GB2067365A - Electric plugs - Google Patents

Abstract

An electric plug comprises a base member (6,56) and a cover member (8,62) adapted to be secured together, each comprising a recess-defining part (28,60; 30,67) which together define an aperture through which a cable may extend into the interior of the plug. In a first embodiment the base member (6) and coves member (8) are secured together by at least one screw and the aperture 26 is defined by a tongue (30) on one part and a corresponding projection (28) on the other (see Figure 2). Alternatively (Figure 8) the plug includes a resilient portion (60) which is deformed by applied pressure and hence grips the cable (72). Mounting means for pins (16,20) comprise apertures (21) in the pins into which protrusions (41) on the base fit, the protrusions being readily deformable to allow easy positioning of the pins in the base. A fuseholder (Figure 5, not shown) is mounted in the base (6,56) by frictional engagement of a projection (47, Figure 5, not shown) with a slot in the base. <IMAGE>

Description

SPECIFICATION Improvements relating to electric plugs In the use of electric appliances, the leads of a current-carrying cable must be connected to the terminals of an electric plug, and to prevent strain on the cable being taken at the point of connection, it is desirable to utilise additional means to hold the cable against withdrawing movement relative to the plug. One such means is provided by opposed clamping strips secured to the plug on screws, such that, on rotation of the screws, the clamping strips may be caused to move relative to one another. In use, the screws are rotated to separate the clamping strips, the cable is threaded between the clamping strips, and the leads thereof are connected to the terminals of the plug.The screws of the plug are then rotated to cause the clamping strips to be moved together, to clamp the cable therebetween, and thereby to prevent movement of the cable relative to the plug.

Presently available means for securing a currentcarrying cable to a plug are in general either expensive in their construction or time consuming in their operation, and it is one of the various objects of this invention to provide a means, adapted to secure a current-carrying cable against withdrawing movement relative to the plug, which means is both inexpensive in its construction and simple in its use.

According to a first aspect of this invention there is provided an electric plug comprising a base member and a cover member adapted to be secured together by at least one screw, the base member and the cover member each comprising a recess-defining part which, when the cover and base are secured together, define an aperture through which a cable may extend into the interior of the plug, the construction and arrangement being such that the size of the aperture may be varied, to accommodate cable of differing sizes, by varying the degree of tightening of the screw or screws.

Preferably, the recess-defining parts of the base member and the cover member are afforded with formations, such as toothed formations, adapted when a cable is within the aperture to grip the cable to resist with-drawing movement of the cable from the interior of the plug. Conveniently on at least one of the base member and the cover member, preferably the cover member, the recess-defining part is afforded by a tongue extending (when the base and cover are secured together) towards the recessdefining part of the base.

Preferably the cover is adapted for hinging movement relative to the base, such that tightening of said screw causes relative angular movement between the base and cover, to vary the size of the aperture.

Alternatively, the cover and base may be adapted to be secured together by one or more screws, so arranged as to ensure generally rectilinear movement of approach and separation between the cover and the base, to vary the size of the aperture.

If desired, the base and cover may be moulded in one-piece, being connected together by a web of material.

An electric plug in accordance with the first aspect of this invention may be moulded of a relatively resilient material, so that a cable is clamped between the recess-defining parts of the cover and base with some resilience. Alternatively however, the base and cover may be moulded from a relatively rigid material resilient clamping of the cable being afforded by a resilience of the cable itself.

According to a second aspect of this invention there is provided an electric plug comprising a base member and a cover member which, when the plug is assembled, are secured together and which define an aperture through which a cable extends to the interior of the plug, wherein a part of the plug which defines said aperture is resiliently deformable, and the size of the aperture may be enlarged by pressure acting against the said part.

In this manner, when the base member and the cover member are separated, an electric cable is connected to the terminals of the base member. On resecuring the cover member to the base member, the cable will be gripped by the said part, conveniently against a further part of the plug, to remove strain on the cable from its connection with the terminals.

Thus, preferably the position adopted by the said part when at rest and when the base member and - the cover member are secured together, is such as to render the aperture smaller in size than the crosssectional area of the thinnest wire likely to be used with the plug. Indeed, if desired, at rest the said part may entirely close the apertures.

Preferably, the base member and/or the cover member are moulded from plastics material, and the said part is integral with the remainder of the base or the cover.

Preferably, the said part of the base or cover is disposed opposite to a further part of the cover or base, respectively: thus, upon assembly of the cover and the base, progressive deformation takes place of the first part whilst it remains stationary relative to said further part.

Conveniently, said further part is less resilient than the first said part.

Another difficulty encountered in a conventional plug is that the pins are normally held in position in the plug base by the plug cover, and when the cover has been removed, for example for rewiring, refusing or the like, there is a tendency for the pins to fall out from the base.

According to a third aspect of this invention there is provided an electric plug comprising a base member and a cover member which when the plug is assembled are secured together, the base member comprising apertures through which pins of the plug extend from the interior thereof, wherein the pins are provided in side faces thereof with at least one aperture into which a protrusion on the base member extends, the construction and arrangement being such that the protrusion may be readily deformed to permit movement of the pin into a desired position in the aperture, but which restrains subsequent movement of the plug pin from said desired position in at least one direction.

in this manner, on initial assembly of the plug, the pins may be inserted in the base member relatively easily, and are unlikely to fall from the base member on subsequent removal of the cover member from the base member, such as for example when the plug is being wired or rewired.

If desired, the construction and arrangement may be such that, assembly of the cover member and base member is effective to restrain or to further restrain deformation of the protrusion, in a manner which renders it less liable to removal from the aperture in the side face of the pin.

Thus, a face of the protrusion may be inclined, such as that face which, when the pin is being inserted through the aperture into its desired position, is engaged by the pin. In this manner, engage mentofthe protrusion by the pin, and deformation of the protrusion, is rendered more easy. However, forces on the pin when in its desired position, in the opposite direction (that is, tending to push the pin towards the interior of the plug) may be taken on planar, abutting faces of the protrusion and pin.

Afurther difficulty encountered in a conventional plug is the securing of a fuse terminal to the plug base. In particular, wheras the pins are inserted in the plug pin apertures, and one fuse terminal is carried by the live pin, the other fuse terminal (which is connected to wire-connecting means) is in general merely located in a recess, to be clamped in position by the cover when it is secured to the base. This renders said other fuse terminal particularly liable to separation from the plug base, and particularly when heavy duty wiring is connected to the connecting means, may be difficult to relocate and hold in said recess, whilst the cover is being manipulated into position relative to the base.

Thus, it is a further object of this invention to provide a method of securing a fuse terminal to a plug base, in a manner in which relative movement therebetween in the event of separation of the base and the cover is reduced.

According to a fourth aspect of the invention there is provided an electric plug in which a terminal member thereof is adapted to be inserted in an aperture or recess, part of or secured to the terminal member frictionally engaging the wall of the plug bounding said aperture or recess.

Thus, insertion of said part into the aperture or recess may involve deformation of either said part or recess, or of the wall bounding said aperture or recess. Said part may be resiliently deformable (for example be made of relatively soft plastics material), being compressed upon the insertion of the terminal member or said part into the aperture or recess.

Preferably however said part is provided by a fixing member of relatively rigid material secured to or extending from an underside of the terminal member, and which resiliently deforms the wall bonding the aperture or recess. Preferably, said fixing member is of metal, and comprises serrations.

Where the terminal member is a fuse terminal, conveniently it comprises a base plate, and two terminal tags extending therefrom at opposite ends, each of which is adapted to be inserted into an associated aperture or recess, to provide fixing members for the fuse terminal at opposite ends of the base member.

Such a construction allows the fuse terminal to be located in a desired position on the base plate of an electric plug relatively easily, resisting undesired movement of the fuse terminal from its desired position, yet allowing removal of the fuse terminal from the base member, should this become desired.

The features set out in the last five preceding paragraphs may be utilised in an electric plug in accordance with the third aspect above set out, and/or one of the first and second aspects, but may if desired be used in fused plugs of other construction.

There will now be given detailed descriptions, to be read with reference to the accompanying drawings, of two electric plugs which are preferred embodiments of this invention, and which have been selected to illustrate the invention by way of example.

In the accompanying drawings: Figure 1 is an underneath plan view of the plug which is the first embodiment of this invention; Figure 2 is a sectional view, taken on the lines 2-2 of Figure 1; Figure 3 is a plan view of the base member of the plug, the cover thereof having been removed; Figure 4 is a sectional view, taken on the lines 4-4 of Figure 1; Figures 5 and 6 are views illustrating the securing of a fuse contact to the plug; Figure 7 is a view corresponding to Figure 3, of the plug which is the second embodiment of this invention; Figure 8 is a view corresponding to Figure 2 of the plug shown in Figure 7; and Figure 9 shows an underside construction of the first embodiment as shown in Figure 2.

The plug which is the first embodiment of this invention comprises a base 6 and a cover 8 adapted to be secured together by two screws 10, inserted through apertures 12 in the base and threadedly received in bores of the cover. The base and cover are moulded from plastics material, and the plug is provided with conventional live, neutral and earth terminals 16, 18 and 20 respectively.

At an end portion adjacent to the earth terminal, the base is provided with an exterior shoulder 22, and the cover is provided with an in-turned lip 24, adapted to engage behind the shoulder 22. On the other sides, the side wall of the cover extends around the side wall of the base.

At the end portion of the plug opposite to the earth terminal, the plug is provided with an aperture 26, through which electric cable connected to the plug pins extends. The aperture 26 is defined by recessdefining parts of the base and cover, specifically an interior wall portions 28 ofthe base 6, and a tongue 30 of the cover 8.

In the use of the plug which is the first embodiment of this invention, with the cover separated from the base, the conductive elements of the cable are connected to the three terminals in conventional manner, as shown in Figure 3.

The lip 24 of the cover is then engaged behind the shoulder 22, and the screws 10 inserted into the threaded bores of the cover, drawing the cover towards the base, and the tongue 30 into engagement with a cable located in the aperture 26, firmly gripping the cable, and in particular (by virtue of serrations 29 and 31 on the wall portion 28 and tongue 30, respectively) preventing withdrawal movement of the cable from the plug, and thereby removing strain from the connection of the conductive elements with the plug pins.

The distance of sepa ration between the wall portion 28 and the tongue 30, as shown in full lines in Figure 2, represents the smallest diameter cable with which the plug is likely to be used: conversely, the position adopted by the front face of the cover, and the tongue 30, as shown in dotted lines in Figure 2, illustrates the largest diameter with which the plug may be used.

In the first embodiment above described, the size of the aperture 26 is decreased to grip the cable by tightening of the screws 10, which effects a pivotal or hinging movement between the base and cover about a pivot axis defined generally by the line of contact between the lip 24 and the shoulder 22. In use, the screws 10 will be thightened to a degree which causes an adequate gripping of the cable between the wall portion 28 and the tongue 30, such gripping being aided by resilient deformation ofthe cable.

Whereas the base and cover 6, 8 are shown in Figure 1 as being moulded in two parts, if desired the base and cover may be produced as a single moulding, as is illustrated in Figure 9, the base and cover in such a construction being connected together by a web 55 of resilient plastics material.

Thus, from the position shown in Figure 9, the cover 8 may be hinged generally about the web 55 into a position corresponding to that shown in Figure 2, with the lip 24 engaging beneath the shoulder 22.

Whereas as above described, the aperture 26 is closed by arcuate movement of the cover 8 relative to the base 6, if desired the cover may be mounted for rectilinear movement relative to the base, for example by the use of three screws arranged generally in the form of a triangle, or by a single centrally positioned screw.

As is shown in Figures 2 and 4, the three terminals 16,18 and 20 each extend through a respective pin aperture 36, 38 and 40, having been inserted therein to the desired position, as shown, from the interior of the base.

Each of the pins is provided, extending into the pin through the face thereof of the smallest dimension, with two apertures 17, 19 and 21 respectively: extending into each of the apertures 36,38 and 40 are pairs of respective protrusions 37,39 and 41.

Inner faces of these protrusions are angled, and by the pressing of the appropriate pin into the aperture, the wall portions bounding the aperture may be outwardly deformed, permitting passage of the pin through the aperture, until the protrusions 37, 39 or 41 enter the associated aperture 17, 19 or 21.

When in this position, forces acting on the pins, tending to move the pins towards the interior of the plug, are taken by abutting planar faces of the protrusion and pin, effectively preventing such movement. Forces acting on the pin, tending to move the pin further outwardly, are taken by abutment of an enlarged head of the pin with planar surfaces of the plug face, bounding the aperture.

If desired, the pin apertures may be constructed n a manner such that, the ability of the protrusions thereof for deformation is easier whilst the cover 8 is separated from the base, and an additional effect of the cover, when secured to the base, is to restrain or make more difficult such deformation of the protrusions as would be necessary for relative movement to take place between the plug pins and the base.

As can be seen in Figure 3, the live lead of the cable is connected to a terminal member 42 of a fuse terminal 43, the opposite fuse terminal 44 being connected to the live pin 16.

The fuse terminal 43 is formed from sheet metal as a pressing, and as can be seen from Figures 5 and 6 comprises a base plate 45, and two fuse-gripping arms 46 extending upwardly therefrom.

At each end of the base plate, there is provided a down-turned tag 47, each of which is provided on its outer side faces with serrations. By location of the two tags 47 in corresponding slots 48 of the base member, the fuse terminal 43 may be pressed into a desired position, and restrained against movement therefrom, by virtue of the frictional engagement between the tags 47 and the walls of the base bounding the slots 48. - In the plug which is the second embodiment of this invention, the means by which the plug pins are secured within their respective apertures is similar to that illustrated and described above in respect of the first embodiment, and will not subsequently be described. In the second embodiment however, the means for clamping an electrical cable between the cover and base differs from that of the first embodiment, and will now be described.

Whereas in the first embodiment part of the cover 8 was resiliently deformed, to vary the size of the aperture 26, in the second embodiment the base 56 is provided with a peripheral wall 57, an outer portion of the wall being rebated, as shown at 58.

Towards the side of the plug opposite the earth pin, the wall turns inwardly, and bounds a channel 59: the base also comprises a tongue 60 which extends into the channel 59, the tongue being capable of being resiliently deformed relative to the peripheral wall portions bounding the channel.

The cover 62 of the plug is provided with a complimentary rebated rib 64, adapted to be seated on the rebate 58 of the wall 57: when in this position, the tongue 60 extends quite close to an abutment 66 (the position of the tongue being shown in dotted lines in Figure 8), the distance of separation of the tongue and the abutment being equal to the diameter of the smallest cable wth which the plus is likely to be used (such as the cable 70, shown in Figure 8). With such a cable, on securing the cover 62 to the base 56, the cable will be gripped by the serrations 61 of the tongue 60 and the serrations 67 of the abutment 66.

However, when the plug is used in conjunction with the cable of a larger diameter (such as the cable 72, Figure 8) securing the cover to the base by the use of the screw 54 will involve the application of pressure to the tongue 60, which will be effective to move the tongue away from the abutment 66, effectively opening the aperture 68 defined therebetween.

By the use of this invention, a plug may be moulded of plastics material, such as nylon, having hardness characteristics appropriate to the provision of the abutments 37,39 and 41 to locate and secure the plug pins 16, 18 and 20, and appropriate to the deformation of a part at least of the plug base or the plug cover, securely to clamp or grip an electric cable, which has been connected to the plug pins.

Claims (22)

1. An electric plug comprising a base member and a cover member adapted to be secured together by at least one screw, the base member and the cover member each comprising a recess-defining part which, when the cover member and the base member are secured together, define an aperture through which a cable may extend into the interior of the plug, the construction and arrangement being such that the size of the aperture may be varied, to accommodate cable of differing sizes, by varying the degree of tightening of the screw or screws.

2. An electric plug according to Claim 1 wherein the recess-defining parts of the base member and the cover member are afforded with formations, adapted when a cable is within the aperture to grip the cable to resist withdrawing movement of the cable from the interior of the plug.

3. An electric plug according to one of Claims 1 and 2 wherein on at least one of the base member and the cover member, the recess-defining part is afforded by a tongue extending (when the base and cover members are secured together) towards the recess-defining part of the other member.

4. An electric plug according to any one of the preceding claims wherein the cover member is adapted for hinging movement relative to the base, such that tightening of said screw or screws causes relative angular movement between the base and cover members, to vary the size of the aperture.

5. An electric plug according to any one of Claims 1,2 and 3 wherein the base and cover members are adapted to be secured together by one or more screws, so arranged as to ensure generally linear movement of approach and separation between the cover member and the base member, to vary the size of the aperture.

6. An electric plug according to any one of the preceding claims wherein the base and cover members are moulded in one-piece, being connected together by a web of material.

7. An electric plug comprising a base member and a cover member which, when the plug is assembled, are secured together and which define an aperture through which a cable extends to the interior of the plug, wherein a part of the plug which defines said aperture is resiliently deformable, and the size of the aperture may be enlarged by pressure acting against the said part.

8. An electric plug according to Claim 7 wherein the said part forms an integral part of either the base member or the cover member.

9. An electric plug according to Claim 8 wherein the said part is disposed opposite to a further part which forms an integral part of either the cover memberorthe base member, respectively.

10. An electric plug according to Claim 9 wherein said further part is less resilient than the first said part.

11. An electric plug according to any one of Claims 7 to 10 wherein the base member and/or the cover member are moulded from plastics material.

12. An electric plug comprising a base member and a cover member which when the plug is assembled are secured together, the base member comprising apertures through which pins of the plug extend from the interior thereof, wherein the pins are provided in side faces thereof with at least one aperture into which a protrusion on the base member extends, the construction and arrangement being such that the protrusion may readily be deformed to permit movement of the pin into a desired position in the aperture, but which restrains subsequent movement of the plug pin from said desired position in at least one direction.

13. An electric plug according to Claim 12 wherein the construction and arrangement is such that, assembly of the cover member and base member is effective to restrain or to further restrain deformation of the protrusion, in a manner which renders it less liable to removal from the aperture in the side face of the pin.

14. An electric plug according to Claim 13 wherein a face of the protrusion is inclined, said face being that which, when the pin is being inserted through the aperture into its desired position, is engaged by the pin, in a manner whereby engagement of the protrusion by the pin, and deformation of the protrusion, is rendered relatively easy.

15. An electric plug in which a terminal member thereof is adapted to be inserted into an aperture or recess, part of or secured to the terminal member frictionally engaging the wall of the plug bounding said aperture or recess.

16. An electric plug according to Claim 15 wherein the insertion of said part into the aperture or recess involves deformation of either said part or said aperture or recess, or of the wall bounding said aperture or recess.

17. An electric plug according to Claim 16 wherein said part is resiliently deformable, being compressed upon the insertion of the terminal member or said part into the aperture or recess.

18. An electric plug according to Claim 15 wherein said part is provided by a fixing member of relatively rigid material secured to or extending from an underside of the terminal member, and which resiliently deforms the wall bounding the aperture or recess.

19. An electric plug according to Claim 18 where- in said fixing member is of metal, and is provided with serrations.

20. An electric plug according to Claim 15 wherein the terminal member is a fuse terminal, comprising a base plate, and two terminal tags extending therefrom at opposite ends thereof, each of which is adapted to be inserted into an associated aperture or recess, to provide fixing members for the fuse terminal at opposite ends of the base member.

21. An electric plug constructed and arranged substantially as hereinbefore described, with reference to any of the accompanying drawings.

22. Any novel feature or novel combination of features hereinbefore described and/or shown in the accompanying drawings.