GB2242576A - Electrical plugs - Google Patents

Abstract

An electrical plug comprises a body 10, 110, pins 12 projecting from one side of the body, pin terminals 18 located on the opposite side of the body, and a cover 14, 114 which when closed overlies the opposite side of the main body to insulate and clamp bared wires to the terminals. The cover may be hinged to the body. The wires may be held captive before clamping in the region of the terminals. <IMAGE>

Description

ELECTRICAL PLUGS The present invention relates to plugs for electrical appliances.

Three pin electrical plugs conventionally require tools to enable them to be fitted to the supply cable of an appliance. A screwdriver is needed to remove the cover from the body of the plug and often a screwdriver of a different size is needed to secure the bared ends of the individual wires to the terminals connected to the pins of the plug.

The present invention seeks to provide a plug which is quicker to fit than conventional plugs onto the supply cable of an electrical appliance and does not require the use of tools.

According to the present invention, there is provided an electrical plug comprising, a main body, electrically conductive pins projecting from one side of said main body for insertion into an electrical socket, terminals electrically connected to the pins and arranged on the opposite side of the main body, and a cover which when closed overlies the opposite side of the main body to insulate the terminals, wherein the terminals comprise contact regions, and the bared ends of the wires of a cable onto which the plug is to be fitted are electrically connected to said terminals by virtue of resting on said contact regions and being urged against said contact regions by pressure applied by the cover when the latter is closed.

Preferably, the cover and the main body together act as a cable grip to prevent withdrawal of the cable from the plug, when assembled.

Advantageously, the cover is hinged on to the main body and conveniently detents may be provided for retaining the cover in a closed position on the main body.

In this way, assembly of the cover requires only for the cable to be placed on the opposite side of the main body with its bared wires resting on the contact regions and for the cover to be folded over the cable and squeezed against the main body until the detents engage. This action grips the cable and at the same time urges the wires against the contact regions so that the plug is ready for use.

The part of the cover which urges the wires into contact with the terminal regions may be formed integrally with the cover. However, in order to accommodate wires of different physical sizes, the cover may include pressure pads which are captive in the cover and are resiliently urged in the direction of the terminal contact regions.

If separate pressure pads are used for live, neutral and earth terminals, they may be formed of a metal or have a metal surface for contacting the bare wires.

It is preferred that the contact regions should be colour coded to match the colours of the live, neutral and earth wires of the cable to assist an inexperienced person in the correct assembly of the plug.

Though the contact regions may simply be formed by flat contact pads, such a construction would permit movement of the wires as the cover is being closed. It is therefore preferred that the contact regions should be designed to hold wires temporarily captive until the cover is closed to grip the wires firmly. To this end, each terminal may comprise a spring clip or a tube having holes for pressure pads on the cover.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a perspective view of a plug in accordance with one embodiment of the invention viewed from the opposite side to the pins, and with the cover hinged open, Figure 2 is a view of a second plug from the opposite side to the pins with the cover hinged open, Figure 2a is a partial end view of the plug of Figure 2, Figure 3 is a section of a detail of an alternative embodiment of the invention, and Figure 4 is a section similar to that of Figure 3 through a still further embodiment of the invention.

In Figure 1, the main body of a three pin plug is designated 10 and is formed as a plastics moulding. The pins 12 project from the downwardly facing side of the main body. From the downwardly facing side, one may also gain access to a fuse 16 without the need to dismantle the plug.

The upwardly facing side has a cover 14 which is connected along one edge to the main body 10 by means of a thin film hinge 30. The cover can be forced down on to the main body 10 and has gripping portions 28 which engage beneath shoulders 22 of the main body 10 to prevent the cover from being opened accidentally.

The main body 10 is formed with three contact pads 18 which are electrically connected to the respective pins 12. Each pad 18 is located within a recess in the plug body 10 and is connected by a buried conductor to its associated pin. The cover 14 has contact posts 24 aligned with the respective recesses in the plug body 10 the purpose of which is to hold the bared ends of the wires of the cable to which the plug is to be fitted firmly against the contact pads 16.

The plug body also has a cable grip portion 20 which cooperates with projections 26 on the cover 14 to define a labyrinth cable grip.

To assemble the plug of Figure 1, the outer insulation of the cable is removed to expose a short length of the individually insulated live, neutral and earth wires and a shorter length at the ends of these wires is bared by removal of the inner insulation. In many cases, electrical appliances are supplied with their cables prepared in this manner and with the ends of the wires tinned to prevent fraying.

The ends of the wires are placed within the recesses for the electrical contact pads 18 and the cable with its outer insulation intact is placed within the cable grip portion 20. To assist in correct positioning of the wires, the contact pads 16 are colour coded in addition to the usual L, N and E markings.

The cover 14 is then hinged closed and pressed firmly against the main body 10 until the gripping portions 28 engage beneath the shoulders 22.

As the cover is closed, first the bared wires are gripped between the contact pads 16 and the post 24. This established the required electrical contact. Next, the cable is bent into a convoluted path defined between the cable grip portion 20 of the main body 10 and the projections 26. This ensures that the cable is correctly gripped by the plug and that the electrical wires cannot be removed easily from their contact pads.

Though the plug can be assembled simply, it requires a tool to prise the gripping portions 28 apart before the plug can be opened and this cannot be done while the plug is inserted into an electrical socket.

The description of the plug of Figure 1 illustrates the main features of the invention, namely that the assembly can be effected easily by merely placing the wires in position and closing the cover of the plug.

Once fitted, it is not intended that the cover should be opened again and it is for this reason that the fuse is preferably designed so that it can be changed without the need to open the plug. If for any reason the plug must be removed, then this is not impossible but requires tools and more effort than the assembly.

Various modifications can be made to the plug without departing from the scope of the invention as defined by the appended claims and some of these will now be described by reference to the remaining drawings.

The plug of Figure 2 differs from that of Figure 1 in that the cover 114 is hinged along one side to the main body 110. The cable grip has been modified as has the mechanism for retaining the cover 114 closed.

In place of the gripping portion 28 extending along the edges of the cover 14, in the embodiment of Figure 2 two chamfered tongues 128 project from the cover 114 and are received in recesses 122 in the main body 110 which have chamfered shoulders. As the cover is closed, the tongues are deflected as a result of the cooperation between the chamfered surfaces and when the cover is full closed, the tongues engage beneath the shoulders to prevent accidental opening. In this case, two small screwdrivers are needed to release the tongues by applying sideways pressure to them, before the cover can be opened. This design is preferred to that of Figure 1 as it can result in smaller yet safe construction.

The cable grip in Figure 2 uses posts 124 on the main body 110 to define a path which is convoluted in the plane of separation of the body and the cover rather than in the normal plane. The contact regions 116 are arranged to one side of the plug centre line and the cable 150 is bent, as shown, through a right angle before leaving the plug. The posts 124 are angled, in a known manner, to grip the cable more tightly as pressure is applied to pull it out of the plug.

To assist in retaining the cable 150, the cover 114 has a matrix of spikes 130 which are slightly flexible and surround the cable when the cover 114 is closed.

In both the embodiments described above, any pull applied to the cable acts to attempt to open the cover 14 or 114.

This can be avoided by forming the plug body with a continuous wall having a hole through which the cable may be inserted, in the same manner as currently done in rubber plugs intended for outdoor use. In this case, pulling the cable acts to remove the plug from its socket rather than open the cover.

There may be a risk of the bared wires being dislodged from their recesses during the closing of the cover.

Figures 3 and 4 show two difference solutions to this problem.

In Figure 3, the contact region for the wire is in the form of a tube 160 with a cut-out out through which the posts 216 on the cover 214 may pass to grip the grip the wire 220 inside the tube 160.

In Figure 4, the contact terminal is a U-shaped a spring clip 318 which lightly grips the end of the wire 220. The post on the cover 314 forces the limbs of the clip firmly together when the cover is closed. In the latter case, the wire is contacted on both sides by a metal and this reduces the contact resistance and avoids damage to the plastics material of the plug body as a result of arcing.

The contact posts on the covers described above have been formed integrally with the cover. To permit greater latitude in the size of cable with which the plug may be used safely, it is possible to replace the posts 24, 126, 216 by compliant contact pads which are resiliently mounted on the cover. In this case, the contact pads may again be of metal for the reasons given above.

The contact pads are illustrated as being next to each other but this of course is not necessary and it is possible, and indeed preferred for safety reasons, to separate the contact regions from one another in such a manner as to make it impossible for two wire to touch while at the same time remaining in contact with their respective terminals. Such design avoids accidental short circuits if any wire should be dislodged during use.

Claims (7)

1. An electrical plug comprising, a main body, electrically conductive pins projecting from one side of said main body for insertion into an electrical socket, terminals electrically connected to the pins and arranged on the opposite side of the main body, and a cover which when closed overlies the opposite side of the main body to insulate the terminals, wherein the terminals comprise contact regions, and the bared ends of the wires of a cable onto which the plug is to be fitted are electrically connected to said terminals by virtue of resting on said contact regions and being urged against said contact regions by pressure applied by the cover when the latter is closed.

2. A plug as claimed in claim 1, wherein the cover and the main body together act as a cable grip to prevent withdrawal of the cable from the plug, when assembled.

3. A plug as claimed in claim 1 or 2, wherein the cover is hinged on to the main body.

4. A plug as claimed in claim 3, wherein detents are be provided for retaining the cover in a closed position on the main body.

5. A plug as claimed in any preceding claim, wherein the contact regions should be colour coded in order to assist in correct assembly of the plug.

6. A plug as claimed in any preceding claim, wherein the contact regions are operative to hold wires temporarily captive until the cover is closed to grip the wires firmly.

7. An electrical plug constructed, arranged and adapted to operate substantially as herein described with reference to any one of the embodiments illustrated in the accompanying drawings.