GB2086558A - A flame-proof light fitting - Google Patents

Abstract

A flame-proof light fitting comprises a single housing (1) receiving both a tubular light bulb (6) and a choke or ballast (5) necessary for the activation of the bulb, the housing (1) having only one access opening (7) closable in a flame-proof manner by a removable plug (13) and through which opening (7) both the tube (6) and the choke or ballast (5) can be introduced into the interior of the housing (1). <IMAGE>

Description

SPECIFICATION A flame-proof light fitting This invention relates to flame-proof light fittings and, more particularly, to light fittings wherein all possible positions where arcing could take place are adequately shielded from an ambient atmosphere which could be explosive or inflammable.

Flame-proof light fittings of the above general type do exist but, are generally composed of a multitude of different parts and cannot easily be opened to replace a light bulb or tube where this becomes necessary. As a conseqeunce of their generally complex construction such flame-proof light fittings are also generally expensive.

In accordance with this invention there is provided a flame-proof light fitting comprising a single housing for receiving both a light bulb or tube and any required choke or ballast necessary for the activation of such bulb or tube, at least one access opening closable in flame-proof manner by a removable closure member and through which opening both the bulb or tube and choke or ballast can be introduced into the interior of the housing.

Further features of the invention provide for the housing to be of a basically tubular construction for receiving a fluorescent light tube therein, and whereof an enlarged region at one end, adjacent the access aperture, is provided for receiving an associated choke or ballast, for the housing to be manufactured in two parts which are substantially mirror images of each other and are permanently secured together along a line of join which is conveniently in a plane of symmetry; for the housing or parts thereof to be manufactured from moulded plastics material, in particular shock resistant plastics material such as suitable polycarbonates or the like; for the housing to be provided with means whereby it may be suspended from an anchorage point or the like, and for the access opening to be cosed by means of a plug which may be in screw-threaded engagement with complementary screw-threads on the housing or which may be simply slid into a plain socket formation and locked therein and through which supply conductors are passed in sealing engage mentwiththe material of the plug.

It is preferred that the housing be divided into a small chamber at a blind end of a tubular body. In such a case, the wall defining such chamber can support a first electrical contact or pair of contacts for a fluorescent light tube. The housing can be provided with a passage extending from said chamber to an enlarged zone for accomodating the choke so that a flexible electrical conductor extending from the contacts to the choke or ballast can be introduced and removed as required.The choke or ballast is preferably supported out of contact with the fluoresecent light tube and, to achieve this, the choke or ballast is held apart from the tube by means of a flange or the like on the choke or ballast and whereby the innermost end is supported by a cooperating flange or formation on the housing and at its other end by a removable contact holder for the operatively outer end of the fluoresencent light tube.

In order to ensure that a plug closing off the access aperture to the interior of the housing remains in proper engagement with the aperture, a suitable circlip is preferably employed which means that removal of the plug must be accompanied by the positive action of removing the circlip which is generally somewhat inconvenient. Also, the conductors passing through the plug in sealing engagement therewith preferably define, at their outwardly projecting ends, electrical contact pins for connection to a co-operating socket arrangement.

There are clearly a variety of different socket or other contact arrangements which can be utilised to co-operate with a light fitting as above defined but, in general, it is preferred that a socket or contact assembly as described in our co-pending patent application of even date entitled "Flame-proof electrical contact assembly" be employed. Briefly, an electrical contact assembly of this type has an electrical supply permanently connected to contacts located within a tubular body and wherein an axially movable contact block is provided which has contacts connectable and disconnectable with the fixed contacts by axial movement of the contact block.The contact block has, in turn, sockets for co-operation with the pins of the plug in the electrical fitting and the arrangement is such that these pins can only be engaged with the sockets when the contact block is in a position in which it is out of contact with the fixed contacts. In this manner no electrical supply can be connected to the contact block when the pins are engaged with the sockets therein and only after axial movement of the contact block to connect its contacts with the fixed contacts will electrical current be supplied to the light fitting.

It must be noted that co-operation between the tubular housing and axially movable contact block must be such that the interior, where the fixed contacts are located, is flame-proof with respect to the outside of the contact block. Such a device doubles as a switch since the contacts on the contact block are moved out of contact with the fixed contacts upon axial movement and prior to the position being reached in which the plug on the light fitting can be released from, or engaged with, the sockets in the contact block.

To effect the required axial movement both the outer surfaces of the portion of the plug on the light fitting and the outer surface of the contact block are provided with the same screw-threaded formations co-operating with complementary formations on the inner wall of tubular housing for the contact block.

Thus, they must be joined together before they can be screwed in unison into the housing to make electrical contact with the fixed contacts.

By the same token they must be screwed out in unison which causes disconnection from the fixed contacts prior to the plug being movable to disengage the pins from the sockets in the contact block.

Further detail of this connection arrangement will be obtainable by reference to our said co-pending patent application.

In orderthatthe invention may be more fully understood, one embodiment thereof will now be described, by way of an example, with reference to the accompanying drawings, in which: Figure lisa longitudinal elevation of a light fitting made according to the invention; Figure2 is a cross-section taken along line II to II in Figure 1; and, Figure 3 is a persective illustration of the light fitting.

In this embodiment of the invention a light fitting is intended to house a fluorescent light tube and its associated ballast or choke. To this end the light fitting consists basically of a tubular housing 1 whereof the major portion of the length is of a diameter just suitable for receiving, with a reasonable space between it and the housing itself, a fluorescent light tube of predetermined dimensions.

This portion of the tubular housing is indicated by numeral 2 and has a blind end 3 which is totally closed off.

Towards the opposite end of the housing 1 is an enlarged region thereof which provides on the one side of the tubular housing 1 a space 4 for housing a ballast or choke 5 for the fluorescent light tube which is indicated by numeral 6. The choke or ballast 5 is located, in the operative position, contiguous with the tube 6 on the one side thereof and an access aperture 7 in the adjacent end of the housing is dimensioned so as to be sufficiently large to enable the choke 5 to be passed therethrough.

In order to support the choke 5 in a spaced position relative to the tube 1, a flange 8 thereof at the operatively inner end of the choke 5 co-operates with a flange 9 made integral with the housing 1 to support this inner end in spaced relationship relative to the tube 6. The operatively outer end is supported by means of a contact holder 10 which has the required electrical contacts 11 for the outermost end of the fluorescent light tube 6. This contact holder 10 abuts, at its inner end, a flange or other form of stop 12 formed in the tubular housing 1 and, is urged into engagement with such stop 12, by means of a plug assembly 13 which closes off the access aperture 7.

The plug 13 has an operative end zone 14 cooperating with the aperture 7 and which may have, for convenience, a multi-start square or other suitably shaped coarse thread 15 thereon. The outwardly projecting portion 16 of the plug 13 is solid, has a similar four start coarse thread 17 thereon but is of somewhat smaller diameter than the inner end portion 14.

Thus there is defined a shoulder 18 between the two parts of the plug 13 and this shoulder 18 co-operates, in the closed position, with a circlip 19 located in a circumferential groove 20 on the inner surface of the access aperture 7. In the fully engaged position, this circlip 19 is in its groove 20 and the inner end of the plug is urging the contact holder 10 against the stop 12 in the body.

At least the outermost portion of the plug 13 is of solid construction and has electrical conductors 21 moulded into the material so that they are in sealing engagement with the plug material. The outermost ends of these conductors 21 define connection pins 22 for co-operation with complementary connection sockets for connecting the plug 13 to an electrical supply source.

There is preferably defined, extending between the portion 4 of the housing 1 in which is located the choke or ballast 5, and the end of the housing opposite the access aperture, a passage 23 for one or more electrical conductors from the ballast 5 to a contact 24 which co-operates with pins or the like on the fluorescent light tube 6. The contact 24 is conveniently mounted in an aperture in a transverse wall 25 spaced inwardly from the end wall 3 and thereby defining a chamber 26 for the contact 24 itself.

Conveniently the housing 1 is provided with a pair of integral eyelets 27 one of which is located towards each end of the housing. These eyelets 27 can be employed to anchor the ends of a chain, string, filament or the like whereby the whole light fitting can be suspended from a suitable anchorage point, for example in an underground mine.

The abovedescribed light fitting is, for practical purposes, made by injection moulding two parts which are shaped and adapted to be joined together in a plane passing through the longitudinal access of the housing and centrally through the portion 4 in which the choke 5 is located. Thus the plane of join would be the plane indicated by numeral 28 in Figure 2 and would pass centrally through the eyelets 27.

Thus, it will be understood, that the passage 23 can easily be moulded into the housing 1 since all that is required is a channel in each of the halves thereof before they are secured together.

Initial assembly of the housing 1 can be carried out by locating a choke 5 connected by means of a wire to a contact in a pre-assembled form in one half of the housing prior to the two halves being connected together. The two halves may be connected together by any suitable adhesive, solvent welding, heat welding or other technique but, it is considered to be most advantageous, to employ high frequency welding. In order to ensure that sufficient surface areas is available to achieve proper location and sealing of the two halves to each other, the peripheral regions of each half may be enlarged as indicated by numeral 29 (see Figure 2) and these enlarged surfaces could be provided with ridges and recesses which co-operate in complementary manner to located the two halves properly relative to each other before securing thereof.

It will be understood that the wires connecting the choke 5 with the various contacts at the ends of the fluorescent tube 6 will be sufficiently long to enable the whole assembly to be assembled and disassembled as required and the wires are generally indicated by numeral 30 in Figure 1.

In order to assemble the fitting finally, the tube 6 can be pushed into its contact 24 at the remote end of the housing and the contact holder, which will already have been installed on the end of the tube opposite said remote end, will be substantially in abutment with the stop 12 as indicated above. The plug can then be installed in position and only a few turns will be necessary in order to bring it into its operative position in view of the four start coarse thread. Thus, at worst, the wires leading from the inner ends of the conductors 21 to the ballast or choke 5 will only be twisted five times which will not have any effect on the physical characteristics of the wires.

It will be understood also that the wire 31 leading from the choke or ballast 5 to the contact holder 10 will generally, unless suitable releasable connections are present, be sufficiently long to enable the contact holder 10 to be removed and released from the end of a light tube 6 without affecting the position of the choke or ballast 5 in any way.

Similarly, the electrical wire 32 extending from the choke or ballast 5 to the contact 24 at the closed end of the housing will also be sufficiently long to enable the choke 5 to be removed by way of the access aperture without the conductor breaking.

It will be understood that in order to disassemble the light fitting described above for service or maintenance, the plug can easily be removed after removal of the circlip 19. Thereafter, the housing is located upside-down so that the choke 5 is urged by the influence of gravity away from the tube 6 and the tube 6 can then be removed by pulling it at least partway out, disconnecting the contact holder and removing the tube completely. Any required pulling tools or instruments may be employed for this purpose and they may have to be specially designed.

The housing can then be turned over again so that the choke 5 falls down into the position previously occupied by the tube 6 and can be slid out of the access aperture 7. Should the contact 24 in the remote end of the housing need attention it can be pulled outwardly by means of a special tool and the conductor 23 is, in such a case, preferably attached to another conductor or a string to ensure that its end is not lost during this operation. In this way at least a pull-through filament or conductor is always present in the passage 23 to avoid complicated or difficult threading operations by hand.

The entire housing is preferably made of suitable polycarbonate material which is totally transparent and this provides added advantages in that the choke and connections can be visually inspected from the exterior without dismantling the light fitting.

As indicated above the light fitting is particularly suitable for use in conjunction with flame-proof electrical contact assemblies of the type described in my said co-pending patent application of even data and further description of this aspect will not be contained in this specification.

It will be understood that numerous variations may be made to the above described embodiment of the invention without departing from the scope of the appended claims. For example, the plug for closing the access aperture and co-operating socket region of the aperture, could be plain cylindrical surfaces and any suitable locking means could be provided to retain the plug in position. The selection in this regard will depend on the exact flameproof characteristics required. Also a single fitting could be employed by suitable design, to house more than one tube or without a second aperture being required. In particular, the materials of manufacture, the shape of the light bulb or tube to be received and, accordingly, the access aperture may be varied as required.The invention is not therefore limited in application to fluorescent or neon light tubes but can be employed for other lights provided any required heat dissipation is taken into consideration in the design thereof.

Regarding the manufacture of the housing it may well be preferable to form it in two longitudinal sections as well. This means that the same access end section including the portion for receiving the ballast or choke can be employed for a variety of different lengths of fittings for tubes of different lengths. This will, it is envisaged, decrease overall die costs since only the plain tubular portion having the blind end need be made in different lengths and only relatively inexpensive dies are required for this purpose.

An alternative method of manufacture is to blow mould portions of the whole of the fitting. A still further alternative is to vacuum form parts of the fitting for attachment to each other.

Claims (10)

1. Aflame-proof lightfitting comprising a single housing for receiving both a light bulb or tu be and any required choke or ballast necessary for the activation of such bulb or tube, at least one access opening closable in flame-proof manner by a removable closure member and through which opening both the bulb or tube and choke or ballast can be introduced into the interior of the housing.

2. A light fitting as claimed in claim 1, in which the housing is of a basically tubular construction for receiving a fluorescent light tube therein, and whereof an enlarged region at one end, adjacent the access opening, is provided for receiving an associatd choke or ballast.

3. A light fitting as claimed in claim 1 or claim 2, in which the housing is manufactured in two parts which are substantially mirror images of each other and are permanently secured together along a line of join which is conveniently in a plane of symmetry.

4. A light fitting as claimed in any of claims 1 to 3, in which the housing or parts thereof are manufactured from moulded plastics material.

5. A light fitting as claimed in claim 5, in which the plastics material is a shock resistant material such as a suitable polycarbonate.

6. A light fitting as claimed in any of the preceding claims, in which the housing is provided with means whereby it may be suspended from an anchorage point or the like.

7. A light fitting as claimed in any of the preceding claims, in which the access opening is closed by means of a plug which is in screw-threaded engagemenu with complementary screw threads on the housing and through which supply conductors are passed in sealing engagement with the material of the plug.

8. A light fitting as claimed in any of claims 1 to 6, in which the access opening is closed by means of a plug which may be slid into a plain socket formation and locked therein, and through which supply conductors are passed in sealing engagement with the material of the plug.

9. A light fitting according to any preceding claim, in which the housing is divided into a small chamber at a blind end of a tubular body, the wall defining the chamber supporting a first electrical contact or pair of contacts for a fluorescent light tube, and the housing is provided with a passage extending from the chamber to an enlarged zone for accommodating the choke or ballast, which is supported out of contact with the fluorescent light tube, the arrangement being such that a flexible electrical conductor extending from the contacts to the choke or ballast can be introduced and removed as required.

10. Aflame-proof light fitting substantially as hereinbefore described with reference to, and as illustrated in the accompanying drawings.