Abstract:
An arc runner is fixedly retained on a load (or line) strap without hardware and without employing a mechanical operation. Either the arc runner or the strap has features, such as legs or holes, which engage notches or pins on either the strap or the arc runner and cause the arc runner to be retained on the strap.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to securing an arc runner to a load or line strap, and more particularly, to securing an arc runner to a load or line strap without using hardware or a mechanical operation. 
     Circuit breakers are one of a variety of overcurrent protective devices used for circuit protection and isolation. The basic function of a circuit breaker is to provide electrical system protection whenever an electrical abnormality occurs in any part of the system. In a circuit breaker, current enters the system from a power line. The current passes through a strap to a stationary contact fixed on the strap and then to a movable contact. The movable contact is fixedly attached to an arm, and the arm is mounted to a rotor. As long as the stationary and movable contacts are in physical contact, current passes from the stationary contact to the movable contact and out of the circuit breaker to down line electrical devices. 
     In the event of an overcurrent condition (e.g., a short circuit), extremely high electromagnetic forces are generated. These electromagnetic forces repel the movable contact away from the stationary contact. Because the movable contact is fixedly attached to a rotating arm, the arm pivots and physically separates the stationary and movable contacts thus blowing open (tripping) the circuit. Upon separation of the contacts and blowing,open the circuit, an arcing condition occurs. It is desirable to suppress the resultant arc in order to avoid a hazardous condition. The typical method of suppressing the arc is to direct it into an arc chute, which is generally a series of metal plates that dissipate the energy of the arc. This arc chute is situated proximate to the stationary contact point of the circuit. 
     An arc runner is used to direct the arc to the arc chute. The arc runner substantially covers the exposed area of the stationary contact disposed on the strap. Blowing a circuit open thus resulting in an arc causes tremendous stress to the parts of the system. Since the arc runner provides a pathway for the arc to follow to the arc chute, it is subject to intensely high temperatures. The construction of an arc runner, and especially its manner of seducement to the strap, is critical to reliable dissipation of an arc. 
     Conventional methods of securing an arc runner to a load or line strap increase the costs of manufacturing a circuit breaker because of the hardware involved. The arc runner is typically screwed onto the strap, as described in U.S. Pat. No. 5,877,467 entitled “Circuit Breaker Current Limiting Arc Runner”. Similarly, U.S. Pat. No. 5,075,520 entitled “Contact Member for Electrical Switching Devices” describes an arc runner having one end inserted into a groove in a block and then having the arc runner secured to the block by a screw. The use of a screw in the fastening operation adds the cost of an extra piece of hardware to the manufacturing process. 
     Bolts are also used to secure an arc runner to a strap. For example, U.S. Pat. No. 4,229,630 entitled “Circuit Breaker Utilizing Improved Arc Chambers” describes using a pair of bolts that extend through openings in an arc runner to secure the arc runner to a stationary contact. Another method of securing an arc runner to a strap includes the use of rivets, as discussed in U.S. Pat. No. 4,771,140 entitled “Circuit Interrupter”, wherein a single rivet pierces the body of an arc runner and a stationary conductor to firmly connect the arc runner to the stationary conductor. Bolts and rivets add the cost of an extra piece of hardware to the manufacturing process in the same way that screws do. 
     Welding, as discussed in U.S. Pat. No. 5,818,003 entitled “Electric Switch with Arc Chute, Radially Converging Arc Splitter Plates, and Movable and Stationary Arc Runners”, provides a further option for securing an arc runner to a strap, wherein the strap is directly welded to a D-shaped arc runner. Although welding does not introduce an additional discrete component into the manufacturing process, it does contribute to the expenses associated with the finished product. 
     In addition to the costs of the hardware used to fasten the arc runner to the strap, tools are required. Automated assembly systems and automated welders are usually expensive to install and run. Furthermore, the maintenance for these systems is costly, and the use of such systems often poses reliability concerns. Hand-held tools such as wrenches and screwdrivers, on the other hand, are far less expensive. The use of small hand-held tools may, however, increase the time required for assembly of an arc runner to a load strap because machine assembly is usually faster than hand assembly is. An increase in the time required for assembly using hand-held tools is becoming cost prohibitive. Furthermore, hand-held tools, because of their size, frequently tend to be misplaced and need to be replaced on a regular basis. Constant replacement of even the most inexpensive tools can be a limiting factor. 
     SUMMARY OF THE INVENTION 
     In an exemplary embodiment of the invention, an arc runner is fixedly retained on a load or line strap proximate an electrical contact in a circuit breaker. The arc runner is comprised of a main body portion capable of directing an arc to an arc dissipating chute and a retaining portion that allows the arc runner to be secured to the strap. The main body portion generally conforms to the shape of the strap on which the arc runner is positioned. The retaining portion is configured and dimensioned to utilize the structure of the strap to hold the main body portion onto the strap without hardware and without employing mechanical operations thus eliminating additional attachment hardware and/or mechanical attachment operations of the prior art. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of an arc runner having legs, retaining clips, and an opening for accommodating a contact, of the present invention; 
     FIG. 2 is a front view of the arc runner shown in FIG. 1; 
     FIG. 3 is an isometric view of a load (or line) strap configured to receive the arc runner shown in FIGS. 1 and 2; 
     FIG. 4 is an isometric view of the arc runner of FIGS. 1 and 2 situated on the strap of FIG.  3  and accommodating a contact; 
     FIG. 5 is an isometric view of an alternate embodiment of an arc runner having a hole to accept a retaining pin and also having an opening for accommodating a contact, of the present invention; 
     FIG. 6 is a plan view of the alternate embodiment of the arc runner, of the present invention; 
     FIG. 7 is a side view of the alternate embodiment of the arc runner showing the detail of a chamfered hole, of the present invention; 
     FIG. 8 is an alternate embodiment of a strap having the retaining pin and being configured to accept the alternate embodiment of the arc runner, of the present invention; and 
     FIG. 9 is an isometric view of the strap having the retaining pin and also having the alternate embodiment of the arc runner positioned on it and accommodating the contact, of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1 and 2, an arc runner of an exemplary embodiment of the present invention is generally shown at  10 . Arc runner  10  is comprised of a main body portion defined by a planar member  12  and a retaining portion defined by legs  14  extending substantially perpendicularly from planar member  12 . Planar member  12  is configured and dimensioned to conform to the shape of a surface of a load (or line) strap  22  (FIG.  3 ). Planar member  12  provides a pathway for an arc to follow and be diverted into an arc chute (not shown) to be dissipated in the event that an overcurrent or short circuit causes a circuit breaker to trip, i.e., to blow open. 
     Legs  14  are positioned on planar member  12  in such a manner so as to form a generally inverted U-shape. This U-shape allows planar member  12  to rest on a top surface of strap  22  while legs  14  extend down on opposing sides of strap  22 . Legs  14  may be flexibly connected to planar member  12  enabling legs  14  to pinch the sides of strap  22  thus allowing planar member  12  to remain secured to strap  22 . Portions along the edges of planar member  12  adjacent legs  14  may be removed to form cutouts  13 . Cutouts  13  are dimensioned to increase the flexibility of legs  14  as legs  14  are mounted on load strap  22 . Legs  14  may also be dimensioned to have thinner portions  15  and wider portions  16 . Thinner portions  15  of legs  14  are positioned at the points at which legs  14  are attached to planar member  12  in order to further increase flexibility. Alternately, legs  14  may depend from strap  22  to secure planar member  12  to strap  22 . 
     Retaining tabs  18  are disposed on the ends of legs  14  and are configured to extend toward each other. Retaining tabs  18  have a tapered or curved surface  19  positioned to facilitate the outwardly urging of legs  14  as arc runner  10  is being mounted on said strap  22 . Positioned adjacent to said tapered or curved surface  19  is a flat surface  21  for engaging an underside surface of strap  22  thus clipping legs  14  to side surfaces of strap  22 . When legs  14  are clipped to the side surfaces of strap  22 , arc runner  10  is secured to strap  22 . 
     Planar member  12  has a portion removed from it to form opening  20 . Opening  20  is dimensioned, configured, and positioned on planar member  12  to accommodate a contact  26  when arc runner  10  is positioned on strap  22 . Contact  26  is illustrated and discussed below with reference to FIG.  4 . Opening  20  functions to mate with contact  26  thereby preventing arc runner  10  from rotating about a longitudinal axis of strap  22 . 
     Retaining tabs  18  can be clearly seen (FIG. 2) depending from the ends of legs  14 . When arc runner  10  is installed on strap  22 , legs  14  extend along and engage opposing side surfaces  23  (FIG. 3) with notches  24  of strap  22 . Retaining tabs  18  then engage an underside surface  25  (FIG. 3) of strap  22  and secure arc runner  10  into position on strap  22 . 
     Referring now to FIG. 3, strap  22  is generally shown. Notches  24  are cut into opposing sides of strap  22  and are of dimensions sufficient to accommodate legs  14  when arc runner  10  is positioned on strap  22 . Notches  24  prevent arc runner  10  from axial movement along strap  22  in the event that legs  14  do not tightly secure arc runner  10  to strap  22 . Furthermore, notches  24  are formed on strap  22  in such a way that when arc runner  10  is positioned onto strap  22 , opening  20  accommodates contact  26  of a circuit breaker (not shown). 
     Referring to FIG. 4, arc runner  10  is shown on strap  22 . Legs  14  are received in notches  24 . Retaining tabs  18  hold legs  14  in place within notches  24  and secure arc runner  10  to strap  22 . Contact  26  is accommodated by opening  20 . 
     Referring to FIGS. 5-7, in an alternative embodiment of the invention an arc runner  110  is formed as a generally planar member  112 . At least one hole  130  extends through planar member  112 . FIGS. 5-7 show planar member  112  having two holes extending therethrough; however, it should be understood that planar member  112  may contain only a single hole. The edges of hole  130  are chamfered so that a corresponding number of pins inserted from the side of planar member  112  having the smaller opening can be countersunk in hole  130 . Planar member  112  has a portion removed from it to form an opening  120 . Opening  120  is dimensioned, configured, and positioned on planar member  112  to accommodate a contact  126  (FIG. 9) when arc runner  110  is positioned on a load (or line) strap  122  (FIG.  8 ). 
     Referring now to FIG. 8, strap  122  has at least one protrusion of material created therefrom which is formed into at least one retaining pin  124 . FIG. 8 shows strap  122  having two protrusions extending therefrom; however, it should be understood that strap  122  may contain only a single protrusion. Retaining pin  124  projects from the surface of strap  122  to mate with hole  130  of arc runner  110 . Alternately, retaining pin  124  may project from planar member  112  to mate with hole  130  in strap  122 . The protrusion of retaining pin  124  into hole  130  prevents axial movement of planar member  112  on strap  122 . 
     Referring now to FIG. 9, arc runner  110  is shown positioned on strap  122 . Retaining pin  124  protrudes through hole  130  of planar member  112 . The protrusion of retaining pin  124  into hole  130  is deformed to provide a countersunk means of securing arc runner  110  to strap  122 . Deforming and countersinking the end of retaining pin  124  prevents separation of planar member  112  from strap  122 . Planar member  112  is positioned on strap  122  in such a way that opening  120  accommodates contact  126 . The combination of the protrusion of retaining pin  124  through hole  130  with the positioning of contact  126  in opening  120  secures arc runner  110  to strap  122 . 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.