Abstract:
A miniature circuit breaker providing arc fault protection and ground fault protection has a common rocker button that selectively deflects orthogonally oriented flat electrically conductive test switch spring contacts of an arc fault test circuit and a ground fault test circuit into engagement with a common contact to test each of these protection functions independently. The pivot axis of the rocker button is parallel to the planes of each of the test switch spring contacts and the button has opposed fingers which preload both of the spring contacts to bias the rocker button to a neutral position.

Description:
RELATED APPLICATION 
     Commonly owned, concurrently filed application entitled “CIRCUIT BREAKER WITH DUAL FUNCTION TEST BUTTON REMOTE FROM TEST CIRCUIT” and bearing attorney docket no. 98-PDC-541. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to circuit breakers provided with both ground fault and arc fault trip circuits, and more particularly, to a common test button for actuating selectively a ground fault test circuit and an arc fault test circuit. 
     BACKGROUND INFORMATION 
     Circuit breakers provide overcurrent and short circuit protection for electric power systems. In the small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. Such a device includes a bimetal which is heated and bends in response to a persistent overcurrent condition thereby unlatching a spring powered operating mechanism which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system. An armature attracted by the sizable magnetic forces generated by a short circuit also unlatches, or trips, the operating mechanism. 
     In many applications, the miniature circuit breaker also provides ground fault protection. An electronic circuit detects leakage of current to ground and generates a ground fault trip signal. This signal energizes a shunt trip solenoid which unlatches the operating mechanism, typically through actuation of the thermal-magnetic trip device. 
     Recently, there has been considerable interest in also providing protection against arcing faults. Arcing faults are intermittent high impedance faults which can be caused for instance by worn insulation, loose connections, broken conductors, and the like. Because of their intermittent and high impedance nature, arcing faults do not generate currents of sufficient instantaneous magnitude or sufficient average current to trigger the thermal-magnetic trip device. Consequently, separate electrical circuits have been developed for responding to arcing faults. 
     Ground fault protection circuits and arc fault protection circuits typically include test circuits for affirming their continued operability. These tests must be performed independently to assure operation of both functions. The simplest approach is to provide separate test switches, each with its own test button, for performing the ground fault and arc fault tests. However, the molded cases of the miniature circuit breakers have been standardized for interchangeable use in load centers. There is limited space available in the standardized miniature circuit breakers for all of the additional circuitry required for ground fault and arc fault protection, let alone the test circuits. 
     Commonly owned U.S. patent application Ser. No. 069,355 filed on Apr. 29, 1998 discloses an arrangement in which a common test button selectively actuates either the ground fault test circuit or the arc fault test circuit. The arc fault test switch and ground fault test switch comprise cantilevered electrically conductive flat springs straddling but spaced from a common flat spring. The free ends of all three of these flat springs are in parallel planes. The common test button is a rocker button rotatable in one direction from a neutral position to deflect the flat spring of the arc fault test switch into contact with the common flat spring to actuate the arc fault test circuit. When the rocker button is rotated in the other direction from the neutral position, the flat spring of the ground fault test switch is rotated into engagement with the common flat spring. One or more leaf springs secured in slots in the rocker button bias it to the neutral position. While this common rocker button separately actuates the two test circuits, its reliability is dependent upon tight manufacturing tolerances. Also, the biasing springs add additional labor and cost to manufacture of the circuit breaker. 
     There is a need, therefore, for an improved arrangement for selectively actuating an arc fault test circuit and a ground fault test circuit in a circuit breaker, and especially in a miniature circuit breaker. 
     There is a further need for such a circuit breaker which is easy to use, is inexpensive to manufacture, and does not require the holding of tight manufacturing tolerances. 
     SUMMARY OF THE INVENTION 
     These needs and others are satisfied by the invention which is directed to a circuit breaker which incorporates an electronic trip circuit which includes two test circuits each having their own test switch, such as for instance, for testing a ground fault protection circuit and an arc fault protection circuit. These test switches include separate first and second test contacts and a common contact. These first and second test contacts comprise cantilevered electrically conductive elongated springs selectively deflectable in generally orthogonal planes into engagement with the common contact. The circuit breaker further includes a common actuator moveable to a first position to deflect only the first test contact into engagement with the common contact to actuate only the first test circuit, and moveable to a second position to deflect only the second test contact into engagement with the common contact to actuate only the second test switch. The common actuator has a neutral position in which neither switch is actuated. 
     Preferably, the first and second test switch contacts and the common contact are flat electrically conductive elongated cantilevered springs having free ends. The free ends of the first switch contact and the common contact extend in parallel planes while the free end of the second switch contact extends in a plane substantially perpendicular to these parallel planes. The free end of the first flat switch contact is deflectable into flat surface contact with the common contact. The free end of the second flat switch contact is deflectable with a flat surface thereof engaging an edge of the common contact. The common actuator is moveable in a first direction from the neutral position to a first position in which the first switch is actuated, and is moveable in a second direction opposite the first direction from the neutral position to a second position to actuate the second switch. In the preferred embodiment, the common actuator is a rocker button mounted for rotation about a pivot axis which is parallel to the planes of the free ends of all three of the contact springs. 
     When the electronic trip means is provided on a printed circuit board, the cantilevered flat springs have fixed ends which are fixed to the printed circuit board with all of the fixed ends extending in parallel planes. The second switch contact is then bent between the fixed end and the free end so that the free end is substantially perpendicular to the plane of the fixed end. 
     Preferably, the rocker button has fingers which engage the flat springs of the first switch contact and second switch contact and are spaced apart so that a preload is applied to the first and second switch contacts to bias the rocker button to the neutral position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
     FIG. 1 is an isometric view of a circuit breaker incorporating the dual test button of the invention. 
     FIG. 2 is a schematic diagram of the circuit breaker of FIG.  1 . 
     FIG. 3 is an exploded fragmentary isometric view of a section of the molded housing of the circuit breaker illustrating the mounting of the common test button. 
     FIG. 4 is an isometric view of a preferred form of the ground fault spring contact in accordance with the invention. 
     FIGS. 5 a  and  5   b  are side and end elevation views, respectively, of the rocker button and spring contacts shown in the neutral position. 
     FIGS. 6 a  and  6   b  are similar to FIGS. 5 a  and  5   b  but showing the switch actuated to implement an arc fault test. 
     FIGS. 7 a  and  7   b  a side elevation view similar to FIG. 5 a  but showing the dual test button rotated to implement a ground fault test. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will be described as applied to a single pole miniature circuit breaker of the type commonly used in residential and light commercial applications. However, it will be evident to those skilled in the art that the invention is also applicable to other types of circuit breakers as well. 
     Referring to FIG. 1, the circuit breaker  1  includes a housing  3  which is assembled from a number of molded sections composed of an electrically insulating material, as is well known. Terminals  5  are provided at one end of the housing  3  for connecting the circuit breaker to a load. Line terminals (not shown) at the opposite end of the housing  3  connect the circuit breaker to a commercial power distribution system. A molded handle  7  projects from the housing for manually opening and closing the circuit breaker. A common test button  9  in accordance with the invention is also accessible through the housing. 
     As shown in FIG. 2, the circuit breaker  1  is connected in an electric power system  11  which has a line conductor  13  and a neutral conductor  15 . The circuit breaker includes separable contacts  17  which are connected in the line conductor  13 . The separable contacts  17  are opened and closed by an operating mechanism  19 . In addition to being operated manually by the handle  7 , the operating mechanism can also be actuated to open the separable contacts  17  by a trip assembly  21 . This trip assembly  21  includes the conventional bimetal  23  which, when heated by persistent overcurrents, bends to actuate the operating mechanism  19  to open the separable contacts  17 . An armature  25  in the trip assembly  21  is attracted by the large magnetic force generated by very high overcurrents to also actuate the operating mechanism  19  and provide an instantaneous trip function. 
     The circuit breaker  1  is also provided with an arc fault detector (AFD)  27  and a ground fault detector (GFD)  29 . The arc fault detector  27  may be, for instance, of the type which detects the step increases in current which occur each time an arc is struck, although other types of arc fault detectors could also be used. The arc fault detector senses the current in the electrical system  11  by monitoring the voltage across the bimetal  23  through the lead  31  in the manner described in U.S. Pat. No. 5,519,561. The ground fault detector  29  may be of the well known dormant oscillator type in which case it utilizes a pair of sensing coils  33  and  35  to detect both line to ground and neutral to ground faults. If the arc fault detector  27  detects an arcing fault in the electric power system  11 , a trip signal is generated which turns on a switch such as the silicon controlled rectifier (SCR)  37  to energize a trip solenoid  39 . Detection of a ground fault by the ground fault detector  29  generates a trip signal which also turns on the SCR  37  and energizes the trip solenoid  39 . The trip solenoid  39  when energized actuates the operating mechanism  19  to open the separable contacts  17 . A resistor  41  in series with the coil of the solenoid  39  limits the coil current and a capacitor  43  protects the gate of the SCR from voltage spikes and false tripping due to noise. 
     Both the arc fault detector  27  and the ground fault detector  29  have test circuits. The arc fault detector test circuit  45  provides signals to the arc fault detector  27  which mimic arc faults in the electrical system  11 . The arc fault detector test circuit  45  is actuated by an arc fault test switch  47 . The ground fault detector test circuit  49  when actuated by a ground fault test switch  51  generates a test signal which is applied to the ground fault detector  29 . If the arc fault detector  27  and the ground fault detector  29  are operating properly, they should generate trip signals which open the separable contacts when the associated test circuit is actuated. 
     The arc fault test circuit  45  and the ground fault test circuit  49  are actuated alternatively by the common test button  9 . The physical arrangement of the test switches and the common test button are shown in the remaining figures. As shown in FIG. 3, the arc fault test switch  47  includes a hot, electrically conductive arc fault spring contact arm  53  and a circuit breaker common electrically conductive spring contact  55  forming a mating contact. The ground fault test switch  51  includes a hot, electrically conductive ground fault spring contact arm  57  and also utilizes the circuit breaker common spring contact  55  as the mating contact. The spring contacts  53 ,  55  and  57  are mounted on a printed circuit board  59  mounted within the housing  3 . The contacts  53 ,  55  and  57  are cantilevered from the printed circuit board  59 . The common spring contact  55  and the arc fault spring contact arm  53  have fixed ends  55   a  and  53   a  which are secured to the printed circuit board in parallel planes. These spring contacts  55  and  53  have a right angle bend so that their free ends  55   b  and  53   b  are in close parallel spaced relation. 
     The ground fault spring contact arm  57  has a fixed end  57   a  which is fixed to the printed circuit board  59  in spaced parallel in relation with the fixed ends  55   a  and  53   a . However, the free end  57   b  is orthogonal to the free end  55   b  of the common spring contact and is laterally spaced from a side edge  55   c  of the free end  55   d  of the common spring contact. The preferred configuration of the ground fault spring contact  57  is shown in FIG.  4 . The fixed end  57   a  has a pair of projections  57   c  which extend through the printed circuit board and are soldered on the far side to electrical traces (not shown) connecting the spring contact arm  57  to the ground fault test circuit. The flat ground fault spring contact is bent into a U-shape  57   d  adjacent the fixed end  57   a . The free end  57   b  extends from the U-shaped section  57   d  at right angles to the fixed end  57   a . The free end  57   b  can be widened to provide extended contact with the edge  55   c  of the common contact. 
     Referring to FIGS. 3,  5   a  and  b,  the common test button or switch  5  actuator  9  has a molded body  61  with a flat main section  63  from which an integral pivot pin  65  extends transversely from both sides. The main section  63  of the molded body  61  has a recess  67  which forms a first actuating finger  69  and a second orthogonally directed actuating finger  71 . The molded body  61  of the common test button  9  has a head section  73  which is wider than the main section  63  forming on either side of the head section downwardly convex undercut rocker surfaces  75 . 
     As shown in FIG. 3, a molded section  77  of the housing  3  has a recess  79  with an escutcheon  81  extending around the opening. A recessed shoulder  83  faces the opening. Under the shoulder  83  is a pair of facing notches  85 . The common test button  9  is inserted in the mounting recess  79  with the pivot pin  65  seated in the notches  85 . A complimentary arrangement of the mounting recess  79 , escutcheon  81 , shoulder  83  and notches  85  is provided in a facing molded section (not shown) of the housing  3 , so that the dual test button  9  is captured with the undercut surfaces  75  seated on the shoulder  83  for rotation in a plane  87  transverse to the pivot pin  65 . 
     As can best be seen from FIGS. 5 a  and  5   b , with the circuit breaker assembled, the first actuating finger  69  on the common actuator  9  engages the top surface of the free end  53   b  of the arc fault spring contact while the second actuating finger  71  engages the side surface of the free end  57   b  of the ground fault spring contact. Neither the arc fault spring contact nor the ground fault spring contact are deflected sufficiently to contact the common spring contact  55 , but the deflection of the arc fault spring contact and ground fault spring contact offset each other and bias the common actuator button  9  to a central neutral position. 
     It would be noted that the head  73  of the dual test button  9  is slightly concave about an axis parallel to the pivot pin  65  and is transversely serrated to form a gripping surface  89 . The dual test button  9  is actuated by a plane pressured to the gripping surface  89  to rotate the test button about the pivot pin  65 . When the test button is rotated clockwise as viewed in FIG. 6 a  to a first actuated position, as also shown in FIG. 6 b , the actuating finger  69  deflects the free end  57   b  of the arc fault spring contact  57  downward until it comes into contact with the common spring contact free end  55   b  and therefore closes the arc fault detector test switch  47  to initiate an arc fault test. The free ends  57   a  and  55   a  of the arc fault spring contact and the common spring contact being in parallel planes, the flat surfaces of these free ends make electrical contact to actuate the arc fault test circuit. When the dual test button  9  is released, the arc fault spring contact  57  rocks it back to the neutral position shown in FIGS. 5 a  and  5   b.  Rocking the dual test button  9  counterclockwise as shown in FIG. 7, causes the second actuating finger  71  to deflect the free end  53   b  of the ground fault spring contact into engagement with the common spring contact  55  thereby closing the ground fault test switch  51  and actuating the ground fault test circuit  49 . As the free ends  57   a  and  55   a  of the ground fault spring contact and common spring contact are in orthogonal planes, the flat surface of the free end  57   a  of the ground fault spring contact makes electrical contact with the side edge  55   c  of the free end  55   b  of the common spring contact. Release of the dual test button  9  results in the relaxation of the ground fault spring contact which returns the rocker button to the neutral position and opens the ground fault test switch. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.