IMPROVEMENTS RELATING TO ELECTRICAL PLUGS

Abstract: An electrical plug, particularly for domestic use for coupling appliances to socket outlet of a mains distribution system, is adapted to be fitted onto an appliance flex or cable without necessitating use of a screwdriver or other tool by virtue of being formed in two parts, namely a body portion (1) formed with terminal pins (4) insertable into the openings of a socket outlet and an insert (2) enterable into a recess (3) in the body portion (1). The insert (2) comprises a cable clamping arrangement (8) and conductor-receiving channels (10) formed with a right-angled bend and each leading to a termination member (19) in which a plunger (20) is axially movable against spring bias, the plungers (20) projecting from the front face of the insert (2). In the body portion (1) of the plug, the recess (3) has in its end wall three bores (18) located and dimensioned to accept the plungers (20) when the insert (2) is entered into the recess (3), and each bore (18) communicates with a terminal pad (17) coupled electrically to a respective one of the terminal pins (4). As the insert (2) is fully entered into the recess (3) in the plug body portion (1), the plungers (20) butt against the terminal pads (17) and are driven back against their spring bias and capture the conductor ends in the termination members (19).

Description: Improvements relating to electrical plugs This invention concerns improvements relating to electrical plugs and particularly, though not exclu¬ sively, concerns electrical plugs of the type employed for coupling domestic and other electrical appliances to socket outlets of the mains electrical supply. In the United Kingdom, the standard domestic electrical plug commonly comprises a rigid plastics material plug body formed in two parts, namely a base and a cover arranged to be secured together by means of one or more screws which are accessible only when the plug is not plugged in to a socket outlet. The plug base has three terminal pins moulded into the plastics material of the base, namely an "earth" pin and "neutral" and "live" pins, with the pins projecting from the under- side of the base to be received in corresponding openings of a socket outlet. The "earth" pin is commonly longer than the "neutral" and "live" pins for camming open the shutters commonly associated with the corresponding "live" and "neutral" openings of a socket outlet, a camming lever being provided in the "earth" opening of the socket outlet. In modern plugs, the Terminal pins are of rectangular cross-section, but in previous and older plugs a circular cross-section was standard. The terminal pins moulded into the plug base are accessible from the other side of the base, that is from the inside OMP of the plug, for connection thereto of the respective "earth", "neutral" and "live" conductors of an elec¬ trical-flex or cable, and commonly are each provided -with a screw-type terminal fixment for securing the conductor to the terminal. A fuse-holder is commonly provided between the "live" terminal pin and its screw-type ixment, and a cable clamp arrangement is commonly provided for securing the flex or cable to the plug base.' The standard British plug abovedescribed differs from the plug used throughou-t the rest of Europe. The European plug, as opposed to the British plug, commonly comprises a generally cylindrical housing formed at one end with an axial cable entry and open at the other end for receiving a plug body. The plug body has a wall portion which defines the plug end face when the plug body is assembled with the housing and two spaced-apart , circular cross-section "live" and "neutral" terminal pins are moulded into and project through the wall portion to be received in corresponding openings of a complementarily- shaped socket outlet. A pair of "earth" terminals con¬ stituted by terminal springs extend from the wall portion backwards with respect to the direction of extent of the two terminal pins to be received in outwardly open grooves formed in the plug housing to be accessible for contacting corresponding "earth" terminal springs provided in the socket outlet. Screw type fixments are provided in the plug body associated with the "live" and "neutral" terminals and with the "earth" terminal for securing the respective cable conductors thereto, and a cable clamp is provided in the plug body. The assembly of a British or European plug onto an appliance flex or cable is a fairly simple and straight¬ forward matter for the person possessed of average elec- trical skills or for the do-it-yourself enthusiast or handyman. However, it is nonetheless a fact that for many people, the .fixing of a plug onto a flex or cable is a task beyond their skills and beyond the scope of their manual dexterity. The number of screw fix ents to be coped with is considered to be primarily respon¬ sible for the difficulty experienced by many people in fixing a plug to a flex or cable, and it is accordingly a primary object of the present invention to provide an electrical mains plug having no (or at least a reduced number of) terminal screw fitments and which can easily be assembled to a flex or cable without the aid of a screwdriver or any other tools. According to the present invention an elec¬ trical plug adapted for use with a socket outlet of a mains electricity distribution system comprises a plug body formed of electrically-insulating synxhetic plastics material and having incorporated therein electrical terminals adapted for cooperation with corres¬ ponding terminal portions in a socket outlet, the plug body having a recess formed therein and an insert of electrically-insulating synthetic plastics material being enterable in said recess, the said insert comp¬ rising a cable clamp arrangement and a plurality of conductor receiving channels each con igured to .receive a conductor end portion having a bend formed therein such as to resist withdrawal of the conductor end from the channel by tension on the conductor, each of said channels being such as to present a respective conductor end portion inserted therein to be contacted when the insert is entered into the plug body recess by an electrically-conductive member providing electrical continuity between the conductor and the respective electrical terminal in the plug body. The invention thus resides in the concept of providing a plug insert which can be readily assembled to the end of an appliance flex or cable by engaging the flex or cable with the clamping means, which is preferably of a type which does not involve screw fit¬ ments, and fitting the conductor ends of the flex or cable into the respective conductor receiving channels. The plug insert then is inserted into its accommodating recess in the plug body and the arrangement of the plug body and the insert is such that when the two are brought together electrical continuity is established between the conductors of the flex or cable and the terminals of the plug. The arrangement could be such that the plug body was provided with pins or other electrical contact establishing means projecting into said recess and the insert was arranged to engage with the recess such that the pins entered * into electrical contact with the con¬ ductor end portions engaged with the insert. Such an arrangement would desirably require there to be a shutter arrangement associated with said recess to close off entry thereto when the insert was not in place, such a shutter being desirable on safety grounds. Alternatively, and preferably, the insert has contact-making terminal pins projecting therefrom, which pins are adapted, to mate with corresponding socket por- tions formed in an inner end wall of the recess and to • enter the said socket portions and contact the plug terminals when the insert is entered into the recess. The contact-making terminal pins are preferably spring loaded so that as the insert is forced home manually into the recess in the plug body, so the contact-making terminal pins are forced back against their spring bias by virtue of their engagement with the plug terminals and, by virtue of being thus forced back, are forced into firmer contact with their respective conductors. In either of the arrangements above entioned, OMPI 7 .-- WH insulation displacement techniques could be utilised to advantage thereby obviating the need to bare the conductor ends of insulation and making assembly of the plug according to the invention to a flex or cable end even more simple. The insert desirably is arranged to make a snap-type locking fit into the recess in the plug body, with a release catch (accessible only when the plug is removed from a socket outlet) provided to enable the insert to be disengaged. For example, the plug body might incorporate a locking catch weakly spring biassed into an inoperative condition out of position to interact with the insert and arranged such that the action of plugging the plug into a socket outlet mechanically urged the locking catch against its bias into an operative condition. The plug according to the invention will preferably incorporate fuse protection of the "live" terminal, for example by means of a pop-up type of fuse mounting accessible on the face of the plug base only when the plug is disengaged from a socket outlet. A polarising arrangement , such as a key formed on the insert to be engageable with a keyway in the plug body recess, is desirably provided to ensure that the insert can be inserted into the recess only in a spec¬ ified orientation. The invention, together with features and ad¬ vantages thereof, will best' be appreciated from consid¬ eration of the following detailed description of exemplary embodiments made with reference to the accompanying drawings wherein:- Figures 1A and IB are respectively top plan and part sectional side elevation views of a first embodiment of the invention with the insert shown detached from its accommodating recess in the plug body, the cross-sectional OMPI view of Figure IB being taken on the line B — B of Figure 1A and internal components within the plug body being shown schematically in Figure 1A; and Figures 2A and 2B show a second embodiment of the invention in views similar to those of Figures 1A and IB respectively. Referring first to Figures 1A and IB, the electric plug shown therein is of the three-pin type employed in the United Kingdom. As shown, the plug comprises a body portion 1 and an insert 2 enterable into a recess 3 in the body portion 1. The body portion 1 and insert 2 are each moulded from high impact, rigid synthetic plastics material and, as is schematically represented in the Figures, brass terminal pins 4 are moulded into the plastics material. A fuse holder 5 also is incorporated into the moulding, the fuse being accessible through a pop-up cover (not shown) provided in the -base of the plug so as to be accessible only when the plug is not plugged in to a socket outlet. Schematically represented conductors 6, cons¬ tituted by brass strappings integral with or otherwise firmly affixed to the terminal pins 4, couple the ter¬ minal pins 4 to insulation displacement type terminal . pins 7 which project into the recess 3 from its end wall. Referring to the construction of the insert 2, it will be seen to comprise a cable clamping arrangement 8 located in a cable input port 9 5 and three conductor- receiving channels 10 which are each formed with a right-angled bend. A bore 11 provides access to the vertically-oriented limb of each channel 10 so that when the insert 2 is entered into the recess 3 in the body portion 1 of the plug, the insulation displacement pins 7 will enter the bores 11 and will penetrate into - the channels 10. A key 12 is formed on the underside of the insert 2 for cooperation with a keyway 13 formed in the base of the recess 3 to ensure that the insert 2 can be entered into the " recess 3 ---- the correct orientation only. A locking member 14 is provided in the body portion 1 of the plug with spring biassing, for example by means of an elastomeric collar 15, towards the base of the plug so that when the plug is inserted into a socket outlet the contact of the locking member l4 with the surface of the socket outlet urges the member 14 against its bias towards the recess 3 and into engagement with a locking formation l6 formed in the underside of the insert 2. I21 use of the plug of Figures 1A and 13 and in order to attach the plug to an end of an electrical flex or cable, it is necessary only to cut back a short section (about 2 cms) of the outer cable sheath so as to expose the conductors. The respective "earth", "neutral" and "live" conductors are inserted to their fullest extent into the respective channels 10, the cable is engaged with the cable clamping arrangement 8 by inserting the cable between the two resilient limbs of the cable clamp, and the insert 2 with cables thus attached is entered into the recess 3 in the plug body 1 to its fullest extent and until the insert becomes flush with the surface of the plug body 1 and does not project therefrom. The arrangement of the locking member 14 and the nature of its cooperation with the formation 16 in the insert 2 are such that if the insert is not fully received in the recess 3, then the locking member 14 cannot engage with the formation 16 and thus cannot be depressed which prevents the plug from being engaged sufficiently with a socket outlet to make live electrical contact therewith; only if the insert 2 is fully entered OMFI WIPO into the recess 3 can the locking member l4 be depressed and the plug engaged with a socket outlet. Referring now to Figures 2A and 2B, where the same reference numerals are used for like parts as were used in Figures 1A and IB, a second embodiment is shown which differs from the first embodiment above- described principally in regard to the manner in. which electrical continuity is established between the con¬ ductors of a flex or cable fitted to the insert 2 and the plug terminal pins 4. Considering first the body portion 1 of the plug, it will be s - _zx that the terminal pins 4 are coupled within the plastics material of the plug to brass terminal pads 17 which may be integral with the terminal pins 4 or can be strapped thereto by elec¬ trically conductive straps 6. The terminal pads 17 are wholly encapsulated within the plastics material of the plug body, but can be accessed for the purpose of making electrical contact thereto through bores lδ which, as shown, extend part way into the terminal pads 17. The insert 2 has moulded into it three brass termination- members 19 each ormed with a bore which serves as part of the vertical limb of a respective one of the conductor-receiving channels 10 as shown. Re¬ tained within each of the members 19 is a spring-loaded axially-displaceable plunger 20, the spring being schematically shown. The plungers 20 are sized to fit within the bores l8 in the body portion 1. In use of the plug of Figures 2A and 2B, the conductors of an electrical flex or cable are bared at the flex or cable end and a short length (less than 1 cm) of the conductor insulation is removed so that each conductor has a bared end. With the flex or cable lodged in the cable clamp 8, the individual conductors are laid into the channels 10 with their bared con¬ ductor ends inserted to their fullest extent into the bores in the members 19• T e insert is then entered into the recess 3 in the plug body 1 which brings the plungers 20 into registry with the bores 18. .As the insertion proceeds, the plungers 20 enter the bores l3 and their leading ends butt against the terminal pads 17 and thereafter, the final stage of insertion of the insert 2 causes the plungers 20 to be driven back against their spring bias and into firm mechanical engagement with the bared conductor ends. Insertion is complete when the locking member 14 clicks into the detent lβ in the base of the insert 2, and in this condition the insert 2 is retained securely in the plug body 1 and the bared conductor ends are retained in secure mechanical and electrical contact with the members 19- From the foregoing, it will be appreciated that the invention provides an electrical plug, for use with a mains socket outlet, which can be assembled to the end of an appliance flex or cable very easily and without the need for any tools other than whatever may be required to release the conductors of an end part of the flex or cable from its outer sheath and, in the case of the second embodiment, to bare the con¬ ductor ends of their insulation. It will of course be appreciated that the second embodiment could readily be adapted for insulation displacement techniques which would obviate the need to bare the conductor ends. Tests have demonstrated that with a plug as above described connected to a flex or cable and the plug engaged with a socket outlet, tension applied on the flex or cable will cause the plug to disengage from the socket and will not pull the insert out of the plug body; the plug is thus safe in use.. G:. ?I While the invention has been described with particular reference to a British type three-pin plug, it will readily be appreciated by those possessed of appropriate skills- that the invention is equally applicable to the continental European type of plug and indeed, so far as the Applicants are aware, to any and all types of domestic plug currently in use. The two embodiments of the invention herein described are examples of how the inventive concept might be applied and various alterations, variations and modi ications are possible and will occur to those possessed of appropriate skills. The invention is therefore not to be considered as limited to the des¬ cribed embodiments but rather as exemplified thereby, and all changes, alterations, variations and modifi¬ cations as come within the spirit and scope of the appended claims are intended to be embraced by the invention.

Claims: CLAIMS : 1. An electrical plug comprising a body portion having terminal pins to be inserted into the corres¬ ponding openings of a socket outlet and an insert portion enterable into a recess in said body portion, the insert portion comprising a cable clamping arra¬ ngement and separate conductor-receiving channels for the separate conductors of the cable to which the plug is to be fitted, each of said channels being configured to receive a conductor end portion therein at a location to be accessed for making electrical contact thereto, and cooperating means being provided in said body portion and in said insert such that when the insert is entered into the recess in the body portion electrical continuity is established between the conductor end portions rece¬ ived in .the channels of the insert and the terminal pins of the body portion. 2. An electrical plug as claimed in claim 1 wherein said cooperating means is constituted by said body portion having terminals projecting into said recess from an end wall thereof and said insert being arranged such that when the insert is entered into the recess the said terminals enter into electrical contact with the conductor end por¬ tions received in said channels. 3 - An electrical plug as claimed in claim 2 wherein said terminals projecting into the recess in the body portion comprise insulation displacing terminal members. ^. An electrical plug as claimed in claim 3 wherein said insulation displacing terminal members comprise insulation piercing pins. 5. An electrical plug as claimed in claim 1 wherein said cooperating means is constituted by said insert having contact-making terminal members projecting from a front face thereof and adapted to be received in corresponding socket members formed in an end wall of said recess and, when received therein, to make electrical contact with the term¬ inal pins of the plug. 6. An electrical plug as claimed in claim 5 wherein said contact-making terminal members proj¬ ecting from a front face of the insert each comprises a spring-biassed plunger displaceable within a bore of a terminal member mounted within the insert, the said bore communicating with a respective one of the conductor-receiving channels formed in the insert such that when the insert is entered into the recess in the body portion the plungers are driven back against their spring bias and into electrical and mechanical contact with the conductor ends in the respective channels. 7- A electrical plug as claimed in any of the preceding claims wherein said insert has a key portion adapted to be received in a key-way formed in a wall of the recess in the body portion whereby the insert can be entered into the recess only in a predeter¬ mined proper orientation. 8. An electrical plug as claimed in any of the preceding claims wherein the body portion of the plug includes a locking member which is spring biassed into an inoperative condition wherein a portion of the locking member protrudes from the base surface of the plug, namely the surface wherefrom the terminal pins project for engagement with the openings of a socket V/I?0 outlet, and the insert has a formation adapted for engagement with said locking member when the insert is fully entered into the recess, the protrusion of the locking member from the base surface of the plug when the insert is not fully entered into the recess of the plug body portion being such as to prevent electrical current carrying engagement of the plug with a socket outlet. 9. A plug as claimed in claim 8 wherein the locking member is secured in the body portion of the plug by means of an elastomeric member providing said spring biassing. 10. A plug as claimed in any of the preceding claims wherein said conductor-receiving channels are of a con iguration such that a conductor laid into a channel will be bent to conform to the channel con¬ figuration whereby the inherent rigidity of the con¬ ductor will act to inhibit- withdrawal of the conduc ¬ tor from the channel under tension applied to the flex cable of which the conductor forms part.

Inventors: CUNNINGHAM D, USHER H
Applicants: CUNNINGHAM D, USHER H
Application year: 1981
Main classification: H01R19
IPC codes: H01R4, H01R13, H01R24, H01R31