Abstract:
Molded insulating shell halves are secured together around a blowout coil, stationary and movable contacts to pivotally trap an armature assembly therebetween. Windows are provided in the shell halves to ventilate the electromagnet coil during operation. The electromagnet is removable through the window without disassembly of the contactor. Contact and armature adjustment is accomplished through additional window openings. An arc chute having left and right-hand arc extinguishing chambers each sub-divided into upper and front chambers splits the arc into four series segments and increases the overall length of the arc significantly over similar prior art devices.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to direct current switching apparatus and more particularly to direct current electromagnetic contactors. Still more particularly, the invention relates to contactors of the aforementioned type which are especially suitable for application in D.C. traction equipment for interrupting high voltages and high currents. 
     In D.C. switching apparatus, an electric are is generated between separating contacts. The voltage of such arc is caused to increase, thereby driving the current in the arc down in order to extinguish the arc and achieve circuit interruption. There are numerous techniques known in D.C. switching technology to extinguish arcs, such techniques often being used in various combinations. For example, lengthening the are generates a rise in are voltage. Separating the arc into a plurality of smaller segments increases its voltage and tends to cool the are. Confining the arc and compressing it to flatten the cross sectional shape thereof also increases the arc voltage. Still another technology is to subject the arc to materials which emit a quenching gas when subjected to the heat of the arc. U.S. Pat. No. 3,511,950 issued May 12, 1970 to D. R. Boyd discloses a direct current electromagnetic contactor having an are chute which utilizes the aforementioned arc interruption technologies to divide the arc into two initial segments and to move the arc segments into respective left and right-hand arc extinguishing chambers. This invention relates to improvements thereover. 
     SUMMARY OF THE INVENTION 
     D.C. switching apparatus in the form of an electromagnetically operated contactor is provided having a molded insulating housing substantially enclosing the operating mechanism of the contactor. The housing is provided with windows to permit heat from the operating coil to escape and to permit removal of the coil through a window without disassembling the contactor housing. Additional windows are provided for adjusting contact engagement at a specified armature gap from the exterior of the apparatus. The armature comprises a magnetic plate secured to a fiber resin molded lever having oppositely directed coaxial trunnions trapped in bearing openings in the molded insulating housing to provide a pivotal mounting for the lever. An improved arc chute comprises side-by-side left and right-hand arc extinguishing chambers which are each subdivided into two additional chambers oriented forwardly and upwardly, respectively. A series of arc runners and split conductors are disposed in the arc chute chambers to divide the arc into four segments. 
     The D.C. switching apparatus of this invention will be more fully understood and its features and advantages will become more readily apparent when reading the following description and claims in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front elevation view of the D.C. switching apparatus of this invention; 
     FIG. 2 is a right elevation view of the D.C. switching apparatus of FIG. 1. 
     FIG. 3 is a view similar to FIG. 2 but having a right-hand housing half removed to disclose internal components of the apparatus; 
     FIG. 4 is an exploded elevation view of the electromagnet of the D.C. switching apparatus of this invention; 
     FIG. 5 is a partial section view taken along line 5--5 in FIG. 2; 
     FIG. 6 is a fragmentary elevation view taken in the direction of arrows 6--6 in FIG. 1; 
     FIG. 7 is a view of a left-hand housing member of an arc chute of the D.C. switching apparatus of this invention with conductive arc runners positioned therein; 
     FIG. 8 is a view of a right-hand housing member of the arc chute having a center insulator and the conductive arc runners positioned thereto, FIGS. 7 and 8 conjunctively illustrating a left-hand arc extinguishing chamber of the arc chute; 
     FIG. 9 is a partial section view taken along line 9--9 in FIG. 8; 
     FIG. 10 is a partial section view taken along line 10--10 in FIG. 8; 
     FIG. 11 is a view of the right-hand insulating housing member of the arc chute similar to FIG. 8, but having the center insulator removed therefrom and illustrating only the portions of the conductive arc runners that are disposed within the right-hand arc extinguishing chamber; 
     FIG. 12 is a view of the left-hand insulating housing element of the arc chute having the center insulator positioned therein and showing the conductive arc runner members disposed therein, FIGS. 11 and 12 conjunctively illustrating the right-hand chamber of the arc chute of this invention; 
     FIG. 13 is a fragmentary section view taken along line 13--13 in FIG. 2; 
     FIG. 14 is a schematic cross sectional depiction of the arc chute of this invention. 
     FIG. 15 Is a partial section view taken along line 15--15 in FIG. 12; 
     FIG. 16 is a schematic elevation view of another embodiment of the arc chute of this invention; 
     FIG. 17 is a schematic end view of yet another embodiment of the arc chute of this invention; and 
     FIG. 18 is a schematic elevation view of the embodiment of FIG. 17. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The direct current electromagnetically operated switching apparatus 2 of this invention has a molded insulating housing comprising a pair of mating insulating shell halves 4 and 6 which abut each other along particular segments. The switching apparatus, more commonly known as an electromagnetically operated contactor, is particularly adapted to have the various components assembled to the left-hand shell half 4, the right-hand shell half 6 subsequently positioned over the assembled components and the two shell halves secured together by respective fasteners such as bolts 8 and 10. A spiral-wound blowout coil 12 is attached to the inside of left-hand shell half 4 by a bolt 14 which extends through a hole (not shown) in the left-hand shell half 4 and takes into an aligned threaded hole in blowout coil 12. A right-hand end 12a of blowout coil 12 projects upwardly as one terminal of the contactor. A stationary contact bar 16 is secured to the left-hand end of blowout coil 12 by a pair of screws 18 which are accessible through a window 4a in left-hand shell half 4 as seen in FIG. 6. Stationary contact bar 16 extends forwardly at a downward angle and has a stationary contact 20 attached to the distal end thereof by a screw 22 extending through a clearance hole in stationary contact 20 and taking into a threaded hole in stationary contact bar 16. A left-hand pole piece 24 is secured to a cylindrical core 26 which extends through a hole in the shell half 4 and through the center of blowout coil 12. Pole piece 24 has the same profile as right-hand pole piece 28 (seen in FIG. 2) which is attached to the right-hand end of core 26 by a screw 30 after right-hand shell half 6 is positioned to the contactor assembly. 
     An armature assembly carrying a movable contact assembly thereon is pivotally mounted in the molded insulating housing of the contactor 2. The armature assembly comprises a magnetic plate 32 attached to the face of a molded fiber resin lever 34 by screws 36. Lever 34 has a pair of depending sides 34a which define a channel therebetween through which electrical conductors extend. A pivot pin 38 is molded into the left-hand leg 34a of lever 34 (FIG. 13) and a similar pivot pin 40, but having a truncated end 40a, is molded into the right-hand leg 34a of lever 34 to provide a pair of oppositely directed coaxial trunnions for lever 34. Flanged cylindrical bushings 42 are disposed over the pivot pins 38 and 40 to fit within corresponding openings in the housing shell halves 4 and 6. A pair of movable contact support posts 44 are pivotally supported between the sides of lever 34 at the upper end thereof by a pivot pin 46. Each of the support posts 44 receives a crimped wire connector 48 and a movable contact 50 secured thereto by a screw 52 (FIG. 3). Each crimped connector 48 has a braided conductor 48a attached thereto and both of the conductors 48a are commonly affixed to the other terminal 54 of the contactor. Terminal 54 is secured to the housing by screws 56. Helical springs 58 disposed between a shelf portion of lever 34 and the under side of the respective movable contact support posts 44 impart a clockwise bias to the movable contacts as viewed in FIG. 3. An insulated wire conductor 60 is also attached to terminal 54 and extends forwardly between legs 34a of lever 34 to be connected to a front stab bracket 62 mounted to a forward cross member 4b of left-hand housing shell half 4. A rear stab bracket 64 is attached to stationary contact arm 16 by a screw 66. 
     One or two interlock switches such as 68 may be mounted on the front of the molded insulating housing for the contactor 2 as desired. Only one is shown, that being mounted to the left-hand housing half 4 by appropriate screws. A spring biased plunger 68a extends through an opening in the housing half to bear against a depending side leg 34a of lever 34 for actuation of the switch 68. Right-hand housing shell half 6 is positioned over the assembled components and secured to the left-hand housing shell half 4 by bolts 8 which threadably engage with nuts 8a as seen in FIG. 1. Right-hand pole piece 28 is positioned against right-hand housing shell half 6 and attached to the core 26 by screw 30. 
     Left-hand housing shell half 4 has a rectangular window 4c disposed obliquely relative to the back plane of the housing. Right-hand housing shell half 6 has a corresponding window 6a aligned with window 4c when the two shell halves are assembled together. Rectangular recessed pockets 6b are provided adjacent window 6a to receive mounting tabs 70a of an L-shaped magnetic frame 70 shown separately in FIG. 4. Magnet frame 70 has a cylindrical core 70b affixed to the upright leg thereof. A coil 72 is disposed over the core 70b and affixed to the frame 70 by a pair of screws 74 which extend through openings (not shown) in a flange 72a of coil 72 and take into appropriate threaded openings (not shown) in the upright leg of frame 70. The assembled coil 72 and magnet frame 70 provide an electromagnet assembly for the contactor 2 which may be installed or removed through the window 6a without disassembling the contactor housing. Tabs 70a rest upon the bottom of the recesses 6b to laterally position the electromagnet assembly within the contactor housing. Bolts 10 extend through openings in the tabs 70a and in the housing shell halves 6 and 4 and threadably engage nuts 10a (FIG. 5) disposed within hexagonal molded pockets in housing shell half 4 to secure the electromagnet assembly in place and to further secure the two housing shell halves 4 and 6 together. The windows 4c and 6a also provide for ambient cooling of coil 72. 
     Contact adjustment for contactor 2 is facilitated by window 4a, the provision of a rectangular notch 6c in the forward edge of window 6a and a similar notch in the forward edge of window 4c. Holes 16a in stationary contact support arm 16 are made particularly oversize to permit movement of the contact support arm 16 relative to the screws 18 prior to tightening the screws. To adjust the contacts, the armature assembly is manually pivoted against a gauge which may be inserted within the notch 6c and positioned against the face of core 70b to effect a desired armature gap at initial engagement of the contacts 20 and 50. Shims 76 are positioned within the window 4a against the back wall of housing shell half 4 to establish the proper longitudinal position of the stationary contact support arm 16 and the stationary contact 20 such that initial engagement of the contacts as shown in FIG. 3 occurs at the desired armature gap. Bolts 18 are then tightened to firmly clamp the stationary contact assembly in place. Full face engagement of movable contact 50 to stationary contact 20 occurs upon sealing of the armature 32 to the pole face of core 70b, whereby movable contact supports 44 are pivoted about pin 46 against the bias of spring 58 to permit flush engagement of the contact faces. 
     An arc chute assembly 78 is attached to the assembled contactor 2 by sliding the arc chute assembly between the pole pieces 24 and 28 and engaging spring clip connectors 80 and 82 with the connector stab blades 62 and 64, respectively. Arc chute assembly 78 comprises a left-hand housing element 84, a right-hand housing element 86 and a center plate 88 secured together by four screws 90 which extend through holes in the housing members 84 and 86 from the right-hand side 86 to take into nuts (not shown) trapped in hexagonal pockets in the left-hand member 84. 
     Referring more particularly to FIGS. 7-12 and 14, the arc chute assembly 78 provides left-hand and right-hand arcing chambers which each are subdivided into forward and upper arcing chambers thereby providing four distinct chambers for extinguishing the arc. The inside face of left-hand arc chute housing member 84 is shown in FIG. 7. Housing member 84 has a rear wall 84a, a lower wall 84b and a boss 84c at the forward upper corner of the housing member, each of which provide a mating surface for corresponding elements of the right-hand housing member 86. Conductive arc runners 92 and 94 are positioned in housing member 84 by the walls 84a and 84b, respectively. The arc runners 92 and 94 extend transversely across both the left-hand and right-hand arcing chambers and therefore the portions of each which are disposed in the left-hand arcing chamber are shown in FIG. 7, crosshatched to indicate that the portions disposed in the right-hand arcing chamber have been broken away. Spring clip 82 is secured to an upright flange of arc runner 92 as seen in FIG. 7. However, spring clip 80 is attached to the right-hand portion of arc runner 94 and therefore does not appear in FIG. 7. 
     The opening or throat of the arc chute is defined between the arc runners 92 and 94 and extends across both the left and right-hand chambers. A positioning rib 84d extends from the opening angularly forward and upward to the boss 84c to position a hairpin conductor 96. Conductor 96 is an elongated U-shaped member, the legs of which extend on either side of rib 84d and the closed end of which extends laterally into both left-hand and right-hand chambers. The closed bight portion of hairpin conductor 96 is disposed essentially centrally of the opening formed between arc runners 92 and 94 and is disposed slightly inwardly of the arc chamber. A pair of V-shaped conductors 98 and 100 have laterally offset divergent legs which are disposed in the left-hand and right-hand arc extinguishing chambers. With particular reference to FIG. 7, the base of conductor 98 extends between both left-hand and right-hand arc extinguishing chambers and is therefore cross sectioned to illustrate that the portion disposed in the right-hand chamber has been broken away. A leg 98a extends obliquely along the rear leg 84a of housing member 84, terminating near the upper rear corner of the housing member 84. A leg 100a of conductor 100 similarly extends obliquely along lower wall 84b of housing 84, terminating near the lower front corner of the housing 84. 
     The inside surface of left-hand housing member 84 comprises a first pair of inclines 84e and 84f leading to the major interior surfaces 84g and 84h, which surfaces are coplanar. A second pair of inclines 84j and 84k rise at a steeper angle than inclines 84e and 84f and terminate at a height coincident with the right-hand surface of a center plate 88 positioned on housing member 84 as will be described hereinafter. Second level surfaces 84m and 84n are raised above the respective adjacent surfaces 84g and 84h. Surface 84m is disposed between rear wall 84a and leg 98a of V-shaped conductor 98 and surface 84n is located between lower wall 84b and the leg 100a of V-shaped conductor 100. An outwardly beveled surface 84p is provided along the upper edge of surface 84g and an outwardly beveled surface 84q is provided along the forward edge of surface 84h. A plurality of ribs 84r are provided on the surfaces 84g and 84p, the ribs being oriented radially from the mouth of the arc chute assembly, particularly the area between arc runner leg 98a and hairpin conductor 96. Similarly, a plurality of ribs 84s extend along the forward surfaces 84h and 84q, the ribs 84salso being oriented radially relative to the mouth of the arc chute assembly, particularly the area between hairpin arc runner 96 and conductor 100a. 
     A center plate 88 is disposed upon the inner surface of left-hand arc chute housing member 84, the center plate resting on surfaces 84m and 84n as well as on the surface of positioning rib 84d and ribs 84r and 84s. Center plate 88 is essentially a planar member having double-beveled upper and forward outer edges to provide an outward flaring at the upper and forward outer edges. The angle of the bevel of the flared outer portions is substantially parallel to the angle of the beveled portions 84p and 84q to provide outwardly directed passageways for arc gasses to exit the arc chute as seen particularly in FIG. 14. Referring particularly to FIG. 8, center plate 88 is illustrated as it is seen from within the left-hand arc extinguishing chamber looking toward the right-hand housing member 86. Outwardly flared upper beveled portion 88a extends along the upper edge of the arc chute assembly and outwardly flared forward beveled portion 88b extends along the forward edge. As can be seen, the extended legs of hairpin conductor 96 and the leg 98 a of conductor 98 and 100a of conductor 100 are disposed within the left-hand chamber against the surface of center insulator plate 88. 
     The right-hand surface of center plate 88 is provided with beveled surfaces 88c and 88d which extend outwardly in the opposite direction to the surfaces 88a and 88b, respectively, to provide the flared outer edges as seen in FIG. 12. The right-hand surface of plate 88 is also provided with a raised rib 88e which extends angularly upwardly and outwardly parallel to the hairpin conductor 96. The right-hand surface of center plate 88 is disposed in mating relationship with the inside surface of right-hand housing member 86 which is shown in FIG. 11. Housing member 86 has a rear wall 86a, a bottom wall 86b and a boss 86c located at the outer, upper corner thereof, each defining surfaces which are coplanar and which mutually engage the corresponding surfaces of left-hand housing member 84. Arc runner 92 is disposed also within right-hand arc chute housing member 86, the arc runner having a leg 92a which extends upwardly along the rear wall 86a. Arc runner 94 is positioned also within the right-hand arc chute housing member 86 and has a leg 94a which extends along the lower wall 86b. The U-shaped portion of hairpin arc runner 96 is common to both the left and right-hand housing members 84 and 86 and is shown in FIG. 11. The other leg 98b  of V-shaped conductor 98 is shown in FIG. 11 and is disposed within the right-hand arc chamber extending angularly outwardly toward the boss 86c. Similarly, the other leg 100b of V-shaped conductive member 100 extends angularly outwardly toward the boss 86c. An elongated slot 86d is provided in the interior surface of right-hand housing member 86 parallel with the disposition of hairpin arc runner 96. The inside surface of right-hand arc chute housing member 86 has a pair of inclines 86e and 86f which lead from the throat of the arc chute to the major coplanar surfaces 86g and 86h of the member 86. Slots are provided in the surfaces 86e and 86g to receive and position the leg 98b of V-shaped conductor 98 as are slots in the surfaces 86f and 86h to receive the leg 100b of V-shaped conductor 100. A pair of inclines 86j and 86k extend along the lower end of hairpin conductor 96 to a height that will be even with the left-hand surface of center plate 88 in the left-hand arc chamber as seen in FIG. 14 when the arc chute assembly is fully assembled. Similarly to member 84, the outer edge along surface 86g has an outwardly flared bevel 86p and the outer edge along surface 86h has an outwardly flared portion 86q. A plurality of ribs 86r are formed on the surfaces 86g and 86p, the ribs being oriented substantially radially from the mouth of the arc extinguishing chamber, particularly the area between legs 92a of arc runner 92 and 98b of V-shaped conductor 98. A plurality of ribs 86s are formed on the surfaces 86h and 86q, the ribs 86s being oriented radially from the area between leg 94a of arc runner 94 and leg 100b of V-shaped conductor 100. A stepped surface 86m is provided in rear wall 86a behind leg 92a of arc runner 92. Likewise, a stepped surface 86n is provided in lower leg 86b behind leg 94a of arc runner 94. The surfaces 86m and 86n and ribs 86r and 86s provide mounting surfaces against which the center plate 88 rests. When center plate 88 is positioned against the right-hand housing half 86, rib 88e extends into slot 86d as seen best in FIG. 10 to provide additional over surface spacing between the conductors 98b and 100b, particularly at the converging ends near boss 86c. 
     The outer ends of surfaces 84m and 84n of housing member 84 are relieved as seen in FIG. 7 to cooperatively define with walls 84a and 84b, respectively, recesses 84t and 84u, respectively. The bottom of recesses 84t and 84u are at the same level as the surfaces 84g and 84h as can be seen in FIG. 15. Similarly, housing member 86 has recessed areas 86t and 86u immediately outward of raised surfaces 86m and 86n, respectively, and adjacent the outer ends of walls 86a and 86b respectively. The bottom of recessed areas 86t and 86u are at the same level as surfaces 86g and 86h, respectively, as seen in FIG. 15. Center plate 88 has L-shaped ribs 88f and 88g projecting from opposite surfaces thereof at the upper and forward corners thereof to interfit with the respective recesses 84t, 84u, 86t, and 86u as seen in FIG. 15, thereby increase over surface distance along the insulating members between conductors of opposite potential. 
     FIG. 12 illustrates the right-hand arc extinguishing chamber as viewed from inside looking at the center plate 88. With the elements so assembled and held together by the screws 90, a left-hand arc extinguishing chamber is formed between left-hand arc chute housing member 84 and center plate 88 and a right-hand arc extinguishing chamber is formed between right-hand arc chute housing member 86 and the center plate 88. Left-hand arc extinguishing chamber is subdivided into a separate forwardly directed arc extinguishing chamber extending between hairpin arc runner 96 and leg 100a of V-shaped conductor 100 and an upwardly directed arc extinguishing chamber extending between hairpin arc runner 96 and leg 98a of V-shaped conductor 98. The right-hand arc extinguishing chamber is subdivided into a forwardly facing arc extinguishing chamber extending between arc runner leg 94a and leg 100b of V-shaped conductor 100 and a second upwardly directed arc extinguishing chamber extending between leg 92a of arc runner 92 and leg 98b of V-shaped conductor 98. 
     An arc generated between contacts 20 and 50 upon separation thereof is moved into the throat of the arc chute by a magnetic field generated by coil 12 and transfers to the arc runners 92 and 94. Further movement into the arc chute causes the arc to split into a first segment between arc runner 92 and hairpin arc runner 96 and a second segment between hairpin arc runner 96 and arc runner 94. Further movement of the arc under the influence of the coil 12 and pole pieces 24 and 28 moves the arc along the various inclines 84e, 84f, 84j, 84k and 86e, 86f, 86j and 86k to the bases of V-shaped conductors 98 and 100, whereupon each segment of the arc again splits in half. One of the newly formed segments of the arc moves into the upper right-hand arc extinguishing chamber and extends between the divergent legs 92a and 98b. The other newly formed segment moves into the left-hand arc extinguishing chamber and extends between leg 98a and one leg of hairpin arc runner 96. Similarly, the other arc segment divides in two and one segment thereof moves into the forward portion of the right-hand arc extinguishing chamber extending between the divergent legs 94a and 100b. The other segment moves into the left-hand arc extinguishing chamber and extends between hairpin arc runner 96 and divergent leg 100a of V-shaped conductor 100. 
     One of the techniques for raising the voltage of an arc and thus extinguishing an arc is to lengthen the arc. The arc initially formed between contacts 20 and 50 is doubled in length by the series arc segments that extend between arc runner leg 92a and V-shaped conductor leg 98b which is common with conductor leg 98a, thereby establishing another arc segment between leg 98a and hairpin arc runner 96. A third segment of the original arc extends from hairpin arc runner 96 to leg 100a of V-shaped conductor 100 which is common with leg 100b in the right-hand arc chamber and a fourth arc established between leg 100b and leg 94a of arc runner 94. The arc is also lengthened as it moves outwardly along the respective divergent conductive arc runners. As mentioned hereinabove, this length is doubled as the arc moves in both the left-hand and right-hand arc extinguishing chambers, yet the length of the four individual segments is shortened. As the arc moves along the diverging conductive members, it moves along the inclines 84e and 84 f and 86e and 86f which converge with the center plate 88 as seen in FIG. 14 to constrict the arc. As the arc moves into the flattened area of 84g, 84h, 86g, and 86h, the arc is constricted and flattened which also operates to raise the arc voltage. The center plate 88 is made from a material that reacts with the heat of the arc when in contact therewith to emit arc quenching gasses. A preferred material is a glass-filled thermoset polyester containing hydrated alumina. Thus the arc is flattened, constricted and subjected to quenching gasses in the areas 84g, 84h, 86g and 86h. Subsequent outward movement of the arc moves it into the insulating ribs 84r, 84s, 86r and 86s. When the arc loses sufficient energy, the diameter of the arc reduces resulting in reduced constriction. The lower energy level of the smaller arc permits the arc to bend around the ribs, thereby again increasing in length and compensating for the reduction in constriction. The ribs prevent the arc per se from exiting the arc chute assembly while arc gasses, on the other hand, do exit the upward and forward sides of the arc chute assembly. 
     FIG. 16 schematically depicts an alternate embodiment of the four-chamber arc chute described hereinabove. In this embodiment, the hairpin arc runner 96&#39; has the legs offset from each other whereby one leg 96a&#39; is in the right-hand arc extinguishing chamber and the other leg 96b&#39; is in the left-hand arc extinguishing chamber. Arc runner leg 94a&#39; is disposed in the left-hand chamber as is the leg 100b&#39; of V-shaped conductor 100. The leg 100a&#39; of the conductor is disposed in the right-hand chamber. Arc runner 92 and V-shaped conductor 98 are the same as in the above described version. An arc formed between contacts 20 and 50 is moved into the arc chute and separated into four segments as before, but the segments are located in a different serial relationship in the four sub-chambers. The arc extends from arc runner leg 92a to conductor leg 98b in the right-hand upper sub-chamber which leg 98b is common with leg 98a. A second segment of the arc extends from leg 98a to hairpin conductor leg 96b in the left-hand upper sub-chamber, which leg 96b&#39; is common with leg 96a&#39; thereof. The third segment of the arc occurs in the right-hand front sub-chamber between hairpin conductor leg 96a&#39; and V-shaped conductor leg 100a&#39;, which is common with leg 100b&#39;. The fourth segment of the arc occurs in the left-hand front sub-chamber between leg 100b&#39; and arc runner leg 94a&#39;. This embodiment permits the arc runner legs 92a and 94a&#39; to be located in different left and right arc extinguishing chambers. In this embodiment, it is preferable to provide an insulating rib-like rib 88e on both surfaces of the center plate and an appropriate groove such as 86d in the other housing half 84 to provide adequate over-surface distance between the conductors of different potential. 
     Another embodiment of the arc chute of this invention is depicted schematically in FIGS. 17 and 18. This arc chute 102 comprises three arc chambers, two outer chambers 104 and 106 and a center chamber 108. FIG. 17 is a view looking at the bottom of the arc chute into the inlet opening 110. Inclines 112 and 114 in one housing part direct the arc segments into outer chamber 104 and center chamber 108, respectively, while inclines 116 and 118 in the other housing part direct arc segments into outer chamber 106 and center chamber 108, respectively. A first arc runner 120 is connected to one of the device contacts and extends across all three chambers within the inlet opening 110. However, the leg 120a of arc runner 120 extends along within one of the outer chambers, e.g. 106, as represented by the dot-dash line in FIG. 18. A first V-shaped conductor 122 is located between chambers 106 and 108 in the inlet opening 110. A first leg 122a is disposed within the outer chamber 106 as depicted by the dot-dash line in FIG. 18, while a second leg 122b is disposed in the center chamber 108 at the left-hand side thereof, substantially parallel with the leg 120a. 
     A second V-shaped conductor 124 is located between chambers 108 and 104 in the inlet opening 110. A first leg 124a is disposed in the outer chamber 108 substantially parallel with leg 122a. A second leg 124b of conductor 124 is disposed in outer chamber 104 along the left-hand side substantially parallel with legs 120a and 122b. A second arc runner is connected to the other of the device contacts and extends through the inlet opening 110, a leg 126a thereof extending within the outer chamber 104 substantially parallel with the legs 122a and 124a. 
     In the arc chute of FIGS. 17 and 18, an arc generated between the contacts of the switching apparatus will be moved into the arc chute through the inlet opening 110. The arc will separate into three segments at the three different levels of the arc chute, thereby generally tripling its length. One segment of the arc will be disposed in chamber 104 between arc runner leg 126a and conductor leg 124b. A second segment of the arc will be in the center chamber 108 between the legs 124a and 122b of the two V-shaped conductors 122 and 124. The third arc segment will be in outer chamber 106 between conductor leg 122a and arc runner leg 120a. 
     The D.C. electromagnetic contactor described hereinabove provides a readily assembled and adjusted device having an improved arc chute assembly for more effectively extinguishing a high voltage arc generated between separating contacts of the contactor. It is to be understood that the described embodiment is susceptible of various modifications without departing from the scope of the appended claims.