Abstract:
An apparatus for defeating an interlock for an electrical cabinet permits a technician qualified to service the equipment within the cabinet to defeat the interlock and open the cabinet while current is flowing through the equipment therein, while permitting the interlock to continue to resist unauthorized access to the interior of the cabinet.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to interlocks for electrical cabinets. More specifically, the present invention provides an apparatus for defeating an interlock, thereby permitting a technician to open the cabinet when the circuit therein is closed, and thereby facilitating servicing of the equipment therein.  
           [0003]    2. Description of the Related Art  
           [0004]    Various interlocks are commonly used on cabinets containing electric equipment, to prevent opening of the cabinet when there is current flowing through the equipment. Such interlocks thereby protect personnel working around the equipment from unnecessary risk of injury. However, such interlocks also add difficulty to servicing of the equipment therein. It is sometimes necessary for a technician servicing the equipment to open the cabinet at a time when current is flowing through the equipment therein in order to maintain or repair the equipment.  
           [0005]    A presently used interlock bypass mechanism utilizes an arm, pivotally mounted at one end, to push the interlock arm away from the hook in the cabinet door, permitting opening of the cabinet door. The movement of the pivoting arm is controlled by a knob rotationally secured to the arm at the pivot point, located outside the cabinet, and preferably at least partially hidden behind the operating lever of the cabinet. This presently used device includes seven components. A reduction of a number of components would reduce both cost and assembly time for a cabinet utilizing the interlock and interlock defeat mechanism.  
           [0006]    Accordingly, there is a need for an improved apparatus for defeating an interlock for an electrical cabinet, thereby facilitating access by technicians qualified to service the cabinet when current is present, while also resisting access by all others to the inside of the cabinet while current is present.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides an apparatus for defeating an interlock for an electrical cabinet. The interlock permits a technician qualified to do so to open the cabinet while current if flowing through the equipment therein, as may be necessary to service this equipment. The interlock also resists attempts by other persons to open the cabinet without first switching off the current.  
           [0008]    The interlock with which the present invention is used works off the position of the power switch for the equipment within the cabinet. When the cabinet door is open, an arm is spring-biased outward, so that its opposite end engages a flange on the power switch, thereby precluding the power switch from being moved from its open position to its closed position. When the cabinet is closed, the cabinet door pushes this arm inward, thereby disengaging the arm from the power switch&#39;s flange and permitting the power switch to be moved between its open and closed positions. Moving the power switch to its closed position moves an interlock latch to a position wherein it engages a hook in the door, thereby resisting the opening of the door until the power is switch is moved from its closed to its open position.  
           [0009]    The interlock defeat of the present invention includes a spring-biased peg protruding through the cabinet&#39;s side wall, adjacent the interlock latch, and behind the power switch. The position of the interlock defeat behind the power switch serves to hide it from persons unauthorized to open the cabinet while current is flowing. When a qualified technician wishes to open the cabinet, he may use a screwdriver or similar object to push the interlock defeat mechanism against the latch, thereby pushing the latch away from the hook and permitting the cabinet to be opened. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is an isometric front view of a cabinet incorporating an interlock and an interlock defeat mechanism of the present invention.  
         [0011]    [0011]FIG. 2 is a top view of an interlock and interlock defeat mechanism according to the present invention, illustrating the interlock in a position wherein it will preclude closing the circuit while the cabinet is open.  
         [0012]    [0012]FIG. 3 is a side view of an interlock and interlock defeat mechanism according to the present invention, illustrating the interlock in a position wherein it will preclude closing the circuit while the cabinet is open.  
         [0013]    [0013]FIG. 4 is a side view of a peg for an interlock defeat mechanism of the present invention.  
         [0014]    [0014]FIG. 5 is a top view of an interlock and interlock defeat mechanism according to the present invention, illustrating the interlock in a position wherein it will resist opening of the cabinet when current is flowing through the equipment within the cabinet.  
         [0015]    [0015]FIG. 6 is a side view of an interlock and interlock defeat mechanism according to the present invention, illustrating the interlock in a position wherein it will resist opening of the cabinet when current is flowing through the equipment within the cabinet.  
         [0016]    [0016]FIG. 7 is a top view of an interlock and interlock defeat mechanism according to the present invention, illustrating the use of the interlock defeat mechanism to defeat the interlock and permit opening of the cabinet.  
         [0017]    [0017]FIG. 8 is a side view of an interlock and interlock defeat mechanism according to the present invention, illustrating the use of the interlock defeat mechanism to defeat the interlock and permit opening of the cabinet. 
     
    
       [0018]    Like reference numbers denote like elements throughout the drawings.  
       DETAILED DESCRIPTION  
       [0019]    The present invention provides a defeat mechanism for an interlock, permitting qualified personnel to open an electrical cabinet secured by the interlock when current is flowing through the electrical equipment therein.  
         [0020]    A cabinet  1 , shown in FIG. 1, with which the interlock defeat will be used will include a pair of sides  2 ,  4 , a top  6 , a bottom  7 , a back  8 , and a hingedly secured door  9 . Typically, if the door is hingedly secured to the second of the two sides, the interlock holding the door closed will be secured to the first of the two sides.  
         [0021]    Referring to FIGS. 2-3, an interlock mechanism  10  with which the present invention will be used is illustrated. The interlock mechanism  10  is best understood through an explanation of the working of the power switch assembly  12 . The power switch assembly  12  includes an operating handle  13  secured to a mechanism drive hub  14 . The operating handle  13  is illustrated in FIG. 1 in the off position, and moves in the direction of arrow A to the on position. The mechanism drive hub  14  is connected to a pair of flanges  16 ,  18 , that rotate simultaneously with the mechanism drive hub  14 . As will be explained below, the flanges  16 , 18  control the pivoting of an interlock actuator  20 , and a switch drive shaft receptacle  22 , both of which pivot coaxially with the mechanism drive hub  14 . The mechanism drive hub  14  further defines at least one lip  34 , located on the outer circumference of the mechanism drive hub  14 .  
         [0022]    The interlock actuator  20  includes a first arm  28 , adjacent to the flange  16 , and a second arm  30  adjacent to the flange  18 . The switch drive shaft receptacle includes a shaft interface aperture  24 , and a side flange  26 . The switch drive shaft receptacle also includes a radial extension  32 , extending outward between the flanges  16  and  18 . The radial extension  32  is preferably sufficiently long so that it will depress a flat spring  100  located on the first side, as it passes the flat spring  100 . A spring  36  connects the side flange  26  with the arm  30 .  
         [0023]    An arm  38 , pivotally secured to the cabinet&#39;s first side at pivot  40 , extends outwards towards the door  9  of the cabinet  1 . The arm  38  includes a door-engaging end  42 , and a pivot-engaging end  44 . The pivot-engaging end  44  is dimensioned and configured to engage the lip  34  when the cabinet&#39;s door  9  is open, and the power switch assembly  12  is in its open position, at which time the arm  38  will be spring-biased outward, preferably by the spring  98 . The power switch assembly  12  will thereby be prevented from moving to the on position when the cabinet door  9  is open. Closing the cabinet door will pivot the door-engaging end  42  inward and the pivot-engaging end  44  away from the lip  34 , permitting movement of the power switch assembly  12 .  
         [0024]    The interlock mechanism  10  also includes a cam  46  pivotally secured to the cabinet&#39;s first side at the cam&#39;s first end  48 , and having a substantially perpendicular flange  50 , defining a slot  52  therein, at its second end  54 . An actuating rod  56  is pivotally secured at its first end  58  to the arm  30 , and passes through the slot  52  at its second end  60 . The first end  58  of the actuating rod  56  includes a spring-retaining lip  62 . A spring  64  fits around the actuating rod  56 , being compressed between the spring-retaining lip  62  and the flange  50 . The first end  48  of the cam  46  also defines a camming surface  66 .  
         [0025]    A latch  68  is pivotally secured adjacent to the first side of the cabinet at its pivot end  70 , typically by being pivotally secured to a mechanism frame assembly  71 , which is secured adjacent to the first side of the cabinet. The latch  68  defines a substantially perpendicular hook-engaging tip  72  at its hook-engaging end  74 . The pivot end  70  includes a cam-engaging surface  76 , dimensioned and configured to engage the camming surface  66  of the cam  46 . The tip  72  is dimensioned and configured to engage a hook  79  depending from the door  9  of the cabinet  1 , when the door  9  is closed. The latch is biased towards the hook  79 , preferably by the spring  98 . The latch  68  further defines a defeat-receiving notch  78 , between its pivot end  70  and its hook-engaging end  74 .  
         [0026]    Referring to FIGS. 2-4, the interlock defeat  80  includes a peg  82  protruding through an aperture  84  within the first side  96  of the cabinet. The peg  84  includes an actuator end  86 , located outside the cabinet, and a latch-engaging end  88 , permitting the peg  82  to have a greater range of angular motion within the aperture  84 . A reduced diameter portion  89  is defined between the actuator end  86  and latch-engaging end  88 . A circumferential groove  90  is defined between the reduced diameter portion  89  and latch-engaging end  88 , and is located inside the cabinet. A spring  92 , having a reduced diameter portion  94  dimensioned and configured to be secured within the circumferential groove  90 , is compressed between the circumferential groove  90  and the cabinet&#39;s first side  2 . The tapered tip  95  of the peg  82  facilitates insertion of the peg  82  through the reduced diameter portion  94  during assembly. The spring  94  biases the peg  82  into a substantially perpendicular orientation with respect to the first side  2 . The peg may also include an O-ring  112 , retained between the actuator end  86  and first side  2 . The spring  94  ensures that the O-ring  112  is pressed against the first side  2  to provide a water-resistant seal between the peg  82  and first side  2 . A shoulder  114  defined around the peg  82 , adjacent to the O-ring  112 , centers the peg  82  within the aperture  84 , ensuring that the O-ring  112  overlaps the first side  2  around its entire circumference.  
         [0027]    When the cabinet door  9  is open, the components will be in the positions shown in FIGS. 2 and 3. The power switch assembly  12  will typically be in the off position as illustrated. The spring  98  will bias the arm  38  outward, engaging the lip  34  with the pivot-engaging end  44  of the arm  38 , preventing the switch  12  from being rotated into the on position. The interaction of the camming surfaces  66 ,  76  will hold the latch  68  away from the hook  79 , against the bias of the spring  98 , thereby permitting the door  9  to open and close freely.  
         [0028]    When the door  9  is closed, the door  9  will push inward in the direction of arrow B on the end  42  of the arm  38 , thereby disengaging the pivot-engaging end  44  from the lip  34 , permitting the power switch assembly  12  to be rotated. The power switch assembly  12  may then be rotated to the on position, illustrated in FIGS. 5-6. As the operating handle  13  is rotated in the direction of arrow A, the flanges  16 ,  18  will engage the arms  28 ,  30  causing the arms  28  and  30  to rotate with the power switch assembly  12 . Additionally, the flange  16  will engage the flange  32 , causing the switch drive shaft receptacle  22  to rotate with the power switch assembly  12 . The power switch assembly  12  will in some embodiments rotate a short distance before the flanges  16 ,  18  engage the arms  28 ,  30  and the flange  32 , so that the switch  12  will move ahead of the other components. As the arm  30  rotates, the spring  64  will be compressed, and the cam  46  will also rotate. Once the arm  30  has rotated slightly more than halfway, the spring  64  will push the arm  30  through the remainder of its rotation. The arm  30  will engage the side flange  26 , thereby rotating the switch drive shaft receptacle  22  through the remainder of its rotation. By using this overcenter camming mechanism, the switch drive shaft receptacle is held in whichever position it is presently in—whether that position is on or off—until the power switch assembly  12  is rotated through most of its rotation, and is then switched into the opposite position once the rotation of the power switch assembly  12  is almost complete. As the spring  64  pushes the arm  30  through the remainder of its rotation, the cam  46  will also rotate, so that the interaction between the camming surfaces  66 ,  76  will push the latch  68  in the direction of arrow C into a position where the tip  72  will engage the hook  79 , preventing the cabinet door from being opened. The latch  68  will be held in this position by the spring  98 .  
         [0029]    To open the cabinet  1 , most personnel will first be required to move the power switch assembly  12  to the off position. As the power switch assembly  12  is rotated, the flange  18  will engage the arm  28 , thereby rotating the interlock actuator  20 . The arm  30  will pull the switch drive shaft receptacle  22  through part of its rotation through the spring  36 , until the flange  32  strikes the flat spring  100 . At this point, because the flat spring  100  is more powerful than the spring  36 , the switch drive shaft receptacle  22  will stop rotating until the arm  30  rotates slightly more than halfway, at which point the spring  64  will extend, forcing the arm  30  through the remainder of its rotation. At the same time, the arm  30  will engage the switch drive shaft receptacle  22 , forcing the switch drive shaft receptacle  22  through the remainder of its rotation. The components are now positioned as illustrated in FIGS. 2-3.  
         [0030]    In the event that servicing the equipment within the cabinet requires the cabinet to be opened while current is flowing through the equipment, personnel qualified to do so may use the interlock defeat  80  to open the cabinet door. The actuator end  86  of the interlock defeat is at least partially hidden from sight behind the power switch assembly  12 , thereby helping to preserve the function of the interlock in preventing unauthorized access to the interior of the cabinet. However, as shown in FIGS. 6-7, by pushing on the actuator end  86  of the peg  82 , for example, with a screwdriver or a similar object, the latch-engaging end  88  of the peg  82  is pushed in the direction of arrow D into the defeat-engaging notch  78  of the latch  68 , thereby pushing the latch  68  away from the hook  78 , and permitting the cabinet door  9  to be opened. When the peg  82  is released, the spring  92  will push the peg  82  back to its original position. The actuator end  86  of the peg  82  may be reached by a screwdriver from either the front or the side of the cabinet.  
         [0031]    While a specific embodiment of the invention has been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.