Switching mechanism with mechanical interlocking and manual override

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 a first actuator plate to operate a first circuit breaker connected to a primary power supply, a second actuator plate to operate a second circuit breaker connected to a secondary power supply, and an actuator. The first and second actuator plates are independently movable between on and off positions. The actuator is operatively connected to the first and second actuator plates so that the actuator moves the first actuator plate to an on position and the second actuator plate to an off position when the actuator is moved in a first direction, and moves the first actuator plate to an off position and the second actuator plate to an on position when the actuator is moved in a second direction. An override enables movement of the first and second actuator plates from the on position to the off position when the other actuator plate is in the off position. The switching mechanism can be installed in an existing distribution panel in a home of building.

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 two actuator plates that are operated by an actuator that can be manually or electrically powered. A first actuator plate is operatively engaged with a main circuit breaker to connect and disconnect with the electrical distribution panel to and from a commercial power supply line. The second actuator plate operatively engages a second circuit breaker to connect and disconnect the electrical distribution panel to and from a local generator. The movement of the actuator plates is timed such that the circuit breakers are operated in a “break before make” fashion so that the load is momentarily isolated during switching. The geometry of the switching mechanism locks one of the circuit breakers in an “off” position when the other is in an “on” position. Thus, the two power supplies can never be connected at the same time. The switching mechanism also allows a user to manually shut off one circuit breaker when the other circuit breaker is off. The switching mechanism is rendered inoperative when a circuit breaker is manually shut off by a user or is tripped by a current overload.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1–3illustrate a switching mechanism indicated generally at10installed in an electrical distribution panel12. The distribution panel12comprises a cabinet14, a back plane16with interior parts (not shown), and a plurality of circuit breakers18including a main circuit breaker20, a backup circuit breaker30and a number of branch circuit breakers24. The main circuit breaker20connects the electrical distribution panel12to commercial power supply lines. The backup circuit breaker30connects the electrical distribution panel12to a local generator. The branch circuit breakers24connect the various loads in the residence or building to the electrical distribution panel12. The switching mechanism10in combination with the main circuit breaker20and backup circuit breaker22function as a transfer switch.

The switching mechanism10comprises three main assemblies—a support assembly100, an actuator assembly200, and a drive assembly300. The support assembly100secures the switching mechanism10to the electrical distribution panel and provides support for the actuator assembly200and the drive assembly300. The actuator assembly200operates the main circuit breaker20and backup circuit breaker30such that power to the branch circuit breakers24can be switched between the commercial power supply and the backup power supply. The drive assembly300includes a drive motor302to drive the actuator assembly200.

FIGS. 3–5illustrate details of the support assembly100. The support assembly100comprises a generally-planar support bracket102and a support plate130. The support bracket102secures the switching assembly to the electrical distribution panel12. The support bracket102includes a top plate103and support legs150. The support legs150extend generally perpendicularly from the top plate103. The outer end of each support leg150is bent at a 90° angle to form a support foot152. The support foot152includes a screw hole154to accept a mounting screw (not shown) for securing the support bracket102to the distribution panel12. The support plate130mounts on top of the support bracket102to provide a stable platform for the actuator assembly200. When mounted in a distribution panel12, the support plate130is oriented generally parallel to the back plane16of the distribution panel12. The support legs150provide the proper spacing from the back plane16.

The support bracket102, in addition to providing support for the switching assembly, also braces the main circuit breaker20and backup circuit breaker30. In the exemplary embodiment shown in the drawings, the support bracket102includes a large frame104that extends around the housing of the main circuit breaker20, and a smaller frame106that extends around the housing of the backup circuit breaker30. Frames104and106prevent the circuit breakers20and30from twisting or otherwise moving during operation. Additionally, frame106serves as a hold-down device to hold down the backup circuit breaker30.

The top plate103of the support bracket102includes clearance holes108and110for a motor shaft306and actuator shaft254, respectively. Threaded screw holes112for mounting the drive motor302surround clearance hole108. Similarly, threaded screw holes114for mounting an actuator shaft bearing256surround clearance hole110. Support bracket102further includes guide screw holes116to accept guide screws120. As will be explained in greater detail below, the guide screws120constrain the movement of the actuator assembly200.

FIG. 5illustrates the support plate130. The support plate130comprises a steel plate that provides a platform for the actuator assembly200. The support plate mounts on top of the support bracket102and can be secured by screws or any other suitable fastening means. The top surface of the support plate130is flat. Clearance holes132and134provide openings for the motor drive shaft306and actuator shaft254respectively. An access opening136provides access to mounting screws used to secure the support bracket102to the distribution panel12. Guide screw holes138align with the guide screw holes116in the support bracket102.

Guide screws120extending through guide slots216and236in the actuator plates210and230respectively constrain and guide the movement of the actuator plates210and230. The guide slots216and236extend parallel to the direction of movement of the actuator plates210and230. Guide slots216and236are parallel to one another so that the actuator plates210and230move in parallel fashion. The guide screws120pass through the guide slots216,236and thread into the guide screw holes138in the support plate and pass through the guide holes116in the support bracket102.

Access opening218in actuator plate210provides access to mounting screws used to secure the support assembly100to the electrical distribution panel12when it is aligned with the access opening136in the support plate130. Clearance opening238provides clearance for the motor shaft306. Clearance opening238is elongated in the direction of movement to accommodate the travel of the actuator plate230. Recesses220and240in the edges of actuator plates210and230respectively provide clearance for the actuator shaft254.

A rotary actuator250shown best inFIGS. 2 and 3moves the actuator plates210and230between on and off positions as the rotary actuator250rotates in first and second directions. The rotary actuator250comprises a rotor252mounted to one end of the actuator rotor shaft254. The outer edge of the rotor252includes gear teeth, which are engaged by the drive gear304to rotate the actuator250. Actuator shaft254extends downward between the actuator plates210and230and passes through openings134and110in the support plate130and support bracket102respectively. Actuator shaft254is journaled in a bearing256that mounts to the underside of the support frame102as shown inFIG. 3. A switch actuator264is attached to the lower end of the actuator shaft. As will be described in more detail below, switch actuator264actuates limit switches (not shown) that control operation of the actuator assembly200.

Actuator pins258,260,262extend from the underside of the rotor252. Actuator pin258moves within slots222and242in actuator plates210and230, respectively. Actuator pin260functions as a drive member and moves within slot224in actuator plate210. Actuator pin262functions as a drive member and moves within slot244in actuator plate230. The geometry of the slots224and244, along with the location of the actuator pins260and262, provide sequential switching of the circuit breakers20and30so that both circuit breakers20and30are both swtiched off before one is swtiched on. This sequential actuation of the circuit breakers20and30ensures that the branch circuit breakers24are momentarily isolated from both power sources when switching from one power source to the other. The actuator assembly200allows a user to manually switch circuit breakers20or30to the off position when the other circuit breaker20or30is in the off position. Thus, the user can simultaneously turn both circuit breakers20and30off.

The actuator assembly200also functions as a mechanical interlock mechanism that prohibits a circuit breaker20or30from being turned on when the other circuit breaker20or30is on. Additionally, the actuator250is mechanically locked when one of the circuit breakers20and30is manually turned off or if a breaker is tripped. Thus, the user is required to manually turn on the circuit breaker20or30, that was manually turned off, or to reset the tripped circuit breaker before automatic operation of the rotary actuator250can resume. These locking features prevent the user from inadvertently connecting the electrical distribution panel12to both the main and backup power sources at the same time, as well as preventing the drive motor302from operating the locked mechanism.

The drive assembly300comprises a drive motor302, a drive gear304and motor controller310. The drive motor302mounts to the underside of the support bracket102and is supported thereby. The motor shaft306passes through the clearance holes108,132and238in the support bracket102, support plate and actuator plate230respectively. The motor shaft306connects to a drive gear304, which engages the periphery of the rotor252. Alternatively, the drive motor302could directly drive the actuator250. One advantage of the drive gear304, however, is that through proper gearing a mechanical advantage is realized that allows use of a smaller and less expensive drive motor302.

When installed in the distribution panel12, the drive motor302occupies a space that would otherwise be used by branch circuit breakers24. To install the switching mechanism10, two branch circuit breakers24are removed to make space for the drive motor302. Although two branch circuit breakers24are sacrificed in this arrangement, locating the drive motor302as shown herein allows the switch assembly10to be mounted within most existing distribution panels12currently in use in residential or light commercial construction. Therefore, there is no need to replace the existing distribution panel12or to add a sub-panel to install the switching mechanism10. Furthermore, the two sacrificed branch circuit breakers can easily be replaced by using commercially available tandem circuit breakers.

FIG. 15illustrates a motor controller310for controlling operation of the drive motor302. The motor controller310is configured to reduce the speed of the drive motor302as the actuator plates210and230reach the limit of their travel. There are two branches in the motor controller circuit. The first branch includes diodes D1, D3, D5, resistor R1, and limit switch S2. The second branch includes diodes D2, D4, and D6, resistor R2, and limit switch S1. The motor controller310dynamically breaks but does not stop the drive motor302when one of the limit switches S1, S2is tripped. Consequently, the speed of the drive motor302is reduced as the actuator plates210,230approach their mechanical limits. The breaking is produced by shunting the drive motor302with a couple—Schottky diodes/zener diode—with a voltage significantly lower than the rated motor voltage. Resistors R1and R2provide bias current to keep voltage on the zener diode so the drive motor302continues 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 motor302to 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 motor302when the mechanical limits are reached.

FIGS. 7–14illustrate the operation of the actuator assembly200.FIG. 7illustrates actuator plate210in an on position, while actuator plate230is in an off position. Thus, main circuit breaker20is switched on while the backup circuit breaker30is switched off. In this position, the engagement of the actuator pins262and258in slots244and242respectively prevent the actuator plate230from moving from the off position. Thus, the actuator assembly200provides a mechanical interlock preventing circuit breaker30from being switched on while circuit breaker20is on. To switch from the commercial power supply to the local generator, the rotary actuator250is rotated counterclockwise from the starting position shown inFIG. 7to the ending position shown inFIG. 11.

InFIG. 8the 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 pin260on the rotary actuator250has moved up into a drive portion224bof the slot224. The actuator pin260applies force against the sidewall of the slot224as the actuator250turns to move the actuator plate210to the left. Actuator pin262is traveling through a clearance portion244aof slot244that allows free movement of the actuator250while actuator plate230remains stationary. Actuator pin258is engaged in slot242to prevent movement of actuator plate230. The main circuit breaker20is in the middle of its travel to the off position, while the backup circuit breaker30remains in the off position. Thus, the switching mechanism10provides a mechanical interlock preventing circuit breaker30from being switched on while circuit breaker20is on.

InFIG. 9, the actuator plate210has moved the main circuit breaker20to the off position. Actuator pin260on the actuator250is now moving into the clearance portion224aof slot224. Actuator pin258has moved out of slot242so that actuator plate230can now move to the right. Actuator plate210will remain stationary while the actuator250turns because the actuator pin260is in the clearance portion224aof slot224. Actuator pin262is moving into the drive portion244bof slot244. At this point, any further counterclockwise rotation of the actuator250will move actuator plate230to the right.

InFIG. 10, the main circuit breaker20is off and the backup circuit breaker30is in the middle of its travel to the on position. The actuator pin260is moving downward in the clearance portion224aof slot224so that actuator plate210is stationary. Actuator pin262is pushing against the sidewall of the slot244to move the actuator plate230to the right. Actuator pin258is moving upward in slot222.

InFIG. 11, the main circuit breaker20is in the off position and the backup circuit breaker30is in the on position. Actuator pin260prevents the actuator plate210from being moved to the right while the actuator plate230is in the on position. Thus, the actuator assembly provides a mechanical interlock preventing circuit breaker20from being switched on while circuit breaker30is on.

When switching in the opposite direction, the actuator rotates in a clockwise direction and the process described above is reversed. Actuator plate230is initially moved to the off position by the actuator pin262. Once the actuator plate230is in the off position, actuator pin260moves actuator plate210to the on position. The mechanical interlocks function the same in both directions.

FIGS. 12–14illustrate a manual override feature of the switching mechanism10. InFIG. 12, the main circuit breaker20has been manually switched off while the backup circuit breaker30is in the off position. Note that a slot extension224cof slot224allows movement of the actuator plate210to an off position when the actuator plate230is also in the off position. It should also be noted that the engagement of the actuator pins260in the slot extension224cof slot224prevents operation of the actuator250until the actuator plate210is returned to the on position. Thus, when the main circuit breaker20is manually switched off, the main circuit breaker20must be manually returned to the on position before the actuator250will be operative.FIG. 13illustrates movement of the actuator plate210to a reset position, which is left of the off position.

A manual override feature is also provided for the backup circuit breaker30as shown inFIG. 14.FIG. 14shows that the actuator plate230moved manually from an on position to an off position while the actuator plate210is also in the off position. Note that a slot extension244cof slot244allows movement of the actuator plate230to an off position when the actuator plate210is also in the off position. The engagement of actuator pin in the slot extension244cof slot244prevents operation of the actuator250until the backup circuit breaker30is returned to the on position. The slot extension244calso allows movement of the circuit breaker30to the reset position.

Slot extensions224cand244calso allow the circuit breakers20and30respectively to move toward the off position responsive to an overload condition, i.e., when the circuit breakers20and30are tripped by excessive current. When the circuit breakers20and30are tripped, the engagement of actuator pins260and262in the slot extensions224cand244cprevent operation of the actuator250as previously described until the tripped circuit breaker20or30is returned to the on position. In this case, the user manually moves the tripped breaker20or30to the reset position and then back to the on position to reset the breaker.

FIG. 16illustrates an alternate configuration of the actuator plates210and230that can be used when operating identical circuit breakers in a symmetrical arrangement. The actuator plates210′ and230′ operate in the same manner as previously described.

The switching mechanism10experiences some mechanical shock during operation. The mechanical shock is created by the action of internal parts of the circuit breakers20and30. In the case of large circuit breakers, the mechanical shock can be severe enough to require strengthening of the switching mechanism10. This would lead to larger parts and increased costs. The present invention avoids this problem by providing a shock absorber400to absorb the mechanical shock created by actuation of the main circuit breaker20. A shock absorber400could also be used for the backup circuit breaker30.

An exemplary embodiment of the shock absorber400is shown inFIGS. 17 and 18. The shock absorber400comprises two shock absorbing bushings402made of a soft latex rubber, or equivalent material capable of absorbing a mechanical shock, that slide over respective fingers406of an adapter plate404. The adapter plate404is mounted on the actuator plate210and held in place by screws (not shown). The adapter plate404includes screw holes408which align with corresponding screw holes226on the actuator plate210. A spacer412spaces the fingers406of the adapter plate404above the fingers212of the actuator plate210to accommodate the shock absorbing bushings402. The spacing between the fingers212and412can be slightly less than the thickness of the busing402so that the bushing402is slightly compressed. A bracket410is sandwiched between the bushings402and the fingers212of the actuator plate210as best seen inFIG. 18. The bushings402absorb the energy of shock produced by the circuit breaker20. Because the bushings402are made of a soft latex rubber, they would wear too fast if engaged directly by the toggle22of the circuit breaker20. Bracket410is interposed between the bushings402and the toggle22to prevent wear of the bushings402. In an alternate embodiment of the invention, the bushings402can be installed directly on the fingers212of the actuator plate210.

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 absorber400could be used.