Abstract:
An industrial lamp fixture employing a high intensity lamp and suitable for use in a hazardous location or atmosphere includes a system for replacing the lamp without having to disassemble the front framework which protects the glass lens and prevents it from breaking or cracking. The fixture includes a shell having a boss extending from the shell along the direction of an elongated lampholder when placed in the operating position. The lampholder is easily removed through the boss, by hand, thereby permitting and facilitating lamp replacement without disassembly of the protective grid or lens. A tongue-in-groove arrangement both aligns the lampholder to insure proper forward orientation of the lamp in use, and fixes the position of the lamp laterally relative to the shell.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of co-pending U.S. Provisional Patent Application No. 61/015,892 filed Dec. 21, 2007, entitled “High Intensity Light Fixture for Use in Hazardous Locations”. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The National Electrical Code (NEC) defines the requirements for the design and construction of electrical devices (e.g., light fixtures) intended for use in “hazardous locations” or “hazardous atmospheres”—terms defined in the NEC. Briefly, hazardous locations or hazardous atmospheres are defined by the conditions or substances present in the area, such as gas or vapor, dust or flyings (e.g., sawdust). 
         [0003]    It is desirable to provide commercial light fixtures which use high intensity (e.g., halogen) light sources because of the greater amount of light they deliver efficiently. However, halogen lamps are known to operate at higher temperatures than, for example, conventional incandescent lamps. Halogen lamps provide much more light per unit of energy and typically have a much longer useful life than conventional light sources. 
         [0004]    Typical light fixtures employing halogen lamps available at retail do not comply with the requirements of Class I, Division 1, Group C for devices operating in hazardous atmospheres. Any light fixture or lighting system which does not comply with the requirements of Class I, Division 1, Group C of the NEC may not be used in hazardous atmospheres. 
         [0005]    In order to comply with the requirements of the NEC for operation in hazardous atmospheres, lighting systems must have an enclosure which meets certain requirements for thermal conductivity and strength—in general, the enclosure must be strong enough to contain an explosion within the device. That is, the walls must be thick enough to withstand the internal strain in the event of an internal (i.e., within the light fixture) explosion. Further, provisions must be made in the event the gas invades the enclosure and ignites within the fixture, that the flame does not escape from the fixture and ignite combustible gases in the ambient atmosphere. Moreover, the lighting system as a whole (that is, not necessarily the light source standing alone) must function at a temperature well below the ignition temperature of the surrounding atmosphere. This requires provisions for efficient transfer of considerable heat to the surrounding atmosphere. 
         [0006]    A lighting system must also provide a means for any burning gases (in the event they should exist within the lamp) to escape from the lamp assembly because they may expand after ignition and thus create a risk of external explosion. However, the gases may be introduced to the ambient atmosphere only after they have been cooled and any possible flames “quenched”. This escape route for exploding gases is typically provided through a “flame path”. One type of qualifying quenching flame path, though not necessarily the only type of flame path, is known as the “ground surface” (i.e., machined surface) flame path. In this type of escape structure, two opposing surfaces (typically metal) are finished or ground and mated in facing configuration. The gap of the flame path must be uniform and within prescribed tolerances; and the length of the flame path and separation of the ground surfaces are also defined to insure flame quenching. This type of flame path permits gases to escape from the enclosure, but only after they have been sufficiently cooled following combustion so that they do not ignite any volatile gases in the surrounding atmosphere. Another type of quenching flame path is known as the threaded joint flame path, and this simply uses a threaded connection which permits expanding gases to escape around threaded shafts and the like to quench flame. In summary, finishing tolerances, length and separation are specified to insure that any burning gases are quenched before they are admitted into the surrounding atmosphere to avoid igniting any combustible gasses in the surrounding atmosphere. 
         [0007]    One difficulty in using halogen lamps as the light source in a light fixture of this type is that some provision must be made for replacing the halogen lamp. In a light fixture designed for use in a hazardous location, many of the design considerations which might facilitate relamping the device, mitigate against the safety requirements for use in hazardous locations. In other words, if one had to dismantle the light fixture entirely, for example, by removing the lens from the lamp assembly in order to replace the lamp, it would be necessary to disassemble the lens from the lamp assembly. Because of the requirements of light fixtures designed for use in hazardous locations, such a design necessarily provides disassembly difficulties and increases the time and requirements for relamping. For example, as will be apparent from the embodiment of the invention disclosed herein, there may be twelve separate bolts which secure the lens to the lamp housing, and these bolts would have to be removed and replaced in accordance with prescribed procedures in order to change the lamp. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a-light fixture for use in hazardous locations or areas and employs a halogen lamp as the light source while facilitating lamp replacement. To facilitate replacement of the halogen lamp in an explosion-proof housing or electrical enclosure, a metal lampholder is mounted to an elongated carrier (thus forming a lamp carrier) which fits longitudinally through an opening of a metal shell forming the housing of the lamp. At one end of the lamp carrier there is an enlarged collar having an annular surface which cooperates with a mating annular ground surface on the housing to form a “ground surface” flame path. 
         [0009]    The lamp carrier is secured to the housing by a threaded lock nut which also secures a bell-shaped metal end cap to the carrier when the lock nut is fastened to the metal housing. This arrangement closes the opening through which the lamp is removed for replacement without interrupting the main flame path of the housing (i.e., surrounding the face of the housing which mounts the lens). 
         [0010]    The lamp carrier assembly is coupled to the housing by a tongue-in-groove structure. This permits the lamp carrier to be inserted or removed readily while preventing the lampholder from rotating when the lock nut is fastened to the housing, thus insuring correct location and orientation of the lamp in the housing while facilitating lamp replacement. 
         [0011]    An electrical insert provides an electrical gland to isolate feed wires from the halogen lamp. The insert is enclosed by the lamp carrier and the metal end cap. Liquid seals are provided between the lamp carrier and the metal shell (i.e., housing), and between the bell-shaped end cap and the electrical insert providing electrical connections to the feed wires. Thus, relamping is accomplished simply by unscrewing the lock nut from the housing and extracting the lamp carrier from the light fixture housing. This completely removes the lamp from the light fixture for replacement while providing a flame path between the lamp carrier and the housing when the new lamp is inserted. The lamp carrier is reconnected to the light fixture housing simply by tightening the lock nut, which may be done by hand. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of a light fixture constructed according to the present invention with the lamp-holder assembly partially removed from the housing, taken from an upper, frontal, left-side perspective; 
           [0013]      FIG. 2  is a perspective view of the light fixture as seen in  FIG. 1  taken from the rear of the light fixture of  FIG. 1 , and from an upper, rear, side perspective; 
           [0014]      FIG. 3  is an upper, front and right side perspective view of the light fixture of  FIGS. 1 and 2  with the components in exploded relation; 
           [0015]      FIG. 4  is a close-up, fragmentary perspective view of the insertion boss showing a tongue or raised member for securing the lampholder; and 
           [0016]      FIG. 5  is a close-up, fragmentary perspective view of the lampholder and threaded lock nut. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]    Turning first to  FIGS. 1 and 2 , reference numeral  10  generally designates a light fixture and electrical enclosure embodying the present invention. The light fixture  10  includes a housing comprising a rear metal shell, generally designated  11  in  FIG. 2 , a front metal cover frame  12  ( FIG. 1 ), and a glass lens  13  ( FIGS. 1 and 3 ) which is shaped to conform to the protective gridwork generally designated  15  ( FIG. 3 ) on the metal cover frame  12 . The glass lens  13  preferably is made of high performance borosilicate glass, which tolerates large thermal fluctuations and sustains substantial impact without breaking or cracking. 
         [0018]    The glass lens  13  has a generally flat flange  16  ( FIG. 3 ) which has a general oblong-round shape extending about the perimeter of the lens, as illustrated, to form a compression seal with a peripheral flange of the shell  11 , as will be further disclosed. The forward surface of the flange  16  of glass lens  13  is received in a recess formed in the rear portion of the border  19  of the metal cover frame  12 , and the flange  16  of the glass lens  13 , preferably lies flush against the corresponding rear surface on the border  19  of the frame  12 . The front surface of the metal cover frame  12  preferably is covered with a synthetic cushioning material such as neoprene, designated  20 , to cushion any inadvertent fall and prevent breakage of the lens  13 . 
         [0019]    Turning now to  FIGS. 2 and 3 , the shell  11 , seen best in  FIG. 2 , has a general dome or bowl shape with a lateral extension greater than the height so that its perimeter forms a corresponding shape to match the flange  16  of the glass lens  13 . The metal shell  11  has a plurality of ribs  21  formed in large curved, raised structures extending from top to bottom across the rear surface of the shell  11 . The ribs  21  add to the strength of the metal shell so that the shell is designed to be capable of resisting internal explosions, in cooperation with the high strength glass lens  13  and the metal cover frame  12 . As will be appreciated from further disclosure, the metal shell  11 , glass lens  13  and cover frame  12  cooperate to form a housing providing an electrical enclosure for the lamp, feed wires and electrical connections. 
         [0020]    Turning now to  FIG. 3 , the forward edge of the shell  11  is formed into a flange  23  conforming to the obround shape of the flange  16  of the glass lens  13 , as well as that of a flat metal ring  18 . The front surface of the flange  23  of the shell  11  has a flat surface  25  which includes a groove  26  which extends circumferentially about the inner portion of the flange  23  and receives a sealing O-ring  27 . The flat surface  25  of the flange  23  of the shell  11  and the opposing rear surface of the metal ring  18  are both ground (or otherwise machined) to conform to the NEC specifications for surfaces forming a “ground joint” flame path in accordance with NEC specifications and requirements. 
         [0021]    Returning now to  FIG. 2 , integrally formed with the dome-like rear portion of the shell  11 , is a cylindrical boss  28  defining a central opening  29  for receiving a lampholder or carrier assembly generally designated  30 , and further described within. The boss  28  has a threaded end  31  for receiving a lock nut  75  which secures the lampholder assembly  30  to the boss  28  of the housing  11 . 
         [0022]    The lampholder  30  may be coupled to the boss  28  of the shell  11  by a tongue-in-groove assembly. The tongue may be on the inner surface of the central opening  29  and the matching groove on the base of the lampholder  30  so that the tongue is placed in the groove when the lampholder is properly oriented and slid longitudinally into the opening  29 . This insures proper orientation of the lamp and permits the lock nut  75  (to be described further below) to be tightened to form the desired flame path without rotating the lamp carrier, as further described below. 
         [0023]    Still referring to  FIG. 2 , in the upper, rear portion of the shell  11 , there are formed a pair of spaced lugs  33  which are provided with internally threaded apertures such as the one designated  34  for receiving screws provided with internally threaded finger grips  35  to secure a mounting bracket  36  (see also  FIG. 1 ) for mounting the light fixture on a tripod or other support structure so that it can be adjusted to a number of different angles or positions, providing flexibility in use. 
         [0024]    In order to provide an explosion-proof electrical enclosure defined by the light fixture, a substantial number of threaded fasteners (see bolts  41  in  FIG. 2 ) are used to secure the shell  11  to the metal cover frame  12 . As many as eight or twelve threaded bores are formed in the rear surface of border  19  of cover frame  12 . Threaded fasteners  41  extend through apertures, such as those shown at  39  in  FIG. 3 , formed in the flange  23  of the metal shell  11  and are received in threaded bores on the rear side of the border  19  of the cover frame  12 , thus forming an explosion-proof electrical enclosure with a flame quenching path between the shell  11  and the cover frame  12  which receives and secures the explosion-proof glass lens  13 . 
         [0025]    With the large number of bolt-type fasteners securing the metal shell to the glass lens  13  and cover frame  12 , it will be seen that it would be time consuming, and require hand tools, to change the halogen lamp within the explosion-proof enclosure. 
         [0026]    Still referring to  FIG. 2 , if desired, a lower metal handle (see  43  in  FIGS. 2 and 3 ), provided with a plastic overmold  44  may be secured to the rear surface of the shell  11  for carrying or adjusting. 
         [0027]    Turning now to  FIGS. 3 and 5 , the lamp-holder assembly  30  is shown with the principal components in exploded relation. The lamp-holder assembly  30  includes a metal bracket  47  with bent end tabs supporting first and second lamp sockets  48 ,  49  for mounting a halogen lamp  50 . 
         [0028]    The metal bracket  47  is secured to a base  57  by means of threaded fasteners or other mounting hardware. A housing  59  formed in the lamp-holder assembly receives an electrical insert  60  ( FIG. 3 ). A bell-shaped end cap  62  is received over the insert  60  and sealed about the outer wall of the insert  60  by means of an O-ring  63 . 
         [0029]    The end cap  62  is provided with an extension  64  in the form of an externally threaded nipple for receiving electrical feed wires which can be connected to the insert  60  ( FIG. 3 ), the lamp-holder assembly also includes wires for coupling the remote end of the insert  60  to the lamp sockets  48 ,  49  in a conventional manner. 
         [0030]    A plastic washer  66  and internally threaded compression nut  67  are placed over the threaded nipple  64 , with the feed wires running through the compression nut  67 . 
         [0031]    A sealing grommet  68  having an external surface  69 , which is frusto-conical in shape (the inner, left side in  FIG. 3  and of the external surface  69  being of a smaller radius) within a correspondingly shaped opening  73  of the nipple  64 . Thus, when the feed wires are fed through the compression nut  67 , washer  66 , sealing grommet  68  and end cap  62 , there is formed a strain-relief coupling for the feed wires. 
         [0032]    The socket  49  is provided with an elongated, axially extending slot  70  which receives a corresponding raised rib or key  72  ( FIG. 4 ) formed on the inner surface  71  ( FIG. 1 ) of the cylindrical, externally threaded boss  28  of the shell  11 . When the lamp-holder assembly  30  is slid into the opening  29  of the boss  28 , the slot  70  on the lamp-holder housing  59  receives and engages the key  72  on the inner surface  71  of the opening  29  and fixes the position of the lamp-holder assembly  30  so that the lamp faces forward (that is, toward the center of the protective gridwork  15 , and prevents rotation of the lamp). The internally threaded lock nut  75  is then placed over the end cap  62  and a circumferential flange  76  of the lock nut  75  engages the rear surface of a correspondingly dimensioned flange  78  (see  FIG. 3 ) of the end cap  62 , forcing the forward opening of the end cap  62  over the O-ring  63  to form a seal with the wires and the electrical insert. The slot  70  is provided with a limit surface  74  which engages the forward end  72 A of the key  72  which locates and fixes the lampholder  30  in an axial direction of the boss  28 . The forward opening of the end cap  62  engages a circumferential surface  81  of the boss  28  of the lamp-holder assembly  30  so that the electrical insert is sealed against water, the O-ring  63  forming a seal between the interior of the end cap  62  and the an outer surface of the electrical insert  60 . This action also secures the lampholder. 
         [0033]    When the lock nut  75  is secured onto the boss  28 , the forward end of the end cap  62  (which comprises a ground surface) cooperates with a corresponding opposing ground surface  82  of the boss  28  of the shell  11 , to form a second flame quenching path, thus permitting the lamp-holder assembly  30  to be safely removed to facilitate lamp replacement, while maintaining the requirements necessary for use in hazardous locations. 
         [0034]    Having thus disclosed in detail an embodiment of the invention, persons skilled in the art will be able to modify the structure illustrated and substitute equivalent elements for those disclosed; and it is, therefore, intended that all such substitutions and equivalents be covered as they are embraced within the scope of the appended claims.