Bi-directional direct current switching apparatus having bifurcated arc runners extending into separate arc extinguishing chambers

Direct current switching apparatus having front and rear arc extinguishing chambers substantially coextensive, the rear chamber being separated into two laterally spaced arc extinguishing chambers, each arc extinguishing chamber comprising rows of non-magnetic parallel splitter plates, a pair of spaced conductors each having a stationary contact element spanning both the front and rear arc extinguishing chambers, power supply terminals connected to the respective spaced conductors, magnetic plates disposed in front of the front chamber and in back of the back chamber having magnetic means providing a magnetic path externally around the chambers, permanent magnets magnetically coupled to at least one of the magnetic plates providing a magnetic field across the respective chambers, a movable contact movable normal to a front to rear direction into and out of bridging engagement with the stationary contacts, and an electromagnetic drive motor disposed coextensive with said arc extinguishing chambers coupled at a lower end to the movable contact. Bifurcated arc runners of the conductors lead from the stationary contact elements into respective front and rear chambers, and a conductor surrounds the laterally spaced arc extinguishing chambers to cooperate with the respective arc runners therein. Arcs established between the stationary and movable contact elements are moved from the contacts into either the front or rear chambers by the magneteic field according to polarity of the power applied to the respective terminals. The electromagnetic motor is readily and inexpensively manufacatured and assembled by utilizing molded housing parts to position and retain elements of the motor. The apparatus is particularly well suited for high voltage, high current applications requiring lightweight, compact apparatus.

CROSS REFERENCE TO RELATED APPLICATIONS 
This invention is related to copending U.S. patent application Ser. No. 
07/435,228, now U.S. Pat. No. 5,005,874, entitled Direct Current Switching 
Apparatus filed Nov. 12, 1989 in the names of Peter J. Theisen, Daniel A. 
Wycklendt, Mark A. Juds and Peter K. Moldovan. This application is also 
related to copending U.S. patent application entitled "Bi-directional 
Direct Current Switching Apparatus Having Arc Extinguishing Chambers 
Alternatively Used According to Polarity Applied to Said Apparatus" filed 
concurrently herewith in the names of Peter K. Moldovan, Mark A. Juds and 
Robert A. Kihn. Both of the above mentioned applications are assigned to 
the assignee of this application. 
BACKGROUND OF THE INVENTION 
This invention relates to apparatus for switching direct current (DC) 
electric power. More particularly it relates to apparatus of the 
aforementioned type which is non-polarized or bidirectional, i.e. its 
performance is independent of polarity of the current at the power 
terminals, and can switch high voltage DC power. Still more particularly, 
the invention is related to apparatus of the aforementioned type which is 
compact, lightweight, may be hermetically sealed and can switch high 
voltage DC power at high altitude. 
High voltage DC power is one of the most efficient, reliable and 
lightweight methods to generate and distribute energy. Development of high 
torque samarium cobalt brushless DC motors has resulted in low weight 
alternatives to hydraulic actuators used in weight and 
reliability-sensitive applications, e.g. aircraft. However, difficulties 
in switching high voltage DC power, particularly at high altitude, and the 
weight and volume of conventional DC switching apparatus capable of 
quenching high voltage circuits at altitudes, preclude the use of such 
switching apparatus in aircraft. As a result, the inability to 
satisfactorily switch high voltage DC power at altitude has delayed use of 
this power in aircraft. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide improved DC switching 
apparatus. 
It is a further object of this invention to provide DC switching apparatus 
capable of switching high voltage DC power. 
It is a further object of this invention to provide DC switching apparatus 
which is non-polarized. 
It is a further object of this invention to provide DC switching apparatus 
capable of switching high voltage DC power at high altitude. 
It is still a further object of this invention to provide DC switching 
apparatus capable of switching high voltage DC power at high altitude, 
which apparatus is compact and lightweight. 
It is still a further object of this invention to provide DC switching 
apparatus of the aforementioned type which is economically and efficiently 
manufactured. 
This invention provides bi-directional DC switching apparatus comprising a 
front arc extinguishing chamber and a pair of laterally arranged rear arc 
extinguishing chambers disposed adjacent and substantially coextensive 
with the front chamber, a spaced pair of conductors traversing the 
respective front and rear chambers, each conductor having a stationary 
contact and an arc runner leading therefrom, the arc runner being 
bifurcated into front and rear arc runners extending into respective 
corresponding arc extinguishing chambers, conductive means cooperating 
with the respective rear arc runners providing divergent paths into the 
respective rear chambers, a movable contact and means driving said movable 
contact into and out of bridging engagement with said stationary contacts, 
movement of the bridging contact out of engagement with the stationary 
contacts establishing respective arcs therebetween, magnetic means 
providing a magnetic field across the arc chambers normal to the arcs, 
current in the arcs combining with the magnetic field to create forces 
assisting in movement of the arc along either the front or rear arc 
runners into the respective arc extinguishing chambers according to 
polarity of DC power connected to the conductors. 
This invention further provides an electromagnetically operated linear 
motor for driving the movable contact, components of the motor being 
positioned within a particularly configured internal cavity of a molded 
housing, one portion of the housing being further configured for 
positioning a portion of the magnetic means and the front arc 
extinguishing chamber and providing guide means for the movable contact. 
The foregoing and other features and advantages of this invention will 
become more readily apparent and understood when reading the following 
description and appended claims in conjunction with the accompanying 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to FIG. 1 of the drawings, a hermetically sealed 
electromagnetic contactor 2 incorporating the bi-directional DC switching 
apparatus of this invention is shown in a perspective view. The contactor 
2 comprises an outer metal envelope comprising a can 4 having a mounting 
plate 6 affixed to the back thereof by welding or the like and a header 8 
hermetically welded over an open front side of can 4. Directional 
references herein, such as "front", "rear", "top", "bottom" and the like, 
are illustrative only for convenience and clarity in description, and are 
not to be construed as limitations to the scope of the invention defined 
in the appended claims. As a reference for the term "compact" as used 
herein, the envelope comprising can 4 and header 8 may be on the order of 
3.42 inches wide by 5.00 inches long by 3.23 inches high. Header 8 has 
outwardly projecting flanges 8a extending from opposite lateral edges. 
Mounting plate 6 has forwardly extending straps 6a at opposite lateral 
sides, the free ends of which terminate in laterally projecting flanges 6b 
secured to flanges 8a by fasteners 10. 
A multipin connector 12 is hermetically attached within an opening in a 
bottom wall of can 4 to provide connection to control electronics (not 
shown) for the bi-directional DC switching apparatus within the envelope. 
DC power terminals 14, 16 are attached and hermetically sealed to header 
8, electrical insulated therefrom, to extend through the header. The 
externally projecting portions of terminals 14, 16 have tapped holes for 
receiving screws 17 which attach power supply conductors (not shown) to 
the terminals. A generally T-shaped insulating barrier 18 is attached to 
header 8 by a pair of nuts 20 which threadably engage threaded posts 8b 
welded to the exterior of header 8. Barrier 18 isolates the power 
terminals 14, 16 and the attached power supply conductors from each other 
and provides a protective cover thereover to reduce electrical shock 
hazard. Header 8 is also provided with a tubular fitting 22 through which 
the seal of the contactor assembly may be checked and the contactor may be 
evacuated and filled with a controlled atmosphere medium such as an inert 
gas or the like, after which the fitting 22 is crimped shut and sealed. 
Referring to FIGS. 2, 3, 6 and 9, the bi-directional DC switching apparatus 
represented generally by the reference numeral 24, is built up upon and 
attached to header 8 prior to joining the external envelope members 4 and 
8. The linear motor, represented generally by the reference numeral 26, is 
first assembled. Referring particularly to FIGS. 3 and 9, motor 26 
comprises a pair of identical coils 28 each comprising an insulating 
bobbin 28a having circular flanges 28b at opposite ends, a winding 28c and 
an insulating cover 28d. Coils 28 are positioned axially end-to-end, 
separated by a cylindrical brass sleeve disposed within a circular opening 
in a rectangular magnetic flux guide 32. Sleeve 30 forms a non-magnetic 
continuance of aligned axial openings in coil bobbins 28a for slidably 
receiving a plunger 34 therein. A pair of rectangular magnets 36 are also 
disposed between adjacent ends of coils 28 on opposite sides of flux guide 
32 in magnetic contact with the flux guide. This assembly is positioned 
within a cavity 38a of an insulating housing 38. Cavity 38a (FIG. 9) 
comprises a pair of generally semi-cylindrical recesses separated by a 
central web to provide a complemental configuration for the coils 28, 
magnets 36 and flux guide 32 for accurate positioning and alignment of the 
coils. Housing 38 is relieved at 38b along the periphery of cavity 38a to 
receive a rectangular magnetic frame 40 therein, surrounding the coils, 
magnets and flux guide assembly. A lower leg of frame 40 has a hole 40a 
which aligns with the axis of coils 28. Housing 38 has a semi-cylindrical 
recess axially aligned with hole 40a, as does a housing cover 42, which 
also has a cavity complementally configured to position the coils, magnet 
and flux guide assembly when cover 42 is positioned over the housing 38. A 
non-magnetic drive rod 44, threadably attached to a lower end of plunger 
34, extends outwardly through hole 40a and the hole formed by the 
complemental semicylindrical recesses in housing 38 and cover 42. Cover 42 
is attached to housing 38 by suitable fastening means such as screws 45 
(FIG. 8) which pass through holes 42a and 38c (FIG. 9) to receive nuts 46 
(FIG. 8). 
Housing 38 and cover 42 are provided with laterally extending wings 38d and 
42b, respectively, which have aligned openings therein to be received over 
the internal ends of power terminals 14 and 16. These terminals are 
provided with a stepped down annular shoulder such as shown at 16a in FIG. 
6 against which wing 42b abuts. The terminals 14 and 16 are alike and each 
comprise a threaded body portion such as 16b in FIG. 6 which projects 
through the opening in wing 38d to receive a nut 44 thereon to clamp the 
housing 38 and cover 42 securely to the header 8. The distal ends of 
terminals 14, 16 have reduced diameter threaded portions 14c, 16c which 
are connected to the respective body such as 16b by frustoconical 
transition sections such as 16d (FIG. 6). 
The rear face of housing 38 is also suitably configured to position 
additional elements of the switching apparatus of this invention. A 
rectangular pocket 38e, open to the rear surface and upper edge, receives 
a generally rectangular insulator block 46. The insulator block 46 is 
notched along an upper edge at 46a to cooperatively create, with housing 
38, a groove which receives a conductive member 48 which will be described 
later. A front magnetic plate 54 is positioned against the rear surface of 
housing 38 and insulator block 46. Although not specifically shown, the 
profile of magnetic plate 54 complementally conforms to ribs formed on the 
rear face of housing 38 to position the plate 54 laterally and vertically. 
Plate 54 overlies a rectangular recess 38f (FIGS. 3 and 8), open to the 
rear surface of housing 38, thereby closing off a rear side of recess 38f, 
leaving it open to the bottom thereof. As will become apparent in later 
description, the closed recess becomes a part of a guide means for a 
movable contact carrier of the switching apparatus. 
A front insulating cover 56 is next disposed over the magnetic plate 54, 
similarly positioned laterally and vertically to the housing 38 by 
complemental formations on the cover 56 and the housing 38. Particularly, 
cover 56 has a pair of laterally extending rectangular bosses 56a which 
rest upon forwardly projecting arms 38g (FIGS. 5 and 9) of housing 38. 
Cover 56 is provided with a plurality of grooves which receive 
non-magnetic splitter plates 58 and 60 arranged in angular rows extending 
upwardly and outwardly from the center of the apparatus. A U-shaped or 
turn-back center arc splitter plate 62 depends substantially downward from 
the plates 58 and 60 between the power terminals 14 and 16, resting upon a 
rearwardly projecting tab 56b of cover 56. The splitter plates are made of 
a non-magnetic material, preferably copper, to provide no influence on 
magnetic fields directed across the switching apparatus as will be 
described later. Plates 58 are longer than plates 60 and are arranged 
alternately with the shorter plates 60 to provide a wider gap between the 
plates 58 at the lowermost ends thereof than the narrower gaps between the 
plates 58 and the intermediate plates 60. 
An intermediate insulating plate 64, provided with grooves for receiving 
the splitter plates 58, 60 and 62, is positioned over the splitter plates 
to receive the plates within the appropriate grooves. As seen best in 
FIGS. 3 and 5, intermediate plate 64 has a forwardly projecting rib 64a 
which extends into the space between legs of the turn-back splitter plate 
62. The rear face of intermediate insulating plate 64 is provided with a 
rearward extending centrally located rib 64b extending over the entire 
height of the plate, the lower end of rib 64b being rounded coincident 
with the lower end of turn-back splitter plate 62 to rest upon the 
forwardly projecting tab 56b. The rear face of intermediate insulating 
plate 64 is also provided with grooves for receiving and positioning a 
second plurality of non-magnetic splitter plates 58' and 60' arranged in 
the same manner as the plates 58 and 60. 
At the time of positioning intermediate insulating plate 64 to the 
assembly, the stationary contacts 66 and 68 are assembled to the power 
terminals 14 and 16, respectively. The contacts 66 and 68 are a mirror 
image of each other. Terminal 66 is shown in perspective view in FIG. 7 
and only contact 66 will be described in particular detail. The contact is 
essentially an L-shaped member made of heavy gauge copper or the like 
having a vertically oriented mounting leg 66a and a rearwardly extending 
leg 66b disposed at substantially right angles to the leg 66a. A 
stationary contact element 66c is attached to the under side of leg 66b. 
An arc runner projects from the leg 66b initially in the plane of leg 66b, 
but at right angles to the rearward extension of that leg. The arc runner 
is bifurcated into separate arc runners 66d and 66e. Arc runner 66d is 
substantially longer than arc runner 66e and is bent upwardly a slight 
reverse angle and subsequently further bent at a reverse angle at its 
distal end 66f. The second arc runner extends farther from leg 66b before 
having a single upward bend. Leg 66b is notched flush with contact 66c at 
the side opposite the arc runners 66d and 66e. A mounting hole 66h is 
provided in vertical leg 66a, hole 66h being counterbored complemental to 
a frustoconical transition section of terminal 14 corresponding to 
transition section 16d. The stationary contacts 66 and 68 are positioned 
with intermediate insulating plate 64 such that the arc runners straddle 
front and rear surfaces of the insulating plate 64. Hex nuts 70 with 
appropriate washers are threaded onto the ends 14c, 16c of terminals 14, 
16, respectively, to clamp the stationary contacts 66, 68, respectively, 
to the terminals 14 and 16 by causing the counterbores of holes 66h and 
the corresponding hole of contact 68 to seat firmly against the 
frustoconical transition section 14d and the respective similar section 
16d on terminal 16. 
Previously mentioned conductive member 52 is next assembled to the 
switching apparatus. Conductive member 52 is essentially an inverted 
U-shaped member having a flat bight portion which is disposed within the 
notch 50a of rectangular insulating block 50 adjacent housing 38. At the 
point of lateral emergence from the insulating block 50 and housing 38, 
the opposite legs of conductive member 52 are bent rearwardly to extend 
along the sides of housing 38 and front insulating cover 56. The opposite 
legs 52a and 52b of conductive member 52 subsequently extend downwardly 
and are bent laterally inwardly toward each other at a point rearward of 
the intermediate insulating plate 64 such that the legs 52a and 52b are 
essentially aligned with the splitter plates 58' and 60' and with the arc 
runner 66e and its corresponding arc runner 68e on stationary contact 68. 
The opposite legs 52a and 52b extend in a serpentine manner downwardly 
wherein the distal ends thereof are disposed in proximity to stationary 
contacts 66 and 68, adjacent the notch 66g and corresponding notch 68g of 
stationary contact 68. 
A pair of channel shaped insulators 72 are slidingly assembled within slots 
formed in the under surface of arms 38g and the upper surface of a second 
pair of arms 38h spaced downwardly from arms 38g of housing 38. A rear 
insulating cover 74 is then assembled against the splitter plates 58', 60' 
and the central rib 64b of intermediate insulating plate 64. The interior 
or forward face of rear insulating cover 74 is provided with slots for 
receiving the splitter plates 58' and 60'. Although not specifically 
shown, a fiberboard insulator or the like may alternatively be provided 
with suitable slots to be disposed over the splitter plates 58' and 60' at 
the rear thereof for positioning the same, and the cover plate 74 may be 
provided with suitable interlocking configuration with the fiberboard 
insulator to facilitate the assembly thereof. In either construction, the 
entire assembly of rectangular insulator block 50, conductive member 52, 
front magnetic plate 54, insulating cover 56, intermediate insulating 
plate 64, channel shape insulators 72, rear insulating cover 74 and the 
splitter plates 58, 60, 62, 58' and 60' , are all held in an assembled 
relation to the housing 38 by a pair of screws 76 which extend through 
aligned holes in housing 38, rectangular bosses 56a of front cover 56 and 
in rear cover 74 to receive nuts 78 thereon (FIG. 2). 
Referring to FIGS. 2 and 3, the rear face of cover provided with a shallow 
recess 74a which has a four point star appearance. The recess 74a 
positions five permanent magnets 80-88 in the star arrangement as shown in 
FIG. 2. This arrangement aligns the magnets 84 and 86 with the stationary 
contacts 66 and 68, magnet 80 with the arc runners 66e and 68e, and 
magnets 82 and 88 with the arc runners 66d and 68d. A rear magnetic plate 
90 is positioned over the magnets 80-88 and the insulating cover 74 and is 
held mechanically thereagainst by screws 92 which extend through aligned 
holes in housing 38, cover 74 and laterally open slots of tabs 90a of 
plate 90 to receive nuts 94 thereon. The upper ends of magnetic plates 54 
and 90 are bent at right angles to project toward each other in alignment 
therewith such that the adjacent edges of the respective members are in 
abutting relationship (FIG. 6) to complete a magnetic path around the 
exterior of the switching apparatus. The top leg of magnetic plate 90 may 
be provided with a notch 90b (FIG. 3) located centrally to provide a vent 
opening for arc gasses. 
The structure resulting from the assembly of elements described above 
provides a front arc extinguishing chamber as shown in FIG. 5 in which arc 
runners 66d and 68d diverge upwardly along the lower edges of the splitter 
plates 58. The turn-back splitter plate 62 depends between the respective 
stationary contacts to create a first division of any arc formed in the 
front arc extinguishing chamber. A pair of rear, laterally adjacent arc 
extinguishing chambers are formed between intermediate insulating plate 64 
and rear insulating cover 74. The arc runner 66e and its counterpart 68e 
on stationary contact 68 extend angularly toward the center of the 
switching apparatus and subsequently upwardly leading toward the lower 
edges of the splitter plates 58'. The opposite legs 52a and 52b of 
conductive member 52 cooperate with the respective arc runners 66e and 68e 
to form a divergent path from the notch such as 66g of the stationary 
contacts into the arc chamber. It will be noted that the total width of 
the front and rear arc chambers plus the intermediate insulator plate 64 
is substantially the same as the width of the stationary contact elements 
66c and 68c of the stationary contacts 66 and 68. This provides a very 
compact switching unit, both in front-to-rear dimension and in lateral 
dimension. The permanent magnets 80-88 are polarized across the width 
thereof to establish a magnetic field B (FIGS. 10 and 11) directed 
front-to-rear through the respective arc chambers, the plates 54 and 90 
forming a magnetic path around the outside of the switching apparatus and 
an air gap across the respective arc extinguishing chambers. 
A movable contact assembly indicated generally by the reference number 100 
is assembled to the switching apparatus 24 and linear motor 26. The 
movable contact assembly comprises a molded insulating contact carrier 102 
to which a movable contact 104 is pivotally mounted upon a fulcrum 102a of 
the carrier 102. Movable contact 104 is held against fulcrum 102a by a 
Z-shaped insulating clip 106 which has one leg overlying a shelf portion 
102b of carrier 102 and the other leg overlying the movable contact 104. 
As seen best in FIG. 3, a channel shaped drive link 108 is hooked to the 
contact carrier 102 at the forward end thereof and extends rearwardly 
adjacent the lower surface of the contact carrier. Carrier 102 is provided 
with a hole 102c in the region of shelf 102b through which a pin 110 
extends. An upper end of pin 110 is firmly secured in abutting 
relationship against the under side of the leg of Z-shaped insulating clip 
106 that overlies shelf 102b by a screw 112 or other suitable fastener. 
The lower end of pin 110 is provided with a reduced diameter projection 
110a which has an annular groove for receiving a C-clip 114 to firmly 
attach the pin 110 to the drive link 108. The forward end of drive link 
108 is attached to the lower end of drive rod 44 which is provided with a 
reduced diameter projection 44a similar to projection 110a of pin 110. An 
annular shoulder formed by rod 44 and reduced diameter projection 44a 
abuts the upper surface of drive link 108. Projection 44a is provided with 
an annular groove which receives a C-clip 116 to firmly attach the lower 
end of drive rod 44 to drive link 108. A helical compression spring 118 is 
disposed around drive rod 44 between drive link 108 and contact carrier 
102, biasing the drive link 108 downwardly away from carrier 102, thereby 
maintaining clip 106 firmly seated against shelf 102b and against movable 
contact 104. 
The opposite ends of movable contact 104 are reversely bent upwardly and 
toward each other in planes that are parallel to the orientation of legs 
66b and 68b and the initial portions of arc runners 66d and 66e, and to 
the corresponding portions of stationary contact 68. Movable contact tips 
104a are provided on the angularly disposed ends of movable contact 104. 
Movable contact assembly 100 is disposed for reciprocal linear motion in a 
vertical direction to bring movable contact elements 104a and 104b into 
and out of engagement with stationary contact tips 66c and 68c, 
respectively. Contact carrier 102 is guided for vertical sliding motion by 
a pair of upstanding legs 102d which are molded integral with the carrier 
and extend upwardly from the area of shelf 102b. The overall lateral width 
of the legs 102d is essentially that of the width of recess 38f and the 
front-to-rear depth of legs 102d is essentially that of the recess 38f 
when covered by the magnetic plate 54. Moreover, the walls of housing 38 
which define the recess 38f depend beyond the lower edge of housing 38 and 
may be provided with laterally outward extending flanges that cooperate 
with grooves formed in the carrier 102. With the assembly thus completed 
of the switching apparatus to the header 8, the can 4 is brought into 
position over the switching apparatus wherein the open end thereof nests 
within the flared rear edge of header 8. The juncture of can 4 with header 
8 is welded entirely around the periphery to provide a hermetic seal. The 
flanges 8a and 6b are joined together by the fasteners 10 to provide 
increased integrity against mechanical damage to the welded joint. The 
interior of the envelope may be exhausted and filled with an inert gas 
through tube 22 which is pinched shut and otherwise sealed following 
completion of the fill process. 
The operation of the switching apparatus of this invention will now be 
described. Power supply conductors may be connected to terminals 14, 16 by 
screws 17. The polarity of the power supplied to the terminals is 
immaterial for this switching apparatus. The magnetic field B directed 
through the respective front and rear arc extinguishing chambers is 
directed front-to-rear as coming out of the plane of paper when viewing 
FIGS. 4, 5, 10 and 11. The linear motor 26 is controlled from a remote 
location through wires connected through multipin connector 12 to the 
electronics (not shown) of the contactor also housed within the envelope. 
When an appropriate coil 28 is energized, a magnetic pattern is 
established within the frame 40 which attracts the plunger 34 against the 
upper wall of the frame. Once in this position, the permanent magnets 36 
establish a holding path that maintains the plunger in this upper position 
after the energized coil 28 is deenergized. In the upper position of 
plunger 34, drive rod 44 pulls drive link 108 upwardly which in turn 
drives contact carrier 102 upwardly by virtue of the resilient connection 
of spring 118 between drive link 108 and carrier 102. As movable contact 
elements 104a and 104b engage stationary contact elements 66c and 68c, 
spring 118 compresses to provide contact closing pressure to the movable 
contacts As the spring 118 compresses, pin 110 is permitted movement 
relative to carrier 102 to move the Z-shaped clip 106 upwardly away from 
movable contact 104, thereby providing no counter forces to the contact. 
In a similar manner, a signal is provided to the other coil 28 to establish 
an opposite flux pattern in the frame 40 whereby the plunger is attracted 
to the lower leg of frame 40, thereby moving projecting drive rod 44 to an 
extended position with respect to the motor housing 38 and 42. In so 
doing, drive rod 44 drives the drive link 108 downwardly which in turn 
carries with it pin 110 and Z-shaped clip 106 as well as carrier 102 by 
virtue of the hook at the forward end of drive link 108. This movement 
effects separation of the movable contact elements 104a and 104b from the 
stationary contact elements 66c and 68c, thereby establishing an electric 
arc between the stationary and movable contacts. 
As seen in FIGS. 3 and 9, plunger 34 has a reduced diameter undercut 34a 
near its lower end. This undercut 34a serves as a flux restrictor to 
reduce the flux and latching strength between plunger 34 and frame 40 at 
the lower end, thereby permitting coils 28 to be identical and an economic 
advantage realized thereby. When plunger 34 is magnetically latched in the 
up position, the contacts are closed, compressing contact pressure spring 
118 which applies an unlatching bias to the plunger, assisting the 
respective coil. Spring 118 provides no assistance when the plunger is 
magnetically latched in the down position, so the latching strength is 
reduced accordingly by restricting the flux and reducing the magnetic 
attractive force. The latter is further reduced by the small surface area 
surrounding hole 40a that is engaged by plunger 34 as compared to the full 
face of the upper end of plunger 34 which seals against frame 40. 
With reference to FIGS. 10 and 11, the polarity of the power supply 
connected to the switching apparatus will determine whether the forward or 
rear arc extinguishing chambers will be operational in interrupting the 
arc. Assuming the positive potential to be connected to terminal 16 and 
the negative potential to be connected to terminal 14 as shown in FIG. 10, 
current flowing in the arc will be from stationary contact 68c to movable 
contact 104a, through the contact 104 and from the other contact 104a into 
stationary contact 66c. With the magnetic field B applied in the 
front-to-rear direction, i.e. out of the paper, the magnetic field and 
current direction cooperate to provide forces on the arcs which drive the 
arcs inwardly toward the center of the switching apparatus. In so doing, 
the forward arc extinguishing chamber would be operative with the arcs 
moving along the movable contact, eventually being lead off the respective 
movable contacts onto the turn-back splitter plate 62, raising the 
potential of the splitter plate 62 above that of the stationary contact 
66. Accordingly, arcs at both contacts 104a and 104b would be lead off the 
movable contacts and onto the stationary contact arc runners 68d and 66d, 
into the area of divergence between the respective arc runners and the 
turn-back splitter plate 62. The arcs on both sides of the chamber would 
ultimately be driven into the wider gaps between splitter plates 58 to 
separate into a plurality of arcs and arc segments and those segments 
would ultimately be separated into two additional segments each when the 
arc moved between the plates 58 and intermediate plates 60, thereby 
driving the arc voltage up and the arc current down to zero. 
If the polarity of the power supply were connected in the reverse manner to 
the terminals 14 and 16, such as is shown in FIG. 11, then current in the 
arc will flow from stationary contact 66c to movable contact 104a, through 
the movable contact 104, and from the movable contact 104b to stationary 
contact 68c. With current directed in this manner and the magnetic field B 
directed out of the paper, the combined effect of the current and magnetic 
field establish a force which directs the arc laterally outwardly into the 
space created by the respective notch 66g and 68g. The arc moves from the 
movable contact 66 to the leg 52a of conductive member 52 and along the 
divergent path on the back side of arc runner 66e and leg 52a, stretching 
the arc as it enters the wider gaps between the longer splitter plates 
58'. The arc then becomes a plurality of separate arcs which subsequently 
move into the narrower spaces between splitter plates 58' and the 
intermediate, shorter splitter plates 60' whereby the arc becomes 
separated into an even greater plurality of separate arc segments, each 
causing the resistance to rise, driving the current to zero. During this 
time, the polarity at the opposite leg 52b of conductive member 52 becomes 
positive and the arc drawn at the stationary contact 68c moves from 
movable contact 104b to the leg 52b and upwardly along that leg and the 
back surface of arc runner 68e to lengthen the arc as it moves upwardly 
into the splitter plates 58' and subsequently between those plates and 
intermediate plates 60' to separate the arc into a plurality of short 
segments, also driving the voltage of the arc upward and the current in 
the arc to zero. Accordingly, the arc is either extinguished in the front 
chamber or the rear chamber, according to the polarity of the power supply 
connection to the switching apparatus. The unique side-by-side arrangement 
of the arc extinguishing chambers of the rear chamber and the coextensive 
front-to-rear arrangement between the arc extinguishing chambers and the 
electromagnetic linear motor provide a particularly compact assembly 
capable of interrupting DC currents of very large magnitude. The 
particular electromagnetic motor is easily assembled in a precise 
alignment with low manufacture costs by providing positioning 
configurations in molded housings wherein tolerances are readily 
controlled. Although the contactor of this invention has been disclosed in 
a preferred embodiment, it is to be understood that it is susceptible of 
various modifications without departing from the scope of the appended 
claims.