GB2428909A - Electrical spring contact - Google Patents

Abstract

A socket for an electrical connector comprises a rigid elongate contact member 1 and a flexible looped spring contact member 2. The flexible contact member comprises a first elongate portion that is connected to a second elongate portion via a first hinge position. The other end of the second elongate portion is connected to a third elongate portion via a second hinge portion. The third elongate portion is formed with a convex sliding shoe that is biased against the first elongate portion. The second contact member 2 is formed by bending a strip of sheet material. A ferrule 4 may go around the contact members. The rigid contact may also act as a plug (5, Fig 1).

Description

O 2428909 Electrical Connector The invention relates to an electrical

connector and a contact element therefore. The invention is particularly, but not exclusively, concerned with high current carrying capability connectors for use with plug-in watt-hour meters, their adaptors and sockets; such as are commonly used in countries such as the USA and Canada.

In some countries, the USA and Canada particularly, many domestic households are provided with a Utility-owned "electrical service" connection, in a so-called "entryway", comprising mainly a watt-hour meter for monitoring the consumption of electrical energy in the household. A key requirement for this system is a positive electrical connection between the meter and it's mating Utility sprung-jaw sockets, which are an integral part of the service "entryway" panel, generally attached to the structure of the building concerned, for providing security and safety. Additionally, the meter is "securitised" to the "entryway" panel by a separate "ring-clip" or an integral panel-lid flanged lip.

The heavy-duty Utility feed cables supplied from the street-side transformer via an underground trench pipe are attached to the socket "supply" terminals within the rear of the "entryway" panel, as a twophase supply, namely, 11 5V + 11 5V with respect to a centre-tapped Neutral. This arrangement provides two 1 15V low-power distributed socket supplies (at 180 degree phase relationship to each other), as well as a 230V supply across phases for devices consuming high power such as washers, dryers, space heaters and air-conditioners Standard supply rating is 200 Amp rms per phase at 60Hz. Metered supplies are fed via socket "load" terminals to the domestic dwelling.

Due to the trend towards the use of plug-in watt-hour meters, so-called meter- "adapters" are conveniently interposed between the de-mountable watt-hour meter and the Utility-owned "entryway" connection. This allows the installation of other devices between the watt-hour meter Utility socket and a plug in meter, for example transient-voltage-surge-suppression (TVSS) devices, comprising for example metal-oxide-varistor discs or blocks, for protection of any downstream electrical equipment, as well as for the meters themselves. Such meter- adapters", into which the watt-hour meter now plugs, are also plugcompatible with the conventional "entryway" Utility sockets as well.

Straight, sturdy, blade-like or "stab" spade terminals protruding from the base of the meter housing, slidably engage with receptive sprung-jaw sockets within such an "entryway" socket, or as part of a de-mountable meter, within such a meter-"adapter". The terminal spacings and blade engagement depths in the sockets etc. are governed by Standard meter specifications. Being heavy-duty connections, appreciable insertion forces are used for promoting good "stab"- to-socket contact, that is a low impedance connection.

Apart from the protective TVSS devices mentioned above, meter-"adapters" may also contain suitable disconnect-contactors, especially if employed as part of a Utility-controlled load-shedding or load-balancing strategy, or as the basis of a pre-payment, bad-payment or safety-disconnect scheme. Switch control may be carried out by one of several remote means, for example power-line carrier, dedicated telephone line, mobile network, pager control, or satellite control.

The front face of the meter-"adapter" (and it's related sprung-jaw sockets) are protected and located within by a slotted "dead-front" moulding, such that when the de-mountable meter is removed, there is no danger of electric shock from the live supply sprung-jaw sockets that would otherwise be accessible.

Various parts of this service entryway" - the meter, the meter-"adapter", and the Utility sprung-jaw socket connections - are each subject to Specifications, stemming from the generalised Installation Guidance National Electrical Code NFPA 70 that applies particularly to North America.

In general terms, adapter socket connectors are robust sprung jaws, which are designed to mate with the terminal "stab" connections of a stand-alone watt- hour meter. In many prior-art documents, they are shown in various constructions, as a standard feature in typical Service "entryway" wall boxes, meter-adapter" sockets, and in some cases, also integrated together with an "adapter"-type disconnect-switch.

Whichever constructional approach is adopted, sprung-jaw socket connectors have certain common features and dimensions, so as to promote a standardised approach of assembly, as far as the "service entry" and metering system is concerned. The connector functions are essentially the same, whether the meter-"adapter" type or the meter base type socket, so also are the terminal "stab" connections, for compatibility with the common "sprung-jaw" socket aspect.

io US Patent No. 5 129 841 (Allina, Edward F), the contents of which are hereby incorporated by reference, discloses some of these "sprung-jaw" aspects that are illustrated as prior-art examples and also improvements, as described here in simple terms, to enable comparison with the connector socket according to the invention.

Figure 2 of US Patent No. 5 129 841 clearly show a typical (prior-art) demountable meter with moulded mounting flange, plugged into an intervening meter-"adapter" also with a moulded front flange, which are fixedly joined together, the combination also being plugged into a Utility wall box Service "entryway". A conventional "sealing ring" (not shown) may be used to lockingly connect and "securitise" the meter and "adapter" to the wall box, to prevent tampering or unauthorised removal.

Also shown are several sprung-jaw connectors and "stab" terminal connections involved, for linking the meter and "adapter", and plugging the combination into the related service wall box "entryway" sockets.

Figure 3A of US Patent No. 5 129 841 shows a (prior-art) sprung-jaw socket connector used very commonly in Service "entryway" connections, which has three main component parts; 1) an external strip folded into a U-form with a flat base portion, the arms of the U-form turned inwardly along and against one another and back toward the base to form a slit throat there-between, 2) an internal "lyre-type" spring receiving the in-curved ends of the formed strip within the neck of the "lyre" spring, and, 3) a flat, bored insert between the 3s inside surface of the base and the outside curved surface of the "lyre" spring.

The insert is bored centrally to receive therein a threaded screw or bolt, stud, or rivet, to effect a good joint to a right-angle ended main stem strip. The assembly is thus strongly sprung-formed to accept a mating "stab" terminal stem with a related entry and clamping force, in order to promote a good connection.

Figures 4A and 4B of US Patent No. 5 129 841 show the means of attaching a main terminal stem to the sprung-jaw as described in Figure 3A, with a screw or bolt, stud, or rivet, which have limitations as regards the quality of the joint io when carrying appreciable current.

Figures 5A and 5B of US Patent No. 5 129 841 show an alternative "sprungjaw" socket arrangement, which lacks the in-curved-jaws (with internal "lyre" spring) limitations of the version as shown in Figure 3A. This new embodiment is composed of a long main stem strip, offset and formed as a half-throat entry, a shorter outer spring strip on the other face, also formed as a half-throat entry, between which is contained a bent tang of thin conductive material, all three parts being retained solidly together by a pair of rivets.

On insertion of a "stab" termina' into the open throat form, it first impinges on the bent thin conductive tang, which deflects outwardly, picking up the outer spring strip, which exerts a greater clamping force for giving a good initial connection. The outer spring strip force exerted does vary with subsequent insertions, especially if carrying substantial current, as any appreciable heating leads to a deteriorated joint. This problem has been addressed in a further prior-art design example, described below.

In US 5 334 057 (Blackwell, Larry), the contents of which are hereby incorporated by reference, Figures 6 to 13, a similar but improved design to the Allina version above, is disclosed. It comprises a long main strip, only half- offset and formed as a throat entry, a shorter outer spring strip on the other face, also formed as a half-throat entry, both parts being retained together by one or two rivets, but in addition containing a special wire spring entrapped within the formed parts, during assembly. As the main strip is only half-offset sideways, on entry of a "stab" terminal a considerable offset force will be generated while picking up and aligning the other spring strip.

The improvement disclosed in US Patent No. 5 334 057 is the addition of the "clothes-peg"-type wire spring entrapped between the formed strips, the open ends of which are arranged to impinge on the outside faces of the throat-entry parts, thus giving a stronger clamping force, but also substantially increasing the "stab" terminal entry force at the same time.

On insertion of a "stab" terminal into the open throat form, it first picks up the outer spring strip (the main strip being only half-offset) with an offset force, at the same time experiencing a greater entry force due to the strong "clothes- peg" spring, which exerts a much greater clamping force, across the throat entry, for giving a good strong initial connection. The outer spring strip (by itself) does vary with subsequent insertions, especially if carrying substantial current, but is bolstered by the presence of the "clothes-peg" spring, giving better performance over a greater number of insertions. The only problem is that the combination does present a larger offset force and even greater initial throat entry force. This can cause a considerable installation problem for meter insertion, since it involves a minimum of four sprung-jaw connections, and in some cases as many as six A third prior-art example detailed in US Patent No. 6 325 666 (Ekstrom Industries mc), the contents of which are hereby incorporated by reference, is a variant on the two previous prior-art examples, suited for use in an adapter extender. Figure 5 of US Patent No. 6 325 666 shows a main strip, only half- offset at the base to form a "stab" terminal, but formed as a substantial C-section along it's length with a throat entry at the top, which not only provides a stronger structure, but conducts more heat when substantial current is passed through. At the top throat entry, within the C-section, is secured (with two rivets) a strong formed leaf spring, constituting the other half-throat entry.

Again, on insertion of a stab" terminal into the open throat form, it first picks up the outer spring strip (the C-section main strip being only half-offset and considerably more robust) with a larger offset force, which in combination, exerts a much greater clamping force, across the throat entry, for giving a good initial connection. The outer spring strip being very strong, varies less with subsequent insertions, especially if carrying substantial current, but still offers an appreciable clamping force, overall.

This example also causes a considerable installation problem for meter insertion because of the initial high insertion force required for each connection, since a minimum of four connections and often as many as six are required simultaneously thus multiplying the insertion force required to be overcome. I0

In a first aspect the invention provides an electrical connector socket comprising a first rigid elongate electrically conductive contact member, and a second flexible electrically conductive contact member electrically connected to the first member and arranged relative to the first member so as to provide an is entry for a corresponding plug member, wherein the second contact member comprises a first elongate portion electrically connected at one end to the first member and spaced from and parallel and opposed to the first member over a major portion of its length, a second elongate portion joined to the first portion at the free end thereof via a first flexible hinge portion and extending towards the first contact member, and a third elongate portion joined to the second portion at the free end thereof via a second flexible hinge portion and extending towards the first portion so as to make sliding contact therewith when a plug is inserted between the first and second members.

A connector according to the invention enables a reduced initial peak insertion force while retaining a sufficient clamping force on a mating plug connector to produce a low contact resistance and consequently minimising the heat generated as the supply current is passed through the connectors.

The flexible contact may be formed by bending a continuous strip of electrically conductive material.

This provides a simple inexpensive method of forming the flexible contact that contacts across its entire width.

The second elongate portion may be formed with a convex curve with respect to the first elongate portion along its length.

Alternatively, the second elongate portion may be formed with two straight elongate parts that join at an obtuse angle.

The alternative form of the elongate portion is generally easier to form consistently by bending the strip of conductive material.

The rigid and flexible contacts may be constrained within a containment ferrule having dimensions arranged to cause the flexible contact to exert a desired force during the insertion of a plug between the rigid and flexible contacts.

In this application and context the term containment ferrule is used to cover any is structure that constrains the movement of the rigid and flexible contacts while a plug is inserted between them. In particular it is not intended that there should be any limitation on the shape of, the material forming or the method of manufacture of the containment ferrule.

The rigid contact may have a portion extending parallel to the plug insertion axis and forming a plug for insertion into the socket of a further electrical connector. The axis of the extending portion may be coincident with the plug insertion axis.

To achieve this the axis of the rigid contact may be offset from the insertion axis by the thickness of the rigid contact.

This may be particularly useful when the connector is used in an adapter between a watt-hour meter and an entry-way panel as there will be no offset between the meter stabs (plugs) and the adapter stabs and consequently lateral forces on the connecters are reduced enabling a lower insertion force for a given contact clamping force to be achieved.

In a second aspect the invention provides a flexible contact element formed by bending sheet material, the contact element comprising a first elongate and substantially straight portion, a second elongate portion joined to the first elongate portion at one end thereof via a first flexible hinge portion, and a third elongate portion joined to the second elongate portion at the opposite end thereof via a second flexible hinge portion, the third elongate potion extending between the first and second elongate portions and ending in a convex curved portion that is in contact with and biassed against the first elongate portion.

The second elongate portion may be curved in its longitudinal direction convexly away from the first elongate portion.

Alternatively, the second elongate portion may comprise two straight parts joined at an obtuse angle to approximate a convex curve away from the first elongate portion.

The sheet material may be selected from copper, phosphor bronze, beryllium- copper, and spring steel.

The above and other features and advantages of the invention will be apparent from the following description, by way of example, of embodiments of the invention with reference to the accompanying drawings, in which: Figure la shows a rear elevation of a first embodiment of a connector socket according to the invention, Figure 1 b is an end elevation of the connector of Figure 1 a, Figure ic is a perspective view of the connector of Figure Ia, Figure 2a is a front elevation of a second embodiment of a connector according to the invention, Figure 2b is a cross sectional view on line X-X of Figure 2a, Figure 2c is a perspective view of the connector of Figure 2a, Figure 3a is a rear elevation of a first embodiment of a flexible contact for use in a connector according to the invention, Figure 3b is an end elevation of the contact of Figure 3a, Figure 3c is a front elevation of the contact of Figure 3a, Figure 3d is a perspective view of the contact of Figure 3a, io Figure 4a is a plan view of the containment ferrule shown in Figure 1 C, Figure 4b is a front elevation of the containment ferrule of Figure 4a, Figure 4c is a side elevation of the containment ferrule of Figure 4a, Figure 4d is a perspective view of the containment ferrule of Figure 4a, Figures 5a to 5d illustrate the insertion of a plug into a connector socket as shown in Figures 1 and 2, Figure 6a shows a rear elevation of a third embodiment of a connector socket according to the invention, Figure 6b is an end elevation of the connector of Figure 6a, Figure 6c is a perspective view of the connector of Figure 6a, Figure 7a is a front elevation of a fourth embodiment of a connector according to the invention, Figure 7b is a cross sectional view on line X-X of Figure 7a, Figure 7c is a perspective view of the connector of Figure 7a, - 10 - Figure 8a is a rear elevation of a second embodiment of a flexible contact for use in a connector according to the invention, Figure 8b is an end elevation of the contact of Figure 8a, Figure 8c is a front elevation of the contact of Figure 8a, Figure Sd is a perspective view of the contact of Figure 8a, io Figure 9a is a plan view of the containment ferrule shown in Figure 6c, Figure 9b is a front elevation of the containment ferrule of Figure 9a, Figure 9c is a side elevation of the containment ferrule of Figure 9a, l5 Figure 9d is a perspective view of the containment ferrule of Figure 9a, and Figures 1 Oa to 1 Od illustrate the insertion of a plug into a connector socket as shown in Figures 6 and 7.

As shown in Figure 1 an electrical connector socket comprises a first rigid contact member 1 to which a flexible contact 2 is connected by a rivet 3. The rivet 3 could be replaced by any connection mechanism that clamps the flexible contact 2 against the rigid contact 1 and ensures a good electrical and mechanical connection between the two contacts.

The contact members 1 and 2 are held within a casting or containment ferrule 4 in the region where a plug member is inserted in operation. As shown in Figure 1 the contact member 1 has a relatively long tail portion 5 which in some applications may act as a plug member for insertion into a socket of a further connector, either of the same form as that illustrated in Figure 1 or of any different form compatible with the tail portion 5.

Figure 2 shows a second embodiment of an electrical connector socket according to the invention. Corresponding elements in Figure 2 have been 11 - given the same reference signs as those in Figure 1. The major difference between the connector socket of Figure 2 compared to that of Figure 1 is that the tail portion 5 has been omitted.

As shown in both Figures 1 and 2 the contact 1 is offset from the axis of insertion of a mating plug by its nominal thickness such that a plug contact inserted between the two contacts will have its longitudinal axis on the same axis as the tail portion 5. Thus if two or more of these connectors are mated together the jaws of each connector socket are on the same axis. This can be io advantageous when, for example, such a connector is used in an adaptor interposed between a plug-in watt-hour meter and a Utility-owned entryway connection, as the plug portion will not experience any sideways offset forces on insertion.

Figure 3 shows the flexible contact 2 in greater detail. As shown in Figure 3 the flexible contact 2 comprises a first elongate portion 20 joined by an s-curved portion 21 to a tail portion 22 having an aperture 23 through which, when assembled onto a rigid contact, a rivet is passed to connect the flexible contact 2 to the rigid contact 1. The first elongate portion 20 is joined to a second elongate portion 25 via a first flexible hinge portion 24, the portion 25 being at a small acute ang'e to the portion 20 when free, that is when assembled into the connector socket and without a plug inserted into the socket The second elongate portion 25 is connected to a third elongate portion 26 via a second flexible hinge portion 27 The portion 26 is provided with a convex curved portion 28 near to its free end which curved portion is arranged to bear against the inside face of the first portion 20 to form a sliding shoe.

The casting or containment ferrule 4 is shown in Figure 4 and comprises four walls 41-44 forming a hollow rectangular box structure whose dimensions are appropriate for the size of the contacts of the connector.

Figure 5 illustrates the action of the flexible contact 2 as a plug is inserted between it and the rigid contact 1.

- 12 - Prior to entry of a plug the inclined-ramp formed by the portion 25 of the contact 2 impinges on the inside face of the main (rigid) fixed contact 1, low down, at a particular biting point and with a preset force. Past this biting point, the contact is formed back on itself as elongate portion 26, towards the first elongate portion 20, the portion 26 ending as a sliding shoe 28 about half way down the active length of the portion 20. Internal clearances of the two fold- back portions 25 and 26 are arranged so that, during the plug or "stab" insertion process, no binding results.

During the initial plug 7 entry phases illustrated in Figures 5b and 5c, the small inclined-ramp, entry throat portion between the rigid I and flexible 2 contacts begins to open and press the plug 7 tightly against the main (rigid) contact 1, and at the same time, just lifting the elongate portion 25 adjacent to the hinge portion 27 of the contact 2 off the lower biting point. This starts the second is phase translation simultaneously, beginning to deflect and tighten the internal hinge portion 27 of the contact away from the biting point, while the shoe end 28 of the third elongate portion 26 slides up the internal surface of the first portion 20. The overall form promotes a gentle, smooth and progressive, sliding-shoe pressure point action.

The entire jaw socket is loosely contained by a sprung-over containment ferrule casting 4 (or similar structure), and retained in place by a semishear pip 11 on the outer surface of the (rigid) contact I. Prior to entry of the plug, the ridge 45 on inside (rigid) surface of the containment ferrule is just clear of the outer surface of the flexible contact 2, the internal inclined-ramp portion of the contact being at the lower biting point, in readiness.

In the embodiment shown in Figure 5 a fulcrum point of the containment ferrule is formed as an internal cross-ridge 45, suitably positioned a few millimetres ahead of the sliding shoe position, of the third elongate portion 26, prior to plug entry. At almost full entry, the pressurised sliding shoe position translates towards the internal ridge 45, creating the final coupled-back closure force on the flexible contact entry throat, clamping the plug tightly between, the rigid and flexible contacts to produce a good electrical connection.

- 13 - The effect produced is a gradual three-stage build up of clamping pressure as the plug is fully inserted into the main (rigid) fixed jaw, all three cantilever fulcrum translations depending entirely on the plug thickness, the related leaf- spring inclined-ramp, and sliding shoe portions of the flexible contact and containment ferrule ridge 45, displacement process.

At full plug insertion, when used in the context of connecting a watthour meter to a Utility supply as described in the introduction, it is pressured intimately flat between the flexible and rigid jaw faces, being perfectly aligned at the correct io centres (no offset) and orthogonal to the meter body. The entire sliding action of the plug entry, under gradually-increasing clamping pressure, provides a wiping/cleaning action, which promotes consistently low contact resistance, enabling low heat production when passing substantial current.

The spring contact 2 is made of conductive spring-strip material, and it will share the total load current in a pressure and electrical resistance related ratio with the main (rigid) fixed contact 1. Also, since the pressure promotes intimate and consistently low contact resistance, on both faces of the plug, low temperature rise may be achieved.

The spring contact is conveniently manufactured using strip bending techniques enabling consistent cantilever forces at the spring hinge portions to give well defined insertion forces.

As shown in Figure 6 a third embodiment electrical connector socket comprises a first rigid contact member 101 to which a flexible contact 102 is connected by two rivets 103 and 113. The rivets 103 and 113 could be replaced by any connection mechanism that clamps the flexible contact 102 against the rigid contact 101 and ensures a good electrical and mechanical connection between the two contacts.

The contact members 101 and 102 are held within a containment ferrule 104 formed as a folded steel box in the region where a plug member is inserted in operation. As shown in Figure 6 the contact member 101 has a relatively long tail portion 105 which in some applications may act as a plug member for - 14 - insertion into a socket of a further connector, either of the same form as that illustrated in Figure 6 or of any different form compatible with the tail portion 105.

Figure 7 shows a fourth embodiment of an electrical connector socket according to the invention. Corresponding elements in Figure 7 have been given the same reference signs as those in Figure 6. The major difference between the connector socket of Figure 7 compared to that of Figure 6 is that the tail portion 105 has been omitted. I0

As shown in both Figures 6 and 7 the contact 101 is offset from the axis of insertion of a mating plug by its nominal thickness such that a plug contact inserted between the two contacts will have its longitudinal axis on the same axis as the tail portion 105. Thus if two or more of these connectors are mated together the jaws of each connector socket are on the same axis. This can be advantageous when, for example, such a connector is used in an adaptor interposed between a plug-in watt-hour meter and a Utility-owned entryway connection, as the plug portion will not experience any sideways offset forces on insertion.

Figure 8 shows the flexible contact 102 in greater detail. As shown in Figure 8 the flexible contact 102 comprises a first elongate portion 120 joined by an s-curved portion 121 to a tail portion 122 having two apertures 132 and 133 through which, when assembled onto a rigid contact, rivets 103 and 113 are passed to connect the flexible contact 102 to the rigid contact 101. The first elongate portion 120 is joined to a second elongate portion 125 via a first flexible hinge portion 124, the portion 125 has a first part 130 at an acute angle to the portion 120 and a second part 131, that is substantially parallel to the portion 120. The second elongate portion 125 is connected to a third elongate portion 126 at the far end of the part 131 via a second flexible hinge portion 127. The portion 126 is provided with a convex curved portion 128 near to its free end which curved portion is arranged to bear against the inside face of the first portion 120 to form a sliding shoe.

- 15 - The containment ferrule 104 is shown in Figure 9 and comprises a box structure having four walls 141-144 forming a hollow rectangular box structure whose dimensions are appropriate for the size of the contacts ofthe connector.

The box structure is formed by folding sheet steel (or other suitable material) and is joined on its rear face 141 with a dovetail joint tightly and solidly integrated. The rear face is provided with two apertures 148 and 149 to enable it to be positioned accurately on pips provided on the rigid first contact 101.

Figure 10 illustrates the action of the flexible contact 102 as a plug is inserted between it and the rigid contact 101.

Prior to entry of a plug the inclined-ramp formed by the part 130 of the portion 125 of the contact 102 forms with the contact 101 an entry throat. The part 131 of the portion 125 lies against the inside face of the main (rigid) fixed contact 101 with a preset force. The contact 102 is formed back on itself as elongate portion 126, towards the first elongate portion 120, the portion 126 ending as a sliding shoe 128 about half way down the active length of the portion 120. Internal clearances of the two fold-back portions 125 and 126 are arranged so that, during the plug or "stab" insertion process, no binding results.

In the third and fourth embodiments the portion 125 is formed as two straight parts 130 and 131 at an obtuse angle to each other such that the part 131 is substantially parallel to the portion 120.

During the initial plug 107 entry phases illustrated in Figures lOb and 1Cc, the small inclined-ramp, entry throat portion between the rigid 101 and flexible 102 contacts begins to open and press the plug 107 tightly against the main (rigid) contact 101, and at the same time, straightening the elongate portion 125 and separating the part 131 and the hinge portion 127 of the contact 102 from the surface of the rigid contact 101. This starts the second phase translation simultaneously, beginning to deflect and tighten the internal hinge portion 127 of the contact 102, while the shoe end 128, of the third elongate portion 1 26,slides up the internal surface of the first portion 120. The overall form promotes a gentle, smooth and progressive, sliding-shoe pressure point action.

- 16 - The entire jaw socket is loosely contained by a sprung-over steel formed containment ferrule box 104 (or similar structure), and retained in place by a semi-shear pips 114 and 115 on the outer surface of the (rigid) contact 101.

Prior to entry of the plug, the inside (rigid) surface of the containment ferrule is just clear of the outer surface of the flexible contact 102, the internal part 131 of the contact 102 being biassed against the rigid contact 101.

In the embodiment shown in Figure 10 a fulcrum point of the containment ferrule is formed as the internal top edge of the containment ferrule 104, io suitably positioned a few millimetres ahead of the position of the sliding shoe 128, of the third elongate portion 126 prior to plug entry. At almost full entry, the pressurised sliding shoe position translates towards the top edge of the containment ferrule 104, creating the final coupled-back closure force on the flexible contact entry throat, clamping the plug tightly between, the rigid and is flexible contacts to produce a good electrical connection.

The effect produced is a gradual three-stage build up of clamping pressure as the plug is fully inserted into the main (rigid) fixed jaw, all three cantilever fulcrum translations depending entirely on the plug thickness, the related leaf- spring inclined-ramp, and sliding shoe portions of the flexible contact and containment ferrule wall 143 displacement process.

At full plug insertion, when used in the context of connecting a watthour meter to a Utility supply as described in the introduction, the plug is pressured intimately flat between the flexible and rigid jaw faces, being perfectly aligned at the correct centres (no offset) and orthogonal to the meter body. The entire sliding action of the plug entry, under gradually-increasing clamping pressure, provides a wiping/cleaning action, which promotes consistently low contact resistance, enabling low heat production when passing substantial current.

Since, nominally, there are no offset misalignments or offset forces involved between the parts of the connection, the connector socket design described herein lends itself to direct insertion in the meter base. Additionally with lengthened main terminals it can be used with adapter "extenders".

- 17 - When used for meters and adaptors in accordance with standard meter specifications using Installation Guidance - National Electric Code NFPA 70 as used in the United States of America and Canada typical dimensions and suitable materials are as follows:

S

Plug/Stab/Rigid Contact. High conductivity copper strip 2 38mm (3/32") thick 19.05mm (3/4") wide Typical socket insertion depth chosen to produce plug/socket overlap contact of 12.8mm (1/2") by 19.05mm (3/4") Spring Contact. Medium-High Conductivity sprung copper, phosphor-bronze, beryllium-copper, or sprung steel 0.5-0.7mm thick 19.05mm (3/4") wide Containment Ferrule: Box structure formed from 1mm thick steel strip, suitably finished with a strong overlap joint.

Dimensions dependent on contact dimensions and chosen for optimum overlap of plug/stab with rigid/spring contacts and low resistance clamping.

Typical initial peak insertion forces are less than 15 KgF (compared with a peak insertion force of approximately 40-50 KgF of some prior-art designs (in particular Blackwell, Larry), giving an intimate contact resistance for the stab" socket of about 0.01 to 0.02 milli.Ohm. This is equivalent to about 0.4 to 0.8 Watt of heating at 200 Amp load current. Thus low contact resistance can be obtained while minimising the contact insertion forces which has particular advantage when applied to watt-hour meter installations where multiple connections have to be made simultaneously.

After many subsequent insertions and removals, typical initial insertion forces are relatively constant at around 12 KgF for the materials and dimensions given above for meter installations - 18 - Although the connector socket and spring contact have been described in the context of demountable watt-hour meters they may be used for any applications where the designed current carrying capacity ranges from several amperes to several hundred amperes. Possible applications include vehicle electrical systems where large currents may be drawn and in principle any application where a plug and socket is used to connect/disconnect a load to/from a supply of electrical current and low insertion forces and low temperature rise when conducting large currents (from several amperes upwards) is desired. I0

Claims (18)

1. - 19 - Claims 1. An electrical connector socket comprising a first rigid

   elongate electrically conductive contact member, and a second flexible electrically conductive contact member electrically connected to the first member and arranged relative to the first member so as to provide an entry for a corresponding plug member, wherein the second contact member comprises a first elongate portion electrically connected at one end to the first member and spaced from and parallel and opposed to io the first member over a major portion of its length, a second elongate portion joined to the first portion at the free end thereof via a first flexible hinge portion and extending towards the first contact member, and a third elongate portion joined to the second portion at the free end thereof via a second flexible hinge portion and extending towards the is first portion so as to make sliding contact therewith when a plug is inserted between the first and second members.
2. 2. A connector socket as claimed in Claim 1 in which the flexible contact is formed by bending a continuous strip of electrically conductive material.
3. 3. A connector socket as claimed in Claim 2 in which the second elongate member has a convex curve with respect to the first elongate member along its length.
4. 4. A connector socket as claimed in Claim 2 in which the second elongate member comprises two straight elongate parts that join at an obtuse angle.
5. 5. A connector socket as claimed in any preceding claim in which the rigid and flexible contacts are constrained within a containment ferrule having dimensions arranged to cause the flexible contact to exert a desired force during the insertion of a plug between the rigid and flexible contacts.

   - 20 -
6. 6. A connector socket as claimed in any preceding claim in which the rigid contact has a portion extending parallel to the plug insertion axis and forming a plug for insertion into the socket of a further electrical connector.
7. 7. A connector socket as claimed Claim 6 in which the axis of the extending portion is coincident with the plug insertion axis.
8. 8. A connector socket as claimed in any preceding claim in which the axis of the rigid contact is offset from the insertion axis by the thickness of the rigid contact.
9. 9. A connector socket as claimed in any preceding claim designed to carry currents of up to 200 Amperes.
10. 10. A connector as claimed in any preceding claim having an initial insertion force of less than 15 KgF.
11. 11. A connector as claimed in any preceding claim designed for use as a connector between a watt-hour meter and a Utility supply.
12. 12. An electrical connector socket substantially as described herein with reference to the accompanying drawings.
13. 13. A flexible contact element formed by bending sheet material, the contact element comprising a first elongate and substantially straight portion, a second elongate portion joined to the first elongate portion at one end thereof via a first flexible hinge portion, and a third elongate portion joined to the second elongate portion at the opposite end thereof via a second flexible hinge portion, the third elongate portion extending between the first and second elongate portions and ending in a convex curved portion that is in contact with and biassed against the first elongate portion.

    - 2]. -
14. 14. A contact element as claimed in Claim 13 in which the second elongate portion is curved in its longitudinal direction convexly away from the first elongate portion.
15. 15. A contact element as claimed in Claim 13 in which the second elongate portion comprises two straight parts joined at an obtuse angle to approximate a convex curve away from the first elongate portion.
16. 16. A contact element as claimed in any of Claims 13 to 15 in which the sheet material is selected from copper, phosphor bronze, berylliumcopper, and spring steel.
17. 17. A flexible contact element as claimed in any of Claims 13 to 15 and suitable for use as the flexible contact element in an electrical connector socket as claimed in any of Claims 1 to 12.
18. 18. A flexible contact element substantially as described herein with reference to the accompanying drawings.