Patent Publication Number: US-2022225518-A1

Title: Apparatus and Method for Module Retention in a Motor Control Center

Description:
BACKGROUND INFORMATION 
     The subject matter disclosed herein relates to a Motor Control Center (MCC). More specifically, a hook plate is mounted to modules inserted into the MCC to prevent inadvertent ejection of the module from the MCC. 
     As is known to those skilled in the art, a Motor Control Center (MCC) is a power distribution center to control multiple motors from a central location. The MCC includes a power infeed configured to receive the power which is, in turn, distributed to each of the motors controlled by the MCC. The power may be a multi-phase alternating current (AC) power supply such as a 230 VAC or a 460 VAC three-phase utility supply. A primary breaker is sized according to the combined current ratings of each module to be included within the MCC and allows for a central disconnect of the MCC from the utility supply. Within the MCC a series of voltage busses extend horizontally and/or vertically to distribute the utility voltage to each module within the MCC. The MCC may include a single vertical unit, configured to receive multiple modules or multiple vertical units stacked adjacent to each other, where each vertical unit is configured to receive one or more modules. 
     The vertical unit includes slots configured to receive modules which are, in turn, configured to control operation of a motor. Each module may include, for example, a contactor configured to enable or disable a motor, a reversing contactor configured to additionally control direction of rotation of the motor, a starter configured to accelerate and/or decelerate a motor according to a preset ramp or acceleration profile, or a motor drive configured to control operation of the motor according to a position, velocity, or torque command. Additional modules may be provided, for example, that measure voltage and/or current being conducted along a bus within the MCC and that display the information to a technician. Each module is inserted into one of the slots on the MCC. Empty slots may receive a cover plate to prevent access internal to the MCC during operation. 
     Modules are configured to be inserted into and removed from the MCC with the module in an off condition. It is contemplated that an individual slot may be accessed with power supplied to the MCC, allowing “hot-swaps” of a module that has failed or insertion of a new module without requiring all motors controlled by the MCC to be shut down. A cover plate is removed, or an old module removed, and a new module is inserted into one of the slots. After insertion into the slot, a handle, also referred to herein as a connection handle, is used to fully engage the module within the MCC. During insertion, the connection handle is initially in an off position. The module is inserted a first distance into the MCC by manual insertion. The connection handle may then be moved between an off position and a test position. In the test position, the module is drawn further into the MCC, establishing connections with control power and network communications. The connection handle may be moved still further to an on position, where moving the handle to the on position mechanically draws the module still further into the MCC, during which contacts on the module engage the bus bars within the MCC and connect the module to the power distributed within the MCC. The physical transition of the connection handle to the on position may also cause a mechanical interlock to engage between the module and housing of the MCC to positively retain the module within the housing, preventing removal while the module is in the on position. 
     However, the MCC may operate with some modules in the on position and some modules in the off or test positions, according to the application requirements. In the off or test positions, the mechanical interlock which engages the housing of the MCC in the on position is not set. Still other modules may not include the mechanical interlock. One hazard associated with a MCC is an arc-flash hazard. An arc-flash may occur when a fault condition causes one phase of the voltage to momentarily connect to ground. Because the MCC is configured to distribute a large amount of current to multiple motors, a temporary ground fault condition can cause a substantial arc-flash, which is a sudden discharge of electrical energy and which may include substantial light, heat, and a concussive force sometimes equated to an electrical explosion. The force generated by an arc-flash condition may be sufficient to eject a module from the MCC without the mechanical interlock being engaged, creating a hazard to personnel and/or other equipment located in the control room. 
     Thus, it would be desirable to provide an apparatus to retain modules within an MCC and to prevent inadvertent ejection of the module from the MCC. 
     BRIEF DESCRIPTION 
     According to one embodiment of the invention, an apparatus for retaining a module in a motor control center includes a plate and a spring. The plate is configured to be mounted on an outer surface of a housing for the module. The plate includes a first end, a second end opposite the first end, and a retaining member configured to extend into the housing for the module. The spring includes a first end and a second end. The first end of the spring is configured to mount to the retaining member within the housing for the module, and the second end of the spring is configured to mount within the housing for the module. The spring is configured to apply a force to the plate in a direction away from the outer surface of the housing for the module when mounted between the retaining member and the housing for the module, and the second end of the plate is configured to resist removal of the module from the motor control center. 
     According to another embodiment of the invention, a method for retaining a module in a motor control center includes inserting the module a first distance into the motor control center, where the first distance is less than full insertion into the motor control center. Inserting the module the first distance into the motor control center includes deflecting a biasing member of an apparatus mounted on an outer surface of a housing for the module from a first position toward the outer surface of the housing to a second position, and expanding a spring mounted between a retaining member of the apparatus and an inner surface of the housing. The method further includes the step of inserting the module a second distance into the motor control center, where the second distance is a difference between full insertion and the first distance into the motor control center. Inserting the module the second distance into the motor control center includes moving the biasing member of the apparatus away from the outer surface of the housing with a force generated by the spring when the module is fully inserted into the motor control center, and engaging the motor control center with the biasing member when the module is fully inserted into the motor control center to resist removal of the module from the motor control center. 
     According to still another embodiment of the invention, an apparatus for retaining a module in a motor control center includes a plate and a spring. The plate is compressibly mounted on an outer surface of a housing for the module. The plate includes a first retaining member configured to extend into the housing for the module and a second retaining member configured to engage the motor control center. The spring is mounted between the first retaining member and an inner surface of the housing for the module. The spring is extended by compressing the plate against the outer surface of the housing during insertion of the module into the motor control center, and the spring applies a force to the plate away from the outer surface of the housing when the spring is extended. The second retaining member is configured to engage the motor control center when the module is fully inserted to resist removal of the module from the motor control center. 
     These and other advantages and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various exemplary embodiments of the subject matter disclosed herein are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which: 
         FIG. 1  is a perspective view of a module housing with one embodiment of a hook plate mounted on one side of the module; 
         FIG. 2  is a partial top plan view of a first side of the module housing of  FIG. 1  being aligned for insertion into a motor control center; 
         FIG. 3  is a partial top plan view of a second side of the module housing of  FIG. 1  beginning insertion into the motor control center; 
         FIG. 4  is a partial top plan view of the second side of the module housing inserted into the motor control center; 
         FIG. 5  is a partial perspective view of a section of the second side of the module housing inserted into the motor control center; 
         FIG. 6  is a perspective view of the hook plate of  FIG. 1 ; 
         FIG. 7  is a lower plan view of the hook plate of  FIG. 6 ; 
         FIG. 8  is an upper plan view of the hook plate of  FIG. 6 ; 
         FIG. 9  is a side elevation view of the hook plate of  FIG. 6 ; and 
         FIG. 10  is a front elevation view of an exemplary motor control center incorporating one embodiment of the present invention. 
     
    
    
     In describing the various embodiments of the invention which are illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word “connected,” “attached,” or terms similar thereto are often used. They are not limited to direct connection but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. 
     DETAILED DESCRIPTION 
     The various features and advantageous details of the subject matter disclosed herein are explained more fully with reference to the non-limiting embodiments described in detail in the following description. 
     The subject matter disclosed herein describes an apparatus to retain modules within a Motor Control Center (MCC) and to prevent inadvertent ejection of the module from the MCC. A plate is mounted to the outside of each side of the module housing. The plate includes a hook at one end which is inserted through an opening in the module housing. The hook allows the plate to pivot about the opening in the module while retaining the plate to the module. The plate also includes a retaining member extending through an opening in the module housing. The retaining member is configured to receive one end of a spring, where the opposite end of the spring is connected to an interior surface within the module housing. The spring is under tension when connected between the retaining member of the plate and the housing, such that the spring pulls the retaining member toward the module housing. 
     The front of the plate includes a biasing member which engages the housing of the MCC as the module is inserted into the MCC. The biasing member compresses the plate against the outer surface of the module housing, stretching the spring internal to the module housing. As the module is inserted still further into the MCC, the biasing member reaches an opening within the MCC housing. The force applied by the spring draws the retaining member toward the inner surface of the module housing and causes the biasing member to move away from the outer surface of the module housing. The biasing member fits into the opening within the MCC housing and positively retains the module within the MCC housing. In order to remove the module from the MCC housing, a technician must manually compress the plate against the outside surface of the module housing, releasing the biasing member from the MCC housing, and then pull the module from the MCC housing. Thus, the plate and spring provide an apparatus to retain modules within a Motor Control Center (MCC) and to prevent inadvertent ejection of the module from the MCC. 
     Turning initially to  FIG. 1 , one embodiment of a module  10  for insertion into a MCC  20  (see also  FIG. 10 ) is illustrated. Each MCC  20  includes at least one and typically a number of vertical columns  22 . Multiple modules  10  may be inserted into each column. The module  10  has a housing  15  which is generally a box-like construction, and is also referred to sometimes as drawer, for insertion into the MCC  20 . The module  10  is illustrated from the front  12 , side  14 , and top  16 . It is noted that relational terms, such as front, rear, top, bottom, upper, lower, left, right, side, and the like, are used with respect to the figures for ease of description and are not intended to be limiting. The module  10  may, for example, be inserted into a slot within the MCC  20  in a horizontal orientation or a vertical orientation by rotation of the module  10  and by which relational terms are similarly rotated. 
     An apparatus  50  for retaining the module  10  in the MCC  20  is shown mounted to one side  14  of the module  10 . The apparatus  50  will also be referred to herein as a hook plate. A second hook plate may be mounted on the opposite side of the module  10 . Turning next to  FIGS. 6-9 , an exemplary embodiment of the hook plate  50  is illustrated. The hook plate  50  may be made from a single piece of sheet material, such as a metal sheet, where the sheet material is formed via cutting, stamping, bending, and the like to form the illustrated hook plate. The hook plate  50  includes a first end  52  and a second end  54 , opposite the first end. A first side  56  and a second side  58 , opposite the first side, each extend between the first and second ends  52 ,  54 . The hook plate  50  has a generally planar segment with an upper surface  60  and a lower surface  62 . 
     The first end  52  of the hook plate  50  is configured to mount to the side  14  of the module  10  before insertion into the MCC  20 . The first end  52  includes a first retaining member  70  configured to retain the hook plate  50  to the module  10  and allow movement of the hook plate  50  with respect to the outer surface of the module. According to the illustrated embodiment, the first retaining member  70  is an elongated hook spanning, in part, the width of the hook plate  50  and, in part, a portion of the width of the hook plate  50 . The elongated hook may be formed by bending a first segment  72  of the hook plate  50  at a first angle and bending a second segment  74  of the hook plate  50  a second angle, the second angle greater than the first angle. The first segment  72  of the elongated hook  70  spans the width of the hook plate  50  and may be bent downwards, for example, about thirty degrees from the generally planar surface of the hook plate  50 . The angle may vary and may be up to forty-five degrees. The second segment  74  of the elongated hook  70  spans about one-half the width of the hook plate  50  and is centrally positioned between the first side  56  and the second side  58  of the hook plate  50 . The second segment  74  may be bent at an angle of approximately ninety degrees with respect to the first segment  72  such that it is angled back toward the second end  54  of the hook plate  50 . The combination of the first segment  72  and second segment  74  define a hook configured to extend through an opening  17  (see  FIG. 3 ) in the side  14  of the housing  15  for the module  10 . The illustrated retaining member  70  is not intended to be limiting but provides one embodiment. It is contemplated that the first retaining member  70  may take other shapes, such as the first segment  72  and the second segment  74  having the same width, the second segment  74  having multiple portions or both the first and second segments having multiple portions defining multiple hooks to engage the housing  15  of the module. Optionally, the first retaining member  70  may be configured with a continuously curving surface rather than a first and second stamped segment  72 ,  74 . 
     The second end  54  of the hook plate  50  is configured to engage the housing  25  of the MCC  20 . The second end  54  includes at least one biasing member  80  configured to engage the housing  25  of the MCC  20  during insertion and to retain the hook plate  50  within the MCC  20  when the module  10  is fully inserted into the MCC. According to the illustrated embodiment, the at least one biasing member  80  includes a first hook portion  82  and a second hook portion  84 . Each hook portion  82 ,  84  extends from the second end  54  of the hook plate  50  and curls up and back toward the hook plate  50 . An upper surface  83  of the first hook portion  82  and an upper surface  85  of the second hook portion  84  are sloped upward from the second end  54  toward the center of the hook plate  50 , and the portion of each hook portion  82 ,  84  facing the center of the hook plate  50  is open. Each hook portion  82 ,  84  is positioned toward one side  56 ,  58  of the hook plate  50 . Optionally, a single hook portion may be included in a central region of the hook plate or still other numbers of hook portions may be formed from the sheet material from which the hook plate  50  is made. Each hook portion may be formed by first cutting or stamping a tab in the second end  54  of the hook plate and curling the end back. It is contemplated that the biasing member  80  may include alternate constructions. According to one aspect of the invention, the second end  54  of the hook plate  50  may include one or more tabs integrally formed on the plate. Each tab may include a tapered surface with a narrow end of the tapered surface proximate to the second end  54  of the hook plate and a wider end of the tapered surface positioned inward toward the center of the hook plate  50 . A flat surface may extend downward at the widest end of the tab to the upper surface  60  of the hook plate  50 . Still other suitable arrangements of biasing members may be included without deviating from the scope of the invention. 
     A second retaining member  90  may be positioned in a middle region of the hook plate  50 . According to the illustrated embodiment, the second retaining member  90  may be formed between the first hook portion  82  and the second hook portion  84 . The hook plate  50  is cut for a distance from the second end  54  of the hook plate toward the center portion of the hook plate along each side of the first and second hook portions  82 ,  84 . The second retaining member  90  is formed from the sheet material remaining between each cut. The sheet material is first bent downward defining a first segment  92  of the second retaining member  90 . The sheet material is then bent such that a second segment  94  is generally orthogonal to the first segment  92  of the second retaining member  90 . At least one opening  96  is formed in the second segment  94 , where each opening  96  is configured to receive one end of a spring  100 . 
     In operation, the hook plate  50  is configured to positively retain the module  10  within the MCC  20  once the module  10  has been fully inserted. With reference to  FIG. 1 , a hook plate  50  is mounted to the side of the housing  15  for each module  10 . Although only one side of the housing  15  is visible, it is contemplated that a first hook plate  50  is mounted on a first side of the module  10 , and a second hook plate  50  is mounted on a second side of the module  10 . The first retaining member  70  on the first end  52  of the hook plate  50  is inserted through a first opening  17  in the housing  15  of the module  10  (see also  FIG. 3 ). The hook shape of the first retaining member  70  allows the hook plate  50  to pivot about the edge of the housing  15 . The second retaining member  90  is inserted through a second opening  19  in the housing  15 . At least one spring  100  is mounted between the second segment  94  of the second retaining member and an inner surface of the housing  15 . According to the illustrated embodiment, the hook plate  50  includes two openings  96  in the second segment  94 . A first spring  100  is mounted to one of the openings  96 , and a second spring is mounted to the second opening  96 . The springs  100  draw the second segment  94  of the second retaining member  90  toward the housing  15  of the module. The second retaining member  90 , in turn, pushes the hook plate  50  away from the outer surface of the module  10  as it is drawn toward the housing  15 . 
     With reference to  FIGS. 2-5 , the steps for inserting the module  10  into the MCC  20  are illustrated. In  FIG. 2 , the module  10  is positioned into a slot for the MCC  20 . The module  10  is inserted for a first distance before the hook plate  50  begins to engage the housing  25  of the MCC  20 . As illustrated in  FIG. 2 , the module  10  has not yet been inserted a sufficient distance for the hook plate  50  to begin engaging the housing  25  of the MCC. As illustrated in  FIG. 3 , the module  10  has been inserted beyond the first distance and the hook plate  50  is already engaging the housing  25  of the MCC. As the hook plate  50  begins to engage the housing  25  of the MCC, the upper surface  83 ,  85  of each hook portion  82 ,  84  meets the edge of the housing  25  for the MCC  20 . The tapered upper surface  83 ,  85  slides along the edge of the housing  25 , compressing the hook plate  50  inward toward the outer surface of the housing  15  of the module  10 . As the hook plate  50  is compressed inwards, the second retaining member  90  is pushed further into the housing  15  and stretches the spring, or springs,  100  within the module  10 . Stretching the springs  100  creates a force applied to the second retaining member  90  in a direction toward the inner surface of the housing  15 . 
     Turning next to  FIGS. 4 and 5 , the module  10  is shown fully inserted into the MCC  20 . When the module  10  is fully inserted into the MCC  20 , the biasing member  80  is located next to an opening  30  in the housing  25  of the MCC  20 . Because the biasing member  80  is no longer adjacent to the surface of the housing  25 , the force of the spring, or springs,  100  applied to the second retaining member  90  draws the second retaining member  90  toward the inner surface of the module housing  15  and, in turn, moves the hook plate  50  away from the outside surface of the module housing. The biasing member  80  is, moved inward to the opening  30  within the housing of the MCC  20 . As shown in  FIGS. 4 and 5 , the hook portions  82 ,  84  of the biasing member  80  extend around the surface of the housing  25  for the MCC. As a result, an attempt to remove the module  10  will cause the hook portion  82 ,  84  to catch on the housing  25  and prevent removal of the module  10 . The hook portions  82 ,  84  can prevent an intentional attempt to remove the module  10  or an inadvertent attempt to eject the module. 
     In order to remove the module  10 , the hook plate  50  must first be compressed toward the outer surface of the housing  15  for the module  10 . With reference to  FIG. 4  and as may be appreciated via the illustration of  FIG. 2 , when the module  10  is fully inserted into the MCC, the front plate  12  of the module  10  does not fully engage the housing  25  of the MCC  20 . A gap exists between the housing  25  and the module through which a technician may access the hook plates  50 . Manual pressure may be applied by the technician to the upper surface  60  of each hook plate  50 , compressing the hook plate against the outer surface of the module  10 . This compression moves the biasing member  80  out of the opening  30  in the housing  25  of the MCC  20 . Because the hook portions  82 ,  84  no longer engage the edge of the housing  25  for the MCC  20 , the module  10  may be pulled out of the MCC. Thus, the module  10  may be intentionally removed from the MCC  20  while preventing an inadvertent ejection. 
     It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. 
     In the preceding specification, various embodiments have been described with reference to the accompanying drawings. It will, however, be evident that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.