US1720844A - Oil switch - Google Patents

Description

A. F. c. LoTz OIL SWITCH 4 sheets-sheet 1 Filed Jan. 4, 1924 l nrrlu July 16, 1929. A. F. c. LOTZ 1.720.844

OIL SWITCH Filed Jan. 4, 1924 4 sheets-sheet 2 `f Y M July 16, 1929- A. F. c. LoTz 1,720,844

OIL SWITCH Filed Jan. 4, 1924 4 Sheets-Sheet 3 July 16,- 1929.

A. F. C. LOTZ OIL SWITCH Filed Jan. 4, 1924 4 Sheets-Sheet 4 @iff/6.5565.'

JV/M @fa/2a.

Patentedv July I6, 1929.

' UNITEo STATES 1,720,844 PAT-ENT OFFICE.

v ALEEED E. o. Lo'rz, or OHIOAGO, ILLINOIS, AssIGNoE 'ro ELECTRICAL ENGINEERS EQUIPMENT co., OE CHICAGO, ILLINOIS, A coEronA'rIoN or ILLINOIS.

OIL SWITCH.

Application led January 4, 1924. :Serial No. 684,278.

This invention relates to improvements in switches and while it has special reference-to switches of the oilimmersed tyfpe 1t is not limited to such switches but is a 5 ed for embodiment in switches of other ally comprise a air of stationary contact members and a ridging contact movable into and out of engagement ytherewith .all 4immersed in oil or other suitable insulatlng Huid. In switches of this sort the magnetic `field in its tendency to straighten out the current iiow, as well understood in the art, usually tends to separate the bridgmg contact from the stationary contact members.

This not only impairs electrical contact be;

tween the stationary and bridging contacts,

but the stresses imposed become relatively great where heavy currentsl are involved and the means holding theswitch closed must be made uite massive to withstand these stresses. arge and heavy holding mechanisms and correspondingly large an heavy mechanisms for releasing and operating the switch have been required. These are costly and usually complicated and their l great inertia makes quick, positive opemng of the switch ditlicult.

In switches of this sort, now in use, the speed of interruption upon which de ends the ability to extinguish the arc an dissipate the energy liberated, is the same as the speed of movement of the movable plunger. The matter of increasin `that speed, especially in oil switches, is iicult because of the requirement for compactness and the problem of housing the contact mechanism in a suitable tank or casing, and the necessity for making the parts strong enough to stand magneticA and mechanical stresses. l

Oil switches are commonly employed to break a flow of current at moderate and high potentials particularly indoors and in confined spaces. Air break switches are useful only in unconiined spaces such as outdoors or open air stations.

The oil has a dual function. First and always it serves as an insulating medium andsecond it serves as means for extinguishing the arc which is drawn between the contacts upon separating the same toopen the switches. The action of extinguishing the arc is somewhat obscure but it is deapt-- candescent conducting vapors.

pes. Switches of the oil break type now usu-l initely known that the cooling property of the oil acting upon the arc tends to extinguish the arc, thecontinued maintenance Of which depends upon` the maintenance of in- In the case of alternating current, this cooling action is particularly useful at the instant that the current ilow passes through zero. Since alternating current transmis- 'sion is universal this particular feature is to be considered carefully and any advantage which arises from the same should be turned to account.

Now the heating that occurs due to the are is a function of the means square of the current value and of the time. If the switch could invariably be opened at the instant that the current fiow drops to zero then there would be no current flow and no heating. This is not possible but nevertheless it is kdesirable to brin the switch from closed to fully open position as rapidly as possible vfor two chief reasons: First in order to have the actual Opening period includev the least number of half cycles or heating impulses, and second because the greater the speed of the contacts in Oil (within limits) the better is the contact between the arc and the surrounding Oil for extinguishing the arc. Also the shorter the period of opening the less is the damage to the oil perv interruption.

A higher speed of openin also prevents setting up a. degree of turbu ence in the oil which is desirable.

According to my present invention I pro vide a switch having a higher rate of speed of opening. This I secure primarily by employing movable parts of a minimum inertia and more particularly by moving both contacts of the switch simultaneously. This gives me a rate of movement of the contacts relative to each other of at least twice the speed of movement of ordinary switches. Furthermore I swing the con- 100 tacts away from each other on arms pivoted on stationary horizontal parts so that the initial break occurs at the central part of the body of oil and extends vertically `both up and down and at the same time 105 the latter part 'of the stroke has a very considerable lateral component so that a long doubly curved path is defined and ample opportunity to extinguish the are is provided particularly since the direction of 11 travel of the contacts is constantly chang- 1n v he break occurs in the central part ofthe tank remote from the Walls of the tank, and there-by there is lessdanger of grounding the arc upon the tank or frame. It is further to be noted that the break occurs in the open and not under any pece of apparatus orunder the bushings. ence less damage to the bushing is likely to occur and free release of the gases is possible.

There are quite a number of advantages that are made possible by the employment of this mechanism. For example thisA type of contact mechanism permits the use of a rotary operating shaft of small inertia and a balanced mechanical connection between thefmova-ble switch arms and said rotary sha t. v l' This operating shaft, and in fact all the operating mechanism, is 'mounted in supports in the frame below the bushing seal and hence the switch is free of .any mechanism between the bushings above the frame. A peculiarly simple and clear construction is hereby possible. Also any desired number of such switches may b connected on the same shaft to be operated simultaneously. By this means it is possible to secure with certaintya simultaneous opening of all three phases of a line.

Now I wish to call attention to another important feature of my invention which involves the matter of dividing the contacts into a plurality of parts. There are two fundamental advantages that I secure there-` by. First, better electrical and mechanical contact is secured while the switch isclosed and second an improved operation of interrupting current flow is secured when the switch is opened.

I divide the ends of the contact arms into two parts each bearing its main contact and follow up contact. This subdivision permits each contact to adjust' itself properly and secure the greatest total area of contact. This provides two paths for current flow, and when the switch is opened there is a tendency to draw two arcs in parallel paths separated by a body of oil. The two arcs having currents flowing in the same direction attract each other and tend by mutual magnetic interaction to assist the interruption of current How by forcing said arcs laterally into the cool oil between them. This proii des a novel method of interrupting current f ow.

The switch of my invention provides certain details of construction which are highly useful.

The balanced connection between the operating shaft and the swinging contact arms relieves the detent or holding means of any load caused by heavy current flow. Hence lighter parts having less inertia are possible.

The yielding brush contact of the main contact pair is so located that magnetic stresses due to current flow tend to press this contact more firmly against its cooperating contact. The contact bearing arms are drilled or otherwise apertured to project 'I a stream of oil into the space when the arc is formed. I provide also improved arcing or follow up contacts.

.In order to acquaint those skilled in the art with the manner -lof constructing and operating my invention I shall now describe in connection with the accompanying drawings one specic embodiment of the same.

In the drawings:

Figure 1 is a vertical section through a switch embodyng the invention;

Fig. 2 is a fragmentary vertical section through the cover showing the upper portion of. the switch operating mechanism in elevation.

Fig. 3 is a continuation of Fig. 2 showing -the contact mechanism and the lower por- Fig. 9 is a fragmentary side elevation of a modified form employing a divided path and a plurality of contacts;

Fig. 10 is a horizontal sectional view taken on line 10-10 of Fig. 9.

Fig. 11 is a vertical sectionalV view taken online 11-11 of Fig. 9; and

Figs. 12 and 13 are diagrams illustrating the course taken by the arc where the same is drawn between the contacts.

The switch shown comprises a closed oil ressel or pot 5 having a cover or lid 6 form- 1ng a main frame which -is pivotally or otherwise connected to the vessel 5.- In practice the pot may be moved and the cover be held statlonary or vice versa. Cover 6 is held in closed position over the open top of vessel 5 as by bolts 7 having threaded engagement with nuts 8. Outward movement of nuts 8 along the bolts 7 may be limited by cotter pins 9 or other suitable stops. Bolts 7 pass through openings in flange 10, rojecting from/a collar 11 secured about t e top of casing 5, and through slotted ears 12 projecting from cover 8.

Conductors provided at their outer ends v with terminal sockets 13 and 14 arel led through cover 6 by means of suitable insulators 15 'commonly termed bushings and terminate within vessel 5 in terminals 16 and 17.V Insulators ma 'be of a-ny suitableor preferred type. ey form no part of the present invention. Their mounting in cover 6, the connections out through the cover and thel details of vessel 5 and cover 6 may all be varied as desired. VIn the embodiment'shown insulators 15 are cemented in rings 18 mounted over openings 19 rin the cover. Packing rings or gaskets 20 and 2l are preferably provided between vessel 5 and cover 6 and between rings 18 and cover 6 to maintain tight joints at these points. Vessel 5 is provided with arms or mounting brackets for mounting the device on supporting channels 22 or. on a pole. wall, crossarm or other suitable support. The form of mounting may be varied as the frame 6 may be stationarily mounted and the pot 5 swung down or moved down. Surrounding one of the bushings 15 is a transformer coil23. This forms no part of the present invention and may be omitted or its details varied as desired.

`The present invention is especially concerned with the, contact mechanismbetween terminals 16 and 17 and with the balanced operating mechanism therefor. The contact' mechanism comprises a pair of contact arms '25 and 26 pivoted at 27 and 28 respectively on terminals 16 and 17. The upper surface 29 of lateral portion 30 of a lug 31 formed integral with arm liust short of lits forward end constitutes the main contact surface of arm 25. A laminated brush contact 32 mechanically and electrically secured to oblique lateral liange 33 at the `forward end of arm 26 by bolt 34 constitutes the main contact of arm 26. When the switch is closed the free end of contact 32 is adapted to make electrical contact with contact surface 29 of arm 25. v

The arms 25 and 26 areconnected electrically to terminals 16 and 17 by laminated strap or ribbon conductors 35 and 36 which thereby shunt the pivot joints 27 and 28. These pivots are Vmechanical connections which are not adapted for current conduction,v Suitable screws 37 and 38 fasten the ends of strap or ribbon 35 to the terminal 16 and to the lug 39 respectively. Similarly screws 40 and 41 secure the ends of the strap or ribbon 36 to the terminal 17 and to lug 42 respectively.

Main contacts 29 and 32 are protected from the action of arcing upon opening the switch by auxiliary or arcing contacts. These comprise a plunger contact 43 slidably mounted in alateral lug 44 carried by arm 25 outwardly beyond contact 29. 4 The upper end of plunger 43 terminates in an enlarged contact tip or head 45 the upper end of which is adapted for butt contact with the under surface of lower lateral contact flange 46 at the forward end of arm 26. The lower reduced end of the' shank of plunger 43 is threaded and secured by clamping nuts 50 in the forward end of a flexible conductor 51 which is connected at 53-53 of the swinging arm 25. A coiled spring 55 between tip or' head 45 of plunger 43 and lug 44 forces the contact tip into secure electrical contact with contact flange 46. Spring 55 maintains contact between contacts 45 and 46 for a period after main contacts 29 and 32 have separated or broken contact to protect the main contacts and draw any arc that may form between the auxiliary contacts-aswell understood in the art.

The auxiliary contact plunger 43 is preferably hollow to permit oil to pass therethrough directly into the space which the are would tend to occupy. Similarly the Contact flange 46 has a hole 46 for the projection of oil into the are.

Rotatable within the upper part of vessel 5 and entirely below the main frame 6 is a horizontal shaft upon which is'keyed at 61 a collar 62 having arms 63 and 64 projecting in diametrically opposite directions. Links 65 and 66 made of suitable insulating material and pivoted at their upper ends to arms 63 and 64 respectively at 70 and 72 extend downwardly through the interior of vessel 5 and are pivotally connected at their lower ends at 73 and 74 vto contact arms 25 and 26 respectively. A coiled tension spring 75 connected between a hook 76 secured at 77 in an internal boss on frame 6 and a hook 78 on `arm 64 normally tends to rotate shaft 60 in a counter clockwise direction (Figs. 1 and 2) and contact arms 25 and 26 in clockwise directions toward their open dotted line positions through links 65 and 66.

The switch may beheld closed in any suitable or preferred fmanner. To impart a clear understanding of the invention va latch arm 80 is shown for this purpose (Fig. 8). Arm 80 has a detent shoulder 81 which engages a shoulder 82 on collar 83 fixed on shaft 60 when the switch contacts are in nected at its opposite end with a latch releasing or trip solenoid 86 operable to swing arm 80 upwardly about its pivot 85 to release shaft 60and permit opening of the switch. Where a transformer overload trip is desired, transformer 23 may be used. The manner of releasing shaft 60 forms no part of the present invention and may be varied and changed as desired.

I have shown in my copending application, Serial`No. 673,465, filed November 8, 1923, a suitable setting and trip mechanism which I have constructed for use in this connection. The releaseof said shaft may be automatic or nonautomatic and the employment of various overload and manually rqplerated arrangements are contemplated.

' or without the casing as desired.

e holding device may be arrangedl within A' spring arm 90 secured to the underside of cover 6'by a screw A92.projects into the pathv of rotation of hook 78 and by engagement with hook 78 as it approaches the osiable" or preferred insulating `or `'arc extinguishing fluid which 'preferably substan-" tially fills the vessel and at least covers terminals 16 and 17 and the contact mecha-- nism therebetween. i From the foregoing it will now be a parent that when the switch' is closed and t e arts in the positions shown in full lines inv igures 1, 2 and 3 that the magnetic field in tending to straighten the pat-h of current flow will force laminated contact 32 and its auxiliary contact 46 toward and'into firm electrical engagementwith contacts 29 and V45. The yieldable nature of the contact end of contact 32 provides uniform engagement with contact 29 over the entire contacting surface. The magnetic stresses hold the laminated contact closed and a downward stress is set up in link 66. At the same time, however, these magnetic stresses tend to move arm 25toward itsdotted line position. This downward tendency of arm- 25 under the action of the magnetic stresses sets up a downward stress in link 65 which bal-` ances the downward stress in link 66 on the opposite side of shaft 60. The result is that the magnetic stresses hold the laminated contact closed with no stress on the detent or other means holding the switch closed because of the balancing action set up in links 65 and 66.

The holding action of the magnetic flux upon the contacts will better be understood when `it is appreciated that the effective len th of arm 26 and its connected contact is s ightly greater than the effective length of arm 25 so long as the switch is closed. When the switch `starts to open and the arc is drawn, then the effective' length of the .arms are substantially equal. The arms 65 and'66 are connected at substantially adequate distance from the respective pivots 27 and 28 respectively. I wish tocall attention however to the fact that even if the lever arms of the two main contacts were equal the yielding character of the laminated contact 32 would permit it to be forced down more firmly into engagement with the solid contact 29. Large and heavy holding mechanism and correspondingly large and heavy mechanisms for releasing and operating the switch with, their increased-cost and great inertia are hereby avoided. The force re- 4 quired for holding the switch closed is substantially independent of the current flowing and thepositive break is simp1ified. The force required to open the switch with respect to the additional holding force and additional holdin and operating mechanismA which would gbe necessary if it were not for the balanced arrany ementdescribed, is substantially indepen ent of the current flowing. 'If it were not for this balanced arrangement the opening force would have to be greatly increased-.to overcomelthe holding force and that would ofcourse make it depr'oblem of securing a. quick,

`\pendent on the current flowing as themagnetic field increases rapidly -as the current flow becomes heavier. However in the present device the increased stress set up in link 66 is substantially balanced under all conditions by the correspondingly increased stress in link 65.

' To open the switch holding detent 80 for shaft 60 is released whereupon arms 63-64 are rotated counter-clockwise by spring 75. This rotation of arms 63-64 forces contact arm 25 downwardl about its pivot-27 and arm 26 upwardly a out its pivot 28. Initial opening movement'of arms 25 and 26 separates contacts 29 andv 32, auxiliary contacts 4:5 and 46 remaining in contact for an interval thereafter under the action of spring 43 to take and draw the arc and thereby protect the main contacts and preserve their normal current carrying capacity. The main and auxillary contacts first have a pure vertical movement in opposite directions in opening vfollowed by lateral movement which takes them out of the way and permits rapid discharge 'of the gases and dissipation of liberal energy and also draws the opposite ends of the vertical arc over laterally into 11n-agitated oil for effectively cooling and extinguishing the arc.

The curved portion 95 of arm 26 and the arrangement and positioning of the main and auxiliary contacts permits butt engagement between each pair of contacts. lThe movement of the contacts in opposite direc= tions in opening separates them and interrupts or breaks the circuit at a speed equal to the'sum of Vthe speeds'of the two instead of at a speed equal to the speed of movement of one contact, as heretofore. There is no appreciable frictional resistance to be overcome in opening. A stop 96 may limit the opening movement of arm 25 and a stop 97 the closing movement of arm 26.

In Figures 9,-10 and 11 I have illustrated a modified form of arm and contact mechanism.

The posts 90 and 91 extending down below the bushings 92 and 93 correspond in all respects to the correspondingY posts and bushings shown in Fig. 1.

-To the lower ends of these posts are pivoted on pivots 94 and 95 the swinging arms and 97 is vslotte lrods 98 and 99 which rods are made of a 96 and 97.` It will be noted from Figure 10 that the posts 90 and 91 lie between ugs which receive the hinge pins 94 and 95. this way the mounting of the arm is nicely balanced with a resulting) easier operation of the arms in swingi a out their pivots.

The main` bod E? each of the arms 96 to 4receive the operating suitable insulating material. These operating rods or links are hinged onpins 100 and 101 which thus 'lpivotally connect the links and the arms. e two side portions of the arm 96 are joined by a relatively small integral connecting portion 102 and in a similar manner the two sides of the arm 97 are connected by a solid portion 103 whichis relatively small in cross section. Otherwise each arm is really composed of two parallel parts so that current tends to iiow normally substantiall equally in the two parts of each arm. he lower arm 96 has a pair of laminated copper straps 104 for bridgin the pivotal joint between the post 90 an said arm 96. These straps 104 are held upon the post 90 by bolts 105 and are fastened at their 106. Thus each side of the arm 96 has its connecting ribbon or strap bridging the pivot joint. In a similar manner the arm 97 has a pair of straps 107 fastened to the post 91 by means of the bolts 108 and fastened to the arm,97 by the bolts 109.

The arms 96 and 97 have in duplicate main and arcing contacts as explained in connection with the embodiment of Figures 1 to `8 inclusive. That is to say each side portion of the arm 96 has a solid contact' ortion 110 which is adapted to be engaged by a laminated yieldi contact 111 mounted upon the adjacent si e of the contact arm 97. Also each side of the arm 96 has a lower extending bracket 112 in which is mounted the auxiliary vcontact. plunger 113 having for engaging a flat solid contact 115 on the bottom side of the arm 97. Each contact plunger 113 is held upward by a suitable spring 116 to maintain contact with the corresponding arcing contact 115 after the main contacts 110 and 111 have separated. This plunger 113 is guided in the bracket 112 in each case and extends Ybelow the bracket and is threaded to receive the clamping nuts 117 which clamp between them t e end of a liexible ribbon or pigtail 118. These flexible ribbons 118 are secured at their other ends under the clamping screws 106.

The plungers 113have axial assageways 119 therethrough as indicate lin dotted ways permit iary contact into is formed, so as other ends to the arm 96 by-bolts' an enlarged head in each case 114 lines in Figures 9 and 11. These passage The auxiliary contact 115 which is f ormed integral with the arm 97 has' a similar passageway indicatedat 120 (see in particular Fig. 10) for the same lpurpose; namely to permit the passage of o' normally be occupied by the arc when the switch contacts are o ned. ThusA not only 1s there a body of oil tween the two sets of contacts but also oil is permitted to enter the s ace which would normally be occupied by t e arc.

There is furthermore a mutual'attraction between the two arcs which are drawn byY the two sides of the arms 96 and 97.

In Figure 12 I have shown diagrammatically by a side view, the manner in which the arms 96 and 97 tend to draw arc. It will be seen that the first motion of the arms 96 and 97 is substantially vertical and that `by the throwing action of these arms, the arc which is shown in dotted lines will be drawn into an S-shaped figure, the ower part o which will be forced out to a greater extent than the upper part is forced in because of the magnetic stresses. Thus a relatively long path will `be provided, which path would have to be traversed if the arc were to be maintained. It will be understood that the arc breaks before the arms 96 and 97 reach their iinal outer osition, but the dotted line of Figure 12 indicates the line which the arc would have to maintain if it persisted. At the same time that the arc isv drawn into an S-shaped ligure las in a vertical plane the mutual interaction between the two arcs which are drawn at the two contacts on the arms .96 and,97 tend to draw each other inwardly as indicated in the dotted lines in Fig. 13.

This constitutes a new mode of interrupting an electric arc by dividing the flow of current into parallel streams and then drawing arcs which mutually interact mag netically to force each other out into the oil or other medium for extinguishing the arc.

This constitutes a new mode of interrupting current iiow further in that it is easier to extinguish two arcs of an aggregate current carrying capacity of .a certain value, than it is to extinguish a single arc of the same current carrying capacity.

While I have described the invention in connection with the details of a particular embodiment the invention is not to be limited to such details as otherembodiments of the invention and modifications and changes are contemplated within the scope of the appended claims.

I claim: Y

1. In combination, a casngcontaininga iiuidl bath, a cover for said casing, insulators mounted in said cover, conductors led into the space which would onl each side as minals, and meansfor separating said contact members vertically'and then moving same laterally through said bath, said means including means balancing the magnetic' stresses 1n the switch. v

2. In combination, a air of switch'members projecting towar each other, said switch members having cooperable contact portions at their ad'acent ends and pivoted at their opposite en s and-a rotatable operating arm plvoted centrally and connected at opposite sides of its pivotal mounting with said switch members. j

3. In combination, a pair of switch mem-` bers projecting toward each other, said switch members having cooperable contact portions at adjacent ends andv pivoted at opposite'ends, an operating shaft, arms projecting from opposite sides of said shaft, and links connecting said arms and the switch members to swing said members apart in ofpposite directions upon rotation of said sha 4. In combination, a air of switch members projecting towar each other, said switch members having overlapping adjacent ends and pivoted at their opposite ends, and a laminated contact between said overlapping ends held closed by the magnetic stresses.

5. In combination, a air of switch members projecting towar each other, said switch members having overlapping adjacent ends and pivoted at their opposite ends, a laminated mam contact between said overlapping ends held closed by the magnetic stresses and a pair of auxiliary contacts between said switch members; j

6. In combination, av casing, a cover for said casing, insulators mounting in said cover, conductors led into the casing through said insulators and terminating within the casing in switch terminals, contact members pivoted on said terminals and having cooperable contact portions at their adjacent ends, a rotatable o erating shaft, arms projecting from said s aft and links connectling said arms with said contact members.

7. In` combination, a; casing, a cover for said casing, insulators mounted in said cover, conductors led into the casing through said lnsulators and terminating within the casing in switch terminals, contact members pivoted on said switch terminals and. having cooperable contactportionsat their adjacent'ends, an operating' shaft, arms projecting in opposite directions from said shaft, a main contact between` said switch members, said main contact being held closed b the magnetic stresses and a pair of auxi 'ary contacts between said switch members.

8. In a switch, a pair of pivotally mounted,

switch arms, a balanced gear connecting said armsand balanci the. magneticstresses in the switch, and arcmg contacts on said arms disposed at substantially equal distances from their respective mountings, the move ment of said arcingcontacts about said pivdifferent d1stances from the pivotal mounts,`` ings of their respective arms, the movement of said main contacts about said pivotal mountings causing a generally S-shaped arc to be struck between them.

. 10. In al switch, a pair of depending 7conducting posts, a pair of swinging 'arms having contacts adapted-to engage each other, said arms being pivoted to said posts, operating gear-connected to said arms for 0perating the arms simultaneously, a laminated contact on one arm engaging a cooperatingcontact on the other arm, said contacts being forced into engagement with each other by the magnetic stresses of current flow.

11. In a switch employing relatively mOv` able contacts, flow of current which comprises dividing the current flow in toparallel paths, each path `including a pair of contacts, then moving said pairs of contacts apart vertically and thereafter laterally to draw two. parallel S-shaped arcs which are forced out laterally and stretched longitudinali 12. In combination, two conductors disposed in substantial parallelism, upper and lower movable contact members between the conductors, said contact members being piv4 oted to said conductorrespectively, a rockably mounted operating shaft, oppositely directed arms secured on the shaft,.and links connecting the respective contact members to the arms.

13. In combination, two conductors disposed in substantialparallelism, upper and lower movable contact 'members between the conductors and pivoted at their outer ends, an operating shaft rockably mounted' between the conductors'and'above the contact members, oppositely directed arms secured on the shaft and links connecting the arms to the respective contact members inside of the pivots thereof.

14. In combination, co-operating movable contacts adapted to open and close an electric circuit, a rockably mounted operatingA shaft, operating connections between said shaft and contacts, said contacts bein so positioned as to cause the current llow t rough them to -set up ma etic stresses tendin t0 maintain said sha in a definite position.

pair of pivotally mount-` the method of interrupting a mms 15. In combination, co-operating movable contacts adapted to o en and close an electric circuit, a rockab y rmountedfoperatng shaft, operating 'connections between said 5 shaft and said contacts for opening said contacts when the shaft is rocked in one directionand for closing said contacts when the shaft is rocked in the other direction, said contacts being so positioned with respect to one another as to cause the current flow 10 through them to set up magnetic stresses which tend to oppose the force exerted by said shaft.

In witness whereof, I hereunto subscribe my name this 31 da of December, 1923.

AFRED F. C.

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