Patent Publication Number: US-9887050-B1

Title: Circuit breakers with metal arc chutes with reduced electrical conductivity overlay material and related arc chutes

Description:
FIELD OF THE INVENTION 
     The present invention relates to circuit breakers. 
     BACKGROUND OF THE INVENTION 
     Circuit breakers are one of a variety of overcurrent protection devices used for circuit protection and isolation. The circuit breaker provides electrical protection whenever an electric abnormality occurs. In a typical circuit breaker, current enters the system from a power line and passes through a line conductor to a stationary contact fixed on the line conductor, then to a movable contact. The movable contact is fixedly attached to a pivoting arm. As long as the stationary and movable contacts are in physical contact, current passes between the stationary contact and 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 can be generated. The electromagnetic forces can be used to separate the movable contact from the stationary contact. Upon separation of the contacts and blowing open the circuit, an arcing condition occurs. The breaker&#39;s trip unit will trip the breaker which will cause the contacts to separate. Also, arcing can occur during normal “ON/OFF” operations on the breaker. 
     Arc chutes can be used to direct an arc away from the electrical contacts into the arc chute. The arc chute can be a shaped body with open slots and may optionally comprise a series of stacked metal plates that dissipate the energy of the arc. The arc chute is situated proximate to the stationary contact of the circuit. The arc chute can be subject to intensely high temperatures during electrical arcing events. Exposure to electrical arcing can reduce the overall lifetime of a circuit breaker by depleting silver in its contacts. 
     SUMMARY OF EMBODIMENTS OF THE INVENTION 
     Embodiments of the invention are directed to circuit breakers with overlay material having reduced electrical conductivity, optionally electrically insulating material (electrically non-conductive) overlying surfaces of a metal (electrically conductive) arc chute. 
     The electrically insulating material can be provided as a three-dimensional rigid or semi-rigid shaped insert comprising a thermoplastic, optionally nylon. 
     The overlay material can be provided as an overmolded layer on at least a portion of an upper surface of a bottom of a single piece, three-dimensionally shaped arc chute. 
     A circuit breaker that includes a metal arc chute having a base and sidewalls extending outward from the base forming an open cavity; a movable arm holding a movable contact adjacent to the arc chute; a line conductor electrically connected to a stationary contact residing adjacent to the arc chute facing the movable contact; and an overlay material attached to the arc chute and residing in the cavity of the arc chute. The overlay material has a significantly reduced electrical conductivity relative to the metal arc chute. 
     The circuit breaker of Claim  1 , wherein the overlay material contacts at least a segment of a primary upper surface of the base of the arc chute and at least a segment of each of the sidewalls. 
     The sidewalls can terminate at a vertical height that is from about 0.1 inches to about 2 inches above the stationary contact. 
     The overlay material can reside on a primary upper surface of the base of the arc chute. Optionally, the overlay material has a bottom and/or sidewall with maximal thickness of 0.2 inches and a minimal thickness of 0.040 inches. 
     The overlay material can include or be an overlay member having a self-supportable three dimensional shape with a base and sidewalls extending outward from the base. The base of the overlay member can abut a primary upper surface of the base of the arc chute body. 
     The overlay member sidewalls can reside inside the cavity adjacent the sidewalls of the arc chute body. 
     The overlay material can be an overmolded overlay material that is attached to a primary upper surface of the base of the arc chute body. 
     The base of the arc chute body can include a plurality of open slots extending between the sidewalls. 
     The overlay material can be overmolded onto the primary upper surface and sidewalls of the chute body and extends about a perimeter edge region of the slots to leave open spaces over the slots. 
     The base of the arc chute body can include a plurality of open slots extending between the sidewalls. The overlay material can extend about a perimeter edge region of the slots and leave an open space over the slots. 
     The base of the arc chute body can include a plurality of open slots extending between the sidewalls. The overlay member can include a plurality of open slots with at least one of the slots of the overlay member aligned with at least one of the slots of the arc chute body. 
     The arc chute body can include first and second parallel slots that are orthogonal to the sidewalls. The overlay member can include first, second and third slots. The first and second slots can be aligned with the first and second slots of the arc chute body. The third slot can be parallel to the first and second slots of the overlay member and can be more narrow than the first and second slots of the overlay member. 
     The third slot of the overlay member can reside between the first and second slots of the overlay member. 
     The overlay member can include a fourth and a fifth slot, and the third, fourth and fifth slots can be more narrow than the first and second slots of the overlay member. 
     The sidewalls of the overlay member can angle outward from the base of the overlay member and abut the sidewalls of the arc chute body. The moving contact can be offset from a centerline of the arc chute and can reside closer to one of the overlay member sidewalls than another. 
     The overlay material can include or be a rigid or semi-rigid body that has a self supporting three dimensional shape and can include outwardly extending projections that align with upwardly extending slots in the sidewalls of the arc chute. 
     The overlay material can include a plurality of rigid or semi-rigid planar members that extend between the sidewalls and rise upward from the base of the arc chute to terminate below an upper end of the sidewalls. 
     The overlay material can be or include a polyimide. 
     The overlay material can be or include a comprises nylon. 
     The overlay material can be or include a thermoplastic with a moisture absorption that is greater than 3%, has a high outgassing rate and a heat deflection temperature (under 0.45 MPa load) that is greater than 250° C. 
     Other embodiments are directed to arc chutes for circuit breakers that include: a unitary metal arc chute body having a three dimensional shape with a base and first and second sidewalls with a cavity between the sidewalls above the base; and an overlay material residing in the cavity of the arc chute body, wherein the overlay material resides directly on the base and at least partially against inner surfaces of the sidewalls of the arc chute body. The overlay material can have a significantly reduced electrical conductivity relative to the metal arc chute. 
     The overlay material can be or include a rigid or semi-rigid overlay body with a base and sidewalls, and the base of the overlay body can reside between the sidewalls of the arc chute body over the base. 
     The base of the arc chute body can have a plurality of open slots extending between the sidewalls. The overlay member can have a plurality of open slots with at least one of the slots of the overlay member aligned with at least one of the slots of the arc chute body. 
     Further features, advantages and details of the present invention will be appreciated by those of ordinary skill in the art from a reading of the figures and the detailed description of the preferred embodiments that follow, such description being merely illustrative of the present invention. 
     It is noted that aspects of the invention described with respect to one embodiment, may be incorporated in a different embodiment although not specifically described relative thereto. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination. Applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to be able to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner. These and other objects and/or aspects of the present invention are explained in detail in the specification set forth below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial view of components of a prior art circuit breaker. 
         FIG. 2  is a greatly enlarged view of a prior art arc chute shown in the circuit breaker of  FIG. 1 . 
         FIG. 3  is a side perspective view of a circuit breaker with an arc chute having an electrically conductive overlay member according to embodiments of the present invention. 
         FIG. 4A  is a greatly enlarged side perspective view of the overlay member shown in  FIG. 3  according to embodiments of the present invention. 
         FIGS. 4B and 4C  are greatly enlarged side perspective views of the arc chute shown in  FIG. 3  with an integral (typically over-molded) overlay material according to embodiments of the present invention. 
         FIG. 4D  is a side schematic view of a laminated or multi-layer overlay material according to embodiments of the present invention. 
         FIG. 4E  is a partial section view of an arc chute with an overlay material having a gradient electrical conductivity configuration according to embodiments of the present invention. 
         FIG. 5  is a partial section and enlarged view of the circuit breaker shown in  FIG. 3  illustrating the arc chute, overlay member and contact according to embodiments of the present invention. 
         FIG. 6A  is a greatly enlarged end view of the arc chute and overlay material contact arm and moving contact according to embodiments of the present invention. 
         FIG. 6B  is a greatly enlarged side perspective end view of the moving contact and arc chute with the overlay material according to embodiments of the present invention. 
         FIG. 6C  is a greatly enlarged side perspective end view of the stationary contact and arc chute with the overlay material according to embodiments of the present invention. 
         FIG. 7  is a top view of the arc chute and overlay member shown in  FIGS. 3 and 4A  according to embodiments of the present invention. 
         FIG. 8  is a side perspective view of another embodiment of an arc chute with electrically insulating overlay material according to embodiments of the present invention. 
         FIG. 9  is a side partial section view of the circuit breaker with the arc chute and overlay material shown in  FIG. 8  according to embodiments of the present invention. 
         FIG. 10A  is a top perspective view of another an arc chute and overlay material configuration according to embodiments of the present invention. 
         FIG. 10B  is a partial top view illustrating the cooperating members of  FIG. 10A  assembled together according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. Like numbers refer to like elements and different embodiments of like elements can be designated using a different number of superscript indicator apostrophes (e.g.,  10 ,  10 ′,  10 ″,  10 ′″). 
     In the drawings, the relative sizes of regions or features may be exaggerated for clarity. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The term “Fig.” (whether in all capital letters or not) is used interchangeably with the word “Figure” as an abbreviation thereof in the specification and drawings. In the figures, certain layers, components or features may be exaggerated for clarity, and broken lines illustrate optional features or operations unless specified otherwise. In addition, the sequence of operations (or steps) is not limited to the order presented in the claims unless specifically indicated otherwise. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. 
     Spatially relative terms, such as “beneath”, “below”, “bottom”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass orientations of above, below and behind. The device may be otherwise oriented (rotated 90° or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     The term “about” refers to numbers in a range of +/−20% of the noted value. 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes,” “comprises,” “including” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     The term “non-ferromagnetic” means that the noted component is substantially free of ferromagnetic materials so as to be suitable for use in the arc chamber (non-disruptive to the magnetic circuit) as will be known to those of skill in the art. 
     The term “electrically insulating” and “electrically non-conductive” are used interchangeably and mean that the noted material and/or component does not conduct a significant amount of current at normal operating voltages of the breaker and typically has a sufficiently greater electrical resistivity than the electrically conductive material of an underlying steel arc chute. That is, the breakdown voltage of the electrically insulating or electrically non-conductive material is above the normal operating range of the circuit breaker, typically by at least one order of magnitude. Breakdown voltage can be expressed in terms of electric strength (kV/mm) according to ASTM D149, IEC 60093 and/or IEC60243. For example, Stanyl TE341 has an electric strength of 25 kV/mm, several orders of magnitude greater than normal operating voltage of a (residential) circuit breaker. The breakdown voltages can meet or exceed and/or be assessed per one or both of these test procedures and can have the volume resistivity and electric strength that meets or exceeds the below values. 
                                                 Electrical properties   dry/cond                              Volume resistivity   1E13/1E10   Ohm * m   IEC 60093           Electric strength   25/20   kV/mm   IEC 60243-1                    
Resistivity is the inverse of conductivity, the resistance to the flow of current through a cross section of said material. In the above chart, an exemplary overlay material (i.e., dry nylon) has a volume resistivity of 1E13 Ohm*m, which equates to an electrical conductivity of 1E-13 S/m. Carbon steel useful for some metal arc chutes, for comparison, has a volume resistivity on the order of 1E-7 Ohm*m and an electrical conductivity of 1E7 S/m. Thus, carbon steel is roughly 20 orders of magnitude more effective for carrying current. Therefore, the term “significantly greater electrical resistivity” refers to an overlay material that is at least 5 orders of magnitude greater than a metal arc chute to which it is attached.
 
     The term “high outgassing” refers to an outgassing rate of about 1.2E-5 Torr-L/cm 2 s or more to quickly out gas any absorbed moisture in the material during an electrical interruption. 
     The overlay material can have a Total Mass Loss (TML) of about 2.38% per ASTM E595. 
     The term “semi-rigid” means that the device may flex under some loading but is able to hold its shape (it is self-supporting) when not attached to another member. The term “rigid” means that the device does not flex under normal loading during use. 
     Turning now to the figures,  FIG. 1  illustrates a prior art circuit breaker  10  with an arc chute  20 , a movable contact arm  40  with an electrical contact  50 , a line terminal assembly  60  comprising a stationary electrical contact  65 . The movable contact arm  40  engages a handle  30  and a mechanism spring  48 . The circuit breaker  10  can also include at least one trip cam  68 , a frame  42 , a cradle  45 , a bimetal member  67 , a collar assembly  80 , a load terminal  69 , a magnet  70 , armature  75  and shunt bracket  77 , for example. 
       FIG. 2  is an enlarged view of the prior art arc chute  20  shown in  FIG. 1 . This arc chute  20  includes a bottom or base  20   b , sidewalls  20   w  extending upwardly from at least two opposing sides of the base  20   b  to an upper portion  20   t  and providing a cavity  20   c . The arc chute  20  can include slots  22  in the base  20   b  extending in a direction between the sidewalls  20   w  and which may also extend upward a partial distance into one or both of the sidewalls  20   w . The inner surfaces  21   i  of the sidewalls  20   w  may include a projection  23  that is orthogonal to the slots  22  and the outer surfaces  210  may include a corresponding recess  24 . 
       FIG. 3  is a partial section view of a circuit breaker  10  according to embodiments of the present invention. As shown, the circuit breaker  10  can include a molded circuit breaker housing  10   h  that holds the components discussed above. In addition, as shown in  FIGS. 3 and 4A , the arc chute  20  includes an overlay material  120  directly on an upper primary surface of the base  20   b  of the arc chute  20 . The arc chute  20  can have a unitary (single piece) body of steel. The arc chute  20  can have sidewalls with tops  20   t.    
     As shown in  FIGS. 4B and 5 , for example, the tops  20   t  of the arc chute  20  can include a pair of laterally spaced apart upwardly project tabs  220 , one on each end of each sidewall  20   w , in some embodiments. 
     As shown in  FIGS. 5, 6A and 6B , the upwardly extending sidewalls  120   w  can terminate at a vertical height “H” that is above the top or vertex of the moving contact  50 , at least when the circuit breaker is ON and able to pass current. In some embodiments, the top of the moving contact  50   t  is at a distance of less than 1 inch, typically about 0.09 inches to about 0.10 inches, below the top of the sidewalls  120   w  when the circuit breaker is ON. 
     Referring to  FIG. 6C , for example, the sidewalls  120   w  of the overlay  120  can have a height sufficient to place the top  120   t  even with or above the top of the stationary contact  65 , at least along a Y-axis. The overlay  120  can be configured to extend a distance “D” of about 0.01 inches to about 0.02 inches, such as about 0.0136 inches, above the top of the stationary contact  65  (along the Y-axis in the orientation shown). In some embodiments, this dimension is greater than or equal to the height of the stationary contact  65 . 
     The sidewalls  20   w  of the arc chute  20   w  can have a height that is under 1 inch, in some embodiments, typically between 0.6 inches and 0.4 inches. The sidewalls  120   w  of the overlay  120 , and/or member  120   m , where used, can have a corresponding height or may be taller or shorter and can reside inside the cavity  20   c  of the arc chute  20  for at least a major segment of their height. In some embodiments, the sidewalls  120   w  can have a height that positions the top thereof  120   t  below the tabs  220  and parallel to the top  20   t  of the sidewalls  20   w  of the metal arc chute  20 . 
     As shown in  FIG. 4A , the overlay material  120  can be provided as a rigid or semi-rigid overlay member  120   m  having sufficient rigidity to provide a self-supportable three-dimensional shape (when not attached to the arc chute). The three-dimensional shape of the overlay member  120   m  can correspond to and/or conform to the shape of the arc chute  20  so as to provide a cavity  120   c  and upwardly extending sidewalls  120   w . The sidewalls  120   w  may taper outward from the base  120   b  at an angle of inclination that corresponds to that of the sidewalls  20   w  of the arc chute  20 . 
     As will be discussed further below, and as shown in  FIGS. 4B and 4C , for example, the overlay material  120  may alternatively be provided as an over-molded layer(s)  120   l  of material formed directly on an upper surface of base  20   b  and typically the sidewalls  20   w  of the metal arc chute  20 . 
     The overlay material  120  has a significantly reduced electrical conductivity relative to the metal arc chute  20  and may optionally be electrically non-conductive, i.e., electrically insulating. The term “significantly reduced” means that the electrical conductivity is at least 50% less than that of the metal chute when measured at 250 degrees C. 
     The overlay material  120  typically comprises a polymer, such as a thermoplastic polymer which may include glass fibers and/or other materials for structural rigidity, flame retardant properties and the like. In some embodiments, the overlay material  120  is or comprises at least one polyamide such as nylon, aramid and/or an aromatic polyamide such as KEVLAR®. 
     As shown in  FIG. 4D , for example, the overlay material  120  can comprise a multi-layer structure, shown as first and second layers  120   a   1 ,  120   a   2 , which may be a laminated structure of one or more materials. More than two layers may be used. The overlay material  120  can comprise a polymer  120   a   2  as an external layer and a semiconductor  120   a   1  (on the inner side facing the upper primary surface of the bottom of the chute  20 ) or combinations of these or other materials. 
     As shown in  FIG. 4E , the overlay material  120  may have a gradient configuration  120   g  of reduced electrical conductivity, such as an electrically insulating outer surface that transitions to have increased electrical conductivity (ies) in depth as the overlay material  120  approaches the (i.e., wall or primary surface of the bottom of) metal arc chute surface(s). 
     In some embodiments, the overlay material  120  is or comprises nylon. The overlay material  120  can be hygroscopic and have a high outgassing rate with a suitable melting temperature of above 250 degrees Celsius. As used herein, the term “hygroscopic” refers to materials with a moisture absorption value (at equilibrium) that is greater than 3% and/or a water absorption value of at least 10% as determined by ISO62. 
     In some embodiments, the overlay material  120  can be or comprise a PA46 grade nylon with or without fillers or other additives. 
     In some embodiments, the overlay material  120  can have the following properties: (a) moisture absorption that is greater than 3% according to ISO62; (b) a heat deflection temperature (under 0.45 MPa load) that is greater than 250° C. according to ISO75; and (c) a total mass loss that is greater than 2% according to ASTM595, the contents of these standards are incorporated by reference as if recited in full herein. 
     Referring again to  FIG. 4A , the overlay material  120  can be a free standing member  120   m  with sidewalls  120   w  that extend up from a base  120   b  and a top  120   t . In the embodiment shown, there are only two sidewalls facing each other across a cavity or depression  120   c . The overlay member  120   m  can have a wall thickness With that is the same for the bottom or base  120   b  as the sidewalls  120   w , as shown, or the wall thickness With may vary. The wall thickness With is typically from about 0.040 inches to about 0.100 inches, such as about 0.088 inches, in some embodiments. 
     The outer surface  1210  of the sidewalls of the overlay member  120   m  can include at least one (shown as two) outwardly projecting members  125  that can engage the slots  22  in the sidewalls of the arc chute  20 . The projecting members  125  can be circular or arcuate and engage an upper end of the slot  22  in a respective sidewall  20   w . The projecting members  125  can have an outwardly extending length that is less than a wall thickness With of the sidewall  20   w  of the arc chute  20 . The projecting members  125  can be configured to position the outer end of the projecting member to be flush or recessed into the outer surface of the arc chute sidewall  20   w  as shown in  FIG. 5 , for example. 
     As shown in  FIG. 4A , the projecting members  125  in  FIG. 5  have a length L of between 0.1 inches and 0.01 inches, more typically between about 0.07 and 0.03 at the midpoint of the top surface  125   t . The projecting member  125  can taper inward below the top  125   t  to have a shorter length at its bottom  125   b . The projecting member  125  may have a maximal length that is about 90% of the steel arc chute&#39;s thickness. The arc chute wall thickness  20   w  can be about 0.032 inches and the projecting member(s)  125  can have a maximal length L that is about 0.029 inches, in some embodiments. In some other embodiments, i.e., for high-rating products (&gt;100 A, typically used as a residential main circuit breaker) the have arc chute  20  can have a metal wall  20   w  with thicknesses of about 0.060 inches and the projecting member(s)  125  can have a maximal length L that is about 0.055 for a residential circuit breaker. 
     Still referring to  FIG. 4A , the outer surface  1210  of the sidewall can include a laterally extending recess  123  that can have a shape corresponding to the laterally extending projection  23  of the arc chute ( FIG. 2 ). In the embodiment shown, the recess  123  has an elongate linear shape between arcuate ends. 
     Referring to  FIGS. 4A and 7 , the overlay member  120   m  can include a plurality of adjacent and spaced apart slots  122  (shown as four). The slots  122  can be provided as alternating slots of different widths, two more narrow  122   n  than the other wider two  122   w . The wider slots  122   w  can align with the underlying slots  22  of the arc chute  20 . The slots can have different shapes and lengths. 
     Arc chutes attempt to channel the arc away from the stationary and moving contacts  65 ,  50 , respectively, during a short circuit fault. After the magnetic trip occurrence, this channeling helps keep the fault&#39;s closing time to one half-cycle, extending the life of the contacts by depleting less silver. The slots  22  in the (typically stamped) steel arc chute  20  can aid in splitting the initial arc into multiple-smaller arcs, encouraging current along the arc chute to jump surfaces. The slots  122  can allow steel of the underlying arc chute to be exposed. The slots  122  can be wider and/or longer than aligned slots  22  of the arc chute to expose more steel. 
     As shown in  FIGS. 3, 5, 6A and 6B , for example, the base  120   b  of the overlay member  120   m  can reside directly on the upper surface of the base of the arc chute  20   b . Referring to  FIGS. 5 and 6A , the overlay material  120  can occupy what was otherwise free space in the cavity of the arc chute  20   c . The movable contact  50  can reside closer to one sidewall  120   w  than the other sidewall as shown in  FIG. 6A . 
     In some particular embodiments, as shown in  FIG. 6A , for example, the contact arm  40  can be biased towards the base or cradle  45  ( FIG. 3 ) of the circuit breaker  10 . In some embodiments, the overlay material  120  can direct the arc towards one side, such as the cover side. In some embodiments, there is less than 0.10 inches in clearance, such as only about 0.040 inch clearance, between the inner surface  121   i  of one of the sidewalls  120   w  and the end of the contact arm  140  with the contact  50 . 
       FIG. 6B  illustrates that the top of the moving contact  50   t  can reside closely spaced apart from the inner surface/top of the overlay material during an ON position of the circuit breaker, typically within a normal/orthogonal distance that is less than 1 inches, more typically about 0.1 inches or less, such as at a normal distance N D  of about 0.094 inches from a top of the overlay material  120   t . The vertex or top of the moving contact  50   t  can reside a distance dz that is about 0.25 inches, a distance dy that is about 0.094 inches and a distance D extending from the vertex of the moving contact  50   t  to the top inner surface  120   i  of the overlay material of less than 0.5 inches, typically about 0.27 inches. 
     Referring to  FIGS. 4B and 4C , the overlay material  120  can be integrally attached to the arc chute  20  as an over mold layer  120   l , typically with a thickness of from about 0.040 inches to about 0.100 inches, such as about 0.088 inches, in some embodiments. 
     The overmolded overlay  120   l  and arc chute  20  can be configured as a unitary body so that the overlay material  120  is not easily manually detachable and can, in some embodiments, require a peel strength above 1 KN/m, and more typically above about 3 KN/m, and/or unless by destructive detachment to destroy the intact configuration of the overlay  120 . 
       FIG. 4B  illustrates that the overmolded overlay material  120   l  can occupy an entire surface area of the base  20   b  and more than a major (greater than 50%) of the surface area of the sidewalls  20   w . The inner surface areas  22   i  of the perimeter of the slots  22  may be free of the overlay material to expose metal, typically leaving at least over a thickness dimension of the base  20   b  free of the overlay material  120   l.    
     As shown in  FIG. 4C , the overlay  120   l  can be provided as disconnected elongate segments that occupy a sub-surface of the metal of the underlying surface in the arc chute base  20   b . The segments  120   s  can reside on each outer side of the arc chute base and a portion of the sidewalls  20   w  and leave inner perimeters  22   i  of the slots  22  uncovered. 
       FIGS. 8 and 9  show another exemplary embodiment of the arc chute  20 ′ and overlay material  120 ′. In this embodiment, the overlay material can comprise an overlay member or members  120   m  with a plurality of rigid or semi-rigid planar members (similar to fins)  120   f  with walls  120   w  that extend between the sidewalls  20   w  of the arc chute  20  in the cavity  20   c , rise upward from the base of the arc chute  20   b  and terminate below an upper end of the sidewalls  20   t . The members  120   m  can be provided as a plurality of discrete members that interlock or attach to slots  21   s  in the sidewalls  20   w  with interlock end segments  1120 . The overlay member  120   m  may also be provided as a unitary member of connected wall segments  120   w . The overlay member  120   m  can have a plurality of a parallel planar wall segments that rise up at the sidewalls of the base  20   w  and the planar segments  126  can extend at a height that is below about half the maximal height of the sidewalls  20   w.    
       FIGS. 10A and 10B  show yet another embodiment of an arc chute  20 ″ and overlay material  120 ″. The arc chute  20 ″ can have a solid, continuous base surface  20   b  and the overlay  120 ″ can cover and/or encapsulate the upper primary surface of the base  20   b.    
     The contacts  50 ,  65  can comprise about 25% Ag to about 97% Ag by weight. In some embodiments, the circuit breakers  10  can be DC circuit breakers, AC circuit breakers, or both AC (alternating current) and DC (direct current) circuit breakers. 
     The circuit breakers  10  can be rated for voltages between about 1V to about 5000 volts (V) DC and/or may have current ratings from about 15 to about 2,500 Amps. The circuit breakers  10  may be high-rated miniature circuit breakers, e.g., above about 70 A in a compact package. However, it is contemplated that the circuit breakers  10  and components thereof can be used for any voltage, current ranges and are not limited to any particular application as the circuit breakers can be used for a broad range of different uses. 
     The circuit breakers  10  can be molded case circuit breakers (MCCB)s. MCCBs are well known. See, e.g., U.S. Pat. Nos. 4,503,408, 4,736,174, 4,786,885, and 5,117,211, the contents of which are hereby incorporated by reference as if recited in full herein. 
     The circuit breakers  10  can be a bi-directional DC MCCB. See, e.g., U.S. Pat. No. 8,222,983, the content of which is hereby incorporated by reference as if recited in full herein. The DC MCCBs can be suitable for many uses such as data center, photovoltaic, and electric vehicle applications. 
     As is known to those of skill in the art, Eaton Corporation has introduced a line of MCCBs designed for commercial and utility scale photovoltaic (PV) systems. Used in solar combiner and inverter applications, Eaton PVGard™ circuit breakers are rated up to 600 Amp at 1000 Vdc and can meet or exceed industry standards such as UL 489B, which requires rigorous testing to verify circuit protection that meets the specific requirements of PV systems. However, it is contemplated that the circuit breakers  10  can be used for various applications with corresponding voltage capacity/rating. In some particular embodiments, the circuit breaker  10  can be a high-rating miniature circuit breaker. 
     The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the invention.