Safety Mounted Explosion Proof Light Fixture

Abstract

Light bulbs in a safety-fixture which includes an enclosure of glass or other translucent material, are replaced after removing the fixture from its mounting. As the fixture is mated with the mounting, it moves through a sufficient distance to pass the fixture through three distinct zones; a first zone in which the fixture and mounting form a first explosion-proof enclosure therebetween; a second zone in which non-energized electrical connectors of the mounting and fixture engage; and a third zone in which the non-energized electrical connectors become energized by switch means on the housing, within the first enclosure. Withdrawal of the fixture from the third to the second zone automatically causes the connectors to be de-energized by the switch means. Making and breaking of electrical connection with live contacts only takes place within a second explosion-proof enclosure in the switch means. The danger of arcing during replacement of bulb or fixture is thus virtually eliminated, even though the lighting circuit energizing fixture is, itself, energized.

Description

BACKGROUND OF THE INVENTION

This invention relates to electrical lighting fixtures designed for use in areas classified as hazardous because of the presence of combustible vapor, gas, dust or other ignitable materials. It is often difficult, and indeed dangerous, for a maintenance man to remove a cover, or considerable a bulb while standing on a ladder. Moreover, the replacement of a bulb or a fixture in a hazardous vapor area can be dangerous because of possible formation of an electrical arc during the replacement of the bulb, or fixture. De-energizing an entire circuit, e.g., a bank or lights, in order to replace one bulb or fixture is most undesirable, since the hazardous area may be left with inadequate lighting during the time required to make the replacement. Also, even if an operator de-energizes a lighting circuit to remove a fixture, or bulb, there is a real risk that a well meaning associate would turn the lights on, just as the exposed electrical connection is being made or broken.

SUMMARY OF THE INVENTION

In accordance with this invention the entire electrical fixture is conveniently joined to, or removed from, its mounting. While the fixture is structurally connected to the mounting, an explosion-proof enclosure is formed therebetween. Fixture and mounting, electrical contacts, and a special switch fixed to the mounting reside within this enclosure. The switch makes and breaks enclosed electrical connection between the mounting's fixture electrical contacts and the live electrical contacts (source circuit connectors) which are enclosed within a second explosion-proof enclosure in the switch itself. The mounting's exposed electrical connectors, which in operation, transmit current to the fixture, are automatically de-energized, that is, disengaged from enclosed, internal, live contacts, and thus cannot form an arc (even a confined arc) when the fixture is threaded or otherwise moved into place or removed from the mounting.

Thus, in accordance with this invention there are two sealed enclosures involved when the fixture's contacts first touch the mounting's connectors: First, the sealed enclosure in the mounting switch in which the live contacts reside; and, secondly, a sealed enclosure formed by mating, e.g., threading, of the fixture on to the mounting. In the second enclosure, mounting switch resides, and the mounting switch's external connectors and the fixture contacts touch each other, or separate from each other.

Also, in accordance with the preferred embodiment of this invention the fixture is threaded onto the mounting, and at least five threads on the mounting are engaged before the electrical contact of the fixture meets the external connectors of the mounting switch mechanism. Thus, this initial contact takes place in what is generally accepted as an explosion proof enclosure.

DESIGNATION OF THE FIGURES

FIG. 1 is a partially cross-sectional frontal view of a lighting fixture which is in accordance with this invention.

FIG. 2 is an enlarged cross-sectional view of a preferred switch mechanism which is in accordance with this invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

Although the following disclosure offered for public dissemination in return for the grant of a patent, is detailed to ensure adequacy and aid understanding, this is not intended to prejudice that purpose of a patent which is to cover each new inventive concept therein no matter how others may later disguise it by variations in form or additions or further improvements. The claims at the end hereof are intended as the chief aid toward this purpose; as it is these that meet the requirement of pointing out the parts, improvements, or combinations in which the inventive concepts are found.

In the illustrated embodiment a fixture, generally 10, is threaded into mounting 11. The fixture includes a light bulb 12 situated within glass enclosure 13 and protected by metallic guard unit 14. Glass enclosure 13 and optional metallic guard unit 14 are secured to the fixture housing, generally 15, by means of threaded ring 16. A gas permeable flame barrier such as porous sintered metal cylinder 20 is incorporated into housing 15. Socket 22, electrical connections 23 and other conventional structures within the fixture will not be discussed in greater detail insofar as these are conventional and are not part of the invention.

Fixture base 25 of housing 15 is generally cylindrical and the interior of the mouth of base 25 is provided with threads 26 for receiving face disc 33 and for threading fixture 10 on to mounting 11.

The fixture's electrical contacts 31 and 32 are secured to the fixture by means of threaded face element 33. Set screw 34 prevents rotation of the electrical contacts within the fixture. Again, the details of the connection between the electrical contacts and the bulb will not be discussed insofar as these features are conventional. Contact pin 31 is a fixed pin positioned at the center rotation of threads 26. Electrical contact or collector ring 32 is cylindrical and is positioned with its center at the center of contact pin 31. Naturally, it is insulated from electrical connection with contact 31, and both contacts 31, 32 are insulated from face disc element 33, and the other non-electrical elements of the structure.

Mounting 11 is fixed to conventional conduit equipment suggested schematically by the shown segment of cross-sectioned end of conduit element 38 by means of threads 34 and set screw 39. Thus, with explosion-proof seal at threads 34, space 65 is sealed from the exterior, though it is continuous with the space within the conventional conduit equipment (not shown).

Mounting 11 is provided with a conduit opening 35 through which electrical wires (not shown) are introduced and affixed to switch-outlet, generally 40, by connections in the form of screws 36 and 36' which are threaded into their respective conducting plates 37, 37'.

Internal contact elements 41 and 42 are molded in place in the rear portion 43 of switch-outlet assembly 40. Internal electrical contacts 41 and 42 terminate within switch-outlet assembly 40 in an enclosed chamber 45, 45'. Internal contacts 42 and 41 are positioned approximately in the center of circular grooves 46, 46'. Springs 47 and 47' are positioned in the bottom of grooves 46, 46'. Generally cylindrical electrically conductive piston-shaped external contacts 50 and 50' having a closed external heads 51, 51' with cylindrical skirts which are positioned around but spaced apart from internal electric contacts 41 and 42 and are snugly but movably seated within cylindrical openings or pockets 46 and 46'. Compression spring 52, 52' and inverted cups or contacts 53, 53' are positioned within their respective external contact members 50 and 50'. Each spring 52, 52' is compressed between the closed end of external contacts 51, 51' and cups 53, 53'. Springs 52, 52' and cups 53, 53' are electrically conductive and can convey current as shown in FIG. 1. The movement of cups 53, 53' is limited by fingers 54 and 54'. The cylindrical spaces receiving external contacts 50, 50' in the rear portion 43 are continuous with corresponding openings in the cover portion 44 of the switch-outlet assembly 40. Shoulders 55 and 55' are provided in the cover portion 44 to limit outward movement of the external contact members 50 and 50' and to retain the electrical contact elements within the switch. Cover portion 44 can be secured to rear portion 43 of the switch-outlet assembly 40 by means of a bolt and sleeve arrangement 60.

OPERATION

Fixture 10 is removed from mounting 11 by rotation of the fixture to unscrew the fixture from the mounting. As the fixture rotates the fixture electrical contact pin 31 and electrical contact cylinder 32 rotates about the center of rotation which is at the center of pin 31. Thus as the fixture is being withdrawn from the mounting the fixture's electrical contacts 31 and 32 move away from the switch-outlet assembly 40 fixed within mounting 11. As these electrical contacts move away from the switch-outlet assembly 40, the external electrical contacts 50 and 50' follow the electrical contacts 31 and 32 due to the compressed resiliency of respective springs 47 and 47'. The external electrical contact elements 50 and 50' will continue to follow the fixture's electrical contacts 31 and 32 until these contacts have been withdrawn sufficiently to permit the switch-outlet external contacts 50 and 50' to engage the shoulders 55 and 55' respectively on the cover housing portion 44 of the switch-outlet assembly 40.

It will be appreciated from a consideration of FIG. 2 that prior to withdrawal to that point inverted cups 53 and 53' will be carried out of contact with their respective internal electrical contact elements 41 and 42. Thus the electrical connections between the power source and the fixture, i.e., between the power source and the mounting's fixture connectors, are broken before the fixture's electrical contacts 31 and 32 are separated from the switch-outlet 40.

As will be appreciated from a consideration of FIG. 1, at the point in time at which the rotation of the fixture causes the fixture's electrical contacts 31 and 32 to be disengaged from the switch-outlet external contacts 50 and 50' a considerably number of threads 26 will still be engaged. Thus contact elements 31 and 32 become disengaged from their respective contacts 50 and 50' while the space 65, enclosed by the mounting and fixture, still remains sealed from explosive connection with the atmosphere by a large number of threads 26.

It is preferred that the dimensions and positioning of the fixture and mounting components be such that at least five threads 26 are engaged at the moment at which elements 31 and 32 break or make contact with elements 50 and 50' respectively.

Thus in accordance with this invention all disengagement and engagement of contacting electrical elements (whether or not they are actually directly connected to the electrical power source) takes place within sealed explosion-proof areas.

Continued rotation of the fixture in the unthreading direction permits complete removal of the entire fixture 10 from mounting 11. Thus an identical replacement fixture can be immediately threaded onto mounting 11.

Rotation of the fixture in the tightening direction causes electrical contacts 31 and 32 to move towards the switch-outlet assembly 40. Initially, however, the external electrical contact elements 50 and 50' of the switch-outlet assembly 40 are disengaged from the power source as illustrated in FIG. 2. After a number of threads 26 become engaged, preferably at least 5, continued threading causes contact elements 31 and 32 to push against external connecting elements 50 and 50' and to continue to depress these elements into the switch-outlet assembly 40. Thus contacts 31 and 32 are not electrically connected to live switch contacts 41 and 42 until after initial contact with non-energized surfaces 51, 51'. The fixture becomes connected to the electrical power source when external connecting elements 50 and 50' are depressed sufficiently to cause the conductive cans 53 and 53' to contact their respective internal electrical contacts 41 and 42. The current passes through the conducting cans 53, and directly through external contacting elements 50 and 50', as well as by way of spring 52 and 52', as the rotation of the fixture continues. Continued depression of the external contacting elements 50 and 50' merely results in greater compression of override springs 52 and 52' within their respective elements, and greater compression of springs 47 and 47' within their respective circular grooves 46 and 46'.

Thus it will be appreciated that in accordance with this invention the mounting means 11 has a sufficient number of threads 26 to provide a sequence of three distinct zones through which the threaded end of the fixture 10 can be moved. Fixture 10 and the mounting means 11 forms a first sealed enclosure 65 after the fixture is first threaded onto the mounting means, i.e., while it is being threaded through the first of these zones. The electrical contact elements 31, 32 of the fixture, and the mounting means 51, 51' are spaced apart while the fixture is in the first zone. The invention also includes means for mating the corresponding electrical contact elements 51, 51' of the mounting means and contact elements 31, 32 of the fixture while the fixture is being threaded through the second of said zone. The electrical contact elements are non-energized while the end of the fixture is in the second zone. The invention includes switch means 40 for energizing electrical contact elements 51, 51' when the fixture is threaded into the third zone and switch means 40 for de-energizing the electrical contact elements when the fixture is threaded from the third into the second zone. Switch 40 includes a second sealed enclosure 45 in which the electrical circuit is opened or closed as the contacts 51, 51' are energized or de-energized.

In accordance with this invention external contacting elements 50 and 50' seat snugly but movably within the spaces 45 and 45' and circular grooves 46 and 46'. Thus should an arc occur upon contact of cans 53 and 53' with their respective internal contacts 41 and 42, and should the gas trapped within spaces 45 or 45' be an explosive mixture, the pressure within the space 45 or 45' would cause the walls of the cylinders 50 and 50' to bear tightly against the outside walls of circular groove 46 and 46'. Also the space between the circular electrical contacts 50 and 50' which is snugly fitted into cylindrical openings 46 and 46' provides an extremely narrow path for gases escaping from within the chamber 45 and 45'. Thus the gases would have to move upwardly as illustrated in FIG. 2 along the inside wall of elements 50 or 50' and then downwardly along the outside wall of that element for a long tortuous path before escape of these gases to the region outside of switch-outlet assembly 40 is possible. In the event that any gases should so escape, the gases would be cooled sufficiently to make it virtually impossible for an igniting gas to pass outside of the switch-outlet assembly 40. In the event, however, that this most improbable occurrence should take place the igniting gases would pass into the space 65 which is enclosed within the threaded fixture 10 and fixture mounting 11. Thus should the gas in space 65 become ignited the increased pressure would be dissipated immediately by passage of gas through the explosion-proof porous sintered metal wall 20 which makes it impossible for flame to propagate therethrough to the exterior of the fixture.

Thus in accordance with this invention double insurance is provided to minimize the risk of an arc-induced explosion in a hazardous area during removal or insertion of the fixture on the mounting. The fixture breaks contact with the switch-outlet assembly while all the elements involved are "sealed", i.e., safely enclosed, within space 65. Moreover, when the fixture's electrical contacts engage or disengage from the switch-outlet assembly the fixture and the external contacts 50 and 50' of the switch-outlet assembly 40 are not electrically connected with the power source. The making or breaking of the live electrical contact between the fixture and the power source occurs within the explosion-proof enclosure of switch-outlet assembly 40. Electrical leads and mounting connector screws 36, 36' are virtually inaccessible to foreign objects while the fixture is removed. Maintenance personnel need not attempt complex manipulations while on a ladder, thereby providing added safety.

While the electrical contacts 41, 42 in switch means 40 are referred to as "live" in the above specification, it is understood that conventional elements such as switches or circuit controllers may be positioned ahead of the contacts in the supply circuit.

Claims

I claim:

1. In the combination of a removable lighting fixture, and mounting means for mounting the fixture, said means being adapted for permanent installation, said fixture and said mounting means being adapted to provide a complete barrier to the passing of ignited gas from the interior of said fixture and said mounting means when the fixture is attached to said mounting means, said fixture being attachable to said mounting means by direct threaded engagement therebetween, the improvement comprising: the fixture having a first set of electrical contacts, each of said contacts forming a complete circular path at or centered around the center of rotation of the fixture when the fixture is being threaded into said mounting means, said first set of electrical contacts being positioned within the threads for face-to-face engagement with corresponding contact elements in the mounting; switch means fixed within said mountings, said switch means defining an enclosed space which is sealed with respect to passage of igniting gases therefrom, said switch means including a second set of electrical contacts enclosed within said space, means for directly and continuously connecting each of said second set of contacts to a power source, and a third set of electrical contacts adapted to engage corresponding contact elements of said first and second sets of contacts, said third set being located in said switch means, and being adapted to be inaccessible to said first set of contacts when the fixture is first being threaded into said mounting, said third set being adapted to abut at least a portion of each of the corresponding elements of said first set substantially before the fixture is completely threaded onto the mounting, each of said third set of contacts being movably mounted in said switch means having one portion of said contact externally exposed with respect to said switch, and having a second portion adapted to make and break connection with corresponding contact elements in the second set within said switch; resilient means for urging said third set of electrical contacts to a position spaced apart from each of the corresponding second set of contacts; whereby said first and third set of contacts do not engage until after the fixture is partially threaded onto the mounting, and the making and breaking of connection between first and third set of contacts takes place within a space sealingly enclosed by the fixture and the mounting as a result of the threading of the fixture onto the mounting; whereby the third set of contacts are not connected to the power source while the fixture is separated from the mounting; whereby the continued threading of the fixture onto the mounting causes the third set of contacts to be compressed by said first set of contacts until each of the third set of contacts moves into engagement with corresponding contact elements in the second set of contacts, the last named engagement taking place within the space sealed within the switch means; whereby during removal of the fixture from the mounting means each of said second set of contacts breaks engagement with corresponding members of said third set of contacts within the space inside the sealed switch means, at a point in time before connection is broken between said first set of contacts and said third set of contacts within the space closed by the fixture and the mounting means.

2. In the combination of a mounting member adapted for permanent installation and a lighting fixture member, one of said members having fixed male threads and the other having fixed female threads engaging said male threads when the two are coupled with said threads being positioned about a vertical axis whereby rotation of the fixture member about said vertical axis will release the threaded engagement and disengage the fixture member from the mounting member after a given amount of vertical downward movement of the fixture member with respect to the mounting member starting from the coupled position, said members defining an internal opening which is closed when the members are coupled and open when the members are separated, mating connectors on the two members which provide an electrical circuit between the two when the members are coupled, said mounting member having electrical connections for power supply thereto, and switch means in the mounting member between said electrical connections and the connectors on the mounting member and actuated by an actuator on the fixture member for opening the circuit between the two in response to movement of the fixture member away from the coupled position and before said portion of said given amount of movement is accomplished, the improvement wherein said switch means comprises:

an insulator defining a pocket therein closed at one end and with an opening at the other end, conductor means in the form of a piston in the pocket and movable axially in the pocket, said piston having a skirt only slightly smaller than the cross-section of the pocket and a head at one end of said skirt, said head being at said other end of the pocket, said skirt and the closed end of the pocket defining an enclosed chamber, a spring between the piston and the insulator resiliently urging the piston to a first position adjacent said other end of the pocket, said piston being moved, by said actuator extending into the opening, against said urging to a second position when the members are in the coupled position, and a conductive part extending from the insulator into said enclosed chamber in a position to be contacted by the conductor means when the piston is in the second position and spaced from the conductor means when the piston is in the first position.

3. In the combination of claim 1, wherein said conductive part extends substantially axially within said skirt from the closed end of the pocket, said conductive means includes a contact within the enclosed chamber and movable therein toward and away from the piston head, means in the piston to limit the extent of movement of the contact away from the head of the piston, and a spring between the contact and the piston head and urging the contact away from the piston head.