US2880291A - Protectors for electric circuits - Google Patents

Description

' Marci: 31, 1959 F. BUSSMANN PROTECTORS FOR ELECTRIC CIRCUITS Filed Jan. 14, 1955 O 2 6 32 8 4 9 2 4 5 3 2 3 6 E O m 0 O m 8 6 5 7/ 8 6 L: O4 6 4 5 5 m M 4 m 0 8 5 7 4 6 y 6 II 0 6 7 2 3 2 9% a 3 M 2 l flflw |NV ENTOR.

H Bussnnmv ATTORNEY FRANK eshares. P n

PROTECTORS FOR ELEoTRro GIRGUITS Frank H. Bussmann, .Qlayton, Mo-,..:a ssignor to McGraw- Edison Company, a. col mation ofv Delaware Application January 14, 1955 Serial No. 481,776 7 Cl ms ((1 acumen action" in opening the circnit, That snapeaction istend t s p rat the ,s'wil Q l Qn actfiifiO rapidly'that rc n o fo m; or if! arcs ShQUidifQl'IIl, to lengthen:

those arcs so rapidly: that they, cannot. bev maintained ut m st xt ngu sh hems lves.

While a snap-action? of the. switch contacts is de.-

sirable in circuit-opening operations on direct current.

installations, a less-rapid action oh the. switch; contacts;

is desirable in circuit-opening operations on alternating current installations, A very 'gapid, opening of the. switch n c su h a s experienced. in. a snap-action?" Cir: p n n op ation. could. be. started and mp during either of the hi hivoltage: portions of a. currentv cycle, and there would, thenea. strong, tendency toward.

arcing However, a. less-rapid openingQitheswitch con.-

tacts would consume an an onnt of, tirne -that. would 611% able the voltage to; drop toward; t ezeIo-value; beforev the circuit-opening operation wasg completed; :anththere would en b a g yessened tendency tewardarcin The.

present invention. utilizes; his mPQttant: principles to provide aself-contained n anuallyeopcrtble.electric switch.

F I e ab y. and: les @0 1: than has; heretofore been p s le. It s h refore an: obj ct of the; res nt invention to provide. a selt-contained, mannallyeoperablcz le tric switchthat hasarelatively sl wireuit-break ng:

action.

The presentinventionhas a movable Contact and a fix d n and h s ahandlethat,is.mQY b e..to.-e us movement of the movable contact Thathanclle, 1S,II1OY:--

able to an on position and to an ofi position; and it has a high point that moves througha dead center posi tion as the handle moves from the on position to the off position. Thathighpointmoves the movable contactaway from the'fixed contact to open the circuityand when thathigh point is in thedead center position'it" will hold the movable contact-a considerable distance away from the fixed. contact;

close-together, when the handles were. be dead; cen, ter. position, arcing could occur, However; byhaving the high Point. of h h ndl h d:.t .:mo able:contact; at

consid ra stanc away f onr hefixed cntactgwhen-a e e h h po nt isuin the ead e nteruce tionathe cause fires.v To pres This is very desirable since the handles of: switches can sometimes, through in-.-- ti n or na v rt nee. H,.thiP3fiTQfi-I the; operator, be. s n. th de c nte Po ti n; a d.itrtheccnta tsrwere-.

present invention avoids any such arcing. It is therefore an object of the present invention to provide a switch with a movable contact and a fixed contact and with a handle that has a high point to hold the contacts apart a considerable .distance whenever said handle is in the dead center position.

The movable contact of the. switch provided by the present invention is acantilever plate. That movable contact is biased toward a fixed contact by a helical compression spring. That spring is strong, :and it urges the movable contact into engagement with the fixed contact at all times; and it will assure a low resistance engagement between the movable and fixed contacts whenever the handle is in the on position. However, the high point on the handle of the switch can overcome the force exerted by the spring. Hence, the switch that is provided by the present invention has a spring which directly biases the movable contact to circuit'closing' position, and has a handle that provides direct and posi tive circuit-opening movement of the movable contact. Itis therefore. an object of. the present invention to provide a self-containedelectrical switch which has a movable contact in the form of a cantilever plate that is biased toward a fixed contactor by a helical compression spring, and that can be moved to circuit opening' position by ahandle.

Where electrical switches are small, they can some-- times be subjected to sufiicient abuse to cause their parts to become separated. from the housing. If those parts are electrically alive, considerable danger can result, since the parts may. cause arcing and sparking. The present. invention oviates any such danger-by providing a method of mounting the parts of the switch Which-'- positively prevents accidental separation of those parts from. the housing. Specifically, the housing of the switch provided by the present invention, hasformed guides into which the electrically alive parts extend; and it has openingsthrough which the binding screws extend. Those openings are adjacent the closed end of the housing, andthey will coactwith that closed end andwitlr theformed" guides of the housing to prevent accidental separation of the electrically alive parts of the switch after those screws have seated in. those parts. In this way, the switch can be assembled at the factory; and" it will be resistant: to the. loss or. separation of any of its parts. Only. by removing. the binding screws can electrically alive. parts he removed; and those partswill not be" alive? when the binding screws are removed; Inthis way, the present invention positively prevents thefree ing of. electrically alive parts ofthe switch.

Otherand further objectsand advantages of theiprese'nt invention shouldbecome: apparent from an-examination of. the drawing and' accompanying description.

In the; drawing andv accompanying description a pre--- ferred embodiment of the present invention has been shQWQanddescribed-but it is to be understood that thedrawing and accompanying description are. for the pur POse of illustrationonly and do not limitthe invention nd hat. the. invention will be: defined by the appended claims.

. In the drawing;

Big. 1- is; a. perspective. view of an electrical switch hat is made in. accordance with the principles and teach ings: of; the. present:v invention,

Fig. Zis. a. longitudinal section of the switch shown in Fig, 15,, and it, is. taken along thenplane defined bythe Fig.- 3. is; another longitudinal section of the switclrof Fig.1 and itis taken along,the plane defined by theline 2.-2;in Fig. 1', and-itshows theswitch-in open-position;

Big, 4; is another longitudinal section of" the switclr ofiliig. 1Lauditistakenalong the plane -defined'by-the I r .3 line 22 inFi'g.- I, and it shows the component parts of the switch in dead center position,

Fig. 5 is a sectional plan-view of the switch of Figs. l 4, and it is taken along the plane defined by the line 55 in Fig. 2, Fig. 6 is an end view of the handle of the switchof Figs. 1-5,

n Fig. 7 is a perspective view of one of the terminals of the switch of Figs. 1-5,

. Fig. 8 is a perspective view of a J-shaped element used in the switch of Figs. 15, and.

,Fig. 9 is aperspective view of another terminal for the switchof Figs. 1-5.

} Referring to the drawing in detail, the numeral 10 generally denotes a housing of insulating material. This housing will preferably bemolded in one piece, but it can be fabricated if desired. The housing 10 has two vertically directed guiding projections 12 that are-spaced from the right handend wall of the housing 10 to define vertically directed recesses 14. Two vertically directed guiding projections 16 are spaced from the left hand end wall of the housing 10 to define two vertically directed recesses 18. The vertically directed guiding projections 12 and 16 extend all the way from the bottom of the housing 10 to the top of the housing, and thus the verticallydirected recesses 14 and 18 also extend from the bottom of the housing 10 to the top of that housing. As a result, the housing 10 coacts with the vertically directed guiding projections 12 and 16 to define a large central recess and four smaller recesses at the corners of the housing 10.

. A generally U-shaped shallow recess 20 is formed in the left hand end of the housing 10, and it is formed in the exterior face of that housing. An opening 22 extends through the left hand end wall of the housing 10 adjacent the upper end of the recess 20; and that opening communicates with the large central recess defined by the housing 10. A generally U-shaped recess 24 is formed in the right hand end wall of the housing 10 and it is formed at the outer face of that end wall. The recess 24 is closely comparable to the recess 20. An opening 26, which is closely comparable to the opening 22, extends through the right hand end wall of the housing 10 and communicates with the large recess at the interior of the housing 10. The openings 22 and 26 are in register with, and in alignment with, each other.

A frusto-conical projection or stud 28 is formed on the bottom of the housing 10 and it projects vertically upwardly into the central recess defined by that housing. This projectionor stud is in register with the openings 22 and 26 in theleft hand and right hand walls of the housing 10. a

'A pair of notches 30 are provided in the longitudinally extending side walls of the housing 10. These notches are in register with each other and are located approximately midway of the length of the housing 10. These notches are preferably U-shaped in configuration.

Ihe numeral 32 denotes a plate of metal with a tab on the upper end thereof. The plate 32 is dimensioned so .it fits snugly within the vertically-directed recesses 14 in the housing 10. The tab on the upper end of the plate 32 extends horizontally inwardly from the right hand end wall of the housing 10. An opening 34 is punched in the plate 32 and that opening is threaded to receive a binding screw 38. The plate 32 carries a contactor 36 on the tab thereof. This contactor coacts with the plate 32 to define a stationary contact and a stationary terminal for the switch of the present invention. The contactor 36 will preferably be made of a material which is resistant to arcing, and it will be made in the form of a disc with a central projection. The central projection will be extended upwardly through an opening in the tab on the plate 32 and will then be riveted over to hold it fixedly in assembled relation with the plate 32. -The shank of the binding screw 38 is threaded and will extend-into and be held by the threaded opening 34.

The head of the binding screw 38 is smaller than the recess 24 in the right hand end of the housing 10.

A short plate 39 of insulation is telescoped between the right hand end wall of the housing 10 and the vertically directed guiding projections 12. Thus, that plate will be held in the recesses 14 and will extend from the upper end of the plate 32 to the upper end of the housing 10.

The numeral 40 denotes a plate of metal which has a generally rectangular opening 42 through it. That plate also has an opening 44 punched through it and the opening 44 is threaded. A notch 46 is provided in the hottom of the plate'40 and that notch is spaced inwardly a short distance from each side of that plate. The plate 40 is dimensioned to fit into the recesses 18 defined by the left hand end wall of the housing 10 and the vertically directed projections 16. There is some looseness and play between the walls of the recesses 18 and the plate 40.

The numeral 48 denotes a J-shaped strip of flexible metal. That strip of metal has an opening 50 punched through it in the closed end of the J; and that opening will be slightly larger in diameter thanis the opening 44 of the plate 40. A contactor 52 is fixedly secured to the long arm of the J-shaped strip 48 and that contactor will be made of an arc-resistant metal and will be suitably riveted to that long arm of the J-shaped strip 48. The numeral 54 denotes a binding screw and the shank of the screw can extend freely through the opening 50 of J-shaped strip 48 and seat in the threaded opening 44 of the plate 40. The head of the binding screw 54 is smaller than the recess 20 in the left hand end of the housing 10.

As pointed out particularly in Figs. 25, the J-shaped strip 48 is set against the left hand face of the plate 40 and the long arm of the J-shaped strip 48 extends through the opening 42 in the plate 40. Simultaneously, the short arm of the J-shaped strip 48 extends into and is confined by the notch 46 at the bottom of the plate 40. At such time, the. opening 50 in the J-shaped strip 48 is in register with the threaded opening 44 on the plate 40. Consequently, the shank of the binding screw 54 can pass freely through the opening 50 and seat in the threaded opening 44 and thus secure the J-shaped strip 48 to the plate 40. At such time the long arm of the J-shaped strip 48 will extend toward the right hand end of the central recess defined by the housing 10. That long arm of the J-shaped strip 48 will be above and out of engagement with the top of the stud or projection 28. Also, the contactor 52 on the long arm of the J-shaped strip 48 will be below and directly in register with the contactor 36 on the tab ofthe plate 32. The long arm of the J-shaped strip 48 will normally hold the contactor 52 in engagement with the contactor 36, but that arm can bend downwardly to permit the contactors 52 and 36 to separate.

A strip of insulating material 55 in the form of a plate is disposed within the upper reaches of the recesses 18. That plate of insulation will extend from the upper end of the plate 40 to the upper end of the housing 10.

A helical spring 56 is mounted concentrically with the stud or projection 28, and that stud or projection will confine the spring 56 to the approximate center of the recess defined by the housing 10. The spring 56 will bear against the under side of the long arm of the J- shaped strip 48, and will urge that arm upwardly. Such upward movement of the long arm of the J-shaped strip 48 will normally hold the contactor 52 in engagehelical spring 56 has an axis which extends upwardly in a direction parallel to the axis of the stud or projection 28. The axis or the stud extends thropgh a line defi ned by the notches in the housinglql A handle 58 is: provided for the switch of the present invention, and that handle has a high "point 59thereon; When the handle '58 is in the fonfi position shown in Fig. 2, the high point 5-9 is. either out of engagement with the long arm .of the J-shaped strip 48 or is loosely resting against that long arm. However, rotationof the handle 58 in a clockwise direction will-bring the high point59. almost immediately into engagement with the long arm of the J-shaped strip 48. That high point will then be moved to the dead center position shown in Fig. 4 and at that time the long arm of the J-shaped strip 48 will have been bent downwardly to move the contactors 52 and 36 apart. Continued rotation .ofthe handle 58 in a clockwise direction will move the high point 59 to its final off position as. shown in Fig. 3;; and at such time the contactors .52 and 36 will be held apart.

The high point 59 is formed by -two intersecting plane surfaces on the handle 58. "Those plane snrfaces'are set so. one of them is closely-parallel to the long arm of the J-shaped strip 48 when'the switch is in the on position, as shown in Big, 2, and so' theother plane surface is closely parallel to the. long arm of the- J-shaped strip 48 when the. switch is in the oil position, as shown in Fig. 3. This angular relationshipbetween the plane surfaces that define. the high point 59 is verydesirable because it enables the spring-applied iorces on the long arm of the Jeshaped strip, 48. to tend to hold the. handle 58 in the off position as well as the on position. As-a result, accidental movement. ofthe handle 58 to either of its two positions is resisted. l

The handle. 58 is. provided withv oppositely disposed; trnnnionsdfl. Thosetrunnions are generallycyliridrical in configuration but. they have. a conical. or filleted section which merges smoothly withthe bodyof the handle 58. The cylindrical portions of the trunnions 60extend into and: are confined and supported by the notches 30 inthe longitudinally..extendingside walls of the housing 1 The runnions 6,0 interact. with the notches 30 to permit guided and: regulated rotation of the handle 58 relative to the housing 10.

A sheet 6 2 of fish paper is provided that overlies the upper. end of the housing 10. This fish. paper has an p i g fiil pll h t receive the. handle.58. Thisfish paper will also overlie the upper end of the insulating Maori? and .5.. i

A cover plate 64, preferably of metal, is provided for the housing 10. That cover Plate. has an opening 66xto receive the handle 58. The opening 66 is in register with the opening 63 in the sheet62 of fish paper. The cover plate .4 has cars 68. that can be bent downwardlyover p ie ti n t he o pos te e ds of' he housing The bending: of the ears 68, over, those projections will fixedly.- secnre the coverplate 64 to he hOLl ing 10. During the assembling of the coverplate 6 4 with the housing 10, the cover plate will press; the fish. paperand the insulating plates and 5 5 downwardly to confine and hold the plates 3; and 4t} .inregister with the. Openings, 22 and 26 in the opposite ends o f th e housing ll). Thecoverplate 6 4 also hasthreaded openings 70 which canreceive h to a suitable mounting screws that will ho ld-g the ed-set. n1.,.p o the 1 2s Once the cover plate 64ha s-been secured to the housing 10, the binding screws 3 8and54 can be telescoped'into the threaded openi s .34 and 44; respectively. During the assembly of plates 3; and,4! );-witl1 thehousing 1Q,

those binding screwshad to-beremoved. Once they have been telescoped into the threaded openings 34 and 44 of the plates and 4t), those binding. screws will positively prevent accidental separation oi the plates 3 2 and 40 from the housing-@104 The bindi n-gscrew-'54 will-also prevent separation of the d shaped lever 4 firomthe housing It) aslong as its shank is seated in the ,ihreaded opening 44 of the plate 40.

T in e a ti n be ween. .11 2 limit 8. 2 .4511

and the 'plate s 32 and 40 is'very important preveptipg the separation of live parts of the switchfrq p. th h us n .19.- throu rpm; unexpected. a ar-len t qre 'nl t 64 ve so .l.@ b ok n. and. w r to b e se a ate the h using. 1 o e of h ri ajlly ve Pa rs. Qu1d. i t ha s t h housing. Th s is of great'importance since it minimizes the risk of electrical shock and of electrical fires. Specifically, if the cover plate 64 were to become separated r m t h si g '10, he h ndl 8- 901 14 a l' y t a n the housing 10, "the sheet 6 2 offish paper could fall away from the housing and the plates39 'an d 55 of insulation might fall away frorn thathonsing. However, the metal plates 52- and 40 and the 'd-shaped strip 48 could not fallaway from the housing .9 the binding screws 38 and 54 positively preventing any such action.

In; the. 9n pos i tion"shown ii Fig. 2 the spring 56 is holding the movable contact in engagement with thefixed contact and the high point 59 is at the right hand Side of the'dea dp ce tefpdsit-ion shown in Fig 4. I11 the oll position sho'wniin Fig. 3, the movable contact is spaced a predetermined distaneefrom the fixed contact; and the high point 59 of the handle 58 is at the lefthand side of the-'dead center position shown'by Fig, 4. In the dead center position shown in Fig. 4, the movable contact is spaced from-the fined contacta; distance closely similar to the distance those contacts are spaced apart in the o position shownin- Fig. 3-, andthe high point 59 is-in the dead-centerposition-. Thef actthat-the spacingbetween the movable and fixed' contactsin dead "center position is closely similar to the spacingbetween those contacts in- 0 position isimportant since its-prevents prolonged-arcing due to the movementof the handle into adeadcenter position where the fixed and'movable con tacts were closely. adjacent each other.'

It will be noted that the handle 58 drives the movable andfixed :contacts. aparti as it. rotatesfrom on position to off positionand that the spring: 56 drives the fixed and moyablecontacts into engagement with each other as .thehandlemoves; in the opposite direction. Hence, thetpresent. switch gives a positive opening action and a spring-biased closing action. The result is that the switch provides a relatively slowcircuit-breakingoperation because. the handle is-havin-gto oppose the strong helical spring'56 whileit will provide a quick circuit making operation because that spring. is then assisting the operator inirotating' the handle t'o. on po sition The relatively slowv circuit breaking operation 'isdesirable because it allowsthe. voltageofz'the alternating electrical current to fallatoward the zerovalue and thus minimize arcing.

Itwill be notedthattl e high point 59 on the handle 58 isalways relatively close tothe. dead center-positionshown in Fig. 4. This is desirable because it reduces the bending IQ QGQES that would .OELCU! if the high point 59 were spaced av considerable distance. from that dead center position.

Thosebending. moments..-w.ould .not-onlybe in the handle Sig-but would also be in the..longarm ofthe J -shaped' it occupiesan otherwise empty portion of the recess within the housing-10. This is desirable since it makes -unnecessary the provision ofa springy metal in the J- shaped-strip 48. -That .l-shaped strip will have some natural resilience nd svshresili nce i he pb s the contacts toward each other but the principal circuit making ciae l e. in, l1sfsmin i 1 di us e.

shap edlfstrip 48 car1 b6 3 deoi a large. numberof metals the h n. us fsp n yme ls.

Wh r a a erred mbodiment h P e en nbee-wh m. d dessribedi dbe und r t W l ing. k lled. in, the-art l ???.Yfipllitha l gssmay: be

7 made in the form of the invention, without affecting the scope thereof,

What I claim is:

1. A manually operable electric switch that comprises a fixed contactor, a movable contactor that is movable relative to said fixed contactor, a helical compression spring, a handle that is selectively movable to on position and off position, a terminal that is secured to the said fixed contactor and is connectible to an electric circuit, a second terminal that is connected to said movable contactor and that is connectible to said electric circuit, said spring being intermediate and closely adjacent said terminals, said spring biasing said movable contactor toward said fixed contactor but being yieldable to permit said movable contactor to move away from said fixed contactor, said handle being movable to said off position to move said movable contactor away from saidpfixed contactor, a pivot for said handle, and a stud that is intermediate said terminals and that extends into and confines. said spring and holds said spring out of shorting engagement with said terminals, said stud holding saidspring so the axis of said spring extends toward said handle.

2. An electric switch that comprises a housing of insulating material, said housing having a closed side and an oppositely disposed open side, a plurality of contacts, grooves in said housing that extend from said open side to said closed side and that guide said contacts, said grooves permitting ready endwise movement of said contacts but preventing sideways or rotative movement of said contacts, and openings in said housing and in said contacts to receive binding screws, said openings in said housing being adjacent and contiguous withsaid closed side, said bindingscrews extending through said openings in said housing to seat in said openings in said contacts, said binding screws substantially preventing said endwise movement of said contacts and thereby coacting with said grooves and with said openings in said housing to prevent accidental sepa ration of said contacts from said housing.

3. An electric switch that comprises a housing of insulating material having a closed side and an oppositely disposed open side, a plurality of contacts, grooves in said housing that extend from said open side to said closed side and that guide said contacts, said grooves permitting ready endwise movement of said contacts but preventing sideways or rotative movement of said contacts, and openings in said housing and in said contacts to receive binding screws, said binding screws extending through said openings in said housing to seat in said openings in said contacts, said binding screws substantially preventing said endwise movement of said contacts and thereby coacting with said grooves and with said openings in said housing to prevent accidental separation of said contacts from said housing.

4. A manually operable electric switch that comprises a fixed contactor, a movable contactor that is movable relative to said fixed contactor, a helical compression spring, a handle that is selectively movable to on position and off position, a terminal that is secured to the said fixed contactor and is connectible to an electric circuit, a second terminal that is connected to said movable contactor by an elongated strip of flexible metal, said second contactor being connectible to said electric circuit, said spring being intermediate and closely adjacent said terminals, said spring acting upon a portion of said elongated strip to bias said movable contactor toward said fixed contactor but being yieldable to permit said movable contactor to move away from said fixed contactor, said portion of said elongated strip being substantially straight, said handle being movable to said oflf position to move said movable contactor away from said fixed contactor, a pivot for said handle, and a stud that is intermediate said terminals and that extends into and confines said spring and holds said spring out of shorting engagements with said terminals, saidstud holding said spring so the axis of said spring extends toward said handle, said substantially straight portion of said elongated strip enabling said spring to be substantially free of forces tending to produce sideways deformation of said spring as said handle is moved.

5. A housing having integral sides, bottom and ends, a flexible conductor that is substantially J-shaped in side elevation, the short leg and the closed end of said J-shaped conductor abutting, respectively, one end of said bottom and one of the ends of said housing, the long leg of said J-shaped conductor extending in a generally horizontal direction from said one end of said housing toward said opposite end of said housing, an L-shaped conductor in side elevation, said L-shaped conductor having the long leg thereof abutting said opposite end of said housing and extending upwardly from said bottom and having the short leg thereof extending from said opposite end of said housing toward said one end of said housing in a generally horizontal direction, said short leg of said L-shaped conductor overlying the free end of said long leg of said J-shaped conductor, a cover, and a handle that has a finger-receiving portion projecting outwardly from said cover and has a conductor-engaging portion underlying said cover and engageable with said long leg of said J-shaped conductor.

6. A housing having integral sides, bottom and ends, a flexible conductor that is substantially J -shaped in side elevation, the short leg and the closed end of said J-shaped conductor abutting, respectively, one end of said bottom and one of the ends of said housing, the long leg of said J-shaped conductor extending in a generally horizontal direction from said one end of said housing toward said opposite end of said housing, an L-shaped conductor in side elevation, said L-shaped conductor having the long leg thereof abutting said opposite end of said housing and extending upwardly from said bottom and having the short leg thereof extending from said opposite end of said housing toward said one end of said housing in a generally horizontal direction, said short leg of said L-shaped conductor overlying the free end of said long leg of said J- shaped conductor, a spring which biases said long leg of said J-shaped conductor toward said short leg of said L- shaped conductor, a cover, and a handle that has a fingerreceiving portion projecting outwardly from said cover and has a conductor-engaging portion underlying said cover and engageable with said long leg of said J-shaped conductor.

7. A housing having integral sides, bottom and ends, a flexible conductor that is substantially J-shaped in side elevation, the short leg and the closed end of said J-shaped .conductor abutting, respectively, one end of said bottom and one of the ends of said housing, the long leg of said J-shaped conductor extending in a generally horizontal direction from said one end of said housing toward said opposite end of said housing, an L-shaped conductor in side elevation, said L-shaped conductor having the long leg thereof abutting said opposite end of said housing and extending upwardly from said bottom and having the short leg thereof extending from said opposite end of said housing toward said one end of said housing in a generally horizontal direction, said short leg of said L-shaped conductor overlying the free end of said long leg of said J-shaped conductor, a spring which biases said long leg of said J- shaped conductor toward said short leg of said L-shaped conductor, a cover, and a handle that has a finger-receiving portion projecting outwardly from said cover and has a conductor-engaging portion underlying said cover and engageable with said long leg of said J-shaped conductor, said conductor-engaging portion of said handle overcoming the bias due to said spring when said finger-receiving portion of said handle is in a predetermined position.

References Cited in the file of this patent UNITED STATES PATENTS 1,470,776 Stevenson Oct. 16, 1923 (Other references on following page) 9 UNITED STATES PATENTS Graham et a1 May 28, 1935 Thirlwell Aug. 18, 1942 Hutt Nov. 9, 1943 Gaynor May 17, 1949 Chrastina Nov. 21, 1950 Minch'et a1 Jan. 16, 1951 Russell et a1 Oct. 9, 1951 Shewnon et a1 June 21, 1955 Great Britain Jan. 17, 1951

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