GB2276781A

GB2276781A - Improvements relating to electrical plugs

Info

Publication number: GB2276781A
Application number: GB9406503A
Authority: GB
Inventors: Anthony James Ridding
Original assignee: CLAMASON IND Ltd
Current assignee: CLAMASON IND Ltd
Priority date: 1993-03-31
Filing date: 1994-03-31
Publication date: 1994-10-05
Anticipated expiration: 2014-03-31
Also published as: GB9406503D0; GB9306733D0; GB2276781B

Abstract

An electric plug is provided with a conductor path 30 from the cable entry 50 through the plug's body to the electrical connectors 19, 20,36 attached to the plug's pins, the path being of the same length for each of the conducting wires 47, 48, 49 concerned. This enables the wires 47, 48, 49 to be cut to the same length so facilitating assembly line production. Preferably the conductor path 30 follows the periphery wall of the plug body for a substantial part of the way. This provides for sufficient space to accommodate the fuse (27) (figure 6) and fuse holder (26) between the pins of the plug in a longitudinal alignment with the cable entry 50. The overall plug size is potentially reduced by this better use of the internal space in the plug. The cable is gripped by ribs 44 when the base and lid of the plug body are permanently interconnected. The plug pins are held in place by lid portions and by snapfit ribs. <IMAGE>

Description

IMPROVEMENTS RELATING TO ELECTRIC PLUGS This invention relates to electric plugs, particularly, though not exclusively, of the kind intended for use with domestic wiring installations.

Conventionally an electric plug, whether having two or three plug pins, has its interior so arranged that for the electric conductors of a multi-conductor supply cable to be connected to the pins the conductors have to be separated from one another just inside the interior of the plug. From there the cable enters the interior the conductors are taken along different paths to the pins. At least for a three pin electric plug it is generally desirable for the conductors to be cut to different lengths inside the plug in order to facilitate their accommodation in the space available in the interior between the cable entry and pins without excess conductor length. Cutting the connectors to different lengths is an undesirable requirement when plugs are to be connected to cables on a production line in a factory, particularly as it is less condusive to automation.

According to a first aspect of the present invention an electric plug is provided which comprises an insulating body having a cable entry for a flexible insulated multi-conductor supply cable into its interior and at least two plug pins carried by and projecting from the body having connector means for the connection of the electric conductors of a supply cable to the pins in the body interior, and which has a conductor path defined in the body interior extending from the cable entry for a substantial part of the distance from the cable entry to a region of the body interior remote from the cable entry, the connector means and the conductor path being relatively arranged such that the electric conductors of a supply cable entered into the body interior are able to be of similar lengths in the body interior and to be laid along the conductor path together from the cable entry for a substantial part of the length of the path to the connector means.

According to a second aspect of the present invention there is provided an assembly comprising an electric plug and a length of flexible insulated multi-conductor supply cable, the plug comprising an insulating body having a cable entry into its interior and at least two plug pins carried by and projecting from the body having connector means in the body interior, the body interior having defined therein a conductor path extending from the cable entry for a substantial part of the distance from the cable entry to a region of the body interior remote from the cable entry, the supply cable being entered into the body interior at the cable entry and having its electric conductors of similar lengths in the body interior and laid along the conductor path, and the conductor path and conductor means being relatively arranged such that the electric conductors extend together along the conductor path from the cable entry for a substantial part of the length of the path to the connector means to which they are respectively connected. The electric conductors may be permanently electrically connected to the connector means, or the connector means way be adapted for the releasable connection of the conductors to the pins.

The conductor path may be defined by walls, ribs, partitions or the like provided in the body interior.

The ribs, partitions or the like may be integral parts of the body. Where the plug body is formed of two halves the ribs may be provided on both or only one of the halves.

Preferably the conductor path extends around part of the perimeter of the body interior between the cable entry and the connector means.

The conductor path may be defined by a rib having a given constant spacing from the perimeter. The rib may be in the form of an arc.

Additional ribs may be provided to guide the separate conductors to their respective connector means. In this arrangement a fuse location may be provided centrally, or substantially centrally, of the body and may be in alignment, or substantially so, with the cable entry.

The connector means may be provided directly on the plug pins themselves in the body interior, for example by holes in the pins to receive bared ends of the electric conductors, or they may be provided on terminals made as separate components from the pins but electrically connected to the pins, or there may be a combination of such directly and separately provided connector means.

By enabling the electric conductors to be of similar lengths in the body interior and to be retained together along the one conductor path for a substantial part of their way to the connector means, assembly of the plug on a, or the, supply cable and connection of the conductors of the cable to the pins is appreciably facilitated, which is a considerable advantage particularly when assembly is to be carried out on a factory production line.

According to a third aspect of the present invention an electric plug is provided which comprises an insulated body having a cable entry for a flexible insulated multi-conductor supply cable into its interior formed with one or more integral cable grip formations adapted to restrain from withdrawal a cable engaged in the entry for use of the plug.

The or each cable grip formation may comprise a rib, fin or the like which projects into the cable entry from a peripheral wall or walls of the entry.

The or each formation may be inclined, or have an inner edge inclined, towards the body interior such as to permit a supply cable to be inserted fairly readily through the entry past the formation or formations but cause the cable to be gripped more tightly if a force is applied to the cable urging the cable out of the entry. Several of the formations may be spaced around, and along, the inside of the entry. In a preferred form ribs are provided on the top, bottom and side walls of the entry.

According to a fourth aspect of the present invention an electric plug is provided which comprises an insulated body carrying at least two plug pins which project from an external face thereof and at least one of which pins is mounted to the body by having been inserted into a socket in the body and engaged in the socket by retention means whereby subsequent withdrawal of the pin from the socket is restrained.

The pin may be introduced through the external face of the body or alternatively it may be introduced through the internal face.

The retention means may have a snap engagement with the pin to retain the pin in the socket. In a preferred example the pin has one or more grooves in the part which is received into the socket with which a projection or projections in the socket snap into engagement. The or each projection may, for example, be an inclined or bevelled lug, pip or'bead. Where the projection is bevelled or inclined the surface is preferably that abutting the pin list on insertion.

The socket may have a blind inner end which the pin abuts when it is fully home in the socket to be restrained by the retention means. As an alternative the socket may be formed by a through passage in a base part of the plug body, and have an inner end or abutment presented by a co-operating stop on a lid part of the body.

Conventionally electric plugs have the plug pins mounted to the body by having shank portions inserted from the inside of the body through holes in the body of complementary cross-section opening to an external face of the body. Larger cross-section head portions of the pins are retained inside the body. Pins for electric plugs are usually made from brass. The shank portions of pins mounted in the conventional manner are most commonly formed by machining away metal from brass bars or blanks of the larger cross-section of the head portion of the pins. There is thus wastage of metal which is undesirable with regard to manufacturing cost.

A pin which is mounted in the plug body in accordance with the fourth aspect of the invention herein set forth need not have a larger cross-section head portion so that the wastage of metal associated with the conventionally mounted plug pins may be avoided. The pin preferably has a groove or slot removed from it to engage with the socket projection, but is otherwise of the cross-section corresponding to the pin. In this way the cost of production both through wastage and machining is reduced.

The electric plug may have a body which has a separable lid part, secured for example by means of a screw or screws, or the body may have a lid part which is permanently secured to the body once the electric conductors of a or the supply cable have been connected to the plug pins.

Thus according to a fifth aspect of the present invention an assembly is provided comprising an electric plug and a length of flexible insulated multi-conductor supply cable, the plug comprising an insulating body having a cable entry into its interior and at least two plug pins carried by and projecting from the body having connector means in the body interior, the supply cable being entered into the body at the cable entry and having its electric conductors connected to the connector means of the plug pins, and the body having a lid part which is bonded, fused or otherwise secured to close the body permanently when the electric conductors of the a cable have been connected to the connector means.

The lid part may, for example, be ultrasonically welded to secure it permanently closed.

An electric plug or plug and cable assembly may be provided which embodies all of the aspects of the invention set forth.

According to a sixth aspect of the invention, we provide an electric plug, comprising an insulating body having a cable entry and having two or more pins carried by and projecting from the plug body, the plug being provided with a fuse or fuse holder, the fuse or fuse holder being positioned between at least two of the pins.

This positioning of the fuse or fuse holder provides for a more compact plug structure.

Where an elongate fuse is used, the fuse is preferably aligned, or substantially aligned, longitudinally in the cable entry to the plug. In a most preferred form, the fuse is longitudinally aligned between the ends in a central position.

This arrangement provides for a most compact structure, particularly where the conductors entering the plug by means of the cable entry are fed from the cable entry around the periphery of the body to be connected to their respective pins.

Access to the fuse or fuse holder is preferably achieved by providing an opening in the portion of the plug carrying the pins. The opening may be provided with a cover portion, which may be integral with the fuse holder.

An embodiment of the various aspects of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a rear view of an electric plug in accordance with the invention; Figure 2 is an underneath view of the electric plug; Figure 3 is a plan view of the plug with a lid part of its body removed; Figure 4 is an inverted plan view of the lid part of the body; Figure 5 and 6 are sections through the complete plug taken on lines 5-5 and 6-6 of Figure 3, and Figure 7 is a view similar to Figure 3 but showing a supply cable connected to the plug.

In this embodiment a three pin electric plug 1 suitable for use with a domestic wiring installation is provided.

The electric plug 1 has a body 2, comprising a base part 3 and a lid part 4 both of which are made as mouldings of suitable electrically insulating plastics material, and three brass plug pins having shanks of rectangular cross-section for engagement in a conventional three pin electric socket, the plug pins being an earth pin 5, a live pin 6 and a neutral pin 7 and projecting from a rear wall 8 of the body at the base part 3. In this embodiment the body 2 is of circular plan shape but it will be appreciated that it may be of rectangular or other plan shape.

The base part 3 and lid part 4 together define a hollow interior 9 of the body 1 and a tubular cable entry 10 which projects radially from the body and opens to the interior 9. Peripheral walls 11, 12 of the base and lid parts mate at lapped edges 13 to form together a circumferential wall 14 of the body. Inside the base part 3 integral partitioning walls 15 are formed on the rear wall 8 which define locations 16, 17 and 18 respectively for the earth pin 5, the live pin 6 and associated live terminal pieces 19 and 20, and for the neutral pin 7. There is an opening 161, 171, 181 in the rear wall 8 at each location 16, 17, 18 through which the shank of the respective pin extends from the location, the opening being of corresponding cross-section to the shank. The earth pin location 16 is adjacent to the circumferential wall, diametrically opposite to the cable entry 10. At opposite sides of the diametral plane of the body containing the central longitudinal axes of the cable entry and the earth pin location 16 are the live pin location 17 and the neutral pin location 18, the live and neutral pins being spaced equal distances from that diametral plane.

Inside the lid part 4 of the body are three integral boss formations 21, 22, 23 of cross-shaped cross-section which are positioned to overlie respectively the earth pin location 16, the live pin location 17 and the neutral pin location 18.

Also formed integrally with base part 3 and the lid part 4 are wall formations which co-operate to form two guide walls 24, 25 which lead from a position intermediate the earth and neutral pin locations and near to the circumferential wall 14, respectively towards the earth pin terminal 16 and one of the live terminal pieces 19.

Further wall formations in the base part, on the rear wall 8, define an oblong box-like fuse housing 26 for a conventional fuse 27 ( for example 13 amp) and its holder 28. The fuse housing 26 has an opening 29, through the rear wall but a cover portion 28 r of the fuse holder 28 snap engages in that opening to close it whilst the fuse 27 is in place. The fuse housing 26 is positioned so that it locates the fuse 27 parallel to but just off centre from the central longitudinal axis of the cable entry 10 towards the live pin 6.

r From the cable entry 10 to the earth pin location 16 a continuous space is left in the body interior 9 between the circumferential wall 14 and the adjacent partitioning walls 15 at the neutral pin location 18 and walls of the fuse housing 26. This space defines a conductor path 30 which extends almost half-way round the body interior and is for the electric conductors of a supply cable which may be connected to the plug for use of the plug. The conductor path 30 takes the conductor leads to the earth and neutral pins and to one live terminal piece 19. The guide walls 24, 25 lead from the conductor path near its end remote from the cable entry.

Earth pin 5 has a head portion 31 of the same rectangular cross-section as its shank. Between the head portion 31 and shank grooves 32 are formed across the two narrow sides of the pin. A plain through hole 33 is provided centrally in the head portion between the two wider sides of the pin. The earth pin 5 is fitted to the base portion 3 of the body 2 by pushing its head portion 31 through the opening 161 in the rear wall and into the earth pin location 16 from the outside of the base part. Inside the location 16 are retention ribs 331 which snap into engagement with the grooves 32 to secure the head portion 31 in the location and restrain the earth pin from movement relative to the base part. The retention 331 ribs 33 have bevelled surfaces inclined away from the opening 161 which facilitate the pushing of the head portion past the ribs and into the location until the grooves 32 are engaged by the ribs. It is also possible to insert the earth pin 5 from the inside of the base portion 3, as the chamfer on the outer end of the pin 5 causes the ribs to flex out of the way. This enables the pin 5 to be wired before Insertion in the plug.

Live and neutral pins 6, 7 are of the more usual form having enlarged head portions 34, 35 respectively which are received into the live and neutral pin locations 17, 18, the shanks of the pins being inserted in this case through the respective openings 171, 181 from the inside of the base part 3 of the body 2. The neutral pin 7 has a central plain through hole 36 in its head portion 35, extending between the two wider sides of the pin. When the lid part 4 of the body is in place closed over the base part the boss formations 21, 22, 23 bear respectively on the head portions of the earth, live and neutral pins to ensure that the head portions are firmly retained in their locations and the pins are restrained from movement relative to the base part.

There are two of the live terminal pieces 19, 20, each made from phosphor bronze sheet. Each piece 19, 20 has a pair of opposed jaws 37 which extend into the fuse housing 26. The jaws 37 of the one terminal piece 19 are positioned near one end of the fuse housing and the jaws 37 of the other terminal piece 20 are near to the other end of the fuse housing.

The pairs of jaws resiliently grip the fuse 27, at it opposite end caps, in the holder 28 when the holder and fuse are in place in the fuse housing 26. One terminal piece 19 is snugly located around its part containing the jaws 37 by adjacent partitioning walls 15 of the base part 3, and has a portion tubularly rolled into a connector 38 positioned between the live and neutral pin locations 17, 18 near to the one guide wall 25.

The other terminal piece 20 has a tab 39 by which it is secured to a short stake 40 on top of the head portion 34 of the live pin. The part of the piece containing its jaws is similarly snugly located by adjacent partitioning walls 15 of the base part 3.

Bearing lugs 41, 42 formed on the inside of the lid part of the body bear on the terminal pieces 19, 20 to assist in holding them firmly in place in the body when the lid part 4 is closed over the base part 3.

The cable entry 10 has a reduced co-axial circular mouth 43 and cable gripping ribs 44 at spaced positions along the length of the entry are formed on the base and lid parts of the body 2. The cable gripping ribs 44 project into the interior of the entry 10 and extend tangentially of a notional cylinder co-axial with the mouth 43 and of a smaller diameter than the mouth. Bevelled inner edges 45 of the ribs 44 slope inwardly away from the mouth 13.

The electric plug described and illustrated is designed to have permanently connected to it a length of standard flexible insulated supply cable 46 having earth, live and neutral conductors 47, 48, 49 respectively in a protective sheath 50. For the connection the lid part 4 of the body 2 is separated from the base part 3. An end portion of the sheath 50 is removed to expose equal lengths of the three conductors 47, 48, 49 the ends of which are bared. The sheath 50 is located in the section of the cable entry 10 in the base part where it is gripped by the cable gripping ribs 44 at that section. From there the exposed conductors are laid along the conductor path 30 in the base part, as shown in Figure 7. The bared ends of the earth and neutral conductors are respectively inserted into the holes 33,36 of the earth and neutral pins 5,7 and soldered in place. The bared end of the live conductor 48 is inserted into the connector portion 38 of the one terminal piece lF associatedwith the live pin 6 and the connector portion is then crimped to secure the live conductor. As will be seen in Figure 7, the guide 24,25 guide the ends of the conductors from the conductor path 30 to the earth and neutral pins and to the connector portion 38.

When the conductors are secured the lid part is fitted over the base part and fused or bonded to it so that the two parts are then essentially inseparable.

The cable gripping ribs 44 of the section of the cable entry at the lid part also grip the sheath of the cable to add to the security of retention of the cable in the entry.

It will be understood that the cable may be connected to the plug, and the two parts of plug body secured together, in a factory on a production line, if desired.

Claims

1. An electric plug comprising an insulating body having a cable entry for a flexible insulated multi-conductor supply cable into its interior and at least two plug pins carried by and projecting from the body having connector means for the connection of the electric conductors of a supply cable to the pins in the body interior, and which has a conductor path defined in the body interior extending from the cable entry for a substantial part of the distance from the cable entry to a region of the body interior remote from the cable entry, the connector means and the conductor path being relatively arranged such that the electric conductors of a supply cable entered into the body interior are able to be of similar lengths in the body interior and to be laid along the conductor path together from the cable entry for a substantial part of the length of the path to the connector means.

2. An electric plug according to claim 1, in which the conductor path is defined by at least one wall or partition formed in the body interior.

3. An electric plug according to claim 1 or claim 2, in which the conductor path extends around part of the perimeter of the body interior from the cable entry towards the connector means.

4. An electric plug assembly comprising an electric plug and a length of flexible insulated multi-conductor supply cable, the plug comprising an insulating body having a cable entry into its interior and at least two plug pins carried by and projecting from the body having connector means in the body interior, the body interior having defined therein a conductor path extending from the cable entry for a substantial part of the distance from the cable entry to a region of the body interior remote from the cable entry, the supply cable being entered into the body interior at the cable entry and having its electric conductors of similar lengths in the body interior and laid along the conductor path, and the conductor path and conductor means being relatively arranged such that the electric conductors extend together along the conductor path from the cable entry for a substantial part of the length of the path to the connector means to which they are respectively connected.

5. An electric plug, comprising an insulating body having a cable entry and having two or more pins carried by and projecting from the plug body, the plug being provided with a fuse or fuse holder, the fuse or fuse holder being positioned between at least two of the pins.

6. An electric plug according to claim 5 in which the fuse is aligned, or substantially aligned, longitudinally with the cable entry to the plug.

7. An electric plug according to claim 5 or claim 6 in which conductors for attachment to the pins follow the periphery of an internal wall of the plug for at least part of their path to the pins.

8. An electric plug according to claims 5,6 or 7 in which the conductors all pass around the same side of the fuse or fuse holder on their path to the pins.

9. An electric plug comprising an insulated body carrying at least two plug pins which project from an external face thereof and at least one of which pins is mounted to the body by having been inserted into a socket in the body and engaged in the socket by retention means whereby subsequent withdrawal of the pin from the socket is restrained.

10. An electric plug in accordance with claim 9, in which the retention means have a snap engagement with the pin to retain the pin in the socket.

11. An electric plug in accordance With claim 9 or Claim 10 in which the socket has a blind inner end which the pin abuts when it is fully home in the socket to be restrained by the retention means.

12. An electric plug in accordance with claim 9 or claim 10 in which the socket is formed by a through passage in a base part of the plug body and has an inner end or abutment presented by a co-operating stop on a lid part of the body.

13. An electric plug in accordance with any one of claims 9 to 12 in which at least one of the pins is provided with a recessed slot or groove.

14. An electric plug substantially as described herein with reference to Figures 1 to 6 of the accompanying drawings.

15. An electric plug assembly substantially as described herein with reference to Figure 7 of the accompanying drawings.

16. An electric plug having a fuse or fuse holder, substantially as herein described with reference to the Figures.