EP0949716A2

EP0949716A2 - Plug protectors

Info

Publication number: EP0949716A2
Application number: EP99301592A
Authority: EP
Inventors: Mark Bagnall
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1998-04-08
Filing date: 1999-03-03
Publication date: 1999-10-13
Also published as: GB2336727B; EP0949716A3; GB9807447D0; GB2336727A; GB9904752D0; GB2336727A8

Abstract

A protector 1 for a mains electrical plug 2 has a plastics housing 10 pushed over the pins 22 to 24 of the plug. A spring metal plate 30 extends transversely across the housing having a tongue 32 inclined forwardly at an angle of about 10 degrees. The tongue 32 engages the earth pin 22 of the plug 2 and grips the pin to prevent it being pulled out rearwardly. The tongue 32 is released by a key 52 inserted in the protector 1 on the rear surface of the tongue and rotated to push the tongue forwardly out of engagement with the pin 22, thereby enabling the protector to be removed from the plug 2.

Description

This invention relates to plug protectors of the kind including a housing arranged to be locked onto a plug.
The invention is more particularly concerned with devices for preventing the use of electrical plugs.
One way of preventing unauthorised use of mains-operated electrical equipment is to use some form of plug protector, which prevents the plug being inserted in the mains socket and thereby prevents power being supplied to the equipment. For example, a parent might wish to prevent children using a television or dangerous electrical equipment.
The plug protector usually comprises some form of housing that encloses the plug and prevents insertion of the pins of the plug into a mains socket. A padlock or similar device is often used to secure the protector on the plug. Examples of plug protectors are described in, for example: GB2278244, GB2259194, GB2231451, US5052939, US4957446, US4957445 and US4592607.
Previous protectors that rely on a padlock or similar device can be relatively expensive, because of the cost of the padlock. Protectors that completely enclose the plug can be bulky, making packaging and point-of-sale display more difficult.
It is an object of the present invention to provide an improved plug protector.
According to the present invention there is provided a plug protector of the above-specified kind, characterised in that the protector includes a gripping member displaceable between a first state in which the gripping member grips the surface of a pin on the plug and prevents withdrawal of the protector from the plug and a second state in which the gripping member allows removal of the protector from the plug, and a key removable from the housing and operable to displace the gripping member between the first and second states.
The gripping member preferably extends substantially transversely of the pin and is a spring metal tongue having an end arranged to grip the pin. The gripping member may include an outer spring metal frame defining a space between the frame and the end of the tongue within which the pin is inserted. The tongue may be inclined at an angle of substantially 10 degrees to the frame in its natural position out of engagement with the pin. The key is preferably insertable between one surface of the frame and an opposite surface of the tongue and may be rotatable about its axis to move the gripping member to its second state. The protector preferably includes a plastics housing having a sleeve enclosing the pin. The plug may be a three-pin mains plug, the gripping member being arranged to grip an earth pin of the plug.
A plug protector for a UK three-pin mains plug, will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1: is a perspective view of the front of the protector;
Figure 2: is a view of the rear of the protector;
Figure 3: is a view of the rear of the protector with its cover plate removed;
Figure 4: is a partly-sectional side elevation view of the protector on a plug and in a locked state;
Figure 5: is a partly-sectional side elevation view of the protector on a plug and in an unlocked state;
Figure 6: is a perspective view of the gripping member of the protector; and
Figure 7: shows the key of the protector.

The plug protector 1 has a hollow housing 10 moulded of a rigid plastics such as nylon or ABS. The housing has a generally triangular base 11 from which project three sleeves 12, 13 and 14 of rectangular section, the sleeves being closed at their forward ends and open at their rear ends to receive respective pins 22, 23 and 24 of a mains plug 2.
The plug protector 1 includes gripping means in the form of a plate 30 (most clearly shown in Figure 6) of zinc-plated spring steel about 0.5mm thick and extending transversely within the housing 10. The plate 30 tapers in width along its length and comprises an outer frame 31 and a tapered tongue 32 extending longitudinally within the frame 31. The tongue 32 inclines forwardly out of the plane of the frame by an angle of 10° in its natural state. The wider end 33 of the tongue 32 is attached with the frame 31. The narrower end 34 of the tongue 32 is free and spaced from the facing inside edge 35 of the frame 31 to form a rectangular aperture 36 through which the earth pin 22 of the plug 2 can extend. The gripping plate 30 extends horizontally within the base 11 of the housing 10, its wider end being located between the two sleeves 13 and 14. The aperture 36 in the gripping plate 30 is aligned with the open rear end of the earth sleeve 12. The gripping plate 30 is retained in the housing 10 by means of a plastics cover plate 40 bonded into the rear of the base 11. The cover plate 40 has the same general shape as the gripping plate 30 and has a rectangular aperture 41 aligned with the earth sleeve 22. The cover plate 40 leaves exposed openings 13' and 14' into the rear end of the sleeves 13 and 14 respectively. The region 15 of the base 11 adjacent the earth sleeve 22 is spaced above the forward surface of the gripping plate 30 so as to allow the tongue 32 to be deflected forwardly.
The base 11 of the housing 10 has a keyhole shape aperture 50 in one side aligned close to the free end 34 of the tongue 32 and between the forward surface of the frame 31 of the plate 30 and the rear surface of the tongue. There is a corresponding recess (not shown) on the inside surface of the housing 10 on the opposite side of the base 11. The aperture 50 is shaped to receive a key 52, as shown in Figure 7. The key 52 is of metal, having a shaft 53 of circular section, a handle 54 at one end and a laterally-projecting rectangular bit 55 close to its opposite end. When the key 52 is inserted in the housing 10 through the aperture 50 to its full extent, its forward end locates in the recess and the bit 55 lies between the rear surface of the tongue 32 and forward surface of the frame 31.
The protector 1 is fitted to the plug 2 simply by aligning the pins 22 to 24 of the plug with the openings 41, 13' and 14' in the rear of the protector, so that the pins can be slid forwardly into respective ones of the sleeves 12, 13 and 14. The distance between the free end 34 of the tongue 32 and the facing inside edge of the frame 31 is such that the tongue will contact one face of the earth pin 22 and be displaced a small distance further forwards as the pin slides over the end of the tongue. When the plug 2 is fully inserted, the end 34 of the tongue 32 lies in a position where it is displaced forwardly at an angle slightly greater than its natural 10°, so that the end of the tongue bears resiliently on the surface of the pin 22 substantially transversely. It can be seen that if any attempt is subsequently made to pull the protector 1 off the plug 2, this will cause the tongue 32 to be pulled rearwardly and bite firmly onto the pin 22, gripping it with sufficient force to resist removal of the protector. The protector 1 is removed from the plug 2 by inserting the key 52 and twisting it through 90° so that the bit 55 engages the rear side of the tongue 32 and moves it forwardly to the position shown in Figure 5, thereby allowing the protector to be removed from the plug. The key 52 has to be rotated back to its initial position in order to remove it from the housing 10.
The plug protector of the present invention can be made at low cost because of its simple construction and because it does not require a separate padlock or the like. The protector locks directly onto the pins of the plug and does not need to enclose the plug, so it can be used with plugs having various different shape bodies, such as on bulky plug-in transformers, time switches, thermostats or the like. Because the protector does not need to enclose the entire plug it is not confined to use on plugs connected to the end of a flying lead but can also be used, for example, on plugs mounted directly on equipment housings, such as on computer housings. The protector can be made very compact leading to a low material cost, and facilitating packing and display. The protector can be used to prevent unauthorised use of electrical equipment, such as to prevent children using dangerous appliances in the home, or to prevent unauthorized equipment in the office. The protector can also be used to prevent use of faulty appliances, for example, if an appliance fails to pass a safety test, the tester can easily fit a protector to prevent use of the appliance until it has been repaired. In such cases, the protector could be brightly coloured or otherwise conspicuously marked to show that no attempt should be made to use the appliance.
The protector need not grip onto the earth pin but could grip on any other pin, or onto several pins. The protector need not fully enclose the pins of a plug providing that the protector provides sufficient obstacle to insertion of the plug in a socket. It will be appreciated that the invention is not confined to use with UK three-pin mains plugs but could be used on other plugs with different numbers of pins or with pins of different shape, such as round pins.

Claims

A plug protector (1) including a housing (10) arranged to be locked onto a plug (2), characterised in that the protector includes a gripping member (30, 32) displaceable between a first state in which the gripping member (30, 32) grips the surface of a pin (22) on the plug (2) and prevents withdrawal of the protector (1) from the plug and a second state in which the gripping member (30, 32) allows removal of the protector from the plug, and a key (52) removable from the housing (10) and operable to displace the gripping member (30, 32) between the first and second states.
A plug protector according to Claim 1, characterised in that the gripping member (30, 32) extends substantially transversely of the pin (22).
A plug protector according to Claim 1 or 2, characterised in that the gripping member includes a spring metal tongue (32) having an end (34) arranged to grip the pin (22).
A plug protector according to Claim 3, characterised in that the gripping member (30, 32) includes an outer spring metal frame (31) defining a space (36) between the frame and the end (34) of the tongue (32), and that the pin (22) is inserted within the space (36).
A plug protector according to Claim 4, characterised in that the tongue (32) is inclined at an angle of substantially 10 degrees to the frame (31) in its natural position out of engagement with the pin (22).
A plug protector according to Claim 4 or 5, characterised in that the key (52) is insertable between one surface of the frame (31) and an opposite surface of the tongue (32).
A plug protector according to any one of the preceding claims, characterised in that the key (52) is rotatable about its axis to move the gripping member (32) to its second state.
A plug protector according to any one of the preceding claims, characterised in that the protector (1) including a plastics housing (10) having a sleeve (12) enclosing the pin (22).
A plug protector according to any one of the preceding claims, characterised in that the plug is a three-pin mains plug (2), and that the gripping member (30, 32) is arranged to engage an earth pin (12) of the plug.