GB2037505A - An Electrical Plug and Socket - Google Patents

Abstract

In an electric power outlet and mating plug for a two or three wire alternating current system, the plug 42 has a single projecting insulating probe 44 which carries contacts 45, 46, 48. The outlet has a blind aperture, which receives the plug probe 44 and has spring biased protective covers 32, which may also be the earth contacts which close off access to the live contact 36 at the bottom of the outlet aperture when a plug is not inserted. The plug is held in the outlet in one of two depth positions, the outermost position preventing live contact, to provide an integral switch function. When the plug 42 is inserted, ring contacts 45, 46 thereon engage respective outlet earth and neutral contacts 32 and 30 and a live contact 48 engages the live outlet contact 36. The protective covers may comprise the neutral contacts, the outlet earth contacts being defined by bulbous portions on a metal casing which engage grooves provided in an earth contact ring on the plug. <IMAGE>

Description

SPECIFICATION An Electrical Plug and Socket This invention relates to electric power outlets and complementary plugs for two or three-wire alternating current mains systems. The preferred form of outlet is particularly adapted for in-line grouping to provide multiple outlets.

The single-phase A.C. distribution system commonly used in domestic and commercial premises may be either a two or three-wire system, the latter being necessary where a multiple earthed neutral system is used.

Accordingly, electrical apparatus which is not permanently connected to the distribution system must connect to the system by a withdrawable plug and complementary outlet. In New Zealand the plug contacts take the form of three spaced apart flat metal pins asymmetrically arranged which pass through corresponding slot apertures in a complementary socket-outlet housing. Other countries have different pin arrangements. Such connections have a number of disadvantages.

These include difficulty in aligning the plug and socket; the ease with which the plug pins may be deformed; special design to provide for fused plugs; and (usually) sockets which are not child proof, in that thin metallic objects may be inserted into the socket phase contact.

A further disadvantage of sockets used hitherto is that if more than two sockets are grouped to form a multiple outlet special arrangements must be made for their mounting and housing and they must be laboriously wired together on a point-topoint basis.

It is an object of the present invention to provide an electrical power outlet and a complementary plug which will go at least some way to overcoming the abovementioned disadvantages or will at least provide the public with a useful choice over existing devices.

Accordingly, in one aspect, the present invention consists in a single-phase alternating current power outlet comprising; an insulating base, a blind aperture therein, a pair of abutting flexible neutral contacts which extend from opposite sides of said aperture to thereby normally close off the aperture, and a phase contact located at the bottom of said aperture.

In a further aspect the invention consists in a single-phase alternating current power outlet comprising: an insulating base, a blind aperture therein, a pair of abutting flexible earth contacts which extend from opposite sides of said aperture to thereby normally close off the aperture, a pair of oppositely located sprung neutral contacts which project into said aperture at a substantial distance below said earth contacts, and a phase contact located at the bottom of said aperture.

In yet a further aspect the invention consists in a single-phase alternating current power plug comprising: an insulating housing, an insulating probe extending therefrom, a phase contact projecting from the end of said probe, a conducting ring round said probe which forms the neutral contact, and terminals in connection with said contacts located within said housing.

In yet a further aspect the invention consists in a single-phase alternating current power plug comprising: an insulating housing, an insulating probe extending therefrom, a phase contact projecting from the end of said probe, a first conducting ring around the root of said probe which forms the earth contact, a second conducting ring around said probe a substantial distance down the probe from said first ring which forms the neutral contact, and terminals in connection with said contacts located within said housing.

Preferred forms of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a cross-section through one form of power outlet, Figure 2 is a cross-section through one form of power plug, Figure 3 is a transverse cross-section showing the plug of Figure 2 in engagement with the outlet of Figure 1, and Figure 4 is a cross-section through a second form of power outlet in which is engaged a second form of plug.

The cross-sectional view of the outlet shown in figures 1 and 3 indicates either a single outlet housed in a similarly sized case or box, or one outlet of many shown in figure 2 is used with either form of outlet configuration and has a probe portion 10 which is substantially circular in cross-section.

The first form of outlet will be described as used as an outlet segment in a linear away housed with a length of trunking. Installation in a single box will be apparent from this description: Referring to figure 1 each outlet includes a base 1 5 which is formed from a material which is an electrical insulator. Each base 1 5 is provided with a slot or aperture 20 shaped so as to accommodate neutral contacts 1 7a and 1 7b and a phase contact 1 6 disposed along the floor of the slot. Mounted on the top surface of each base 1 5 is a pair of hinged covers 21 a and 22b extending from opposite sides of the slot walls and meeting along one edge at the centre line of the slot to close off the slot when a plug is not inserted.

Similarly the neutral contact comprises two pairs of conductors 1 7a and 1 7b which extend into the slot from the side walls with edges which abut along the centre line of the slot to effectively close it off at a level below that of covers 21a and 21b.

Thus in the absence of a mating plug the phase contact 1 6 is shielded by first the top covers, and second the neutral contacts.

Upon the insertion of a mating plug as indicated in figure 3, covers 21 a and 21 b hinge downwardly at the edges of the slot 20 to allow entry of the plug probe 10. Continued application of the plug insertion force causes probe 10 to depress neutral contacts 1 7a and 1 7b downwardly to allow the end of the probe to make contact with the phase contact 1 6. The neutral contacts 1 7a and 1 7b open by pivoting about mounting pieces 1 8 against the influence of biasing means 1 9 located in grooves provided in the slot walls.In the "piug inserted" position the neutral contacts bear against a conductive shroud or ring which surrounds probe 1 0. Since a plug may be inserted at the join between two adjacent outlets and thereby possibly expose some portion of a phase contact 16, the plug housing is dimensioned so as to be capable of covering the top surface of two outlets.

The metal casing or trunking 1 3 comprises the system earth conductor and electrical contact is made with the plug by way of the bulbous portions 14 forming the edge of the casing walls bearing against a peripheral earth ring 5 which encompasses the plug housing. In use the projections of the metal case 1 3 which extend above the surface of the base sections 1 5 produce a spring action which maintains contact between extremities 14 and a corresponding groove 22 provided in the plug earth ring 5.

Referring to figure 2 there is shown a mating plug for use with the outlet described. The plug comprises a housing 6 formed from an electrical insulator, a cover plate 8 fastened to the under surface of housing 6 by means of screws 7 to clamp the plug probe 10 and its associated components to the plug housing. The plug terminals 2 are accessed from the top of the housing which is covered with a cap 1 also held in position by means of the screws 7. Cylindrical probe 10 which is formed from an electrical insulator carries an external metallic ring or shroud 9 which forms the neutral contact and includes within a longitudinal bore a projecting phase contact 12. The phase contact abuts against one end of a cylindrical shaped fuse 11 which rests against the bottom of the probe bore.

Phase contact 12 is thus a sprung contact and when inserted in the mating outlet, as shown in figure 3, is pushed upwardly and held in contact with the phase contact 1 6 by the downwardly directing force due to compression spring 4. As has already been mentioned the plug neutral contact 9 bears against the sprung neutral contacts 1 7a and 1 7b of socket. The housing 6 of the plug carries a peripheral metal ring 5 which forms the earth contact and in use engages with the corresponding contacts 1 4 of the socket as previously described. The earth and neutral contacts, and the fuse spring are connected to the plug terminals in a manner well known in the art.

Preferably a second groove is provided in the plug earth ring 5 below groove 22 to provide an off-on switch action by depression and withdrawal of the plug. Socket extremities 1 4 engage with groove 22 when power is to be supplied to the plug and engage with the second groove when power is to be disconnected. In the latter position the plug phase contact 1 2 does not touch the outlet phase contact 16, but the plug still remains in engagement with the socket and maintains earth and neutral contact.

The construction of the second, and preferred form, of plug and socket illustrated in figure 4 will be described by referring to the modifications which have been made to the plug and socket already described in order to reach the figure 4 embodiment. Referring first to the socket, which forms a segment for insertion into a trunking trough similar to case 13 (figure 1) or a flush box, the most significant modification is the location of the neutral contacts 30 deeper in slot 31 and the placement of earth contacts 32 at the mouth of slot 31 to provide the protective cover when a plug is not inserted. The construction of earth contacts 32 is similar to that for neutral contacts 1 7a and 1 7b illustrated in figures 1 and 3.

Provision for wiring the sockets is made by providing a total of five apertures running through the socket base 33 parallel to the direction of slot 31 and locating terminals in these apertures, the screws of which are accessed from the outside of the base. Internal connectors link the terminals to the socket contacts. This enables a number of sockets located in a common trunking to be wired together by simply passing conductors through the in-line wiring apertures, of all outlets and tightening the terminal screws of each socket.

In figure 4 the earth and neutral contacts are provided with pairs of terminals 34 and 35 since there are two oppositeiy located contacts for earth and neutral connections and since an internal connection between each member of the pair would present practical difficulties. The phase contact 36 is located in a recess 37 provided in the floor of slot 31. Phase contact 36 is a spring contact as opoosed to the flat contact 1 6 of figures 1 and 3, and in use grips a central pin which projects from the mating plug. Only a single terminal 38 is required for the phase contact. The terminals 35 and 38 are integral with the contacts themselves and obviate the need for a separate connecting conductor. Earth contact 32 is separate from terminal 34 although terminal 34 is integral with a conductor which connects with contact 32.

Each socket may be placed singularly or together with other sockets in a trunking or in a flush box having flanged top edges which engage within slots 41 provided at the top of the socket bases 33. The base material is sufficiently resilient to allow the top to be deformed inwardly to permit engagement of slots 41 with the trunking or flush box flange. Where a trunking system is used and there are spaces between sockets these spaces, and thus the socket connecting conductors, are covered by plates of suitable length.

The plug 42 varies from the plug illustrated in figure 2 as a consequence of the changes in socket configuration. The base 42 and the cap 43 of the plug are different from the previous plug embodiment but this is not material, the configuration and interelation of these elements being determined by production requirements.

Probe 44 extending from base 42 now carries two conductive rings-an earth ring 45 and a neutral ring 46. These are positioned along the length of the probe so as to engage with respective earth socket earth and neutral contacts 32 and 30. An internal connection between contact 46 and the plug neutral terminal is made by an internal co-axial conductor which is separated from earth ring 45 by insulating material 47. The plug phase contact now takes the form of a spring loaded pin 48 which projects centrally from the end of the probe 44 and in use projects through an opening 49 in the socket to connect with socket phase contact 36. The phase pin 48 is biased upwardly by a compression spring 50 so as to make contact with a cylindrical fuse element 51 which is connected at its opposite end to the plug phase terminal. The use of a phase pin and spring socket contacts 36 provides greatly improved contact over the phase contact described in relation to the previous embodiment.

The switch action previously described is retained by the provision of a second circumferential groove 52 around the lower end of probe 44 which engages with neutral contact 30 upon the plug being withdrawn a predetermined distance. This distance is calculated to result in phase pin 48 being disconnected from the socket phase contact 36.

Compression spring 50 must be made sufficiently strong to provide an upward force which is greater than the frictional forces between socket contact 36 and phase pin 48 to ensure proper operation of this switch function.

Claims (18)

Claims

1. A single phase alternating current power outlet comprising: an insulating base, a blind aperture therein, a pair of abutting flexible neutral contacts which extend from opposite sides of said aperture to thereby normally close off the aperture, and a phase contact located at the bottom of said aperture.

2. A power outlet according to claim 1 wherein a pair of sprung earth contacts are provided above said neutral contacts.

3. A power outlet according to either of claims 1 or 2 wherein said base is adapted to clip within a casing having a correspondingly sized cross section.

4. A single phase alternating current power outlet comprising: an insulating base, a blind aperture therein, a pair of abuting flexible earth contacts which extend form opposite sides of said aperture to thereby normally close off the aperture, a pair of oppositely located sprung neutral contacts which project into said aperture at a substantial distance below said earth contacts, and a phase contact located at the bottom of said aperture.

5. A power outlet according to claim 4 wherein wiring apertures are provided through said base running at right angles to the disposition of said neutral and earth contacts, said apertures containing terminals each connected internally to a corresponding contact.

6. A single phase alternating current power plug comprising: an insulating housing, an insulating probe extending therefrom, a phase contact projecting from the end of said probe, a conducting ring around said probe which forms the neutral contact, and terminals in connection with said contacts located within said housing.

7. A power plug according to claim 6 wherein said housing carries a peripheral conductive ring which forms an earth contact.

8. A power plug according to either of claims 6 and 7 wherein said housing includes a first circumferential groove which in use engages with a resilient member forming part of a complementary outlet, and a second circumferential groove disposed below said first groove so that in use said plug may be partially withdrawn from said complementary socket, the outlet resilient member then engaging with said second circumferential groove in a manner such that the plug and outlet phase no longer connect.

9. A power plug according to any one of claims 6 to 8 wherein said probe is hollow and contains a cylindrical fuse link having end caps one of which makes contact with said plug phase contact and the other of which makes contact with the plug phase terminal through a compression spring which provides contact pressure for the fuse end caps.

1 0. A single phase alternating current power plug comprising: an insulating housing, an insulating probe extending therefrom, a phase contact projecting from the end of said probe, a first conducting ring around the root of said probe which forms the earth contact, a second conducting ring around said probe a substantial distance down the probe from said first ring which forms the neutral contact, and terminals in connection with said contacts located within said housing.

1 A power plug according to claim 10 wherein said housing carries a peripheral conductive ring which forms an earth contact.

12. A power plug according to either of claims 10 or 11 wherein said housing includes a first circumferential groove which in use engages with a resilient member forming part of a complementary outlet, and a second circumferential groove disposed below said first groove so that in use said plug may be partially withdrawn from said complementary outlet, the outlet resiliant member then engaging with said second circumferential groove in a manner such that the plug and outlet phase contacts on longer connect.

13. A power plug according to any one of claims 10 to 12 wherein said probe is hollow and contains a cylindrical fuse link having end caps one of which makes contact with said plug phase contact and the other of which makes contact with the plug phase terminal through a compression spring which provides contact pressure for the fuse end caps.

14. An electric power outlet according to claim 1 and mating plug for a two or three wire alternative current system comprising a plug with a single projecting probe which carries all the plug contacts and in which the outlet has a slotted aperture into which the probe is inserted at any point along the slot.

1 5. A power outlet and mating plug according to claim 14 in which a plurality of outlets are grouped together to form a segmented track.

1 6. A power outlet and mating plug according to claim 14 or claim 1 5 in which the live terminal of the outlet has protective covers which are displaced by insertion of the plug probe.

1 7. A power outlet and mating plug according to claim 1 6 in which the protective covers comprise the earth terminal of the outlet.

18. An electric power outlet and mating plug substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

1 9. A power trunk comprising electric power outlets which received mating plugs according to any of claims 14 to 18.