Abstract:
A switch lever lock out assembly engagable with a switch. The assembly includes a lock out body engageable with a switch to prevent operation of the switch. A lever engaging member is mounted to the body, and has a lock position and an unlock position. In the lock position, the lever engaging member prevents disengaging the body from the switch. A blocking member is movably fixed to the body, and is engageable with the lever engaging member to prevent movement of the lever engaging member relative to the body when the lever engaging member is in said lock position. The blocking member is locked relative to the body by a key engageable mechanism. In another aspect of the invention, the key is fixed to a tether forming part of the assembly, and the key is lockable in a lock rail fixed within an area defined by the tether.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
         [0001]    Not Applicable.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
         [0002]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0003]    The field of invention is switch lever lock outs for locking switch levers in a desired position, and more particularly to key operated switch lever lock outs.  
           [0004]    Switches are used in many applications to control the flow of electrical energy. The switches can be used to redirect electrical energy from one circuit to another, and can be used to stop the flow of electrical energy through a circuit. In both cases the circuits become de-energized, that is without a voltage. One particular type of switch is a circuit breaker which cuts off the flow of electrical energy when the flow of electrical energy through the switch exceeds a predetermined value. Many of these circuit breakers include a lever which is movable between an “On” position and an “Off” position.  
           [0005]    Maintenance personnel often use a circuit breaker to interrupt the flow of electrical energy through a circuit when the circuit, or electrical components connected thereto, require maintenance. The circuit breaker, however, is often remote from the location requiring maintenance. Therefore, it is desirable to lock out the circuit breaker to prevent an individual from inadvertently energizing the circuit while maintenance is being performed.  
           [0006]    Known circuit breaker lock out assemblies engage the circuit breaker lever to prevent unauthorized movement of the lever. Lock outs, such as disclosed in U.S. Pat. Nos. 5,593,020; 5,794,760; and 5,900,600, include a lock arm cantilevered from a lock rail. The lock arm includes a head which engages or covers the circuit breaker lever to prevent unauthorized movement of the lever. This particular type of lock out requires the lock rail be positioned adjacent the specific circuit breaker being locked out. If there is insufficient space adjacent the specific circuit breaker for a lock rail, these lock outs cannot be used. Therefore, a need exists for an improved lock out which can be used with or without a lock rail, and if a lock rail is used, the lock rail can be located remote from the specific circuit breaker being locked out.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a switch lever lock out assembly engagable with a switch. The assembly includes a lock out body engageable with a switch to prevent operation of the switch. A lever engaging member is mounted to the body, and has a lock position and an unlock position. In the lock position, the lever engaging member prevents disengaging the body from the switch. A blocking member is movably fixed to the body, and is engageable with the lever engaging member to prevent movement of the lever engaging member relative to the body when the lever engaging member is in the lock position.  
           [0008]    The blocking member and body can be locked relative to each other by a latch member engaging a latching member. The latch member is fixed relative to one of the body and the blocking member. The latching member is engagable with the latch member in an engaged position, and fixed relative to the other of the body and the blocking member, wherein in the engaged position, the blocking member is locked relative to the lever engaging member in the lock position. A key is engageable with at least one of the latch member and the latching member to disengage the latching member from the latch member and allow the blocking member to move relative to the body to allow the lever engaging member to move from the lock position to the unlock position.  
           [0009]    In another aspect of the invention, the key is attached to a tether forming part of the assembly. The tether has a first end and a second end, and the key is slidably fixed to the tether for slidable movement between said first and second ends. The key can be locked in a lock rail fixed within an area defined by the tether either inside or outside the circuit breaker enclosure.  
           [0010]    A general objective of the present invention is to provide a lock out assembly which prevents unauthorized actuation of a switch. The present invention provides a lock out assembly which requires a key to disengage the assembly from the switch to allow operation of the switch.  
           [0011]    Another objective of the present invention is to provide a lock out assembly which can be used with a lock rail which does not require aligning the lock rail with the switch being locked out. This objective is accomplished by providing a lock out assembly requiring a key, and fixing the key onto a tether, wherein the key is locked to the lock rail fixed within an area defined by the tether.  
           [0012]    The foregoing and other objects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a perspective view of a circuit breaker lock out assembly incorporating the present invention;  
         [0014]    [0014]FIG. 2 is a perspective view of the lock out assembly of FIG. 1 with the blocking member in the lock position;  
         [0015]    [0015]FIG. 3 is a top perspective view of the lock out assembly body of FIG. 1;  
         [0016]    [0016]FIG. 4 is a bottom perspective view of the lock out assembly body of FIG. 1;  
         [0017]    [0017]FIG. 5 is a cut away, rear perspective view of the lock out assembly of FIG. 1;  
         [0018]    [0018]FIG. 6 is a perspective view of the latching arms of FIG. 5;  
         [0019]    [0019]FIG. 7 is a cross sectional top view of the lock out assembly of FIG. 1 with the latch member in the lock position;  
         [0020]    [0020]FIG. 8 is a cross sectional top view of the lock out assembly of FIG. 1 with the latch member in the unlock position;  
         [0021]    [0021]FIG. 9 is a top perspective view of a lock rail for use with the lock out assembly of FIG. 1;  
         [0022]    [0022]FIG. 10 is a front perspective view of the lock rail of FIG. 9;  
         [0023]    [0023]FIG. 11 is a perspective view of an alternative lock out assembly incorporating the present invention;  
         [0024]    [0024]FIG. 12 is a perspective view of the lock out assembly of FIG. 11 with the blocking member in the lock position;  
         [0025]    [0025]FIG. 13 is a perspective view of the lock out assembly of FIG. 11 clamped onto a multipole circuit breaker;  
         [0026]    [0026]FIG. 14 is a perspective view of another alternative lock out assembly incorporating the present invention; and  
         [0027]    [0027]FIG. 15 is a top perspective cut away view of the lock out assembly of FIG. 14. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Referring to FIGS.  1 - 10 , a switch lever lock out assembly  10  engages at least one circuit breaker  14  to prevent circuit breaker operation. The circuit breaker  14  includes a lever  16  movable between an “On” position and an “Off” position. The lock out assembly  10  engages the lever  16 , and prevents movement of the lever  16  between the “On” position and “Off” position. A key  12  is required to disengage the lock out assembly  10  from the lever  16 . The key  12  can be connected to the lock out assembly  10  by a tether  18  which can be locked to a lock rail  21  (shown in FIGS. 9 and 10) to prevent unauthorized use of the key  12 , and thus unauthorized disengagement of the lock out assembly  10  from the lever  16 . Advantageously, the lock rail  21  can be positioned anywhere within reach of the tether  18  regardless of the location of the lever  16 .  
         [0029]    The circuit breaker  14  can be any commercially available circuit breaker  14  having a lever  16  movable between two or more positions. Although, locking out a circuit breaker is disclosed herein, the present invention can be used to lock out any switch having a lever movable between two or more positions.  
         [0030]    The circuit breaker lock out assembly  10  includes a body  20  which slips over the lever  16 . A lever engaging member  22  fixed relative to the body  20  engages the lever  16  such that the lock out assembly  10  cannot be lifted away from the circuit breaker  14  and allow undesired movement of the lever  16 . A blocking member  24  is slidably fixed to the body  20 , and is slidably moveable between an unlocked position (shown in FIG. 1) and a locked position (shown in FIG. 2). In the locked position, the blocking member  24  prevents disengagement of the lever engaging member  22  from the lever  16 , and thus, unauthorized removal of the lock out assembly  10  from the lever  16 .  
         [0031]    Referring to FIGS.  3 - 5 , the body  20  is substantially rectangular, and has a top  26  and bottom  28  connected by sides  30  and ends  32 ,  34 . A slot  36  formed in the bottom  28  and through the sides  30  receives the lever  16 . Rails  38  formed on the body sides  30  engage the blocking member  24  to slidably fix the blocking member  24  thereto. A groove  40  formed in the bottom  28  proximal the rear end  34  intersects grooves  42  formed in the body sides  30  for receiving the U-shaped lever engaging member  22  formed from wire. A receptacle  44  opening to the rear end  34  intersects a key hole  46  formed through the body top  26 . The key hole  46  intersects, and is coaxial with, a stop hole  48  formed through the body bottom  28  for receiving a cylindrical tether stop  50 .  
         [0032]    The receptacle  44  receives a latch member  52  extending from the blocking member  24  which engages a pair of opposing inwardly biased latching arms  54  disposed in the receptacle  44 . The receptacle  44  is preferably a substantially rectangular cavity which is open to the body rear end  34  and one side  30 . Advantageously, the receptacle  44  having an open side  30  simplifies molding the body  20  and assembling the lock out assembly  10 . Although an open sided receptacle  44  is preferred, the receptacle  44  can be formed with two open sides or no open sides without departing from the scope of the invention.  
         [0033]    Referring to FIGS.  5 - 8 , the pair of opposing inwardly biased latching arms  54  are disposed in the receptacle  44 , and latch onto the latch member  52 . Each arm  54  has a base end  56  and a distal end  58 . The base end  56  is disposed proximal the closed front end of the receptacle  44 , and the distal end  58  extends toward the receptacle opening  62  at the body rear end  34 . Preferably, the arms  54  are formed from a flat spring steel, and are connected at the arm base ends  56  by a connecting piece  64  to form a U-shape.  
         [0034]    The arms  54  bow around the intersecting key hole  46 , and are flared outwardly at the distal ends  58  for engagement with the latch member  52 . Advantageously, when the arms  54  initially engage the latch member  52 , the flared distal ends  58  force the arms  54  outwardly to receive the latch member  52  between the arms  54 . When the latch member  52  is fully received in the receptacle  44 , tabs  66  extending inwardly and forwardly (away from the open end of the receptacle) from the arms  54  hook the latch member  52  and prevent withdrawal of the latch member  52  from the receptacle  44 . Preferably, the tabs  66  are formed as an integral part of the arms  54  to simplify the assembly of the lock out assembly  10 .  
         [0035]    The lever engaging member  22  disclosed in FIGS.  1 - 5  includes a pair of opposing resilient legs  68  having inwardly extending pins  70  for engagement with each end  72  of a transverse through hole  74  formed in the lever  16 . The legs  68  and pins  70  are, preferably, formed as an integral piece from a U-shaped wire wrapped around a portion of the body  20 , wherein each leg  68  of the U-shaped lever engaging member  22  is joined by the connecting piece  64  received in the body bottom groove  40 .  
         [0036]    Each leg  68  is received in the outwardly opening groove  42  formed in the body  20 , and has a proximal end  75  and a distal end  77 . The proximal end  75  of the leg  68  is proximal the body rear end  34 , and the distal end  77  is biased away from the body side  30  proximal the body slot  36 . The pin  70  extends inwardly toward the body slot  36  from the leg distal end  77 , and moves from a disengaged position (shown in FIG. 1) to an engaged position (shown in FIG. 2) as the leg distal end  77  is urged toward the body  20  into the side groove  42  by the blocking member  24 . In the engaged position, the pins  70  are inserted into the ends  72  of the lever through hole  74 . In the disengaged position, the pins  70  are withdrawn from the ends  72  of the lever hole  74 . Advantageously, when the pins  70  are in the engaged position, the lock out body assembly  10  cannot be easily removed from the lever  16 .  
         [0037]    Referring to FIGS.  1 - 5 , the blocking member  24  slidably moves over the resilient lever engaging member legs  68  from the unlocked position to the locked position to urge the pins  70  from the disengaged position to the engaged position. Although movably fixing the blocking member to the body, such that the blocking member is slidable relative to the body is preferred, the blocking member can be movably fixed to the body, such that the blocking member is pivotable or rotatable relative to the body, without departing from the scope of the invention.  
         [0038]    The blocking member  24  includes a top wall  76  and bottom wall  78  joined by side walls  80  and a rear end wall  82 . The blocking member top wall  76 , bottom wall  78 , side walls  80 , and end wall  82  define a cavity  84  which receives the rear end  34  of the body  20 . A longitudinal slot  85  is formed in the blocking member top wall  76  to provide access to the key hole  46  formed in the body  20 . Inwardly opening grooves  86  formed in each side wall  80  are aligned with the outwardly opening grooves  42  formed in the body sides  30 . The blocking member grooves  86  receive the lever engaging member legs  68  and guide the legs  68  as the outwardly biased leg distal ends  77  are urged inwardly by the blocking member side walls  80  to move the pins  70  into engagement with the lever  16 .  
         [0039]    Inwardly opening grooves  88  formed in each blocking member side wall  80  proximal the blocking member top wall  76  engage the rails  38  extending from the body sides  30  to slidably fix the blocking member  24  to the body  20 . Although inwardly opening grooves  88  for slidably fixing the blocking member  24  to the body  20  are disclosed, the blocking member  24  can be slidably fixed to the body  20  using methods known in the art, such as by forming grooves in the blocking member top wall which engage rails formed in the body top, formed grooves in the body which are engaged by lips formed in the blocking member which wrap around the rails, and the like, without departing from the scope of the invention.  
         [0040]    Referring to FIGS. 1 and 5, the blocking member side walls  80  are substantially rectangular, and a cutout  90  formed in the forward bottom comer of each side wall  80  conforms with a portion  92  of the body slot  36  when the blocking member  24  is in the unlocked position. A notch  94  formed in the lower edge  96  of each side wall  80  is open to the cutout  90 , and extends rearwardly from the cutout  90  a distance sufficient to disengage the side wall  80  from the outwardly biased distal end  77  of the engaging member leg  68  while still covering the proximal end  75  of the engaging member leg  68 , such that the proximal end  75  of the engaging member leg  68  is retained in the groove  42  formed in the body  20 . Although blocking member sides having a specific shape is disclosed, the sides can have any shape, or in certain embodiments, such as described below, be omitted, without departing from the scope of the invention.  
         [0041]    Referring to FIGS. 7 and 8, the latch member  52  extends forwardly from the blocking member end wall  82 , and is received in the body receptacle  44  to engage the latching arms  54 . The latch member  52  engages the latching arms  54 , and prevents the blocking member  24  from slidably moving relative to the body  20 . The latch member  52  includes a stem  93  having proximal end  95  joined to the blocking member end wall  82  and a distal end  97 . A head  98  joined to the distal end  97  extends laterally past the stem  93 , and includes rearwardly facing surfaces  100  on the lateral portions  102  of the head  98 . The rearwardly facing surfaces  100  engage the tabs  66  extending inwardly from the latching arms  54  to prevent the blocking member  24  from slidably moving relative to the body  20 .  
         [0042]    Referring back to FIG. 5, a support post  104  extending forwardly from the blocking member end wall  82  supports a biasing member  106  interposed between the blocking member  24  and body  20 . The post  104  is received in an opening  108  (shown in FIG. 4) formed in the body rear end  34 , and supports the biasing member  106  as it urges the blocking member  24  and body  20  apart. Preferably, the post  104  and latch member  52  are formed as an integral part of the blocking member end wall  82 . However, the post  104  and latch member  52  can be formed independently of the blocking member  24  and fixed thereto using other methods known in the art, such as fasteners, adhesives, and the like, without departing from the scope of the invention.  
         [0043]    The biasing member  106  interposed between the blocking member  24  and body  20  biases the blocking member  24  away from the body  20 . In the embodiment disclosed herein, the biasing member  106  is a helical spring having one end  107  engaging the body rear end  34  and an opposing end  109  engaging the blocking member end wall  82 . Advantageously, when the blocking member  24  is in the lock position, the biasing member  106  maintains the latching arms  54  in positive engagement with the latch member  52 . Although a single helical spring is preferred, other biasing members can be used, such as multiple helical springs, leaf springs, elastomeric materials, and the like, or the biasing member can be omitted, without departing from the scope of the invention.  
         [0044]    Referring to FIGS. 1, 5,  7 , and  8 , the key  12  is received in the key hole  46  formed in the body  20 , and engages the latching arms  54  to disengage the latching arms  54  from the latch member  52 . An axial passageway  110  is formed through the key  12  between a key head end  112  and toe end  114 , and the tether  18  is routed through the passageway  110  to slidably fix the key  12  to the tether  18 . The key toe end  114  includes a pair of opposing radially extending teeth  116  which engage the latching arms  54  when the toe end  114  is received in the key hole  46  to disengage the latching arms  54  from the latch member  52 . Rotation of the key  12  about a key cylindrical axis  118  engages the teeth  116  with the latching arms  54  to spread the latching arms  54  apart and disengage the tabs  66  from the latch member  52 . Wings  120  radially extending from the cylindrical key  12  midway between the head end  112  and toe end  114  can be provided to provide engagement surfaces for a user&#39;s fingers to rotate the key  12  about the key cylindrical axis  118 .  
         [0045]    As shown in FIGS. 1, 3, and  5 , a key guide  128  having a cylindrical neck  130  extending upwardly through the key hole  46  includes an axial passageway  132 . The tether  18  passes through the axial passageway  132 , and the key  12  slips over the neck  130  which guides the key  12  into the key hole  46  for engagement with the latching arms  54 . The key guide  128  is preferably formed from a metal, such as aluminum, and is held in the key hole  46  using a friction fit. Other methods for rigidly fixing the guide  128  in the key hole  46  can be used, such as molding the body around the guide, adhesives, and the like without departing from the scope of the invention. Advantageously, the key guide  128  reduces the open area of the key hole  46 , and prevents an unauthorized user from inserting a sharp object into the key hole  46  to manipulate the latching arms  54  and disengage the latching arms  54  from the latch member  52 . Although a metal key guide, as disclosed, is preferred, the key guide can be modified or omitted without departing from the scope of the invention.  
         [0046]    Referring to FIGS. 5, 9, and  10 , the tether  18  is preferably a multistrand metal cable, and passes through the axial passageway  110  in the key  12 , the slot  85  formed in the blocking member  24 , and the key hole  46  formed in the body  20  between the latching arms  54 . One end  122  of the tether  18  is anchored to the body  20  by the cylindrical stop  50  fixed onto the tether end  122 . The stop  50  is received in the stop hole  40  which has a diameter that is greater than the diameter of the key hole  46  to prevent the stop  50  from passing through the key hole  46 . A second stop  124  (shown in FIG. 9) fixed to the free end  126  of the tether  18  prevents the tether  18  from slipping out of the key passageway  110 . The stops  50 ,  124  can be fixed to the respective tether ends  122 ,  126  using methods known in the art, such as molding, crimping, soldering, adhesives, friction fits, and the like without departing from the scope of the invention.  
         [0047]    Referring now to FIGS. 9 and 10, the free end  126  of the tether  18  is locked to the lock rail  21  to prevent unauthorized use of the key  12 . The lock rail  21  is fixed adjacent to a surface  135  within an area defined by the length of the tether  18 . The lock rail  21  has a base  129  including a top  131  and a bottom  133 , and is fixed to the surface  135 , such as a surface of the circuit breaker box, panel, and the like, in proximity to the circuit breaker  14  (shown in FIG. 1). The base  129  can be fixed to the surface  135 , using methods known in the art, such as by an adhesive applied to the base bottom  133 , screws extending through the base  129 , and the like.  
         [0048]    A plurality of arches  136  extend from the base top  131 , and define a plurality of transverse openings  134  above the base  129 . Preferably, the arches  136  are formed as an integral part of the base  129 . Although arches  136  are described herein, other structures can be provided to form openings  134  above or in the base  129  for receiving the key  12  therethrough, such as open ended boxes, through bores formed in the base  129 , a clamp structure which pivots away from the base  129 , and the like, without departing from the scope of the present invention.  
         [0049]    Pins  138  extend upwardly from the base top  131  in front of and behind each opening  134  to block the lower portion  140  of the opening  134 . The pins  138  prevent transverse movement of the key  12  through the lower portion  140  of the opening  134 . Preferably, each opening  134  is sized such that the key  12  can be slipped into the opening  134  above the pins  138 , and the tether  18  can be pressed downwardly into the lower portion  140  of the opening  134  adjacent to the pins  138 . A lock hasp  137  can be slipped through the opening  134  above the pins  138  to prevent passage of the key  12  through the opening  134  above the pins  138 .  
         [0050]    Referring to FIGS.  1 - 10 , in use, the circuit breaker lock out assembly  10  is locked onto the lever  16  by slipping the lever  16  into the lock out head body slot  36 , and aligning the lever engaging member pins  70  with each end  72  of the hole  74  formed in the lever  16 . An unauthorized user is prevented from disengaging the lock out assembly  10  from the lever  16  by sliding the blocking member  24  forwardly to urge the pins  70  into the hole ends  72  until the latch member  52  is fully engaged with the latching arms  54 . Once the circuit breaker lock out assembly  10  is locked onto the lever  16  and the blocking member  24  is in the locked position, the key  12  is slipped through one of the openings  134  in the lock rail  21 , and the lock hasp  137  is slipped through the opening  134  and locked in place to prevent unauthorized removal of the key  12 .  
         [0051]    The circuit breaker lock out assembly  10  is disengaged from the lever  16  by first unlocking the lock hasp  137 , and removing the hasp  137  from the lock rail opening  134 . The key  12  is slipped through the lock rail opening  134  along the tether  18 , and inserted into the key hole  46  over the key guide neck  130 . Once the key toe end  114  is fully inserted into the key hole  46  such that the key teeth  116  are aligned between the latching arms  54 , the key  12  is rotated about the key axis  118  to engage the teeth  116  with the latching arms  54  and urge the latching arms  54  outwardly away from the latch member  52 . This causes the latch arm tabs  66  to disengage from the latch member  52 .  
         [0052]    Once the arm tabs  66  are disengaged from the latch member  52 , the biasing member  106  urges the blocking member  24  rearwardly to uncover the lever engaging member legs distal ends  77 . The outwardly biased distal ends  77  of the lever engaging member  22  spring outwardly to disengage the pins  70  from the lever hole ends  72 , and release the lever  16 , such that the lever  16  can be slipped out of the lock out head body slot  36 .  
         [0053]    In a second embodiment shown in FIGS.  11 - 13 , a lock out assembly  210  includes a threaded bore  250  formed through the front end  232  of the body  220  which intersects the body slot  236  for receiving the lever  216 . Although a threaded bore  250  is disclosed, an internally threaded insert can be fixed in the body  220  using methods known in the art, such as by molding the insert into the body, slipping the insert into an unthreaded bore and adhesively fixing the insert in the bore, and the like without departing from the scope of the invention. The bore  250  threadably engages the lever engaging member  222  to clamp the lock out assembly  210  to the lever  216 .  
         [0054]    The lever engaging member  222  shown in FIGS.  11 - 13  is a thumbwheel  252  including a threaded post  254  having a head end  256  and a lever engaging end  258 . The threaded post  254  threadably engages the threaded bore  250  to axially move the post  254  through the bore  250  between an engaged position and a disengaged position. In the engaged position, the substantially flat lever engaging end  258  engages the lever  216  extending into the body slot  236  to clamp the lever  216  against the body  220 , and thus clamp the assembly  210  onto the lever  216 . Although, the lever engaging end  258  shown in FIGS.  11 - 13  is substantially flat, the lever engaging end  258  can have any shape, such as a cup form, a pointed form, a flat form, and the like, for engaging the lever  216  without departing from the scope of the invention.  
         [0055]    A thumbwheel head  260  fixed to the thumbwheel head end  256  is square to include flat surfaces  262  which fit between blocking member side walls  280  when the blocking member  224  is in the locked position. Although any shaped thumbwheel head  260  can be used, a head having at least one flat surface which can engage the blocking member in the locked position is preferred to prevent rotation of the thumbwheel when the blocking member is in the locked position.  
         [0056]    The blocking member  224  slidably moves over the thumbwheel head  260  from the unlocked position (shown in FIG. 11) to the locked position (shown in FIG. 13) to prevent disengagement of the lock out assembly  210  from the lever  216 . In the embodiment disclosed herein, the blocking member  224  covers the thumbwheel head  260  to prevent access thereto. Advantageously, the blocking member  224  disclosed herein also engages the thumbwheel head flat surfaces  262  to prevent rotation of the thumbwheel head  260 . The blocking member  224  is locked in the lock position using latching arms and a latch member, as described above, wherein a key is required to disengage the latching arms from the latch member. Advantageously, as shown in FIG. 13, the circuit breaker lock out assembly  210  having a thumbwheel lever engaging member  222  can accommodate a lever  216  which does not fit between the blocking member side walls  280 .  
         [0057]    In use, the circuit breaker lock out assembly  210  is clamped onto the lever  216  by slipping the lever  216  into the lock out head body slot  236 , and rotating the thumbwheel  252  to engage the thumbwheel lever engaging end  258  with the lever  216  until the lever  216  is sandwiched between the thumbwheel lever engaging end  258  and the body  220 . An unauthorized user is prevented from disengaging the lock out assembly  210  by aligning the flat surfaces  262  of the thumbwheel head  260  with the blocking member side walls  280 , and sliding the blocking member  224  forwardly toward the locked position over the thumbwheel head  260  until the latch member is fully engaged with the latching arms, as described above in the first embodiment. Once the circuit breaker lock out assembly  210  is clamped onto the lever  216  and the blocking member  224  is in the locked position, the key can be locked to a lock rail, as described above in the first embodiment.  
         [0058]    The circuit breaker lock out assembly  210  is disengaged from the lever  216  by retrieving the key and inserting it into the into the key hole  246  such that the key teeth are aligned between the latching arms. As described above, the key is rotated to urge the latching arms outwardly away from the latch member and disengage the latch member. As shown in FIG. 11, the blocking member  224  is moved rearwardly to the unlock position to uncover the thumbwheel head  260 . The thumbwheel  252  is then rotated to disengage the thumbwheel lever engaging end  258  from the lever  216 , such that the lever  216  can be slipped out of the lock out head body slot  236 .  
         [0059]    In a third embodiment shown in FIGS. 14 and 15, a lock out assembly  310  includes lock posts  362  which extends axially from a thumbwheel head  360  of a thumbwheel  352 . The posts  362  engage a frame lock plate  380  extending upwardly from the slidable blocking member  324 . When the blocking member  324  is in the lock position, as shown in FIGS. 14 and 15, the lock plate  380  engages the lock posts  362  and prevents rotation of the thumbwheel  352 . In the unlock position, the lock posts  362  are not engaged with the lock plate  380  and allow rotation of the thumbwheel  352 . As shown in FIG. 15, in this embodiment, latching arms  354  are fixed to the blocking member  324 , and the latch member  356  forms part of the body  320 .  
         [0060]    In use, the circuit breaker lock out assembly  310  is clamped onto the lever  316  by slipping the lever  316  into the lock out head body slot  336 , and rotating the thumbwheel  352  to engage the thumbwheel lever engaging end  358  with the lever  316  until the lever  316  is sandwiched between the thumbwheel lever engaging end  358  and the body  320 . An unauthorized user is prevented from disengaging the lock head by sliding the blocking member  324  rearwardly toward the locked position and slipping the lock plate  380  between the posts  362  until the latch member  356  is fully engaged with the latching arms  354 . Once the circuit breaker lock out assembly  310  is clamped onto the lever  316  and the blocking member  324  is in the locked position, the key  312  can be locked to a lock rail, as described above.  
         [0061]    The circuit breaker lock out assembly  310  is disengaged from the lever  316  by first retrieving the key  312 , and inserting the key  312  into the key hole  346  such that the key teeth are aligned between the latching arms  354 . The key  312  is rotated to urge the latching arms  354  outwardly away from the latch member  356 , and disengage the latching arms  354  from the latch member  356 . The blocking member  324  is slid forwardly to disengage the lock plate  380  from the lock posts  362  to allow rotation of the thumbwheel  352 . The thumbwheel  352  is then rotated to disengage the thumbwheel lever engaging end  358  from the lever  316 , such that the lever  316  can be slipped out of the lock out head body slot  336 .  
         [0062]    While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention defined by the appended claims.