GB2165403A - A safety guard for electrical plugs - Google Patents

Abstract

A safety guard for the plug of a conventional electrical plug and socket connector consists of a retractable or removable barrier member which may be locked in a position to prevent the insertion of a plug pin into its respective socket in the coacting part of the connector. The barrier member is either a separate dummy socket (12) carrying a device (18) for securing the plug therein (fig 2), or a retractable element (32) projecting from the base of the plug (30) which, in its operative position, is interposed between a plug and its socket (eg fig 6). <IMAGE>

Description

SPECIFICATION A safety guard for electrical plugs This invention relates to electrical plugs, and more particularly but not exclusively, to plugs ofthe conventional three-pin, 13-amp type customarily used for connecting an electrical appliance to the domestic power supply. One object of the present invention is to protect an electrical appliance from unauthorised use.

This is particularly relevant to mobile appliances having dangerous moving parts-e.g. hedge-trim mers-which are accessible to children or inexpert users who can do themselves or other people, or property, serious damage by plugging the appliance in to a live supply.

So-called safety socket outlets are almost universal ly used wherein the mouths of the current-carrying sockets are covered, when not in use, by insulating shutters. But such precautions against accidental injury are unavailing when a legitimate plug is inserted into the socket. The danger is then transferred to the appliance at the other end of the cable. It is to avoid this transfer that the present invention seeks to provide a baulkto the energisation ofthe appliance.

The present invention is a safety guard or protector which can be used to shield the pins of the plug and preventtheirinsertion into the socket until it is positively removed or rendered inactive. Although the invention is primarily directed to the protection of an ordinary domestic plug, its scope embraces industrial plugs, and also envisages, as an alternative, the design of a special-bodied plug in which the protection is incorporated.

According to the present invention, a safety guard or protectorfor an electrical plug comprises a lockable rigid barrier adapted, in its operative position, to occupy at least some ofthe space between or around the pins, or both, fortheirfull lengths orthereabouts, and means for locking it in its operative position.

The basic principle of the invention is the blanking off, in actual factor in effect, ofthe space around and between the pins of a plug in such a way as to prevent the insertion thereof into a complementary socket outlet. Thus, ifthe pins are enveloped in a rigid detachable shield, or if the space between them is occupied to the depth of their exposed lengths by a detachable solid block; or if a retractable rigid rod extends parallel to the pins at approximatelythe mid-pointbetweenthem, all these constitute barriers which obstruct or prevent the insertion ofthe plug into its socket. The first two alternative forms of barrier represent an article which is normally separate from the plug, and is therefore available for use as a safety guard with any standard size of plug.The third alternative, however, involves a special design of plug and is therefore peculiarto each specific appliance.

The "blanking" principle is common to all three alternatives, and ifthe rendering ofthe respective guard operative depends on a special tool or key, the safety factor ofthe device is enhanced.

The barrier or safety guard in thefirsttwo alternatives may be a body into or around which, in its operative position, the pins ofthe plug can be fitted for substantiallytheirfull lengths, and the locking means includes a rigid bridge or keep pivoted on the bodyfor angular displacement between an unlocked position in which the appropriate face of the body is exposed forfitting ofthe plug and a locked position in which it spans the back of the plug so asto prevent removal of the latter. A lock mechanism secures the bridge in its operative position.

Preferably, the lock is a dead bolt mechanism operated by a key, the bolt engaging a hole in the bridge when the lock is operated.

One practical embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure lisa perspective view of a safety guard for a standard 3-pin plug when in its inoperative state; Figure 2 is a viewsimilarto Figure 1 showing a plug engaged with the guard while the latter is in its operative position; Figure 3 is an end elevation ofthe assembly shown in Figure 2; Figure 4 is a part-sectional underplan view, the section being taken on the plane A-A of Figure 2; Figure 5 is a plan view of an alternative design, and Figure 6 is a longitudinal section through another modification in which a 3-pin plug has its own built-in safety guard.

Referring first to Figures 1-4 ofthe drawings, a 3-pin plug 10 forthe supply of powerto an electrical appliance (not shown) is protected against inadvertent or improper connection to a complementary power supply socket by being held captive in a safety guard 12. This is a solid block or hollow shield of any convenient, but preferably insulating, material such as a synthetic resin plastic which constitutes a barrier between the plug and its socket outlet. If it takes the form of a solid block, as represented in Figures 1-4, its "top" face 14 is pierced bythree holes 16 which are replicas of the sockets in a socket outlet.If it is a hollow shield, there will be no "top"face 14 except as a geometrical concept, the boundaries ofthe space which substitutes forthetop face being substantially identical to the side walls ofthe solid block illustrated.

'Whether solid or hollow, the barrier structure 12 has pivoted thereon a bridge or keep 18 of a size to fit snugly over the plug 10 when in the operative position (Figures 1 and 3). The pivot 20 is placed at a point which will allowthe bridgeto be swung overthe front (or rear) end of the plug lotto orfrom its operative position in which it prevents removal ofthe plug from the body 12.

In orderto retain the bridge 18 in its locking or operative position (Figures 2 and 3), one ofthe limbs 1 8a is pierced at 22 by a hole of a size and shape to permit the passagetherethrough of a dead bolt 24 (Figures 1 and 4) movable on an axis perpendicular to the limb 18a. The dead bolt 24 is part of a lock (not shown) fixed within the block 12 and operable by a key inserted through a keyhole 26 in the base 28 ofthe block.

Thus,when an electrical appliance having a plug 10 in its power supply circuit is to be rendered safe against accidental or unauthorised energisation,that plug can be fitted in the block 12 byway of the socket holes 16forthe pins, and the plug can then be rendered inaccessibleto unauthorised users by swinging up the bridge 18 and locking it in the operative position by actuation ofthe bolt 24.

Figure 5 is a variant of the guard device shown in Figures 1-4 in thatthe pins ofthe plug 10 are not inserted into holes 16 but partly straddle a smaller block 13, as indicated at 15, in such a waythatthe plug 10 cannot be separatedfrom its block 13 in any direction otherthan parallel to the pins. The bridge or keep 18 is substantially the same as its counterpart in Figures 1-4, and the locking arrangement can be the same as ordifferentfrom that described above.

The foregoing designs of safety guard are usable for all plugs 10 ofthe same size and pin configuration.

Figure 6, however, shows a specially designed plug 30 having its own built-in guard intheform of a retractable barrier post or pillar 32. The base 34 ofthe plug 30 which carries the pins 36 is pierced perpendicularto its plane on an axis approximatelysymmetrically located with respectto the pins 36. Atube 38 is secured to the body 34 so as to lie on this axis, and projectsthroughthe detachable cover 40 ofthe plug as indicated at 39. The internal wall surface ofthe tube 38 is formed with a quick-pitch screwth read 42. The head ofthe post 32 slidesfreelywithin this internal screw-thread and has a tooth 44 projecting laterally therefrom to engagethescrew-thread 42.The post 32 is non-circular in transverse cross-section and passes through a plate 46 fixed on the underside ofthe base 34 which is piercedwith a hole of the same shape as the cross-section ofthe post to prevent rotation thereof about its axis. Thus, on rotation of the captive tube 38 the post 32 is made to advance and retract axially. By choosing the dimensions of the parts so that the exposed tip 33 of the post 32 moves from a retracted position which is almostflush with the plate 46 to an operative position which is substantially flush with the tip of either ofthe power supply pins, the post 34 acts as a barrier orguard to prevent insertion ofthe plug 30 into its socket outlet until it is retracted.

Rotation of the tube 38 can be by any convenient means. The dome shape of the end 39 ofthe tube which projects through the cover 40 is purely symbolic in that it is intended to indicate an optional configuration which may require the application of a special tool orkeyto rotatethetube38.

Clearly, otherforms of retractable guard according to the present invention can be designed to replace the post 32 and threaded tube 38, buttheirfunction will remain that of a barrier against insertion ofthe plug 30 into its socketoutletwithoutthe performance of a deliberate actto retractthe guard, and such act can be made difficult or impossible for an unauthorised person in any convenient way. The tip 33 ofthe post 32 can be steadied by means of a rigid insulating plate (not shown) secured to its free end and pierced with holes to allow itto slide overthe pins 36 with the mimimum practicable friction.

Instead ofthe retractable barrier post 32 in the plug 30, a guard in theform of a stirrup (not shown) may be pivoted on the body 34 ofthe plug about a horizontal transverse axis which intersects the axis ofthe earth pin orofthesL:pply pins, this stirrup guard acting in its operative position asa barrierto prevent the earth in orthetwo supply pins, respectively, from entering their respective sockets, the guard being secured in its operative position by any convenient locking mechanism.

The plug 10 or 30 described above will normally be used for the connection of an appliance to its source of motive power, as in the case of an electric hedge trimmer instanced above. It is, however, to be understood thatthe invention is equally applicable to situations where the motive powerfortheappliance is derived from another source, but the plug is part of a circuitwhich is used to supply a triggerforthe motor driving the appliance.

In this specification, a lock means a device which is operableto maintain a barrier element in its operative position until the plug is required to be used. The manner of releasing the lock to permitthis to be done is optional, atthe requirementofthe user. Itis not necessaryto adopta design of lock requiring operation by a removable key. The crucial function of the lockisto maintain the safety guard in its operative position until such time as it is deliberately released by whatever means. Theterms "locking" and "lockable" have compatible meanings.

Claims (12)

1. Asafety guardforan electrical power supply plug comprising a barrierelementadaptedtobe interposed between the plug and its coacting socket outlet in such a way as to prevent the current-carrying pins from entering the relevant sockets, and lockable means for retaining the barrier element in its operative position.

2. A safety guard according to claim 1 wherein the barrier element is a block adapted to receivethe pins ofthe plug and to which the plug is clamped by a releasable retainer.

3. Asafety guard accordingto claim 2 wherein the block has its top face pierced with holes to register with and acceptthe plug pins when in the operative position.

4. Asafetyguard according to claim 2 wherein the blockhas an open top and surroundsthe plug pins when in the operative position.

5. Asafetyguardaccordingtoclaim 2whereinthe top ofthe block is not coextensive with the base ofthe plug but coacts with the pins in such a way asto prevent separation ofthe plug in any direction other than parallel with the pins.

6. A safety guard according to anyofclaims 1-5 wherein the lockable means comprises a bridge pivotally connected to the barrier element and movable angularly between an inoperative position in which the plug is separable from the safety guard and an operative position in which it retains the plug in engagement with the barrier element.

7. Asafety guard according to claim 6 wherein a lock is mounted on the barrier element and is operable to retain the bridge in its operative position.

8. Asafety guard according to claim 1 wherein the barrier element is carried on the plug itself.

9. Asafety guard according to claim 8 wherein the barrier element is a reciprocable rigid member located between the pins and reciprocable on an axis parallel to those of the pins between an inoperative position in which its extremity is retracted towards the base of the plug sufficiently to allow the pins to engage fully in their respective sockets and an operative position in which itsextremityliessubstantiallyflush with the extremities ofthe current-carrying pins.

10. A safety guard according to claim 8wherein the barrier element is a rigid generally U-shaped member pivotally mounted at its ends on the base of the plug and adapted to be swung between an inoperative position in which the yoke ofthe U is clear ofthe path of entry of any pin into its respective socket and an operative position in which it underlies at least one ofthe pins so asto obstruct its entry into its respective socket.

11. A safety guard for an electrical power supply plug substantially as herein before described.

12. A safety guard according to claim 11 substan tially as described herein with reference to Figures 1-4, Figure 5, or Figure 6 ofthe accompanying drawings.