Patent Publication Number: US-6700087-B2

Title: Arc chute assembly

Description:
FIELD OF THE INVENTION 
     This invention relates to the field of electrical switches, and more specifically to an arc chute for a switch. 
     BACKGROUND 
     Electrical switches such as circuit breakers and transfer switches typically include arc chutes located proximate the contacts of the switch to extinguish the arc that is produced when the switch is tripped and the contacts of the switch are rapidly opened. An arc chute typically includes a series of metallic plates that are configured in a spaced apart relationship and held in place by dielectric side panels. When the contacts of the switch are opened, the resulting arc is driven to the metallic plates of the arc chute where the arc is then extinguished by the plates. Typically, the metallic plates are held in place by tabs on the plates which extend through holes in the side panels so that the tabs can be either staked in place or fastened by external fasteners. Such an assembly process is time consuming and the resulting arc chute structure can be bulky requiring a relatively large mounting area within the switch. 
     SUMMARY 
     The present invention provides an arc chute having features to allow for easy manufacture and assembly of the arc chute and allow for an improved switch incorporating the arc chute. In one aspect, an arc chute includes a first side wall having a plurality of holes, a second side wall having a plurality of holes and spaced apart from the first side wall, and a plurality of arc chute plates mounted between the first and second side walls. Each of the plurality of arc chute plates include one or more laterally extending tabs extending from the sides of each plate. Each of the laterally extending tabs are shaped to be interference fitted within one of the plurality of holes. Each of the laterally extending tabs are dimensioned to not substantially extend beyond an outer surface of each of the side walls. 
     Another aspect includes a method of manufacturing an arc chute. In one embodiment, a method for assembling an arc chute includes interference fitting one or more tabs on a first side of an arc chute plate into a hole on a first arc chute side wall, and interference fitting one or more tabs on a second side of the arc chute plate into a hole on a second arc chute side wall. 
     Another aspect provides a switch. In one embodiment, a switch includes a case having an arc chute mounting area having a ridge near a back portion of the arc chute mounting area. An arc chute is mounted within the arc chute mounting area. The arc chute includes a pair of side walls and a plurality of arc chute plates mounted between the pair of side walls, wherein each of the pair of side walls includes a movable tab which is removably engageable with the ridge. 
     Among other advantages, one or more embodiments of the present system provide an arc chute which is easily manufactured, has a relatively small design, and is easily removable from a switch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an exploded view of a transfer switch having an arc chute according to one embodiment of the present invention. 
     FIG. 2 shows further details of the arc chute of FIG.  1 . 
     FIG. 3 shows an exploded view of portions of the arc chute of FIG.  1 . 
     FIG. 4 shows a top view of the arc chute mounted within the transfer switch of FIG.  1 . 
     FIG. 5 shows a side view of the arc chute mounted within the transfer switch of FIG.  1 . 
     FIG. 6 shows a perspective view of the transfer switch of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents. 
     FIG. 1 shows a portion of a transfer switch  100  according to one embodiment. The portion of transfer switch  100  shown is understood to be one out of many possible such portions. For instance a three-phase transfer switch can include three back to back members similar to the portion shown in FIG.  1 . Other circuit breakers and switches using arc chutes can be configured using the teachings of the present system and are considered within the scope of the present discussion. 
     In one example, transfer switch  100  is used for switching between a utility and a generator for feeding an electrical load. Current ranging from 30 Amps to 300 Amps can flow through an example transfer switch. Transfer switch  100  generally includes a case  110 , a pair of movable contacts  120 A and  120 B, a pair of stationary input contacts  130 A and  130 B, and one or more arc chutes  140 . Only one arc chute  140  is shown in FIG.  1 . However, two are usually provided with one mounted in a lower mounting area  112  and one in an upper mounting area  121 . 
     Case  110  is a molded two-part case having various features for holding members of the transfer switch. Movable contacts  120 A and  120 B are rotatably coupled within case  110  to strike or contact stationary contacts  130 A and  130 B, respectively, when closed. Each of the moveable contacts  120 A and  120 B is connected to an output contact  134 . 
     Movable contact  120 A is adapted to be intermittently connected to a corresponding primary input contact  130 A, while movable contact  120 B is adapted to be intermittently connected to corresponding secondary input contact  130 B. 
     Cams  135 A and  135 B are mounted to maneuver the movable contacts  120 A and  120 B into, and out of, engagement with their respective input contacts  130 A and  130 B. As the cams  135 A and  135 B rotate, the tips on the cams eventually begin to engage the movable contacts  120 A and  120 B to force the contacts away from their respective input contacts  130 A and  130 B. Conversely, once the tips of the cams rotate in the opposite direction past the movable contacts  120 A and  120 B, a spring  137  forces each movable contact into engagement with their respective stationary input contact. 
     In one use of switch  100 , for example, movable contact  120 B is engaged with the primary input contacts  130 B when power is being supplied from a primary power source, such as a utility. When there is an interruption in the primary power supply, cam  135 B rotates to disengage the movable contact  120 B from the primary input contacts  130 B, and cam  135 A rotates to allow movable contact  120 A to engage the secondary input contacts  130 A so that power can be supplied from a secondary power source, such as a generator. Other features of transfer switch  100  are described in co-pending and co-assigned U.S. patent application Ser. No. 10/202,260, filed Jul. 24, 2002, which is incorporated herein by reference in its entirety. 
     Case  110  includes arc chute mounting areas  112  and  121 . Arc chute mounting areas  112  and  121  are shaped to match the profile shape of arc chutes(s)  140 . In this example, arc chute mounting area  112  includes a pair of flat, parallel side walls  113  and  114  and a sloping lower surface  117 . Near the outer portion of arc chute mounting are  112  is a ridge  115 . Ridge  115  is a slightly raised section which is designed for retaining arc chute  140  within the arc chute mounting area. Arc chute  140  includes a pair of movable tabs  143  which engages ridges  115  when the arc chute is mounted within switch  100 . A used can squeeze tabs  143  together to remove arc chute  140  from arc chute mounting area  112  without the need for tools and without removing any fasteners. This allows contacts  120 A,  120 B,  130 A, and  130 B to be visually inspected if necessary without having to disassemble portions of the switch. For example, FIG. 6 shows switch  100  with mounting areas  112  and  121  without any arc chutes mounted therein. 
     Referring again to FIG. 1, arc chute  140  can be located within arc chute mounting area  112  such that movable contact  120 A goes through U-shaped open area  116  of arc chute  140  when the movable contact  120 A is rotated open. When contacts  120 A or  120 B are opened, the resulting arc is driven to one or more metallic plates  148  of the arc chute where the arc is extinguished by the plates. 
     FIG. 2 shows a bottom isometric view showing further details of arc chute  140  according to one embodiment. Arc chute  140  includes a first side wall  142 , a second side wall  144 , a back wall  146 , and the plurality of arc chute plates  148 . 
     First side wall  142  and second side wall  144  are similar and only first side wall  142  will be described in detail. First side wall  142  includes a first series of mounting holes  152 . Mounting holes  152  are located near the front of the side wall. In one example, each mounting hole  152  includes an elongated slot having a first rounded profile end  153  and a second rounded profile end  154 . First side wall  142  also includes a second series of mounting holes  156 . Mounting holes  156  run generally downward from an upper portion  155  of the side wall to a lower portion  157 . In this example, each of mounting holes  156  is circular, presenting a substantially round profile. Other embodiments provide an oval hole, an elliptical hole, or other equivalent shape. Each side wall also includes a back plate mounting hole  158 . Back plate mounting hole  158  is a vertically oriented slot running from the upper to the lower portion of the side wall. Hole  158  includes a first round profile end  160  and a second round profile end  161 . 
     Each of arc chute plates  148  is a flat, U-shaped member formed of an electrically conductive material, typically metal. The U-shaped area of each arc chute plate  148  defines open area  116  for contact  120  to move through (See FIG.  1 ). 
     FIG. 3 shows an exploded view of arc chute  140 . Extending laterally from each side of each arc chute plate  148  are one or more tabs. In this example, each plate  148  includes four laterally extending tabs  162 - 165 . Front tabs  162  and  163  have a rectangular cross-section defining a square-edged profile having squared edges  166 . Front tabs  162  and  163  are dimensioned to interference fit within mounting holes  152  of the arc chute side walls. Tabs  162  and  163  arc sized so that the square edges  166  of the tabs deform the round edge ends  153  and  154  of mounting holes  152  when the tabs are pressed within the holes. This provides a tight interference fit which holds the arc chute assembly together without any extraneous hardware and without any extra staking or fastening steps to the manufacturing process. In one embodiment, mounting holes  152  and laterally extending tabs  162  and  163  have similar cross-sectional or profile shapes with the tabs being slightly larger than the holes and thus allowing for an interference or friction fit mounting. 
     In one example, back tabs  164  and  165  also have a rectangular square edge profile. Thus, in a similar manner as described above for tabs  162  and  163 , tabs  164  and  165  fit within and deform the edges of mounting holes  156  when the tabs are pressed into the mounting holes. Again, in some embodiments mounting holes  156  and laterally extending tabs  164  and  165  have similar cross-sectional or profile shapes with the tabs being slightly larger than the holes, thus allowing for an interference or friction fit mounting. In a likewise manner, each of a plurality of arc chute plates  148  are mounted between first and second side walls  142  and  144 . 
     In one example, each of first side wall  142  and second side wall  144  include an electrically non-conductive material which is softer than the material of the arc chute plates  148 . Example materials include vulcanized paper or glass fiber reinforced polyester. This provides that mounting holes  152  and  156  plastically deform when tabs  162 - 165  are pressed into the mounting holes. This allows for a tight interference fit when the tabs are pressed within the mounting holes. 
     Back wall  146  is a non-metallic planar structure and includes laterally extending tabs  170  and  171  which interference fit within mounting holes  158  in a manner similar to that described above for tabs  162 - 165  of arc chute plate  148 . Tabs  170  and  171  have squared ends  172  which deform the round profile ends  159  and  160  of mounting hole  158  when the tabs are pressed into the mounting holes. Back wall  146  is shaped and located relative to plates  148  to direct the flow of outwardly expanding gasses produced by an arc. Some embodiments omit back wall  146 . 
     FIG. 4 shows a top view of arc chute  140  within arc chute mounting area  112 . Each of side walls  142  and  144  is flushly mounted against walls  113  and  114  of arc chute mounting area  112 . Referring again to FIGS. 2 and 3, it is seen that laterally extending tabs  162 - 165  and  171 ,  172  are dimensioned to not extend beyond an outer surface  159  of each of the side walls  142  and  144 . This allows arc chute  140  to be flushly and tightly fitted within arc chute mounting area  112  such that the outer surface of the side walls  142  and  144  flushly contact walls  113  and  114  of arc chute mounting area. This configuration allows for a saving of space within switch  100  since the tabs of each arc chute plate do not extend substantially past the outer surfaces, so no room within the switch is needed to accommodate the tabs. Furthermore, this configuration allows the side walls  113  and  114  of the arc chute mounting area to help hold the arc chute  140  together since the arc chute mounting area walls  113  and  114  are in direct contact with the arc chute walls  142  and  144 . 
     FIG. 5 shows a side view of arc chute  140  within arc chute mounting area  112 . Tabs  143  have a lip or extension portion  181  which contacts ridges  115  to hold the arc chute within the switch. Tabs  143  extend beyond an outer end  182  of the main body portion of the arc chute so as to be easily accessible. A cut-out  178  running along side wall  142  of arc chute  140  defines tab  143  and provides for lateral movement of the tab. In one example, tabs  143  are squeezed together so bottom lip  181  of each tab  143  moves beyond the highest portion of ridge  115  (See FIG.  1 ). This allows the arc chute to loosen from arc chute mounting area  112  and provides easy removal of the arc chute to inspect the contacts  120  and  130  without disassembling the whole switch. 
     In one example use of the present system, an arc chute is assembled by interference fitting one or more tabs  162 - 165  on a first side of an arc chute plate  148  into a mounting hole  152  and/or  156  on a first arc chute side wall  142 , and interference fitting one or more tabs on a second side of the arc chute plate into a second arc chute side wall  144 . The completed arc chute  140  can then be mounted with an arc chute mounting portions  112  and/or  121  of a switch  100  as shown in FIGS. 1,  4 ,  5 , and  6 . 
     The present arc chute structure and assembly technique requires fewer steps and hardware than a typical arc chute which requires a staking process to hold the arc chute plates in place. Moreover, a switch holding a typical arc chute needs to have space provided to hold the outwardly extending tabs. The arc chute plate tabs of the present invention do not extend beyond the outer surface of the arc chute side walls so the overall size of the switch can be smaller since the arc chute mounting area walls are flush against the arc chute. 
     It is understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.