The present invention relates to electric sockets through which, in use, mains electrical supply is delivered via a plug insertable into the socket. - 5 There are occasions when it may be desirable to lock off the supply of electricity from a particular socket without interfering with the rest of the mains system. For example in school workshops it would be desirable to be able to prevent the use of specific

10 equipment without supervision. On work sites it could be useful to lock off particular sockets to prevent misuse of equipment. In the domestic situation such a locked socket could prevent accidents with children, as well as unauthorised use of equipment.

15 According to the present invention there is provided an electric socket comprising at least one outlet adapted to receive an electric plug, the socket being characterised by i) a lock fitted in the socket and operable between at

20 least first and second positions, ii) a movable element movement of which affects the supply of power to the outlet, iii) a cam turnable by operation of the lock between the said first and second positions between an open position

25 in which the plug can be used normally and a locked position in which movement of the said element is influenced.

The supply of power to the outlet may be affected by a switching of the electrical circuitry, or an

30 obstruction to the switching of the circuitry, or by obstruction of the insertion of a plug to the socket. ^ζ The movement of the element may be influenced by causing movement, or by preventing movement. The element may be an electrical switch, the switching-off movement of

which is caused, or the switching-on movement of which is obstructed. The element may alternatively be a safety shield which is obstructed from moving to allow the insertion of a plug. It is advantageous in some circumstances to incorporate more than one type into the same socket. Where the lock has a lock shaft a second cam, which may be eccentrically mounted, could then be mounted on the lock shaft. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a front elevation of a double switched socket outlet with a locking mechanism in accordance with the invention,

Figure 2 is a cross-section through the socket outlet of

Figure 1, Figure 3 is a longitudinal section through the socket outlet of Figure 1 Figure 4 is an exploded view of the components of the locking mechanism of Figure 1, Figures 5 is a front view of the lock shield of mechanism of Figure 1, Figure 6 is a side view of the lateral slide of Figure 3 showing the right hand socket unusable,

Figure 7 is a sketch illustrating the operation of the primary locking mechanism shown in Figure 2, Figure 8a is sketch illustrating the operation of the secondary locking mechanism shown in Figure 3, Figure 8b is a slide view of the locking plunger of Figure 8a showing the neutral position. Figure 9 is a sectional view of the apparatus of Figure 8a,

Figure 10 is a side view of the socket outlet illustrating the outlet in use, but with the

plunger primed to obstruct the outlet on removal of the plug, Figures 11a,lib,lie, and lid show underneath, logitudinal section, top and cross section views of the plunger shown in Figure 9,

Figure 12 is a side view of the socket outlet illustrating the secondary locking mechanism in the locked position, Figure 13 is a side view of the socket outlet illustrating the secondary locking mechanism in the unlocked position ready to receive a plug, Figure 14 illstrates the operation of a primary locking mechanism incorporating micro switches, and Figure 15 is a side view of the apparatus of Figure 14.

Figures 1,2 and 4 illustrate a primary locking system for an electrical mains supply socket as supplied by VOLEX. The locking system described can be used on a single switch, but all the illustrations are of a double switched socket with a body 21 attached to a face plate 22 and having for each side three access slots 23, forming an outlet for the reception of a three-pin plug 25 (Figure 10) and a moveable element in the form of a rocker switch 26 for turning on and off the electrical supply to the respective outlets. A radial pin tumbler lock 28 is fitted into the body 21 of the socket with its key hole 31 accessible from the front of the face plate 22. The lock 28 can be rotated by a key 33 through 360° and be locked and the key removed at 260° , 180° , 270° , or 0° . The lock comprises a body 28a and shaft 30 fitted through an aperture in the face plate 22 and locked by a ring nut 36. An electrically non-conductive primary lock shield 38 having a substantially 180° cam 39 on the front end (see Figure 2) is fitted over the metal body 28a and nut 36. The cam 39 has lead ramps 37 (Figure 4) at each end thereof. The shield 38 is located

firmly over the lock shaft 30, both being of double-D shape to prevent rotational slip.

Figure 2 illustrates the on and off positions of the rocker switch 26 from which it will be seen that when the switch is off (solid lines) there is a gap 40 between the face plate 22 and the main body of the socket 21. When the lock shield 38 is rotated to the position illustrated in Figure 4 the cam 39 moves into this gap 40 and so prevents one of the two switches 26 being rocked to the ON position. If the switch is ON when the lock is operated the ramp 37 causes the switch to rock to the OFF position before the cam 39 occupies the gap 40. If the shield 38 is rotated through a further 90° both switches are locked in the OFF position.

The secondary locking system (Figures 6 to 13) comprises an eccentrically mounted disc cam 42 fitted onto the lock shaft 30, separated from the shield 38 by a washer 44 and held onto the shaft by a washer 45 and nut 46. The disc cam is drilled to a double-D to prevent rotational slip on the shaft 30. The main body of the cam 42 is positioned laterally opposite the lock shield flange 39 and will move a lateral sliding plate or slide 47 by its rotation through an elliptical arc in contact with a trough 48 in the plate 47. The plate 47 is held in place, but allowed to slide, by screws 49 passing through respective slots 51 in the plate and screwed into the body 21. A safety cap 53 protects and covers the back of the trough 48. The socket has moveable elements in the form of safety shields 55 which are slidable within the body 21 of the socket to insulate the access slots 23 when not in use. These shields 55 are moveable automatically by the insertion of a plug 25 by means of a downward pressure on a head 54 of the shield 55 created by contact with a pin of the plug 25. For each socket a

respective plunger 56 is spring loaded in a recess 57 by a compression spring 58 in a housing 59. The housing 59 is fitted opposite the safety shield 55 with the plunger in line with a circular gap 61 which is in place when the safety shield is in position to insulate the socket. The housing 59 rests on the main body 21 of the socket and is balanced by a compression spring 62 in a second recess 63 which engages the surface of the socket body 21. The housing has a lip 59a. on which the underside of the plate 47 rests and slides. It also has a roof-shaped upper surface 59b which protrudes above the lip 59a. and which engages an inclined or ramped surface 47a _. on the under side of the plate 47. As the plate 47 moves across the roof of the housing 59 the housing is pushed increasingly downwardly against the resilient bias of the spring 62. Figures 9 and 13 illustrate the highest position of the housing with the tip of the plunger 56 above the shield 55. If there is a plug 25 in the outlet when the slide 47 is moved over the housing 59 depressing the plunger 56 (Figure 10) , the plunger will be spring loaded against the shield 55. If the plug is removed (Figure 12) , the shield 55 moves to cover the three socket slots leaving a gap 61 into which the plunger 56 is forced by the resilient bias. The safety shield 55 can now not be moved to allow a plug 25 to be inserted until the plate 47 has been moved to allow the plunger 56 and housing 59 to restore to their neutral positions.

The rotation of the lock 28 to create the locking positions of the shield 38 and the plate 47 is described in relation to Figures 6 to 9.

In Figure 9 the lock is at 0° and the cam 39 occupies the bottom 180° of the circumference. In this position both switches 26 can be rocked freely between the ON and OFF positions and as the plate 47 is central

the plungers 56 do not interfere with the free use of the sockets.

Figure 7 illustrates a position of the lock 90° on. In this position the cam 39 extends into the gap 40 on one side only of the double socket. In this position the left hand switch 26 is locked and the right hand switch can be used. The disc cam 42 has moved the plate 47 to the right. This does not effect the left hand socket but it operates the housing 59 and plunger 56 as described above, (see Figure 6) If there is already a plug in the socket, the outlet can be operated as usual and mains supply is delivered via the outlet when the switch 26 is on. However if the plug is removed, or if there is no plug in the socket, it is not possible to insert a plug into the socket with the lock in this position.

Rotation of the lock through a further 90° causes the cam 39 to lock both the switches 26 and the sliding plate 47 remains central (Figures 8 and 9} .

The final locking position, 270° , is a mirror image of that illustrated in Figures 6 and 7 in that the right hand rocker switch 26 is prevented from moving and the sliding plate 47 has been moved to the left so preventing reinsertion of a plug into the left hand socket. The only metal parts in the assembly are the key 1, the lock 28, the retaining nut 36, the lock washer 45, the nut 46 and the plunger springs 62 and 58. The other parts can be manufactured in durable non conductive material. If required the lock 28 and the lock ring 36 can be earthed by extending the earthing wiring already in the socket.

It will be appreciated that the two locking systems can be used independently of one another. In a single switched socket, the cam profile on the lock shield arrangement is sufficient.

In an unswitched double socket, it would be sufficient to operate a disc-cam controlled sliding arrangement to obstruct the socket slots 23 without the need for a cam 39 on the lock shield 38, and by having the bearing faces of the ramp 47a, in parallel

(illustrated as 47b in dotted lines on one end of the plate 47 of Figure 9) .

Where the rocker switches are not centrally mounted, or in an unswitched socket, it may be preferable to use microswitches. If the microswitches are positioned adjacent the cam 39 similarly to the switches 26 then the identical locking mechansim can be used. Figures 14 and 15 illustrate such an arrangement in which movable elements in the form of microswitches 71 are disposed adjacent the lock shield 38 with their plungers 72 in the path of the cam 39. As the shield is turned so the ramps 37 push the plungers 72 inwardly to operate the microswitch. This can be used directly to break the electric circuit to the relevant socket or it can be used switch a remote rocker switch.

There are a number of advantages with such locking arrangements:

Sockets according to the invention can replace existing sockets with no need to modify boxes or electrical wiring. Moreover the key for the tumbler lock cannot be inserted into the socket slots as it is the wrong shape. There is also the advantage with a double socket that one socket can be locked off without interfering with the supply of current to a plug already in the other socket until that plug is removed, rendering both inoperable.