Abstract:
A manually operated transfer-type switch has an electrically interlocked isolating plug and plugboard arrangement to isolate two power supplies, e.g., utility and electric generator, from one another. The switch functions to connect electrical loads with either the utility or generator power supply without performing making and breaking of current. The plug is engaged with the plugboard in a first position for supplying utility power and in a second position for providing generator power. A locking arrangement prevents the disengagement of the plug from the plugboard when power is supplied from either the utility or from the generator.

Description:
FIELD OF THE INVENTION 
     This invention relates to a switch of the type that is adapted to be interconnected with an auxiliary power supply, such as an electrical generator, for controlling the supply of electrical power from the generator to branch electrical circuits in an electrical load center. More particularly, the invention relates to a transfer switch having an electrically interlocked isolating plug and plugboard arrangement to isolate two power supplies from one another without performing making and breaking of current functions. 
     BACKGROUND OF THE INVENTION 
     A building, such as a home or other dwelling, typically includes critical and non-critical loads to the primary power supply of the building, which is generally a utility power supply. The critical loads for a home, for instance, may include the HVAC system, sump pump, refrigerators, freezers, dishwasher, washer/dryer, and life-sustaining medical equipment. Other loads of the home are generally considered non-critical. The non-critical loads are generally connected to non-critical branches that are hardwired to a load center, and the critical loads may be connected to critical branches that are hardwired to a separate subpanel; both of which are powered by the primary power supply during normal operation. 
     To ensure power to the critical loads during primary power supply failure or interruption, it is known to connect the subpanel and, thus, the critical loads (or at least the branches that feed those loads), to an auxiliary power supply, such as an electrical generator, using a transfer switch. Many prior art transfer switches are manually operated. With transfer switches of this type, the operator initiates operation of an auxiliary power supply, such as an electrical generator, and connects the auxiliary power supply to the transfer switch, unless there is a permanent connection between the generator and the transfer switch. The individual switches or circuit breakers of the transfer switch are then actuated to supply power from the auxiliary power supply to the circuits in which the individual switches are connected. 
     Conventional transfer switches use classical switching devices, such as double-throw switches or relays, linked single-throw switches or circuit breakers, linked contactors or relays, semiconductors (triacs, IGBTs, etc.), and the like. These classical switching devices perform two general functions: isolation and current making/breaking. In the case of the former, these classical devices electrically isolate the primary power supply and the auxiliary power supply from one another. This is critical to prevent backfeeding of power. Regarding the latter, when energizing a load, the switch for that load (or at least the branch to which that load is connected) must be moved from an OFF position to an ON position. When moved to the ON position, a classical switching device will close the circuit between the load and the power supply. Thus, when the switching device is moved to the ON position when there is a voltage across the switching device, the switching device will “make” current. Similarly, a classical switching device may be moved from the ON position to the OFF position to open the circuit between the load and the power supply and thereby “break” current. Such a classical device may perform this current breaking in response to a manually throwing of the device or may include an overload feature so that the device is “tripped” or automatically thrown to the OFF position when an undesirable current condition is detected. 
     Despite their widespread use, conventional transfer switches fall within this single class or type thereby reducing consumer choices and variability in designing a power management system for a building, home, or other dwelling. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a new class or type of switch for accomplishing a transfer-type function in order to supply power to selected circuits from an auxiliary power source. In particular, the present invention contemplates a switch that utilizes an electrically interlocked and isolating plug and plugboard arrangement to isolate two power sources from one another, but does not require the arrangement to make or break full-rated current. The switch uses an isolating plug and plugboard arrangement to selectively connect loads to a primary power supply or an auxiliary power supply. A solenoid is powered by either the primary power supply or the auxiliary power supply, and when energized actuates a locking feature to lock the isolating plug in the plugboard when power is being delivered to the switch. When neither the auxiliary power supply nor the primary power supply is delivering power to the switch, the isolating plug may be removed from the plugboard. 
     The isolating plug may be engaged with the plugboard in two different positions. In one position, the isolating plug electrically connects a load to the primary power supply. In the other position, the isolating plug electrically connects the load to the auxiliary power supply. The plugboard has two sets of sockets that receive prongs of the isolating plug. When the isolating plug is seated at the primary power position, one set of sockets receive the prongs of the isolating plug. When the isolating plug is seated in the auxiliary power position, the other set of sockets receive the prongs of the isolating plug. 
     In normal operation, the isolating plug is seated in the plugboard at the primary power position so that the loads of the switch are normally powered by the primary power supply. However, when the primary power fails or is otherwise interrupted, the loads will not be powered and must be connected to the auxiliary power supply to restore their operation. When the primary power is lost, the isolating plug is no longer locked in the plugboard. Thus, the isolating plug may be removed manually and reinserted at the auxiliary power position. Specifically, to connect the switch to auxiliary power, the isolating plug is rotated 180 degrees from its primary power position and then reinserted into the plugboard. 
     The auxiliary or backup power supply may then be energized and auxiliary-side breakers may be thrown to energize the loads with auxiliary power. When the auxiliary power source is operating, the isolating plug is locked into the plugboard. When primary power is restored, both power supplies will be operative. As such, the auxiliary power supply should then be shut-down, i.e., disconnected from the switch, which causes unlocking of the isolating plug. The isolating plug may be extracted from the plugboard, rotated to the primary power position, and reinserted into the plugboard. Thereafter, the primary power is reconnected to the switch, which causes primary power to not only be delivered to the loads, but also locks the isolating plug into the plugboard. 
     In one embodiment, the isolating plug and the plugboard sockets are made of non make-and-break current material, such as brass, since the isolating plug and plugboard arrangement does not make or break current. 
     Therefore, in accordance with one aspect, the present disclosure is directed to a transfer-type switch having a first power input connected to a first power supply and a second power input connected to a second power supply. The switch also has an interlock assembly positioned between the first and second power inputs and that electrically isolates the first power supply and the second power supply from one another without performing making and breaking of current functions. 
     In accordance with another aspect of the present disclosure, a transfer-type switch is disclosed and includes a plugboard and removable plug. The plugboard and plug are constructed such that insertion of the plug in the plugboard in a first position connects a load to a first power supply and insertion of the plug in the plugboard in a second position connects the load to a second power supply. A powered actuating device, such as a solenoid, is coupled to a locking feature and is used to bias the locking feature so as to lock the plug in the plugboard, when the plug is fully inserted into the plugboard. 
     According to a further aspect, the present disclosure is directed to a power management system having a first switch that detects a current overload between a utility power supply and a load center when the load center is connected to the utility power supply through the first switch, and a second switch that detects current overload between an electric generator and the load center when the load center is connected to the electrical generator through the second switch. The power management system further has a manual transfer-type switch that connects the load center to the utility power supply when in a first position and connects the load center to the electrical generator when in a second position. The manual transfer-type switch however does not detect current overload when in either the first position or the second position. 
     Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate one preferred embodiment presently contemplated for carrying out the invention. 
       In the drawings: 
         FIG. 1  is an isometric view of a manual transfer-type switch having a plug and plugboard arrangement with the plug seated in the plugboard according to one aspect of the present invention; 
         FIG. 2  is an isometric view of the manual transfer-type switch shown in  FIG. 1  with the plug removed from the plugboard; 
         FIG. 3  is a cross-sectional view of the manual transfer-type switch shown in  FIG. 1  with the plug seated in the plugboard in a first position; 
         FIG. 4  is a cross-sectional view of the manual transfer-type switch shown in  FIG. 1  with the plug seated in the plugboard in a second position; 
         FIG. 5  is a simplified circuit diagram of the manual transfer-type switch with the plug seated in the plugboard in the position shown in  FIG. 3 ; and 
         FIG. 6  is a simplified circuit diagram of the manual transfer-type switch with the plug seated in the plugboard in the position shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIGS. 1-2  illustrate a manual transfer-type switch  10  according to one embodiment of the invention. For convenience, the switch  10  will be referred to as a transfer switch, although it is understood that the switch  10  functions much differently than the type of switch conventionally referred to as a transfer switch that is used to supply electrical power from an alternate power source. 
     The transfer switch  10  has a housing  12  that encloses circuitry, as will be described herein, to selectively connect loads to either a primary power supply, such as utility power, or an auxiliary power supply, such an electrical generator. The housing  12  includes a top faceplate  14  that supports a plugboard  16  and a series of circuit breakers  18 . The plugboard  16  includes a socket arrangement  20  that receives a set of prongs  22  carried by an isolating plug  24 . Specifically, the isolating plug  24  includes a block or gangway  26  to which the prongs  22  are mounted. Mounted opposite and electrically isolated from prongs  22  is a handle  28  that may be used to insert the prongs  22  into the plugboard  16  or to extract the prongs  22  from the plugboard  16 . 
     The socket arrangement  20  is composed of two sets of sockets, shown at  29   a ,  29   b . Each socket set  29   a ,  29   b  is composed of a series of hot sockets  30  and a series of neutral sockets  32 . The neutral sockets  32  have a construction that is distinct from the hot sockets  30 . Representatively, the neutral sockets  32  may each be formed to have a larger diameter than the hot sockets  30 , although it is understood that any other satisfactory distinguishing construction may be used. The hot sockets  30  are each designed to receive a hot prong  34  of plug  24 , whereas the neutral sockets  32  are designed to receive neutral prongs  36  of plug  24 . 
     As shown in the figures, the isolating plug  24  has fewer prongs  22  than sockets  30 ,  32  of the plugboard  16 . Thus, when the isolating plug  24  is seated in the plugboard  16 , some of the sockets  30 ,  32  will not receive a prong  34 ,  36 . Thus, in one preferred embodiment, the gangway  26  is sized such that all the sockets are covered by gangway  26  regardless the orientation of the isolating plug  24  when the isolating plug  24  is seated in the plugboard  16 . Alternately, the isolating plug  24  may be equipped with dummy plugs (not shown) made of non-conductive material. In this alternate embodiment, the prong arrangement  22  has the same number of prongs as sockets in the socket arrangement  20 . 
     The socket arrangement  20  is such that the plugboard  16  may receive the isolating plug  24  in two different orientations. In one orientation, as shown in  FIG. 3 , socket set  29   a  receives hot prongs  34  and neutral prongs  36 . In this orientation, the lower row of hot sockets  30  and the lower neutral sockets  32  in socket set  29   b  do not receive a prong. The orientation shown in  FIG. 3  corresponds to a primary power orientation. Accordingly, when the isolating plug  24  is seated in the plugboard  16  at the orientation shown in  FIG. 3 , the loads of the transfer switch  10  are connected to the primary power supply. On the other hand, when the isolating plug  24  is inserted into the plugboard  16  in a second orientation as shown in  FIG. 4 , socket set  29   b  receives hot prongs  34  and neutral prongs  36 . In this orientation, the upper row of hot sockets  30  and the upper neutral sockets  32  in socket set  29   a  do not receive a prong. The orientation shown in  FIG. 4  corresponds to an auxiliary power orientation. Accordingly, when the isolating plug  24  is seated in the plugboard  16  at the orientation shown in  FIG. 4 , the loads of the transfer switch  10  are connected to the auxiliary power supply, such as an electrical generator. As shown by a comparison of the orientations illustrated in  FIGS. 3-4 , the auxiliary power supply position of plug  24  ( FIG. 4 ) is rotated 180 degrees from the primary power supply position ( FIG. 3 ). 
     The face  37  of plug  24  may include identifiers that identify the position of the prongs  34 ,  36 . Accordingly, when the plug  24  is seated in the plugboard  16 , the orientation of the prongs may be easily determined. It is contemplated that other means may be used to provide a visual identification as to the orientation of the prongs when the plug is seated in the plugboard. 
     Operation of the transfer switch  10  will now be described with respect to  FIGS. 5-6 .  FIG. 5  is a circuit diagram corresponding to the isolating plug  24  seated in the plugboard  16  at the primary power position ( FIG. 3 ) whereas  FIG. 6  is a circuit diagram corresponding to the isolating plug  24  seated in the plugboard  16  at the auxiliary power position ( FIG. 4 ). 
     When the isolating plug  24  is inserted into the plugboard  16  at the primary power position as shown in  FIG. 5 , a primary-side solenoid power supply  38  provides power to a solenoid  40  operably coupled to a locking feature  42  that locks the isolating plug  24  into the plugboard  16 . Current can then flow from the primary power supply through the prongs  34  of the plug  24  and ultimately to the loads that are interconnected with the hot sockets  30  of socket set  29   a . The solenoid  40  will remain energized as long as the primary-side power supply  38  is receiving power from the primary power supply, e.g., utility. Moreover, the locking feature  42  secures the isolating plug  24  in the plugboard  16  under the force imposed by the solenoid  40  thereby preventing removal of the isolating plug  24  from the plugboard  16  so long as power is being provided by the primary power supply. As such, an operator cannot remove the isolating plug  24  from the plugboard  16 . To disconnect a load (representatively shown as resistors  46 ) that is powered by the primary power supply through the transfer switch  10 , the load center circuit breaker  48  for the load  46  must be thrown to an OFF position. In this regard, the load center circuit breakers  48  perform current making and breaking, rather than the isolating plug  24  and plugboard  16 . 
     When the utility power fails, the primary-side solenoid power supply  38  can no longer power the solenoid  40  to maintain the locking feature  42  in a position that locks the isolating plug  24 . Thus, the isolating plug  24  can be removed manually by an operator. To connect the transfer switch to the auxiliary power supply, the operator rotates the isolating plug  24  180 degrees from the utility power position ( FIG. 3 ) to the auxiliary power position ( FIG. 4 ) and then reinserts the isolating plug  24 , at the rotated orientation, into the plugboard  16  such that the prongs  34  are engaged with the hot sockets  30  of socket set  29   b .  FIG. 6  is a circuit diagram showing the circuit that is formed when the isolating plug  24  is inserted into the plugboard  16  at the auxiliary power position. 
     The operator can then energize the auxiliary or backup power supply and activate any of the branch circuit breakers  18  to selectively energize the loads  46  that are interconnected with the hot sockets  30  of socket set  29   b . That is, current can be fed from the auxiliary power supply through the prongs  34  of the plug  26  to the loads. When the auxiliary power supply is operating, the solenoid  40  is powered by the auxiliary-side solenoid power supply  50  to maintain the locking feature  42  in a position that locks the isolating plug  24  into the plugboard  16 . 
     When primary power is restored, both power supplies will be operative; however, because the isolating plug  24  is seated in the plugboard  16  at the auxiliary power supply position, primary power is not delivered to the loads  46 . To reconnect the loads to primary power, both the primary and auxiliary power supplies must be deactivated or disconnected from the transfer switch, which causes the solenoid  40  to undergo a loss of power thereby removing the bias placed on the locking feature  42 , which results in unlocking of the isolating plug  24 . Once both power supplies have been deactivated, the isolating plug  24  may be removed from the plugboard  16 , rotated to the primary power position, and reinserted into the plugboard  16 . Thereafter, the primary power supply may be reactivated by switching the main breaker  52  into the ON position, which causes primary power to not only be delivered to the loads  46 , but also activates the solenoid  40  to bias the locking feature  42  so as to lock the isolating plug  24  into the plugboard  16 . 
     Referring again to  FIGS. 5-6 , to ensure that the isolating plug  24  is fully inserted into the plugboard  16 , at either the primary power position or the auxiliary power position, a proximity sensor  54  may be used to sense the position of the locking feature  42 . In this regard, if the isolating plug  24  is not fully seated in the plugboard  16 , a sonic  44  sounds an alarm to alert a user accordingly. When a fully seated position of the isolating plug  24  in the plugboard  16  is reached, the sonic  44  automatically silences the alarm. 
     Referring again to  FIGS. 1-2 , the manual transfer switch  10  may also have a lower faceplate  56  supporting a current and voltage meter  58 ,  60 . The lower faceplate  56  may also include an access panel cover plate  62 , as is known in the art. It is recognized that the manual transfer switch  10  may include additional meters, dials, control buttons, displays, and the like, as is known in the art. 
     It is understood that the drawings and the above description pertain to a representative embodiment of the present invention, and that various alternatives and modifications are possible and are contemplated as being within the scope of the present invention. For example, and without limitation, it is contemplated that the arrangement of prongs on the plug  26  and sockets on the plugboard  16  may be reversed, in that the plug  24  may carry sockets and the plugboard and  16  may have prongs with which the plugboard sockets may be engaged. It is also contemplated that the particular arrangement of the sockets in the plugs may take any desired, and are not limited to the linear arrangement as shown and described. It is also contemplated that any satisfactory type of locking mechanism may be employed to maintain the plug in engagement with the plugboard when power is supplied to the switch  10  from any source, and the locking mechanism is not limited to a solenoid-type arrangement as shown and described. It is preferable, however, that the locking arrangement be automatically responsive to the supply of power to the switch  10  from a power source, so that the locking arrangement is automatically actuated so as to secure the plug to the plugboard when power is supplied to the switch  10  and the plug is engaged with the plugboard. 
     The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the impending claims.