WO1994018721A1

WO1994018721A1 - Electric plugs

Info

Publication number: WO1994018721A1
Application number: PCT/GB1994/000216
Authority: WO
Inventors: Henry Guy Stevens
Original assignee: Henry Guy Stevens
Priority date: 1993-02-05
Filing date: 1994-02-04
Publication date: 1994-08-18
Also published as: GB2291546A; ZA94789B; AU5976094A; GB9517978D0; GB9302229D0

Abstract

The plug pins (3, 4, 5) of an electric mains plug have insulation-displacement connectors (6) fixed at their top ends. The connectors (6) have downwardly-opening slots forced onto unstripped connecting wires by pushing the pin downwardly relative to the plug base (1). Grooved support plates (8), or bosses (164) integral with the plug base, provide a reaction support and alignment of the wire being connected. The plug may incorporate a magnetically-actuated or thermally-actuated circuit breaker (9).

Description

ELECTRIC PLUGS

This invention relates to electric plugs, being particularly envisaged as useful for standard mains plugs e.g. for domestic use.

In the UK and in many other countries, a conventional mains plug has an insulating plug body generally of plastics, with two or three conductive pins mounted through a base of the plug body and projecting below the base for insertion in corresponding holes of an AC supply socket. The individual wires of an electric cable leading to the plug are connected to respective pins by connecting terminals accessible above the plug base, typically inside a cavity of the plug body covered by a movable cover. The most commonly used connecting terminals involve holes bored through the tops of the plug pins for insertion of stripped wire ends, and threaded side-holes for small bolts to clamp the inserted ends in place.

For the live pin, it is in many places common practice to provide a destructible fuse as a circuit breaker, connected between the live pin and the live connection terminal within the plug body. Once fused, t'.v.- fuse must be replaced.

The conventional operations of connecting -wires to pin terminals and exchanging fuses are time consuming, and found difficult by many people.

Proposals have been made for connections eliminating the need for wire stripping and/or screwing. None have achieved wide use, however. The constructions tend to be complicated and/or unreliable. For example, GB-A-2203603 discloses a three-pin domestic electric plug in which three equal-length, unstripped wire ends can be inserted and clamped against insulation-piercing spikes in respective conductive channels connected to the respecting pins. A relatively complicated system of conductors is involved here.

GB-A-2157900 also describes a three-pin domestic electric plug in which a separate insert is used to align the three wires of the cable for insertion into the plug body where each is contacted by a conductive spike connected to a respective one of the pins. Again, the construction is complicated. GB-A-2229588 proposes slotted, upwardly-opening insulation-displacement connectors at the tops of the pins, co-operating with push-button slotted bosses mounted movably in the cover. A complicated cover construction is needed, and alignment of the bosses with the connectors may be unreliable.

I now present some new proposals, which may be used separately or in combination, useful in electric plugs of the type described.

A first proposal is that an insulation-displacement type connecting terminal for a plug pin can be provided as an integral portion of the top of the plug pin, having a slot which opens at one end towards an adjacent wire path for an insulation-coated wire. Relative n.ovement in the slot direction between the wire and insulation- displacement portion, to force the wire into the slot and establish electrical contact therewith, may be effected e.g. by an axial movement of the plug pin relative to the body base to which that pin extends.

The insulation displacement portion having the slot, which may be in a plate form, may be in one piece with the plug pin or may be fixed thereto e.g. by spot-welding or riveting. Where the portion projects laterally relative to the plug pin, the slot can open at an edge thereof towards the base. More preferably the slot is part of an enclosed aperture defined through the insulation displacement portion, communicating with a larger hole through which the insulation-coated wire is passed, along the wire path, for connection. A "keyhole"-shaped aperture may thus be used. Desirably the hole is convergent towards the slot e.g. circular or rhomboidal, to guide the wire into the slot without jamming. An open- ended slot may have chamfers for this purpose. Where the plug has a fuse/circuit-breaker between the live pin and its connecting terminal, that connecting terminal may also be formed in accordance with the teachings above (albeit separate from the live pin).

A second proposal is the provision on the plug body base of a support portion which underlies a wire being engaged by an insulation-displacement connector, to give a reliable and uniform connection. In particular, it is desirable to be able to connect wires reliably by positioning them along their wire paths and then closing a cover of the plug body. A preferred support portion is a projecting boss, relative to which the insulation- displacement connector is movable in the direction of a slot thereof which engages the wire. A support on the base, through or adjacent which the insulation- displacement connector projects axially slidably, is one preferred proposal.

Most preferably the support has a surface recess such as a notch or groove, in which the wire lies to help align it with the slot of the connector. This may be provided on the base surface, without a boss being necessary.

Another preferred option is use of a separate cover positioned on the base and having a through-opening through which the insulation-displacement connector projects. The cover, which can provide a support as described above, lends itself to coding, e.g. colour coding, to identify the respective terminals for the user. Where the connector terminals extend as top continuations of the plug pins, the use of a pin cover overlying the plug pin top enables the connected wire to be supported on both sides of the connector slot.

In any of the above proposals, it is particularly preferred that a main cover of the plug body bear on the insulation-displacement connectors in its closed condition.

A third proposal relates to a circuit-breaker for use in the plug. Instead of the conventional fuse, I propose a thermally- or magnetically-actuated circuit breaker housed in the plug body. This may be connected between the top of the live plug pin and a separate live connecting terminal. Such circuit breakers are known as such, but have not previously been used in domestic plugs. They are reusable and need not be replaced. Preferably the circuit breaker has a reset member exposed at the exterior. When the circuit is broken owing to excess current, the reset member is moved e.g. by a spring, from a set position to a tripped position which is appreciable from the exterior e.g. the member protruding from the plug body. Moving the member, e.g. a spring push-button, back to the set position restores the electrical connection. The plug body may be made from tough resilient plastics material, such as is already conventionally used. It may be injection-moulded.

Embodiments of my new ideas are now described with reference to the accompanying drawings, in which

Fig. 1 is a perspective view from above of a first embodiment of plug with the cover removed;

Fig. 2 is a perspective view of the first embodiment from one end with the cover in place and closed;

Fig. 3 is a perspective view from above and the other end; Figs. 4(a) and 4(b) are respectively edge and side views of an earth pin usable in the first embodiment;

Figs. 5(a) and 5(b) are respectively edge and side views of a neutral pin usable in the first embodiment; Figs. 6(a) and 6(b) are respectively edge and side views of a live pin usable in the first embodiment;

Figs. 7(a) and 7(b) are respectively end and side views of a live connection terminal usable in the first embodiment;

Fig. 8(a) is a plan view of a pin cover and support usable in the first embodiment, and Fig. 8(b) is a section thereon at X-X;

Figs. 9(a) and 9(b) show connection of a wire as would occur in the first embodiment;

Fig. 10 shows the base of a second embodiment of plug with the cover removed;

Fig. 11 shows detail of an insulation displacement portion of a pin of the second embodiment; Fig. 12 is a cross-sectional view of a thermally- actuated circuit-breaker;

Fig. 13 is a plan view of the base of the second embodiment with the pin removed, and

Fig. 14 shows the underside of the plug body cover of the second embodiment.

Referring firstly to Figs. 1 to 3, a three-pin electric plug for a mains socket of the type standard e.g. in the UK for 3-phase AC mains supply has a plastics injection-moulded body 1 having a top cover 2 pivoted to a base unit 25, defining between them a generally rectangular cavity housing various plug components. The base unit 25 has a base plate 11 and side wall 12, interrupted by a cable entry port 13 having a conventional resilient cable grip 14. Three plug pins (neutral pin 3, earth pin 4 and live pin 5 ) fit through rectangular holes in the base plate 11, in a conventional triangular layout. Connecting terminals 6 of the pins project up into the internal cavity from the base plate, as described in more detail below.

A circuit breaker assembly 9 is housed in the plug body along one side, adjacent the live pin 5. The top of the live pin has an upstanding flange 95 connecting to an input terminal 96 of the circuit-breaker 9. An output terminal 97 of the circuit breaker connects to a separate connecting terminal 56, used for connecting the live pin 5 to a wire via the circuit breaker.

As seen in Fig. 2, a reset button 91 of the circuit breaker is exposed at the front of the side wall, and that side wall also has a front recess 18 engaged by a downward snap projection 19 of the cover 2, to hold the plug body releasably closed without the need for screws.

The connecting terminals 6 of the neutral and earth pins 3,4, which operate on generally similar principles, are now described.

The pins 3,4 are made of metal e.g. brass, of a generally uniform rectangular cross-section. See also Figs. 4 and 5. The top of the rectangular-section shaft has a small lateral flange 41,31 to limit downward movement of the pin through the plug base. The pin top is horizontal and flat except for an upstanding flange 42,32 functioning as an insulation-displacement connector. The upstanding flange 42,32 has a keyhole-shaped opening, with an enlarged circular lower region 43,33 communicating with a vertical elongate slot 44,34 at an upper region. The thickness of the flange 43,32 is substantially less than that of the pin; for example about 1mm. The illustrated rectangular shape may be modified by chamfering.

Around the rectangular through-hole, the plug base 11 has an integral upstanding boss 15,16 defining a surface level; the flat pin top lies below this level when the pin is pushed down. Overlying the boss and pin top is a pin cover or support plate 8, here taking a saddle form with side limbs 81 snap-fitting down around divergent side surfaces of the boss 15,16. In Fig. 1, the cover plate 8 of the earth pin 4 is shown detached, and the pin 4 slightly raised, for illustrative purposes. The cover 8 on the neutral pin 3 is shown in place. The pin cover or support plate 8 is generally flat, with an elongate through-slot 83 through which the upstanding flange 32,42 of the pin projects, and a surface groove - here of generally semicircular cross-section - running across the surface and across the through-slot. The groove 84 is vertically aligned with the elongate slot 34,44 of the pin top terminal. The main unslotted area of the pin cover overlies the horizontal flat top surface of the pin but does not rest on it; it rests on the boss 15.

The connection terminal 56 for the live connection also fits in a vertical slot of an upstanding integral boss 16 of the plug base. The- terminal 56 itself is an L- shaped metal member having a keyhole-shaped aperture similar to those described above on one limb of the L, and a plane elongate slot 58 on the other limb. See Fig. 7. The elongate slot 58 is contactingly retained on the outlet terminal of the circuit-breaker 9; a headed pin so that the L-shaped terminal 56 can slide up and down. The boss 16 has a flat top surface with a groove 164, corresponding in structure and function to the grooves 84 of the pin covers 8 described earlier, but in relation to the keyhole aperture 57 of the connector 56. A separate cover element may be used instead, but is not necessary. An advantage of the cover elements is that, being separate, they may conveniently be made in different colours and therefore identify the terminals. The connection operation for the neutral and earth pins is now described, with reference to Fig. 9.

The cable to be connected is in this case a three- strand cable having three individual insulation-coated wires within an outer insulation jacket. The outer jacket is removed for a given length from the end, but the individual wires need not be stripped.

With the plug cover raised, the pin is pushed upwardly until its flat top surface meets the underside of the cover plate 8. In this condition, the enlarged circular portion of the keyhole aperture aligns with the groove 84 (Fig. 9(a)). The insulation-coated wire strand 99 is easily passed through the enlarged hole, resting in the location groove 84. The pin is then pushed down, as shown in Fig. 9(b). It may be pushed directly manually, or conveniently merely by pushing the cover 2 back on. The pin moves down until its limit flange meets the corresponding abutment of the plug base plate. The extent of movement corresponds substantially to the diameter of the enlarged circular hole, so that the wire 99 is constrained (against the reaction of the cover plate 8 ) to enter the narrow slot part of the keyhole aperture, penetrating its insulation and establishing contact in a manner known as such. The groove 84 ensures that the wire is correctly presented to the slot, assisted by the convergent nature of the circular hole edges adjacent the slot mouth.

It should be noted that, with the downwardly-opening insulation-displacement slot proposed here, there is the significant advantage that only a very simple mechanical interaction with the cover 2 is involved in making the electrical contact. The slotted body construction and the slotted insulation-displacement construction are combined on the same plug part, enabling much more precise and reliable operation with better support, not to mention a greatly simplified construction of the cover compared with GB-A-2229588.

Figs. 10 to 14 illustrate another embodiment with different ways of implementing certain technical features. The plug base 25' has a screw hole 19 to engage a corresponding screw hole 119 of the cover 2'.

The construction of the base plate 11' is simpler than the previous embodiment. Instead of using separate cover plates for the pins, the guide and support conformations necessary for interaction with the plate for insulation-displacement connector are formed directly in the plug base itself. Fig. 13 shows the plug base with other components removed. Each of the neutral and earth pins is fitted through a rectangular through-hole 103,104, movement desirably being limited by engagement of a downward shoulder on the pin with an upward shoulder 105,106 at the edge of the hole.

Adjacent the holes are elongate rectangular-sectioned troughs 183 which do not penetrate right through the base plate (although they may do so). Each trough 183 is traversed by an elongate surface groove 184. Referring back to Figs. 10 and 11, the insulation- displacement connectors in this embodiment project laterally from the top of the pin, rather than directly above it as previously. The lateral projection may be formed in one piece, or as shown here by a separate plate welded or riveted to the pin top. The plate 202 has a downwardly opening vertical slot 203 having an outwardly- chamfered entry portion 204. The plate 202 is e.g. 1mm thick. When the pin is inserted in the plug base hole from above, the insulation-displacement plate 202 is aligned with the trough 183 of the base, its slot 203 being aligned with the groove 184. By slightly lifting the pin, the chamfered opening 204 of the slot can be lifted clear of the trough 183 for the unstripped end of a wire to be inserted beneath, guided by the groove 184. By then pushing down on the pin e.g. manually, or by screwing the lid back on, the plate 202 is driven back down into the trough and the slot 203 effects insulation displacement against the reaction of the surface of the groove 184.

The output terminal 56 ' of the circuit breaker 9 ' can be connected in the same way, into a corresponding trough 183 with guide groove 184. In this embodiment the circuit breaker is connected to the live pin 5' by a projecting end terminal 96' which pushes down into a sprung compact fork 95' at the top of the live pin.

Fig. 14 shows a raised land pattern 120 on the underside of the lid 2', partly for aligning the lid accurately with the side walls of the base unit 25' and partly to bear on the ends of the plug pins and their insulation-displacement plates 202, to achieve the electrically-connected state when the cover is secured and to maintain it thereafter.

The circuit breaker is now described in more detail, with reference to Fig. 12. This is the circuit breaker for the Fig. 10 embodiment, but the essential functioning of that in the Fig. 1 embodiment may be the same. A rectangular plastic housing 190 fits snugly into a corresponding recess of the housing. It may snap into place. At one end of the enclosed housing 190 an outwardly-sprung push button 191 is mounted. The button carries an extension plate 192 extending along the inside wall of the housing, adjacent the output terminal 197. The output terminal 197 connects through the housing wall to a contact 193 which, with the button 191 in the inward (set) position, is exposed through a hole 194 in the button extension 192.

The input terminal 96' is a metal bar extending in through the end wall of the housing 190, and mounting at its inner end a bimetallic strip 195 having an end contact 196 opposing the other contact 193.

Under normal operating conditions the contacts 193,196 are held together by spring force of the bimetallic strip, and prevent the reset button 191 from moving outwardly under the influence of its spring 198. In the event of excess current along the bimetallic strip, causing that strip to overheat, the bimetallic strip flexes bringing the contacts 193,196 apart and allowing the button 191 to pop out, visible at the plug exterior (see Fig. 2). The extension plate 192 then keep the contacts apart. Any electrical fault having been identified and remedied, the circuit can be restored by pushing the button 191 to bring the hole 194 back into alignment with the contacts so that they meet again. The operational principles of thermal contact-breakers of this type are well known, and suitable devices are available which trip reliably at a specified current value.

An alternative (not illustrated) is a magnetically- actuated circuit-breaker in which the current flow gives rise to magnetic force using a coil, the magnetic force being deployed to separate the contacts and allow escape of a reset button in generally the same manner as described above. The advantages of circuit-breakers of this type in a mains plug will be apparent. The circuit-breaker is almost infinitely reusable. There is no need to search for replacement fuses of the correct rating. Once the relevant fault has been identified, it is necessary only to push the reset button back in.

Claims

CLAIMS :

1. An electric plug having an insulating plug body with a base plate, and conductive plug pins mounted through the base plate, the plug pins comprising projecting portions projecting below the base plate and adapted for engagement in recesses of an electric socket, and integral connecting terminals accessible above the base plate and adapted for connection to respective insulation-coated wires which in use extend along wire paths of the plug base; the integral connecting terminal of at least one of said plug pins comprising an insulation displacement portion at the top of the plug pin, the insulation displacement portion having a slot which opens at one end downwardly onto the adjacent respective wire path whereby in use relative movement in the direction of the slot between a said insulation-coated wire disposed along the wire path and the insulation displacement portion can force the wire into the slot to establish electrical contact thereof with the insulation displacement portion, and wherein the base of the plug body has a support portion underlying the wire path and opposing the opening of the slot, the plug pin being movable axially relative to the base plate to provide said relative movement whereby the slot is pushable onto the wire against the reaction of the support portion on which the wire rests.

2. An electric plug according to claim 1 in which the support portion has a local recess to align the wire with the slot of the insulation displacement portion.

3. An electric plug according to claim 1 or claim 2 in which the support portion is provided on a separate pin cover which has a hole and is located on the base overlying the top of the plug pin, with the insulation displacement portion of the plug pin projecting up through the hole.

4. An electric plug according to any one of claims 1 to 3 in which the plug body comprises a cover, the cover being movable between an open condition in which it exposes the connection terminal and a closed condition in which it bears on the insulation displacement portion of the plug pin, whereby closing of the cover can effect the relative movement.

5. An electric plug according to claim 4 in which the cover is pivoted relative to the base plate.

6. An electric plug according to any one of the preceding claims in which the insulation displacement portion is in one piece with the plug pin.

7. An electric plug according to any one of the preceding claims in which the insulation displacement portion comprises a plate having said slot.

8. An electric plug according to any one of the preceding claims in which the insulation displacement portion projects laterally relative to the plug pin, and the slot opens at a lower edge thereof.

9. An electric plug according to any one of claims 1 to 7 in which an enclosed aperture is defined through the insulation displacement portion, the enclosed aperture being constituted by said slot in communication with a relatively enlarged hole around the wire path.

10. An electric plug according to any one of the preceding claims in which the insulation displacement portion has a convergent portion at the opening of the slot, to guide engagement with the wire.

11. An electric plug according to any one of the preceding claims, one of said conductive plug pins being a live plug pin and having a live connecting terminal separate therefrom, the electric plug comprising a thermally-actuated or magnetically-actuated non-fusing circuit breaker housed in the plug body and connected electrically between the top of the live plug pin and the live connecting terminal.

12. An electric plug according to claim 11 in which the circuit breaker comprises a reset member exposed at the plug body exteri_^_. , the reset member moving from a set position to a tripped position when the circuit breaker is actuated to break the electrical connection between the live plug pin and the live connecting terminal, and being manually movable back to the set position to restore the electrical connection.