GB2232017A

GB2232017A - Pre-wired lamp holder

Info

Publication number: GB2232017A
Application number: GB9007830A
Authority: GB
Inventors: Victor J Spencer
Original assignee: CONTACTUM Ltd
Current assignee: CONTACTUM Ltd
Priority date: 1989-04-11
Filing date: 1990-04-06
Publication date: 1990-11-28
Anticipated expiration: 2010-04-06
Also published as: GB9007830D0; GB8908120D0; GB2232017B

Abstract

A lamp holder in which the terminals (7) of the electrical contacts (5) have wires (8) preassembled therewith, has the contacts and wire connections encapsulated in a moulded body (1) so as to be irremovable therefrom. The lamp holder can take the form of a "pendant drop" fitting in which the wires (8) emerge from the top of the fitting in an outer sheath (9), each wire 8 having a kink (11) formed in it to provide strain relief. The lamp holder may include a metal insert and may be moulded in one piece as a one-shot moulding or in two stages where the contacts (5) and wires (8) connected thereto are first moulded or assembled into a sub-assembly (6) which is then placed in a second mould to enable the body (1) to be moulded therearound. The sub-assembly may also be formed as two shell halves. <IMAGE>

Description

PRE-WIRED LAMP HOLDER This invention relates to pre-wired lamp holders in which the wires connected to the electrical contacts housed in the body of t.he lamp holder are irremovably retained therein by encapsulating then in the body during manufacture by a moulding process.

Conventional lamp holders generally ccmprise a pair vi metal contacts housed in a lamp holder body. One end of the cylindrical body is open-ended to receive a light bulb therein which can be either of a screw or bayonet fitting type to make contact with the electrical contacts protruding into this open end of the body.

The electrical contact are mounted in the body to project into the open end thereof to enrage eX light bulb when inserted therein ar,d are r.ormally provided with terminals to each of which a wire is connected.

These wires can be connected to the electrical contacts i.n any suitable way but a screw connection is common.

The lamp holder body usually also includes a metal liner to prevent distortion ci. the body due to heat generated by the light bulb wher. inserted therein.

If the lamp holder is to form part of a "pendant drop" fitting (i.e. a fitting which would be connected by a length of flexible cable to a ceiling rose) then the wires connected to the electrical contacts project through the top of a screw cap on the lamp holder body, this cap being necessary to provide access to the contact terminals. Alternatively, the wires can project laterally from the lamp holder body so that it can form part of a festoon arrangement where a plurality of lamp holders are connected in parallel with each other. The lamp holder can also take the form of a batten fixing where it is incorporated into a mounting assembly which is screwed directly onto another surface such as a wall or ceiling.

It will be appreciated from the foregoing discussion that having the wiring separate from the lamp holder body results in additional assembly work for the eventual customer. In the case of "pendant drop" lamp holders, in the past, it has been left to the electrical contractcr who installs the fittings to attach a suitable length of wire cable to the lamp holder to form the "pendant drop" fitting. However, increasingly these days such fittings are being sold pre-assembled to include the flexible cable so that the contractor only has to attach its other end to the ceiling rose, thereby saving assembly time. The lamp holder and wires can be pre-assembled in the factory but this can prove to be complicated and therefore costly due to the limitations imposed by the lamp holders themselves in the assembly process.For instance, the lamp holders often use terminal screws as a means of attaching the wire to the contact but this means that the terminals have to be cross drilled and tapped which involves additional machining and therefore extra costs.

It is an object of the present invention, therefore to provide a lamp holder in which the w.iring thereto is attached to the terminals and encapsulated in the lamp holder body during the moulding process thereby overcoming or substantially reducing the above disadvantages.

According to one aspect of the invention there is provided a lamp holder comprising a body having an open end to receive a light bulb, the body housing a pair of electrical contacts which project into said open end, an insulated wire being connected to each cf said contacts and extending to the exterior of the body, the body being moulded from a rigid heat resistant plastics material to hold and locate the connected wires and contacts permanently in position therein and also to intimately encapsulate the connections between the contacts and the wires to provide a permanent non-removable connection therebetween.

Conveniently, the wires extend from the body generally coaxial with its longitudinal axis to provide a "pendant drop" fitting. The wires may be juxtaposed to emerge together frcm the body enclosed .in an outer protective sheath whose end portion adjacent the connections with the contacts is encapsulated in the lamp holder body. Alternatively, the wires are spaced from each other and emerge separately from the body to provide a batten fixing. In another arrangement, the leads emerge from the body laterally in opposite directions with respect to its longitudinal axis to provide a lamp holder which can form part of a festoon assembly.

Desirably, a metal insert is fitted in the open end of the body and irremovably attached thereto. In the preferred embodiment, the metal insert has a cylindrical upper part with a pair of locating legs or protrusions extending therefrom, said legs being encapsulated in the material of the body to prevent removal therefrom.

"Pendant drop" lamp holders have to conform to British Standard 5042 in that they must include means to prevent the flexible cable placing a strain on the terminals. Accordingly, the lamp holder of the present invention can include a small kink or convolution on the wire adjacent to its connection to each electrical contact to provide such strain relieving means. During the encapsulation process, plastic material flows around the convoluted wire thus locking it in position and preventing pulling strain being transmitted to the terminals.

According to a preferred feature of the invention, the body comprises two parts, namely an outer part enclosing an inner sub-assembly. In one embodiment, the inner sub-assembly is moulded from a first plastics material and encapsulates the electrical contacts and the wires connected thereto. The outer part can be moulded from the same plastics material or from a different plastics material to surround and encapsulate the inner sub-assembly. In another embodiment, the sub-assembly is formed as two shell halves which enclose the contact pins. Preferably, the shell halves snap-fit together.

Another feature of the preferred lamp holder is that the portion thereof from which the wire protrudes includes cooling fins.

According to another aspect of the invention, there is provided a method for moulding a pre-wired lamp holder comprising the steps of (a) attaching an electrical wire to a respective one of a pair of electrical contacts, (b) inserting the pre-assembled wires and contacts in a mould adapted to form a lamp holder body, and (c) admitting plastics material into the mould to form the lamp holder and encapsulate the pre-assembled wires and contacts and irremovably retain them therein.

Preferably, the pre-assembled wires and contacts are inserted into a first mould into which a plastics material is admitted to form a sub-assembly encapsulating the wires and contacts therein, the sub-assembly then being removed from the first mould and inserted into a second mould to form a lamp holder body around said sub-assembly, a plastics material being admitted to the second mould to form the lamp holder body around the sub-assembly and fuse t thereto whereby a one-piecsz unit is formed with the pre-assembled wires and contacts are irremovably retained therein. The encapsulation may be carried out in two stages using the same plastic material or using compatible plastics materials having different physical properties. For example, it may be found desirable to have a degree of elasticity in the portion of the moulding surrounding the lead wires whilst the body may require a more rigid material capable of withstanding the stress of retaining a hot lamp in position. In the case of the manufacture of a "pendant drop" type of lamp holder where the wires connected to the terminals project from the lamp holder body enclosed in a protective sheath, it may be necessary to form the outer lamp holder body from a different material to that of the sub-assembly enclosing the contacts because the plastics material forming the sub-assembly may have to be moulded at a lower temperature to avoid melting the protective sheathing on the wires.

Alternatively, the lamp holder can be made by: a) attaching a wire to each of a pair of electrical contacts, b) inserting the pre-assembled wires and contacts into a moulded plastics first shell half, c) fitting a second moulded plastics shell half to said first shell half to encapsulate the wires and contacts therein and form a sub-assembly, d) inserting the sub-assembly into a mould to form a lamp holder body and e) admitting a heat resistant rigid plastics material to the mould to form the lampholder body around the sub-assembly and fuse it thereto.

The moulding process can be carried out by the injection moulding process using thermoplastic or thermoset materials.

Several embodiments of the invention will now be descibed by way of example only, with reference to the accompanying drawings, in which Figure 1 is a cross-section through a 'pendant drop" lamp holder including one form of sub-assembly for the contact pins, Figure 2 is a cross-section through a metal insert for fitting into a lamp holder such as that shown in Figure 1, Figure 3 is a cross-section through an alternative form of lamp holder, and Figure 4 is a cross-section through yet another form of lamp holder.

Figure 5 is a plan view of an alternative sub-assembly for the contact pins to that shown in Figure 1 and Figure 6 is a side elevation of the sub-assembly of Figure 5.

Referring to Figure 1 of the drawings, there is shown a preferred lamp holder of the invention which is of the "pendant drop" type. It can be seen from the drawing that the lamp holder comprises a moulded body 1 having a cylindrical open ended portion z to receive a light bulb (not shown). In the illustrated embodiment, the wall of the cylindrical open ended portion 2 is provided at its opposite sides with an L-shaped slot 3 to receive the laterally protruding pins 0L the light bulb (not showr.) in know. mariner.

The exterior of the cylindrical portion 2 is provided with an annular shoulder 10 and a threaded portion 4 immediately adjacent thereto onto which a ring (not shown) may be screwed to retain a lampshade on the lamp holder by clamping its frame between the ring and the shoulder 10.

A pair of electrical contacts 5 (spring loaded in the illustrated embodiment) are mounted in the body 1 so that a portion thereof protrudes into the cylindrical open ended portion 2. The other end of each electrical contact 5 is provided with a terminal portion 7 to which a wire 8 is attached. Preferably, the wire 8 is attached in permanent fashion using any convenient form of fixing, for instance by welding, swaging, riveting, or soldering or using a pre-formed self-gripping tag.

The wires 8 are enclosed in an insulating covering and the two wires 8 are contained in a protective outer sheath 9. As can be seen from the arrangement shown in Figure 1, the wires 8 are each formed with a small convolution or kink 11 in them immediately adjacent the contact terminal portion 7 to provide therein means to prevent any strain exerted on the wires 8 acting on the terminal portions 7 and thereby possibly breaking the connection between the wire 8 and the terminal portion 7 which would be extremely dangerous.

As can be seen from Figure 1, the contact terminal portion 7, the wires 8 and the end part of the sheath 9 protruding from the lamp holder 1 are encapsulated in a sub-assembly 6. This sub-assembly is moulded in one piece and totally encapsulates and seals the terminal portions 7, wires 8 and sheath end part 9 therein.

This sub-assembly is itself enclosed in top part 19 of the lamp holder 1.

With the arrangement shown in Figure 1, it will be seen that the customary screw connections for the wire leads are replaced by term.nations 7 suitable for permanent connection as part of the manufacturing process. Such connections may be made by welding, swaging, riveting, soldering or spring grip or other fixing. In the manufacturing process, the pre-assembled contacts 5 and wires 8 are placed in a moulding tool in such a way that they are in their correct operating positions. The wires 8 can also be bent to form the convolution 11 illustrated in Figure 1. The moulding tool is then closed and filled with a suitable plastics material to form the lamp holder body 1.However, in the embodiment shown in Figure 1, the pre-wired contact/wire arrangement is positioned in the moulding tool in its correct operating position and the mould is filled with a plastics material to form the sub-assembly 6 encapsulating the contact terminal portions 7, the wires 8 connected thereto and the end part of the outer sheathing 9. During this moulding process, care has to be taken to use a suitable plastics material at a temperature which does not melt the outer sheathing 9 but instead fuses itself to it to provide a weather proof connection. The moulded sub-assembly 6 can then be lifted out of the mould and placed in a second mould in which the lamp holder body i including its upper part 19 is moulded as a single moulding around the siib-assembly 6.The sub-assembly 6 and the lamp holder body 1 can be moulded from the same plastics material or from different materials. For exaTnple, it may be found desirable to have a degree of elasticity in the portion of the moulding surrounding the wires 8 whilst the body 1 may require a more rigid material capable of withstanding the stress of retaining a hot lamp in position.

Instead of moulding the sub-assembly 6 in one piece, it can be formed in two halves as shown in Figures 5 and 6. In this embodiment, a pair of brass contacts 5 complete with wires 8 attached thereto in known manner are housed in a sub-assembly 6a comprising two shell halves 30 shaped to receive and locate the contacts 5.

Each shell half 30 has a pair of primary recesses 31 each provided with a locating rib 32 therein adapted to fit into a corresponding annular recess 33 formed around the neck of each contact 5. A secondary recess 34 communicates with each primary recess 31 to receive the wires 8 with their protective outer insulating sheath 9. Each shell half has a peg 35 protruding from it which cooperates with and is received in a corresponding hole 36 on the opposite shell half. In the illustrated embodiment, each shell half has one peg 35 and one hole 36. It will be appreciated however that each shell half could hare two pegs or two holes or that additional holes and pegs can be provided. If desired, the pegs can make a "snap" fit in the holes for ease of assembly.

Once the sub-assembly 6a has been assembled, it can then be placed in the tool which moulds the lampholder body 1 around it as has been previously described.

A metal liner 12 such as that shown in Figure 2 can be incorporated into the lamp holder 1 shown in any of Figures 1-4 if required. As can be seen from Figure 2, the liner 12 comprises a cylindrical part 13 whose wall includes a pair of L-shaped slots 3a to receive the laterally extending pins of a light bulb (not shown).

A pair of protrusions or legs 14 extend from the cylindrical portion 13 and these preferably include retaining means in the form of a hole 15 at one end and notches 16 along each side. The purpose of the hole 15 and the notches 6 is to ensure that the metal insert is properly retained in the lamp holder body 1 during the moulding process. It w-ll be appreciated that when the mould is filled, plastics material will flow through the hole 15 and into the notches 16 so that the insert 12 is fixedly retained in the body 1. The hole 15 and notches 16 are only preferred. Other shaped retaining means can be provided to perform the same function.

The top portion 19 of the lamp holder can also include heat dissipating fins (not shown) extending between the abutment lip 10 and the extremity of the upper portion 19 where the wire sheath 9 emerges from the fitting.

Referring now to Figure 3, there is shown an alternative lamp holder for use as part of a festoon assembly. It will be seen that the arrangement is very similar to that shown in Figure 1 except that each contact 5 has a pair of wires 8 connected thereto which extend laterally from the lamp holder body 1 in a protective sheath 9 for connection to another lamp holder (not shown) so that a number of lamp holders in a parallel connected chain can be manufactured. In the illustrated embodLinent, the lamp holder body 1 is moulded as a one piece moulding to encapsu.iäte all the relevant parts therein, the upper portion 19 having a hole 20 by means of which the lamp holder may be attached to a support surface.It will be appreciated that the arrangement shown in Figure 3 can, however, be formed by a two stage moulding process in which the contacts 5 with the wires 8 connected thereto are initially encapsulated in a sub-assembly during a first moulding step and then subsequently the lamp holder 1 is moulded around the sub-assembly and fused thereto as has already been described with respect to Figure 1.

The arrangement shown in Figure 4 is very similar to that shown in Figure 1 except that the assembly is intended to be used as a "batten" fixing which is a fixing which screws directly on to a ceiling rose or other assembly. There is therefore no ned for a flexible wire to extend from the lamp holder base 1 along the lines illustrated in Figure 1 for the "pendant drop" lamp holder, so there is no need to provide strain relieving means in the form of the convolutions 11 shown in Figure 1 so the pre-wired wires 8 connected to the terminals 7 can simply be encapsulated in a one-piece lamp holder moulding 1 as shown in Figure 4, the wires 8 emerging from the body 1 being encapsulated in projections 21 extending from the lamp holder 1 in spaced relationship with each other.This embodiment can also be moulded in two stages as has already been described with reference to the embodiments of Figures 1-3.

The described embodiments shown in the drawings have the following advantages 1. Improved safety for the user due to the use of permanent factory made connections to suitably insulated wires instead of relying on the user to choose the correct wire, strip the ends of the wire, feed the wires through the screw cap and properly tighten the clamping screws on the terminals to attach the wires thereto. In the illustrated embodiments, safety is further improved by the elimination of the conventional screw cap terminal cover as there is no need for such a cover because the lamp holder is non-rewirable and the connections between the wires and the terminals are permanently sealed and encapsulated within the insulation provided by the lamp holder body.

Furthermore, because all the parts are totally encapsulated in intimate contact with the plastics material of the moulding, better heat transfer/conduction results than in a conventional fitting where only point contact is made.

2. The lamp holders illustrated in the drawings substantially simplify the manufacturing process and reduce the cost thereof as there is no need for a screw cap to cover the terminal connections 7 and there is no need for the terminal 7 to include conventional screw connections. The proposed terminals are neither cross drilled nor tapped enabling faster production of the component as there is no need to cross drill and tap the terminals. ìlanufacture is further improved by reducing the number of component pars needed to assemble the lamp holder so the need to store ready moulded components pricr to assembly is substantially reduced thus sawing on committed capital, warehouse and handling costs.

The lamp holder described and illustrcted in the drawings lends Itself very sat-sXactorily t;o a small moulding machine for use on a conventional or automated assembly line. Thus, the high cost of multi-impression mould toois and large moulding machines is avoided. The moulding process can be carried out using single impression moulds on a small rotary or shuttle type moulding machine. The pre-wired contacts 5 (and metal liner 13 if required) can be inserted into the mould before it is filled with plastics material. A moulding set up such as this could be used as an assembly plant, in other words the operator may well have time to perform preliminary sub-assembly tasks during the cycle time, e.g. swaging lead wires into terminals and preforming ready for loading into the mould tool. Instead of using a rotary table moulding process, a shuttle type moulding machine could be used which transfers two moulds between a single injector head.

Claims

1. A lamp holder comprising a body having an open end to receive a light bulb therein, a pair of electrical contacts in the housing projecting into said open end, an insulated wire connected to each of said contacts and extending to the exterior of the body, the body being moulded from a rigid heat resistant plastics material to hold and locate the connected wires and contacts permanently in position therein and also to intimately encapsulate the connections between the contacts and the wires to provide a permanent non-removable connection therebetween.

2. A lamp holder as claimed in claim 1 wherein the entire body is moulded from the same plastics material.

3. A lamp holder as claimed in any one of the preceding claims wherein the body has a longitudinal axis and the wires extend from the body generally coaxial therewith.

4. A lamp holder as claimed in claim 3 wherein the wires are juxtaposed and emerge together from the body enclosed in an outer sheath whose end portion adjacent the connections with the contacts is encapsulated in the lamp holder body.

5. A lamp holder as claimed in claim 3 wherein the wires are spaced from each other and emerge separately from the body.

6. A lamp holder as claimed in claim 1 or claim 2 wherein the body has a longitudinal axis and the leads emerge from the body laterally with respect thereto in opposite directions for connection to other similar lamp holders to provide a festoon assembly.

7. A lamp holder as claimed in any one of the preceding claims wherein the body is provided with opposed L-shaped slots to receive the laterally protruding pins of a bayonet type light bulb.

8. A lamp holder as claimed in any one of claims 1-6 wherein the body is provided with an internal thread to receive a screw threaded light bulb.

9. A lamp holder as claimed in any one of the preceding claims wherein a metal insert is provided in the open end of the body and irremovably attached thereto.

10. A lamp holder as claimed in claim 9 wherein the metal insert has a cylindrical part from which a pair of locating protrusions extend, said protrusions being encapsulated in the material of the lamp holder body to prevent removal therefrom.

11. A lamp holder as claimed in any one of claims 7-10 when dependant on claim 3 or claim 4 wherein a convolution is formed in each wire closely adjacent its end connected to the contact to provide strain relieving means to prevent any strain acting on the terminals via the wires connected thereto.

12. A lamp holder as claimed in any one of the preceding claims wherein the wires are irremovably attached to the contacts.

13. A lamp holder as claimed in any one of the preceding claims wherein the top of the lamp holder body where the wires emerge includes heat dissipating cooling fins.

14. A lamp holder as claimed in any one of the preceding claims wherein the body is moulded in two parts comprising an outer part enclosing an inner sub assembly, the inner sub-assembly being moulded from a first plastics material and encapsulating the electrical contacts and the wires connected thereto and the outer part being moulded from a different plastics material and fused to the inner sub-assembly to provide a one-piece unit.

15. A lamp holder as claimed in claim 14 wherein the inner sub-assembly comprises two shell halves which enclose the contact pj.nE an6. the wires leading therefrom.

16. A lamp holder as claimed in claim 15 wherein each contact pin is received in a recess formed in a shell half and located therein by means of a rib extending around the wall of said recess to cooperate with a corresponding recess on the contact pin.

17. A lamp older as claimed in claim '6 wherein the two shell halves each have cooperating pegs and hol.es by means of whi.ch the two halves are held together.

18. A lamp holder as claimed in claim 17 wherein the pegs are shaped to make a snap fit in the holes.

19. A method of moulding a pre-wired lamp holder comprising the steps of (a) attaching a wire to a respective one of a pair of electrical contacts, (b) inserting the pre-assembled wires and contacts in a mould to form a lamp holder body, and (c) admitting a plastics material into the mould to form the lamp holder and encapsulate the pre-assembled wires and contacts and irremovably retain them therein.

20. A method of moulding a pre-wired lamp holder comprising the steps of (a) attaching a wire to each of a pair of electrical contacts, (b) inserting the pre-assembled wires and contacts into a first mould, (c) admitting a plastics material to the mould to form a sub-assembly, and encapsulate the wires and contacts therein, (d) removing the sub-assembly from the first mould and inserting it into a second mould to form a lamp holder body around said sub-assembly and, (e) admitting a plastics material to the second mould to form the lamp holder body around the sub-assembly and fuse it thereto whereby a one-piece unit is formed with the pre-assembled wires and contacts irremovably retained therein.

21. The method of claim 20 wherein a different plastics material is admitted to the second mould.

22. The method as claimed in any one of claims 19-21 wherein a small convolution is formed in the wire immediately adjacent each contact prior to insertion thereof into the first mould to provide strain relieving means which prevent any pulling strain being exerted on the connections between the wires and the contacts.

23. The method as claimed in any one of claims 19-22 wherein a thermoplastic or thermoset plastics material is injected into the or each mould.

24. A method of moulding a pre-wired lamp holder comprising the steps of: a) attaching a where to each of a pair of electrical contacts.

b) inserting the pre-assembled wires and contacts into a moulded plastics first shell half, c) fitting a second moulded plastics shell half to said first shell half to encapsulate the wires and contacts therein and form a sub-assembly.

d) inserting the sub-assembly into a mould te form a lamp holder body and, e) admitting a heat resistant rigid plastics material to the mould to form the lamp holder body around the sub-assembly and fuse it thereto.

25. A method of manufacturing a lamp holder substantially as herein described with reference to the accompanying drawings.

26. A lamp holder substantially as herein described with reference to the accompanying drawings.