Abstract:
An interlock arrangement operatively associated with utility and generator side switches of an electrical panel including a first main switch associated with the first power supply and a second main switch associated with the second power supply. The interlock arrangement includes a first neutral switch associated with the first power supply, and a second neutral switch associated with the second power supply. A lockout sequencer arrangement has a first lockout that restricts simultaneous switching of the first and the second neutral switch, a second lockout configured to engage the first lockout to restrict movement of the first lockout when the first main switch is a conductive position, and a third lockout configured to engage the first lockout to restrict movement of the first lockout when the second main switch is in a conductive position.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention relates to a transfer switch and, more particularly, to a separately-derived transfer switch having a lockout sequencing arrangement that sequences manual switching of a load between power supplies to prevent open neutral transients during the switching. 
     In an electrical supply system, there are occasions when an alternate source of electric power is necessary or desirable. For example, the capability of switching from utility power to emergency generator power is important for businesses, hospitals and industries, and is also employed in residential applications. 
     It is desirable for separate electrical circuits, or 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 so as to prevent power supply to the circuits from two different power sources at the same time, e.g. from both a utility power supply and a generator power supply. In an arrangement such as this, a switch is typically provided for each power source to control the supply of electrical power. Accordingly, it is important to ensure that the switches are prevented from both being in the ON position at the same time, to ensure that power is supplied to the switch from only one power source. 
     To this end, switch interlocks have been developed that are designed to prevent simultaneous connection of circuits to two different power sources, such as described in U.S. Pat. No. 6,096,986, the disclosure of which is incorporated herein and assigned to the assignee of the present application. For some transfer switches, providing linkages that prevent the inadvertent switching of circuits to two power supplies is sufficient. However, for some types of transfer switches, more than an interlock is needed. For instance, if a separately-derived transfer switch is not properly switched, open neutral switching transients may be introduced. 
     The present invention is directed to a sequencing lockout arrangement for use with a separately-derived transfer switch that sequences manual switching of main and generator side switches to prevent the introduction of open neutral switching transients. A separately-derived transfer switch typically includes a utility mains switch or breaker and a utility mains neutral switch as well as a generator mains switch or breaker and a generator mains neutral switch. In one embodiment of the present invention, two slidable lockout sequencers together with a rocker lockout functions to sequence switching of a load from one power source to another power source. In this embodiment, seven separate operations must be performed to switch the load between power sources. In another embodiment, the utility mains neutral and generator mains neutral switches are linked together such that switching of the utility mains neutral to a conductive position automatically switches the generator mains neutral switch to a non-conductive position, and vice-versa. In this embodiment, five separate operations are required to switch a load between power sources. 
     The slidable lockout sequencers together with the rocker lockout in the first-mentioned embodiment allow only one of the utility mains breaker, the utility mains neutral switch, the generator mains breaker, and the generator mains neutral switch to be switched at a time. Moreover, the lockout sequencers and the rocker lockout cooperate such that a pre-defined order or sequence of the one-at-a-time switching must be followed to switch a load from one power source to another. The slidable lockout sequencers similarly define the sequence of switching with the interlinked neutral switches of the second-mentioned embodiment. Thus, in both embodiments, the slidable lockout sequencers provide limited and ordered switching of the utility and generator switches. 
     Thus, it is one object of the present invention to provide a lockout arrangement for use with a separately-derived transfer switch that is operable to prevent open neutral switching transients. 
     It is another object of the present invention to provide a separately-derived transfer switch having a pair of slidable members that restrict movement of switch handles such that a load is switched from one power source to another in a pre-defined, unalterable sequence. 
     In accordance with one aspect of the present invention, these and other objects are achieved with a lockout arrangement for use with a separately-derived transfer switch having a mains switch, a generator switch, a mains neutral switch, and a generator neutral switch. The lockout arrangement includes a neutral interlock associated with the mains neutral switch and the generator neutral switch, and configured to prevent both neutral switches from being in a conductive position simultaneously. The neutral interlock includes a first bracket engaged with the mains neutral switch and a second bracket engaged with the generator neutral switch. The brackets are adapted to move in response to movement of a neutral switch. The lockout arrangement further includes a first interlock configured to engage the first bracket to prevent movement of the first bracket, and a second interlock configured engage the second bracket to prevent movement of the second bracket. The first and second interlocks are arranged such that the interlocks cannot be engaged with their respective brackets simultaneously. 
     In accordance with another aspect, the invention is directed to a separately-derived transfer switch having a first mains switch associated with a first power supply and a second mains switch associated with a second power supply. The transfer switch further includes a first neutral switch and a second mains neutral switch associated with the first and the second power supplies, respectively. A lockout sequencing arrangement has a first lockout that restricts simultaneous switching of the first and the second neutral switch and further includes a second lockout configured to engage the first lockout to restrict movement of the first lockout when the first main switch is a conductive position, and a third lockout configured to engage the first lockout to restrict movement of the first lockout when the second main switch is in a conductive position. 
     The present invention may also be embodied in a method of disconnecting a load from a utility power supply and connecting the load to a generator. The method includes switching a mains switch from an ON position to an OFF position. The method continues with disengaging a mains side lockout from engagement with a neutral switch assembly lockout to allow movement of a mains neutral switch and a generator neutral switch. The method further includes switching, in tandem, the mains neutral switch from an ON position to an OFF position and the generator neutral switch from an OFF position to an ON position. In addition, the method includes engaging a generator side lockout with the neutral switch assembly lockout to prevent switching of the mains neutral switch and the generator neutral switch, and switching a generator switch from an OFF position to an ON position The above series of steps may be performed in a reverse order to disconnect the load from the generator and to connect the load to the utility power supply. 
     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 elevation view of a transfer panel containing a utility mains breaker, a utility mains neutral switch, a generator mains breaker, and a generator mains neutral switch together with a lockout arrangement containing two slidable lockout sequencers and a rocker lockout according to one embodiment of the present invention and shown with the utility mains breaker and the mains neutral switch in an ON position and the generator mains breaker and the generator mains neutral switch in an OFF position; 
         FIG. 2  is an enlarged view of the transfer panel of  FIG. 1  showing the utility mains breaker and the utility mains neutral switch in the ON position and the generator mains breaker and the generator mains neutral switch in the OFF position; 
         FIG. 3  is a front elevation view of the transfer panel shown in  FIG. 2  with the utility mains breaker switched to an OFF position; 
         FIG. 4  is a front elevation view of the transfer panel shown in  FIG. 2  with a mains side lockout sequencer having been slid to free the utility mains neutral switch; 
         FIG. 5  is a front elevation view of the transfer panel shown in  FIG. 2  with the utility mains breaker and the utility mains neutral switch switched to the OFF position and positioned within a recess formed in the mains side lockout sequencer; 
         FIG. 6  is a front elevation view of the transfer panel shown in  FIG. 2  with the rocker lockout pivoted upward to block the utility mains neutral switch from being switched to the ON position and to free the generator mains neutral switch; 
         FIG. 7  is a front elevation view of the transfer panel shown in  FIG. 2  with the generator mains neutral switch shown switched from an OFF position defined within a recess of a generator side lockout sequencer to an ON position; 
         FIG. 8  is a front elevation view of the transfer panel shown in  FIG. 2  with the generator side lockout sequencer having been slid to free the generator mains breaker; 
         FIG. 9  is a front elevation view of the transfer panel shown in  FIG. 2  with the generator mains breaker switch moved to the ON position thereby resulting in connection of a load to the generator power supply; 
         FIG. 10  is a front enlarged elevation view of a transfer panel similar to that shown in  FIG. 2  according to another embodiment of the present invention containing a utility mains breaker, a generator mains breaker, and an interlinked utility mains neutral switch and generator mains neutral switch together with a lockout arrangement containing two slidable lockout sequencers and shown with the utility mains breaker and the mains neutral switch in an ON position and the generator mains breaker and the generator mains neutral switch in an OFF position; 
         FIG. 11  is a front elevation view of the transfer panel shown in  FIG. 10  with the utility mains breaker switched to an OFF position; 
         FIG. 12  is a front elevation view of the transfer panel shown in  FIG. 10  with a mains side lockout sequencer having been slid to free the utility mains neutral switch; 
         FIG. 13  is a front elevation view of the transfer panel shown in  FIG. 10  with the utility mains breaker and the utility mains neutral switch switched to the OFF position and positioned within a recess formed in the mains side lockout sequencer and the generator mains neutral switch switched from the OFF position to the ON position; 
         FIG. 14  is a front elevation view of the transfer panel shown in  FIG. 10  with the generator side lockout sequencer having been slid to free the generator mains breaker; 
         FIG. 15  is a front elevation view of the transfer panel shown in  FIG. 10  with the generator mains breaker switch moved to the ON position thereby resulting in connection of a load to the generator power supply; 
         FIG. 16  is an isometric view of a lockout assembly according to another aspect of the invention and shown with a portion of an electrical panel having a utility mains breaker switch, a generator mains breaker switch, a utility neutral switch, and a generator neutral switch; 
         FIG. 17  is an exploded view of the lockout assembly of  FIG. 16 ; 
         FIG. 18  is a front elevation view of the lockout assembly of  FIG. 16  with the utility mains breaker and the utility neutral switch in conductive ON positions and the generator mains breaker and the generator neutral switch in non-conductive OFF positions; 
         FIG. 19  is a front elevation view of the lockout assembly of  FIG. 16  with the utility mains breaker in a non-conductive OFF position, the utility neutral switch in the conductive ON position, and the generator mains breaker and the generator neutral switch in non-conductive OFF positions; 
         FIG. 20  is a front elevation view of the lockout assembly of  FIG. 16  with a first movable interlock moved to clear switching of the neutral switches; 
         FIG. 21  is a front elevation view of the lockout assembly of  FIG. 16  with the utility mains breaker and the utility neutral switch in non-conductive OFF positions, the generator neutral switch in a conductive ON position, and the generator mains breaker in a non-conductive OFF position; 
         FIG. 22  is a front elevation view of the lockout assembly of  FIG. 16  with a second movable interlock moved to clear switching of the generator mains breaker; and 
         FIG. 23  is a front elevation view of the lockout assembly of  FIG. 16  with the utility mains breaker and utility neutral switch in non-conductive OFF positions and the generator mains breaker and the generator neutral switch in conductive ON positions. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a load center assembly  10  according to one embodiment of the present invention, which is configured to supply power to a series of electrical circuits from one of at least two power sources. Representatively, load center assembly  10  controls the supply of power to the electrical circuits from a primary power source, such as utility power, and an alternate or secondary power source, such as an electric generator, which is adapted to supply power in the event power from the primary power source is unavailable. Typically, the alternate or secondary power source is an electric generator, although it is understood that any other source of secondary or alternate power may be employed. The following description utilizes terminology which makes reference in various instances to a generator, and it is understood that such terminology is used for the sake of convenience and that the term “generator” is meant to encompass any secondary or alternate power source, and is not limited to a generator as the alternate power source. Similarly, it is understood that use of the term “utility” is meant to encompass any primary power source, and is not limited to power provided through a utility company power grid. 
     Load center assembly  10  includes a cover  12  adapted to be mounted to wall  13  and having a door  14  pivotably connected thereto. Cover  12  includes a series of knockouts constructed to be removed as load breakers  16  are added. In the illustrated embodiment, each of the knockouts has been removed and loaded with breakers  16 . Further, in the illustrated embodiment, the knockouts, and thus breakers  16 , are arranged in two columns, but it is understood that other layouts are possible. A utility mains switch or breaker  18  is constructed to be connected to a utility power input. A generator mains neutral switch  20 , generator mains breaker  22 , and a utility mains neutral switch  24  are constructed to be electrically connected to the respective power sources, as known in the art. The load center assembly  10  further has an interlock assembly  26  that prevents the inadvertent connection of the utility power input via utility mains breaker  18  and generator power input via generator mains breaker  22  from being concurrently connected to the load terminals of the load center assembly  10 . As will be explained, the interlock assembly  26  also controls movement of the neutral switches  20 ,  24  to ensure that the breakers and switches are actuated in a predefined sequence. 
     Referring now to  FIG. 2 , the interlock assembly  26  includes a pair of slidable lockouts  28 ,  30  and a centrally positioned rocker lockout  32 . Lockout  28  is associated with the utility mains breaker  18  and the utility mains neutral switch  24 , and thus will be referred to as “utility side lockout” whereas lockout  30  is associated with the generator mains breaker  22  and the generator mains neutral switch  20 , and thus will be referred to as “generator side lockout”. 
     The utility side lockout  28  includes a header  34 , a shorted base  36 , a first leg  38 , and a second shortened leg  40 . It is understood that the lockout  28  may fabricated as a single unitary body or the header  34 , base  36 , and legs  38 ,  40  may be fastened together using conventional fasteners. The first leg  38  includes first and second slots  42 ,  44  that are vertically spaced from and aligned with one another. Respective alignment pins  46 ,  48  extend through the openings and define a range of motion for the utility side lockout  28 . The arrangement of the header  34 , shortened base  36 , leg  38 , and shortened leg  40  collectively define a recess  50  sized to receive the handles  52  and  54  of the utility mains breaker  18  and the utility mains neutral switch  24 , respectively. 
     The generator side lockout  30  is similar in construction to the utility side lockout  28 . The generator side lockout  30  includes a header  56 , a shorted base  58 , a first leg  60 , and a second shortened leg  62 . It is understood that the lockout  30  may also be fabricated as a single unitary body or the header  56 , base  58 , and legs  60 ,  62  may be fastened together using conventional fasteners. The first leg  60  includes first and second slots  64 ,  66  that are vertically spaced from and aligned with one another. Respective alignment pins  68 ,  70  extend through the openings and define a range of motion for the utility side lockout  30 . In addition, the alignment pins  68  and  70  are aligned with pins  46  and  48 , respectively. The lockout  30  also includes a recess  72  sized to receive the handles  74  and  76  of the generator mains breaker  22  and the generator mains neutral switch  20 , respectively. 
     The rocker lockout  32  includes a rocker body  78  that is positioned generally between utility mains neutral switch  24  and the generator mains neutral switch  20 . The rocker body  78  is coupled to a pivot pin  80  in a manner that allows the rocker body to be pivoted. Ears  82 ,  84  extend from the rocker body  78  and as will be explained limit the range of motion of the rocker lockout  32 . The ears  82 ,  84  may be integrally formed with the rocker body  78  or may be separate components that are fastened to the rocker body  78  in a conventional manner. 
     In  FIG. 2 , the utility mains breaker switch handle  52  and the utility mains neutral switch handle  54  are both in the ON position and the generator mains breaker handle  74  and the generator mains neutral switch handle  76  are in the OFF position. When the breakers and switches are in this position, the load circuits of the load center assembly  10  are electrically connected to the utility power source. The interlock arrangement  26  is constructed and associated with the breakers and switch handles such that generator side handles  74 ,  76  cannot be moved to their ON positions when the utility side handles  52 ,  54  are in the ON position. Moreover, the utility mains neutral switch handle  54  is blocked from being moved to the OFF position by the shortened base  36  of the generator side lockout  28 . For the utility mains neutral switch handle  54  to be in the ON position shown in  FIG. 2 , the rocker lockout  32  must be pivoted counterclockwise. This movement is only possible if the generator mains neutral switch handle  76  is in the OFF position. In addition, once the rocker lockout  32  is pivoted to the position shown in  FIG. 2 , the generator mains neutral switch handle  76  cannot be switched from the OFF position to the ON position. 
     The interlock assembly  26  forces an operator to complete a seven step sequence to manually disconnect the load center from one power source and connect it to the other power source. The seven step sequence for disconnecting the load center from the utility power source and connecting it to the generator is shown in  FIGS. 3 through 10 . 
     In the first step, shown in  FIG. 3 , the utility mains breaker handle  52  is moved outwardly in the direction of arrow  86  from the ON position to the OFF position. As a result of this outward movement, the switch handle  52  is moved to a position within recess  50  of the utility side lockout  28 . Additionally, as a result of this movement, the switch handle  52  no longer blocks downward movement of the lockout  28 . More specifically, when the switch handle  52  is in the ON position,  FIG. 2 , the shorted leg  40  of the lockout  28  is generally adjacent the switch handle  52 . As a result, the lockout  28  cannot be slid downward along arrow  88 , shown in  FIG. 4 . 
     In step  2 , downward movement of the generator side lockout  28  causes the shorted leg  40  to move adjacent the utility mains breaker handle  52 , as shown in  FIG. 4 . In this position, the switch handle  52  cannot be moved back to its ON position until the lockout  28  is slid upward. In addition, as shown in  FIG. 4 , the shortened base  36  of the lockout  28  also slides downward to a position below that of the utility mains neutral switch handle  54  thereby freeing the switch handle  54  to be moved to the OFF position. 
     Thus, at step  3 , the utility mains neutral switch handle  54  can be moved outwardly along arrow  90 , as shown in  FIG. 5 . In this position, both of the utility side switches  52 ,  54  are in the OFF position as are the generator side switch handles  74 ,  76 . As such, the electrical loads are not being fed power from either power source. 
     In step  4 , shown in  FIG. 6 , the rocker lockout  32  must be pivoted clockwise, represented by arrow  92 , to free the generator mains neutral switch handle  76 . This clockwise movement also causes the body  78  of the rocker lockout  32  to move adjacent to the utility mains neutral switch handle  54 , which effectively impedes switching back of the switch handle  54  to its ON position. Additionally, ear  82  of the rocker lockout  32  abuts the lower surface of the shortened leg  40  of the utility side lockout  28  when the rocker lockout is fully pivoted to the position shown in  FIG. 6 . This abutment limits further pivoting of the rocker lockout  32  past the desired position. 
     With the generator mains neutral switch  76  free by clockwise movement of the rocker lockout  32 , in step  5 , the operator may then move the generator mains neutral switch handle  76  from the OFF position in the direction of arrow  94  to the ON position, as shown in  FIG. 7 . As further shown in  FIG. 7 , when the generator mains neutral switch handle  74  is moved to the ON position, the generator side lockout  30  is free to slide upwardly. More particularly, when the generator mains neutral switch handle  74  is in the OFF position, the switch handle  74  is adjacent the base  58  of the generator side lockout  30  and therefore impedes upward movement of the lockout  30 . 
     In step  6 , the generator side lockout  30  is slid upward in the direction of arrow  96 , as shown in  FIG. 8 . As a result of this upward movement, the shorted leg  62  of the lockout  30  that previously was adjacent the generator mains breaker handle  74  is also moved upward away from the switch handle  74 . Similarly, the base  58  of the lockout  30  slides upward to sit adjacent the generator mains neutral switch handle  76 . In this position, the base  58  blocks the switch handle  76  from being moved back to its OFF position. 
     In step  7 , shown in  FIG. 9 , the generator mains breaker handle  74  is switched from the OFF position to the ON position in the direction of arrow  98 . When the generator mains breaker handle  74  is switched to the ON position, the load center is then electrically connected to the generator power source. 
     One skilled in the art will appreciate that the interlock assembly  26  forces an operator to first switch OFF the utility mains breaker, then switch OFF the utility mains neutral switch, then switch ON the generator mains neutral switch, and then switch ON the generator mains breaker to disconnect the load center  10  from the utility power supply and connect it to the generator power supply. The mechanical configuration of the interlock assembly  26  does not allow the sequence to be adjusted by the operator. In addition, one skilled in the art will appreciate that the steps described above are carried out in reverse to disconnect the load center from the generator power source and connect it to the utility power source. 
     Referring now to  FIG. 10 , an interlock assembly  100  according to another representative embodiment of the present invention is shown. Interlock assembly  100  sequences an operator through five steps to disconnect the load center  10  from one power source and connect it to another power source. 
     The interlock assembly  100  includes a pair of slidable lockouts  102 ,  104 . Lockout  102  is associated with the utility mains breaker  18  and the utility mains neutral switch  24 , and thus will be referred to as “utility side lockout” whereas lockout  104  is associated with the generator mains breaker  22  and the generator mains neutral switch  20 , and thus will be referred to as “generator side lockout”. 
     The utility side lockout  102  includes a header  106 , a shorted base  108 , a first leg  110 , and a second shortened leg  112 . It is understood that the lockout  102  may fabricated as a single unitary body or the header  106 , base  108 , and legs  110 ,  112  may be fastened together using conventional fasteners. The first leg  110  includes first and second slots  114 ,  116  that are vertically spaced from and aligned with one another. Respective alignment pins  118 ,  120  extend through the openings and define a range of motion for the utility side lockout  102 . Further, the arrangement of the header  106 , shortened base  108 , leg  110 , and shortened leg  112  collectively define a recess  122  sized to receive the handles  52  and  54  of the utility mains breaker  18  and the utility mains neutral switch  24 , respectively. 
     The generator side lockout  104  is similar in construction to the utility side lockout  102 . The generator side lockout  104  includes a header  124 , a shorted base  126 , a first leg  128 , and a second shortened leg  130 . It is understood that the lockout  104  may also be fabricated as a single unitary body or the header  124 , base  126 , and legs  128 ,  130  may be fastened together using conventional fasteners. The first leg  128  includes first and second slots  132 ,  134  that are vertically spaced from and aligned with one another. Respective alignment pins  136 ,  138  extend through the openings and define a range of motion for the utility side lockout  104 . In addition, the alignment pins  136  and  138  are aligned with pins  118  and  120 , respectively. Further, the lockout  104  also includes a recess  140  sized to receive the handles  74  and  76  of the generator mains breaker  22  and the generator mains neutral switch  20 , respectively. 
     The interlock assembly  100  further has an interlinking bar  142  that is connected to the utility mains neutral switch handle  54  and the generator mains neutral switch handle  76 . This interlinking of handles  54  and  76  causes the switch handles to be moved simultaneously. Thus, when handle  54  is switched to the OFF position, switch handle  76  is switched to the ON position, and vice-versa. The interlinking bar  142  represents one known means of interconnecting handles  54  and  75 . It is understood that other types of interlinking configurations may be used and are considered within the scope of the present invention. One such in-line interlinking configuration is shown in U.S. Pat. No. 6,031,193, the disclosure of which is incorporated herein by reference. Another representative interlinking configuration is described in U.S. Pat. No. 6,927,349, the disclosure of which is incorporated herein by reference. 
     In general, the interlock assembly  100  is similar to the interlock assembly  26  shown in  FIGS. 1 through 9 , with the exception that the rocker lockout has been removed and replaced with the interlinking bar  142 . By interlinking the neutral switch handles  54 ,  76 , the number of steps to disconnect the load center from one power source and connect it to another power source, relative to the sequence shown in  FIGS. 3 through 9  is reduced by two steps. A five-step sequence for disconnecting the load center  10  from the utility power source to the generator power source will be described with respect to  FIGS. 11 through 15 . 
     In the first step, shown in  FIG. 11 , the utility mains breaker handle  52  is moved outwardly in the direction of arrow  144  from the ON position to the OFF position. As a result of this outward movement, the switch handle  52  is moved to a position within recess  122  of the utility side lockout  102 . Additionally, as a result of this movement, the switch handle  52  no longer blocks downward movement of the lockout  102 . More specifically, when the switch handle  52  is in the ON position,  FIG. 10 , the shorted leg  112  of the lockout  102  is generally adjacent the switch handle  52 . As a result, the lockout  102  cannot be slid downward along arrow  146 , shown in  FIG. 12 . 
     In step  2 , downward movement of the generator side lockout  102  causes the shorted leg  112  to move adjacent the utility mains breaker handle  52 , as shown in  FIG. 12 . In this position, the switch handle  52  cannot be moved back to its ON position until the lockout  102  is slid upward. In addition, as shown in  FIG. 12 , the shortened base  108  of the lockout  102  also slides downward to a position below that of the utility mains neutral switch handle  54  thereby freeing the switch handle  54  to be moved to the OFF position. 
     Thus, at step  3 , the utility mains neutral switch handle  54  is moved outwardly along arrow  148 , as shown in  FIG. 13 . In this position, both of the utility side switches  52 ,  54  are in the OFF position as are the generator side switch handles  74 ,  76 . As such, the electrical loads are not being fed power from either power source. Further, because the utility mains neutral switch handle  54  is interlinked with the generator mains neutral switch handle  76 , movement of the utility neutral switch handle  54  in the direction of arrow  148  automatically causes the generator mains neutral switch handle to move in the direct of arrow  150  from the OFF position, shown in  FIG. 10 , to the ON position. 
     When the generator mains neutral switch handle  74  is in the ON position, the generator side lockout  104  is freed to slide upwardly. More particularly, when the generator mains neutral switch handle  74  is in the OFF position, the switch handle  74  is adjacent the base  126  of the generator side lockout  104  and therefore impedes upward movement of the lockout  104 . 
     In step  4 , the generator side lockout  104  is slid upward in the direction of arrow  152 , as shown in  FIG. 14 . As a result of this upward movement, the shorted leg  130  of the lockout  104  that previously was adjacent the generator mains breaker handle  74  is also moved upward away from the switch handle  74 . Similarly, the base  126  of the lockout  104  slides upward and is positioned adjacent the generator mains neutral switch handle  76 . In this position, the base  126  blocks the switch handle  76  from being moved back to its OFF position, which because of the interlinking of the neutral switches  54  and  76 , also prevents the utility mains neutral switch  54  from being switched to the ON position. 
     In step  5 , shown in  FIG. 15 , the generator mains breaker handle  74  is switched from the OFF position to the ON position in the direction of arrow  154 . When the generator mains breaker handle  74  is switched to the ON position, the load center is then electrically connected to the generator power source. 
     One skilled in the art will appreciate that the interlock assembly  100  forces an operator to first switch OFF the utility mains breaker, then switch OFF the utility mains neutral switch, which causes the generator mains neutral switch to be switched to the ON position, and then switch ON the generator mains breaker to disconnect the load center  10  from the utility power supply and connect it to the generator power supply. The mechanical configuration of the interlock assembly  100  does not allow the sequence to be adjusted by the operator. In addition, one skilled in the art will appreciate that the steps described above are carried out in reverse to disconnect the load center from the generator power source and connect it to the utility power source. 
       FIG. 16  shows a lockout assembly  162  according to another embodiment of the invention. Similar to the lockout assemblies described previously, lockout assembly  162  sequences switching of a separately-derived transfer switch in a pre-defined and fixed order to electrically disconnect an electrical panel from a primary power source and electrically connect the electrical panel to an alternate or secondary power source, such as an electric generator, and vice-versa. The lockout assembly  162  will be described with respect to a transfer switch apparatus  164  consisting of a utility mains breaker or switch  166  having a switch handle  167 , and a generator mains breaker or switch  168  having a switch handle  169 , that are generally aligned with one another such that a breaker is in a conductive ON position when switched toward the other breaker. Conversely, a breaker is in a non-conductive OFF position when switched away from the other breaker. The utility mains breaker  166  and the generator mains breaker  168  are each double-pole breakers and, as such, each includes a pair of switch members tied together in a manner that is known. The transfer switch apparatus  164  also includes a utility neutral switch  170  having a switch handle  171 , and a generator neutral switch  172  having a switch handle  173 , that are interlinked together so that the switches switch in tandem, as will be described in greater detail below. 
     With additional reference to  FIG. 17 , the lockout assembly  162  is generally comprised of three separate lockout members  174 ,  176 , and  178  that are arranged to define the order by which the transfer switch apparatus can be switched between power sources. Lockout member  174  interlinks the neutral switch  170 ,  172  and generally includes brackets  180  and  182  that interface with neutral switches  170  and  172 , respectively. The brackets  180 ,  182  have a generally U-shape defined by a generally planar base  184 ,  186  and respective pairs of upturned walls  188 ,  190  and  192 ,  194 . Openings  196 ,  198  are formed in planar bases  184 ,  186  and are sized to receive the switch handles of neutral switches  170  and  172 , respectively. Additionally, openings  200 ,  202  are defined in upturned walls  190  and  194  of brackets  180  and  182 , respectively. A bridging plate  204  is fastened to the planar bases  184 ,  186  so as to interlink the two bases. Each switch handle  171 ,  173  is configured to receive a pin or dowel  206 ,  208  to prevent the planar bases  184 ,  186  and the bridging plate  204  from being removed from engagement with the neutral switches  170 ,  172 . In addition to interlinking planar bases  184 ,  186 , the bridging plate  204  is also used as an actuator. The bridging plate  204  has a depth that is sufficient to engage the switch handles when the neutral switches  170 ,  172  are being manually switched. More particularly, when one neutral switch is being switched to the ON position, the switch handle will press against the bridging plate  204  which will then push against the opposite switch thereby causing the other switch to follow the movement of the first-mentioned switch. When a neutral switch is being switched to an OFF position, the bridging plate will pull the bracket for the other neutral switch in the same direction thereby causing the other switch to switch in the same direction, e.g., to its ON position. The bridging plate  204  is fastened to the brackets  180  and  182  by a pair of fasteners  209 . 
     As further shown in  FIG. 17 , a support bar  210  is located in a channel  211  that extends between the utility mains and the generator mains breaker switch handles as well as the neutral switch handles. In this regard, the support bar  210  is located beneath brackets  180  and  182  of the neutral interlock  174  and does not interfere with operation of the neutral interlock  174  or the neutral switches  170 ,  172 . A pair of posts  212 ,  214  extend upwardly from the support bar  210  and are generally aligned with one another. A base bar  216  is oriented transversely to the support bar  210  and sits atop the support bar  210  so as to pass through gaps  218  and  220  formed between the tied-together switch handles of the utility mains breaker  166  and the generator mains breaker  168 , respectively. 
     An alignment plate  222  having a pair of holes  224 ,  226  is positioned atop the base bar  216  and the support bar  210  with the posts  212 ,  214  received by holes  224  and  226 , respectively. A screw  228 , or suitable fastener, interconnects the support bar  210 , base bar  216 , and the alignment plate  222 . Lockout member  176 , which includes a slide  230 , is positioned atop the alignment plate  222  and lockout member  178 , which includes a slide  232 , is positioned atop slide  230 . Slide  230  includes an elongated channel  234  that receives posts  212  and  214  and, similarly, slide  232  has an elongated channel  236  that also receives posts  212  and  214 . In this regard, channels  234  and  236  are generally aligned with one another when the lockout assembly  162  is assembled. A retention plate  238  is used to secure the slides  230  and  232  in place, but does so in a manner that allows longitudinal displacement of the slides but prevents lateral displacement of the slides, as will be described. Plate  238  has a pair of holes  240  and  242  that are within the footprint of channels  234  and  236  and align with posts  212  and  214 , respectively. A pair of fasteners  244  and  246  may then be used to secure the retention plate  238  to the posts  212  and  214  without impacting the slidability of the slides  230  and  232 . 
     Slides  230  and  232  each have a protruding tab  248  and  250 , respectively, that is designed to be received in a respective one of the openings  200 ,  202  of brackets  180 ,  182 . When a slide is moved such that its tab is inserted into and received by one of the aforementioned openings, the neutral switches cannot be switched. That is, the slides are permitted to slide longitudinally about posts  212 ,  214  but cannot move laterally. In this regard, the slides prevent lateral movement of the brackets  180 ,  182  when engaged therewith by tabs  248 ,  250 . Each slide  230 ,  232  also includes a leg  252  and  254 , respectively. The legs  252 ,  254  extend along axes that are perpendicular to that of the tabs and are designed to block switching of the utility mains breaker  166  and the generator mains breaker  168 , respectively, as will be described. 
     With reference now to  FIGS. 18 through 23 , the aforedescribed lockout assembly  162  and its lockout members  174 ,  176 , and  178 , sequences manual switching of the neutral switches and the mains breakers. More particularly, the lockout assembly  162  is designed and the lockouts  174 ,  176 , and  178  are arranged such that the loads on the transfer switch may be disconnected from one power source and connected to another power source in five separate and unalterable steps or sequences. 
     In  FIG. 18 , the utility mains breaker switch handle  167  and the utility neutral switch handle  171  are in the conductive or ON position whereas the generator mains breaker switch handle  169  and the generator neutral switch handle  173  are in the non-conductive or OFF positions. With the switch handles in these positions, the tab  250  of slide  178  is received in opening  200  formed in the upturned wall  190  of bracket  180 . When the opening  200  is aligned with tab  250  so that tab  250  may be received in the opening  200 , opening  202  formed in the upturned wall  194  of bracket  182  is positioned out of alignment with tab  248  of slide  176 . Moreover, the tab  248  is aligned with a solid portion of the upturned wall  194  adjacent the opening  202 . As a result, tab  248  cannot be slid upward. Since the tab  248  cannot be slid upward, the leg  252  of slide  176  cannot be moved to clear switch handle  169 . As such, the leg  252  blocks switching of switch handle  169  to the ON position. Additionally, with the tab  250  received within opening  200 , the neutral switch handles  171  and  173  cannot be switched. As noted above, the switch handles  171 ,  173  are interlinked and therefore move in tandem during a switching action. It will thus be appreciated that with the lockout members  174 ,  176 , and  178  positioned in the orientations shown in  FIG. 18 , the only permitted switch movement is switching of utility mains breaker  166  and, more particularly, switching of switch handle  167  away from switch handle  169  in the direction represented by arrow  256  to the OFF position, as shown in  FIG. 19 . 
     As shown in  FIG. 19 , when the utility mains breaker  166  is switched to the OFF position (step  1 ), the leg  254  of slide  178  is no longer blocked by the switch handle  167  and, as such, the slide  178  may be slid downward in the direction of arrow  258  to withdraw tab  250  from opening  200  (step  2 ), as shown in  FIG. 20 . With the slide  178  slid downward to withdraw tab  250  from opening  200 , movement of the brackets  180 ,  182 , and thus neutral switches  170 ,  172 , is no longer prevented by slide  178 . As such, the neutral switch handle  171  may be moved in the direction of arrow  260  to the OFF position (step  3 ). Since the neutral switch handles  171 ,  173  are interlinked by the aforedescribed lockout  174 , switch handle  173  follows movement of switch handle  171  in the direction of arrow  260  to the ON position, as shown in  FIG. 21 . Preferably, the neutral switches and the neutral lockout are constructed such that when a switch handle is moved to the OFF position, the opposite switch handle moves to the ON position in tandem but is placed in the ON position slightly after the switch handle is in the OFF position. In this regard, a neutral switch handle is not placed in the ON position until after the opposite neutral switch handle is in the OFF position. 
     As a result of the switching of the mains neutral switch handle  171  to the OFF position and the generator neutral switch handle  173  to the ON position, opening  202  of bracket  182  will align with tab  248  of slide  176 . As such, slide  176  may be slid upward in the direction of arrow  262  (step  4 ) to insert tab  248  into opening  202 , as shown in  FIG. 22 . When the tab  248  is inserted into the opening  202 , the neutral switches  170 ,  172  cannot be moved. Movement of the slide  176  upward also moves its leg  252  upward to free the generator mains breaker  168  so that its switch handle  169  can be moved in the direction of arrow  264  from the OFF position to the ON position (step  5 ) as shown in  FIG. 23 . 
     One skilled in the art will appreciate that the interlock assembly  162  forces an operator to first switch OFF the utility mains breaker, then switch OFF the utility mains neutral switch, which causes the generator mains neutral switch to be switched to the ON position, and then switch ON the generator mains breaker to disconnect the load center  10  from the utility power supply and connect it to the generator power supply. The mechanical configuration of the interlock assembly  162  does not allow the sequence to be adjusted by the operator. In addition, one skilled in the art will appreciate that the steps described above are carried out in reverse to disconnect the load center from the generator power source and connect it to the utility power source. 
     While the embodiments of the invention have been shown and described in connection with manual movement of the various components, it should also be understood that movement of some or all of the components may be accomplished using conventional actuating devices. 
     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.