Abstract:
A switching apparatus and method, the apparatus comprising a relay including a relay coil and at least one normally open relay contactor that closes when the relay coil is energized, a normally closed stop contactor and a stop member moveable between a deactivated position in which the stop contactor is closed and an activated position wherein the stop member forces each of the stop contactor and the relay contactor open.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     The field of the invention is power controls and more specifically emergency stop and safety relay controls for use with power equipment.  
         [0004]     This section of this document is intended to introduce various aspects of art that may be related to various aspects of the present invention described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the present invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.  
         [0005]     In many industrial systems, high levels of power are required by loads (e.g., manufacturing equipment, HVAC systems, etc.). Power relays are commonly employed to link and de-link power sources to and from loads, respectively. A typical power relay includes a coil and a plurality (e.g., four) of contact pairs or contactors where each contact contactor is either normally open (NO) or normally closed (NC) and changes its state (e.g., open or closed) when the coil is excited. In the case of a relay used with three phase power lines, the relay typically includes at least three NO contactors that close when an associated coil is energized and open when the coil is de-energized. In the case of an NO contactor, a relay spring usually biases the contactors into the normally open state. Typically the force applied by the spring to the contactors upon de-energization of the coil is on the order of one-fourth to one-half pound.  
         [0006]     In addition to the components above, most high power control configurations also include several other components. To this end, a typical control configuration will include a start button and associated NO contactor, an emergency stop (ES) button and associated NC contactor and a fourth normally open power relay contactor (i.e., a fourth normally open contactor that opens and closes when the power relay is de-energized and energized, respectively) where the start and ES contactors are in series with the power relay coil and the fourth NO contactor is in parallel with the start contactor. In this case, to provide power to the load, the start button is pressed to close the NO start contactor thereby providing power through the ES contactor to the power relay coil which causes the power contactors in the power lines as well as the power contactor in parallel with the start contactor to close. When the start button is released, the parallel contactor remains closed so that the relay coil remains energized and the NO contactors remain closed.  
         [0007]     If a problem occurs, a system operator can quickly cut off power to the load by simply pressing the ES button to open the ES contactor which cuts off power to the power relay coil and in turn, at least in theory, should open the NO relay contactors in the power lines as well as the NO contactor that is in parallel with the start button. Here, the force applied by the ES button to the ES contact pair is relatively large (e.g., on the order of 10 to 50 pounds, depending on the force applied by the system user when the ES button is pressed).  
         [0008]     Unfortunately, as well known in the industry, despite cutting off power to the relay coil by pressing an ES button, under certain circumstances, the power relay contactors have been known to remain closed due to mechanical failure, heating/welding of contact pairs, residual magnetism within the relay structure, relay corrosion, frictional forces or a combination of the above. Hereinafter, in the interest of simplifying this explanation, the term “failed” will be used to refer to any NO contactor that remains closed when an associated relay coil is de-energized. Where any contactor in a relay fails, all of the NO contactors within a relay remain in the closed state. When the NO power line contactors fail, a load becomes uncontrollable as the system operator has no way to cut off power to the load.  
         [0009]     To reduce the likelihood of uncontrollable loads, it has become common practice within the industry to design redundant power control configurations. For instance, one common redundant relay configuration includes two power relays where the relay coils are arranges in series with the NC ES contactor and the NO start contactor, a separate NO contactor from each of the two relays is arranged in series in each of the three power supply lines and an arrangement including series linked NO contactors from each of the relays is arranged in parallel with the NO start contactor. In this case, when a power relay contactor in the first relay fails (e.g., welds, sticks closed, etc.), in most cases the contactors in the second relay will remain operational and the load will remain controllable. Thus, even when one relay fails, when the NC ES button is pressed, the NO power line contactors in the second relay should open and cut off power to the load.  
         [0010]     To better ensure redundancy, circuits have been developed that preclude providing power to a load after a relay fails until after the failure is eliminated via either manipulation of the relay or replacement of the relay. For instance, where corrosion causes a contactor to stick in the closed position, some times the contactor can be reopened by cycling through energizing and de-energizing cycles in an effort to overcome the binding effect of the corrosion. Where the spring force is insufficient to separate the NO relay contactors (e.g., in most cases where contacts weld together), the entire relay typically has to be replaced. While redundant relay designs and replacement relays are a solutions to the uncontrolled load and failure problems described above, unfortunately, these solutions are relatively expensive for several reasons. To this end, redundant relay designs require additional relay hardware which increases design and implementation costs. In addition, when the relay spring force fails to open NO contactors during energizing cycles and a relay has to be replaced, the replacement costs include loss of productivity due to down time of equipment linked to the power lines associated with the relay and maintenance costs (e.g., a system operators time) in addition to the cost of the replacement relay.  
         [0011]     Moreover, in at least some cases conditions can occur wherein even redundant relay configurations fail to cut off load power when an ES button is pressed. For instance, when a large unexpected current surge passes through power lines it is possible for both series NO power line relay contactors in each power line to fail (e.g., weld) such that the ES button becomes effectively useless.  
         [0012]     Therefore, it would be advantageous to have an inexpensive power control configuration wherein power to loads could be cut off despite the operational condition of line relays and where failed relays could be salvaged whenever possible despite contactor failure.  
       BRIEF SUMMARY OF THE INVENTION  
       [0013]     Certain aspects commensurate in scope with the originally claimed invention are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.  
         [0014]     It has been recognized that in many cases NO contactors that remain closed for some reason after an associated relay coil is de-energized, would open if more force (e.g., 5 pounds instead of a half a pound applied by a typical relay spring) were applied to the NO contactors. Thus, in many cases relays are replaced despite the fact that the relay contactors are still in condition to operate effectively—the only problem being that the NO relay contactors will not open under the applied spring force.  
         [0015]     It has also been recognized that where contactors fail due to welding or the like, the contactors may still be opened if sufficient force (e.g. 5-10 pounds) is applied thereto. Moreover, it has been recognized that the force applied to an emergency stop button typically is on the order of five or more pounds.  
         [0016]     Based on the above realizations, it has been recognized that a new type of hybrid emergency stop/relay device can be configured wherein an emergency stop button can be used to manually and mechanically open both a normally closed emergency stop contactor and normally open relay coils. Here, the relatively large five or more pound force applied to the emergency stop button is, in addition to being applied to the emergency stop contactor, applied to the relay contactors thereby opening the relay contactors irrespective of whether or not the contactors are stuck in the closed state.  
         [0017]     Consistent with the above comments, at least some embodiments of the invention include a switching apparatus comprising a relay including a relay coil and at least one normally open relay contactor that closes when the relay coil is energized, a normally closed stop contactor and a stop member moveable between a deactivated position in which the stop contactor is closed and an activated position wherein the stop member forces each of the stop contactor and the relay contactor open.  
         [0018]     In some cases the relay contactor is a first relay contactor and the relay includes at least a second normally open relay contactor. In some cases the relay includes third and fourth normally open relay contactors.  
         [0019]     Some embodiments further include a housing forming a cavity and the relay and the stop contactor are mounted within the cavity. In at least some cases the housing forms an opening and the stop member includes a distal end that extends from the opening, when the distal end is pressed, the stop member moving form the deactivated position to the activated position. In some cases the distal end forms a button surface. In some cases the stop contactor is linked in series with the relay coil.  
         [0020]     In some cases the apparatus is for use with a power supply, a load and a start assembly, the apparatus for controlling power provided by the supply to the load via at least one power line, the start assembly including a start member and a normally open start contactor, the first relay contactor linked within the at least one power line between the source and the load, the stop contactor linked in series with the start contactor and the second relay contactor linked in parallel with the start contactor. More specifically, in some cases the apparatus is for use with a three phase load and a three phase source where each load phase is linked to a separate one of the supply phases via a unique power line, the relay further including third and fourth normally open power contactors linked within the second and third power lines between the source and the load, respectively.  
         [0021]     In at least some cases the relay is a first relay and the apparatus further includes a second relay including a second relay coil and at least one normally open second relay contactor that closes when the second relay coil is energized, the stop member, when moved to the activated position, also forcing the second relay contactor open.  
         [0022]     In some embodiments the relay includes an armature that moves along an activation axis when the coil is energized and de-energized, the at least one relay contact linked to the armature to move therewith between the closed and open states, the stop member including a proximal end that bears against at least one of the armature and the stop contact when in the activated position. In some cases the proximal end of the stop member bears against the armature when the stop member is in the activated position. In some cases the stop member includes a coupler that engages the stop contact when the stop member is in the activated position. In some cases the stop member includes a distal end opposite the proximal end and the stop contactor is positioned between the distal end and the relay.  
         [0023]     Other embodiments include an assembly for use with a power supply and a load, the assembly for controlling power provided by the supply to the load via at least one supply line, the assembly comprising a relay including a relay coil and at least a first normally open relay contactor that closes when the relay coil is excited, the relay contactor positioned within the line between the source and the load, a normally closed stop contactor in series with the relay coil and a stop member moveable between a deactivated position in which the stop contactor is closed and an activated position wherein the stop member forces each of the stop contactor and the relay contactor open.  
         [0024]     Some embodiments include a switching apparatus comprising a rigid support structure, a relay mounted within the support structure, the relay including a relay coil, an armature and at least one normally open relay contactor, the contactor including at least one moveable contact and one stationary contact, the moveable contact mounted for movement to the armature, the armature and moveable contact moving between a de-energized position and an energized position along an armature axis when the coil is energized and de-energized, respectively, the moveable contact closed with the stationary contact when the armature is in the energized position, a normally closed stop contactor mounted within the support structure, the stop contactor including at least one moveable contact and at least one stationary contact and a stop button mounted to the support structure for movement between an activated position and a deactivated position along a stop axis that is substantially parallel to the armature axis, the stop button operably juxtaposed with respect to each of the stop contactor and the armature such that when the stop button is activated, the stop button opens each of the stop contactor and the normally open relay contactor.  
         [0025]     Still other embodiments include a switching apparatus comprising a relay including a relay coil and at least one normally open relay contactor that closes when the relay coil is energized and a manual open button moveable between a deactivated position in which the button is de-linked from the relay contactor and an activated position wherein the button forces the relay contactor open. Here, in some cases the apparatus will further include a housing that forms a cavity and at least one opening into the cavity, the relay mounted within the cavity and the button mounted within the opening.  
         [0026]     The invention also includes a method for cutting off power from a source to a load when a stop button is activated, the method comprising the steps of providing a normally closed emergency stop contactor that is mechanically linked to the stop button such that when the stop button is activated, the stop contactor is opened and providing a relay including a coil in series with the stop contactor and at least one relay contactor in series between the source and the load wherein the contactor is mechanically linked to the stop button such that when the stop button is activated, the relay contactor is opened.  
         [0027]     These and other objects, advantages and aspects of the invention will become apparent from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention and reference is made therefore, to the claims herein for interpreting the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0028]      FIG. 1  is a schematic diagram illustrating a system including an emergency stop/relay module according to at least some aspects of the present invention wherein components are in normal states when a relay coil is deenergized;  
         [0029]      FIG. 2  is similar to  FIG. 1 , albeit illustrating the components when a start button is pressed and the relay coil is energized;  
         [0030]      FIG. 3  is similar to  FIG. 1 , albeit illustrating the components when an emergency stop button is pressed to open both an emergency stop contactor and relay contactors via mechanical force;  
         [0031]      FIG. 4  is a perspective view of an exemplary emergency stop/relay module according to one embodiment of the present invention;  
         [0032]      FIG. 5  is an exploded view of the module of  FIG. 4 ;  
         [0033]      FIG. 6  is a cross-sectional view taken along the line  6 - 6  of  FIG. 4  where components are shown in positions that occur when a relay coil is energized and when an emergency stop button is released;  
         [0034]      FIG. 7  is similar to  FIG. 6 , albeit illustrating the module components when the emergency stop button  20  is pressed; and  
         [0035]      FIG. 8  is similar to  FIG. 1 , albeit illustrating another emergency stop/relay module embodiment that includes two relays. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0036]     While the present invention may be embodied in any of several different forms, the present invention is described here with the understanding that the present disclosure is to be considered as setting forth an exemplification of the present invention which is not intended to limit the invention to the specific embodiment(s) illustrated.  
         [0037]     Referring now to the drawings wherein like reference numerals correspond to similar elements throughout the several views and, more specifically, referring to  FIG. 1  the present invention will be described in the context of an exemplary power control system  10  including a control voltage source  12 , a three-phase voltage source  14 , a load  16 , a start button  20  and associated start contactor  21  and an emergency stop/relay module  18 . As its label implies, source  14  provides three-phase voltages on three supply lines  46 ,  48  and  50  to module  18  which controls three-phase output voltages provided to load  16  on lines  52 ,  54  and  56 . To this end, module  18  includes emergency stop button  22  and an associated emergency stop contactor  73  and a relay  62 .  
         [0038]     Herein, each of contactor  73  and other contactors includes stationary and moveable contacts where, as the labels imply, moveable contacts are moved with respect to the stationary contacts to open or close an associated contactor. Thus, for instance, contactor  73  includes a moveable contact  11  (or moveable contact sub-assembly) that moves with respect to stationary contacts (not separately labeled) to open and close contactor  73 . Similarly, start contactor  21  includes moveable contact  61  that moves with respect to stationary contacts (not separately labeled) to open and close contactor  21 .  
         [0039]     Emergency stop button  22  includes a button spring  15  and, for illustrative purposes only, two extension members  35  and  36  that extend into a housing that accommodates other module components. The button spring  15  biases button  20  out of the housing and into a released position. The proximal end of extension member  36  is mechanically linked to the movable contact  11  associated with normally closed contactor  73  so that contact  11  moves along with button  22  (i.e., when spring  15  forces button  22  into the released position illustrated in  FIG. 1 , moveable contact  11  follows button  22  and is closed and, when button  22  is pressed, movable contact  11  is forced open (see  FIG. 3 )).  
         [0040]     Referring still to  FIG. 1 , relay  18  includes four normally open contactors  26 ,  28 ,  30  and  32 , an armature or yoke identified by numerals  34 ,  34   a ,  34   b ,  34   c  and  34   d  and a coil  24 . Hereinafter, unless indicated otherwise, the relay armature will be identified by numeral  34 . As well known in the industry, armature  34  is mechanically linked to the movable contacts (not separately labeled) of each of the normally open contactors  26 ,  28 ,  30  and  32  so that the moveable contacts associated with contactors  26 ,  38 ,  30  and  32  move with armature  34 . These mechanical linkages between the armature and the movable contacts are schematically represented by armature extensions  38 ,  40 ,  42  and  44 .  
         [0041]     Armature  34  can assume two different steady-state positions. First, as illustrated in  FIG. 1 , armature  34  may be in a de-energized position where each of the normally open contactors  26 ,  28 ,  30  and  32  is open. Second, as illustrated in  FIG. 2 , armature  34  may be in an energized position wherein the armature physically moves within the relay and forces the movable contacts of each of contactors  26 ,  28 ,  30  and  32  into a closed state. A spring  19  is provided within relay  62  to bias armature  34  into its de-energized position as illustrated in  FIG. 1 .  
         [0042]     Referring still to  FIG. 1 , coil  24  is arranged with respect to armature  34  such that, when coil  24  is energized, a magnetic field created thereby causes armature  34  to move from the de-energized position into the energized position. Thus, when coil  24  is energized, armature  34  is forced into the position illustrated in  FIG. 2  and each of contactors  26 ,  28 ,  30  and  32  is closed. When coil  24  is de-energized, spring  19  forces armature  34  into the deactivated position illustrated in  FIG. 1 .  
         [0043]     Referring again still to  FIG. 1 , to control three-phase power to load  16 , each of normally open relay contactors  28 ,  30  and  32  is placed in series with a separate one of the three load phases. Thus, for instance, contactor  28  is placed in series between source supply line  50  and load supply line  52 . Similarly, contactors  30  and  32  are placed in series between lines  48  and  54  and between lines  46  and  56 , respectively. When contactors  28 ,  30  and  32  are closed, power is provided from source  14  to load  16  via lines  52 ,  54  and  56  and when contactors  28 ,  30  and  32  are open power is cut off from load  16 .  
         [0044]     Referring to still  FIG. 1 , start button  20  is mechanically linked via an extension member  23  with a movable contact  61  of normally open start contactor  21 . When start button  20  is not pressed, a spring  17  forces button  20  and movable start contact  61  into the open position illustrated in  FIG. 1 . However, when button  20  is pressed as indicated by arrow  69  in  FIG. 2 , movable start contact  61  is forced into the closed position.  
         [0045]     Referring once again to  FIG. 1 , start contactor  21  is linked in series with emergency stop contactor  60 , coil  24  and control source  12  to form a start-stop circuit. Fourth normally open relay contactor  26  is arranged in parallel with the start contactor  21 .  
         [0046]     Importantly, under certain circumstances, extension member  35  contacts armature  34  when emergency stop button  22  is pressed. More specifically, when armature  34  is in the energized position as illustrated in  FIG. 2 , extension member  35  mechanically contacts actuator  34  (see  FIG. 2 ) such that, if energy stop button  22  is pressed, in addition to forcing emergency stop contactor  73  open, the pressing action forces armature  34  from the energized position (see  FIG. 2 ) toward the de-energized position (see  FIG. 3 ).  
         [0047]     In operation, referring once again to  FIG. 1 , prior to providing power to load  16 , normally open start contactor  21  is open, normally closed emergency stop contactor  73  is closed, armature  34  is in the de-energized position and each of relay contactors  26 ,  28 ,  30  and  32  is open. To provide power to load  16 , start button  20  is pressed as indicated by arrow  69  in  FIG. 2  thereby closing start contactor  21 . When contactor  21  is closed, power is provided from source  12  to coil  24 . When power is provided to coil  24 , coil  24  is energized which in turn forces armature  34  from the de-energized position illustrated in  FIG. 1  into the energized position illustrated in  FIG. 2 , each of the normally open contactors  26 ,  28 ,  30  and  32  is closed and extension member  35  is in contact with armature  34 . When button  20  is released, spring  17  forces button  20  into the released state and start contactor  21  opens. However, because relay contactor  26  in parallel with start contractor  21  is now closed, coil  24  remains energized and hence contactors  28 ,  30  and  32  remain closed thereby providing power to load  16 .  
         [0048]     To quickly cut off power to load  16 , referring once again to  FIG. 2 , emergency stop button  22  is pressed. Referring also to  FIG. 3 , when button  22  is pressed as indicated by arrow  70 , emergency stop contactor  73  is opened thereby momentarily cutting off power to coil  24  and causing coil  24  to be deenergized. When coil  24  is deenergized, in theory, the spring associated with armature  34  should force armature  34  into the deactivated position as illustrated in  FIG. 3  wherein contactors  26 ,  28 ,  30  and  32  open. Once contactor  26  is open, when stop button  22  is released and spring  15  forces button into the released position thereby closing stop contactor  73 , power should still be cut off to coil  24  as neither of the start contactor  21  or relay contactor  26  is closed.  
         [0049]     Referring once again to  FIG. 2 , as described above, in at least some cases, relay contactors  26 ,  28 ,  30  and  32  have been known to remain closed even after an emergency stop button  22  has been pressed. In the case of the present invention, sticking or welded relay contactors are forced open by contacting the emergency stop button  22  to armature  34  via extension member  35 . Thus, referring again to  FIG. 3 , when stop button  22  is pressed as indicated by arrow  70 , in addition to opening emergency stop contactor  60 , the pressing activity mechanically forces armature  34  from the energized position to the de-energized position thereby opening each of relay contactors  26 ,  28 ,  30  and  32 . Here, where a five or more pound force is applied to button  22  when the button is pressed, a large force is applied to armature  34  which, it has been observed, is sufficient to open stuck or even welded contactors. When button  22  is released, spring  15  again forces button  22  and the mechanically linked moveable contact  11  into the released positions illustrated in  FIG. 1 . Because extension member  35  is not mechanically linked to armature, when button  22  is forced into the released state, extension member  35  separates from armature  34  (see  FIG. 1 ) and contactors  26 ,  28 ,  30  and  32  remain open.  
         [0050]     Referring now to  FIGS. 4-7 , an exemplary emergency stop/relay module  18  consistent with the description above is illustrated. In the exemplary embodiment, module  18  includes a housing  19  that forms a cavity  81  and at least one opening  27  that opens into the cavity  61 . A normally closed emergency stop contactor assembly  60 , extension members  35   a  and  35   b  and a relay  62  are all mounted within cavity  81 . More specifically, button  22  is mounted within opening  27  and emergency stop contactor module  60  is sandwiched between relay  62  and button  22 .  
         [0051]     Although not illustrated in  FIGS. 4-7 , contactor module  60  includes stationary and movable contacts and a spring that biases the movable contacts into a normally closed position (see again  FIGS. 1-3 ).  
         [0052]     Referring still to  FIG. 6 , extension members  35   a  and  35   b  are mounted within openings  93   a  and  93   b  formed by module  60  and are biased against an undersurface  83  of button  22  by springs  43 . Thus extension members  35   a  and  35   b  move along with button  22  during operation.  
         [0053]     Referring still to  FIG. 6 , relay  62  includes, among other things, a coil  24 , an armature  34 , a spring  51  and a contact block  79 . Armature  34  includes several components that are rigidly mechanically connected including a magnetic member  34   a , a plunger  34   b  and armature extensions  34   c  and  34   d . Each of extensions  34   c  and  34   d  includes an upper end  85   a  and  85   b  that is received in openings formed by module  60  where the openings align each of ends  85   a  and  85   b  with a lower end of one of extension members  35   a  and  35   b . While ends  85   a  and  85   b  are received in module  60  openings, ends  85   a  and  85   b  are nevertheless able to slide lengthwise within the openings (i.e., along a trajectory parallel to arrow  70  in  FIG. 7 ). Thus when button  22  is pressed and forces members  35   a  and  35   b  downward, force is also applied to drive members  34   c  and  34   d  downward. However, because extensions  34   c  and  34   d  are not mechanically linked to extension member  35   a  and  35   b  when button  22  is released and moved back to the released position, while springs  43  moves extension members  35   a  and  35   b  along with button  22 , extensions  34   c  and  34   d  do not automatically follow.  
         [0054]     Referring still to  FIG. 6 , magnetic member  34   a  is generally shaped to be received within a cavity formed by coil  24  and forms an opening in a lower surface for receiving an upper end of plunger  34   b . Plunger  34   b  is an elongated member that includes a distal end  97  that extends from member  34   a . A pin  53  or the like passes through apertures  89   a  and  89   b  and similarly sized openings formed in member  34   a  and plunger  34   b  to secure extensions  34   c  and  34   d , member  34   a  and plunger  34   b . Lower ends  87   a  and  87   b  of members  35   a  and  35   b  form apertures  89   a  and  89   b.    
         [0055]     Referring still to  FIG. 6 , member  34   a  is received within coil  24  and is biased downward by spring  51 . The lower end of plunger  34   b  is mounted to a yoke that carries the movable contacts of normally open contactors  26 ,  28 ,  30  and  32 . For example, in  FIG. 6 , contactor  26  includes a stationary contact  49  and a movable contact  47  where movable contact  47  is carried by the yoke that is rigidly attached to the distal end of plunger  34   b.    
         [0056]     Referring still to  FIG. 6 , when coil  24  is energized, member  34   a  and plunger  34   b  are pulled upward which in turn causes the normally open contacts in block  79  to close. When button  22  is pressed as indicate by arrow  70 , the emergency stop contacts (not illustrated in  FIGS. 6-7 ) are opened. In addition, referring to  FIG. 7 , the lower ends of extension members  35   a  and  35   b  contact the upper ends of extensions  34   c  and  34   d  and, through extensions  34   c  and  34   d , force magnetic member  34   a  and plunger  34   b  downward. As illustrated in  FIG. 7 , when plunger  34   b  moves downward, the normally open relay contactors (e.g.,  26 ) are opened. When button  22  is released, springs  43  forces extension members  35   a  and  35   b  to follow button  22  while spring  51  maintains member  34   a , plunger  34   b  and the relay contactors in the normally open state. Here, until the relay contactors are again closed, the upper ends of extensions  34   c  and  34   d  will be separated from the lower ends of members  35   a  and  35   b . However, once the emergency stop contactors again close and magnetic member  55  is forces upward, extensions  34   c  and  34   d  are also forced upward until the top ends thereof contact the lower ends of members  35   a  and  35   b.    
         [0057]     Referring now to  FIG. 8 , another exemplary power control system  100  that is consistent with at least some aspects of the present invention is illustrated. In  FIG. 8 , many of the components illustrated are similar to the components described above and are therefore identified by similar numbers. For instance, the start button in  FIG. 8  is identified by numeral  20 . Similarly, the three-phase power source is identified by numeral  14  in  FIG. 8  as is the source in each of  FIGS. 1-3  above.  
         [0058]     The main difference between system  100  and the system described above with respect to  FIGS. 1-3  is that the emergency stop/relay module  118  in  FIG. 8  includes two separate four contactor relays instead of a single relay so that additional redundancy can be provided via an assembly located within a single housing. To this end, in addition to the relay  62  described above, emergency stop/relay module  118  includes a second relay  162  including a second relay coil  124 , a second relay armature  134  and first through fourth normally open contactors  126 ,  128 ,  130  and  132 . Here, relay contactor  126  is linked in series with contactor  26  and both of those contactors are in parallel with the start contactor  36 . Contactor  128  is in series with contactor  28  between source  14  and load  16 . Similarly, contactors  30  and  130  are in series between the source and load while contactors  32  and  132  are in series between the source and load.  
         [0059]     Referring still to  FIG. 8 , the start-stop circuit includes start contactor  36  in series with emergency stop contactor  73 , coil  24 , second relay coil  124  and control voltage source  12 . As illustrated, armature  134  is movable to open and close the second relay contactors  126 ,  128 ,  130  and  132 . In addition, another extension member  135  is provided that extends from emergency stop button  22  and that contacts armature  134  when button  22  is pressed or when armature  134  is in the energized position. In  FIG. 8 , button  22  is shown pressed such that each of armatures  34  and  134  are in the deactivated positions and all of the relay coils are open.  
         [0060]     From the foregoing, it will be observed that numerous modifications and variations can be effected without departing from the true spirit and scope of the novel concept of the present invention. It will be appreciated that the present disclosure is intended as an exemplification of the invention, and is not intended to limit the invention to the specific embodiment illustrated. For example, while the invention is described in the context of a relay including four normally closed contactors, other relay types are contemplated. In addition, while several embodiments include a button for simultaneously controlling an emergency stop contactor and relay contactors, other embodiments are contemplated where a button is solely provided for manually opening relay contactors without affecting an emergency stop contactor. Moreover, other embodiments are contemplated wherein a relay contactor block may be sandwiched between an emergency stop button and an emergency stop contactor. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.  
         [0061]     To apprise the public of the scope of this invention, the following claims are made: