GB2169749A - Electrical outlet accessories with incorporated automatic circuit breaker - Google Patents

Abstract

A mains electrical outlet accessory incorporating automatic circuit protection provisions has contacts which are opened by fault detection provisions. In order to employ automatic circuit protection provisions in a mains electrical outlet accessory of a resettable type, the present invention provides contacts which are of materials capable of withstanding much heavier currents, at least on a transient basis, for multiples of the normal fuse disintegration times, to allow the aforesaid contacts to be automatically opened without disintegration or welding together. Such contacts utilise a high conductivity material such as silver intimately associated with other materials having a much higher resistance to physical disintegration and/or welding together, such as tungsten, titanium oxide and molybdenum. It is also proposed to use contacts of the aforesaid materials and properties in other switched mains electrical accessories intended for use with any circuit incorporating automatic circuit protection provisions of a resettable type having the aforesaid contacts. <IMAGE>

Description

SPECIFICATION Electrical accessories with incorporated automatic circuit breaker The invention relates to mains electrical outlet accessories that have incorporated automatic circuit protection provision of a resettable type, i.e. that relay on mechanical breaking of contacts automatically in fault conditions rather than or supplementary to fuses that disintegrate at predetermined overload.

We have been engaged in a development programme for such mains electrical accessories with such incorporated circuit breaker provisions, and such programme has resulted in copending patent applications nos. 8404351 (P1119), 8430850 (P1190), 8425344 (P1238), 8411600 (P1324) and 8430852 (P1417).

Specific product development includes an electrical socket outlet accessory, and other accessories are plainly feasibly, for example of an adaptor type to fit into an existing socket accessory and afford appliance circuit connection therefrom, and spur type or permanently wired connection accessories, whether or not such are otherwise switched, even to switch accessories as such. Basic fault detection and consequent circuit breaking centres on earth leakage conditions at or above a prescribed level, usually measured in tens of milliamps, and generally indicating a served-circuit and/or appliance fault resulting effectively in current flow from live line to earth line.However, for various reasons, there are other fault conditions that we believe it can be of benefit to detect and respond to, specifically concerning the condition of the neutral line and including reversal of polarity, at least in circumstances where, as is probably inevitable for accessories hereof, they will be installed, or at least connected to, by persons not professionally trained and thus of varying skill and competence.

It is against this background that the present invention has arisen, and as our investigations have demonstrated the clear practical possibilities of occasionally encountering very high current values, actually as high as 2000 amps or more. For such heavy current fault conditions, the contact operation time of our preferred circuit breakers, typically measured in tens of milliseconds, must, of course, remain an order of magnitude greater than the disintegration time of fuses, typically five milliseconds or less for cartridge fuses, and, at least if there is no proper fuse protection, there is a consequent danger of severe damage to present-day contacts, inciuding welding in the ON state.It will be evident both that such risk of damage extends to other switch contacts in the served circuit and/or appliance and that the full extent of such danger is masked by correct fusing, i.e. as currently required in this country by regulation for consumer power circuits, generally via fused plugs. However, we take the view that risks of such dangers should be guarded against, whether arising from bridging (or absence) of fuses or wiring with wrong polarity, or whatever.

Accordingly, we now propose herein that contacts automatically opened by fault detection provisions incorporated into mains electrical outlet accessories shall be of materials capable of withstanding much heavier currents at least on a transient basis for multiples of the normal fuse disintegration times, i.e. normally for tens of milliseconds, to allow the aforesaid contacts to be automatically opened.

Thus, instead of simple copper and/or silver based or coated contact materials, we specifically propose the use of contact materials in which high conductivity material, such as silver, is intimately associated with and disseminated through other material such as tungsten, titanium oxide or molybdenum having a much higher resistance to physical disintegration and/or welding together when subject to heating by heavy current transients. Such contact materials are, of course, known in themselves for various applications outside of the specific applications proposed herein, usually in relation to switch gear for equipment that is of an inherently heavy-current operating type.As thus available or specifiable from various suppliers, those contact materials may be of sintered alloy type in which a matrix of an aforesaid other material is impregnated with silver in a proportion that is found to be suitable, in connection with which we believe that a silver content of between 25% and 75% by weight will normally apply, preferably 35% to 65%, and 50% having been found satisfactory in prototype socket outlets.

Affixing of such contacts to carriers therefore is readily achieved, for example by resistance-welding directly to such carriers or to a member otherwise affixing to such carriers, e.g. by rivetting. In either case, welding may involve a contiguous eutectic interface to the carrier or member.

It is, of course, logical for electrical accessories hereof that have a consumer's switch further to have the contacts for that switch also of materials as above proposed. In fact, for any served circuit having switching over and above the aforesaid automatic fault breaking, contacts for such switching are advantageously as above proposed. It will be appreciated that use of such contacts meets the damage possibilities of by-passed or absent fusing and wrong polarity wiring. Indeed, the absolute need for fusing is eliminated in favour of reliance on our accessories with incorporated fault break provisions.

Specific implementation of this invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is an outline circuit diagram; Figure 2 shows, diagrammatically, a socket outlet accessory with automatic break contacts; and Figures 3A and 3B show preferred contact affixing provisions.

Referring first to Fig. 1, a consumers mains distribution circuit, such as a ring main, is shown at 20 with live, neutral and earth lines 20L, 20N, 20E, with an exemplary outlet accessory 10 connected therein. There may, indeed will for ring main circuits, be more than one such outlet accessory 10 in the circuit 20.The accessory 10 has an incorporated fault detection and automatic contact opening provision comprising contacts 12 at least in a live line branch, a switch link 14 with contacts 16 normally closing on the contacts 12, a mechanical system 18 for breaking the contacts 12, 14 by moving the switch link 14 (usually releasing a latch to allow spring bias to move the switch link) and fault detect and mechanism drive circuitry 22 for causing such contact breaking, the conventionai reset button operated means also being indicated at 24 (usually mechanically to reengage the latch) and test button-operated means at 26 (usually to operate via the fault detect and drive circuitry 22).

It is, of course, the contacts 12 and 16 that we specifically propose herein shall be of the aforesaid contact materials. However, the outlet accessory 10 is further shown with a normal consumer-operated switch 30 also of single pole action, i.e. controlling the live line branch only via contents 32, 34. Served circuit connections 36L, 36N and 36E are shown simply exiting the accessory 10 at 38 in any suitable way, for example as an individual appliance supply cord or cable.

It is, of course, further proposed herein that the contacts 32, 34 also be of the aforesaid contact materials.

It will further be appreciated that the accessory 10 could be a socket outlet, see 40 in Fig. 2, which is a highly diagrammatic representation showing flat three-pin connection at 42 without regard to the fact that same will, of course, normally be on the uppermost face of the accessory going through the drawing, i.e. the same face as gives access to the operators for the consumers switch 30 and reset latch system 44, shown as a normally-acting rocker 46 and push button 24.

Internal connections between the socket connection 42, the switch 30 and the contacts 12, and the fault detection circuitry and test facility, are not shown. However the latter circuitry and test facility can readily be viewed as being to the left of what is shown in Fig.

2, so as to operate a solenoid 48 to drive an armature 50 in knocking a latch member 52 out of its illustrated state holding the switch link 14 to close the contacts 14, 16.

As shown, the latch member 52 is pivotted at 54 to a body 56 movable in a well 58 by the push button 24 against a first compression spring 60 acting between a seat in the body 56 and an abutment surface of the socket body about a latch entry 62 into a well 64 in which the switch link 14 can move under ledging carrying the contacts 12. The latch member 52 has an extending latch part 66 to go through a hole 68 in a switch link carrier 70, and is both biassed and centred by a second compression spring 72 acting between the switch link/carrier 14, 70 and a seating on the latch member. The whole is much as shown in our copending application no. 8425344 (P1238), i.e. the first compression spring 60 being stronger than the second 72.

Turning to Figs. 3A and 3B, contacts hereof are shown at 80 and 82 suitably secured directly to an electrically conductive carrier 84 and to a member 86 for mechanical connection to such a carrier by rivetting. Materials of the carrier 84 and member 86, such as copper or brass, generally permit resistance-welding for their securement, usually with an eutectic interface 88 or 90.

Having mentioned and shown inclusion of a consumers switch in accessories hereof, and application of contacts hereof thereto in addition to the automatic fault breaking contacts, it should be evident that this invention is similarly applicable to a switched or unswitched electrical accessory whether or not same has a specific coupling/connection to an appliance, i.e. including such as an electric light switch.

Moreover, the invention is further applicable to an adaptor for a socket outlet not itself of the type specifically described above, i.e. with the adapter affording the automatic fault break provision whether directly from the socket or as a unit on a trailing lead from a plug fitting to the socket.

In general, of course, accessories hereof are compact and of low cost compared with separate provision of fault condition circuit breaking as used to be the general rule in relation to specific appliances/equipment considered to need special protection.

It will also be appreciated that the only requirement on mechanical etc systems of the automatic resettable break mechanism is its capability of incorporation into an electrical accessory, i.e. it could be different from what is shown in Fig. 2.

Contacts hereof will, of course, withstand both fault occurrence and an attempt to remake with the faults still present.

Claims (8)

1. A mains electrical outlet accessory incorporating automatic circuit protection provisions of a resettable type having contacts which are automatically opened by fault detection provisions and wherein said contacts are of materials capable of withstanding much heavier currents, at least on a transient basis, for multiples of the normal fuse disintegration times, to allow the aforesaid contacts to be automatically opened.

2. A mains electrical outlet accessory as claimed in claim 1 in which the contacts use a high conductivity material intimately associated with and disseminated through other material having a much higher resistance to physical disintegration and/or welding together when subject to heating by heavy current transients.

3. A mains electrical outlet accessory as claimed in claim 2 in which the high conductivity material is silver.

4. A mains electrical outlet accessory as claimed in claim 2 or 3 in which said other material is tungsten, titanium oxide or molybdemum.

5. A main electrical outlet accessory as claimed in claim 2, 3 or 4 in which the contacts are of sintered alloy type in which a matrix of the aforesaid other material is impregnated with silver.

6. A mains electrical outlet accessory as claimed in claim 3 in which the silver content is in the range 25% to 75% by weight.

7. A switched mains electrical accessory for any served circuit incorporating automatic circuit protection provisions of a resettable type, wherein the switch contacts are made of the same materials as the circuit protection contacts of claims 1 to 6.

8. A mains electrical outlet accessory incorporating automatic circuit protection provisions of a resettable type constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.