GB2219895A

GB2219895A - Connectors for rigid electric cables

Info

Publication number: GB2219895A
Application number: GB8906739A
Authority: GB
Inventors: Terence Alan Woodgate
Original assignee: Rotaflex Ltd; GTE Rotaflex Ltd
Current assignee: Rotaflex Ltd; GTE Rotaflex Ltd
Priority date: 1988-06-20
Filing date: 1989-03-23
Publication date: 1989-12-20
Anticipated expiration: 2009-03-23
Also published as: GB8814581D0; GB2219895B; GB8906739D0

Abstract

Apparatus for distributing electric current, especially in a low voltage track lighting system includes: (i) a cable in the form of a rigid rod having coaxial conductors (5, 8) and male and female couplings at its opposite ends allowing the cable rod to be connected end-to-end with other similar cable rods, and the inner conductor having a spring loaded contact (10) at one end; and (ii) a coupling unit which may be used to connect rotatably one cable rod to another cable rod or an appliance, the unit having relatively rotatable housing parts (31, 32) defining respective male couplings at the opposite ends of the unit, and contacts (36) arranged to project axially at the opposite ends, the contacts being connected by a flexible braided conductor (38) and urged apart by a coil spring (37). <IMAGE>

Description

ELECTRIC CABLES This invention concerns electric cables, and in particular relates to cables of rigid construction and finite length so that they take-the form of stiff rods capable of providing firm support for an electrical device, such as a distribution track, appliance e.g.

light fitting, or the like, to which the cable supplies electric current. For convenience such cables are referred to herein as "cable rods".

The particular embodiments of the invention described in detail below are specifically adapted for low voltage electric current supply applications.

Stated broadly the invention resides in a cable rod comprising coaxial conductors and coupling means at each end thereof to enable the cable rod to be connected releasably but securely end-to-end with another substantially identical cable rod to form a rigid cable rod assembly, with electrical continuity of the inner and outer conductors being maintained over the length of the assembly, the inner conductor including a contact portion at one end retractable against a spring force exerted thereon to ensure firm axial abutment with the inner conductor of another cable rod coupled to said one end.

In one embodiment the contact portion is provided by a pin urged axially outwardly with respect to an axially fixed conductor rod by a spring interposed therebetween. According to another embodiment the inner conductor comprises a rod extending continuously from one end to the other end of the conductor, the contact portion being an end of the rod, and a spring being arranged to bias the rod longitudinally in the direction towards said end.

The invention also provides a coupling unit for use with the cable rods of the invention, the coupling unit comprising a body, coupling means of essentially the same or complementary form at either end of the body to enable the unit to be connected between two cable rods in axial alignment, a contact at each end of the unit for engaging the inner conductor of a cable rod attached to that end, spring means accommodated in the body and acting on the contacts to urge them away from each other. In a preferred construction the contacts are connected by a flexible conductor, e.g. a braided conductor, to ensure good electrical continuity therebetween, and the body is made in two relatively rotatable parts to enable rotational adjustment of the cable rod secured to one end of the coupling unit relative to the cable rod secured to the opposite end of the coupling unit.A better understanding of the invention will be gained from the following detailed description of some specific embodiments, reference being made to the accompanying drawings, in which: Figure 1 shows schematically a light fitting suspended from a ceiling by an assembly of cable rods; Figure 2 is a similar view of a light fitting supported by means of a single cable rod; Figure 3 is a side elevation of a cable rod; Figure 4 shows the cable rod of Figure 3 in axial cross section; Figure 5 is an axial section through a second embodiment of a cable rod; and Figure 6 is an axial cross section through a rotating coupling unit or adaptor for use with the cable rod of Figure 5.

In Figure 1, a light fitting 1 is shown suspended from a ceiling by means of a rigid rectilinear support formed by a string of three cable rods 2 connected end-to-end. The upper end of the cable rod string is secured to a suitable socket 3 to provide the necessary electrical connections and mechanical support, and the lower end of the string is connected to a suitable coupling provided on the light fitting 1. It will be appreciated that the length of the support can be selected by increasing or reducing the number of cable rods used, and to allow greater choice over the length of the string, cable rods of different lengths may be provided. Figure 2 also shows a light fitting 1 suspended from a ceiling socket 3, in this case by a single cable rod 2.As will become clear from the description which follows, the cable rods have male and female screw threaded couplings at their respective ends enabling them to be screwed together end-to-end and to be threadedly engaged with the sockets 3 and fittings 1 to provide the necessary mechanical connection and with the electrical connections being completed automatically upon screwing the parts together. The cable rods of the invention can be used for other applications besides those shown in Figs. 1 and 2 and they may be employed with particular advantage in electric track distribution systems in which the cable rods may be used to support and supply current to a track length as well as to support an appliance, such as a light fitting, from the track so that it is powered from the track.In such installations the cable rods may be coupled to the track by means of the coupling arrangement described in our copending application filed on the same date as this application.

Turning to Figures 3 and 4 there is shown an exemplary embodiment of a cable rod 2 having coaxial conductors. The outer conductor comprises a metal tube 5 which is internally screw threaded at both ends, and an externally threaded bush 6 screwed into one end of the tube. The bush projects from the tube to form a male coupling while the opposite end of the tube defines a female coupling or socket adapted to receive the male coupling of another identical cable rod.The inner conductor is held axially within the outer conductor by a layer of insulation 7, and the inner conductor comprises a metal rod 8 extending from the socket into which it protrudes a-little to form a contact pin, to a spring pin assembly which includes a cylindrical cup 9 having its base fixed to the end of rod 8 a metal pin 10 having an enlarged head held captive by an inturned flange on the cup 9, and a coil spring 11 interposed between the base of the cup and the pin for urging the pin to an outermost position (as shown) in which it projects beyond the insulation 7 and the end of bush 6.

When the cable rod is screwed together end-toend with another rod of the same form, the pin 10 bears against the exposed end of the inner conductor rod 8 of the second rod and becomes pushed back into the cup 9 as the threaded joint is screwed up tight.

In this way firm abutting contact is ensured between the inner conductors to ensure their electrical continuity along the length of the cable rod assembly, such continuity of the outer conductors being similarly ensured by the conductive bush and abutment between the ends of the metal tubes 5. Any number of cable rods can be connected together to form a cable rod string of required length.

A modified cable rod is shown in Figure 5. It has an outer metal tube 15 into one end of which is inserted a insulating spacer 16 followed by an internally screw threaded bush 17. To secure the spacer in the tube it has a spigot which is screwed into the inner end of the bush 17. Inserted into the other end of tube 15 is a metal plug 18 formed with an externally threaded boss and having an axial through bore accommodating a spring housing 19 and an insulating sleeve 20. The sleeve 20 has a flange in abutment with the end of the boss and serves to close the end of the spring housing. A stiff metal rod or bar 21 extends continuously through the length of the cable rod with one end exposed in the female socket defined by bush 17 and the other end projecting beyond sleeve 20 to define a contact pin 24. At a position within the spring housing the rod 21 is provided with a spring abutment 22, conveniently formed by flattening a short section of the rod. A coil spring 23 surrounds the bar and acts between the inner end of the spring housing and the abutment 22 to urge the latter against the sleeve 20. By providing a continuous unitary inner conductor electrical continuity through the cable rod is more easily ensured. When the male coupling of the cable rod is screwed into the socket of another similar rod, the inner conductor of the latter engages the protruding pin 24 and pushes it inwardly against the force of the spring 23, the whole inner conductor in this case being displaced longitudinally.

With the cable rod as shown in Figure 5 it may be desirable, in order to avoid having to maintain very tight manufacturing tolerances, to provide in a device connected to the socket at the end of a cable rod or string of a cable rods means for taking up the longitudinal movement of the inner conductor. For example such means could be included in a connection part of a light fitting or in a ceiling socket.

Alternatively, it could be incorporated in a separate connection device e.g. for connecting the cable rod to a socket, light fitting, distribution track or the like. The means in question may take the form of a pair of contacts electrically interconnected by a flexible conductor such as a braided wire conductor, and a spring urging the contacts apart. The end of the inner conductor of the cable rod will be arranged to press on one contact which will move towards the other contact against the spring action to take up the excess projection length of the cable rod conductor.

A device which combines the function of such a means and a rotary coupling unit is shown in Figure 6.

This device, which will be referred to as an adaptor, has at each end a male coupling of substantially the same form as that of the cable rod shown in Figure 5, allowing either or both ends of the adaptor to be connected to cable rods with the adaptor being capable of accommodating the displacement of their inner conductors. The adaptor has a two-part housing, an inner end of one part 31 being telescoped into the inner end of the other part 32, with a circlip 33 holding the two parts axially together so that they are relatively rotatable. A generally cylindrical chamber within the housing is lined by a sleeve 34 of insulating material.The threaded boss of each housing part is fitted with an insulating insert 35 through which a pin contact 36 passes, the contact having an enlarged head which abuts the insert 35 to limit outward movement of the contact, and a collar on the head providing an abutment shoulder for one end of a spring 37 which urges the contacts apart. The contacts are interconnected by a flexible, braided wire conductor 38. Each pin contact can slide inwardly against the action of the spring under a force applied against the outer tip, and hence the adaptor will absorb the longitudinal displacement of the inner conductors of cable rods secured to the adaptor. The electrical continuity is completed by the housing 31, 32 for the outer conductors and by the contacts 36 and flexible wire 38 for the inner conductors.Furthermore, by virtue of its split housing the adaptor enables axially rotative adjustment of a device or cable rod attached to one side of the adaptor relative to the cable rod or device attached to the other side of the adaptor, and such rotation may be continuous as there are no stops, which can be of benefit such as when adjusting the beam direction of a light fitting supported by the adaptor. A further advantage of the adaptor is that it allows male couplings to be located at both ends of a cable rod assembly, which simplifies the connections of the assembly to devices at both ends thereof.

It will be appreciated that a device, such as a light fitting, could be constructed to incorporate a connector including a rotatable coupling of essentially the same form as the adaptor of Figure 6, but in that case one housing part 31, 32 may be fixed to the light fitting and means other than a pin may be used for electrical connection to the corresponding contact 36 of the assembly.

It should be noted that the male couplings of the cable rod shown in Figure 5 and the adaptor shown in Figure 6 are of suitable design to enable connection to a distribution track by a coupling assembly as described in the aforementioned application being filed on the same day as this application and the contents of which are incorporated herein by this reference.

Claims

CLAIMS:-

1. An electric cable consisting of an elongate rigid rod and comprising inner and outer conductors, and complementary coupling means at the opposite ends thereof, thereby to enable the cable rod to be connected releasably but securely end-to-end with another cable rod of substantially identical form to construct a rigid cable rod assembly with electrical continuity of the inner and outer conductors being maintained over the length of the assembly, the inner conductor including at one end of the cable rod a contact portion retractable axially against a spring force exerted thereon, whereby to ensure firm axial abutment of said contact portion with the inner conductor of another cable rod coupled to said one end of the cable rod.

2. A cable rod according to claim 1, wherein the coupling means comprise male and female screw-threaded couplings at the respective ends of the cable rod.

3. A cable rod according to claim 2, wherein said contact portion is located at the end of said male coupling.

4. A cable rod according to claim 2 or 3, wherein the outer conductor comprises a metal tube, and the inner conductor is spaced from the tube by insulating material.

5. A cable rod according to claim 4, wherein the male coupling is formed by a threaded part secured into and projecting from one end of the metal tube.

6. A cable rod according to claim 4 or 5, wherein the insulating material extends continuously along the cable rod.

7. A cable rod according to claim 4 or 5, wherein members of insulating material are spaced apart along the length of the cable rod.

8. A cable rod according to any one of claims 1 to 7, wherein the contact portion is a pin, the inner conductor includes an axially fixed part, and a spring means is interposed between said fixed part and said pin to urge the pin axially outwardly.

9. A cable rod according to claim 8, wherein the spring means is located in a spring housing and said spring housing limits the outward movement of the pin.

10. A cable rod according to claim 4 or 5, wherein the female coupling means comprises an internally screw threaded sleeve fixed in the end of the metal tube.

11. A cable rod according to claim 10, wherein the insulating material comprises separate insulating spacers spaced apart along the cable rod, one said spacer being secured to said threaded sleeve.

12. A cable rod according to claim 11, wherein said one spacer is threadedly connected to said sleeve.

13. A cable rod according to any one of claims 1 to 7 or 10 to 12, wherein the inner conductor comprises a stiff unitary element, an end of said element constituting said contact portion.

14. A cable rod according to claim 13, wherein said conductor element has an abutment and spring means acts between said abutment and a confronting, axially fixed shoulder.

15. A cable rod according to claim 14, wherein said contact end portion is received slidably in an insulating spacer, and said abutment engages the spacer to limit the movement of the conductor element under the action of the spring means.

16. A cable rod according to claim 14 or 15, wherein said abutment is an integral projection on said conductor element.

17. A cable rod according to claim 14, 15 or 16, wherein the spring means is accommodated in a spring housing having said axially fixed shoulder thereon.

18. A cable rod according to any one of claims 14 to 17, wherein the spring means comprises a coil spring surrounding the conductor element.

19. A cable rod substantially as herein described with reference to Figures 2 and 3 of the accompanying drawings.

20. A cable rod substantially as herein described with reference to Figure 5 of the accompanying drawings.

21. An assembly for supporting an electrical device on a structure and supplying electric current to said device, comprising at least two substantially identical cable rods each as defined in any one of the preceding claims.

22. A coupling for use with a cable rod as claimed in any one of claims 13 to 18 or 20, comprising a housing having coupling means for cooperation mechanically and electrically with a coupling means of the cable rod, contacts spaced apart longitudinally of the housing and interconnected by a flexible conductor, and spring means arranged within the housing to urge the contacts apart.

23. A coupling according to claim 22, wherein the housing has a respective coupling means at each end thereof.

24. A coupling according to claim 23, wherein the two coupling means are of the same form.

25. A coupling according to claim 24, wherein each coupling means comprises a screw-threaded male connector.

26. A coupling according to any one of claims 22 to 25, wherein the housing comprises two parts connected for rotation relative to'teach other.

27. A coupling according to any one of claims 22 to 26, wherein an insulating sleeve is received in the housing and said spring means and flexible conductor are positioned within the sleeve.

28. A coupling according to any one of claims 22 to 27, wherein the flexible conductor is a braided wire conductor.

29. A coupling unit substantially as herein described with reference to Figure 6 of the accompanying drawings.

30. An assembly for supporting and supplying electric current to an electrical device, comprising one or more cable rods each as defined in any one of claims 13 to 18 or 20, and a coupling as defined in any one of claims 21 to 28, the coupling being secured to an end of a cable rod.