Patent Publication Number: US-8525057-B2

Title: Switching unit for a circuit breaker having a rocker lever

Description:
RELATED APPLICATION 
     This application claims priority as a continuation application under 35 U.S.C. §120 to PCT/EP2010/057145, which was filed as an International Application on May 25, 2010 designating the U.S., and which claims priority to European Application 09161024.6 filed in Europe on May 25, 2009. The entire contents of these applications are hereby incorporated by reference in their entireties. 
    
    
     FIELD 
     The invention relates to circuit breakers, such as automated circuit breakers which can be operated manually by rocker levers. 
     BACKGROUND 
     DE-A-102 44 231, for example, discloses a switching unit such as this. This known apparatus allows mechanical circuit breakers, which are intended to be operated manually, to be operated by remote control by a switching unit from a remote control center. For this purpose, this known apparatus has a driven claw for operation of a rocker switch on the circuit breaker. With this known apparatus, correct operation of the circuit breaker is not ensured if the claw is not moved away from the rocker lever. 
     EP-A-0 801 411 discloses a further switching unit. 
     SUMMARY 
     An exemplary switching unit for operation of a rocker lever of a circuit breaker is disclosed, comprising: a drive unit which has at least one driven first element which can be moved linearly through a distance, wherein the drive unit has a second element, which can move freely through a free-play distance with respect to the first element, and wherein the free-play distance is selected to ensure that operation of the rocker lever is not impeded by the switching unit. 
     An exemplary circuit breaker is disclosed, comprising: a rocker lever having a switching unit, which is fitted to the circuit breaker for operation of the rocker lever, wherein the switching unit includes: a drive unit which has at least one driven first element which can be moved linearly through a distance, wherein the drive unit has a second element, which can move freely through a free-play distance with respect to the first element, and wherein the free-play distance is selected to ensure that operation of the rocker lever is not impeded by the switching unit. 
     A method is disclosed for operation of a switching unit for operation of a rocker lever of a circuit breaker, wherein the switching unit includes a drive unit which has at least one driven first element which can be moved linearly through a distance, wherein the drive unit has a second element, which can move freely through a free-play distance with respect to the first element, and wherein the free-play distance is selected to ensure that operation of the rocker lever is not impeded by the switching unit, the method comprising moving the first element with catching of the second element being driven in a switching-on direction until the rocker lever reaches an “on” position; and moving the first element through a free-play distance in a switching-off direction, with the second element not being moved. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will be explained in detail in the following text with reference to the drawing, in which, purely schematically: 
         FIG. 1  shows a section view of a circuit breaker having a switching unit in accordance with an exemplary embodiment; 
         FIG. 2  shows a partial view of a switching unit and rocker switch of a circuit breaker having a rocker lever with a slide in accordance with an exemplary embodiment; 
         FIG. 3  shows a partial view of a circuit breaker having a switching unit and rocker lever in an “off” position and a slide in an “off” position in accordance with an exemplary embodiment; 
         FIG. 4  shows a partial view of a circuit breaker having a switching unit and rocker lever with the slide being shown during a switching-on movement in accordance with an exemplary embodiment; 
         FIG. 5  shows a partial view of a circuit breaker having a switching unit and a rocker lever in an “on” position and the slide being shown in an extreme position in the switching-on direction in accordance with an exemplary embodiment; 
         FIG. 6  shows a partial view of a circuit breaker having a switching unit and rocker lever in an “on” position and the slide likewise being shown in its “on” position in accordance with an exemplary embodiment; 
         FIG. 7  shows a partial view of a circuit breaker having a switching unit and rocker lever in a “trip” position in accordance with an exemplary embodiment; 
         FIG. 8  shows a partial view of a circuit breaker having a switching unit and rocker lever in an “off” position and the slide in an extreme position in the switching-off direction in accordance with an exemplary embodiment; and 
         FIG. 9  shows a partial view of a switching unit of a blocking apparatus for blocking a spindle in accordance with an exemplary embodiment. 
     
    
    
     The reference symbols used in the drawing and their meaning are listed in summary form in the list of reference symbols. In principle, the same parts are provided with the same reference symbols in the figures. The described embodiments represent examples of the subject matter of the invention, and have no restrictive effect. 
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present disclosure provide an apparatus of the type, which can ensure reliable operation of a circuit breaker. 
     In an exemplary embodiment, the switching unit for operation of a rocker lever of a circuit breaker has a drive unit that has at least one driven first element that can be moved linearly through a distance. The drive unit can also have a second element, which can move freely through a free-play distance with respect to the first element. This free-play distance makes it possible to ensure that the freedom of movement of the rocker lever is not restricted by the switching unit. This can ensure that the rocker lever of the circuit breaker can move freely, thus ensuring that there is no adverse effect on the operation of the circuit breaker. 
     In another exemplary embodiment, a method for operation of a switching unit for operation of a rocker lever of a circuit breaker, with the switching unit having a driven, linearly moving first element and a second element which interacts with the first element and can be moved along a distance by means of the first element, in which case, during a movement of the second element in the switching-on direction from the “off” position to the “on” position, and during a movement of the second element in the switching-off direction of the rocker lever from the “on” position to the “off” position, the rocker lever can be moved by means of the second element. The includes moving the first element with the second element being driven in the switching-on direction until the rocker lever reaches the “on” position; moving the first element through a free-play distance in the switching-off direction, with the second element not being moved. 
     The exemplary methods of the present disclosure provide for operation of a switching unit, which allows a circuit breaker, which has been developed for manual operation to be automated in a simple manner. Because of the exemplary method, the circuit breaker can be operated from a control center. 
     In an exemplary embodiment, the switching unit has a driven spindle, a spindle nut which interacts with the spindle and can be moved along the spindle by rotation of the spindle, and a slide which interacts with the spindle nut and can be moved along the spindle by means of the spindle nut, with the slide being designed for operation of the rocker lever, and with the slide being movable through the free-play distance relative to the spindle nut. The exemplary drive unit of the present disclosure allows a particularly simple refinement of the drive unit, which has a free-play distance. Since there is rotary movement on the drive side with respect to the spindle nut, an appropriate motor can be used, which specifies relatively little power for operation. 
     In another exemplary embodiment of the present disclosure, the switching unit includes a drive unit that can be blocked. As a result, during maintenance tasks the rocker lever of the circuit breaker cannot be operated by the switching unit. This serves in particular to protect the person who is carrying out the maintenance tasks. 
       FIG. 1  shows a section view of a circuit breaker having a switching unit in accordance with an exemplary embodiment. The circuit breaker  10  has a rocker lever  12 , by means of which the electrical switching contacts of the circuit breaker  10  can be opened or disconnected. Circuit breakers  10  such as these can be used, for example, for voltages up to 1200 V and current levels up to 0.5 A. If the circuit breaker is subject to an unacceptable operating condition, for example, an excessively high voltage or an excessively high current level is present, the circuit breaker can automatically open the electrical switching contacts. 
     The rocker lever  12  of the circuit breaker  10  has three stable switching positions, an “off” position in which the electrical switching contacts are disconnected, an “on” position in which the electrical switching contacts are closed, and a “trip” position. 
       FIG. 2  shows a partial view of a switching unit and rocker switch of a circuit breaker having a rocker lever with a slide in accordance with an exemplary embodiment. As shown in  FIG. 2 , the rocker lever  12  can be moved manually in a switching-on direction E from the “off” position to the “on” position. During a manual movement in the switching-off direction A, the rocker lever can be moved from the “on” position to the “off” position. In the event of a fault, for example, when an unacceptable operating condition occurs, the electrical switching contact opens, and the rocker lever  12  is moved from the “on” position to a “trip” position, which is located between the “on” position and the “off” position of the rocker lever  12 . This makes it possible for an operator viewing the circuit breaker  10  to determine whether the contacts of the circuit breaker  10  have or have not been opened because of an unacceptable operating condition. If the rocker lever  12  is in the “trip” position, the rocker lever  12  should first be moved to the “off” position to allow the electrical switching contacts to be closed by moving the rocker lever  12  from the “off” position to the “on” position. 
     In principle, circuit breakers do not specify the “trip” position although, in the case of circuit breakers such as these, it is not possible to determine whether the electrical contacts have been opened manually or because of an unacceptable operating condition. The exemplary embodiments of the present disclosure can be used for circuit breakers with a “trip” position and for circuit breakers without a “trip” position. 
     The movement of the rocker lever  12  from the “off” position to the “on” position, because of which the electrical switching contacts are closed, typically loads a spring. The energy that is stored in the spring can be used to open the electrical switching contacts in the event of a fault. When disconnecting the switching contacts, the contacts should be disconnected from one another quickly, such that an arc, which is struck between the switching contacts to be disconnected, is quenched quickly and the arc does not damage the circuit breaker. 
     Since the movement of the rocker lever  12  is coupled to the relative movement of the electrical switching contacts to be disconnected with respect to one another, during disconnection of the electrical switching contacts, the movement of the rocker lever  12  should not be impeded, in order that the circuit breaker  10  operates correctly. If the freedom of movement of the rocker lever  12  is impeded, it is not possible to ensure that the circuit breaker  10  will operate correctly in a desired, specified manner. 
     A switching unit  20  for automatic operation of the rocker lever  12  of the circuit breaker  10  is fitted to the circuit breaker  10 . The switching unit  20  allows the rocker lever  12 , which is designed for manual operation, to be operated automatically via the switching unit  20 . As a result, the switching unit  20  is on the one hand supplied with its own current feed, and is connected via a data line to a control center or the like. 
     As shown in  FIG. 1 , the switching unit  20  has a supporting structure  22  that is formed by two clamping arms  24  and a bridge  26 , which connects these clamping arms  24 . The supporting structure  22  has studs (not shown) on the clamping arms  24 , which studs engage in depressions that are formed on the housing of the circuit breaker  10 . In another exemplary embodiment of the present disclosure, the supporting structure  22  can also be attached in a force-fitting manner to the housing of the circuit breaker  10 . Further assembly options are likewise possible, for example by means of adhesive bonding. 
     For example, an exemplary drive unit  31  can be held on the supporting structure  22 . The drive unit  31  converts a rotary movement to a linear movement, with the linear movement taking place along a distance S. The drive unit  31  has a first element  32 ′ that moves through the distance S. Furthermore, according to the present disclosure, the drive unit  32  has a second element  34 ′, which can move freely through a free-play distance L with respect to the first element  32 ′. 
     The first element  32 ′ is formed by a driven spindle nut  32 , and the second element  34 ′ is formed by a slide  34 , in which case the slide  34  can move freely through the free-play distance L relative to the spindle nut  32 . By way of example, the free-play distance L has a minimum length from 1 mm to 3 mm, for example, and more preferably of 5 mm. A maximum length of the free-play distance L has, for example, a length up to 40 mm, such as 30 mm in some exemplary embodiments, and more preferably of 15 mm. 
     The rocker lever  12  of the circuit breaker  10  is operated by means of the second element  34 ′ or the slide  34 . Since, according to the present disclosure, the second element  34 ′ or the slide  34  can move freely through the free-play distance L, the exemplary switching unit  20  of the present disclosure means that the operation of the circuit breaker  10  is not adversely affected, in particular that the correct operation of the rocker lever  12  is not impeded by the switching unit  20 . 
     A driven spindle  30  of the drive unit  31  of the switching unit  20  is held on the supporting structure  22  such that it can rotate. An axial direction X of the spindle  30  runs at right angles to the rotation axis D of the rocker lever  12  of the circuit breaker  10 . In particular, the axial direction X of the spindle  30  runs at least approximately in the direction of a linear movement direction of the rocker lever  12 , which linear movement direction approximates to the circular movement path of the rocker lever  12 , and therefore in the direction of the distance S. 
     The spindle nut  32  is fitted to the spindle  30  and is guided by the supporting structure  22  such that rotation of the spindle  30  about its own axis results in the spindle nut  32  being able to move in the axial direction X of the spindle  30 , and therefore through the distance S. As a result, the drive unit  31  converts a rotary movement to a linear movement, by means of the driven spindle  30  and the spindle nut  32 . 
     Furthermore, the switching unit  20  has the slide  34 , which is associated with the drive unit  31 , can move in the axial direction X of the spindle  30 , and is guided by the supporting structure  22 . The slide  34  surrounds the spindle  30  in the circumferential direction of the spindle  30 . In the axial direction X of the spindle  30 , the slide  34  has a first mating contact surface  36  and a second mating contact surface  38 , which interact at times with contact surfaces  40  which are formed on the end face on the spindle nut  32 , in order to move the slide in the axial direction X. The first mating contact surface  36  is separated from the second mating contact surface  38  by a distance in the axial direction X which is greater than the distance between the contact surfaces  40  and the spindle nut  32 . The free-play distance L is formed on the drive unit  31  by the distance between the first mating contact surface  36  and the second mating contact surface  38 , which is greater than the distance between the contact surfaces  40 . 
     Furthermore, the slide  34  is designed to operate the rocker lever  12  of the circuit breaker  10 . For this purpose, the slide  12  has two drivers  42 ,  44 , with the first driver  42  being intended to operate the rocker lever  12  in the switching-on direction E, and with the second driver  44  being intended to operate the rocker lever  12  in the switching-off direction A. The switching-on direction E is defined by the switching-on movement of the rocker lever  12  from its “off” position in the direction of the “on” position. The switching-off direction A is defined by the switching-off movement of the rocker lever from its “on” position in the direction of the “off” position. In an exemplary embodiment of the present disclosure, the first driver  42  and the second driver  44  are integral components of a claw  46 , which is intended to clasp the rocker lever  12 . 
     The spindle  30  is driven by a motor  50 . The rotary movement of the motor  50  is converted via the spindle  30  and the spindle nut  32  to a linear movement in the axial direction X. The motor  50  is controlled by control logic  52  for the circuit breaker  10 . 
     In order to allow the switching unit  20  to detect the “trip” position of the circuit breaker, the switching unit  20  has a pushbutton  54 . When the rocker lever  12  moves the slide  34  to its position, which corresponds to the “trip” position, the pushbutton  54 , is closed, as a result of which a signal is emitted to the control logic  52 , until the slide  34  leaves the position which corresponds to the “trip” position. With every movement of the slide  34  from the position of the slide  34  which corresponds to the “off” position to the position of the slide  34  which corresponds to the “on” position, the pushbutton  54  likewise passes a signal to the control logic  52 , since the pushbutton  54  is briefly closed and opened. A signal is likewise passed to the control logic if the slide  34  is moved in the opposite direction. 
     The supporting structure  22  and the elements held on it are at least partially enclosed in a housing  60  of the switching unit  20 . The housing  60  has a viewing window  62 , through which the position of the slide  34  in the axial direction X of the spindle  30  is indicated. For this purpose, the slide  34  has an indicating needle  64 . The indicating needle  64  makes it possible for a user to tell whether the rocker lever  12  is in the “on” position, the “off” position or in the “trip” position. 
     A maximum possible movement distance of the slide  34  in the axial direction X of the spindle  30  is preferably chosen to be greater than an operating distance of the rocker lever  12  from the “on” position to the “off” position of a specific type of circuit breaker. This makes it possible for the switching unit  20  to be fitted to different types of circuit breakers. 
     Furthermore, a blocking apparatus  70 , as shown in  FIGS. 1 and 9 , for the spindle  30  is arranged on the housing  60 . This blocking apparatus  70  makes it possible to mechanically prevent the operation of the circuit breaker  10  via the switching unit  20 . This is particularly important for maintenance tasks on a circuit that is protected by the circuit breaker. 
       FIG. 9  shows a partial view of a switching unit of a blocking apparatus for blocking a spindle in accordance with an exemplary embodiment. As shown in  FIG. 9 , the blocking apparatus  70  is formed by a blocking slide  72  that is held on the housing  60  and has two locking surfaces  74 , which interact with the spindle  30  in order to block it. The blocking slide  72  can be moved backward and forward from an unlocking position to a locking position, in a direction R at right angles to the axial direction X of the spindle  30 . In the locking position, the blocking slide  72  can be locked in its position, for example by means of a padlock. Furthermore, a screw which is intended for fitting the switching unit  20  to the circuit breaker  10 , for example a screw for fixing the switching unit  20  to the circuit breaker  10 , can be arranged such that, when the blocking slide  72  is in the locking position, the screw is not accessible for fitting or removing the switching unit  20  to or from the circuit breaker  10 . 
     The spindle  30  has a quadrilateral shape on its end area  75  that is remote from the motor  50 . The two locking surfaces  74  are arranged on two projections  76 , which are formed on the blocking slide  72 . Movement of the blocking slide  72  at right angles to the axial direction X of the spindle  30  results in the end area  75  of the spindle  30  moving between the two locking surfaces  74 , with these locking surfaces  74  resting on two side surfaces of the quadrilateral end area  75 , thus blocking the spindle  30 . 
     In order to allow the blocking apparatus  70  to be moved reliably from its unlocked position, in which the locking surfaces  74  are remote from the spindle  30 , to the locked position, in which the locking surfaces  74  rest on the side surfaces of the quadrilateral end area  75  of the spindle  30 , in any rotation position of the spindle  30 , the blocking slide  72  has an apparatus which rotates the spindle  30 —if necessary—such that the locking surfaces  74  are aligned parallel to two side surfaces of the quadrilateral end area  75 . For this purpose, a surface  78  for alignment of the spindle is provided on each of the projections  76 , on that side which faces the spindle  30  when the blocking slide  72  is in the unlocked position. The surfaces  78  are arranged offset with respect to one another, for example, not opposite one another, in the movement direction R of the blocking slide  72 . This prevents the spindle  30  from sticking to an insertion into the blocking apparatus  70 . 
     The spindle  30 , and in consequence the drive unit  31 , can be blocked by the described blocking apparatus  70 . 
     The circuit breaker  10  can be operated as follows. 
     Before the switching unit  20  is fitted to the circuit breaker  10 , the rocker lever  12  of the circuit breaker  10  is in its “off” position. As shown in  FIG. 2 , the switching unit  20  is fitted to the circuit breaker  10  such that the claw  46  clasps the rocker lever  12 . 
     Before the switching unit  20  can reliably operate the rocker lever  12 , without adversely affecting the operation of the circuit breaker  10 , the switching unit  20  is calibrated for the respective circuit breaker  10 . 
       FIG. 3  shows a partial view of a circuit breaker having a switching unit and rocker lever in an “off” position and a slide in an “off” position in accordance with an exemplary embodiment. As shown in  FIG. 3 , the rotation of the motor  50 , the rotation of the spindle  30  which is coupled to the rotation of the motor  50 , and the linear movement of the spindle nut  32  caused by the rotation of the spindle  30  result in the slide  34  being moved from its initial position in the switching-on direction E to that position in which the first driver  42  touches the rocker lever  12 . This position is detected by monitoring a load current of the motor  50 , which drives the spindle  30 . As soon as the first driver  42  touches the rocker lever  12 , and because the rocker lever  12  can be moved from the “off” position only by exerting force, the load current rises suddenly. This position of the slide, in which the first driver  42  rests on the rocker lever  12  in its “off” position, is referred to as the “off” position of the slide  34 . 
     The “off” position of the slide  34  is preferably moved twice in the switching-on direction E, in order to reference this position. 
       FIG. 4  shows a partial view of a circuit breaker having a switching unit and rocker lever with the slide being shown during a switching-on movement in accordance with an exemplary embodiment. As shown in  FIG. 4 , in order to move the rocker lever  12  from its “off” position to its “on” position, the slide  34  is moved further in the switching-on direction E. In the process, the rocker lever  12  jumps to its “on” position. 
       FIG. 5  shows a partial view of a circuit breaker having a switching unit and a rocker lever in an “on” position and the slide being shown in an extreme position in the switching-on direction in accordance with an exemplary embodiment. As shown in  FIG. 5 , the slide  34  is moved in the switching-on direction E until the first driver  42  makes contact with the rocker lever  12  in its “on” position (see  FIG. 5 ). This position can once again be detected by measurement of the load current, and is referred to as the extreme position of the slide  34  in the switching-on direction E. 
       FIG. 6  shows a partial view of a circuit breaker having a switching unit and rocker lever in an “on” position and the slide likewise being shown in its “on” position in accordance with an exemplary embodiment. In order to avoid adversely affecting the operation of the circuit breaker  10 , it is desirable to release the rocker lever  12  in its “on” position, such that the rocker lever  12  can rock to the “trip” position when the circuit breaker detects a fault situation—or can rock directly to the “off” position if the circuit breaker does not have a “trip” position. For this purpose, the motor  50  is operated in the opposite rotation direction to the rotation direction of the motor  50  for movement of the slide  34  into the switching-on direction E, as a result of which the spindle nut  32  is moved away from the first mating contact surface  36  of the slide  34 , in the switching-off direction A. While the spindle nut  32  is being moved toward the second mating contact surface  38 , the slide  34  is first locked in the extreme position in the switching-on direction E. As soon as the spindle nut  32  touches the second mating contact surface  38 , the slide  34  is moved in the switching-off direction A. As shown in  FIG. 6 , the slide  34  can, for example, be moved until the second driver  44  of the slide  34  makes contact with the rocker lever  12  in its “on” position. This position of the slide  34  can once again be detected by measurement of the load current. This position of the slide  34 , in which the second driver  44  rests on the rocker lever  12  in the “on” position, is referred to as the “on” position of the slide  34 . 
     The “off” position and the “on” position of the slide  34  are stored in the control logic  52  as absolute positions by counting Hall sensor signals with respect to one another, thus making it possible to move directly to these positions. Furthermore, the two extreme positions in the switching-on direction E and in the switching-off direction A can also be determined by measurement of the load current, and can be stored. This makes it possible to prevent the motor  50  from inadvertently moving to a mechanical stop, and thus being overloaded. 
     After the calibration of the switching unit  20 , which has been fitted to the circuit breaker  10 , the switching unit  20  operates as follows. 
     As shown in  FIGS. 3 ,  4 ,  5 , and  6 , when the switching unit  20  receives a switch-on signal from the control center, the slide  34  is moved via the extreme position in the switching-on direction E to the “on” position. 
       FIG. 8  shows a partial view of a circuit breaker having a switching unit and rocker lever in an “off” position and the slide in an extreme position in the switching-off direction in accordance with an exemplary embodiment.  FIGS. 3 ,  6 , and  8  illustrate that when the switching unit  20  receives a switch-off signal from the control center, the slide  34  is moved via the extreme position in the switching-off direction A to the “off” position. As a result, of the movement of the slide via the respective extreme position in the switching-on direction E or in the switching-off direction A to the “on” position or, respectively, to the “off” position, the system comprising the circuit breaker  10  and the switching unit  20  is directly ready to carry out a further switching command from the control center. 
       FIG. 7  shows a partial view of a circuit breaker having a switching unit and rocker lever in a “trip” position in accordance with an exemplary embodiment. As shown in  FIGS. 6 and 7 , if the switching unit  20  is in the “on” position and, in consequence, the electrical contact in the circuit breaker  10  is closed, the rocker lever  12  should be able to pivot freely from the “on” position to the “trip” position in the event of a fault. This is desirable because interference-free operation of the circuit breaker  10  would not be ensured if there were any impediments to the free movement of the rocker lever  12 . In particular, the circuit breaker  10  and/or the electrical devices to be protected could be damaged and/or destroyed. 
     As shown in  FIGS. 6 and 7  (the “on” position is shown by dotted lines), this free movement of the rocker lever  12  from the “on” position to the “trip” position (see  FIG. 7 ) is achieved by the free-play distance L (illustrated in  FIG. 2 ) of the slide  34  relative to the spindle nut  32 . When the slide  34  is in the “on” position, the spindle nut  32  rests on the second mating contact surface  38  of the slide  34 .  FIG. 7  illustrates that when the rocker lever  12  moves from the “on” position to the “trip” position, the slide  34  is moved by the moving rocker lever  12  in the switching-off direction A through the fault movement distance F. This movement is not impeded by the spindle nut  32  because of the free-play distance L between the first mating contact surface  36  and the second mating contact surface  38 . In consequence, the operation of the circuit breaker  12  can be ensured. 
     If the rocker lever has a “trip” position, the free-play distance L is designed such that, when the rocker lever  12  moves from the “on” position to the “trip” position, the spindle nut  32  does not come into contact with the first mating contact surface  36  since, otherwise, correct operation of the circuit breaker  10  would not be ensured. If the rocker lever does not have a “trip” position, that is to say if the rocker lever  12  pivots directly from the “on” position to the “off” position in the event of a fault, the free-play distance L is designed (i.e., configured) such that, when the rocker lever  12  moves from the “on” position to the “off” position, the spindle nut  32  does not make contact with the first mating contact surface  36  since, otherwise, the correct operation of the circuit breaker  10  would not be ensured. 
     In other words, in the event of a fault, the rocker lever  12  operates the second element  34 ′, which in the exemplary embodiment is formed by the slide  34 . In the process, the second element  34 ′ is moved through the fault movement distance F in the switching-off direction A. In order to prevent this movement of the second element  34 ′ that is caused by the rocker lever  12  in the event of a fault from adversely affecting the operation of the circuit breaker  10 , as has already been described, the free-play distance L is chosen to be at least as great as the fault movement distance F. For example, the free-play distance L can be chosen to be greater than the fault movement distance F. 
     As shown in  FIG. 1 , the “trip” position of the slide  34 , and in consequence of the rocker lever  12 , is fixed by means of the pushbutton  54 . The pushbutton  54  is positioned in the axial direction X of the spindle  34  such that the pushbutton  54  produces a continuous signal when the slide  34  is in the “trip” position. The signal from the pushbutton  54  is passed on by the control logic  52  to a remote control center for controlling the switching unit  20 . 
     After the circuit breaker  10  has been switched off because of a fault, that is to say when the rocker lever  12  has been automatically moved from the “on” position to the “trip” position, and after a switch-on command initiated by the control center, in response to which the slide  34  is moved via the extreme position in the switching-off direction A to the “on” position, it is possible that the fault in the circuit which is protected by the circuit breaker has not been rectified. In consequence, the circuit breaker  10  will once again detect a fault and will immediately open the electrical contacts; as a result, the rocker lever  12  is once again moved from the “on” position to the “trip” position. 
     An attempt such as this to switch on the circuit breaker  10  while a fault is present in the circuit to be protected, for example because of a short in the circuit to be protected, should not be carried out indefinitely often in a short time interval, since the circuit breaker  12  and/or the switching unit  20  could otherwise be damaged. The control logic  52  is therefore designed such that only a limited number of switching-on processes are carried out in a certain time interval. 
     In another exemplary embodiment, which is not shown in the drawing, the drive unit of the switching unit has a linear motor. This linear motor is used instead of a motor, as disclosed in relation with the other exemplary embodiments, the spindle, which is caused to rotate by means of the motor, and the spindle nut that is driven by the spindle. A linearly driven first element of the linear motor forms an element that acts in an equivalent manner to the spindle nut and interacts with the slide. Otherwise, this exemplary embodiment is designed (i.e., configured) in a similar manner to the other exemplary embodiments, and is likewise operated in a similar manner to the other exemplary embodiments. 
     It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein. 
     LIST OF REFERENCE SYMBOLS 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 10 
                 Circuit breaker 
               
               
                   
                 12 
                 Rocker lever 
               
               
                   
                 20 
                 Switching unit 
               
               
                   
                 22 
                 Supporting structure 
               
               
                   
                 24 
                 Clamping arms 
               
               
                   
                 26 
                 Bridge 
               
               
                   
                 28 
                 Stud 
               
               
                   
                 30 
                 Spindle 
               
               
                   
                 31 
                 Drive unit 
               
               
                   
                 32 
                 Spindle nut 
               
               
                   
                 34 
                 Slide 
               
               
                   
                 36 
                 First mating contact surface 
               
               
                   
                 38 
                 Second mating contact 
               
               
                   
                   
                 surface 
               
               
                   
                 40 
                 Contact surfaces 
               
               
                   
                 42 
                 First driver 
               
               
                   
                 44 
                 Second driver 
               
               
                   
                 46 
                 Claw 
               
               
                   
                 50 
                 Motor 
               
               
                   
                 52 
                 Control logic 
               
               
                   
                 54 
                 Pushbutton 
               
               
                   
                 60 
                 Housing 
               
               
                   
                 62 
                 Viewing window 
               
               
                   
                 64 
                 Indicating needle 
               
               
                   
                 70 
                 Blocking apparatus 
               
               
                   
                 72 
                 Blocking slide 
               
               
                   
                 74 
                 Locking surfaces 
               
               
                   
                 75 
                 End area of the spindle 
               
               
                   
                 76 
                 Projections 
               
               
                   
                 78 
                 Surface 
               
               
                   
                 A 
                 Switching-off direction 
               
               
                   
                 D 
                 Rotation axis of the rocker 
               
               
                   
                   
                 lever 
               
               
                   
                 E 
                 Switching-on direction 
               
               
                   
                 F 
                 Fault movement distance 
               
               
                   
                 L 
                 Free-play distance 
               
               
                   
                 X 
                 Axial direction of the spindle