Abstract:
An interlock for first and second circuit breaker switch mechanisms which respectively have first and second operating handles thereon oriented such that the direction of operation is transverse in relation to the other. The interlock includes an interlock mechanism disposed between the first and second switch mechanisms and includes a support, a first interlock member interconnected with the first operating handle, and a second interlock member interconnected with the second operating handle. The first and second interlock members are mounted to the support for movement relative to each other along with the respective first and second operating handles. The interlock members include interference structure to prevent the second switch mechanism from being in an ON position when the first switch mechanism is in its ON position and likewise to prevent the first switch member from being in an ON position when the second switch member is in its ON position. The interlock mechanism allows both switch mechanisms to be in an OFF position simultaneously. The interlock mechanism may be used to prevent simultaneous delivery of electrical power from two alternate sources.

Description:
FIELD OF THE INVENTION 
     This invention is generally related to an interlock for circuit breaker switches and, more particularly, pertains to a circuit breaker linkage assembly interlocking two opposing circuit breaker handles and preventing both circuit breakers from being ON at the same time. 
     BACKGROUND OF THE INVENTION 
     In today&#39;s electrical supply systems, there are occasions when alternate sources of electrical power are necessary or desirable. For example, the capability of switching from utility power to emergency generator power is very important for many businesses, hospitals and industries, and is also being employed in residential applications. 
     In certain applications, it is desirable for separate electrical circuits or even separate groups of electrical circuits to be arranged so that when one group of circuits is switched to a conductive state, another group of circuits is switched to a non-conductive state in alternating fashion. In some arrangements, it may be desirable to alternately switch a common load between separate power sources so that, as one power source is disconnected from the load, the second power source is connected to prevent interruption of power to the load. In order that the alternate switching may be effective essentially simultaneously, a need has been recognized to employ a coupling mechanism which functions to switch one circuit OFF as the other circuit is switched ON. Prior art interlocking systems provide an interlock for first and second aligned circuit breakers having first and second external operating handles oriented thereon such that the operating handles are parallel and disposed away from each other when the switches are OFF, and towards each other when the switches are ON. The interlock includes a linkage arrangement disposed across the face of the circuit breaker switches for applying a linear force between the first operating handle and the second operating handle. The linkage arrangement is formed such that pushing the first operating handle from an OFF position to an ON position pushes the second operating handle from an ON position to an OFF position. An example of an interlock of this type is disclosed in Flegel U.S. Pat. No. 5,648,646 issued Jul. 15, 1997. 
     The above-described interlock functions satisfactorily for switches which have parallel handles and which move along a common axis between their ON and OFF positions. However, it is common to feed utility or primary power to a load center through a main circuit breaker which is oriented perpendicularly to the branch circuit breakers. With this arrangement, the switch handle of the main circuit breaker moves between its ON and OFF positions in a direction perpendicular to the direction of movement of the branch circuit breaker switch handles. This construction prevents use of known prior art interlocks with the main circuit breaker, since known interlocks can only be used with aligned switch handles which move along a common axis. 
     It is thus desirable to provide an interlock mechanism which prevents two circuit breakers in nonparallel relation to each other, and possibly of different sizes, from being turned ON simultaneously. It is also desirable that the interlock mechanism permits both of the circuit breakers to be switched OFF at the same time. 
     Accordingly, it is an object of the present invention to provide a circuit breaker interlock which is useable when the circuit breakers have switches operational in transverse directions. A further object of the invention is to provide an interlock that prevents two power sources from supplying power to an electrical panel simultaneously. Yet another object of the invention is to provide an interlock that allows the circuit breakers to reside simultaneously in an OFF position so that no power is supplied to the electrical panel. Yet another object of the invention is to provide an interlock that is easily adaptable to commonly available circuit breakers and electrical panels. Yet another object of the invention is to provide an interlock which is relatively simple in its components and construction, and adaptable to other switching applications. 
     SUMMARY OF THE INVENTION 
     The present invention advantageously provides an interlock for circuit breakers installed in a standard electrical load center panel for the purpose of providing a safe and simple arrangement for providing power to the selected circuits from an alternate power source, such as a portable generator, during a utility power outage. The present invention enables the use of standard, off-the-shelf circuit breakers that, due to differences in size, construction and orientation when installed, cannot be arranged so that their handles more in the same direction. 
     In one aspect of the invention, an electrical panel has a first switch mechanism that is movable in a first direction, and a second switch mechanism movable in a second direction, non-parallel to the first direction. Both switches are operable between an ON and an OFF position, and are preferably associated with circuit breaker mechanisms which control the supply of electrical power to the electrical panel from a first or second power source, respectively. An interlock mechanism is interconnected between the first switch mechanism and the second switch mechanism to prevent movement of the second switch mechanism to an ON position when the first switch mechanism is in its ON position. The interlock mechanism also prevents movement of the first switch mechanism to its ON position when the second switch mechanism is in its ON position. In a preferred embodiment, the first and second switch mechanisms include first and second manually operable switch handles, and the interlock mechanism is interconnected between the first and second switch handles. In a preferred form, each switch mechanism is adapted for removable mounting to the electrical panel. The interlock mechanism includes a support structure adapted for engagement with the first and second switch mechanisms. A first interlock member is movably mounted on the support structure, and is engaged with the first switch handle for movement therewith in the first direction. A second interlock member is also movably mounted to the support structure, and is engaged with the second switch handle for movement therewith in the second direction. The first and second interlock members include interference structure to prevent movement of the second switch member to an ON position when the first switch member is in its ON position, and for preventing the movement of the first switch member to an ON position when the second switch member is in its ON position. 
     The interference structure of the first and second interlock members preferably includes structure defining a notch. The notch is formed in one of the interlock members, hereafter referred to as the notched interlock member, and extends in a direction transverse to the direction of movement of the notched interlock member. The other interlock member is preferably in the form of an engagement interlock member having corresponding interference structure adapted to be selectively received within the notch. When the first switch member, to which the notched interlock member is mounted, is moved to its OFF position, the notch is aligned with the interference structure of the engagement interlock member. This enables movement of the second switch member, to which the engagement interlock member is mounted, to its ON position. Preferably, the notched interlock member defines an interference surface adjacent the notch which is in alignment with the interference structure of the engagement interlock member. Movement of the second switch member to its ON position is prevented by the interference structure when the first switch member, to which the notched interlock member is mounted, is in its ON position. 
     The support structure preferably includes a support plate configured to engage a shoulder defmed by each of the first and second switch mechanisms adjacent to the first and second switch members, respectively. A post member is engaged with and extends from the support plate, and the first and second interlock members each include a slot extending in the direction of its movement. The post member is received within the slots for providing movement of the first and second interlock members relative to the support plate. Each interlock member is preferably formed of a planar member slidably mounted to the support plate for movement relative to each other. 
     Another aspect of the invention involves an improvement in an electrical panel including a first switch mechanism having a first switch member or handle movable in a first direction between an ON and an OFF position for controlling the supply of electrical power from a first source. The improvement contemplates a second switch mechanism having a second switch member or handle movable in a second direction, transverse to the first direction, for controlling the supply of power from a second power source, and an interlock mechanism for controlling movement of the first and second switch members or handles. Details of this aspect of the invention are substantially as summarized above. 
     The invention further contemplates a method of preventing movement of a first switch mechanism to an ON position when an adjacent second interlock mechanism is in an ON position, substantially in accordance with the foregoing summary. 
     Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings illustrate the best mode presently contemplated of carrying out the invention. 
     In the drawings: 
     FIG. 1 is a front elevational view of a load center panel having an array of circuit breakers, at least one pair of which is interconnected by the interlock mechanism embodying the present invention; 
     FIG. 2 is an isometric view of the interlock mechanism of the invention interposed between two transversely oriented circuit breakers in the load center panel of FIG. 1, in which a first one of the circuit breakers is in an ON position and a second one of the circuit breakers is in an OFF position; 
     FIG. 3 is an exploded isometric view of the interlock mechanism of FIG. 2; 
     FIG. 4 is a partial sectional view taken on line  4 — 4  of FIG. 2; 
     FIG. 5 is a partial sectional view taken on line  5 — 5  of FIG. 2; 
     FIG. 6 is a partial sectional view taken on line  6 — 6  of FIG. 2; 
     FIG. 7 is a partial sectional view taken on line  7 — 7  of FIG. 2; 
     FIG. 8 is a top plan view of the interlock mechanism of FIG. 2 wherein each circuit breaker is in an OFF position; and 
     FIG. 9 is a top plan view similar to FIG. 8 showing the first circuit breaker in an OFF position and the second circuit breaker in an ON position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an electrical panel assembly  10  incorporating the interlock mechanism of the invention, shown generally at  12 . A primary source of electrical power, such as utility power, is supplied to electrical panel assembly  10  through a conduit  14 , and electrical panel assembly  10  includes a primary switch mechanism  16  which is interconnected with the primary source of electrical power, for controlling the supply of electrical power to electrical panel assembly  10  from the primary electrical power source. A secondary source of electrical power, such as from a generator, is supplied to electrical panel assembly  10  through a conduit  18 . Electrical panel assembly  10  incorporates a secondary switch mechanism  20  interconnected with the secondary electrical power source, for controlling the supply of electrical power to electrical panel assembly  10  from the secondary electrical power source. A series of branch circuit breakers  22  are incorporated into electrical panel assembly  10 , for controlling the supply of electrical power from either primary switch mechanism  16  or secondary switch mechanism  20  to the various electrical circuits of the building in which electrical panel assembly  10  is mounted, in a manner as is known. 
     Apart from interlock mechanism  12 , electrical panel assembly  10  is of conventional construction, and may incorporate a standard, commercially available electrical load center such as is available from Siemens Energy &amp; Automation, Inc. of Tucker, Ga. (Siemens) under its designation G4040MB1200CU, although it is understood that any other similar component may be employed. Primary switch mechanism  16  may be that such as is available from Siemens under its designation EQ9685, and secondary switch mechanism  20  may be that such as is available from Siemens under its designation Q230. Again, it is understood that other similar components may be employed. 
     Referring to FIGS. 1-3, primary switch mechanism  16  includes a switch body, shown generally at  24 , and a primary switch handle  26  movably mounted to body  24 . Primary switch mechanism  16  is mounted toward the top end of electrical panel assembly  10 , in a manner such that its handle  10  is movable in a direction parallel to the longitudinal axis of electrical panel assembly  10 , i.e. in an upward and downward direction with reference to FIG.  1 . Primary switch handle  26  is movable between an ON position in which electrical power is supplied to electrical panel assembly  10  from the primary source of electrical power, and an OFF position for cutting off the supply of electrical power to electrical panel assembly  10 . In FIG. 2, primary switch handle  26  is shown in its ON position. Similarly, secondary switch mechanism  20  includes a switch body  28  and a secondary switch handle  30  movably mounted to body  28 . The panel bus of electrical panel assembly  10  is constructed such that secondary switch mechanism  20  is mounted perpendicularly to primary switch mechanism  16 . Secondary switch handle  30  is movable relative to switch body  28  in a direction perpendicular to the direction of movement of primary switch handle  26 . Secondary switch handle  30  is movable between an ON position for supplying power to electrical panel assembly  10  from the secondary source of electrical power, and an OFF position for cutting off power from the secondary power source. In FIG. 2, switch handle  30  of secondary switch mechanism  20  is shown in its OFF position. 
     FIG. 2 illustrates the assembled components of interlock mechanism  12  as mounted to primary switch mechanism  16  and secondary switch mechanism  20 , and FIG. 3 illustrates switch mechanisms  16 ,  20  and the components of interlock mechanism  12  in exploded fashion. In a manner as will be explained, interlock mechanism  12  is operable to prevent primary and secondary switch handles  26 ,  30 , respectively, from both being in the ON position at the same time, so as to ensure that electrical panel assembly  10  is supplied with electrical power from only one source. In this manner, interlock mechanism  12  is operable to prevent the adverse consequences which may result if both primary switch mechanism  16  and secondary switch mechanism  20  are simultaneously in an ON condition. 
     Generally, interlock mechanism  12  includes a stationary mounting assembly incorporating a mounting member  32 , an intermediate plate  34  located vertically above mounted member  32 , and an upper plate  36  located vertically above intermediate plate  34 , together with a movable notched interlock member  38  and a movable engagement interlock member  40 . 
     Mounting member  32  includes an upper planar portion  42  which defines a lower longitudinal edge  44  and a lower transverse edge  46 , which extends perpendicularly to longitudinal edge  44  across approximately half the width of upper planar portion  42 . Upper planar portion  42  further defines an upper transverse edge  48  extending parallel to lower transverse edge  46  across the entire width of upper planar portion  42 . An opening  49  is formed in upper planar portion  42  inwardly of lower longitudinal edge  44 . A pair of arms  50 ,  52  are formed integrally with upper planar portion  42  of mounting member  32 . Arms  50 ,  52  extend upwardly from upper planar portion  42 , and terminate in inwardly extending lips  54 ,  56 , respectively. Mounting member  32  may be a stamped and bent member formed of a any satisfactory material such as steel or aluminum, although it is understood that other materials or forming methods may be employed. 
     Intermediate plate  34  is a generally planar member, defining a lower longitudinal edge  58  and a lower transverse edge  60  oriented at right angles to each other. Intermediate plate  34  further defmes a pair of upwardly extending ears  62  and a transverse edge  64  extending therebetween parallel to lower transverse edge  60 . An opening  65  is formed in intermediate plate  34  inwardly of lower longitudinal edge  58 . Again, intermediate member  34  may be a stamped member formed of any satisfactory material such as steel or aluminum, although it is understood that other materials or forming methods may be employed. 
     Upper plate  36  is also a generally planar member, and includes a lower longitudinal edge  66  and a lower transverse edge  68  oriented at right angles to each other. A tab  70  extends outwardly from lower longitudinal edge  66 . Intermediate plate  36  further defines an upper transverse edge  72  extending parallel to lower transverse edge  68 . A pair of tabs  74  extend outwardly from upper transverse edge  72 . An opening  76  is formed in upper plate  36  inwardly of longitudinal edge  66 . Upper plate  36  may be a stamped member formed of any satisfactory material such as steel or aluminum, although it is again understood that other materials or forming methods may be employed. 
     As noted above, mounting member  32 , intermediate plate  34  and upper plate  36  make up a mounting subassembly secured together by means of a pair of fasteners, one of which is shown at  78 , extending through aligned openings in mounting member  32 , intermediate plate  34  and upper plate  36 . The opening in mounting member  32  is preferably threaded, so as to receive the threads of fastener  78 . When mounting member  32 , intermediate plate  34  and upper plate  36  are assembled together, openings  49  and  65  on mounting member  32  and intermediate plate  34 , respectively, are in alignment with each other, and opening  76  in upper plate  36  is in alignment with openings  49  and  65 . 
     The mounting subassembly made up of mounting member  32 , intermediate plate  34  and upper plate  36  is engaged with primary switch mechanism  16  and secondary switch mechanism  20  by placing arms  50 ,  52  of mounting member  32  one on either side of primary switch mechanism body  24 , such that arm  50  extends along a first side of body  24 , shown at  80 , and arm  52  extends along the side of body  24  opposite side  80 . Lips  54 ,  56  are placed into engagement with the end of primary switch mechanism body  24 , shown at  82 . 
     Referring to FIG. 3, primary switch mechanism body  24  further defines an upper shoulder  84  and a lower shoulder  86  which are parallel to each other. A pair of end shoulders, one of which is shown at  88 , extend between upper and lower shoulders  84 ,  86 , respectively, and a series of internal channels  90  extend parallel to end shoulders  88  between upper and lower shoulders  84 ,  86 , respectively. As shown in FIGS. 5 and 6, mounting member  32  is positioned such that its upper transverse edge  48  is located adjacent the lower end of primary switch mechanism body  24 , shown at  92 , adjacent lower shoulder  86 . 
     In a similar mainer, secondary switch mechanism body  28  defines an inner shoulder  94 , a pair of transverse outer shoulders  96  and a channel  98  extending outwardly from inner shoulder  94  between outer shoulders  96 . As shown in FIG. 7, lower longitudinal edge  44  of mounting member  32  is located adjacent the inner end of primary switch mechanism body  28 , shown at  100 , below inner shoulder  94 , and lower transverse edge  46  of mounting member  32  is located adjacent the upper sidewall of primary switch mechanism body  28 , shown in FIG. 5 at  102 , below upper outer shoulder  96 . 
     When assembled to mounting member  32 , intermediate plate  34  is positioned such that its upper transverse edge  64  is in alignment with upper transverse edge  48  of mounting member  32 . Similarly, lower longitudinal edge  58  and lower transverse edge  60  of intermediate plate  34  are in alignment with lower longitudinal edge  44  and lower transverse edge  46 , respectively, of mounting member  32 . Ears  62  of intermediate plate  34  are located outwardly of the end shoulders, such as  88 , of primary switch mechanism body  24 . 
     When mounted to intermediate plate  34  and mounting member  32 , upper plate  36  is positioned such that its upper transverse edge  72  overlies lower shoulder  86  defined by primary switch mechanism body  24 , and its longitudinal edge  66  overlies inner shoulder  94  defined by secondary switch mechanism body  28 . Transverse tab  70  extending from longitudinal edge  66  extends into channel  98  defined by secondary switch mechanism body  28 , and longitudinal tabs  74 , which extend from upper transverse edge  72 , extend into channels  90  defined by primary switch mechanism body  24 . In this manner, the lateral position of the mounting assembly defined by mounting member  32 , intermediate plate  34  and upper plate  36  is fixed relative to primary and secondary switch mechanisms  16 ,  20 , respectively, by arms  50 ,  52  and the associated lips  54 ,  56 , respectively, in combination with engagement of tabs  70  and  74  within channels  98  and  90 , respectively. Relative downward vertical movement is prevented by engagement of upper plate  36  with shoulders  86  and  94  defined by primary and secondary switch mechanism bodies  24  and  28 , respectively. 
     Referring to FIG. 3, notched interlock member  38  is a substantially planar member, and a cut-out  104  is formed at its lower end. Cut-out  104  is defmed by a transverse edge  106  in combination with an end edge including an inner section  108  and an outer section  110 , between which a notch or recess  112  is located. Recess  112  is defmed by a pair of side edges  114 ,  116  extending from inner and outer end edge sections  108 ,  110 , respectively, in combination with an end edge  118  extending therebetween. 
     An axially extending slot  120  is formed in notched interlock member  38 , inwardly of recess  112 . 
     Notched interlock member  38  further includes a pair of outer tabs  122  extending upwardly from an upper end edge  124 . A recess  126  extends inwardly from upper end edge  124  between outer tabs  122 . 
     A pair of bracket members, one of which is shown at  128 , are adapted for engagement with notched interlock member  38  for interconnecting notched interlock member  38  with primary switch handle  26 . Each bracket member  128  includes a base strip  130  having a pair of threaded openings  132  formed therein, and an upwardly extending end tab  134 . As shown in FIGS.  2  and  4 - 6 , notched interlock member  38  is mounted to handle  26  of primary switch mechanism  16  by first placing notched interlock member  38  on the outer face of primary switch mechanism body  24  such that outer tabs  122  are located adjacent the inner surface of switch handle  26 . Bracket members  128  are placed below notched interlock member  38  over channels  90 , and extend through an opening defined by switch handle  26  such that each bracket end tab  134  is located on the side of primary switch handle  26  opposite that of outer tabs  122 . Threaded fasteners  136  extend through openings formed in notched interlock member  38  and into the threaded openings  132  in bracket members  128 , for securing brackets  128  and notched interlock member  38  together. The spacing between bracket member end tabs  134  and outer tabs  122  of notched interlock member  38  is such that tabs  122  and  134  are located closely adjacent the sides of switch primary switch handle  26 . In this manner, any movement of primary switch handle  26  results in movement of notched interlock member  38 . 
     Slot  120  formed in notched interlock member  38  extends along a longitudinal axis parallel to the direction of movement of switch handle  26 . 
     Referring to FIG. 3, engagement interlock member  40  is in the form of a planar strip defining a base  138  and a finger  140  extending from base  138 . A slot  142  is formed in base  138 , and extends along a longitudinal axis coincident with a longitudinal axis along which base  138  and finger  140  extend. A series of openings, shown at  144 , are formed in base  138  and finger  140 . 
     A pair of bracket members  146  are adapted for mounting to engagement interlock member  40  for interconnecting engagement interlock member  40  with secondary switch handle  30 . Each bracket member  146  defines a planar base  148  and an upstanding tab  150 . Openings are formed in each base  148  in alignment with openings  144  in engagement interlock member  40 . 
     An engagement member  152  is adapted for placement over base  148  of the inner one of bracket members  146 . Engagement member  152  includes a pair of openings in alignment with the openings in base  148  and the inner pair of openings  144  in engagement interlock member  40 . 
     Engagement interlock member  40  is interconnected with secondary switch handle  30  as shown in FIGS. 2 and 7 by positioning finger  140  within an opening defined by secondary switch handle  30  such that base  138  is located inwardly of switch handle  30  and the outer end of finger  140  is positioned outwardly of switch handle  30 . The outer one of bracket members  146  is then positioned over the outer pair of aligned openings  144  formed in finger  140  adjacent its outer end, and a threaded fastener  154  extends through the openings in bracket member  146  and into engagement with threads formed in the outer pair of openings  144 , for mounting the outer one of bracket members  146  to the outer end of finger  140 . In this manner, tab  150  of the outer one of bracket members  146  is located closely adjacent the outer surface of switch handle  30 . In a similar manner, the inner one of bracket members  146  is positioned such that its tab  150  is located closely adjacent the inner surface of secondary switch handle  30 . Engagement member  152  and the inner one of bracket members  146  are engaged with engagement interlock member  40  in any satisfactory manner, such as by use of a pair of rivets, one of which is shown at  156 , which extend through the openings formed in engagement member  152  and base  148  of inner bracket member  146 , and into the inner pair of openings  144  in engagement interlock member  40 . With this construction, the inner bracket member  146  and engagement member  152  are first fixed to engagement interlock member  40 , such that finger  140  can be passed through the opening defined by secondary switch handle  30 , and the outer bracket member  146  is then mounted to the outer end of finger  140  as described above. Tabs  150  of bracket members  146  are located closely adjacent the sides of secondary switch handle  30 , such that any movement of secondary switch handle  30  results in movement. of engagement of interlock member  40  therewith. Slot  142  in engagement interlock member  40  is oriented such that its longitudinal axis is parallel to the direction of movement of secondary switch handle  30 . 
     In assembly, base  138  of engagement interlock member  40  is disposed between notched interlock member  38  and upper plate  36  such that slot  120  of notched interlock member  38  and slot  142  of engagement interlock member  40  overlap each other. A post  158  is mounted to upper plate  36 , and extends through a spacer  160  which is sandwiched between the lower surface of engagement interlock member  40  and the upper surface of intermediate plate  36 . Post  158  includes a downwardly facing shoulder, and a reduced diameter portion therebelow, shown at  161  (FIGS.  6 , 7 ), is received within openings  76  in upper plate  36 . Post  158  is mounted to upper plate  36  using a standard rivet machine process which forms a head  162  on the lower end of post  158 , such that head  162  has a diameter greater than that of opening  76 . A threaded passage is formed in the upper end of post  158 , and a threaded fastener  162  extends through a washer  164  and into the passage in post  158 . Washer  164  has a diameter greater than the transverse dimension of slot  120  in notched interlock member  38 , so as to secure notched interlock member  38  and engagement interlock member  40  to upper plate  36 . Post  158  extends both through slot  120  in notched interlock member  38  and slot  142  in engagement interlock member  40 , and guides movement of interlock members  38  and  40  in response to movement of primary and secondary switch handles  26  and  30 , respectively. 
     In operation, interlock mechanism  12  functions as follows to prevent primary and secondary switch handles  26  and  30  from being in the ON position at the same time. With reference to FIG. 8, switch handles  26  and  30  are both illustrated as being in the OFF position. In this position, recess  112  in notched interlock member  38  is in axial alignment with engagement member  152  of engagement interlock member  40 , such that secondary switch handle  30  can be moved to its ON position as shown in FIG.  9 . When secondary switch handle  30  is moved to its ON position in this manner, movement of engagement interlock member  40  is enabled by the provision of slot  142  in base  138  of engagement interlock member  40 , and engagement member  152  is received within recess  112  of notched interlock member  38 . With secondary switch handle  30  in its ON position of FIG. 9, engagement member  152  is located in close proximity to side edge  116  of recess  112  in notched interlock member  38 . Movement of primary switch handle  26  away from its OFF position is prevented by engagement of side edge  116  with engagement member  152 , such that primary switch handle  26  cannot be moved to its ON position. Engagement member  152  thus defines interference structure in the path of movement of notched interlock member  38  and its associated recess  112 , to prevent movement of primary switch handle  16  to its ON position as long as secondary switch handle  26  is in its ON position. 
     When it is desired to move primary switch handle  26  to its ON position, secondary switch handle  30  must first be moved to its OFF position as shown in FIG. 8, which moves engagement member  152  out of recess  112  in notched interlock member  38 . Such movement of engagement member  152  out of recess  112  enables movement of notched interlock member  38  along with primary switch handle  26  to its ON position, as shown in FIG.  2 . Movement of notched interlock member  38  along with primary switch handle  26  is enabled by the provision of slot  120  in notched interlock member  38 , and results in the positioning of end edge outer section  110  of notched interlock member  38  in alignment with engagement member  152 . End edge outer section  110  thus defines interference structure in the path of movement of engagement member  152 , to prevent movement of secondary switch handle  30  to its ON position as long as primary switch handle  26  is in its ON position. 
     It can thus be appreciated that interlock mechanism  12  provides a simple and efficient mechanism for preventing two switches which are movable in perpendicular directions from being in an ON position at the same time. The components of interlock mechanism  12  are relatively inexpensive to manufacture and assemble, and take advantage of the existing switch body and handle structure to secure the components of interlock mechanism  12  to each other and to the switches. Interlock mechanism  12  can either be installed during original assembly of electrical panel assembly  10  or can be retrofit after assembly if an existing electrical panel is being outfitted with a secondary source of power. 
     While interlock mechanism  12  has been shown and described with respect to switch handles which move in a direction perpendicular to each other, it is understood that interlock mechanism  12  can be easily adapted to accommodate arrangements in which the direction of movement of the switch handles includes any transverse component, i.e. when the switch handles do not move along the same or parallel axes. Further, while interlock mechanism  12  has been shown and described with respect to an electrical panel assembly, it should be understood that interlock mechanism  12  could be used in any other application in which it is desired to interlock two switches or switch handles which are oriented relative to each other such that movement of the switch handles is non-parallel. 
     Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.