GB2251523A

GB2251523A - Electric plug

Info

Publication number: GB2251523A
Application number: GB9114707A
Authority: GB
Inventors: Meng Wee Lim
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-07-09
Filing date: 1991-07-08
Publication date: 1992-07-08
Also published as: GB9114707D0; GB9015093D0

Abstract

An electric plug is constructed to allow access to the terminals 3, 5, 7 of the plug pins, the fuse 8 and fuse links and cable clamp 9, all through one face 13A of the plug body 1. The plug body 1 is of a unitary construction and access to the plug components is via the underneath face of the plug, i.e. that surface through which the pins protrude. The cable clamp may comprise a screw (9) or an adjustable resilient finger (figs 3, 4, not shown). A base cover (not shown) may comprise a resilient, transparent sheet flexible enough to allow a tool to flex it and thereby have access to fuse and plug terminals. The plug pins may be gold plated. <IMAGE>

Description

ELECTRIC PLUG AND SOCKET-OUTLET This invention relates to electric plugs. It also relates to a socket-outlet. In particular it relates to three pin electric plugs such as are in common use in UK households.

Conventional three pin electric plugs (hereinafter conventional electric plugs) comprise a base member which houses various components such as earth, neutral and line pins, and their associated terminals, a fuse link, fuse grips, a fuse terminal and cord grip means, and a cover member which is secured to the base member by means of a single screw.

Conventional electric plugs are unsatisfactory in many respects. First, fabrication of moulds for the members which comprise the electric plugs (i.e.. the base and cover member) is expensive because the design of both members tends to be complicated. Also, because the design of the members is complicated, a lot of material is used during their manufacture.

Assembly of the plug from its various components entails frequent turning over of the base member and the cover member for insertion of the various components and thus is cumbersome and time consuming; assembly of the cord grip means is particularly awkward in this respect. A further disadvantage is that in conventional plugs, the distance between the earth pin and the line terminal or fuse grip (the "creepage distance") is small: this is dangerous in the event that an earth wire or a live wire connected to one of their respective pin terminals becomes loose. Further, when wiring the plug or changing the fuse in the plug it is necessary to separate the base and cover member and to turn them over for access to the various components and screws. This is awkward and time consuming: also the pins often fall out of the base member of the plug.Finally, in many conventional electric plugs the base member and cover member are held together by a single screw and are aligned by two protrusions on the base member engaging in corresponding recesses in the cover member. Often, particularly if the plug is dropped, the protrusions and fixing screw housing will fracture.

It is an object of the present invention to alleviate some or all of the above-mentioned disadvantages of conventional electric plugs.

Thus, in a first aspect of the present invention, there is provided an electric plug in which access to terminals of the plug pins, fuse link, fuse grips, cord grip means, terminal connections and their associated screws may all be effected through one face of the plug body.

Providing access to the various plug components from one face only eliminates the need for repeatedly turning the plug over during wiring and/or assembly of the plug, thus making the process of wiring and/or assembly of the plug more efficient.

In one preferred embodiment the plug body is of a unitary construction and access to the plug components is via the underneath of the plug i.e. that surface through which the pins protrude for insertion into a socket.

The plug may include a thin cover formed from a sheet or film of preferably transparent material.

Advantageously the terminals of the pins may comprise pairs of jaws or plates for clamping wires there between.

Specific embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 is a perspective view of an electric plug; Figure 1A is a side view of the neutral pin of the plug of Figure 1 which is also similar for the earth pin; Figure 2 is a plan view of the underside of an electric plug in accordance with a further embodiment of the invention; Figure 2A is a side view of the terminal of the line terminal of the plug of Figure 2; Figure 2B is a side view of the line pin of the plug of Figure 2; Figure 2C is a side view of the earth pin and associated clamp-plate of the plug of Figure 2; Figure 3 is an underneath plan view of an electric plug in accordance with a yet further embodiment of the invention;; Figure 3A is the side view of the earth pin of the plug of Figure 3 incorporating a clamp terminal; Figure 3B is a perspective view of a generally U-shaped clip; Figure 3C shows the clip of Figure 3B in side plan view being used to clamp wire; Figure 4 is an inside view with a cover taken off a plug; Figure 5 shows an electric plug provided with a snap-on cover; and Figure 6 shows a further electric plug fitted with a different design of snap-on cover.

Referring to the drawings, Figure 1 shows an electric plug comprising a unitary plug body 1, together with various plug components including an earth pin member 2 including a terminal 3, a line pin member 4 including a terminal 5, a neutral pin member 6 including a terminal 7, a fuse 8 and a cord grip 9.

The plug body 1 is moulded in one piece and includes a number of interconnected recesses and side walls. All the recesses extend to the same depth, which may not necessarily be so depending on the plug components as in Figure 2 and 2C, within the plug. The recesses define housings 10, 11, 12 for the pin members 2, 4, 6 respectively, a cord channel 13 and areas for locating other plug components such as the fuse 8. The upper surface of all the side walls is located in the same plane and defines an engagement surface 13A (if no bottom cover described later is used) face 13A so that when the plug is pushed into a suitable socket that engagement surface 13a is flush with the surface of the socket to render the plug components inaccessible.The design of the neutral pin member which is also the same for the earth pin is shown in Figure 1A and includes a conventional screw terminal: the pins may be inserted and secured by known means.

Alternatively the plug may comprise a base body and a cap. The base will have recesses into its body to form pin housings and location of the other plug components and also apertures through its body for plug components like pins, terminals etc. to insert from the other side and restrain from passing through by provision of side protrusions 6A at bases of the plug components. A cap is used to cover up the bases of the plug components and it is secured to the base body by a screw, a snap on arrangement or it is even moulded to the base body.

The design of the cord grip 9 is not conventional and will be described in detail with reference to the embodiment shown in Figure 2.

Where appropriate, the same reference numerals will be used to denote similar components and features which appear in several of the embodiments already described or to be described hereinafter.

Figure 2 shows a plug of a similar design to that of Figure 1, but having different terminals for the pin members.

As shown, and as oriented, in Figure 2, a threaded tunnel bore 14 extends from the cord channel 13 to the wall 15 at the right hand side of the plug body 1. On the side wall of cord channel 13, opposite the bore 14, there are serrated ridges 16. Inside the bore 14 there is a, preferably non-metallic, screw 17 which has a rounded end 18 adapted to clamp a wire cord against the serrated ridges 16, and a head 19 adapted to receive a screw-driver for turning the screw.

The pin terminals of the plug are shown in detail in Figure 2C. Figure 2C shows that the earth pin member 2 includes a side arm 20 which extends in a direction perpendicular to the earth pin 21. That side arm 20 defines a first (upper) part of a clamp and opposes a clamp plate 23 located below the arm 20. There is a recess 24 which is part of the overall interconnected recesses in the plug body below plate 23. Holes 25 (unthreaded) and 26 (threaded) extend coaxially through the side arm 20 and clamp plate 23 respectively. A correspondingly threaded terminal screw 27 extends through the holes 25 and 26: adjusting the terminal screw alters the gap between the side arm 20 and clamp plate 23 to enable an (earth) wire to be clamped therebetween.A fixing screw 28 extends through a further hole in the side arm 20 located between the terminal screw 27 and the pin 21 to fix the pin member 2 to the body 1.

The neutral pin member 6 has two side arms 30, 31 perpendicular to each other and to the neutral pin.

One side arm 30 serves to secure the pin member 6 to the plug body 1 by means of a fixing screw 32 which extends through a hole in the side arm into the plug body 1: the other arm 31 forms an upper part of a clamp similar to the clamp of the earth pin.

It is possible to replace the "fixing" screws and "terminal" screws of the neutral and earth pin members by a single screw to serve both functions of fixing the pin members to the plug body and adjusting the clamps of the terminals and in this case, the clamp plate 23 is located on top instead of below the side arm 20 as mentioned earlier.

Figures 2, 2A and 2B illustrate the line pin member and fuse holder. A fuse clip 40 is fixed by a rivet 41 to a side arm 42 of the line pin member 4; a further fuse clip 44 to which line terminal 45 is attached is shown in Figure 2A; this line terminal includes a clamp similar to that of the earth pin.

The fuse 8 extends between the fuse clips 40 and 44 and is held in place by them. A clamping strip 46 extends over the fuse body 8 and is secured in place by a fixing screw 47 to ensure efficient electrical contact between the fuse cap 8A and the fuse clips 40 and 44. The fixing screw 47 also serves to secure the pin member 2 to the plug body 1. The location of the line (fuse) terminal in line with and above the fuse as oriented in Figure 2 increases the creepage distance between the earth pin and the line terminal and also enables the three wires viz earth, live and neutral to be cut to equal lengths for insertion into the plug, unlike conventional plugs where the line wire has to be cut to a shorter length than the earth and neutral wires.

Figure 3 shows another electric plug. The plug body includes a channel 51 which extends into the cord channel 13 at an angle of about 600 to the cord channel 13. A resilient plastic strip 50 is inserted into the channel 51 bent to engage side channel 54 at the end of channel 51.

The end portion of the clamping strip 50 which clamps the wire cord is curvature in semi-circle configuration to fit the round contour of the wire cord.

The wall of the channel for insertion of the clamping strip is curved at the portion 51A indicated by the dotted lines in Figure 3 with an over-hanging ledge formed by part of the engagement surface over the curved wall of the said channel When the clamping strip clamps the wire cord, portion of the said strip will bend against the curved channel wall to be underneath the said ledge restraining its vertically upward movement. (The width of the clamping strip is slightly smaller than the measurement taken from the underneath surface of the said ledge to the bottom of the channel). This arrangement together with the curved end of the clamping strip clamping the wire cord will prevent it from being easily dislodged from the cord channel of plug body.

The strip may be arranged to hold a wire cord against the serrated wall 16 of the cord channel 13. Two further side channels 52, 53 communicate with channel 51 and the resilient plastic strip may be inserted into either of those channels to adjust the length of the strip which extends into the cord channel 13 to cater for wire cords of different diameters or to adjust the tension in the plastic strip 50.

The earth and neutral pin members 60 of the plug are shown in Figure 3A. Each pin member 60 includes a hollow portion 61. The roof of the hollow portion is serrated and defines an upper jaw 62. At the base of the hollow portion there is a protrusion 64. A sprung metal strip 66 is located inside the hollow. The strip is configured to match the inside of the hollow and includes a serrated portion 68 defining a lower jaw to mate with upper jaw 62, a lever portion 70 located adjacent jaw 68 and which extends away from the pin 60 and a kinked portion 72 which extends from the base of the hollow towards lever 70. A wire may be clamped between the upper jaw 62 defined by the pin and the lower jaw 68 defined by the sprung metal strip. A downward force on the lever 70 will prise open the lower clamp jaw 68.A wire may then be inserted between the open jaws: releasing the lever causes the jaws to clamp shut securing the wire in place.

For the line conductor, a 'U' shaped clip 80 is used as a wire clamp. As illustrated in Figures 3B and 3C, slots 86 are provided on gripping arms 82, 84 of the clip just above the portion where the cap of the fuse link is clamped 87 by the 'U' shaped clip. Strands of the line wire are placed into one or both of the slots 86 and the fuse cap is inserted into the 'U' shaped clip, thus clamping the fuse cap and wire strand together in the 'U' shaped clip. This construction has the advantage of greater creepage distance between the earth pin and the line terminal than conventional plugs where the creepage distance is only about 3mm.

A metal strip may be utilised to wrap around the fuse cap with the line conductor inserted in between and secured by a screw and nut arrangement to ensure efficient electrical contact. For the line pin side, one end of the metal strip is rivetted bnto the line pin while the strip is then wrapped around the fuse cap with the other end screwed onto the line pin.

It is to be noted that in all the embodiments of the invention so far described, no cover is provided to cover the exposed bottom face of the plug since, once the plug is engaged in a socket, the surface of the socket outlet will act as a cover for the bottom face of the plug thus rendering all line and other plug components inaccessible in compliance with BS1363.

However, should a cover be required, a thin sheet or film of transparent plastic material could be used. It would not be necessary to cut out apertures for the pins in sheet: instead 'H' shaped cutting lines may be provided, the pins being simply forced through the cutting lines with excess film forming flaps on sides of the pins. If a thicker sheet is used, apertures may be provided for insertion of the pins through the sheet. The apertures are smaller than the cross section of the pins and having cutting lines at their corners, so that the portions bounded by the prolonged cutting lines will flap upwards when the cover is placed on the plug body exerting a force on the pins which helps to secure the cover in place.

Alternatively if the apertures are provided for insertion of the plug pins through the cover they may be equal either lengthwise or breadthwise to the actual cross section of the pins, excess portions of the cover forming flaps on two opposite sides of the pin. This arrangement can be used in resilient base member to clamp the pins preventing fall-out in conventional plugs when the top cover is taken off.

Alternatively, the flapped portion can be made to engage into grooves provided on the walls of the pins to secure the bottom cover in place. Another alternative is that the bottom cover may have exact apertures according to the cross-sections of the pins but provide a snap-on arrangement to engage the internal wall of plug body.

An aperture 89 may be provided in the base of a conventional plug for access to the line terminal for insertion of a probe connected a circuit tester also connected to the line pin for testing the fuse. As shown in figure 4, this feature of fuse testing can also be used in conventional plugs as well if they are provided with a suitable aperture in their cover. The plug of figure 4 incorporates various features described in respect of earlier embodiments including greater creepage distance and a clamping strip 51.

In a bottom accessed plug body the aperture is located in a cover.

Clear transparent plastic film is preferred for fabrication of the bottom cover because it facilitates visual inspection of the fuse 8 useful if the fuse has a glass body and the wire connections of the plug without having to take the cover off.

If the thick bottom cover is resilient enough, then H-letter or U-letter cutting lines are provided directly corresponding or above the locations of the terminals for fuse - probe and tightening of screw terminals without taking off the cover. If the thick cover is not resilient, then apertures which will be covered by adhesive tape are provided for the said purpose.

Figures 5 and 6, illustrate plugs having snap-on covers. In Figure 5, the cover 90 has a leg 91 which depends from the cover and is provided with a hook portion 92. An adjacent resilient leg 93 depends generally parallel to leg 91 and is of a length longer than the internal depth between the cover and the base 94. The base 94 of the plug includes a recess 95 arranged to receive the hook 92 of the leg 91 and a ledge 96 at the base of a wall of the plug on which the lower end of leg 93 rests when the cover is on the base. Once the cover is pressed down for the hooked leg to engage the recess as shown in figure 5, the resilient leg 93 bends against the hook leg to force it into the recess.Resilient leg 93 facilitates the release of the cover from the base since once the hook is prised out of the recess in the base, the compressed resilient leg will expand to force the cover off the base.

Alternatively, as illustrated in Figure 6, the cover can be provided with a pair of legs with hooks 92 and a pair of resilient legs 93. The hooks 92 are arranged to engage apertures 97 in opposite side walls of the base 94 of the plug.

Other slide on or snap-on arrangements are possible.

The pins of any of the above embodiments, or any conventional plugs may be partially or wholly gold plated to prevent their tarnishing which results in contact resistance affecting electrical conductivity.

The fabrication of sleeved pins is a cumbersome and costly process. This is simplified by having heat-shrinking plastic tubings inserted into the line and neutral pins and applying heat to form sleeves around the said pins.

The bottom accessed plug and top cover of conventional plug may be made of a transparent plastic material resulting in a see-through concept so that loose connections of terminals resulting in, arcing or sparking are immediately detected visually and remedied to prevent fire hazard. This also eliminates the need for a neon indicator lamp.

The sleeved pins arrangements can be dispensed with if a barrier wall slightly larger than the periphery of the plug engagement surface is provided on the surface of a socket-outlet or have an area of the socket-outlet engagement surface slightly larger than the periphery of the plug bottom surface recessed to sufficient depth to prevent fingers touching the pins thus removing the necessity of sleeved pins.

The features set out above may be used in various combinations in plugs of various constructions.

Claims

1. An electric plug in which access to terminals of the plug pins, a fuse link, cord grip means, and means for inserting wires into the plug may all be effected via one face of the plug body.

2. An electric plug as claimed in claim 1 wherein the plug body is of a unitary construction and in which access to the terminals, fuse link and cord grip means is provided via the face from which the pins protrude.

3. An electric plug as claimed in any preceeding claim including a cover for the face comprising a sheet or film of a plastics material.

4. An electric plug as claimed in claim 3 wherein the thin sheet or film is transparent.

5. An electric plug as claimed in any preceeding claim wherein the pin terminals comprise pairs of jaws or plates for clamping wires therebetween.

6. An electric plug wherein the cord grip means includes a threaded bore extending from a channel for the cord and a non metallic screw disposed in said channel and adapted to locate a wire cord in said cord channel against a wall of said cord channel.

7. An electic plug wherein the cord grip means includes a resilient strip of material located in a recess extending from a channel for the cord, the resilient strip being adapted to locate a wire cord in said channel against a wall of said channel with adjustments or tension adjusters for different cord diameters.

8. An electric plug as claimed in Claim 6 or Claim 7 wherein at least that part of the wall of the channel against which a cord is to be located is ridged.

9. An electric plug in which the pin terminals are disposed to allow the earth, line and neutral wires of a wire cord to be cut to equal lengths for connection to those terminals.

10. An electric plug having a snap-on cover including two generally parallel legs depending from the cover, are provided with a hook for engagement with the base of the plug, the other biased to hold the hook in engagement with the base.

11. A terminal for an electric plug including two plates for clamping a wire therebetween for connection to the terminal.

12. An electric plug including partially or wholly gold plated pins.

13. An electric plug in which the fuse is located to one side of the line pin and the line terminal is atop the fuse cap to effect greater creepage distance.

14. An electric plug or a cover for a plug made of a transparent plastics material to enable loose connections or the like to be detected visually.

15. An electric plug including a thin bottom cover made from a thin transparent plastics material which is sufficiently resilient to allow the insertion of a fuse probe or a screw driver to tighten any loose screws in the plug without removal of said cover.

16. A cover as claimed in claim 15 wherein H letter cutting lines are provided for the plug pins.

17. An electric plug including a bottom cover made from a plastics material including apertures for insertion of pins which apertures are smaller than the cross section of the pins so that flaps are formed when the pins are inserted through the apertures.

18. An electric plug including a cover including H-letter or V-letter cutting lines disposed to correspond with the locations of the terminals for insertion of a fuse probe or a screw driver to enable tightening of the terminal screws.

19. An electric plug including apertures in a bottom cover, which may be covered by adhesive when not in use, said apertures being disposed to correspond to location of the plug terminals to allow insertion of a fuse probe or a screw driver.

20. An electric plug substantially as hereinbefore described and as shown in either figure 1 and la or figure 2, 2a, 2b and 2c, or figure 3, 3a, 3b and 3c or figure 4 or figure 5 or figure 6 of the drawings.