GB2346018A - Electrical terminal - Google Patents

Abstract

An electrical terminal is disclosed whose body includes an attachment portion for attaching the body to an earth rail, the attachment portion including a gripper member movable transversely relative to the body and locatable in, sequentially, an unlocked position, a first locking position and a second locking position, the attachment portion also including a catch located in opposed relationship to the gripper member; wherein in use the catch is engageable with one edge of preformed earth rail of predetermined width and the gripper member is engageable with another edge of the rail when in one of the first or second locking positions. This allows the terminal to attach to both BT and DIN earth rails. An earth terminal is also disclosed, comprising a U-profile contact portion that can be formed from a single strip of conductive material and which is less susceptible to loss of contact through creep. The application also discloses lateral fixing fingers which extend from the side of the terminal at a non-perpendicular angle and fix the terminals both at US 19mm (0.75") pitch and BT 25mm pitch between 22mm castellations.

Description

ELECTRICALTERMINAL The present invention relates to an electrical terminal.

It is particularly, but not exclusively, concerned with an electrical terminal for use in telecommunications devices.

It is common practice in the art, both within the telecommunications field and outside, to mount electrical terminals, controllers and connectors in a lateral array, i. e. side by side. Since the terminals will generally use a common earth contact, much additional wiring can be avoided if the terminals are fixed to a common earth rail. If the earth rail is made sufficiently robust, then this can provide the physical support for the terminals. This is now a standard method of mounting such terminals, controllers and connectors, i. e. by clipping them to a metallic rail to which the devices are earthed via a contact.

Two designs of earth rail have developed. The first, known as the DIN rail, is that which conforms to the Deutsche Industrie Normen. Corresponding British and European standards exist. This rail provides a 35mm width between locating surfaces, and is of a substantially smooth form, i. e. its profile does not change aiong the length of the rail apart from necessary fixing holes placed in the centre.

The other standard rail is the"BT rail", originally designed by British Telecommunications pic. This rail also has a 35mm overall width, but inclues castellations along the external edges of the rail to stop devices from sliding therealong. The locating surfaces of the rail are situated between the castellations and are spaced 33mm apart.

Thus, a device designed to snap fit onto the DIN rail will not engage a BT rail, whilst a device designed to fit the BT rail cannot be mounted onto a DIN rail.

So far as the Applicants are aware, practice to date in the design of telecommunications devices such as these has been to produce alternative designs, one suitable for each type of rail. Then, the appropriate product will be supplied to the customer depending on the rail standard employed. Thus, so that existing stocks are not rendered redundant, and to allow repair and replacement of existing installed equipment, customers are constrained in all future purchases of earth rails by their initial choice. Our copending application GB 2309835, from which this application has been divided, describes and claims a connector able to attach to either DIN or BT rails.

The two earth rails also differ in the manner in which the earth contact with the rail is made. In the DIN rail, a flat earth contact is provided on the insulating undersurface of the device body. Thus, once the device body is clipped to the rail, the earth contact is held against the rail. This is permissible in certain jurisdictions, but softening of the device body will cause earth contact to be lost. Such softening might be seen in a plastics moulded body due to relaxation or creep over time, or at elevated temperature or stress levels.

In the BT system, a forked contact straddles a bar between adjacent holes formed in the rail. This produces an electrical connection which is not dependent on the continued creep free strength of the device body.

These two forms of earth connection can be seen in Figures 1 and 2 of the accompanying drawings.

Figure 1 shows a DIN rail 10 in transverse section, to which a schematically represented telecommunications device 12 has been attached via resilient catches 16. An earth contact 14 extends beneath the device 12 and is held in contact with the earth rail 10 by the catches 16 which hold the device 12 as a whole to the rail 10. Clearly, in the event that one or both catches 16 fail, or if the body of the device 12 softens, the earth contact 14 may lose contact with the earth rail.

Figure 2 shows the edge of a BT rail 18 and demonstrates schematically its inter-relationship with an earth contact 20. An adjacent pair of holes 22a and 22b are formed in the edge of the rail 18, and define a bar 24 therebetween. The earth contact 20 terminates in a pair of prongs 26a and 26b which project into respective holes 22a and 22b. Thus, the internal opposed faces of the prongs 26a and 26b make contact with either side of the bar 24. Thus, an earth contact is formed which is unaffected by small positional variations of the rail 18 and device body, at the cost of limiting the lateral position of the device.

WO 95/12226 shows an earth contact, in which an initially flat metal part is shaped so as to have several prongs and then folded so as to separate the prongs into distinct fingers. When installed, the fingers engage on opposite sides of an earth rail, and it is claimed that this gives a particularly resilient contact. However, the earth clip design is such that the initial blank must be formed in a complex shape and then folded to a convoluted profile. Individual fingers must be folded to different profiles. This manufacturing operation will be difficult and hence expensive.

The present invention also, in its first aspect, to an earth contact. This earth contact has been found to be particularly suitable for a universal electrical terminal able to fit either rail, for example as described in GB 2309835, but is also applicable to terminals designed to fit on to a single proprietary earth rail.

The present invention therefore provides an electrical terminal being attachable to an earth rail and having an earth contact for making electrical contact with the earth rail, the earth contact being formed from a resilient strip of conducting metal, a portion of the contact having been bent to a substantially U-shaped profile thereby to accept an edge of the earth rail, wherein a major portion of the sides of the U-profile converge toward the opening thereof.

Such dual-face contact overcomes the need of contacts to the BT standard to engage with proprietary formations in the BT rail, and also overcomes the creep relaxation difficulties associated with the contact of Figure 1.

Preferably, the terminal is attachable to the rail via a projection extending when fitted beneath the rail, and the earth contact then lies between the projection and the body of the terminal. It is preferable if the axis of the U-portion is nonparallel to the underside of the body. This provides a more positive electrical contact with the earth rail. Preferably, the axis of the U-profile is closest to the underside of the body proximate the opening of the U-profile.

It is also preferred if the convergence of the U-profile is reversed at the opening, to aid insertion of an edge of an earth rail.

Since the contact. portion of the earth contact is formed in a simple U-shape, rather than a plurality of opposed fingers as in WO 95/12226, the earth contact can be formed from a single linear strip of conducting metal, bent into an appropriate shape. Such a formation is a preferred feature of this aspect of the invention.

A further problem that arises through providing an electrical terminal which can be attached to either style of earth rail is the pitch of the terminals. The US standard is for a maximum inter-terminal pitch of 19.1mm. Thus, the centres of the terminals are spaced at approximately 19mm positions along the rail. The choice of 19mm is a historical one, the original standard having been. 75 inches.

The BT standard is, however, a 25mm pitch and the 3mm wide castellations along the edge of the BT earth rail are at 25mm spacing to provide lateral fixing at this distance. Thus, a terminal capable of being used on either rail should be fixable at a 19mm pitch, yet also be able to engage castellations at 25mm pitch with a gap of 22mm between opposing faces. These two requirements are apparently irreconcilable.

In its second aspect, the present invention therefore provides an electrical terminal whose body inclues an attachment portion for attaching the body over an earth rail ; the terminal including laterally extending resilient fingers on either side thereof, each finger extending from the body at a non-perpendicular angle and being shaped such that, when the terminal is attached to an earth rail, the fingers project downwardly toward the rail.

To attach the terminal to a BT rail, the terminal is designed such that the tips of the fingers are at a 22mm spacing, and that the positioning of the fingers on the body portion is such that the tips of the fingers engage on opposite internal faces of two castellations. This then enables terminals to be fixed in place at 25mm spacing. It is of course a simple matter to re-design the exact length and positioning of the fingers so as to engage on other proprietary terminals of similar design but differing dimensions to the BT rail, such as may become available.

However, the non-perpendicular nature of the fingers enables them to interengage alongside each other when the terminals are at a closer spacing, such as the 19mm spacing approximate to the US requirements. Hence, the terminals can be fitted to a DIN rail at closer spacing. The resilient nature of the fingers will allow them to be flexed upward away from the DIN rail preventing any interference.

Preferably, the fingers extend from the body at an angle of between 45 and 75 , or a subtended angle of approximately 60 .

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying Figures ; in which: Figures 1 and 2 (already described) show prior art arrangements for attachment to existing earth rails ; Figure 3 shows a perspective view of an electrical terminal according to the present invention; Figures 4,5,6 and 7 show, in side view and partial section, four sequential stages in the attachment of the electrical terminal of Figure 3 to a 33mm earth rail ; Figure 8 is an enlarged section view of part of Figure 7 ; Figure 9 shows in side view the electrical terminal of Figure 3 attached to a 33mm rail ; Figure 10 is an enlarged section view of Figure 9; Figure 11 is a side view of the earth contact of the present invention; Figure 12 is a perspective view of Figure 11 ; Figure 13 is a view of part of Figure 11 in-more detail, in the form of a section on XIII-XIII of Figure 16, later.

Figure 14 is a top view of two terminals according to the present invention, attached to a DIN rail at 19mm centres; Figure 15 is a top view similar to Figure 14, partly cut away for clarity ; and Figure 16 is a top view of terminals according to the present invention attached to a BT rail at 25mm centres.

Figures 1 and 2 have been described already, and no further description will be given here.

Figures 3 to 10 show the terminal described and claimed in GB 2309835, and are presented so as to explain the context within which these examples of the intention operates.

The terminal 30 shown in figure 3 comprises a body portion 32 which is adapted to be attached to an earth rail as will be further described later. On top of the body portion 32 sit a functional portion 34 and a connection portion 36 which includes internal IDC connectors and ports 38 for receiving exchange wires. This portion of the electrical terminal is not of specific relevance to the present invention and need not be described in any greater detail.

On the underside of the body portion 32 are a pair of lugs 35,36 which extend inwardly from a downwardly depending portion 39 at one edge of the body portion 32. Thus, the inwardly directed lugs 35,36 form a"hook"portion which can engage beneath an edge of an earth rail.

On the other edge of the body portion 32 are a pair of outwardly extending flanges 40,42. A cross-bar extends from one flange 40 to the other flange 42, but is not visible in this Figure.

A catch 44 is positioned between the flanges 40,42 : The catch 44 is free to slide back and forth toward and away from the lugs 35,36. The catch 44 comprises a generally vertical (in Figure 3) pusher plate 46 from the rear of which extend two upper arms 48 lonly one of which is visible) and two lower arms 50 (only one of which is visible). The upper arms 48 are each identical and extend from the rear of the pusher plate 46 between the side flanges 40,42, over the cross-bar (not visible in Figure 3), and then downwardly to end at an outwardly projecting lug 52 which sits beneath the lower edge of the respective flange 42.

The lower arms 50 also extend rearwardly, by a distance approximately the same as the lugs 35,36, and then end in a latching bar 54 which extends from one arm 50 to the other (not visible).

On the lower edges of each of the side flanges 40,42, in the vicinity of the lugs 52 on the upper arms 48, are two downwardly projecting ridges 56,58. The purpose of these ridges will be discussed later.

The operation of the connector will now be described with reference to Figures 4 to 8. These Figures show sequential stages in the installation of the electrical terminal 30 on an earth rail 60 of 33mm width between engagement surfaces.

In Figures 4 to 8, the electrical terminal is shown in part section by the removal of side flange 42 such that details of the catch 44 are visible. The crossbar 62 between the side flange 40 and side flange 42 is now visible, and it can be seen that the upper arms 48 of the catch 44 rest on this cross-bar and allow the catch 46 to slide back and forth therealong.

Also visible in Figures 4 and 5, partly shown in shadow, is the earth contact 64. For the purposes of Figures 4 to 8, it is only necessary. to note that the earth contact 64 extends to the region between the body part 32 and the lugs 35,36.

In this part, the earth contact 64 is formed in a U-profile 66 such that one side of the U substantially follows the lower surface of the body portion 32 whilst another side of the U substantially follows the top surface of the lugs 35,36 and the opening 66 is directed toward the catch 44. Thus, an edge portion engaged between the lugs 35,36 and the body portion 32 will enter the U-profile and make electrical contact with the contact 64.

Figure 4 shows the terminal 30 immediately before installation takes place.

It is tilted upwards by approximately 8 and positioned over the earth rail such that the movable catch 44 is above one edge and the other edge faces the U-section 66 of the contact 64. From the position in Figure 4, the terminal is moved forward towards the rail in the direction of arrow A, such that an edge of the rail engages within the U-profile 66 of the earth contact 64 and lugs 35,36 project beneath the earth rail 60. The terminal is then in the position shown in Figure 5, with the earth rail engaged on one edge only.

From the position in Figure 5, the terminal 30 is rotated as per arrow B toward the earth rail 60 until the free edge of the earth rail 60 contacts the underside of the body portion 32. In this position, shown in Figure 6, the pusher surface 46 of the movable catch 44 is then pressed to move the catch 44 as far rearwardly as possible, to the position shown in Figure 7. In this position, the latching bar 54 extending between the two lower arms 50 of the movable catch 44 then extends beneath the edge of the earth rail 60, and the lower arms 50 trap the edge of the earth rail 60 between themselves and the cross-bar 62. Thus, the body portion 32 is firmly held to the earth rail 60. In this position, the outwardly directed lugs 52 of the upper arms 48 are now positioned behind both of the ridges 56,58, having being deformed resiliently as they passed thereover. Thus, the movable catch 44 is biased to remain in the Figure 7 position and small disturbances or vibration will not disengage the catch 44.

The position shown in Figure 7 is shown in more detail in Figure 8, on a larger scale. It can be seen that the catch 44 is restrained from outward movement by the lugs 52 and ridges 58. Meanwhile, the earth rail 60 is held between the lower arms 50, catch bar 54 and cross-bar 62.

Figures 9 and 10 show the installation of the electrical terminal 30 of the previous Figures on an earth rail 60'which is of 35mm width between engagement surfaces. Figure 9 shows a state corresponding to Figure 7, and Figure 10 shows an enlargement of the relevant part of Figure 9.

The early installation steps corresponding to Figures 4 to 6 are generally identical and need not be elaborated. However, as a result of the slightly wider rail 60', the catch 44 simply comes to rest after travelling a shorter distance. Thus, the lugs 52 engage behind the first ridge 56 without passing over second ridge 58.

The latching bar 54 still however projects beneath the lip of the earth rail 60'as is visible in Figures 9 and 10. Thus, the engagement of the electrical terminal 30 the rail 60'is equally firm as with the slightly narrower rail 60.

Hence, through the invention the electrical terminal 30 can accommodate alternative widths of earth rail. The skilled person will appreciate that the range of widths that can be accommodated is dictated by simple design choice of the length of upper arms 48 and the positioning of ridges 56 and 58. Further such ridges could be provided.

Figures 11 and 12 show an earth contact according to the present invention.

The earth contact 64 is formed from a single continuous strip of metallic material and is shown in Figure 11 in profile. The strip is bent to the shape shown in Figures 11 and 12. The contact can be seen in context in Figures 4 and 5.

At the lower end of the contact is a U-shaped portion 66 which defines two opposed side walls 68 and 70. This portion is shown in more detail, and in context, in Figure 13. The U-shape is slightly compressed in that the side walls 68 and 70 are convergent towards the open end of the U. The side wall 70 ends at a free end 72 at which point a divergent angle is given to aid insertion.

An extended straight portion 74 is formed alongside the U-portion, in terms of its position on the original metaliic strip. Thus, once the contact is formed to shape, the U-portion depends from the extended straight portion 74. When installe in the electrical terminal 30, the straight portion 74 and U-portion 66 are free to move within small limits, and thus the straight portion 74 acts as a resilient leaf spring to bias the U-portion 66 to remain in contact with the edge of the earth rail 60 or 60'.

Figure 13, shows the U-portion 66 of the earth rail 64 when at rest and unstressed. The upper side wall 68 of the U-portion 66 is at a slight angle to the underside of the terminal 32, such that the outer edge of the U-portion 66 protrudes downwardly towards the intended position of the earth rail by a greater amount than the inner edge thereof. Equally, the lower side wall 70 rises more steeply such that the gap between the walls 68,70 is significantly narrower at the entry to the U-portion 66 than in the interior thereof. Thus the convergence of the U-shape is predominantly, but not entirely, provided by virtue of the shape of the lower wall 70.

Adjacent the straight portion 74, in terms of its position on the strip, is a second contact 76, formed into a further U-shape for accepting a conventional blade terminal. This second contact 76 is positionally fixed once installe in the electrical terminal 30, to hold the straight portion 74 and U-shape portion 66 in place.

Thus, the earth contact of the present invention provides a fully functional contact which can be formed from a simple rectangular blank of metal by bending operations only.

Figures 14 to 16 show how the electrical terminal 32 of the invention can be accommodated on either a BT or a DIN rail at a range of spacings. Figures 14 and 15 show the terminals at 19mm spacings on a DIN rail, whilst Figure 16 shows the terminals at the standard 25mm spacing on a BT rail. Figure 15 is identical to Figure 14 except that part of the terminal body 32 has been cut away to show the relevant parts in more detail.

Figures 14 and 15 show two terminals 32 clipped to a DIN rail 60'. At the front (lower) edge of the terminal 32 can be seen the ports 38 for receiving exchange wires, and the outwardly extending flanges 40,42. Extending outwardly from the side of each flange 40,42 is a resilient finger 80,82. The finger 80 is also visible on figure 3. Each finger 82,80 extends from the respective side flange 40,42 in a direction which is both downward with respect to the terminal 32, i. e. toward the DIN rail 60', and non perpendicular in plan with respect to the side flange 40,42, i. e. toward or away from the centre of the DIN rail 60'. Finger 80 extends away from the centre of the DIN rail 60', whilst finger 82 extends toward the centre of the DIN rail 60'. It is not necessary that it is this way round, so long as all units on the same rail are like.

Because the fingers 80,82 extend downwardly, they press against the upper surface of the DIN rail 60'and are resiliently deflected upward. In doing so, of course, they bias the terminal 32 such that the latching bar 54 and the lower arms 50 are pressed into firmer contact with the underside of the DIN rail 60'. This may serve to increase frictional contact between these and the DIN rail.

Because the fingers 80,82 extend non-perpendicularly and in opposite directions, it is possible, as is more clearly visible in figure 12, to site the terminals 32 at a spacing along the rail 60'which is less than the distance between the extremities of the fingers 80,82. Thus, each finger 80,82 co-operates to sit in a nested arrangement where no fingers interfere with each other. Each finger then projects into the space between the adjacent finger and terminal.

Figure 16 shows the same terminals 32 on a BT rail 60. The terminals are now spaced at 25mm, so the fingers 80,82 no longer nest. However, the length of the fingers 80,82 has been selected such that their tip-to-tip distance corresponds to the distance between opposed faces of the castellations along the BT rail 60. This, combined with the downward direction of the fingers 80,82 means that their tips extend in to the region between the castellations of the BT rail 60 and are, when the terminal 32 is in position, closely adjacent or touching the opposed faces of those castellations. Thus, lateral sliding of the terminal 32 along the rail 60 is prevented.

Thus, the fingers 80,82 satisfy the two apparently irreconcilable requirements of the DIN rail, that the terminals 32 be capable of closely adjacent positioning, and of the BT rail, that they engage between longitudinally spaced castellations whose inter-face distance is greater than the nominal spacing on the DIN rail.

The skilled person will appreciate that the above-described embodiments are by way of example only, and that many variations can be made to the present invention without departing from the scope thereof. For example, although the Applicants presently prefer to engage the lugs 52 behind ridges 56,58, this is not strictly essential to the invention and frictional engagement could be used instead.

This would enable the terminal to engage a wider variation of earth rail widths, should this become necessary.

Claims (11)

1. CLAIMS 1. An electrical terminal being attachable to an earth rail and having an earth contact for making electrical contact with the earth rail, the earth contact being formed from a resilient strip of conducting metal, a portion of the contact having been bent to a substantially U-shaped profile thereby to accept an edge of the earth rail, wherein a major portion of the sides of the U-profile converge toward the opening thereof.
2. 2. An electrical terminal according to Claim 1 wherein the terminal is attachable to the rail via a projection extending, when fitted, beneath the rail, and the earth contact lies between the projection and the body of the terminal.
3. 3. An electrical terminal according to Claim 1 or Claim 2 wherein the axis of the U-portion, i. e. the line about which the U-portion is closest to symmetrical is non parallel to the body.
4. 4. An electrical terminal according to Claim 3 wherein the axis of the U-portion is closest to the body proximate the opening of the U-profile.
5. 5. An electrical terminal according to any preceding claim wherein the convergence of the U-profile is reversed at the opening thereof, thereby to aid insertion of an edge of an earth rail.
6. 6. An electrical terminal according to any preceding claim wherein the earth contact is formed from a single linear strip of conducting metal, bent into an appropriate shape.
7. 7. An electrical terminal whose body inclues an attachment portion for attaching the body over an earth rail ; the terminal including laterally extending resilient fingers on either side thereof, each finger extending from the body at a non-perpendicular angle and being shaped such that, when the terminal is attached to an earth rail, the fingers project downwardly toward the rail.
8. 8. An electrical terminal according to Claim 7 wherein the fingers extend from the body at an angle of between 45 and 75 .
9. 9. An electrical terminal according to Claim 8 wherein the fingers extend from the body at a subtended angle of approximately 60 .
10. 10. An earth contact substantially as one described herein and/or as illustrated in Figures 11 and 12.
11. 11. An electrical terminal substantially as herein described with reference to and/or as illustrated in the accompanying Figures 13 to 15.