Patent Publication Number: US-8110759-B2

Title: Electrical panel input interlock assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. Ser. No. 11/759,063, filed Jun. 6, 2007 now U.S. Pat. No. 7,531,762 and now allowed, which claims the benefit of U.S. Ser. No. 60/804,016, filed Jun. 6, 2006, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to electrical panels and, more particularly, to a power supply or input interlock assembly constructed to electrically isolate different inputs connected to an electrical panel. 
     Electrical panels, breaker boxes, or load centers frequently include a main contactor, switch, or breaker, which electrically isolates a series of load breakers from a primary or utility power input. Occasionally, such load panels are configured to receive another input power source, such as from a generator, to provide electrical power to the individual loads in the event of a primary power failure. During interruption of primary power, the generator supplies power to the load center, which the load center distributes to the selected or designated circuits of the building. Before activating the generator power supply, the main switch must be disconnected or turned “OFF” to prevent the generator power from back-feeding through the primary power supply conductors. A user must manually configure the switches of the load center to electrically connect the generator power with the series of loads and electrically isolate the primary power from the generator power, and vice-versa. In order to maintain electrical isolation between the generator power input and the primary power input, the connection/disconnection of the primary power supply and generator power supply must be performed in a specific sequence to ensure electrical isolation of the respective input powers. An interlock system has been developed for carrying out this function, and is shown and described in Flegel U.S. Pat. No. 6,621,689 issued Sep. 16, 2003, the disclosure of which is hereby incorporated by reference. While the system shown in the &#39;689 patent controls operation of a main power supply ON/OFF switch and an auxiliary power supply ON/OFF switch, it contains no provisions for controlling operation of neutral switches associated with the main and auxiliary power supplies. 
     When a bonded neutral generator is connected to the wiring system of a building, the grounding conductor and the neutral conductor are connected in two places within the system. This allows for the return of current back to the generator to flow on both the grounding conductor and on the neutral conductor. Having normal current flow on the grounding conductor limits the ability of the grounding conductor to perform its safety function, and is therefore undesirable. Switching the neutral conductor(s) when switching the power supply conductors prevents any neutral current from flowing on the grounding conductor. Furthermore, it is important to control the sequence of operation of the generator and primary power supply neutral switches when switching between power sources, since supplying power to a device without a neutral may result in failure of the device due to an unpredictable voltage being supplied to the device. To prevent this occurrence, the switching sequence is as follows when switching from main primary power to generator power:
         1. Turn off main power;   2. Turn off main neutral;   3. Turn on generator neutral;   4. Turn on generator power.
 
This sequence is reversed when switching from generator power to primary power.
       

     For the above reasons, it is desirable to provide an input interlock assembly that ensures electrical isolation of the primary power and the generator power during a transfer of the input power from one source to another, and which controls the sequence of operation of neutral switches associated with the primary and generator power supplies. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a main power switch interlock assembly that prevents inadvertent simultaneous electrical connection of both a primary or utility power input and an input from an alternate power supply, such as a generator, to a breaker panel, and controls actuation of primary and alternate power supply neutral switches. 
     A system and method of controlling operation of a plurality of electrical panel switches includes an assembly having an interlock. The interlock has a first position that allows power to be supplied to the electrical panel from one power source, such as primary power or an alternate power supply such as a generator, and prevents the supply of power to the electrical panel from the other power source. The interlock also includes a feature that controls movement of neutral switches associated with the alternate power supply and primary power inputs to ensure that the neutral connection of the alternate power supply is ON when the alternate power supply is activated, and that the alternate power supply neutral connection is OFF and the primary neutral is ON when the primary power supply is activated. 
     Various other features, objects and advantages of the present invention will be made apparent from the following detailed description of the drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate one preferred embodiment presently contemplated for carrying out the present invention. 
       In the drawings: 
         FIG. 1  is a perspective view of an exemplary load center assembly having one embodiment of an interlock assembly according to the present invention; 
         FIG. 2  is an elevational view of the load center assembly shown in  FIG. 1  with the interlock assembly configured to enable the supply of primary power to the loads interconnected with the load center assembly; 
         FIG. 3  is an elevational view of the load center assembly shown in  FIG. 2  with the primary power and alternate power disconnected from the loads interconnected with the load center assembly; 
         FIG. 4  is an elevational view of the load center assembly shown in  FIG. 3  with the interlock assembly configured to enable a pair of neutral switches to switch OFF the primary power supply neutral and switch ON the generator neutral; 
         FIG. 5  is an elevational view of the load center assembly of  FIG. 4  showing movement of a switch associated with the alternate power input connected to the loads interconnected with the load center assembly; 
         FIG. 6  shows the load center assembly of  FIG. 1  with the cover removed therefrom; 
         FIG. 7  shows the load center assembly of  FIG. 1  with the switches positioned such that primary power is isolated from the load terminal bars and power from the alternate power supply is connected thereto; 
         FIG. 8  is an elevational view of a load center assembly equipped with another embodiment of an interlock assembly according to the invention; 
         FIG. 9  is an elevational view of the load center assembly shown in  FIG. 8  with the switches positioned such that primary power and power from the alternate power supply are both isolated from the load terminal bars and the primary power supply neutral ON and the alternate power supply neutral OFF; 
         FIG. 10  is an elevational view of the load center assembly shown in  FIG. 9  with the switches and interlock assembly configured to prevent connection of primary power to the load terminal bars and allow connection of alternate power thereto; 
         FIG. 11  is an elevational view of the load center assembly shown in  FIG. 10  with the switches and interlock assembly positioned such that alternate power is communicated to the load terminal bars and the primary power supply neutral OFF and the alternate power supply neutral ON; 
         FIG. 12  is an isometric view of an interlock assembly for use with a transfer switch designed to control connection of a load center to a primary power supply and an alternate power supply according to another embodiment of the invention; 
         FIG. 13  is an elevation view of the interlock assembly of  FIG. 12  positioned such that primary power may be communicated to the load center; 
         FIG. 14  is an elevation view of the interlock assembly of  FIG. 12  positioned such that the primary power supply and the alternate power supply are both isolated from the load center; 
         FIG. 15  is an elevation view of the interlock assembly of  FIG. 12  positioned such that a primary power supply neutral switch is in the OFF position and an alternate power supply neutral switch is in the ON position; and 
         FIG. 16  is an elevation view of the interlock assembly of  FIG. 12  positioned such that alternate power may be communicated to the load center. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       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 supply, such as utility power, and an alternate or secondary power source which is adapted to supply power in the event power from the primary power supply is unavailable. Typically, the alternate or secondary power source is an electrical 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 the 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. 
     Load center assembly  10  includes a cover  12  having a door  14  pivotably connected thereto. Cover  12  includes a series of knockouts  16  constructed to be removed as load breakers are added to load center assembly  10 . A main switch  18  passes through cover  12  and is constructed to be connected to a primary power input. A generator neutral switch  20 , generator switch  21 , and a primary power supply neutral switch  22  are constructed to be electrically connected to load center assembly  10 . An interlock assembly  24  is connected to load center assembly  10  and prevents the inadvertent connection of the primary power input via main switch  18  and generator power input via generator switch  21  from being concurrently connected to a the load terminals of load center assembly  10 . As will be explained, interlock assembly  24  also controls the movement of neutral switches  20  and  22  relative to main switch  18  and generator switch  21 , to ensure that the switches are actuated in the correct sequence. 
       FIG. 2  shows load center assembly  10  with interlock assembly  24  configured to enable the supply of primary power via main switch  18  such that the loads connected to load center assembly  10  are powered by primary power. Interlock assembly  24  is positioned to prevent the connection of generator power communicated via generator switch  21  to the load terminal bars of load center assembly  10 , by preventing movement of generator switch  21  to the ON position. Interlock assembly  24  includes a first movable interlock  26  and a second movable interlock  28 , the operation of which are described in  FIGS. 2 through 7 . 
     Referring to  FIG. 3 , during interruption of primary power, a user translates switch handle  30  of main switch  18  from an ON position  32 , as shown in  FIG. 2 , to the OFF position  34 , as shown in  FIG. 3 . Such manipulation electrically isolates the load terminals and generator switch  21  from primary power conductors connected to main switch  18 . With switch  18  positioned in OFF position  34 , movable interlock  26  is manually translated upwardly in the direction of arrow  36  (shown in  FIG. 4 ), thereby preventing movement of handle  30  away from the OFF position  34  and locking handle  30  OFF (shown in  FIG. 4 ). A tab  38  of interlock  26  also moves in direction  36  and passes behind an interlock assembly retainer plate  40 . Prior to movement of interlock  26  in direction  36 , tab  38  extends into the throw of a switch handle  42  of generator neutral switch  20 . Accordingly, prior to movement of interlock  26  in direction  36 , tab  38  prevents the movement of generator neutral switch  20  away from the generator neutral OFF position. Because generator neutral switch handle  42  and the switch handle  44  of primary power supply neutral switch  22  are interconnected for linear movement together by an inline interlock assembly  46 , tab  38  also prevents the movement of primary power supply neutral switch  22  away from the primary neutral ON position. 
     As shown in  FIG. 4 , translation of interlock  26  in direction  36  relative to interlock assembly plate  40  obstructs handle  30  of main switch  18 , thereby preventing primary power from being communicated to the load terminal bars of load center assembly  10 . At the same time, tab  38  translates in direction  36  behind interlock assembly plate  40  and out of the way of the throw of handle  42  of generator neutral switch  20 . Accordingly, when handle  30  of main switch  18  is located in OFF position  34 , generator neutral switch  20  can be moved to the ON position by translation of handle  42 . Due to the presence of inline interlock assembly  46  between switch handle  42  and switch handle  44  of generator neutral switch  20  and primary power supply neutral switch  22 , respectively, generator neutral switch  20  is operable to an ON position and primary power supply neutral switch  22  is moved to an OFF position, represented as position  48  as shown in  FIG. 4 . This connects the generator neutral to a neutral bar of load center assembly  10  common to switches  20  and  22 . 
     Representatively, inline interlock assembly  46  may have a construction as is shown and described in Flegel U.S. Pat. No. 6,031,193 issued Feb. 29, 2000 or Flegel U.S. Pat. No. 6,927,349 issued Aug. 9, 2005, the disclosures of which are hereby incorporated by reference. 
     Referring to  FIG. 3  and  FIG. 4 , second interlock  28  is movable from a first position  52 , as shown in  FIG. 3 , to a second position  54 , as shown in  FIG. 4 , when generator neutral switch handle  42  is in the ON position and primary power supply neutral switch handle  44  is in the OFF position. As shown in  FIG. 3 , when second interlock  28  is located in first position  52 , interlock  28  obstructs the operation of a switch handle  56  of generator switch  21 . Also, interlock  28  is prevented from moving by a post  55  of interlock assembly  46 . When second interlock  28  is allowed to be moved to second position  54  by the change in position of interlock assembly  46 , as shown in  FIG. 4 , a switch handle  56  of generator switch  21  is operable to connect the generator power input to the input of load center assembly  10 . Accordingly, when switch handles  30 ,  42 ,  44 , and  56  are oriented in the positions as shown in  FIG. 5 , load center assembly  10  is electrically connected to a generator power input and electrically isolated from a primary power input, and the generator neutral is connected to the neutral of load center assembly  10 . Furthermore, interlock assembly  24  prevents the reconfiguration of switches  18 ,  20 ,  22 , and  21  to such an orientation wherein generator power and primary power are concurrently delivered to the load terminal bars of load center assembly  10 . As such, interlock assembly  24  is constructed to sequence the operation of switches  18 ,  20 ,  22 , and  21  and thereby control and segregate the input power delivered to the load terminal bars of load center assembly  10  relative to the neutral connections of the primary and generator power supplies. 
     As shown in  FIG. 6 , removal of cover  12  from load center assembly  10  exposes a series of terminal bars  58  located therebehind. Terminal bars  58  include a first and a second neutral bar  60 ,  62  and a first and a second hot lead terminal bar  64 ,  66 , respectively. A neutral connector plate  68  extends behind interlock assembly  24  and electrically connects first neutral bar  60  and second neutral bar  62 . Generator neutral switch  20  is electrically connected to neutral connector plate  68 , as is primary power supply neutral switch  22 . Generator switch  21  is electrically connected to hot terminal bars  64  and  66 . 
     Main switch  18  includes a first input terminal  70  and a second input terminal  72  constructed to be electrically connected to a primary power conductor connected to load center assembly  10 . When switch handle  30  of main switch  18  is positioned in an ON position, as shown in  FIG. 6 , primary power communicated to input terminal  70  and input terminal  72  is communicated through main switch  18  to hot terminal bar  64  and hot terminal bar  66 , thereby communicating primary power to the load breakers connected to load center assembly  10 . Referring to  FIG. 7 , switch handle  30  of main switch  18  is moved to an OFF position, thereby electrically isolating input terminal  70  and input terminal  72  of main switch  18  from hot terminal bars  64 ,  66 . Movement of first interlock  26  of interlock assembly  24  prevents switch handle  30  from being moved to an ON position and translates tab  38  of interlock assembly  24  such that switch handle  42  of generator neutral switch  20  is free to be moved to an ON position, which also results in movement of switch handle  44  of primary power supply neutral switch  22  to an OFF position. Translation of second interlock  28  relative to interlock assembly  46  allows switch handle  56  of generator switch  21  to be moved to an ON position. In this manner, generator switch  21  is connected to hot terminal bars  64  and  66  and the generator neutral switch  20  is connected to neutral bars  60  and  62  via neutral connector plate  68 . Accordingly, when switch handles  30 ,  42 ,  44 , and  56  are oriented in the positions shown in  FIG. 7 , generator power is communicated through generator switch  21  to hot terminal bars  64 ,  66  and generator neutral is communicated through generator neutral switch  20  to neutral plate  68 , thereby electrically connecting loads connected to either of first hot terminal bar  64  or second hot terminal bar  66  to the generator-provided input power associated with generator switch  21 . This also isolates primary power supply neutral from generator neutral and thus, the neutrals cannot be switched back unless generator and primary supply switches are both OFF. Generator power delivered to load center assembly  10  and communicated to hot terminal bar  64  and hot terminal bar  66  is electrically isolated from primary power supply input terminals  70 ,  72  of main switch  18 . Interlock assembly  24  prevents the concurrent electrical connection of generator switch  21  and main switch  18  with hot terminal bars  64 ,  66 . Such a construction electrically isolates primary power supply input terminals  70  and  72  from hot terminal bars  64 ,  66  when generator power is supplied, thereby preventing communication of generator-derived power beyond load center assembly  10  via primary power supply conductors connected thereto. 
       FIG. 8  shows another breaker box assembly or load center  78  according to another embodiment of the present invention. Load center  78  includes an alternate embodiment of an interlock assembly  80  according to the present invention. Interlock assembly  80  is disposed between a primary power supply or main switch  82  and a series of switches mounted to load center  78 . Main switch  82  includes a first input terminal  86  and a second input terminal  88  constructed to be electrically connected to primary power conductors, respectively. A switch  82  electrically connects input terminals  86 ,  88  with hot terminal bars  92 ,  94 . Interlock assembly  80  includes a movable interlock  96  that has a tab  98  extending therefrom. Tab  98  extends into a throw of a switch handle  100  of generator neutral switch  102 , thereby preventing movement of generator neutral switch handle  100  when tab  98  is so positioned. 
     An inline interlock assembly  104  extends between generator neutral switch handle  100  and a switch handle  106  of a primary power supply neutral switch  108  such that generator neutral switch handle  100  and primary power supply neutral switch handle  106  are operatively associated such that neither switch can be independently moved. A bracket  110  is connected to connector assembly  104  and disposed between switch handle  100  and switch handle  106 . Bracket  110  includes a first extension  112 , which interferingly engages another tab  114  of interlock  96 . First extension  112  and tab  114  are associated to allow movement of interlock  96  into a space  116  formed between first extension  112  and switch handle  100  of generator neutral switch  102 . Such an orientation ensures a snug engagement therebetween, thereby preventing movement of switch handle  100  or switch handle  106  relative to interlock  96  when tabs  98 ,  114  are disposed in space  116 . 
     Bracket  110  includes a second extension  118 , which extends in a direction generally opposite the direction of extension of first extension  112 . Second extension  118  is operatively connected to a switch handle  120  of a generator switch  122 . Generator switch  122  is electrically connected to hot terminal bars  92 ,  94 . Neutral switches  102  and  108  are electrically connected to neutral bar  60  and  62  via neutral connector plate  68 . Accordingly, regardless of which side of load center  78  load circuits are connected, generator power can be utilized to power any desired load connected to load center  78 . 
     As shown in  FIG. 9 , switch handle  90  of main switch  82  is located in an OFF position, thereby electrically isolating hot terminal bars  92 ,  94  from the primary power connected to input terminals  86  and  88  of load center  78 . Positioning of switch handle  90  in the OFF position allows interlock  96  to be moved in a direction, indicated by arrow  124  (shown in  FIG. 10 ), toward switch handle  90 . As interlock  96  moves in direction  124 , tabs  98 ,  114  translate therewith and out of interfering engagement with switch handles  100 ,  106  and  120 . 
     As shown in  FIG. 10 , when switch handle  90  is located in an OFF position and interlock  96  is displaced in direction  124 , interlock  96  prevents switch handle  90  from being moved to the ON position. Accordingly, when interlock  96  is oriented in the position shown in  FIG. 10 , switch  82  is configured to electrically isolate the primary power input terminals  86 ,  88  from hot terminal bars  92 ,  94 , thereby electrically isolating primary power supply conductors connected to inputs  86 ,  88  from generator power communicated to hot terminal bars  92 ,  94 . Furthermore, as shown in  FIG. 10 , when interlock  96  is positioned to obstruct handle  90 , tabs  98 ,  114  translate in direction  124  and pass behind a cover plate  126  of interlock assembly  80 . Switches handles  100 ,  106 ,  120  are interconnected via bracket  110  such that, when interlock  96  is translated in direction  124 , as shown in  FIG. 10 , movement of any of switch handles  100 ,  106 ,  120  in a transverse direction, indicated by arrow  128 , electrically connects generator input power from generator switch  122  to hot terminal bars  92 ,  94 , respectively, and connects the generator neutral switch  102  to neutral bar  60 . The connection of generator switch handle  120  to bracket  110  is positioned such that, as bracket  110  is translated laterally, the primary power supply neutral switch handle  106  is first moved OFF and the generator neutral switch handle  100  is moved ON, before generator switch handle  120  is moved ON. Similarly, the generator switch handle is turned OFF before the generator neutral is switched OFF. This ensures proper sequence of operation of the switches as the supply of power from utility to generator is transferred. 
     As shown in  FIG. 11 , bracket  110  has been translated in direction  128 , thereby moving switch handles  100 ,  106 ,  120  to an ON position, and electrically connecting generator power communicated to generator switch  122  to hot terminal bars  92 ,  94  and connecting generator neutral switch  102  to neutral bars  60 ,  62 . Furthermore, when generator power is communicated through generator switches  122  to hot terminal bars  92 ,  94 , movable interlock  96  of interlock assembly  80  prevents the electrical connection of primary power supply power input terminals  86 ,  88  of primary power supply switch  82  with hot terminal bars  92 ,  94 , thereby electrically isolating input terminals  86  and  88  from power communicated to load center  78  via the primary power source. Understandably, to convert load center  78  from primary power supply-derived power to generator-derived power, a user must simply orient handle  90  of main switch  82  in the OFF position, translate interlock  96  in direction  124 , and translate switch handles  100  and  120  to an ON position, thereby electrically connecting the generator-type power to hot terminal bars  92 ,  94  and the neutral to neutral bars  60 ,  62 . Such a configuration allows a user to conveniently and expeditiously configure load center  78  to power desired loads from a desired input power supply. 
       FIGS. 12-16  illustrate an interlock assembly according to another embodiment of the invention. Like the interlock assembly described with respect to  FIGS. 1-11 , interlock assembly is designed to prevent a load center assembly from being electrically connected to receive power from two power supplies simultaneously.  FIGS. 12-13  show a portion of a load center assembly  130  with interlock assembly  132  configured to enable the supply of primary power via primary power supply switch  134  such that the loads of the load center assembly  130  are powered by primary power. Interlock assembly  132  is positioned to prevent the connection of generator power communicated via generator switch  136  to the load center assembly  130 , by preventing movement of generator switch  136  to the ON position. The interlock assembly  132  also interfaces with primary power supply neutral switch  138  and alternate power neutral switch  140  to prevent both switches  138 ,  140  from being in the ON position simultaneously. The neutral switches  138 ,  140  are aligned with one another with a switch being in the ON position when thrown toward the other switch. Thus, in  FIGS. 12-13 , the primary power supply neutral switch  138  is in the ON position and the alternate power neutral switch  140  in the OFF position. As will be described more fully below, the interlock assembly  132  includes a first movable interlock  142 , a second movable interlock  144 , and an inline neutral interlock  146 . 
     The primary power supply switch  134  is comprised of a pair of breakers  148 ,  150 , each having switch handles  152 ,  154 , respectively, that are tied together in a known manner by member  156 . Similarly, the alternate power switch  136  is comprised of a pair of breakers  158 ,  160 , each having switch handles  162 ,  164 , respectively, that are tied together in a known manner by member  166 . Neutral switches  138  and  140  similarly include respective switch handles  168  and  170 .  FIG. 12  shows the arrangement of the interlock assembly  132  as well as the switches  134 ,  136 ,  138 , and  140  when the load center is operative to receive power from the primary power supply, e.g., utility grid, and is electrically isolated from the alternate power supply, e.g., electric generator. 
     Interlock  142  has a generally planar and slotted body  172  designed to slide along pins  174 ,  176 . The body  172  has an upper portion  178  from which a leg member  180  downwardly extends. As shown in  FIG. 13 , the leg  180  is spaced from the slotted body  172 . The upper portion  178  as well as the leg  180  sit beneath a portion of the inline interlock  146 . Interlock  144  also has a planar and slotted body  182  that is designed to slide along pins  184 ,  186 . The body  182  has a lower portion  188  from which a leg  192  axially extends and an upper portion  191 . As will be described more fully below, when the body  182  is slid fully upward, a portion of the body  182  will slide beneath the inline interlock  146 . The inline interlock  146  is generally comprised of a plate  194  that abuts against both switch handles  168  and  170 , and is designed to slide with movement of the switch handles  168 ,  170 . Interlocks  142  and  144  slide independently of one another but along generally parallel axes. 
     During interruption of primary power, a user translates switch handles  152 ,  154  of switch  134  from an ON position, as shown in  FIG. 13 , to the OFF position, as shown in  FIG. 14 . With switch  134  positioned in the OFF position, movable interlock  142  is manually translated downward in the direction of arrow  196  (shown in  FIG. 14 ). Leg  180  of interlock  142  thereby moves in direction  196  and passes behind switch handle  152 . Prior to movement of interlock  142  in direction  196 , upper portion  178  extends into the throw of switch handle  168  of primary power supply neutral switch  138 . Accordingly, prior to movement of interlock  142  in direction  196 , upper portion  178  prevents the movement of primary power supply neutral switch  138  away from the ON position. Because primary power supply neutral switch handle  168  and the switch handle  170  of alternate power neutral switch  140  are interconnected for linear movement together by the inline interlock  146 , upper portion  178  also prevents the movement of alternate power neutral switch  140  toward the alternate power neutral ON position. As shown in  FIG. 13-14 , when the primary power supply neutral switch  138  is in the ON position, the inline interlock  146  blocks upward movement of the movable interlock  144 . It will also be appreciated that the primary and alternate power switches can both be OFF but cannot both be ON at the same time. 
     Referring now to  FIG. 15 , when the interlock  142  is moved downward in direction  196 , the upper portion  178  of the interlock  142  is cleared from blocking movement of switch handle  168  of the primary power supply neutral switch  138 . In this regard, the neutral switch  138  can only be moved to its OFF position after the primary power supply switch  134  has been moved to its OFF position. Additionally, because the neutral switches  138 ,  140  are linked together by inline interlock  146 , the alternate power neutral switch  140  is automatically moved in direction  197  to its ON position when the primary power supply neutral switch  138  is moved to its OFF position. Preferably, switch  138  reaches its OFF position before switch  140  reaches its ON position, such as described in U.S. Pat. No. 6,031,193 or U.S. Pat. No. 6,927,349, the disclosures of which are hereby incorporated by reference. 
     When the primary power supply neutral switch  138  is thrown to its OFF position, the plate  194  of the inline interlock follows that movement and, in effect, moves to a position whereby upward movement of the interlock  144  is no longer blocked by the inline interlock  146 , as illustrated in  FIG. 15 . Thus, when the switch handles  152 ,  154  are thrown to the OFF position and the primary power supply neutral switch  138  is moved to the OFF position, interlock  144  may be slid upwardly in direction  198  along pins  184 ,  186  to clear alternate power switch  136  as shown in  FIG. 16 . As also illustrated in  FIG. 16 , the upper portion  191  slides beneath the inline interlock  146  to free switch  136 . In this position, interlock  144  prevents the inline interlock  146  from sliding and thus prevents the neutral switches  138 ,  140  from changing position and also blocks the primary power supply switch  134  from being switched ON. 
     When the interlock  144  is slid upward in the direction represented by arrow  198 , the switch handles  162 ,  164  of switch  136  may be thrown from the OFF position to the ON position. As a result, the load center assembly is now electrically isolated from the primary power supply and is connected to receive power from the alternate power supply. When primary power is restored, the switch sequence described above, is reversed to disconnect the load center assembly from the alternate power supply and connect it to the primary power supply. 
     It will thus be appreciated that the present invention provides an interlock assembly that sequences disconnection of the load center from a primary power supply and connection to an alternate power supply in a controlled manner to prevent the load center assembly from being electrically connected to both power supplies simultaneously. 
     It will also be appreciated that the inline interlock  146  described herein is designed to move the neutral switches  138 ,  140  in tandem such that one of the switches is always in the OFF position and the other one of the switches is always in the ON position. However, it is understood that the inline interlock could be constructed such that both neutral switches cannot be in the ON position at the same time, but that both neutral switches could be in the OFF position at the same time. Such an inline interlock is described in U.S. Ser. No. 12/509,779, the disclosure of which is incorporated herein. 
     Various alternatives are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.