shutter into said closed condition, and guide means in said shutter and in said housing and whereby said shutter is linearly guided, said guide means being disposed after said openings in the direction of movement of said shutter from said closed condition to said open condition, characterised in that stop means on said guide means in said housing prevents said shutter from being opened by insertion of only one of said pins.
[0020] The provision of the stop means on the guide means is a very simple way of improving the electrical safety of the socket.
[0021] The present invention is applicable to a wide range of electrical sockets, for example to wall sockets and to electrical adaptors.
[0022] In one preferred embodiment, the construction of the safety device is such that, in order to open the shutter it is necessary not only to displace the shutter linearly parallelly to a front wall of a housing of the socket, but first a rearward displacement is necessary, without which the shutter cannot be opened. This characteristic may be complemented by another safety feature consisting of the fact that, when the shutter is pushed by some object which is inserted into only one of the openings, not only can the shutter not be opened, but rather its blocking action is increased to some extent by the incorrect pushing action. The housing and the shutter are provided with a system of stops and counter-stops, so that, in order to be able to displace the shutter parallelly to the wall to free the openings for the pins of a plug, a rearward, pushing action is required, which causes the counter-stops to move rearward with respect to the stops, allowing the subsequent linear opening displacement. The counter-stops are formed by the free end faces of tongues which are formed by sets of straight slots in the shutter. The shutter may be mounted between the front wall and the ends of contact strips of the socket in such manner as to allow for limited transverse rocking in the event of a push in only one of the openings. In this respect, the foremost edges of the contact strips and the shutter surface portions directly facing them may diverge progressing laterally outwards. In particular, the shutter may have recesses to accommodate the foremost ends of the contact strips and these recesses may have their bases obliquely inclined so as to diverge progressing towards the wall, allowing limited transverse rocking of the shutter. Alternatively or additionally the foremost edges of the contact strips may diverge progressing away from the wall, in order to allow the shutter to rock transversely. Further alternatively or additionally, there may be a certain amount of play between the foremost ends of the contact strips and the bases of the recesses of the shutter, in order to allow the shutter to rock transversely. There is not only the system of stops, preferably in the rear face of the front wall, and counter-stops, but also some means of resiliently allowing rearward movement of the shutter so that the system of stops and counter-stops is by-passed, which is achieved by means of a system of forwardly-acting springs urging the shutter continuously and resiliently against the front wall, or by giving the shutter rearwards flexibility. The contact strips may constitute the forwardly-acting springs. Additionally or alternatively, there may be provided, between the shutter and the surrounding housing, one or more resilient projections designed to force the shutter against the front wall. These projections may take the form of projecting tongues at the upper edge of the shutter which have a certain amount of resilience perpendicularly to the front wall. There may also be projections next to the lower edges of the recesses in the shutter. The slots in the shutter facilitate the fitting of the shutter and provide for guiding of the shutter by co-operating with fins attached to the housing, the guidance of the shutter being effected for the whole of its displacement from its closed position to its open position. The stops and counter-stops may have associated therewith ramps and counter-ramps to facilitate the return of the shutter from its open position to its closed position.
[0023] In an alternative preferred embodiment, the guide fins may provide stops, in the form of end faces thereof or lateral protrusions therefrom, to cooperate with counter-stops, in the form of end faces of the tongues of the shutter, to prevent opening of the shutter in the event of lateral tilting of the shutter such as would tend to occur in the event of insertion of an elongate member into only one of the openings.
[0024] In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-
Figure 1 is a front elevation of an electrical adaptor in the direction I-I in Figure 3, the adaptor being of circular form,
Figure 2 is a view similar to Figure 1, but of a wall socket of rectangular form,
Figure 3 is an axial section on the line III-III of Figure 1,
Figure 4 is a view on the line IV-IV of Figure 3,
Figure 5 is a view on the line V-V of Figure 3,
Figure 6 shows a section taken on the line VI-VI of Figure 4,
Figures 7 and 8 show respective sections taken on the line VI-VI of Figure 4, but through modified versions of the adaptor,
Figure 9 shows a section taken on the line IX-IX of Figure 5,
Figures 10 and 11 show sections taken on the lines X-X and XI-XI of Figure 5,
Figure 12 is a front elevation of a shutter of the adaptor,
Figures 13 to 17 respectively show sections taken on the lines XIII-XIII to XVII-XVII of Figure 12,
Figure 18 is a view similar to Figure 4, but of an alternative embodiment of the adaptor, and
Figures 19 to 21 are views similar to Figure 18, but illustrating the shutter subjected to various forces.
[0025] Referring to the drawings, an adaptor 1 is shown in Figures 1 and 3 to 21, whilst a wall socket 2 is shown in Figure 2. Each has openings for the introduction of rectangular-section pins of a three-pin plug and of round-section pins of a two-pin plug. These openings are referenced 3, 4 and 5 for the adaptor 1, and 6, 7 and 8 for the wall socket 2.
[0026] As seen in Figure 3, the adaptor has pins 10 on the face opposite to that of the openings 3 to 5. Inside the adaptor there are arranged U-shaped, resilient, electrical contact strips 12, connected by means of screws 14 or other appropriate fixings to the housing of the adaptor.
[0027] The strips 12 include two lateral strips 13 and 13' which have their lower limbs inserted into horizontal recesses 38 and 37 in the linearly displaceable safety shutter 15. The lower limbs of the strips 13 and 13' act on the shutter 15 in such manner that they tend to return the shutter to its closed position. This action may be supplemented by internal helical compression springs 17 and 19.
[0028] In Figure 5 the complete arrangement of the springs can be seen. It shows the three helical compression springs 17, 19 and 16, which act respectively on the strips 13 and 13', which correspond to the socket openings 4 and 5 (or 7 and 8), and on another similar strip 20 corresponding to the opening 3 (or 6) for an earth pin.
[0029] The linearly displaceable shutter 15 of Figures 3 to 17 requires a rearward displacement in order for the linear displacement of that part to be possible to allow access of the plug pins to the contact strips 13 and 13'. As can be seen from Figures 10 and 11, the shutter 15 has upwardly extending tongues 21 whose upper end faces abut fully against horizontal shoulders 22 of stops 23 formed on the internal face of the front wall of the housing. In this way, in the closed condition of the shutter 15 and thus of the openings 4 and 5, as can be seen from Figures 10 and 11, the upper end faces of the tongues 21 remain fully against the shoulders 22, so that the shutter 15 cannot be displaced upwards by simply introducing one pin 24 of a plug, but rather it is necessary first for the shutter 15 to be rearwardly displaced by separating it from all of the shoulders 22, when it will be able to carry out its upward displacement, freeing the openings 4 and 5. Once that displacement has been carried out, ramps 21' on the tongues 21 and ramps 23' on the stops 23 will coincide, which will allow the shutter 15 a smooth displacement downwards to the closed position when pins 24 have been withdrawn, this action being forced by the combined action of the strips 13 and 13' and springs 17 and 19.
[0030] The detailed construction of the shutter 15 can be appreciated from Figures 12 to 17 inclusive, in which it can be seen that the shutter 15 has the shape of a flat central nucleus with two identical lateral arms 27 and 28 providing ample areas for cams 25 and 26 for receiving plug pins 24 to cause rearward and then upward displacement of the shutter 15. The top of the shutter 15 is formed with wider vertical slots 31, 32 and 58 and narrower vertical slots 33 to 36. Oppositely from the cams 25 and 26, the shutter 15 has the recesses 37 and 38, from the lower edges of which project small ribs 39 and 40 to give better support to the lower limbs of the strips 13' and 13. At the top and on the same face there are some small projections 41 and 42, which are formed on resiliently thin tongues 59 and 60 and which make contact under pressure with adjacent vertical webs 61 and 62 (see Figure 6) of the housing. In this way, it is possible to take up play between the shutter 15 and the front wall of the housing, and thus obtain better guidance and rocking of the shutter.
[0031] Referring to Figure 6, in order to obtain transverse rocking capability of the shutter 15, the straight bases 45 and 46 of the recesses 37 and 38 are complemented by the oblique orientations of the foremost edges 47 and 48 of the lower limbs of the strips 13 and 13' to permit the shutter 15 to rock transversely about the innermost end of the relevant edge 47 or 48 in the event that a pin 24 is inserted into only one of the relevant openings 4 and 5.
[0032] Alternatively, as shown in Figure 7, the bases of the recesses 37 and 38 can be slightly inclined obliquely, as indicated at 43 and 44, which will permit the shutter 15 to rock on the inner ends of the perpendicular foremost edges of the lower limbs of the strips 13 and 13'.
[0033] In Figure 8 it has been shown that the perpendicular bases 49 and 50 of the recesses in the shutter 15 have a predetermined spacing with respect to the similarly perpendicular edges 51 and 52 of the lower limbs of the strips 13 and 13'. This likewise permits transverse rocking of the shutter 15 and thus, in the event of only one of the cams 25 and 26 being acted on, greater blocking of the shutter 15 at its other arm, to prevent it from being unblocked.
[0034] The socket includes a system of longitudinal guidance for the shutter 15 which comprises several fins which are straight and parallel to each other, such as those indicated at 53, 54 and 55 in Figure 4. These fit into the longitudinal slots 32, 58 and 31, respectively, for the purpose of guiding the shutter 15 during its linear displacement. The shutter 15 includes a downwardly projecting central tongue 63 closely guided between two horizontal platforms 64 which support the shutter in its closed position. The shutter 15 is guided by at least the tongues 54 and 63 throughout its movement between its open and closed positions.
[0035] Figures 18 to 21 illustrate an adaptor embodiment which is considerably simpler than that of Figures 1 and 3 to 17. The shutter 15 is formed with the slots 32, 58 and 31 only, forming flat tongues 66 to 69, whilst the fins 53, 54 and 55 terminate just short of their slots 32, 58 and 31, respectively, in the closed position of the shutter. Part-way up the fins 53 and 55, they are formed with laterally inward protrusions 64 and 65, respectively. On correct insertion of the appropriate plug, substantially equal upward forces F are exerted symmetrically on the shutter 15 and it is thereby displaced upwardly into the open position shown in Figure 19 against the action of the springs 13, 13', 17 and 19, the fins 53, 54 and 55 simply being received in the slots 32, 58 and 31. If, however, a single pin 24 is inserted, then, as shown in Figures 20 and 21, an asymmetrical force F is thereby exerted on the shutter so that it is immediately slightly tilted laterally clockwise (Figure 20) or anticlockwise (Figure 21), so causing the free end faces of the tongues 66 and 67 (Figure 20) or 68 and 69 (Figure 21) to abut against the lower end faces of the fins 53 and 54 (Figure 20) or 54 and 55 (Figure 21) and the free end face of the tongue 68 (Figure 20) or 67 (Figure 21) to abut against the protrusion 65 (Figure 20) or 64 (Figure 21).
1. An electrical socket comprising a wall through which are formed openings (4,5; 7,8)
for receiving electrical contact pins (24) of an electrical plug, a shutter (15) having
a closed condition behind said openings (4,5; 7,8) and linearly movable from said
closed condition to an open condition by pushing action of said pins (24) inserted
through said openings (4,5; 7,8),and biassing means (13,13',17,19) urging said shutter
(15) into said closed condition, characterised by preventing means (23; 53-55) preventing
said shutter (15) from being opened by insertion of only one of said contact pins
(24).
2. A socket according to claim 1, wherein said preventing means (23; 53-55) comprises
stop means (23; 53-55).
3. A socket according to claim 2, wherein said stop means (23) is arranged to restrict
the linear displacement of said shutter (15) from its closed condition to deter the
shutter (15) from leaving a protection active condition, so that a displacement of
said shutter (15) away from said wall is necessary in order to enable the shutter
(15) to by-pass the stop means (23) and move to said open condition.
4. A socket according to claim 2 or 3, wherein said stop means (23; 53-55) takes the
form of projections (23; 53-55) from the inside surface of said wall.
5. A socket according to any one of claims 2 to 4, wherein said preventing means (23)
comprises ramp means (23' ,21') which facilitates return of the shutter (15) from
said open condition to said closed condition.
6. A socket according to claim 5, wherein said ramp means (23') is provided on the inside
surface of said wall.
7. A socket according to claim 5 or 6, wherein said ramp means (21') is provided on a
surface of said shutter (15) facing towards said wall.
8. A socket according to any preceding claim, wherein said biassing means (13,13') is
in the form of internal contacting laminar means (13,13') which continuously and elastically
urges said shutter (15) against the front wall.
9. A socket according to any preceding claim, wherein said openings (4,5; 7,8) comprise
two side-by-side openings (4,5; 7,8) for two side-by-side contact pins (24) of said
plug, and said biassing means (13, 13') comprises two side-by-side laminar units (13,13')
extending towards the two openings (4,5; 7,8), the foremost edges (47,48; 51,52) of
said laminar units (13,13') and their respective directly facing surface portions
(43,44;45,46) of the shutter (15) are so arranged relative to each other as to permit
limited transverse rocking of the shutter (15).
10. A socket according to claim 9, wherein said foremost edges (51,52) are spaced from
said directly facing surface portions (49, 50).
11. A socket according to claim 9 or 10, wherein said foremost edges (47,48) and said
directly facing surface portions (43,44; 45,46) diverge progressing laterally outwardly.
12. A socket according to claim 11, wherein said foremost edges (47, 48) extend obliquely
relative to said wall so as to diverge progressing away from said wall.
13. A socket according to claim 11 or 12, wherein said directly facing surface portions
(43,44) extend obliquely relative to said wall so as to diverge progressing towards
said wall.
14. A socket according to any preceding claim and further including, between said shutter
(15) and a housing including said wall, resiliently arranged projecting means (41,42)
which serves to urge the shutter (15) against the wall.
15. A socket according to claim 14, wherein said resiliently arranged projecting means
(41,42) comprises means (59,60) of leaf spring form included in said shutter (15).
16. A socket according to any preceding claim, and further comprising guide means (31,32,53-55,58)
in the shutter (15) and on said wall and whereby said shutter (15) is linearly guided,
said guide means (31,32,53-55,58) being disposed after said openings (4,5;7,8) in
the direction of movement of said shutter (15) from said closed condition to said
open condition, said guide means (31,32,53-55,58) guiding the shutter (15) throughout
its displacement from said closed condition to said open condition.
17. A socket according to claim 2, and further comprising guide means (31,32,53-55,58)
in the shutter (15) and on a housing including said wall and whereby said shutter
(15) is linearly guided, said guide means (31,32,53-55,58) being disposed after said
openings (4,5;7,8) in the direction of movement of said shutter (15) from said closed
condition to said open condition, said stop means (64,65) being provided on said guide
means (53-55) on said housing.
18. A socket according to claim 17, wherein said guide means (31,32,53-55,58) comprises
a plurality of guide fins (53-55) fixed relatively to said housing and a plurality
of guide slots (31,32,58) formed in said shutter for cooperating with the respective
guide fins (53-55), the arrangement being such that lateral tilting of said shutter
(15) from said closed condition brings said shutter (15) against said stop means (64,65)
on said guide fins (53-55).
19. A socket according to claim 18, wherein said stop means on said guide fins (53-55)
comprises an end surface portion of at least one of said fins (53,55).
20. A socket according to claim 18 or 19, wherein said stop means on said guide means
comprises lateral protrusions (64,65) from said fins (53,55).
21. An electrical socket, comprising a wall through which are formed openings (4,5;7,8)
for receiving electrical contact pins (24) of an electrical plug, and a shutter (15)
having a closed condition behind said openings (4,5;7,8) and linearly movable by the
pushing action of the pins (24), against the action of biassing means (13,13', 17,19),
from said closed condition to an open condition, which shutter (15) is guided by guide
means (31,32,53-55,58) in the shutter (15) and in the housing of the socket, which
guide means (31,32,53-55,58) is disposed after the openings (4,5;7,8) in the direction
of movement of the shutter (15) from its closed condition to its open condition, characterized
in that said guide means (31,32,53-55,58) guides the shutter (15) throughout its displacement
from its closed condition to its open condition.
22. An electrical socket, comprising a wall through which are formed openings (4,5; 7,8)
for receiving electrical contact pins (24) of an electrical plug, a shutter (15) having
a closed condition behind said openings (4,5; 7,8) and movable by the pushing action
of the pins (24), against the action of biassing means (13,13', 17,19), from said
closed condition to an open condition, and an arrangement of stop means (23) to restrict
the displacement of the shutter (15) from its closed condition to deter the shutter
(15) from leaving a protection active condition, so that a rearward displacement of
the shutter (15) is necessary, in order to enable the shutter (15) to by-pass the
stop means (23) and move to its open condition, characterised in that the stop means
(23) comprising ramp means (23') which facilitates return of the shutter (15) from
its open condition to its closed condition.
23. An electrical socket, comprising a wall through which are formed openings (4,5; 7,8)
for receiving electrical contact pins (24) of an electrical plug, and a shutter (15)
having a closed condition behind said openings (4,5; 7,8) and movable by the pushing
action of the pins (24), against elastic action of internal contacting laminar means
(13,13'), from said closed condition to an open condition, characterised in that the
laminar means (13,13') continuously and elastically urges the shutter (15) against
the wall.
24. An electrical socket comprising a wall through which are formed two side-by-side openings
(4,5;7,8) for two side-by-side connecting pins (24) of an electrical plug, and a shutter
(15) having a closed condition behind said openings (4,5; 7,8) and movable by the
pushing action of the pins (24), against elastic action of two side-by-side internal
contacting laminar units (13,13') extending towards the two openings (4,5;7,8), characterised
in that the foremost edges (47,48;51,52) of the laminar units (13,13') and their respective
directly facing surface portions (43,44;45,46) of the shutter (15) are so arranged
relative to each other as to permit limited transverse rocking of the shutter (15).
25. An electrical socket comprising a housing including a wall through which are formed
openings (4,5; 7,8) for receiving electrical contact pins (24) of an electrical plug,
and a shutter (15) having a closed condition behind said openings (4,5; 7,8) and movable
by the pushing action of the pins (24), against elastic action of internal contacting
laminar units (13,13'), from said closed condition to an open condition, characterised
in that one or more resiliently arranged projections (41,42) which serve to urge the
shutter (15) resiliently against the wall are arranged between the shutter (15) and
the housing.
26. An electrical socket comprising a housing including a wall through which are formed
openings (4,5;7,8) for receiving electrical contact pins (24) of an electrical plug,
a shutter (15) having a closed position behind said openings (4,5; 7,8) and linearly
movable from said closed condition to an open condition by pushing action of said
pins (24) inserted through said openings (4,5;7,8), biassing means (13,13' ,17,19)
urging said shutter (15) into said closed condition, and guide means (31,32,53-55,58)
in said shutter (15) and in said housing and whereby said shutter (15) is linearly
guided, said guide means (31,32,53-55,58) being disposed after said openings (4,5;7,8)
in the direction of movement of said shutter (15) from said closed condition to said
open condition, characterised in that stop means (64,65) on said guide means (53-55)
in said housing prevents said shutter (15) from being opened by insertion of only
one of said pins (24).
27. A socket according to claim 26, wherein said guide means (31,32,53-55,58) comprises
a plurality of guide fins (53-55) fixed relatively to said housing and a plurality
of guide slots (31,32,58) formed in said shutter (15) for co-operating with the respective
guide fins (53-55), the arrangement being such that lateral tilting of said shutter
(15) from said closed condition brings said shutter (15) against said stop means (64,65)
on said guide fins (53-55).
28. A socket according to claim 27, wherein said stop means on said guide fins (53-55)
comprises an end surface portion of at least one of said fins (53-55).
29. A socket according to claim 27 or 28, wherein said stop means (64,65) on said guide
means (53-55) comprises lateral protrusions (64,65) from said fins (53,55).