GB2310548A

GB2310548A - An electrical terminal having an insulating plug

Info

Publication number: GB2310548A
Application number: GB9604032A
Authority: GB
Inventors: Robert William Taylor
Original assignee: Cliff Electronic Components Ltd
Current assignee: Cliff Electronic Components Ltd
Priority date: 1996-02-26
Filing date: 1996-02-26
Publication date: 1997-08-27
Anticipated expiration: 2016-02-26
Also published as: GB9604032D0; GB2310548B

Abstract

An electrical terminal mounted on a body or casing comprises, an elongate connector having a longitudinally extending terminal hole at its end, a screw knob mounted on the end of the threaded elongate connector in a longitudinally adjustable manner and a connection portion disposed on the connector between the knob and the body or casing. The knob provides access to and encloses the connection portion whilst covering the end of the elongate connector. A cavity in the knob also provides access to the terminal hole in the end of the elongate connector. Thus allowing a further live connection. The present invention is characterised in that a removeable plug in the form of an insulated screw which co-operates with a thread inside the terminal hole, may be inserted into said hole. Hence, the live end of elongate connector is shielded and may be regarded as "touch-proof".

Description

TITLE "An Electrical Terminal" TECHNICAL FIELD & BACKGROUND ART The present invention relates to an electrical terminal of the type comprising an insulating body carrying an elongate electrical connector whereby the body member is designed for attachment to a mounting. More particularly, the invention relates to a terminal in which the connector has a electrical connection portion to facilitate the connection of a wire, and which connection portion may be exposed or enclosed by adjusting a knob longitudinally along the length of the connector. Such terminals further include longitudinally extending terminal holes in one end of the connector for receiving cylindrical electrical plug connections.

Such terminals are well known and are widely used in electrical audio systems for the connection, by unqualified persons, of speaker wires to power amplifiers whereby such wires are connected to the connection portion and clamped in this position by adjusting the knob along the connector.

Additional connections may then be made by the insertion of electrical connector plugs into the longitudinally extending terminal hole.

A connector of this type is disclosed in our corresponding British patent No. 2,270209 for an electrical terminal.

While such terminals are well known to facilitate the straightforward connection of wires they also present possible safety hazards. Conventionally, the terminal holes of such connectors have a 4 mm diameter hole for receiving a 4 mm diameter plug. However, the use of the 4 mm plugs in certain countries can promote dangerous situations whereby such 4 mm connector plugs may fit within the domestic power sockets and create a safety hazard. In such situations the use of 4 mm diameter terminal posts should not be encouraged for use with equipment that is used domestically, although it is very convenient to use plugs of this type in a professional and industrial environment.In addition, the use of terminals and terminal posts of this size and design may be safely used in other countries, such as the United States, whereby the main power sockets are of a different size to those in most European countries whereby the 4 mm cylindrical plug cannot fit into the domestic power sockets and therefore the dangerous situation does not exist. There are situations whereby electrical terminals of this type are required without the longitudinally extending terminal hole and certain situations whereby terminals incorporating this terminal hole are required.

However, it will be appreciated that it is expensive and time consuming to incorporate the manufacturing processes and equipment specifically designed for terminals with and without electrical connector holes.

In addition, it should be noted that British and International safety standards (those concerned with the checking of the inaccessibility of live parts of electrical components for this standard test finger so that such parts in the terminal may be regarded as "touchproof") require that all electrically live components should be inaccessible with a standard "finger". To this end, it will be appreciated that where a plug is not inserted into the longitudinally extending hole of such a terminal and the knob is in the fully closed position it is possible that a child or adult's small finger may be inserted through the knob aperture to touch the internal electrical components.

It is an object of the present invention to provide a terminal of a kind discussed above which is adaptable to receive or block reception of a cylindrical plug connection and which is relatively simple and inexpensive to manufacture and, where required, provided with the structural characteristics which satisfy the requirements of British Standard 3042:1971 and International Standard IEC 335-1.

STATEMENT OF INVENTION & ADVANTAGES According to the present invention there is provided an electrical terminal comprising an elongate electrical connector carried by an insulating body member whereby means are provided to restrain the connector from displacement relative to the body member, the connector having a connection portion disposed between the body member and one end thereof and carrying an knob mounted on and longitudinally adjustable over one end length thereof for providing access to and closing the connection portion whilst providing an insulating cover for the end part length, whereby the electrical connector has at its one end a longitudinally extending end terminal hole and the knob has a longitudinally extending cavity to provide access to the end terminal hole, and having a removable plug inserted in the end terminal hole wherein the plug has a first engaging means for engagement with a second engaging means on an inner surface of the end terminal hole to restrain the plug in the terminal hole.

In this preferred embodiment, the first engaging means of the plug will comprise an external screw thread and the second engaging means will comprise an internal screw thread for screw threaded engagement.

Alternatively, the first engaging means may comprise a first projection on the plug and the second engaging means will comprise a second projection inwardly from the terminal hole wall for reciprocal snap engagement when the plug is inserted in the terminal hole.

In either case, it is preferable that the plug will comprise a disengagement means which is capable of cooperation with a tool to facilitate disengagement of the first and second engagement means. Usually this disengagement means will comprise a rebate for engagement with a tool to enable the plug to be rotated about a longitudinal axis relative to the connector to facilitate disengagement of the first and second engaging means. Usually, the rebate will be of a design to facilitate normal engagement with a screw driver or allum key.Alternatively, where the plug is in snap engagement with the terminal any disengagement means may comprise means for engagement with the tool to restrain the tool from longitudinal displacement relative to the plug so that a longitudinally applied force applied in the direction away from the connector may be applied to the plug by the tool to move the first and second engaging means out of snap engagement with each-other.

Preferably, the knob will be insulated, either by being made wholly of an insulating material such as plastics or by having an insulating coating on all external or accessible portions of the knob which may be touched. Furthermore, in its prefered form, the closing plug of the present invention will be insulated, again either by comprising wholly of an insulating material or by having an external coating or shell of an insulating material such as plastics.

Terminals of this type will usually comprise a connection portion which comprises a transversely extending hole there through which is open and closed by the longitudinal displacement of the knob along the connector.

DRAWINGS One embodiment of an electrical terminal constructed in accordance with the present invention will now be described, by way of example only, with reference to the company illustrative drawings in which: Figure 1 is a cross-sectional view of the electrical terminal; Figure 2 is an enlarged sectional view of an end part length of the connector of the terminal in Figure 1 with a closing plug rotated through 900C relative to the closing plug shown in Figure 1.

DETAILED DESCRIPTION OF THE DRAWINGS The electrical terminal 10 has an insulating body 12 comprising an upper body portion 12a and a lower body portion 12b carrying an elongate electrical connector 14.

For convenience in this particular embodiment, the connector 14 is substantially cylindrical with the upper and lower body portions 12a and 12b being substantially circular and concentric about a longitudinally extending central axis 16 of the connector 14. In this particular embodiment, the connector 14 comprises an elongate conducting rod usually metallic, having three sections, an upper part length 18 a central part length 20 and lower part length 22. The rod has a circular cross-section with each of the three sections 18, 20, 22 being of different diameter. The lower length 22 is externally screw threaded with a free end 24 having a circumferential recess 26 which in use may have an electrical lead attached thereto.The lower length 22 extends from a lower face 28 of the central portion 20, which latter portion 20 has a greater diameter than the lower length 22 so that the lower face 28 presents a shoulder. This central portion 20 has formed therein a recess 30 extending longitudinally part way along the length of the central portion from the lower face 28.

Extending from an upper flat face 32 of the central portion 20 is the upper length 18 having a diameter less than that of the central portion. Formed in the upper length 18 is a transversely extending hole 34 which is designed to facilitate passage of an electrical connecting wire. The free end part of the upper length 18 is substantially tubular having a longitudinally extending terminal hole 36 extending into the connector 14. The upper length 18 is externally screw threaded.

Mounted on the upper length 18 of the connector 14 is an insulating knob 38. This knob is generally cylindrical and has a longitudinally extending bore 40 extending co-axially there through. Mounted in the bore 40 is a tube 42 having an internal screw thread which is received on the screw thread of the upper length 18 of the connector, thereby allowing the knob to be rotatably adjusted along the upper length 18 of the connector until it abuts with the central portion 20. The knob 38 comprises a one piece plastic moulded body. To restrain the knob 40 on the connector 14, an upper end stop position is defined by an external flange 44 formed on an end of the upper length 18 of the connector 14.The flange 44 is of greater diameter than the inner diameter of the tube 42 but of smaller diameter than the bore 40, so that the knob may be rotatably adjusted along the respective connector until-the upper end of the tube 42 abut against the flanges 40 when the knob is an upmost position to prevent further longitudinal adjustment in that direction. In the upper end position the knob clears and exposes the hole 34 of the connector.

As the knob 38 is rotatably adjusted along the length of the connector towards the central part length 20 it encompasses the free end part length of the upper length 18 of the connector and, at a certain longitudinal position of the connector, the body of the knob 38 fully closes the hole 34.

The upper body member 12a a passage 49 extending longitudinally therethough and has an upper cavity 48, so that the connector 14 is received longitudinally within the cavity 48 so that the lower part length 22 extends through the passage 49 and the central part length 20 is received as a substantially complimentary fit within the cavity 48. In addition the cavity 48 has a projection 51 for engaging the recess 30 to restrain the connector from rotation about its longitudinal axis relative to the body member 12a. The lower face 28 of the central length 20 abuts an inner face of the cavity 48 to restrain the connector from further displacement relative to the body 12a. The lower part length 22 of the connector extends through a body mounting 52 (such as a casing of an electrical appliance on which the connector is mounted) and passes through a coaxial passage 54 in the lower body 12b.

A washer ring 53 and a nut 55 are then tightened on the lower part length 22 of the connector to move the lower body member towards the upper body member 12a so as to clamp the terminal to the body mounting 52 disposed therebetween.

In use, the knob 38 is unscrewed sufficiently to expose the hole 34 to allow a wire to be inserted and the knob 38 is then screwed down along the connector to close the hole 34 and exert a high clamping pressure on the wire to prevent it from being withdrawn. Alternatively a spigot plug, with a wire attached thereto may be inserted through the hple 34 when the knob is in an upper position. It will also be appreciated that the hole 34 may be replaced by a solid metal body to facilitate direct connection of a wire by bending it around the connector and clamping it in position between the knob and the body 12a.

In addition, a further connection may be made to the connector by soldering, or otherwise attaching, a wire to the circumferential recess 26 on the lower length 22.

Also, where desired, yet another connection may be made to the terminal 10 by inserting a spigot plug of the appropriate dimensions, usually 4mm diameter, through the knob bore 40 to engage the terminal hole 36 in the upper part length 18 of the connector. The dimensions of the knob bore 40 are preferably sized to permit passage of a 4mm plug and also the insulating body of the spigot plug (to allow the knob to be adjusted freely along the connector even when this plug is inserted in the terminal hole 36).

However, it will be appreciated that when the knob 38 is adjusted to close the hole 34 the it will almost expose the end 46 of the electrical connector, to the extent where it may be possible to accidentally touch the live conductor of the terminal with a finger. Alternatively, the terminal hole connection may not be required for certain terminals or may be considered dangerous by encouraging the use of 4mm plugs and therefore discouraged in certain countries. This gives rise to the need for certain terminals to have an end terminal hole and for others (especially for domestic use) not to have such terminal holes.However, it is expensive and time consuming to adapt manufacturing equipment to produce two types of terminal and a more realistic solution has been to insert insulating plugs into the terminal holes to seal such holes when they are not required, by frictional engagement with the inner wall of the hole. However, once inserted these plugs are difficult to remove and effectively prevent use of the terminal hole.

The preferred embodiment shown in Figure 1 incorporates an insulted knob 38 and an insulating plug 62 to reduce the exposure of live components of the terminal which could be touched so as to alleviate the risk of possible electric shock.

The knob 38 and plug 62 may be wholly made of an insulating material or may comprise an insulating coating around a conductive core. However, it should be appreciated that the present invention is equally applicable to terminals having either or both the knob 38 and plug 62 made wholly or partially of a conductive material, such as brass. In such cases, the inclusion of the plug 62 is intended to discourage the need for 4mm plugs (i.e. for certain countries). Therefore, reference to an insulating plug 62 in the preferred embodiment may be equally applicable to a non-insulating plug 62.

In the present invention the terminal hole 36 has an inner screw threaded bore 60 and a removable screw threaded insulating plug 62, which may be readily inserted into the terminal hole 36 by rotating the plug relative to the terminal to screw it in. The plug 62 will usually be of plastics material (although other insulating materials may be employed) and has an cylindrical body 64 with a flattened head 66 with a rebate 68 for -engagement with a conventional flat bladed screwdriver. This plug is readily removable from the threaded bore 60 of the terminal hole be reversing the direction of relative rotation between the terminal and the plug 62. It will also be appreciated that the rebate 68 may be adapted for engaging a phillips screwdriver or even made hexagonal (or square) for cooperation with standard allum keys.Whatever means of screwing the plug into or out of the terminal hole 36 is employed this invention provides for a terminal which is readily adapted to facilitate electrical connection via an upper terminal hole where desired or to seal such a connection means with an insulating cover in the form of a plug. However, this plug is easily removes should the user wish to change the application of the connector.

Furthermore, since the plug 62 and connector 14 employ a positive connection in the form of screw threaded engagement, then there is a reduced possibility of the plug being accidentally removed or lost as when only frictional forces are employed to restrain the plug in the terminal hole.

It is further envisaged that an additional benefit of the present invention is the use of screw threaded spigot plug connectors for screw threaded engagement within the threaded bore 60 of the terminal hole 36. Although conventional 4mm plugs may fictionally engage the walls of the screw threaded bore 60 (and a smooth bored lower section 70), such plugs may be adapted to be screw threaded for screw threaded engagement with the terminal. This provides for a more secure electrical connection but one which is readily removable by rotation relative to the terminal.

By reference to a screw threaded engagement between the insulating plug 62 and the terminal hole of the terminal it is also intended to include an insulating plug having a bayonet fitting for engagement with a reciprocal bayonet fitting in the terminal hole. In its simplest form. not shown, the plug will have two laterally extending projections which are received within two corresponding grooves within the terminal hole when the plug is inserted therein whereby relative rotation (as effected by a screwdriver) between the plug and the connector may then rotate the plug projections to engage a transverse rebate (standard bayonet fitting) in the terminal hole to restrain the plug from displacement relative to the connector.

This arrangement may easily be reversed so that the terminal hole comprises projections and the plug comprises grooves for receiving these projections.

In an alternative embodiment of the present invention, not shown, other means of positively engaging and disengaging an insulating plug with the terminal hole may be employed. In particular an insulating plug may comprise a resiliently deflectable circumferential ridge about its cylindrical body snap engagement with a corresponding circumferential ridge extending around the bore of the terminal hole, each of these ridges having inclined faces to facilitate the ridges riding over one another during snap engagement and such snap engagement occurring as the plug is forcefully pushed into the terminal hole. Here the ridges replace the screw threaded arrangement previously discussed. Further, the flattened head of the plug will be provided with a rigid handle to facilitate connection with a hooked tool allow a disengagement force to be applied longitudinally to the plug in a direction away from the terminal to move the plug out of snap engagement with the terminal hole.

It will be appreciated that the main feature of the present invention is to provide an insulating plug with positive engaging means for reciprocal engagement with engagement means on the inner bore of the terminal hole together with means of readily engaging and disengaging such engagement means.

Furthermore, the electrical connector described herein was by way of example only and the invention is readily applicable to other connectors designed to receive electrical spigot plug connections.

Claims

1. An electrical terminal comprising an elongate electrical connector carried by a body member whereby means are provided to restrain said connector from displacement relative to said body member, the connector having a connection portion disposed between said body member and one end thereof and carrying a knob mounted on and longitudinally adjustable over one end part length thereof for providing access to and enclosing the connection portion whilst providing a cover for said end part length, in which said electrical connector has at its one end a longitudinally extending end terminal hole and said knob has a longitudinally extending cavity to provide access to said end terminal hole, and having a removable plug inserted in the end terminal hole wherein said plug has a first engaging means on an inner surface of said end terminal hole to restrain said plug in said terminal hole.

2. A terminal as claimed in claim 1 in which said first engaging means comprises an external screw thread and said second engaging means comprises an internal screw thread for screw threaded engagement.

3. A terminal as claimed in claim 1 in which said first engaging means comprises a first projection and said second engaging means comprises a second projection for reciprocal snap engagement when plug is inserted in said terminal hole.

4. A terminal as claimed in any one of the preceding claims in which said plug further comprises a disengagement means for cooperation with a tool to facilitate disengagement of said first and second engaging means.

5. A terminal as claimed in claim 4 when appended to claim 2 in which said disengagement means comprises a rebate for engagement with a tool to enable said plug to be rotated about a longitudinal axis relative to the connector to facilitate disengagement of first and second engaging means.

6. A terminal as claimed in claim 4 when appended to claim 2 in which said disengagement means comprises a projection for engagement with a tool to enable said plug to be rotated about a longitudinal axis relative to the connector to facilitate disengagement of first and second engaging means.

7. A terminal as claimed in claim 4 when appended to claim 3 in which said disengagement means comprises means for engagement with a tool to restrain said tool from longitudinal displacement relative to said plug whereby a longitudinally applied force away from the connector may be applied to the plug by the tool to move said first and second engaging means out of snap engagement with each other.

8. A terminal as claimed in any one of the preceding claims in which said connection portion comprises a transversely extending hole.

9. A terminal as claimed in any one of the preceding Claims wherein one or more of the body member, knob and cover are insulated from the electrical connector.

10. A terminal as claimed in Claim 9, wherein one or more of said body member, knob and cover are made of insulating material.

11. A terminal as claimed in any one of the preceding Claims wherein the plug is insulated and/or is made of insulating material.

12. An electrical terminal substantially as herein described with reference to the accompanying illustrative drawings.