Abstract:
A method for restricting travel of a moving contact in a lighting contactor is provided. The lighting contactor includes the moving contact and a contact carrier. The method includes the steps of providing a spacer, and a biasing member and positioning the biasing member though the spacer. The method also includes installing the biasing member and the spacer in the contact carrier.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates generally to contactors, and more particularly to contactor movement and arc reduction in lighting contactor block assemblies.  
           [0002]    Contactor block assemblies refer to single or multiple pole power switching devices located in a branch circuit, used to switch (make or break) one or more pieces of equipment. Frequently, automated lighting control applications use contactor block assemblies that include fixed and moving contacts. Lighting contactor block assemblies can be differentiated by many characteristics, including, but not limited to, lighting load type, load current, contact holding method, lighting contactor type, and number of poles. Further features include enclosure type, pole configuration, fusing type, control circuit, indicating lights, and auxiliary contacts.  
           [0003]    In the past, contactor block assemblies were generally placed near the controlled equipment. In some applications, however, contactor block assemblies are located in a central cabinet located in an electrical equipment room near a panelboard. A shortened conductor length between the panelboard and the contactor block assembly central cabinet increases a fault current at the contactor. Regardless of the contractor assembly location, during a short circuit a large and rapid influx of electromagnetic energy pushes a moving contact in the lighting contactor away from a fixed contact. As the moving contact separates from the fixed contact an arc forms, causing an energy release. As the arc length grows longer, more energy is released. In some short circuits, the energy release is sufficient to breakdown plastic components in the contactor block assembly causing out-gassing. The out-gassing can result in physical damage to the contactors, contactor block assemblies and the central cabinet.  
         SUMMARY OF INVENTION  
         [0004]    In one aspect, a method for restricting travel of a moving contact in a lighting contactor is provided. The lighting contactor includes the moving contact and a contact carrier. The method includes the steps of providing a spacer and providing a biasing member. The method also includes positioning the biasing member though the spacer and installing the biasing member and the spacer in the contact carrier.  
           [0005]    In another aspect, a lighting contactor including a contact carrier, a moving contact extending through the contact carrier, and a biasing member housed in the contact carrier is provided. The biasing member biases the moving contact. The lighting contactor further includes a spacer and the biasing member extends through the spacer. The spacer limits travel of the moving contact within the contact carrier.  
           [0006]    In a further aspect, a lighting contactor including a contact carrier, a moving contact, a spring, and a stainless steel spacer is provided. The contact carrier includes an access slot and a centerline axis. The moving contact includes a front, a back, a first end, a second end, and a retaining boss on the back substantially midway between the first end and the second end. The moving contact extends substantially perpendicular to the centerline axis through the contact carrier. The spring is within the contact carrier, engages the moving contact retaining boss, and biases the moving contact. The spring extends through the stainless steel spacer. The spacer includes a proximate end substantially parallel to the back. The spacer limits travel of the moving contact within the contact carrier.  
           [0007]    In yet another aspect, a contactor block assembly including a block case, a plurality of fixed contacts, a plurality of terminal connections, and a lighting contactor is provided. The lighting contactor includes a contact carrier, at least one moving contact extending through the contact carrier, at least one biasing member housed in the contact carrier, one of the biasing members biasing one of the moving contacts, and at least one spacer. One of the biasing members extends through each of the spacers. Each spacer is configured to limit travel of one of the moving contacts within the contact carrier. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]    [0008]FIG. 1 is a perspective view of a contactor block assembly with an assembly cover removed.  
         [0009]    [0009]FIG. 2 is a perspective view of a lighting contactor of FIG. 1.  
         [0010]    [0010]FIG. 3 is an enlarged top view of a portion of the lighting contactor of FIG. 2.  
         [0011]    [0011]FIG. 4 is an enlarged top view of a portion of a lighting contactor in a compressed condition. 
     
    
     DETAILED DESCRIPTION  
       [0012]    [0012]FIG. 1 is a perspective view of a contact block assembly  10  with an assembly cover (not shown) removed. Contactor block assembly  10  includes a lighting contactor  12 , a plurality of fixed contacts  14 , a plurality of terminal connections  16 ,  18 , and a block case  20 . Lighting contactor  12  also includes a centerline axis  22  perpendicular to fixed contacts  14 . Lighting contactor  12  moves within contact block assembly  10  to engage fixed contacts  14 .  
         [0013]    [0013]FIG. 2 is a perspective view of lighting contactor  12 . FIG. 3 is an enlarged top view of a first portion  28  of lighting contactor  12 . Lighting contactor  12  includes a contact carrier  30 , a first moving contact  32 , a second moving contact  34 , a first biasing member  36 , a second biasing member  38 , a first spacer  40 , and a second spacer  42 .  
         [0014]    In an exemplary embodiment, contact carrier  30  includes a first portion  28  and a second portion  48 . First portion  28  includes first moving contact  32 , first biasing member  36 , and first spacer  40 . Second portion  48  includes second moving contact  34 , second biasing member  38 , and second spacer  42 . As first portion  28  and second portion  48  are substantially identical, only first portion  28  will be discussed. Further, in an alternate embodiment, contact carrier  30  includes only first portion  28 . First portion  28  further includes an access slot  50  defined by a front wall  52 , a rear wall  54 , a first side wall  56  and a second side wall  58 . In an exemplary embodiment, rear wall  54  includes a mounting tab  62 . In an alternative embodiment, rear wall  54  includes a mounting socket (not shown). Access slot  50  includes a longitudinal length  64  aligned with the lighting contactor centerline axis  22 .  
         [0015]    First moving contact  32  includes a contact front  70 , a contact back  72 , a contact first end  74 , a contact second end  76 , and a retaining boss  78  on contact back  72 . First moving contact  32  extends through first portion  28  in access slot  50  and is biased by first biasing member  36  to abut front wall  52 . Contact front  70  includes a first engagement face  80  and a second engagement face  82 , which facilitate electrical contact with fixed contacts  14  (shown in FIG.  1 ). First moving contact  32  is substantially perpendicular to and symmetrical about centerline axis  22 . Retaining boss  78  is substantially midway between contact first end  74  and contact second end  76 . First moving contact  32  also includes a thickness  84 .  
         [0016]    In an exemplary embodiment, biasing member  36  is a coil spring  36 . First spring  36  includes a front end  88  and rear end  90 . First spring  36  is positioned in access slot  50  and extends from rear wall  54  to contact back  72 . More specifically, front end  88  is engaged with contact back  72  and rear end  90  is engaged with rear wall  54 . As shown in FIG. 3, spring front end  88  receives and is mounted on retaining boss  78 . Spring rear end  90  receives and is mounted on mounting tab  62 . In an alternative embodiment, first spring  36  is a leaf spring (not shown).  
         [0017]    As shown in FIG. 4, first spring  36  further defines a compressed biasing member length  92 , where spring  36  is compressed such that spring  36  presents a substantially closed cylindrical outer surface  94 . First spring  36  also defines a cylindrical outer diameter  96 .  
         [0018]    As shown in FIGS. 3 and 4, first spacer  40  includes a proximate end  100 , an inner surface  102 , an outer surface  104  and a distal end  106 . First spring  36  extends through first spacer  40  and first spacer  40  extends circumferentially around first spring  36 . Inner surface  102  is sized larger than spring cylindrical outer diameter  96  to allow first spring  36  to move freely in first spacer  40 . In an exemplary embodiment, first spacer  40  is a tube. Alternative embodiments of first spacer include, but are not limited to a tube with chamfered ends, a tube with a solid distal end, a tube with longitudinal openings, a hollow rectangle, and a hollow prism. Distal end  106  abuts rear wall  54 . Proximate end  100  is planar and substantially parallel to contact back  72 .  
         [0019]    First spacer  40  further includes an axial length  108 . In one embodiment, axial length  108  is slightly larger than or equal to compressed biasing length  92 . In another embodiment, axial length  108  is determined based on a safe travel distance  110  for first moving contact  32 . Safe travel distance  110  is determined based on allowable arc length, associated energy release, and contactor block assembly material. In an exemplary embodiment, first spacer  40  is fabricated from stainless steel. In alternative embodiment, other suitable material is used, including but not limited to, high temperature plastic.  
         [0020]    To assemble lighting contactor  12 , first spring  36  is compressed and a compressed biasing length  92  is determined. Alternatively, safe travel distance  110  is ascertained, by calculation or experimentation, and spacer axial length  108  is determined in conjunction with access slot longitudinal length  64  and first moving contact thickness  84 . First spacer  40 , with determined axial length  108 , is then matched with first spring  36  having a smaller compressed biasing length  92 .  
         [0021]    Lighting contactor  12  is assembled by inserting first moving contact  32  in access slot  50 , such that first moving contact  32  extends substantially symmetrically through access slot  50 . First spring  36  is inserted through first spacer  40 . Spring rear end  90  is installed on mounting tab  62 . First spring  36  and first spacer  40  are placed in access slot  50  so that spring front end  88  receives and is frictionally engaged with retaining boss  78 . First spring  36  biases first moving contact  32  to abut access slot front wall  52  when moving contact  32  is not in contact with fixed contact  14 . Contactor block assembly  10  is disengaged. Proximate end  100  is aligned substantially parallel to moving contact back  72  and thus substantially perpendicular to centerline axis  22 .  
         [0022]    When contactor block assembly  10  is engaged, first moving contact  32  is in physical contact with fixed contact  14 . More specifically, first engagement face  80  and second engagement face  82  engage fixed contact  14  (shown in FIG. 1). First spring  36  facilitates electrical contact between first moving contact  32  and fixed contact  14 , while safe travel distance  110  facilitates small alignment differences between fixed contacts  14  and moving contact  32 .  
         [0023]    If a large current flow or short circuit occurs, the electromagnetic force pushes moving contact  32  out of physical contact with fixed contact  14 , producing an electrical arc. As moving contact  32  is pushed axially rearward toward access slot rear wall  54 , it engages first spacer  40 . Specifically, planar proximate end  100  engages moving contact  32  and maintains moving contact  32  perpendicular to centerline axis  22 . Thus, first engagement face  80  and second engagement face  82  are substantially equidistant from fixed contacts  14 , minimizing the maximum arc length. If moving contact  32  were not perpendicular to centerline axis  22 , the electrical arc would be longer, releasing greater energy, with increased possibility of damage to contactor block assembly  10 .  
         [0024]    Accordingly, lighting contactor  12  is a cost-efficient and effective switching device which reduces the travel of moving contacts in a contactor block assembly while maintaining the moving contact engagement faces equidistant from the fixed contacts. Lighting contactor  12  therefore reduces damaging arcs and provides for a long lasting and reliable contact block assembly.  
         [0025]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.