Abstract:
A switching mechanism provides sequential switching of first and second circuit breakers to enable switching between a primary power supply and a backup power supply. The switching mechanism comprises an actuating mechanism to sequentially actuate a pair of circuit breakers. The actuator mechanism including a shock absorber to absorb energy due to switching of one of the first and second circuit breakers.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to transfer switches for switching between alternate power sources, such as commercial power supply lines and a local generator. 
   Many residents now have a stand-by power supply such as a gas-powered generator for use in homes and other buildings during power outages. Power from the local generator can be supplied to a main distribution panel or sub-panel through a transfer switch when a power outage occurs. The transfer switch disconnects the home or building from the commercial power supply lines and connects the home or building to the local generator. 
   The installation of a transfer switch typically requires the replacement of the main distribution panel in the home or building with a larger distribution panel to accommodate the transfer switch, or the installation of a separate sub-panel containing the transfer switch and additional circuit breakers. The cost of parts and labor to install a transfer switch can be prohibitively expensive to many persons. Another potential problem that can occur during installation is lack of space to accommodate an additional distribution panel if one is required. 
   A transfer switch that can be accommodated in an existing distribution panel of a home or building would eliminate much of the cost of installing a transfer switch in an existing home or building, and would not be precluded by space constraints. 
   SUMMARY OF THE INVENTION 
   The present invention provides a switching mechanism that can be installed in an existing electrical distribution panel of a home or building to actuate circuit breakers in a predetermined sequence. The switching mechanism in combination with the circuit breakers functions as a transfer switch. The device is simple in construction and easily installed into an existing distribution panel. 
   The switching mechanism comprises an actuating mechanism operatively engaged with the main circuit breaker and backup circuit breaker. The actuating mechanism includes a drive motor to drive the actuating mechanism. A shock absorber protects the drive motor from damage by absorbing shock caused by operation of the circuit breaker. A shock absorber may be used for only the main circuit breaker, or for both circuit breakers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a switching mechanism according to the present invention installed in an electrical distribution panel. 
       FIG. 2  is a close-up perspective view of the switching mechanism and two circuit breakers. 
       FIG. 3  is an exploded perspective view of the switching mechanism. 
       FIG. 4  is a top view of a support frame for the switching mechanism. 
       FIG. 5  is a top view of a support bracket for the switching mechanism. 
       FIG. 6  is a top view of two actuator plates for the switching mechanism. 
       FIG. 7  is a top view of the switching mechanism at the beginning of a switching cycle showing the main circuit breaker in an on position and the backup circuit breaker in an off position. 
       FIG. 8  is a top view of switching mechanism showing the main circuit breaker in the middle of its travel towards the off position and the backup circuit breaker in the off position. 
       FIG. 9  is a top view showing the switching mechanism in the middle of a switching cycle with both circuit breakers in an off position. 
       FIG. 10  is a top view of switching mechanism showing the main circuit breaker in the off position and the backup circuit breaker beginning its travel to the on position. 
       FIG. 11  is a top view of switching mechanism at the end of the switching cycle showing the main circuit breaker in the off position and the backup circuit breaker in the on position. 
       FIG. 12  is a top view of switching mechanism showing the main circuit breaker moved manually to an off position while the backup circuit breaker is in the off position. 
       FIG. 13  is a top view of switching mechanism showing the main circuit breaker moved manually to a reset position while the backup circuit breaker is in the off position. 
       FIG. 14  is a top view of the switching mechanism showing the backup circuit breaker manually moved to the off position while the main circuit breaker is in the off position. 
       FIG. 15  is an electrical diagram of a motor controller. 
       FIG. 16  is a top view of two actuator plates for an alternate embodiment of the switching mechanism. 
       FIG. 17  is an exploded perspective view of a shock absorber for the switching mechanism. 
       FIG. 18  is an end view of the shock absorber mounted to the switching mechanism. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1–3  illustrate a switching mechanism indicated generally at  10  installed in an electrical distribution panel  12 . The distribution panel  12  comprises a cabinet  14 , a back plane  16  with interior parts (not shown), and a plurality of circuit breakers  18  including a main circuit breaker  20 , a backup circuit breaker  30  and a number of branch circuit breakers  24 . The main circuit breaker  20  connects the electrical distribution panel  12  to commercial power supply lines. The backup circuit breaker  30  connects the electrical distribution panel  12  to a local generator. The branch circuit breakers  24  connect the various loads in the residence or building to the electrical distribution panel  12 . The switching mechanism  10  in combination with the main circuit breaker  20  and backup circuit breaker  22  function as a transfer switch. 
   The switching mechanism  10  comprises three main assemblies—a support assembly  100 , an actuator assembly  200 , and a drive assembly  300 . The support assembly  100  secures the switching mechanism  10  to the electrical distribution panel and provides support for the actuator assembly  200  and the drive assembly  300 . The actuator assembly  200  operates the main circuit breaker  20  and backup circuit breaker  30  such that power to the branch circuit breakers  24  can be switched between the commercial power supply and the backup power supply. The drive assembly  300  includes a drive motor  302  to drive the actuator assembly  200 . 
     FIGS. 3–5  illustrate details of the support assembly  100 . The support assembly  100  comprises a generally-planar support bracket  102  and a support plate  130 . The support bracket  102  secures the switching assembly to the electrical distribution panel  12 . The support bracket  102  includes a top plate  103  and support legs  150 . The support legs  150  extend generally perpendicularly from the top plate  103 . The outer end of each support leg  150  is bent at a 90° angle to form a support foot  152 . The support foot  152  includes a screw hole  154  to accept a mounting screw (not shown) for securing the support bracket  102  to the distribution panel  12 . The support plate  130  mounts on top of the support bracket  102  to provide a stable platform for the actuator assembly  200 . When mounted in a distribution panel  12 , the support plate  130  is oriented generally parallel to the back plane  16  of the distribution panel  12 . The support legs  150  provide the proper spacing from the back plane  16   
   The support bracket  102 , in addition to providing support for the switching assembly, also braces the main circuit breaker  20  and backup circuit breaker  30 . In the exemplary embodiment shown in the drawings, the support bracket  102  includes a large frame  104  that extends around the housing of the main circuit breaker  20 , and a smaller frame  106  that extends around the housing of the backup circuit breaker  30 . Frames  104  and  106  prevent the circuit breakers  20  and  30  from twisting or otherwise moving during operation. Additionally, frame  106  serves as a hold-down device to hold down the backup circuit breaker  30 . 
   The top plate  103  of the support bracket  102  includes clearance holes  108  and  110  for a motor shaft  306  and actuator shaft  254 , respectively. Threaded screw holes  112  for mounting the drive motor  302  surround clearance hole  108 . Similarly, threaded screw holes  114  for mounting an actuator shaft bearing  256  surround clearance hole  110 . Support bracket  102  further includes guide screw holes  116  to accept guide screws  120 . As will be explained in greater detail below, the guide screws  120  constrain the movement of the actuator assembly  200 . 
     FIG. 5  illustrates the support plate  130 . The support plate  130  comprises a steel plate that provides a platform for the actuator assembly  200 . The support plate mounts on top of the support bracket  102  and can be secured by screws or any other suitable fastening means. The top surface of the support plate  130  is flat. Clearance holes  132  and  134  provide openings for the motor drive shaft  306  and actuator shaft  254  respectively. An access opening  136  provides access to mounting screws used to secure the support bracket  102  to the distribution panel  12 . Guide screw holes  138  align with the guide screw holes  116  in the support bracket  102 . 
     FIGS. 2 and 6  illustrate details of the actuator assembly  200 . The actuator assembly  200  comprises a main actuator plate  210  operatively engaged with the main circuit breaker  20 , a secondary actuator plate  230  operatively engaged with the backup circuit breaker  30 , and a rotary actuator  250  to move the actuator plates  210  and  230  between on and off positions. The main actuator plate  210  includes a pair of spaced-apart fingers  212  defining a finger slot  214  to receive the toggle  22  of the main circuit breaker  20 . Similarly, the secondary actuator plate  230  includes a pair of spaced-apart fingers  232  defining a finger slot  234  to receive the toggle  32  of the backup circuit breaker  30 . As will be described in more detail below, the actuator plates  210  and  230  slide laterally in first and second directions on the surface of the support plate  130 . The fingers  212  and  232  apply force to respective toggles  22  and  32  to switch on and off the circuit breakers  20  and  30 . 
   Guide screws  120  extending through guide slots  216  and  236  in the actuator plates  210  and  230  respectively constrain and guide the movement of the actuator plates  210  and  230 . The guide slots  216  and  236  extend parallel to the direction of movement of the actuator plates  210  and  230 . Guide slots  216  and  236  are parallel to one another so that the actuator plates  210  and  230  move in parallel fashion. The guide screws  120  pass through the guide slots  216 ,  236  and thread into the guide screw holes  138  in the support plate and pass through the guide holes  116  in the support bracket  102 . 
   Access opening  218  in actuator plate  210  provides access to mounting screws used to secure the support assembly  100  to the electrical distribution panel  12  when it is aligned with the access opening  136  in the support plate  130 . Clearance opening  238  provides clearance for the motor shaft  306 . Clearance opening  238  is elongated in the direction of movement to accommodate the travel of the actuator plate  230 . Recesses  220  and  240  in the edges of actuator plates  210  and  230  respectively provide clearance for the actuator shaft  254 . 
   A rotary actuator  250  shown best in  FIGS. 2 and 3  moves the actuator plates  210  and  230  between on and off positions as the rotary actuator  250  rotates in first and second directions. The rotary actuator  250  comprises a rotor  252  mounted to one end of the actuator rotor shaft  254 . The outer edge of the rotor  252  includes gear teeth, which are engaged by the drive gear  304  to rotate the actuator  250 . Actuator shaft  254  extends downward between the actuator plates  210  and  230  and passes through openings  134  and  110  in the support plate  130  and support bracket  102  respectively. Actuator shaft  254  is journaled in a bearing  256  that mounts to the underside of the support frame  102  as shown in  FIG. 3 . A switch actuator  264  is attached to the lower end of the actuator shaft. As will be described in more detail below, switch actuator  264  actuates limit switches (not shown) that control operation of the actuator assembly  200 . 
   Actuator pins  258 ,  260 ,  262  extend from the underside of the rotor  252 . Actuator pin  258  moves within slots  222  and  242  in actuator plates  210  and  230 , respectively. Actuator pin  260  functions as a drive member and moves within slot  224  in actuator plate  210 . Actuator pin  262  functions as a drive member and moves within slot  244  in actuator plate  230 . The geometry of the slots  224  and  244 , along with the location of the actuator pins  260  and  262 , provide sequential switching of the circuit breakers  20  and  30  so that both circuit breakers  20  and  30  are both switched off before one is switched on. This sequential actuation of the circuit breakers  20  and  30  ensures that the branch circuit breakers  24  are momentarily isolated from both power sources when switching from one power source to the other. The actuator assembly  200  allows a user to manually switch circuit breakers  20  or  30  to the off position when the other circuit breaker  20  or  30  is in the off position. Thus, the user can simultaneously turn both circuit breakers  20  and  30  off. 
   The actuator assembly  200  also functions as a mechanical interlock mechanism that prohibits a circuit breaker  20  or  30  from being turned on when the other circuit breaker  20  or  30  is on. Additionally, the actuator  250  is mechanically locked when one of the circuit breakers  20  and  30  is manually turned off or if a breaker is tripped. Thus, the user is required to manually turn on the circuit breaker  20  or  30 , that was manually turned off, or to reset the tripped circuit breaker before automatic operation of the rotary actuator  250  can resume. These locking features prevent the user from inadvertently connecting the electrical distribution panel  12  to both the main and backup power sources at the same time, as well as preventing the drive motor  302  from operating the locked mechanism. 
   The drive assembly  300  comprises a drive motor  302 , a drive gear  304  and motor controller  310 . The drive motor  302  mounts to the underside of the support bracket  102  and is supported thereby. The motor shaft  306  passes through the clearance holes  108 ,  132  and  238  in the support bracket  102 , support plate and actuator plate  230  respectively. The motor shaft  306  connects to a drive gear  304 , which engages the periphery of the rotor  252 . Alternatively, the drive motor  302  could directly drive the actuator  250 . One advantage of the drive gear  304 , however, is that through proper gearing a mechanical advantage is realized that allows use of a smaller and less expensive drive motor  302 . 
   When installed in the distribution panel  12 , the drive motor  302  occupies a space that would otherwise be used by branch circuit breakers  24 . To install the switching mechanism  10 , two branch circuit breakers  24  are removed to make space for the drive motor  302 . Although two branch circuit breakers  24  are sacrificed in this arrangement, locating the drive motor  302  as shown herein allows the switch assembly  10  to be mounted within most existing distribution panels  12  currently in use in residential or light commercial construction. Therefore, there is no need to replace the existing distribution panel  12  or to add a sub-panel to install the switching mechanism  10 . Furthermore, the two sacrificed branch circuit breakers can easily be replaced by using commercially available tandem circuit breakers. 
     FIG. 15  illustrates a motor controller  310  for controlling operation of the drive motor  302 . The motor controller  310  is configured to reduce the speed of the drive motor  302  as the actuator plates  210  and  230  reach the limit of their travel. There are two branches in the motor controller circuit. The first branch includes diodes D 1 , D 3 , D 5 , resistor R 1 , and limit switch S 2 . The second branch includes diodes D 2 , D 4 , and D 6 , resistor R 2 , and limit switch S 1 . The motor controller  310  dynamically breaks but does not stop the drive motor  302  when one of the limit switches S 1 , S 2  is tripped. Consequently, the speed of the drive motor  302  is reduced as the actuator plates  210 ,  230  approach their mechanical limits. The breaking is produced by shunting the drive motor  302  with a couple—schottky diodes/zener diode—with a voltage significantly lower than the rated motor voltage. Resistors R 1  and R 2  provide bias current to keep voltage on the zener diode so the drive motor  302  continues to operate at a low speed. For example, a 3.6 volt zener diode connected to a 24 volt rated motor quickly slows down to approximately 10% of its full speed. The second branch in the controller circuit allows the drive motor  302  to operate at full speed in the opposite direction if necessary. A current sensor (not shown) can sense the current in the controller circuit and shut off power to the drive motor  302  when the mechanical limits are reached. 
     FIGS. 7–14  illustrate the operation of the actuator assembly  200 .  FIG. 7  illustrates actuator plate  210  in an on position, while actuator plate  230  is in an off position. Thus, main circuit breaker  20  is switched on while the backup circuit breaker  30  is switched off. In this position, the engagement of the actuator pins  262  and  258  in slots  244  and  242  respectively prevent the actuator plate  230  from moving from the off position. Thus, the actuator assembly  200  provides a mechanical interlock preventing circuit breaker  30  from being switched on while circuit breaker  20  is on. To switch from the commercial power supply to the local generator, the rotary actuator  250  is rotated counterclockwise from the starting position shown in  FIG. 7  to the ending position shown in  FIG. 11 . 
   In  FIG. 8  the main circuit breaker is in the middle of its travel to the off position and the backup circuit breaker is in the off position. Actuator pin  260  on the rotary actuator  250  has moved up into a drive portion  224   b  of the slot  224 . The actuator pin  260  applies force against the sidewall of the slot  224  as the actuator  250  turns to move the actuator plate  210  to the left. Actuator pin  262  is traveling through a clearance portion  244   a  of slot  244  that allows free movement of the actuator  250  while actuator plate  230  remains stationary. Actuator pin  258  is engaged in slot  242  to prevent movement of actuator plate  230 . The main circuit breaker  20  is in the middle of its travel to the off position, while the backup circuit breaker  30  remains in the off position. Thus, the switching mechanism  10  provides a mechanical interlock preventing circuit breaker  30  from being switched on while circuit breaker  20  is on. 
   In  FIG. 9 , the actuator plate  210  has moved the main circuit breaker  20  to the off position. Actuator pin  260  on the actuator  250  is now moving into the clearance portion  224   a  of slot  224 . Actuator pin  258  has moved out of slot  242  so that actuator plate  230  can now move to the right. Actuator plate  210  will remain stationary while the actuator  250  turns because the actuator pin  260  is in the clearance portion  224   a  of slot  224 . Actuator pin  262  is moving into the drive portion  244   b  of slot  244 . At this point, any further counterclockwise rotation of the actuator  250  will move actuator plate  230  to the right. 
   In  FIG. 10 , the main circuit breaker  20  is off and the backup circuit breaker  30  is in the middle of its travel to the on position. The actuator pin  260  is moving downward in the clearance portion  224   a  of slot  224  so that actuator plate  210  is stationary. Actuator pin  262  is pushing against the sidewall of the slot  244  to move the actuator plate  230  to the right. Actuator pin  258  is moving upward in slot  222 . 
   In  FIG. 11 , the main circuit breaker  20  is in the off position and the backup circuit breaker  30  is in the on position. Actuator pin  260  prevents the actuator plate  210  from being moved to the right while the actuator plate  230  is in the on position. Thus, the actuator assembly provides a mechanical interlock preventing circuit breaker  20  from being switched on while circuit breaker  30  is on. 
   When switching in the opposite direction, the actuator rotates in a clockwise direction and the process described above is reversed. Actuator plate  230  is initially moved to the off position by the actuator pin  262 . Once the actuator plate  230  is in the off position, actuator pin  260  moves actuator plate  210  to the on position. The mechanical interlocks function the same in both directions. 
     FIGS. 12–14  illustrate a manual override feature of the switching mechanism  10 . In  FIG. 12 , the main circuit breaker  20  has been manually switched off while the backup circuit breaker  30  is in the off position. Note that a slot extension  224   c  of slot  224  allows movement of the actuator plate  210  to an off position when the actuator plate  230  is also in the off position. It should also be noted that the engagement of the actuator pins  260  in the slot extension  224   c  of slot  224  prevents operation of the actuator  250  until the actuator plate  210  is returned to the on position. Thus, when the main circuit breaker  20  is manually switched off, the main circuit breaker  20  must be manually returned to the on position before the actuator  250  will be operative.  FIG. 13  illustrates movement of the actuator plate  210  to a reset position, which is left of the off position. 
   A manual override feature is also provided for the backup circuit breaker  30  as shown in  FIG. 14 .  FIG. 14  shows that the actuator plate  230  moved manually from an on position to an off position while the actuator plate  210  is also in the off position. Note that a slot extension  244   c  of slot  244  allows movement of the actuator plate  230  to an off position when the actuator plate  210  is also in the off position. The engagement of actuator pin in the slot extension  244   c  of slot  244  prevents operation of the actuator  250  until the backup circuit breaker  30  is returned to the on position. The slot extension  244   c  also allows movement of the circuit breaker  30  to the reset position. 
   Slot extensions  224   c  and  244   c  also allow the circuit breakers  20  and  30  respectively to move toward the off responsive to an overload condition, i.e., when the circuit breakers  20  and  30  are tripped by excessive current. When the circuit breakers  20  and  30  are tripped, the engagement of actuator pins  260  and  262  in the slot extensions  224   c  and  244   c  prevent operation of the actuator  250  as previously described until the tripped circuit breaker  20  or  30  is returned to the on position. In this case, the user manually moves the tripped breaker  20  or  30  to the reset position and then back to the on position to reset the breaker. 
     FIG. 16  illustrates an alternate configuration of the actuator plates  210  and  230  that can be used when operating identical circuit breakers in a symmetrical arrangement. The actuator plates  210 ′ and  230 ′ operate in the same manner as previously described. 
   The switching mechanism  10  experiences some mechanical shock during operation. The mechanical shock is created by the action of internal parts of the circuit breakers  20  and  30 . In the case of large circuit breakers, the mechanical shock can be severe enough to require strengthening of the switching mechanism  10 . This would lead to larger parts and increased costs. The present invention avoids this problem by providing a shock absorber  400  to absorb the mechanical shock created by actuation of the main circuit breaker  20 . A shock absorber  400  could also be used for the backup circuit breaker  30 . 
   An exemplary embodiment of the shock absorber  400  is shown in  FIGS. 17 and 18 . The shock absorber  400  comprises two shock absorbing bushings  402  made of a soft latex rubber, or equivalent material capable of absorbing a mechanical shock, that slide over respective fingers  406  of an adapter plate  404 . The adapter plate  404  is mounted on the actuator plate  210  and held in place by screws (not shown). The adapter plate  404  includes screw holes  408  which align with corresponding screw holes  226  on the actuator plate  210 . A spacer  412  spaces the fingers  406  of the adapter plate  404  above the fingers  212  of the actuator plate  210  to accommodate the shock absorbing bushings  402 . The spacing between the fingers  212  and  412  can be slightly less than the thickness of the busing  402  so that the bushing  402  is slightly compressed. A bracket  410  is sandwiched between the bushings  402  and the fingers  212  of the actuator plate  210  as best seen in  FIG. 18 . The bushings  402  absorb the energy of shock produced by the circuit breaker  20 . Because the bushings  402  are made of a soft latex rubber, they would wear too fast if engaged directly by the toggle  22  of the circuit breaker  20 . Bracket  410  is interposed between the bushings  402  and the toggle  22  to prevent wear of the bushings  402 . In an alternate embodiment of the invention, the bushings  402  can be installed directly on the fingers  212  of the actuator plate  210 . While the present invention employs a cushion type shock absorber, other types of shock absorbers could also be used. For example, a spring-type shock absorber  400  could be used.