GB2097601A - Cord grips for electrical plugs or appliances especially for non-rewireable plugs - Google Patents

Abstract

A plug or appliance casing has a tapering housing (21) defined by base (2) and/or cover (3, Figure 1, not shown) which receives a cable gripping member (10) which fits tightly around the cable (1) and has an exterior tapering shape matched to the housing (21). Because of the taper, member (10) is retained spaced from end (22) and if tension is applied to cable (1), the cable gripping member (10) is compressed more tightly round the cable (1), so as to prevent it being pulled out unless very substantial forces are applied. If such forces are applied, an earth wire may be made to be the last to sever its connection with a terminal pin (4) by leading live and neutral conductors around posts (20) moulded integral with the plug base (2). The cover (3, Figure 1, not shown) may be secured to the base (2) by ultrasonic welding. <IMAGE>

Description

SPECIFICATION Cord grips, particularly for plugs especially nonrewirable plugs This invention relates to electrical cord grips and electrical apparatus incorporating such cord grips, particuarly electrical plugs, and most particularly non-rewirable electrical plugs.

Portable electrical apparatus for use when connected to a mains supply is conventionally provided with a flexible electrical cable lead, usually of 3-core construction, which, on its end remote from the apparatus is provided with a plug. The lead may be wired into the apparatus directly, or it may terminate in a female connector member adapted to fit in a housing in the apparatus provided with complementary male-pin connectors. In either case, both ends of the flexible cable need to be gripped securely and not merely held in place by the connection of the conductor wires to terminal pins or parts of the apparatus.

Conventionally, clamp connectors in which the cable was gripped between a bar and a seating, grip being tightened by two grip screws passing through holes in the ends of the bar, have been used. These are complex to manufacture and assemble and can fail in use. Resilient tongues biased together have been used in electrical plugs to hold cable against withdrawal, but these tend to dig into the cable excessively and can even cause rupture of its insulating sheathing.

Particularly in the case of plugs, it is necessary that the cable clamp be adequate to restrain the cable against movement under a given axial pull. Thus British Standard Specifications BS 1363 and BS 1363Afor13-ampfused plugsspecifytensionfi- gures which the clamp must take up without allowing pull on the cable to pull on the electrical connections.

According to a first feature of the present invention there is provided an electrical fitting or appliance to which a cable is to be connected which comprises a base member and a cover member which, when assembled together, define a tapered housing, the cross-section of which tapers inwardly away from members within the fitting or appliance to which electrical connection is to be made by the cable conductors, and a cable gripping member adapted to be assembled round the cable and to be located, when so assembled, within the housing, the cable gripping member having an interior passage the inner walls of which bear cable retaining or cable gripping means, and having an exterior tapering shape matched to the interior of the housing, the cable gripping member being so dimensioned that when fitted into the housing it is retained spaced away from the narrower end of the housing.

With such an arrangement, if the cable is pulled from outside, the cable gripping member is pulled towards the narrower end of the housing and so caused to grip round the cable more tightly, so resisting being pulled out from the fitting or appliance. The cable gripping member is preferably a simple plastics moulding formed of a smaller number of sectors (preferably two) hinged together and assemblable round the cable prior to insertion in part of the housing, and assembly together of the base and cover member to complete the housing.

The arrangement can be applied to electrical appliance lead-ins, particularly portable electrical appliance such as irons, mixers and hand-drills where there is a risk of sudden cable tension as the appliance is moved. It is particularly valuable, however, when applied to plugs, or other electrical wiring fittings. Its simplicity of manufacture and operation, and its particular effectiveness, makes it very valuable for use in connection with so-called non-rewirable electric plugs.

In recent years, there has been a move away from electric plugs fitted to appliance by the user and purchaser of that appliance to plugs which are supplied as part of an electrical appliance when it is sold. Such plugs tend to be safer and are, of course, invariably wired up correctly. Danger can, of course, arise particularly in the home if plugs are incorrectly wired up, but despite colour coding wires and, e.g.

indicating which colour wire goes where on the plug itself, errors still occur and give rise to accidents.

Additionally, in many cases the the cable clamp provided in such plugs is simply not used at all, or used ineffectively.

According there has been a tendency in recent years, for reasons of safety, to fit domestic appliances with so-called non-rewirable plug connectors. These take the form of a plug unit having terminal pins projecting from one face and having some form of body including an externally accessible fuseholder, and the body enclosing means connecting the electrical conductors in the cable with the terminal pins, via the fuse in the case of the live pin.

Non-rewirable connector plugs are described in published British Patent Applications 2,003,676 and 2,057,792 and in British Patent Specifications 1,490,690 and 1,581,662.

Up till now, commercial attempts by various manufacturers to produce such non-rewirable cable and plug assemblies have tended to be expensive and to require substantial assembly steps.

According therefore specifically to the present invention there is provided a non-rewirable plug and cable assembly which consists of a base member, three terminal pins mounted in the base member, a fuse and fuseholder assembly and an extra terminal assembly, the fuse and fuseholder assembly being adapted to connect electrically one of the terminal pins with the extra terminal assembly, the extra terminal assembly and the other two pins being electrically connected to electrical conductors in the cable, and a cover member permanently secured to the base member and acting to cover the exposed wire ends and terminal members, the base and/or cover member defining a tapered housing the cross-section of which tapers inwardly in a direction away from the terminals and towards the external end of the cable, and, surrounding the cable and located within the housing, a cable gripping member the outer walls of which are shaped to fit the tapering housing, the inner walls of which bear cable retaining or cable gripping means, the member being so dimensioned that when fitted into the housing it is retained spaced away from the narrow emend of the housing.

In such a plug, the cable is very firmly restrained in any case but if the cable is tugged, the member in the housing moves towards the narrower end of the housing thus increasing its grip on the cable and preventing the cable being ripped from the terminals.

According to a particularly preferred feature of the invention, the earth and neutral pins and the extra terminal member are attached to the conductors of the cable by simple crimping. Preferably, all three terminal pins are formed of sheet material folded to shape in a fashion analogous to the terminal pins disclosed in British Patent Specification 2,013,045.

It is a requirement of British Standard 1363 that if despite cable clamping a cable is pulled from a plug, the earth connection is the last to separate. In order to assist in fulfilling this requirement, the base or lid member of the plug assembly of the present invention may bear one or more projecting spigots around which the live and neutral conductors of the cable are looped. Because of the tortuous path which those conductors have to follow, compared to the earth conductor, assuming that all three conductors are initially cut to equal length, which is convenient when using certain cable cutting and stripping machinery, if the cable despite the retaining means noted above is pulled from the plug, the earth wire is the last to sever its connection with the terminal pin.

There are many ways of putting the present invention into practice but it is believed that the preferred embodiment is one leading to the construction of a cable and plug assembly including a minimum number of discrete components. This naturally eases manufacture and keeps the ultimate cost down. Indeed, it is believed that the present invention enables a three-pin plug and cable assembly to be made with the minimum number of parts theoretically possible while making the plug compatible with the provisions of B.S. 1363.

The materials from which the cable and plug members may be made may be conventional. The preferred material is nylon for the plug base and top and the permanent connection between the base and top is preferably secured by ultrasonic welding though other systems may, of course, be employed.

The invention is illustrated by way of examplen with reference to the accompanying drawings in which: Figure 1 is a general view of a completed assem bly of a non-rewirable plug according to the invention; Figure 2 is a perspective exploded view of the assembly; Figure 3 is a top plan view of the base member, and Figure 4 is a bottom plan view of the top member.

Referring to the drawings, the assembly consists basically of an electric cable 1, a plug base member 2, a plug top member 3, three terminal pins 4, 5,6, a fuse 7, a fuseholder 8, an extra terminal assembly 9 and a cable gripping member 10.

As can be seen most clearly from Figure 3, the base member 2 consists of a substantially flat member 11, having integrally moulded therein a raised fuse housing 12 on the top if which are integrally moulded guide walls 13,14, 15 which serve to assist in positioning the cable conductors.

The base member is pierced by three rectangular apertures 16, 17 and 18forterminal pins 4, sand 6 respectively and by four smaller apertures 19 through which the metallic clips which engage the ends of fuse 7 and which form part of terminal pin 6 and the extra terminal assembly 9 may pass. In addition, two upstanding pins 20 are integrally moulded with the base member 2 and one end of the base member consists of a box-like structure 21 open at its upper face and having two opposite side walls relieved by cut-outs 22 and 23 to enable passage of the cable therethrough.

The cover member 3 consists of a substantially flat portion 24 with an upstanding edge 25. Also upstanding from base 24 are a pair of abutments 26, which act to hold the members 9 and 6 firmly in position when the base member and cover are assembled together and a pair of pin-receiving sockets 27, which fit round pins 20 when such assembly takes place.

The cable gripping member 10 consists of an integrally moulded split rectangular block of plastics material. Each half bears a substantially semicircular section groove 28, having moulded in its base three projections 29. The hardness of the material used to make member 10, relative to the hardness of the material contituting the outer sheath of cable 1, should be so chosen that when the two halves of member 10 are closed together around cable 1,the members 29 deform the outer surface of the cable and dig into it a little to restrain axial movement of the cable in the block.

In order to manufacture the assembly according to the invention, a cable 1 is first stripped of its outer insulation to expose the three conductors, the ends of the three conductors then stripped of their insulation whereafter terminals 4, 5 and extra terminal assembly 9 are attached in conventional fashion. Terminals 4,5 and 6 are preferably of the type made from folded metal sheet in a manner analogous to the terminal members described in British Patent Specification 2,013,045.

Terminal pins 4 and 5 are pushed into position and extra terminal assembly 9 likewise inserted with the prongs of the fuse clip passing through to apertures 19. Terminal pin 6 and its associated fuse clip are inserted likewise.

The block 10 is then positioned on and assembled round the cable 1, and the cable then swung down to located block 10 in the housing 21 on the base member 2. The cable gripping member 10 fits snugly into housing 21 and lies within its end face a little removed from the wall containing aperture 22.

The cover 3 is then fitted over the top of base member 2 and secured permanently thereto, conve niently by ultrasonic welding, to complete the assembly.

During the assembly, the conductors to the live and neutral pins are preferably taken around the mutually outwardly facing sides of pins 20 to ensure that, in the unlikely event of a force being exerted on cable 1 sufficient to pull the cable from the plug, the last connection to sever is that to earth pin 4. Such a force has to be very substantial since, if an attempt is made to pull cable 1 from the plug, because of the tapered side walls of housing 21, the cable gripping member 10 is compressed very tightly about cable 1 as it moves towards the end wall containing aperture 22, when strain is initially applied.

Claims (6)

1. An electrical fitting or appliance to which a cable is to be connected which comprises a base member and a cover member which, when assembled together, define a tapered housing, the crosssection of which tapers inwardly away from members within the fitting or appliance to which electrical connection is to be made by the cable conductors, and a cable gripping member adapted to be assembled round the cable and to be located, when so assembled, within the housing, the cable gripping member having an interior passage the inner walls of which bear cable retaining or cable gripping means, and having an exterior tapering shape matched to the interior of the housing, the cable gripping member being so dimensioned that when fitted into the housing it is retained spaced away from the narrower end of the housing.

2. A non-rewirable plug and cable assembly which consists of a base member, three terminal pins mounted in the base member, a fuse and fuseholder assembly and an extra terminal assembly, the fuse and fuseholder assembly being adapted to connect electrically one of the terminal pins with the extra terminal assembly, the extra terminal assembly and the other two pins being electrically connected to electrical conductors in the cable, and a cover member permanently secured to the base member and acting to cover the exposed wire ends and terminal members, the base and/or cover member defining a tapered housing the cross-section of which tapers inwardly in a direction away from the terminals and towards the external end of the cable, and, surrounding the cable and located within the housing, a cable gripping member the outer walls of which are shaped to fit the tapering housing, the inner walls of which bear cable retaining or cable gripping means, the member being so dimensioned that when fitted into the housing it is retained spaced away from the narrower end of the housing.

3. A non-rewirable plug and cable assembly according to claim 2 wherein the earth and neutral pins and the extra terminal member are attached to the conductors of the cable by simple crimping.

4. A non-rewirable plug and cable assembly according to claim 2 or 3 wherein the base or lid member of the plug assembly bears one or more projecting spigots around which the live and neutral conductors of the cable are looped.

5. A non-rewirable plug and cable assembly according to any one of claims 2 to 4 wherein the permanent connection between the base and top is secured by ultrasonic welding.

6. A non-rewirable plug and cable assembly substantially as hereinbefore defined with reference to the accompanying drawings.