Abstract:
An arc-resistant door and casing design having a frame structure covered by a skin enhancing protection from damage and injury resulting from explosion and internal electrical fault. Thru-the-door breaker operation is provided by a racking mechanism having a threaded shaft operated by a user outside the door. An air cooling system for an arc-resistant switchgear cubicle having at least one insulated ventilation shaft longitudinally at a side of the cubicle whereby cooling air is drawn into the shaft from an inlet at a top end of the shaft and enters into the cubicle through an outlet of the shaft provided at a bottom area of the cubicle by convection. The cooling air mixes with warm air inside the cubicle and hot exhaust air flows upward to exit through at least one blow vent at a top area of the cubicle.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to an arc-resistant switchgear door and frame assembly and a “through-the-door” racking system, and an air cooling and ventilation system for an arc-resistant switchgear cubicle. 
       BACKGROUND OF THE INVENTION 
       [0002]    Recent safety standards mandate additional personal safety measures be taken to protect workers and prevent injury that may be caused by electrical faults in medium voltage electrical cabinets. An internal electrical fault in a switchgear cabinet generates a large quantity of hot gas and vaporized material, some of which is toxic and harmful to workers that may be in or around the cabinet. The electrical fault acts much like an explosion and the heat intensity at the centre of the arc can be over 10,000 degrees Fahrenheit. Such explosions in standard electrical equipment cause a lot of damage to the cabinet, including flying parts or superheated particles, and the emission of hot gases is harmful to workers. 
         [0003]    Known art door securing mechanisms use first and second tabs which are longitudinally positioned at the sides of the frame and door, respectively. The first and second tabs can be vertically translated into an overlapping arrangement when the door is swung on its hinges into a secure position. While the overlapping tabs provide some resistance to the door being blown off the frame as a result of the force caused by explosive gases produced by an arcing fault, the tabs do not “lock” with each other. The tabs are merely aligned in an overlapping arrangement and are susceptible to bending in the same direction when a sufficient force is applied to the door. 
         [0004]    Another door securing mechanism uses a pin and hole arrangement. A pin is positioned at the edge of a door and can be fitted into a hole in a plate provided in a door casing to lock the door when closed. However, such a securing mechanism is disadvantageous as the pin is subjected to shearing forces when a corresponding force is applied to the face of the door in the event of an electrical fault. 
         [0005]    Therefore, there is a need to provide means to contain the electrical fault safely and to redirect its force such that it will not harm an operator and also to minimize the resulting damage. 
         [0006]    There is also a need to enable a user to operate breakers through a door to an electrical cabinet without having to open the door or expose the user to a harmful electrical fault explosion. 
         [0007]    A majority of existing switch gear cubicles require that the main breaker which connects and disconnects to the main high voltage bus be installed with the cubicle door open thereby exposing an operator to a higher risk of injury due to an inadvertent arcing event. Thus, a “through-the-door” racking system enables the connection and disconnection procedure to be completed with the cubicle door closed thereby enhancing protection of the operator. The “through-the-door” racking system also provides a tilting feature that enables connection and disconnection of a rack end of a racking shaft to a breaker. When the racking shaft is connected to a breaker, the breaker can be pushed or pulled in or out of position. 
         [0008]    Such a “through-the-door” racking system can either be incorporated in a door to a switch gear cabinet, such as the door enhanced securing mechanism described above, or can be a retrofit racking system installed in an existing door enabling breakers to be modified to allow for the connection or disconnection procedure to be completed with the cubicle door closed. 
         [0009]    Furthermore, for safety purposes, arc-resistant switchgear cubicles require that, under a fault condition, hot gases are prevented from being emitted from the cubicle. The most reliable method to ensure that this condition is met is to not have any air vents in the various access doors and panels to the cubicle. 
         [0010]    As the electrical equipment in the cubicle generates heat, the need for cooling an arc-resistant switchgear cubicle has always resulted in a conflict with the structural design process. In the past, manufacturers have resolved this problem by designing collapsible air vents or incorporating elaborate shrouds which permit cooling of a cubicle; however prohibit venting of hot and harmful gases. However, the applicant has appreciated that the prior art constructions introduce a weak point in the art-resistant capabilities of the cubicle. As a result, the prior art constructions result in more elaborate contraptions which require mechanical moving parts. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention provides an arc resistant door which shuts into a door casing at an access opening to an electrical cabinet. The door comprises a reinforced structure including an internal frame and a skin. The frame and skin design provides a reinforced door which is capable of withstanding a great amount of force without using an excessive amount of material. To protect the hinge side of the door from the force of an explosion and flying material, an overlapping angle can be provided on the door casing and wrapped around part of a hinge side of the casing. In addition, unique hook style “gang” operated latches hook themselves into reinforcing pins at a latch side of the casing to add additional strength to the frame and resist bending of the door and/or frame in the event of an explosion. By providing the unique frame on skin design, forces are transferred to the frame rather than the steel skin which is not as strong. Because of the reinforcing features mentioned herein, the expulsion of hot gasses is limited by maintaining a sealed front compartment. 
         [0012]    The present invention also provides a racking mechanism to accommodate operation of various breakers without opening the equipment access door. The racking mechanism can be retrofitted to an existing access door. In one aspect, the racking mechanism uses a door mounted screw that interfaces with the breaker inside the cubicle. Such a mechanism allows a circuit breaker to be changeably withdrawn or connected to a live bus while maintaining the Arc-resistant barrier intact. The user is safely protected by the door from any flying parts, hot gases and harmful vapours caused by an explosion. 
         [0013]    The present invention also provides an arc-resistant switchgear cubicle which provides for cooling of the cubicle while maintaining the structural integrity of the cubicle to better protect users against harm during a fault condition in the switchgear cubicle. The applicant has appreciated that the introduction of insulated vents, provided at least at one side of the cubicle, advantageously provides incoming air which is cooler than the exhaust air due to the insulation of the vent. Also, by introducing the cooler air into a lower portion of the cubicle, the cool air will mix with the hot air in the cubicle and the resulting warmer exhaust air can be vented through a top of the cubicle. Thus, the cooling air flow is created by a convection flow of air through the cubicle. 
         [0014]    Furthermore, each section of the cubicle can be isolated from another section and multiple air cool vents can be introduced for each section. Each of the intake vents can be separated from another intake vent to maintain a maximum flow rate within each section of the cubicle. 
         [0015]    The features described herein can be altered as to size and material gauge to accommodate various standard electrical parameters such as voltage class and interrupting rating and current carrying capacity of various breakers and individual specifications. 
         [0016]    The features described herein can be incorporated as new equipment in a new application, and can also be installed with existing equipment in a retrofit application, for example to meet new safety standards. 
         [0017]    It is an object of this invention to provide means to contain an electrical fault safely and to redirect its force to protect an operator and minimize any resulting damage. 
         [0018]    It is a further object of this invention to provide ventilation for an arc-resistant switchgear cubicle, which does not require fans or other means to create air flow, while maintaining the structural integrity of the cubicle to resist failure during an arc fault. 
         [0019]    In one aspect, the present invention resides in a door for sealing an opening to an electrical panel, said door comprising a supporting frame and a door skin connected to a side of the supporting frame, the supporting frame comprising: an elongated hinge side member having a top end and a bottom end, an elongated latch side member having a top end and a bottom end, a top member having a proximal end and a distal end, the top member proximal end being connected to the top end of the hinge side member and the top member distal end being connected to the upper end of the latch side member, and a bottom member having a proximal end and a distal end, the bottom member proximal end being connected to the bottom end of the hinge side member and the bottom member distal end being connected to the bottom end of the latch side member, the door further comprising a latching mechanism to lock the door to a door casing, the latching mechanism comprising at least one latch hook having a latch body and a latch hook end, the latch body being connected to a latching mechanism base at a first side of the latch hook and connected to a linkage member at a second side of the latch hook at a position on the latch body spaced laterally from the attachment to the latching mechanism base so that movement of the linkage member in an upward or downward direction causing the latch hook to pivot through a plane parallel to a to engage or disengage a pin provided in a channel of a door frame, the latching mechanism base being mounted to the door at or near the hinge side member with at least one mounting latch plate and a fastener, and the door further comprising a door handle having a handle lever and a post orthogonally connected thereto, the door handle being mounted on the door skin with the elongated post passing through an aperture in the door skin and an aperture in the latching mechanism base, the post mating with a hole in a post plate which is connected to the linkage member at a position above or below a position of an attachment of the latch hook to the linkage member, such that turning the door handle lever moves the linkage member to selectively engage or disengage the at least one latch hook on a respective at least one pin of a door case. 
         [0020]    In another aspect, the present invention resides in a racking mechanism mountable to a door comprising: a threaded shaft having a racking end and a user end, and a mounting plate, the mounting plate having an aperture with a threaded hub positioned there through, the threaded shaft being movable through the hub to extend the racking end closer and further from the mounting plate. 
         [0021]    In another aspect, the present invention resides in a racking mechanism mountable to a door comprising: a threaded shaft having a racking end and a user end, the racking end having a socket adapter connected thereto and the user end having a socket adapted to connect with a wrench; a first mounting plate having at least one mounting hole and a second mounting plate having at least one mounting hole, the first and second mounting plates being hingedly connected; a hollow cylindrical hub support is fixed to the first mounting plate and a hub hole is formed through the first mounting plate so that the hub support is accessible at both ends and provides a hollow cylindrical channel; and a cylindrical hub having a threaded core is threadably movable on the threaded shaft and the hub is securable within the hollow cylindrical channel of the hub support. 
         [0022]    In a further aspect, the present invention resides in a door for sealing an opening to an electrical panel, said door comprising a supporting frame and a door skin connected to a side of the supporting frame, the supporting frame comprising: an elongated hinge side member having a top end and a bottom end, an elongated latch side member having a top end and a bottom end, a top member having a proximal end and a distal end, the top member proximal end being connected to the top end of the hinge side member and the top member distal end being connected to the upper end of the latch side member, and a bottom member having a proximal end and a distal end, the bottom member proximal end being connected to the bottom end of the hinge side member and the bottom member distal end being connected to the bottom end of the latch side member, the door further comprising a latching mechanism to lock the door to a door casing, the latching mechanism comprising at least one latch hook having a latch body and a latch hook end, the latch body being connected to a latching mechanism base at a first side of the latch hook and connected to a linkage member at a second side of the latch hook at a position on the latch body spaced laterally from an attachment to the latching mechanism base so that movement of the linkage member in an upward or downward direction causing the latch hook to pivot through a plane parallel to a to engage or disengage a pin provided in a channel of a door frame, the latching mechanism base being mounted to the door at or near the hinge side member with at least one mounting latch plate and a fastener, and the door further comprising a door handle having a handle lever and a post orthogonally connected thereto, the door handle being mounted on the door skin with the elongated post passing through an aperture in the door skin and an aperture in the latching mechanism base, the post mating with a hole in a post plate which is connected to the linkage member at a position above or below a position of an attachment of the latch hook to the linkage member, such that turning the door handle lever moves the linkage member to selectively engage or disengage the at least one latch hook on a respective at least one pin of the door case, the door further having a threaded aperture through which a racking mechanism is positioned, the racking mechanism comprising a threaded shaft having a racking end and a user end, the racking end having a socket adapter connected thereto. 
         [0023]    In a further aspect, the present invention resides in an air cooling system for an arc-resistant switchgear cubicle, wherein: at least one insulated ventilation shaft is positioned longitudinally at a side of the cubicle, the at least one insulated ventilation shaft having an inlet at an upper end and an outlet at a lower end; at least one blow vent is provided at a top of the cubicle; and whereby cold air is drawn into the cubicle through the inlet of the at least one insulated ventilation shaft and enters the cubicle through the outlet, and warm air is exhausted from the cubicle through the at least one blow vent, the flow of air being generated by convection current. 
         [0024]    In yet a further aspect, the present invention resides in an air cooling system for an arc-resistant switchgear cubicle having three sections formed by vertically disposed walls within the cubicle, wherein: each section has two insulated ventilation shafts, each shaft being positioned longitudinally at each side wall of the section, each insulated ventilation shaft having an inlet at an upper end and an outlet at a lower end; one blow vent is provided at a top surface of the section; and whereby cold air is drawn into each cubicle section through the inlets of the insulated ventilation shafts and enters the cubicle section through the outlets, and warm air is exhausted from each cubicle section through the blow vent, the flow of air being generated by convection current. 
         [0025]    Further and other features of the invention will be apparent to those skilled in the art from the following detailed description of the embodiments thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    Reference may now be had to the following detailed description taken together with the accompanying drawings in which: 
           [0027]      FIG. 1  shows a door and frame design of the present invention; 
           [0028]      FIG. 2  shows the door shown in  FIG. 1 ; 
           [0029]      FIG. 3  shows the frame shown in  FIG. 1 ; 
           [0030]      FIG. 4  shows the latching mechanism of the present invention; 
           [0031]      FIG. 5  shows an exploded view of the latching mechanism shown in  FIG. 4 ; 
           [0032]      FIG. 6  shows a latch hook of the latching mechanism of the present invention; 
           [0033]      FIG. 7  shows a racking mechanism of the present invention; 
           [0034]      FIG. 8  shows a racking mechanism mounting plate with a hinge in perspective view; 
           [0035]      FIG. 9  shows the racking mechanism mounting plate of  FIG. 8  from a top view; 
           [0036]      FIG. 10  shows a racking mechanism including a threaded shaft and mounting plate in exploded view; 
           [0037]      FIG. 11  shows the racking mechanism of  FIG. 10  with the threaded shaft fitted with the mounting plate shown in perspective from a back side of the mounting plate; and 
           [0038]      FIG. 12  shows a racking mechanism of  FIG. 11  in perspective view from a front side of the mounting plate. 
           [0039]      FIG. 13  shows an arc-resistant cubicle in perspective view; 
           [0040]      FIG. 14  shows the arc-resistant cubicle of  FIG. 13  from a front view; and 
           [0041]      FIG. 15  shows the arc-resistant cubicle of  FIG. 13  from a top view section through line A-A. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0042]    As shown in the preferred construction in  FIG. 1 , a door  2  is connected to a door case  4  by hinges  6 . The door case  4  is suitable for positioning at an entrance to an electrical panel or circuit breaker cabinet, not shown. The door  2  is movable between open and closed positions, the closed position being shown in  FIG. 1 . When in the closed position, the door  2  seals the entrance to the electrical panel from the area surrounding the entrance from any gas or vapour exiting therefrom. 
         [0043]    The door  2  has an internal door frame comprised of an elongated tubular metal hinge side member  8  having a top end  10  and a bottom end  12  for vertical positioning at a hinge side of the door  2 . A similar elongated tubular metal latch side member  14  has a top end  16  and a bottom end  18  for vertical positioning at a latch side of the door  2 . 
         [0044]    A tubular elongated metal top member  20  having a proximal end  22  and a distal end  24 . The top member  20  is positioned horizontally along a top of the door  2  with the top member proximal end  22  welded to the top end  10  of the hinge side member  8 , and the top member distal end  24  welded to the top end  16  of the latch side member  14 . A tubular elongated metal bottom member  26  has a proximal end  28  and a distal end  30  and is positioned horizontally along the bottom of the door  2 . The bottom member proximal end  28  is welded to the bottom end  12  of the hinge side member  8 , and the bottom member distal end  30  is welded to the bottom end  18  of the latch side member  14 . 
         [0045]    While the connections of the ends metal hinge side member  8 , latch side member  14 , top member  20  and bottom member  26  are preferably formed with mitre cuts and are connected by weld joints, it is appreciated that other suitable means of connecting these members would also be suitable, for example corner brackets. Also, the metal hinge side member  8 , latch side member  14 , top member  20  and bottom member  26  are preferably made of steel. 
         [0046]    A door skin  32  forming a covering is connected at an outer side of the hinge side member  8 , latch side member  14 , top member  20  and bottom member  26  to provide a covering for the door  2 . The door skin  32  is shown more clearly on the door  2  in  FIG. 2 . Preferably, the door skin  32  is a metal sheet or plate and is made of steel. 
         [0047]    The dimensions of the door  2  depend on the size of the arc-resistant switchgear cabinet which varies depending on the voltage and current rating. In a conventional embodiment, the door  2  has a width between 29 to 48 inches and a height between 40 and 90 inches. 
         [0048]    As shown in  FIG. 1 , the door  2  is hingedly attached to the door case  4  so as to move between open and closed positions. The door case  4  is shown in  FIG. 3  and is comprised of elongated metal channel members which are welded together. An elongated casing top channel  34  is provided at a top of the door case  4 . The casing top channel  34  has a proximal end  34  and a distal end  36 . An elongated casing hinge side channel member  40  extends vertically at a hinge side of the door case  4  and has an upper end  42  and a lower end  44 . Similarly, an elongated casing latch side channel member  46  extends vertically at a latch side of the door case  4  and has an upper end  48  and a lower end  50 . 
         [0049]    The door case  4  is formed by connecting the proximal end  36  of the casing top channel member  34  to the upper end of the casing hinge side channel member  40 . The distal end  38  of the casing top channel member  34  is connected to the upper end  48  of the casing latch side channel member  46 . Preferably, the proximal end  36  and distal end  38  and upper ends  42  and  48  are formed with mitre cuts and weld joints although it is appreciated that other suitable fastening means could be used. 
         [0050]    The door  2  is connected to the door case  4  by three hinges  6 A,  6 B and  6 C which are welded to the casing hinge side channel member at intervals spaced along a vertical length thereof. The hinges  6 A,  6 B and  6 C are also welded to the door hinge side member  8 . 
         [0051]    As shown in  FIG. 3 , three pins  52 A,  52 B and  53 C are positioned horizontally in the casing latch side channel member  46  and spaced at a vertical distance from one another. A latching mechanism  54  is provided on the door  2  and has three latch hooks  56 A,  56 B and  56 C which engage the three pins  52 A,  52 B and  52 C, respectively when the door  2  is locked. 
         [0052]    The latching mechanism is shown in  FIGS. 4 and 5 . The latch hooks  56 A,  56 B and  56 C are mounted on a latching mechanism base  58  which is a rectangular plate which has, at one edge, a strip of the base  58  which is bent orthogonal to a plane of the base  58 . The strip has slots  60 A,  60 B and  60 C through which the respective latch hooks  56 A,  56 B and  56 C are positioned. 
         [0053]    One latch hook  56  is shown in  FIG. 6 . The latch hook  56  is formed from a plate of metal and has a latch body  62  at one end and a latch hook end  64  at an opposite end. The latch body  62  has a latch hook mounting hole  66 , for mounting the latch hook  56  to the base  58 . The latch body  62  also has a link bar mounting hole  68  beside the latch hook mounting hole  66  at a position closer to the latch hook end  64 . 
         [0054]    As shown in the exploded view in  FIG. 5 , Latch hook  56 A is pivotably attached to the latching mechanism base  58  by a latch hook bolt  70  which is passed through a latch hook hole  72  punched or drilled through the base  58 . The latch hook  56 A is positioned with the latch hook end  64  passed through slot  60 A and is pivotably attached to the base  58  by passing the latch hook bolt  72  through the latch hook mounting hole  68  on the latch hook body  62  and screwing a threaded latch hook nut  74  thereon. By the pivotal mounting of the latch hook  56 A on the latching mechanism base  58  and with the latch hook end  64 A positioned through slot  60 A, the latch hook  56 A can pivot through the slot in a direction of arrow  76  shown in  FIG. 4 . The direction of travel of the latch hook  56 A is through a plane orthogonal to a longitudinal axis A-A of pin  52 A. Thus, the latch hook  56 A can selectively engage and disengage pin  52 A. 
         [0055]    Each of latch hooks  56 B and  56 C are pivotally attached to the base  58  as has been described with reference to latch hook  56 A. 
         [0056]    As shown on  FIG. 5 , the latch hooks  56 A,  56 B and  56 C are also connected to a link bar  78 . The link bar  78  is an elongated metal bar having three link bar holes  80 A,  80 B and  80 C drilled there through. The link bar holes  80 A,  80 B and  80 C are drilled at a spacing selected in-line with the link bar mounting holes of the respective latch hooks  56 A,  56 B and  56 C. 
         [0057]    The attachment of the link bar  78  should be done before the attachment of the latch hooks  56 A,  56 B and  56 C are attached to the base  58 . The attachment of the link bar  78  will be described with respect to latch hook  56 A. A link bar bolt  82  is passed through the link bar mounting hole  68  from a side of the latch hook  56 A that will be facing the base  58  when the latching mechanism  54  is assembled. The link bar bolt  82  is then passed through the link bar hole  80 A of the latch body  62  and a threaded link bar nut  84  is fastened thereon. 
         [0058]    As shown in  FIG. 4 , moving the link bar  78  in a direction of a longitudinal axis B-B, the latch hooks  56 A,  56 B and  56 C are moved through the respective slots  60 A,  60 B and  60 C selectively engaging the respective pins  52 A,  52 B and  52 C. 
         [0059]    A door handle  86  is provided to move the link bar  78 . As shown in  FIG. 5 , the door handle has a lever  88 , which can be gripped by a user, and a handle post  90  which is rotated corresponding to a rotation of the lever  88 . The handle post  90  has a square cross-sectional shape. 
         [0060]    As shown in  FIG. 2 , the door handle  86  is mounted to the door skin  32  using three mounting bolts  92  fastened through holes in a handle mounting plate  96 . Three flat washers  94  are placed between the head of the respective mounting bolts  92  and the handle mounting plate  96 . 
         [0061]    When the door handle  86  is mounted on the door skin  32 , the handle post  90  projects through a handle post aperture  98  on the latching mechanism base  58 . The handle post  90  projects through a post hole  100  on a handle post plate  102  at a side of the latching mechanism base  58  opposite to the door skin  32 . The post hole  100  has a square shape corresponding to the square cross-sectional shape of the handle post  90 . Thus, the handle post  90  mates with and engages the post hole  100 , such that rotation of the post  90  causes the handle post plate  102  to rotate. 
         [0062]    The post plate  102  is also connected to the link bar  78  using a link bar bolt  82 P fitted through a link bar hole and a link bar nut  84 P, in a similar manner as the latch hooks  56 A,  56 B and  56 C are fixed, as shown in  FIG. 5 . 
         [0063]    Before mounting the door handle  86 , the latching mechanism base  58  is attached to the door  2  using three door mounting latch plates  104 A,  104 B and  104 C. The door mounting latch plates  104 A,  104 B and  104 C are positioned on a side of the door skin  32  at a side opposite to a side which the latching mechanism base  58  is to be attached. Three sets of mounting latch plate bolts  106 A,  106 B and  106 C, each having lock washers  108 A,  108 B and  108 C thereon, are positioned through three respective pairs of mounting apertures  112 A,  112 B and  112 C on the latching mechanism base  58 . The latching mechanism base  58  is positioned at the door skin  32  and holes, not shown, are drilled through the door skin  32 , at locations corresponding to the mounting apertures  112 A,  112 B and  112 C. The three sets of mounting latch plate bolts  106 A,  106 B and  106 C are positioned through the holes in the door skin  32  and through corresponding pairs of mounting latch plate holes  114 A,  114 B and  114 C in the three door mounting latch plates  104 A,  104 B and  104 C, which are positioned at the opposite side of the door skin  32 . Three sets of threaded mounting latch plate nuts  110 A,  110 B and  110 C are screwed onto the respective mounting latch plate bolts  106 A,  106 B and  106 C, to secure the latching mechanism to the inside of the latch edge of the door  2 . 
         [0064]    Thus, when a user turns the door handle lever  88 , the door handle post  90  rotates to, in turn, rotate the handle post plate  102  to move the link bar  78  up or down through axis B-B. This movement of the link bar  78  causes each of the latch hooks  56 A,  56 B and  56 C to rotate to selectively engage or disengage the respective pins  52 A,  52 B and  52 C. Thus the door  2  can be locked, where the latch hooks  56 A,  56 B and  56 C engage or hook around the respective pins  52 A,  52 B and  52 C, and unlocked, where the latch hooks  56 A,  56 B and  56 C disengage or are unhooked from the respective pins  52 A,  52 B and  52 C. 
         [0065]    As shown on  FIG. 2 , the door handle lever  88  has a lever locking tab  116  with an aperture there through. A corresponding mounting plate locking tab  118  is provided on the mounting plate, so that, when the door handle lever  88  is perpendicular, and the latch hooks  56 A,  56 B and  56 C are engaged with corresponding Pins  52 A,  52 B and  52 C, the apertures of the respective tabs  116  and  118  are aligned. The alignment of the apertures of the tabs  116  and  118 , enables a lock, not shown, can be placed through the apertures to secure the door  2  from access unless the lock is removed. 
         [0066]    As shown in  FIG. 1 , to enhance the structural integrity of the door  2 , cross brace bars  120 A,  120 B and  120 C are welded horizontally between the door hinge side member  8  and the door latch side member  14 . The cross brace bars  120 A,  120 B and  120 C are spaced from each other at longitudinal intervals of the door hinge side member  8  and the door latch side member  14  to provide additional strength to the frame of the door  2 . 
         [0067]    Also shown in  FIG. 1 , an overlapping angle  122  is wrapped around the casing hinge side channel member  40 . The overlapping angle is preferably steel to create an overlap with the casing hinge side channel member  40  to provide additional structural strength to the hinge side of the door casing  4 . 
         [0068]    As shown in  FIG. 2 , the door skin  32  has a generally square aperture  150 . The aperture  150  can be covered with a Plexiglas sheet  152  so that the inside of a cabinet can be visible by a user from the outside, but a seal can be maintained at the door  2 . The Plexiglas sheet  152  is mounted to the door skin  32  using an upper window clamp  154  and a lower window clamp  156 . The upper and lower window clamps  154  and  156  are formed by bending sheet metal steel plates to have a z-shaped profile. By fastening the upper and lower window clamps  154  and  156 , respectively, to an inside of the door skin  32  horizontally at an upper and lower edge of the aperture  150 , the Plexiglas sheet  152  can be slidably inserted between the upper and lower window clamps  154  and  156 , respectively, to cover the aperture  150 . 
         [0069]    Shown in  FIG. 7  is a screw raking mechanism  200 . The screw racking mechanism  200  has a threaded shaft  202  screwed through a hub  204  having corresponding threads. The threaded end  202  has a racking end  206  with a socket adapter  208 , preferably one-half inch, fixed thereto. The socket adapter  208  can be fitted with ratchet sockets of various sizes, not shown, to activate and deactivate various types of breakers. 
         [0070]    The diameter and length of the threaded shaft  202  varies depending on the size and weight of the breaker, which can be between 300 and 4000 lbs. The diameter of the threaded shaft can range from 2 inches to 3 inches in a conventional embodiment. In a conventional embodiment, the length of the threaded shaft  202  is equal to the distance between the switchgear door to the breaker plus 12 inches. In a typical embodiment, the distance between the door and breaker is between 7 inches and 20 inches. 
         [0071]    The hub  204  is fixed at an aperture through a racking mechanism mounting plate  210 . At an opposite side of the mounting plate  210 , a hollow cylindrical hub support  212  is provided such that the threaded shaft  202  is screwed through the hub  204 , and the hub is fitted in the hub support  212 , so that the threaded shaft  202  extends through both sides of the plate  210 . 
         [0072]    The racking mechanism mounting plate  210  can be fixed to the door  2 , although not shown, to provide “thru-the-door” racking so that a user can operate various breakers from outside an electrical cabinet. In a more preferred form, the threaded racking bar  202  can be screwed through a threaded hole in the door  2  as a more simplified construction. 
         [0073]      FIG. 8  shows a racking mechanism mounting plate  210  which comprises a first plate portion  214  and a second plate portion  216  connected by a hinge  218 . The hinge  218  enables manipulation of the first plate portion  214  with respect to the second plate portion  216  to adjust an angle of axis A-A extending through a centre axis of the hub support  212 . 
         [0074]    The mounting plate  210  can be fixed to a door of an electrical cabinet using fastening means, for example screws or bolts (not shown), which are positioned through the first and second pairs of mounting holes  220  and  222 , on the respective first and second mounting plates  214  and  216 . To enable the tilting of the first mounting plate  214  by the hinge  218 , the fasteners used to fix the first mounting plate  214  to the door through mounting holes  220  can be loosened. Preferably, wing nuts are fastened on bolts positioned through the first pair of mounting holes  220  so that a user can selectively loosen and tighten the first mounting plate  214 . By loosening the fasteners securing the first mounting plate  214 , the first mounting plate  214  and therefore hub  204  and threaded shaft  202  can be selectively tilted from a substantially horizontal plane towards a vertical plane. While the required degree of tilting of the threaded shaft  202  to selectively connect and disconnect a breaker varies depending on the size of breaker and distance from the door to the breaker. In a conventional embodiment, the degree of tilting is preferably  15  degrees at a minimum. 
         [0075]      FIG. 9  shows the mounting plate of  FIG. 8  in top view. As shown in both of  FIGS. 8 and 9 , the hub support  212  is provided with two hub positioning nuts  224  fixed to the sides of the hub support  212 . As shown in  FIG. 8 , two hub support holes  226  are formed at the same location as the hub mounting nuts  224 . As shown in  FIG. 9 , a hub hole  213  is formed on the first plate portion  214  so that the hollow cylindrical hub support  212  is accessible at both ends thereof. 
         [0076]    As can be seen in the exploded view in  FIG. 10 , two hub mounting screws  228  can be threadably secured in the respective hub mounting nuts  224  to be positioned within respective hub holes  230  formed on the sides of the hub  204 , to thereby secure the hub  204  within the hub support  212 . 
         [0077]    As can be envisaged from  FIG. 10 , to assemble the screw racking mechanism  200 , the hub  204  is threaded onto the threaded shaft  202  and the cylindrical hub  204  is positioned within the cylindrical channel of the hub support  212 . Hub mounting screws  228  are screwed into hub mounting nuts  224  to engage within hub holes  230  of the hub  204 . 
         [0078]    The threaded shaft  202  can then be threadably moved within the hub  204  by a user, for example using a wrench or a speed wrench (not shown) which is inserted into a socket  232  at a user end  234  of the threaded shaft  202 . 
         [0079]      FIG. 11  shows the screw racking mechanism  200  in perspective view from a back side of the racking mechanism mounting plate  210 . As shown in  FIG. 11 , the racking end  206  has a custom socket  236  fitted thereto. 
         [0080]      FIG. 12  shows the screw racking mechanism  200  assembled and in perspective view. 
         [0081]      FIG. 13  shows an arc-resistant switchgear cubicle  302  which houses electrical equipment (not shown). The arc-resistant switchgear cubicle  302  has a planar top surface  304 , a planar side surface  306  and a planar front surface  308 . A second planar side surface, a planar bottom surface and a planar back surface are not shown, but exist to provide an enclosed cubicle. 
         [0082]    As shown, the front surface  308  has three access doors  310 A,  310 B and  310 C which can be opened to access the interior of the arc-resistant switchgear cubicle. The doors  310 A,  310 B and  310 C can be designed as the aforementioned door  2  and all of its features and locking assembly, in a preferred embodiment. 
         [0083]    Also shown are three insulated ventilation shafts  312 A,  312 B and  312 C. The insulated ventilation shafts  312 A,  312 B and  312 C are preferably insulated with a rigid insulation such as dense styrofoam insulation panels adhered to an outside surface of the ventilation shafts using adhesive or other suitable mechanical fasteners. The three insulated ventilation shafts  312 A,  312 B and  312 C have respective inlets  314 A,  314 B and  314 C, and respective outlets  316 A,  316 B and  316 C. The inlets  314 A,  314 B and  314 C are provided at a top of the insulated ventilation shafts  312 A,  312 B and  312 C, and are shown as being positioned at the top surface  304  of the arc-resistant switchgear cubicle  302 . The outlets  316 A,  316 B and  316 C are provided at a lower end of the insulated ventilation shafts  312 A,  312 B and  312 C, as shown. 
         [0084]    To cool the arc-resistant switchgear cubicle  302 , cooling air is drawn in through the inlets  314 A,  314 B and  314 C, flows through the insulated ventilation shafts  312 A,  312 B and  312 C, as indicated by arrows  318 A,  318 B and  318 C, and then enters the arc-resistant switchgear cubicle  2  through the outlets  316 A,  316 B and  316 C. Because the ventilation shafts  312 A,  312 B and  312 C are insulated, the cooling air remains cool while being drawn through the insulated ventilation shafts  312 A,  312 B and  312 C. 
         [0085]    After entering the arc-resistant switchgear cubicle  302 , the cooling air mixes with the hot air inside the arc-resistant switchgear cubicle  302  to provide cool air to the arc-resistant switchgear cubicle  302 . Hot air is generated by the electrical parts (not shown). The mixing of cooling air generates warm exhaust air flows upwards through the arc-resistant switchgear cubicle  302 , to exit the arc-resistant switchgear cubicle  302  via respective blow vents  320 A,  320 B and  320 C positioned at the top surface  304  of the arc-resistant switchgear cubicle  302 . 
         [0086]    The cooling air flow is established by convection currents and therefore there is no requirement for a fan or other means to direct the air flow. Because the cooling air enters into the insulated ventilation shafts  312 A,  312 B and  312 C to be introduced into the interior of the arc-resistant switchgear cubicle  302 , at a bottom thereof, the mixing of the cooling air with warm air inside the arc-resistant switchgear cubicle  302 , generates warmer air which, by its nature, flows upwards to exit the arc-resistant switchgear cubicle  302  through blow vents  320 A,  320 B and  320 C. 
         [0087]      FIG. 14  shows the arc-resistant cubicle  302  of  FIG. 13  however an additional insulated ventilation shaft  312 ′A is shown as longitudinally extending along a side of the cubicle  302  opposite the surface  306 . Thus, two insulated ventilation shafts  312 A and  312 ′A are provided with inlets  314 A and  314 ′A and outlets  316 A and  316 ′A, respectively. Each of the insulated ventilation shafts  312 A and  312 ′A has insulation  322 A and  322 ′A provided longitudinally along each of the insulated ventilation shafts  312 A and  312 A, as shown. 
         [0088]      FIG. 14  illustrates the flow of cooling air into and through the cubicle  302 . As shown by the arrows, the cooling air enters the ventilation shafts  312 A and  312 ′A through inlets  314 A and  314 ′A, respectively. The cooling air travels downwardly through the insulated ventilation shafts  312 A and  312 ′A and enters into the cubicle  302  through the outlets  316 A and  316 ′A. The cooling air then mixes with the warm air in the cubicle  302  in the mixing zone generally indicated as  324 . The mixed cooling air with the warm air inside the cubicle  302  generates warmer exhaust air which travels upwardly through the interior of the cubicle  302  and exits from the top of the cubicle  302  through the blow vent  320 A. 
         [0089]    The flow of air is established by the convection current created by the rising warmer air which in turn draws the cooler cooling air into the cubicle  302 . 
         [0090]      FIG. 15  is a sectional view of the cubicle  302  through section A-A shown in  FIG. 14 . As shown in  FIG. 15 , three compartments are provided within the cubicle  302 , being a first compartment  326 , a second compartment  328  and a third compartment  330 . Each of the compartments  326 ,  328  and  330  is separated from the adjacent compartment so as to form segregated independent sections. As shown, the insulated ventilation ducts  312 A and  312 ′A are provided to cool the first compartment section  26 , insulated ventilation ducts  312 B and  312 ′B are provided to cool the second compartment section  328  and insulated ventilation ducts  312 C and  312 ′C are provided to cool the third compartment section  330 . 
         [0091]    Although this disclosure has described and illustrated certain preferred embodiments of the invention, it is also to be understood that the invention is not restricted to these particular embodiments rather, the invention includes all embodiments which are functional, or mechanical equivalents of the specific embodiments and features that have been described and illustrated herein. 
         [0092]    It will be understood that, although various features of the invention have been described with respect to one or another of the embodiments of the invention, the various features and embodiments of the invention may be combined or used in conjunction with other features and embodiments of the invention as described and illustrated herein.