GB2321790A

GB2321790A - A cam operated clamping terminal

Info

Publication number: GB2321790A
Application number: GB9702173A
Authority: GB
Inventors: Paul Bollinghaus; Martin Anthony Serrao
Original assignee: CONTACTUM Ltd
Current assignee: CONTACTUM Ltd
Priority date: 1997-01-30
Filing date: 1997-01-30
Publication date: 1998-08-05
Also published as: GB9702173D0

Abstract

A cam operated terminal is disclosed and comprises an electrical contact (1) and a rotatable cam member (2) spaced therefrom in a first position to define a gap therebetween for insertion of the cores (4) of one or more electrically conductive wires (5). The cam member is preferably shaped to receive a screwdriver by means of which it can be rotated into a second position whereby the bared ends (4) of the wires (5) are pushed laterally towards and into contact with the terminal and gripped between the electrical contact (1) and the cam member (2). The cam member (2) is also rotatable in the opposite direction to release its grip on the conductive wires (5).

Description

A CAM OPERATED TERMINAL The present invention relates to an electric terminal for connecting a current carrying wire to an electrical conductor.

A commonly used electric terminal is the pillar type which in one form simply comprises a short cylindrical tube made from a conductive material open at one or both ends for insertion of the bared end of one or more electrically insulated wires. A screw is threaded in a hole in the wall of the cylinder and can be tightened to sandwich the wire between the end of the screw and the inner wall of the cylinder to provide an electrical connection between the wire and the cylinder and retain it therein.

Pillar type terminals such as the one described are available in various different shapes and configurations but they all work in a similar fashion by retaining the wire between the end of the screw and the body of the terminal.

A general problem with all pillar type terminals is that they tend to be quite large and so take up a considerable amount of space in what is often a small electrical component in which they are used. Furthermore, a relatively large area of space surrounding the terminal is required to provide room for the screw which protrudes from the terminal.

Another disadvantage is that pillar type terminals are time consuming to use as the screw must be rotated many times with a screwdriver to grip the wire between the screw and the wall of the terminal. This is an important factor when an electrician has many units to instal and is being paid for the time it takes him to complete the task.

Many of these problems can be overcome by the use of screw-less terminals. A commonly used terminal of this type is the so-called push fit or push and lock terminal.

These often take the form of an insulated casing housing a sprung metal conductor mounted opposite a fixed metal plate. A number of apertures in the casing enables wires to be inserted between the sprung metal conductor and the fixed plate so that when a wire is pushed into the casing through the aperture, the pressure of the wire releases the spring so that the wire is pushed against the metal plate and is gripped between the sprung metal connector and the plate. This type of terminal has the benefit of being easy to use and allows for rapid connection of wires.

A disadvantage with the type of terminal described above is that the wires cannot be removed from the terminal once they have been inserted therein. Thus, the terminal cannot be re-used and should the wires need to be released for repair or maintenance of the electrical component they must be cut.

The aforementioned disadvantage has been substantially overcome by the lever type of screwless terminal which is very similar to the terminal described except that a slot is provided for insertion of a screwdriver into the terminal to release the spring and allow the wires to be removed. Alternatively, a push button can be provided which is depressed to release the spring pressure.

A major problem with the terminals described above is that they cannot be used with stranded wire. This is because the strands tend to deform when pushed into the connector resulting in a poor connection. This is a particular problem in the UK as both stranded and nonstranded wires are used as standard and so it is preferable that a terminal should therefore be able to accommodate both.

The present invention seeks to provide a terminal which overcomes or substantially alleviates all the problems and disadvantages discussed above, and provides a reusable terminal which is cheap to manufacture and quick to use.

According to an aspect of the present invention, there is provided a cam operated terminal comprising a terminal member and a cam member rotatable between a first position in which at least one electrical wire may be removably inserted between the terminal member and the cam member, and a second position in which the cam member engages the or each wire and releasably clamps it against the terminal member.

Preferably, the cam member is mounted for rotation about an axis parallel to a linear contact surface on a spring biased contact on the terminal member against which the wire is clamped by the cam member when rotated into the second position.

In the preferred embodiment, the cam member is cylindrical and said axis of rotation is positioned eccentrically with respect to the longitudinal axis of the cylinder.

Conveniently, the cylinder has a longitudinally flattened portion to provide a space between the cam member and the terminal member when the cam member is in its first position to enable a wire to be removably inserted between them.

Preferably, the cam member is moved between its first and second positions in less than one revolution.

In an alternative embodiment, the cam member is made from a resiliently flexible material.

Advantageously, the spring biased contact is separated into a plurality of individual wire gripping surfaces, each wire gripping surface being deflectable independently of its adjacent surface to accommodate at least two wires of different diameters.

In the preferred embodiment, the terminal member and the cam member are mounted within a housing, said housing including an aperture for insertion of the or each wire into the terminal.

Preferably, the aperture is a slot which comprises an interconnected series of holes each of which is shaped to receive a single wire.

Preferably, the spring biased contact is an integral part of the terminal member.

A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIGURE 1 is a side view of a terminal shown with the cam member in a first position but with a wire inserted therein.

FIGURE 2 is the same view as shown in Figure 1 but showing the cam member in a second position with a wire retained in position between the terminal member and the cam member.

FIGURE 3 is a perspective view of the terminal member of the terminal shown in Figure 1 and Figure 2.

FIGURE 4 is a perspective view of the cam member shown in Figure 1 and Figure 2.

Referring now to the drawings, there is shown in Figure 1 a terminal comprising a terminal member 1 and a cam member 2 mounted within a housing 3 (only part of the housing 3 is shown in Figures 1 and 2). Electrically conductive wires 5 each having an end 4 stripped of a predetermined length of insulation material are positioned between the terminal member 1 and the cam member 2 having been inserted into an opening 18 in the housing 3 (only a single wire can be seen in Figures 1 and 2).

The terminal structure 1 is made from a single piece of electrically conductive material such as metal which is bent into the required shape to form a contact holder as shown by folded portions 7,8 (see Figure 3). A further upstanding portion 9 of the terminal member 1 is folded back on itself at 12 to form a spring biased contact 10 for engaging the bared ends 4 of the wires 5 and forms an angle of approximately 30 degrees with the rear portion 11 of the terminal member 1 (see angle A in Figure 1).

The fold 12 acts as a hinge to enable the spring biased contact 10 to be deflected inwardly to reduce the above angle when a lateral force is applied thereto, the resilience of the material returning the spring biased contact 10 to its position shown in Figure 1 when the applied lateral force is removed.

The spring biased contact 10 is cut into separate wire gripping tabs 13,14,15 at cut lines 14a, so that each tab 13,14,15 can be deflected inwardly by a different amount from its adjacent tab 13,14,15. The reason for the resilient deformability of the spring biased contact 10 and the separate tabs 13,14,15 will become apparent from the following description.

The cam member 2 is made from an insulating material as it does not need to be electrically conductive. However it will be appreciated that it could also be made from a metal material to assist in improving heat dissipation from the electrical connection. The cam member 2 is generally cylindrical in shape although a section of the curved surface 19 of the cylinder is removed to provide a flattened portion 16 which is positioned directly opposite and facing the terminal member 1 when the cam member 2 is in its first position shown in Figure 1, to provide a space between the terminal member 1 and the cam member 2 for insertion of the bared ends 4 of the wires 5 therebetween.

One end 20 of the cylindrical cam member 2 has an eccentrically positioned cylindrical boss 15a on it mounted in a circular aperture (not shown) in the housing 3 to provide an axis of rotation for the cam member 2.

The opposite end 21 of the cam member 2 protrudes from the housing 3 and has a slot 17 formed therein which can be engaged with the head of a screwdriver to enable rotation of the cam member 2. Alternatively, a lever (not shown) can be provided on the end 21 of the cam member 2 in place of the slot to enable manual actuation of the cam member 2.

Only part of the housing 3 is shown in Figures 1 and 2 but it can be seen that it encloses and mounts the terminal member 1 and cam member 2 therein. The housing 3 has a slot to receive the bared ends 4 of the wires 5 which is formed as a series of circular holes which overlap each other and join up to provide an interconnecting series of openings 18 for insertion of a single bared wire end 4 into each. This particular slot configuration prevents bunching of the wire ends 4 in the terminal and also permits them to be inserted easily.

Each opening is of a dimension small enough to allow only the bared ends 4 of the insulated wire to be inserted, the insulated portion of the wires 5 being of a diameter which is greater than that of the openings 18.

The spring biased contact 10 of the terminal member 1 is positioned within the housing 3 so that the wire gripping tabs 13,14,15 are each aligned with one of the openings 18 on the housing 3 so that the bared end 4 of a wire 5 inserted therethrough will be positioned adjacent one of the tabs 13,14,15.

The inside of the housing 3 is formed with protrusions (not shown) which engage the cam member 2 when in its first and second position to prevent the cam member 2 from being rotated beyond its first and second position.

The operation of the screwless terminal will now be described. A predetermined length of the end of a wire 5 is stripped of its insulation and the bared end 4 is inserted through the slot in the housing 3 through one of the openings 18 while the cam member 2 is in its first position shown in Figure 1 in which the flattened portion 16 of the cam member 2 is vertically aligned and spaced from the end facing the spring biased contact 10 of the terminal member 1. The bared end 4 is held in position between the cam member 2 and one tab 13,14,15 of the spring biased contact 10 while additional bared ends 4 of wires 5 of the same or of a different diameter are inserted into the housing 3 through the other openings 18 of the slot having first stripped the required amount of insulation from each of them.

Once all the bared ends 4 of the wires 5 to be connected to the terminal have been inserted therein, the cam member 2 is rotated through an angle of approximately 90180 degrees to its second position shown in Figure 2.

This rotation of the cam member 2 brings its curved surface 19 into engagement with the bared wire ends 4 and pushes each of them against one of the tabs 13,14,15 of the spring biased contact 10 thereby deflecting it by an amount depending on the thickness of the bared wire end 4 pushed against that particular tab 13,14,15.

It will be appreciated that a bared wire end 4 having a large diameter will cause deflection of the tab 13,14,15 against which it is pushed by a larger amount than a bared wire end 4 having a lesser diameter pushed against an adjacent tab 13,14,15. A number of bared ends 4, some or all of which may be of differing diameters can therefore be gripped between the curved surface of the cam member 2 and the spring biased contact 10.

It will be appreciated that the function of the tabs 13,14,15 is to allow the terminal member 1 to retain a number of bared wire ends 4 of the same or differing diameters at the same time.

From the foregoing description, it can be seen that the curved surface 19 of the cam member 2 pushes the bare ends 4 of wires 5 in a lateral direction against the spring biased contact 10 as a result of the rotational movement of the cam member 2.

Removal of the wires 5 from the terminal is simply achieved by counter-rotating the cam member 2 by approximately 90 - 180 degrees in the opposite direction to release the grip between its curved surface 19 and the spring biased contact 10 so that the wires 5 can be pulled from the terminal.

A particular advantage of the terminal is apparent from the foregoing description of its operation. The cam member 2 need only be rotated through less than one complete revolution between its first position for insertion of bared ends 4 into the terminal and its second position in which the bared ends 4 of wires 5 are clamped between the terminal member 1 and the cam member 2.

In a second embodiment (not shown), the terminal member 1 may comprise the flat conductive plate 11 without the spring biased contact 10. In this embodiment, the cam member 2 is cylindrical and made from a resiliently flexible material without any flattened portion 16. The terminal operates in the same way as described above except that the body of the cam member 2 is squashed against the terminal member 1 when rotated into its second position so that the bare ends 4 of the wires 5 are squeezed between the flexible cam member 2 and the terminal member 1.

In a third embodiment (not shown) insulated wires 5 without a stripped bare end 4 are inserted through enlarged openings 18 in the housing and the tip of the spring biased contact 10 is sharpened to form a blade which slits the insulation and contacts the metal core of the wire 5 to provide an electrical connection when the wires 5 are pushed against the spring biased contact 10 by rotating the cam member 2 into the second position.

Claims

1. A cam operated terminal comprising a terminal member and a cam member rotatable between a first position in which at least one electrical wire may be removably inserted between the terminal member and the cam member and a second position in which the cam member engages the or each wire and releasably clamps it against the terminal member.

2. A cam operated terminal as claimed in claim 1, wherein the cam member is mounted for rotation about an axis parallel to a linear contact surface on a spring biased contact on the terminal member against which the wire is clamped by the cam member when rotated into the second position.

3. A cam operated terminal as claimed in claim 2, wherein the cam member is cylindrical.

4. A cam operated terminal as claimed in claim 3, wherein the axis of rotation is positioned eccentrically with respect to the longitudinal axis of the cylinder.

5. A cam operated terminal as claimed in claim 3 or claim 4, wherein the cylinder has a longitudinally flattened portion to allow insertion of the or each wire into the terminal.

6. A cam operated terminal as claimed in claim 4, wherein the cam member is made from a resiliently flexible material.

7. A cam operated terminal as claimed in any of claims 2 to 6 wherein the spring biased contact is split into a plurality of individual wire gripping surfaces, each wire gripping surface being deflectable independently of its adjacent surface to accommodate at least two wires of different diameters.

8. A cam operated terminal as claimed in any of claims 2 to 7 wherein the spring biased contact is an integral part of the terminal member.

9. A cam operated terminal as claimed in any preceding claim, wherein the terminal member and the cam member are mounted within a housing, said housing including an aperture for insertion of the or each wire into the terminal.

10. A cam operated terminal as claimed in claim 9 wherein the aperture is a slot is defined by an interconnecting series of holes for insertion of a single wire into each hole.

11. A cam operated terminal as claimed in claim 9 or claim 10 wherein the housing includes means for preventing turning of the cam member beyond the first and second position.

12. A cam operated terminal as claimed in any preceding claim, wherein the cam member is operable between the first and second positions in less than one revolution.

13. A cam operated terminal as claimed in any preceding claim, wherein an end of the cam member includes means to receive a screwdriver by means of which the cam member can be rotated.

14. A cam operated terminal as claimed in any of claims 1 to 12 wherein an end of the cam member is provided with a lever.

15. A cam operated terminal substantially as hereinbefore described with reference to the accompanying drawings.