US2226385A - Switch - Google Patents

Description

A. RAMSEY Dec. 24, 1940.

SWITCH Filed De. 14. 193e 7 Sheets-Sheet l ow/V/Af/v/wn v A. RAMSEY Dec. 24, 1940.

swI'TcH Filed Dec. 14,l 1936 7 Sheets-Sheet 2 Il. I l I I I I I IIIIIII'IIIIIILIIIIIILI xl f Dec. 24, 1940. A. RAMSEY 2,226,385

SWITCH Filed Dec. 14, 1936 7 Sheets-Sheet 3 A. RAM SEY Dec. 24, 1940.

SWITCH Filed pee. 14, 193e 7 sheets-sheet 4 A. RAMSEY SWITCH Filed Dec. 14, 1936 '7 Sheets-Sheet 5 A. RAMSEY Dec. 24, 1940.

SWITCH Filed Dec. 14, 19:56

Y 7 Sheets-Sheet 6 Patented Dec. 24, 1940 PATENT lOFFICE SWITCH Allan Ramsey,

Evanston,

lll., assignor to Schweitzer & Conrad,lnc., Chicago, Ill., a corporation of Delaware Application December 14, 1936, serial No. 115,691

21 claims. (c1. 26o- 162) My invention relates, generally, yto electric switches and it has particular relation to the construction and mounting of disconnecting switches and the like. This invention constitutes an im- 5 provement upon the switch construction shown in my copending application, Serial No. 445,548, filed April 19, 1930, Patent No. 2,063,954, and assigned to the assignee of this applicationi In -my copending application, Patent No.

l 2,063,954, I have disclosed a switch having a switch 4blade that is movable into and out of contact engagement with a plurality of stationary contact fingers each of which has a small area high pressure contact portion and each of which l is individuallyresilient and prestressedl to provide a relativelyrhigh contact pressure inthe switch closed position without requiring highly accurate alignment of the contact fingers. The prestressing feature reduces the work required to 2o close the switch. If the prestrssing is not provided, a relatively long motion would be necessary after the .switch blade engages the contact clip, thereby requiring an excessive movementof the clip or of the blade. 25 is obtained by biasing one or more contact ele'- ments vor iingersinto the path of relative movement of the switch members and providing restraining means which limits the movement of the contact elements or lingers to positions which 30 are slightly within this path of movement.

Without this'restraining means the contact ngers would be moved underthe biasing influence more fully into the path of relative movement of the switch members arid, in closing the switch for 35 example, it would be necessary to exert sufficient effort to move them completely out of the path.

Whenthe prestressed contact fingers are limited in their movement to positions slightly ,within the path, it is only,necess'ary to move them -40 through this slight distance with the result that a correspondingly smallmeiiort is'required to operate the switch. At the same time the contact pressure which is exerted between the contact members will be thesame as if, on closing the' 45 switch, the contact iingers had been moved from an initial unstressed condition to the position corresponding to the switch closed position.

Movement of the 'contact fingers from their position when the switch blade is open to that 50 when the switch blade is closed is produced by sliding movement of the beveledl edge of the switch blade in engagement with and relative to the rounded head of the contact points on the contact fingers. 'I'he force that is required to be l55 applied to the switch blade in order to move the The prestressing effectA contact linger depends upon the angle of bevel on the edge of the switch blade. The flatter the angle the less will be the force that is required to move the switch blade to spread the contact iinger's.` Without a prestressed contact rigerf I and using the same compressive stress and the same angle of bevel, it would be necessary to cut so deeply into the blade as to mechanically weaken its edge at the point where it first engages. the contact points on the contact fingers.

In the conventional type of switch construction one or more iiat switch blades are provided for engaging switch clips formed by upstanding spaced apart contact iingers. Each switch blade engages a pair of fingers along the sides thereof '15 and it is intended that surface contact engagement shall take place( This switch'is generally called a knife blade switch. When a switch voi this type is originally installed, it is possible to approach the desired surface contact engagement, between the relatively movable switch members. However, after the switch has been in service for some time this condition no longer exists under ordinary circumstances because the Vcontact iin'gers may become bent or the switch blade may, 25

,be moved slightly out of alinement therewith.

Moreover, corrosion of the contact surfaces may take place. As a result of these various factors instead of having surface contact engagement only point contact engagement actually is pres-z ent. The .entire current flowing through each switch blade then must iiow through the point Acontact engagement'with the result that heating Iof the switch members takes -place if any appreciable amount of current ows.

It is recognized that in a given switch there is a denite relationship between the area of the contact surface and the contact pressure; Thus if the area of contact engagement is reduced, the

contact pressure should correspondingly be increased. It has been proposed to construct a switch in which the contact engagement between the relatively movable switch members takes place at substantially a single point or a pair of spaced apart points represented for example by a pair of oppositely extending projections on a switch blade. Very high pressures are required in this type of construction because of the limited area of contact engagement. It is then necessary to provide a relatively massive construction in the stationary switch member to resist the high contact pressure. In this construction yit is not practical to employ more than one point of con-l tact engagement for each contact surface because of the difliculty in obtaining the necessary alignment between two or more contact points. This will be obvious when it is considered that the contact surface is substantially in a fixed plane and the contact point is moved into engagement therewith. If more than a single contact point is employed, it would be necessary to keep them in exact alignment for the reason that a slight misalignment would result in only a single point of contact engagement.

In my copending application, Patent No. 2,063,954, I have provided for contact engagement between the relatively movable switch members at a plurality of points at each of which a relatively high pressure is applied. When the principle of prestressing is employed it is possible to provide a plurality of point contacts each being independent of the others and each engaging the cooperating contact surface with about the same contact pressure and at the same time a highly accurate alignment is not required.

It is well known in the art to provide contact engaging surfaces of silver for the contact members of relays and the like. Such a construction is ordinarily expensive in switches of large size because of the relatively large amount of silver` that would be required. However, when the small area high pressure contact construction of my copending application is employed, it becomes `practical to employlimited quantities of solid silver in the form of silver inserts in the relatively movable switch members of large current, capacity switches and consequently the advantage of silver contact engaging surfaces is obtained in a construction that is economical.

A n object of the present invention, generally stated, is to embody the principles of small area high pressure, contact construction set forth in my copending application in other types of switches.

An important object of my invention is to provide a relatively great short time current carrying capacity in a switch employing individually resilient and prestressed contact fingers having small area contact engaging portions.

Another object of my invention is to prestress certain of the contact members of a switch in addition to the resilient eiiect that may be inherent in the contact members themselves.

Still another object of any invention is to arrange compression springs and stops in one or more contact members of a switch in such manner as to prestress the springs 'before operation of the switchto the circuit closing position.

Another object of my invention is. to provide resilient means for prestressing the contact fingers in such location that current doesl not flow therethrough.

Another object of my invention is to reduce the contact resistance of a prestressed switch contact member to a minimum.

Still another object of my invention is to pro-l vide a low contact resistance and a high contact pressure between the relative movable contact members of a switch while still requiring a minimum of effort to operate the switch to and from the switch closing position.

Still another object of my invention is to provide a plurality of small area high pressure contact members that are individually resilient and self aligning.

A further object of my invention is to construct a switch having the foregoing desirable characteristics and adapted to use solid silver contact members Without excessive cost. This is permitted since the contact engagement takes place in limited areas in each of Which a small solid silver insert -may be positioned.

, An ancillary object of my invention is to provide for maintaining an electrical connection between a switch blade and one of two contact members bridged thereby until the switch blade is moved toa predetermined position.

Another ancillary object of my invention is to provide for clamping a conductor to a contact memberA of a disconnecting switch or the like in such manner that the surface of the conductor will not be pierced thereby rendering it liable to SeVeIlng.

A further ancillary object of my invention is to provide for frictionally holding the cover of a box housing a disconnecting switch or the like in the open or the closed position while readily permitting the movement of the cover to either position.

Other objects of my invention will, in part, be obvious and in part appear hereinafter.

My invention, accordingly, is disclosed in the embodiments hereof shown in the accompanying drawings and it comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the constructions hereinafter set forth and the scope of the application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of my invention, reference may be had to the following detailed description taken in connection with the accompanying drawings, in which:

Figure 1 is a perspective view illustratingthe arrangement and construction of one form of my novel switch mounted in a box and positioned on a cross-ann;

Figure 2 is a v iew, in end elevation at a reduced scale, of the switch 'box and mounting therefor illustrated in Figure 1;

' Figure 3 is a View in end elevation of an alternate form of clamp which may be employed for mounting the switch box on a cross-arm; l

Figure 4 is a view, in top plan, of the clamp shown in Figure 3;

Figure 5 is aview, in front elevation, of the switch box which contains one form of my novel switch;

Figure 6 is a View taken along the line 6-6 of 'Figure 5;

Figure 7 is a view in front elevation of the switch box and switch, the cover being shown in the open position to disclose the features of construction of the switch; v

Figure 8 is a detail. sectional view taken along the line 8 8 of Figure 7, showing the relation- .the 1ine.| I-II of Figure 7 and showing the construction of the friction rings with the switch blades;

Figure `12 is a view, in side elevation, of the switch shown in Figure 6, the box being omitted, and a quick break attachment being provided to prevent arcing between the switch blade and the main contact members;

Figure 13 is a view, in front elevation, of the taken along the front elevaun of the switch shown in Figure 15, the cover being broken away partly to more clearly illustrate the construction details of the switch;

Figure 17 `is a detail sectional View taken along the line |1 -|1 of'Figure 16 and showing the construction of another embodiment of the prestressed contact members;

Figure 18 is a View in front elevation of another embodiment of my novel switch construction a-rranged for mounting in a box, the cover being broken partly away;

Figure 19 is a sectional view taken along `the line |9|9 of Figure 18;

Figure 20 is a detail sectional view taken along the line 2li- 20 of Figure 18;

Figure 21 is a view, in end elevation, of a modlfled form of terminal connector which may be employed in conjunction with the contact members of my novel switch assembly;

Figure 22 is a sectional view taken along the line 22-22 of Figure 21; and

Figure 23 is a view of a modied form of the contact member shown in Figure 20.

Referring now yparticularly to Figure 1 of the drawings, it will be observed that the reference character 25 designates a switch box that opensI outwardly and which. is arranged to be mounted in a vertical position. The box 25 may be formed of any suitable insulating material, such as porcelain. An upper stationary contact member 26 and a lower stationary contact member 21 are secured to the rear wall of the box 25 by any suitable means such as by cement. A switch arm, shown generally at 28, and rotatably mounted in a fulcrum member 29 is provided for engaging the upper and lower stationary contact members to bridge them in the circuit closing position. Suitable apertures 30 and 3| are provided on opposite sides of the box 25 to permit the introduction therethrough of the circuit conductors. It will be observed that the apertures 30 and 3| are aligned with the upper and lower stationary contact members 26 and 21 respectively.

The front side of the box 25 is open to permit operation of the switch arm- 28'. It is desirable to close this opening in order to shield the various parts of the switch from the weather. For this purpose a cover 32 is provided and is hinged at its upper end adjacent the upper end of the box 25. As will be hereinafter set forth in detail, the cover 32 is so mounted that it is frictionally maintained in either the open or closed position, although movement between these two positions is also permitted.4

The box 25 may be mounted in any suitable po- Isition suchas on the cross-arm 33 which, in turn, may be mounted on a suitable pole or the like. A clamp, 'shown generally at 34 is provided for mounting the box 25 on the cross-arm 33. As

shown in Figure 2 of the drawingsvthe clamp 34 comprises angle brackets 35 and 36 that are arranged tobe positioned-on opposite sides of the cross-arm 33 and to be secured thereto by means of transversely extending bolts 31. In the embodiment of the clamp 34 shown in this figure, the angle bracket 36 is provided with an outwardly extending vertical flange 38 in which suitable apertures, such as illustrated at 39 and 40 in Figure 3 of the drawings, may be positioned. Bolts 4| extend through these apertures and through suitable apertures in a tongue 42 rearwardly extending from the box 25 to secure it in the desired position. It will be noted that the apertures 39 and are arranged to register with the apertures in the tongue 42. It will further be noted that the aperture 39 is slotted to a limited extent about the lower aperture 40 as a center. This construction permitsy the box 25 to rotate in a vertical plane about the aperture 40 as a center, thereby providing a limited range of adjustment therefor.

With a .view to providing for swiveling the box 25 in a horizontal plane, the construction shown in Figure 3 of the drawings may be employed. A strap 43 is provided having inturned end portions instead of the angle bracket 36, shown in Figure 2 of the drawings. An angle bracket 44 is provided having rearwardly extending arms 45 provided with suitable apertures for registering with corresponding apertures in the inturned ends of the strap 43. Bolts 46 are provided in these apertures for securing the angle bracket 44 and permitting swiveling thereof. The angle bracket 44v is provided ,with` a flange 41, corresponding to the flange 38 of the angle bracket 36, and the apertures 39 and 40 permit adjustment of the box 25 in a vertical plane as described hereinbefore. It will be understood that either form of mounting may be employed for supporting the box 25 on a cross-arm or the like.

The cover 32 is formed preferably of a suitable insulating material such as Bakelite The manner in which the cover 32 is mounted and the screws 54, only one of which is shownA in Figure 6. y

of the drawings. Suitably securedl to the ends of theU-shaped support member 53 are arms 55 formed preferably of insulating material. At the upper end of the cover 32 a pair of c-am members 56 is mounted by means of suitable threaded pins 51. The pins 51 are preferably made of a suitable insulating material such as Bakelite, and they are threaded for their full length. The cam members 56 and the cover 32 are clamped together and the holes for the pins 51 are drilled and tapped therein. Both the holes and the pins 51 are then coated with an adhesive and insulating cement and the pins are screwed into place. The cam members 56 are provided with notches 58 and 59 that interflt with fingers 69 carried by resilient brackets 6|, which may be mounted in position by means of the screws 54 which also hold the support member 53. The ngers 60 are formed preferably of insulating material such as Bakelite. A shaft 62 extends through suitable apertures in the arms and in the cam members 56 for rotatably mounting the cover 32, as will be readily understood.

Because of the resilient mounting of the fingers and the engagement thereof with the surface of the cam members 56, a certain amount of friction is maintained therebetween. However' this friction is not sufficient to prevent movement of -the cover 32 when suflicient force is applied. In the closed position of the cover 32 the fingers- 66 engage the notches 59 in the cam members 56.

When the cover 32 is opened the ends of the fingers 66 ride along the cam surfaces of the cam members 56 until they engage the slot 58. No 5 further movement in this direction is permitted, since the ends of the fingers 68 abut against the one side of the slot 58. At the same time the cover 32 is prevented from swinging downwardly because of the engagement of the fingers 60 with the other side of the slot 58.

Referring now particularly to Figures 6 and 7 of the drawings, it will be observed that a base member 65 is cemented to the rear wall of the -box` 25. Terminal clamps 66 and 61 are secured, as by screws 68, to the base members 5| and 65, as illustrated. I'he terminal clamps 66 and 61 are provided with transversely extending apertures 69 and 10 for receiving the line conductors and for this purpose they are positioned in alinement with the apertures 30 and 3| respectively in the side walls of the box 25. Set screws 1| are positioned in staggered relation at each end of the terminal clamps 66 and 61 and extend into the apertures 69 and 10, as shown, for the purpose of engaging the line conductors therein, as will be readily understood. It will be noted that the line conductors may be connected to the terminal clamps 66 and 61 from either side of the box 25. Ordinarily one side or the other will be more convenient and therefore provision is made for connection from either side. When connection is made from one side only the apertures 38 and 3| on the other side of the box 25 are plugged by any suitable means. Blade stops 12 are integrally formed with the terminal clamp 66 to insure the positioning of the switch arm 28 in the desired location. The terminal clamps 66 and 61 are formed preferably of cast copper in order to provide a high degree of conductivity and to A40 more readily facilitate the manufacture and assembly thereof.

The upper and lower stationary contact members 26 and 21 are mounted on the terminal clamps 66 .and 61 respectively and are secured 45 thereto by screws 15, Figure 8. It will be observed that each of the stationary contact members 26 and 21 comprises a pair of contactJ fingers 16, the construction of which is shown more `clearly in Figures 8 and l0 of the drawings. The

50 contact nger or assembly 16 comprises a U- shaped copper strap, the upper ends o-r branches of which are slightly offset inwardly from the remaining lower portions thereof Alined apertures 11 are provided near the upper ends of these 55 branches and transverse slots 18, formed preferably by a saw cut, extend through `the apertures 11 and divide each branch into sections 19 and 88 to provide a certain degree of independent flexibility. A spacer or stop member 8|, having 60 reduced end necks 82 slidably mounted in the apertures 11 is provided having the outer ends headed over washers 83. A compression spring 84 is positioned around the spacer 8| and between the inside faces of vthe upper ends of the 55 sections 19 and 8|). The external diameter of the central portion of the spacer 8|) is slightly less than the internal diameter of the compression spring 84 in order to secure the spring in the desired location. The inside faces of the 70 sections 19 and 88 are upset to form ridges 85 so that substantially point contact engagement with the ends of the compression spring 84 is provided. With this construction full spring pressure will be applied to each of the sections g5 19 and 80 to bias them outwardly regardless of any slight misalignment or possible cooking of vthe spring 84. While only a. single compression spring 84 is employed, this construction functions as if an independent compression spring were provided for each pair of sections 19 and 80.

It will be understood that the spring 84 is held in compression bythe headed ends of the spacer 8|. With this construction a relatively high contact pressure is provided although relatively little effort is required to operate the switch to and from the switch closed position. The branches of the contact assemblies 16 could be constructed to inherently provide a lresilient effect which would be the equivalent of that afforded by the compression spring 84. In such case the spacer 8| would hold vthe branches of the contact assemblies 16 in the prestressed condition in the same manner that it holds them when biased outwardly to obtain the same condition by means of the compression spring 84. In addition, the floating spacer 8| with headed ends, which limits the outward movement of each pair of contact fingers 16, nullies small differences in the resiliency of the contact fingers and the compression' spring 84 mounted between them. Without this restraint an impractical degree of uniformity in the manufacture and assembly of the contact fingers and springs would be required.

Referring again to Figures 6 and 7 of the drawings, it will be observed that the switch arm 28 comprises a pair of switch blades 88 and 89 that are held in spaced apart relation by transversely extending rivets 90. At their lower ends the switch blades 88 and 89 are mounted for rotation on a shaft 9| that extends through the branches 92 of the fulcrum member 29, which it will be observed, is substantially U-shaped and is secured by screws 93 to a base member 94 which may be cemented to vthe lower end of the rear wall of the box 25. The fulcrum member 29 is spaced from the lower stationary contact member 21 and in alinement with it and with the upper stationary contact member 26 so that they may be bridged when the contact arm 28 is moved to the switch closed position.

The switch blades 88 and 89 are formed preferably of strap copper and at their lower ends friction rings 95 are integrally formed, as by an upsetting operation, to provide the sole engagement with the branches 92 of the fulcrum member 29. A compression spring 96 is positioned around the shaft 9| and serves to bias the blades 88 and 89 apart. By means of the raised friction rings 95 it is possible to predetermine and to maintain constant the friction force that is present between the switch blades 88 and 89 and the branches 92 of the U-shaped fulcrum member 29. If the friction rings 95 were not provided, the entire outer surface ofthe lower ends of the blades 88 and 89 would engage with the inner surfaces .of the branches 92, resulting in variable rather than constant frictional engagement. The pressure which must be exerted by the spring 96, or its equivalent, in such case may vary widely, particularly after the switch has been in operation for some time. The length of the lever arm or effective length thereof at which the frictional force reacts when the raised friction rings 95 are used vis substantially constant and does not change appreciably during the life of the switch. Consequently with a given initial ladjustment of the spring 96, the same friction force is always present. This effect is desirable in holding the switch arm 28 in either the closed or opened position.

vIn order to permit manual operation of the switch arm 28 with the customary hook stick a pull ring 91 is mounted between the switch blades 88 and 89 on a rivet 98 that extends thereof may be readily engaged by the hook stick.

When the cover 32 is closed, the pull ring 91 is moved thereby to its position between the switch blades 88 and 89, as shown in Figure 6.

When the switch arm 28 is operated to the position shown in Figures 6 and '1, the upper and lower stationary contact members 26 and 21 are bridged and the circuit is completed therethrough, -as will be readily understood. According to the generally accepted practice in the prior art this contact engagement has been provided by causing surface engagement between the blades 88 and 89 and the surfaces of the contact ngers 16. That is, the prior art teaches surface contact engagement with the switch blades 88 and 89 for whatever construction is employed for the stationary contact members. Although the specific construction of the contact assemblies 16 with the bifurcated sections 19 andA 80 is new, and although this construction provides new and useful results, I have gone still further and departed from the usually accepted teaching of the prior art in the partic- Yular manner in which the contact engagement between the relatively movable parts is made, as will be presently set forth.

As set forth, surface contact engagement was desired between the relatively movable switch members. From a theoretical standpoint such contact engagement is possible and to a certain extent it is obtained in practice. However, after a switch has been in operation for a considerable length of time, the contact surface conditions change and it is actually a fact that only point contact engagement is present rather than complete surface contact. The entire current flow takes place then through these point contacts and, consequently, the entire capacity of the switch is not available.

lAccording to my present invention I have initially provided for point rather thanl surface contact. For this purpose I have provided a silver insert in each of the sections 19 and 80 of the contact assemblies 16. These inserts are provided with outwardly extending headed ends which engage corresponding flat headed silver inserts |06 in the switch blades 88 and 89. as shown in Figure 9 of the drawings. Since the silver inserts |05 are mounted for substantially individual movement with'their supporting sections 19 and 80, complete contact engagement with the corresponding insert |06 in the switch blade 88 or 89 is assured. This independent operation is further insured by the'provision of the inwardly extendingridges 85 which permit the compression spring 84 vto have substantially point contact only with the sections 19 and 80 of the contact assemblies 16. The bladestops 12 serve to accurately align the inserts. |05 and |06 so that they are definitely positioned in the desired relation when the switch is closed.

I have chosen silver for the inserts |05 and |06 because of its relatively high conductivity and relatively low contact resistance. Even when silver is exposed to thecorrosive effects of the surrounding atmosphere the coating that forms on its surface is not unfavorable to good electrical conductivity and therefore the contact resistance remainssubstantially constant and does not change even though the switch arm 28 remains in the open position for long periods of time.

Since the contact resistance is a the pressure which is exerted on the engaging contact members, it is desirable to provide la relatively-high contact pressure in order to reduce the contact resistance to a minimum. It is primarily for this purpose that the contact assemblies 16 are formed of material which inherently is resilient or the compression springs 84 are provided therebetween. Since the resulting biasing effect must be overcome in operating the switch to and from the closed position, it is desirable toso control the disposition of the biasing force as to require a minimum of effort to operate the switch. It is for this purpose that the spacer 8| with the headed ends isl provided which limits the movement apart of the branches of the contact assemblies 16. As shown in Figure 8 of the drawings, when the switch blades 88 and 89 are moved to the switch closed position in the directionof the arrows |01, the outer ends of the inserts |05 are disposed in the path of travel of the inner surface of the switch blades. The adjacent edges of the switch blades 88 and 89 are beveled, as illustrated with a slope that is sufficient to properly engage the heads of the silver inserts |05 so that they will be moved inwardly the distance required to place them in engagement with the flat heads of the silver inserts |06 in the inner surfaces of the switch blades. An appreciable relative movement takes place in a direction normal to the direction in which the switch blades move which is not found in switches of the conventional knife blade type. The continued movement in the direction of the arrows |01 causes the branches of the contact assemblies 16 to be, moved inwardly, as shown in Figure 9 of the drawings, relieving the spacer 8| of the biasing effects4 of the compression spring 84 and of the branches of the assemblies 16 and transferring its entire force to apply pressure between the silver inserts |05 in the assemblies 16 and the inserts |06 in the switch blades 88 and 89. The same contact pressure is provided between the silver inserts |05 and |06 with this construction as would be provided if the compression spring 84 were fully compressed by the movement of the switch arm 28 to the closed position and a minimum of effort is required to operate the switch arm 28 to and from the switch closed position. It will also be understood that the small movement of the branches of the contact assemblies 16, when the resilient force of the spring 84 is transferred from the spacer 8| to the switch blades- 88 and 89, assures a reliable contact engagement between each 'of the projecting portions of the inserts |05 and the adjacent faces of the switch blades or the inserts |06 therein at about the same pressure without requiring accurate alignment.

It will be understood that any other material may be employed in lieu of silver for the inserts function of' |05 and |06 that may hereafter become available and which has the properties of silver in providing the desired contact surface characteristics. At the present time, however, silver appears to be the most practical material to employ. It will also be understood that the Dositions of the inserts |05 and |06 can be reversed in which casethe headed portions would be carried by the blades 88 and 89 and the flat portions would be carried by the contact assemblies 16.

While it is highly desirable to provide the inserts I05`and |06 in the switch construction, as described, it is not essential to do so and my invention may be practiced, in so far as remaining construction of the switch is concerned Without using them. This construction would merely include the arrangement of the contact assemblies 16 and the switch blades 88 and 89 for surface contact engagement, as practiced in the prior art. If it is desired to provide the small area high pressure contact surface Without the use of inserts, the contact fingers can themselves be upset to the same shape as the heads of the rivets |05. However, when the construction is employed, as disclosed herein, using the prestressed sectionalized construction for the contact assembly 16, improved operating characteristics are obtained because ofthe relatively high contact pressure which is available between lthe relatively movable switch parts while at the same time a minimum of effort isI required to operate the switch from and to the closed position. Therefore, it will be understood that my invention may be practiced without employing the inserts |05 and |06, although it is highly desirable to use them for the reasons set forth hereinbefore.

In applications where the disconnecting switch is opened under load, it is desirable to provide a quick-break auxiliary contact member for effecting the nal circuit opening, thereby avoiding arcing at the main contact members. For this purpose the construction illustrated in Figures 12, 13, and 14 of the drawings may be employed. As there shown, a disconnecting switch is provided which is similar to that shown in Figures 6` and 'l of the drawings, and in addition there is provided an auxiliary 6r quick-break blade |I0 which is mounted on a shaft I |I that extends through the switch blades 88 .and 89. A coll spring ||2 is provided for biasing the shaft |I| and the blade I0 carried thereby in the direction indicated by the arrow ||3 in Figure 12. A stop II4, mounted in and extending outwardly from the switch blade 89 is provided to limit the movement of the auxiliary blade I0 as biased by the spring ||2 and to carry this blade into engagement with spaced apartswitch jaws |I5 that are associated with the upper stationary contact member 26. A similar stop Illa, located near the shaft of the quick break blade |I0, pulls this blade out of engagement with the jaws |I5 as soon as its upper end is clear of the plates ||8. The jaws |I5 are mounted on a suitable angle bracket |I6 which is carried by an arm I|1, mounted between the upstanding fingers of the upper stationary contact member 26 and secured to the terminal connector 66. 'I'he outer ends of the jaws ||5 are flared outwardly and have latching members or plates II8 mounted thereon.

In operation when the switch arm 28 is moved toward the switch closed position, the auxiliary blade IIO is moved therewith by the stop |I4 and it approaches the ared ends of the jaws ||5 as indicated by the arrow |I9 in Figure 14. 'Ihe continued movement of the switch arm 28 causes the auxiliary blade I I 0 to pass the latching members or plates 8 and to come to rest against the outer end of the bracket II6 as illustrated. When the switch arm 28 is moved toward the open position, the auxiliary blade I |0 is prevented from following it by the latching members I I8. As a result a circuit connection is maintained between the switch arm 28 and the upper stationary contact member 26 until after the switch blades 88 and 89 are moved out of Contact engagement with the upper terminal member 26.

lThe continued rotation of the switch arm 28 toward the open position causes the auxiliary |I0 to move downwardly with a translatory motion until its upper end is below the inner edges of the latching members II8. The auxiliary blade IIO is then rotated in a counterclockwise direction, as indicated by the arrow I I3, from engagement with the lower portion of the jaws I I5 with a snap action, thereby quickly effecting the iinal' circuit break. It will be understood that the latching members |I8 extend downwardly over only a portion of the flared out ends of the jaws |I5, as shown in Figure 13, thereby permitting the final break to be made when the auxiliary blade I 0 is rotated out of the lower contact portions of the jaws |I5.

In order to insure that the circuit is not opened by disengagement of the switch blades 88 and 89 from the lower stationary contact member 21 before the auxiliary blade ||0 leaves the jaws |I5, an auxiliary contact member |20, formed preferably of a flexible strap of copper, is secured to the lower stationary contact member 21 and extends outwardly between the switch blades 88 and 89. The auxiliary contact member |20 is arranged to maintain engagement with one of the transversely extending rivets and is of suflicient length to maintain engagement therewith until after the auxiliary blade |I0 has opened the circuit by leaving the jaws I I5 with the snap action as previously described.

Another form of disconnecting switch construction embodying certain of the features of my in vention for mounting in the switch box 25 is shown in Figures 15 and 16 of the drawings. As there shown upper and lower stationary contact members 25 and |26 are mounted on suitable terminal connectors |21 and |28 which may be cemented or otherwise secured in the box 25. 'I'he stationary contact members |25 and |26 are bridged by a switch blade assembly |29 which may be mounted for rotation in a fulcrum member |30 that is secured to the rear wall of the box 25 by cementing or any other suitable means. The switch blade assembly |29 comprises a pair of blades 3| and |32 which are secured in spaced apart relation by transversely extending rivets |33. A pull ring |34, mounted on one of the rivets |33 is provided to permit operation of the switch arm |29 by means of the usual hook stick. The upper end of the pull ring |34 is provided with a cut-away portion |35 which cooperates with the adjacent rivet |33 to limit the movement of the pull ring |34. A stop member I21a. in the form of a pin is mounted on the terminal connector |21 to serve as a stop for the movement of the switch blade assembly |29 inwardly.

It will be observed that the fulcrum member |30 is provided with an upwardly opening slot |36 into which the lowermost rivet |33 may be positioned when it is desired to operate the switch arm |29 to the closed position. The lower end of the switch blades |3I and |32 are rounded and slide along the outer edges of side members I30a forming the fulcrum member |30. This construction prevents removal of the switch blade assembly |29 until it has been rotated to its lowermost position. As soon as the switch arm |29 is moved to the lowermost position, it may be removed thereby preventing the operation of the switch by unauthorized persons or for any other suitable reason.

With a view to maintaining contact engagement with the lower stationary contact member |26 until the switch arm |29 has moved to a predetermined position corresponding to a minimum required distance from the upper stationary contact member |25, an auxiliary contact member |31 is rotatably mounted on the switch blades |3| and |32 and is varranged to maintain contact engagement with the lower stationary contact member |26. This precaution is taken to prevent the formation of an arc between the switch blade assembly |29 and the lower stationary contact member |26, in the event that theswitch is opened under load. This is required because the switch blade assembly |29 is mounted for rotation on the Afulcrum member |30 that is insulated from the contact member |26 ratherthan being mounted for rotation on the latter. Any arc that is formed is drawn between the switch arm |29 and the upper stationary contact member |25 and it will ordinarily be broken before the auxiliary contact member |31 disengages the lower stationary contact member |26.

The cover 32 for the box 25, shown in Figures 15 and 16 of the drawings, is mounted in a somewhat diflerent ma-nner than that illustrated in Figures 5 and 6 of the drawings. As shown a pair of spaced apart resilient support arms |40 is secured to opposite sides of the upper terminal connector |21 and they are arranged to be biased apart by a compression spring |4| positioned between the outer ends thereof. block |42 of suitable insulating material is secured to the inside of the cover 32 by threaded pins |43 that are similar to the pins 51 shown in Figure 5 .of the drawings and described hereinbefore. The block |42 constitutes a part of a support bracket which further comprises a pair of straps |44 that are secured to the block |42 by a transversely extending bolt |45. The upper ends of the straps v |44 are apertured and a shaft |46 extends therethrough and through corresponding apertures in the support arms |40. It will be observed that the spring |4| is positioned around the shaft |46, the

ends of which are headedto maintain it in position. A pair of latching members |41, in the form of wires extend through the shaft |46 and into the rectangular block |42. The outer ends of the latching members |41 are bent outwardly, as illustrated, into engagement with notches |48 in the upper ends of the straps |44.y *The latching members |41 are arranged to intert with a vertical slot |49 in each of the outer surfaces of theV support arms |40 at their upper ends when the cover 32 is in the closed position and to intert with a horizontal slot |50 located in the same surface when the cover 32 is in the open position.

When the cover 32 is moved from one position to the other, the support arms |40 are moved inwardly and toward each other against the biasing force of the spring |4|. Aslsoon/ as the latching members |41 engage either of the grooves |49 or |50, the cover 32 will be frictionally held in the corresponding position. f

Advantage may be taken of the principle of prestressing the contact members by providing the construction illustrated in Figure 1'1 of the draw- A rectangular y cient force to further compress the springs ings. In this figure the'construction of the lower contact member |26 is illustrated and it will be understood that the upper contact member |25 is of identical construction.

As shown, the contact member |26 comprises a U-shaped contact member |53 the ends |54 and |55 of which are turned inwardly for engagement with the blades |3| and |32. In this embodiment of the invention surface contact is relied upon rather than point contact using silver inserts, as previously described. A U-shaped bracket |56 having upstanding branches |58 and |59 is positioned inside of the contact member |53 and is spaced slightly therefrom, as illustrated. The flexible inturned ends |54 and |55 are biased toward each other by compression springs |60 and |6| which are positioned rbetween these ends and the branches |58 and |59fof the bracket |56. Sufcient pressure is provided with this construction to permit a. relatively complete contact 'engagement between the surfaces of the switch blades |3| and |32 and the coacting surfaces of the end portions |54 and |55.

In order to limit the movement of the endv portions |54 and |55 under the influence of the biasing springs |60 and |6|, stop members |62 and |63 are secured by suitable means, such as rivets, to thebracket |56 at oneend and the other end projects upwardly into thepath of movement of the end portions |54 and |55. The upper ends |58 and |59 of the vbracket |56 limit the inward movement of the upper portions of the end portions |54 `and |55 in the same manner as stop members |62 and |63 limit the inward movement of the lower portions thereof. In this manner the inner surfaces of the end portions |54 and |55 move in parallel planes and satisfactory. surface contact engagement therewith may be had. It is thus possible to prestress the springs |60 and |6| and to so construct the stop members |62 and |63 as to position the end portions |54 and |55 slightly within the path of movement of the switch blades |3| and |32. When the switch blades are moved to the switch closed position, it is only necessary to exert suill- |60 and |6| to permit the movement to the fully closed position. The full forceof the springs |60 and |6| is then available for providing contact pressure between the relatively movable switch parts.

While the contact member |53 has been illus-- ltrated as being of substantially U-shape, it lwill be understood that it could be formed by two independent contact on a suitable base. However,-I have found that a relatively economical construction is provided when the contact member |53 is formed of one piece, but it will be understood that the alternative form of construction comes within the scope prises a singlel blade which is mounted for rotation on a fulcrum member A stop pin |68a carried by the terminal connector |68 fingers, mounted separately In this embodiserves to limit the inward movement of the y switch arm |10.

The fulcrum member |1| comprises a pair of more complete engagement therewith.

spaced apart jaws |12, the outer ends of which are ared outwardly. A rivet |13 extends through the lower end of the switch arm |10 and its ends are headed, as illustrated, for interfitting with suitable openings in the jaws |12 the inner edges of which are beveled to provide It will be understood that the switch arm |10 may be readily removed by merely withdrawing it from the jaws |12 after it has been operated to the open circuit position. In order to close the switch, the switch arm |10 is rst inserted in the jaws |12 and then is rotated about the rivet |13 as an axis to contact engagement with the stationary contact members |66. and |61.

In order to permit operation ,of the switch arm |10, a pull ring |14is rotatably mounted on a suitable rivet |15 that extends through the switch blade. 'Ihe pull ring |14 is provided with a nose portion |16 that is arranged to engage a stop pin |11 for limiting this movement in a counterclockwise direction, `as viewed in Figure `19 of the drawings. -An auxiliarycontact member |18 is rotatably mounted on the switch arm |10 in order to maintain contact engagement with the lower stationary contact member |61 until the switch arm |10 is moved a, predetermined distance from the upper stationary contact member |66.

With a view to rotatably mounting theAcover 32 a rectangular block |8| is provided near its upper end and is secured thereto by threaded pins |82 that are similar to the pins 51 s hown in Figure of the drawings and described hereinbefore. The block |8| is formed preferably of insulating material and it has positioned along its opposite sides straps |83 that are secured thereto by means of a transversely extending bolt |84 and by dowel pins |85. The straps |83 extend upwardly and alongsideof a support member |86 that is formed of a suitable insulating material and secured to the terminal connector` |68, as illustrated. A bolt |81 extends transversely through the straps |83 and the support member |86 in order to rotatably mount the cover 32. Spring washers |88 are provided at each end of the bolt |81, as shown, in order to provide a certain amount of friction between the inner surfaces of the straps |83 and the support member |86while still permitting the cover 32 to be moved to and from the closed position and to hold the cover 32 in the Aopen position so that the switch blade may be opened and Aclosed without interference therewith.,

The construction of the upper and lower stationary contact members |66 and |61 may be identical and similar to the construction of the stationary contact members in the switch shown in Figures and 16 of t e drawings and in detail in Figure 17. The de ails of construction of the stationary contact member |61 are more clearly illustrated in Figure 20, to which reference will now be had. As shown, a U-shaped contact member |9| is provided having inturned flexible ends |92 and 93 between which the switch arm |10 is moved for contact engagement. The auxiliary contact member |18 is also positioned therebetween, as illustrated. A U-shaped bracket |94 is positioned inside of the contact member |9| and is provided with upwardly extending branches |96 and |91. Compression springsl |98 and |99 are provided between the branch |96 and the end portion |92 and between the end portion |93 and the branch |91 to provide the desired contact pressure. Stop brackets 200 and 20|, mounted by rivets or other suitable means on the bracket |94 'and extending upwardly to limit the inward movement of the ends |92 and |93, are provided. The upper ends |96 and |91 of -the bracket |94 serve to limit the inward movement of the upper portions of the flexible ends |92 and |93 in the same relation as the stop brackets 200 and 20| limit theinward movement 'of the lower portions thereof. 'Ihe stop brackets 200 and 20| and the bracket |94 serve to prestress the springs |98 and |99 by retaining them in this condition prior to the movement of the switch arm |10 to the switch closed position.

In operation when the switch arm |10 is moved to the position illustrated in Figure 20 of the drawings, it will be understood that only suilicient force must be exerted to compress the springs |98 and 99 a slight distance to permit the movement of the switch arm |10 to the desired position. The inturned ends |92 and |93 are then lifted off of the upturned ends of the stop brackets 200 and 20| and the full spring pressure is applied to provide the desired contact pressure.

In the construction of the various forms of conductor clamps shown in connection with the different embodiments of the disconnecting switch set screws are provided for directly engaging the conductor that is positioned therein.

In some cases I have found that it may be undesirable to provide for this direct engagement because of the nicking of the conductor that results. If the conductor is subjected to considerable tension and vibration, it may break off. If flexible conductors are employed the strands may be severed to a certain extent and complete contact may not be obtained.

In order to provide a terminal clamp in which the conductor is not directly engaged by the set screws, the construction illustrated in Figures 21 and 22 may be employed. As there shown a conducto'r clamp 205 is provided which comprises a casting 206 of suitable conducting material, such as copper, and having a transversely extending aperture 201 therein. It will be observed that the lower surface of the aperture 201 is inclined to permit the insertion of various sizes of conductors without requiring special sizes of clamps therefor. A contact plate 208 is provided in the upper portion of the aperture 201 and extends substantially entirely therethrough. The contact plate 208 is provided for'engaging the conductor that is inserted in the aperture 201, as will be readily understood. Set screws 209 are threaded in the upper side of the casting 206 and the lower ends .2 I0 extend through suitable apertures in the contact plate 208 and are headed over to cause conjoint movement therewith. The lower ends 2|0 of the set screws 209 are so constructed that they arefpermitted to turn relative to the contact plate 208 and therefore the latter is moved downwardly or upwardly depending upon the direction of rotation of the set screws 209. Moreover, the

lower ends 2 0 are sol foi-med that they do not ex-v tend downwardly a sufficient distance to engage the conductor. As a result the only engagement therewith is provided bythe contact plate 208 which, because it is flat, does not cause a nicking of the conductor as might otherwise be the case.

In Figure 23 of the drawings I have shown a modified form of the contact member |61 that is illustrated in Figure 20 and described hereinbefore. In the embodiment of the contact member |61 shown inFigure 23 the switch blade |10 is provided with a rivet 2|2, the headed ends of which are arranged to engage corresponding rivets or inserts 2|3 in the flexible ends |92 and |93 of the U-shaped contact member |9I. The lower ends` of the flexible end portions |92 and |93 are provided with aligned apertures in which the stop member 2|4 is slidably mounted. It will be observed that the central portion of the stop member 2 I4 is enlarged to provide a limit to the movement-of the end portions each other under theinuence of the springs |98 and |99. In this manner these springs are prestressed as will be readily understood. The ends of the stop member 2|! are headed to limit the movement apart of the end portions |92 and |93. In this manner a floating construction is provided which permits considerable latitude in the movement of the end portions |92 and |93 within the confines of the bracket |94.

It will be understood that the inserts or rivets 2I2 and 2|3 are preferably formed of silver or of a silver alloy to provide thedesired contact surface characteristics as described in detail hereinbefore. y f

While I have disclosed herein various types of prestress stationary contact members, it will be4 understood that these contact members may be mounted on a movable arm for engagement with stationary contact members in the form of blades or the like. This alternative form of construction is disclosed in my copending application iiled December 14, 1936, Serial No. 115,692, and assigned to the assignee of this application.

Since furtherchanges may be made in thelforegoing constructions and different embodiments of the invention may be made without departing from the scope thereof, it is intended that all matter .contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense. Y

I claim as my invention:

l. A switch comprising, in combination, a pair of switch members mounted for relative movement to open and close an electric circuit, a plurality of individually iiexible contact fingers on one of said switch members, a small area high pressure contact member extending from each of said contact fingers, resilient means cooperating with each of said contact fingers and disposed out of the path of current ow therethrough for individually biasing the contact member carried thereby into high pressure contact engagement with the vother switch member, and stop means extending transversely through said contact fingers and arranged and adapted to limit the movement of said small area high pressure con-` tact-members to positions slightly within the path of relative movement with said other switch inember whereby said contact fingers are prestressed.

2. A switch comprising, in combination, a pair of switch members mounted for relative movement to open and close an electric circuit, a plurality of contact fingers carried by one of said switch members, a small area high pressure con tact` portion extending from each of said fingers and .constituting the sole contact engaging portion with the other switch member, resilient means biasing said contact iingers, and stop means extending transversely through and limiting thelmovement of said fingers to position said contact engaging portions carried thereby slightly within the path of relative movement with vsaid other switch member, said other switch member being beveled sufficiently to move said contact |92 and |93 toward y movement with of said switch members be engaged contact member into ling portions with theother switch member, said small area contact engaging portions being disposed in substantially a straight line, resilient prestressing means disposed out of the path of current flow through said contact ngers for biasing said contact engaging portions into high pressure contact engagement with said other switch member, and stop means extending transversely through said contact fingers to limit the movementv of said contact engaging portions to positions slightly within the path of relative said other switch member.

4. A switch comprising, in combination, a pair of switch members mounted for relative movement to open and close an electric circuit, one

including a flexible contact finger arranged and adapted to engage the other switch member, the contact engaging portions being limited to a small area of said contact finger and said other switch member, solid silver insert means in said switch members forming the contact engaging portions in said small areas, resilient means disposed to bias said contact finger into the path of relative movement of said switch members and to provide relatively high unit pressure therebetween, stop means for limiting the movement of said contact finger to a `position slightly inside of said path whereby said resilient means is prestressed before said other switch member engages said contact nger, and additional stop means limiting the relative movement of said switch members toward the switch closed position to accurately align the silver insert means carried by said switch members.

5. A switch comprising, in combination, an arm guided for movement in substantially a predetermined plane, a contact member adapted to by the arm with a wiping motion when the arm is moved to switch closing position, the .contact engaging portions being limited to a small area of said arm and said contactmember, silver inserts in said arm and contact member forming the contact engaging portions in said small areas, resilient means disposed to bias said the rpath of movement of said arm and to provide a relatively high` unit pressure, stop means for limiting the movement of said contact member to a position slightly inside of said path whereby said resilient means is prestress'ed before said arm engages said contact member, and additionalstop means limiting the movement of saidLarm toward the switch closed position to accurately align said silver inserts.

Y 6. A switch comprising, in combination, a pair of switchmembers mounted for relative movement to open and close an electric circuit, one of said members including a pair of prestressed contact fingers, the other of said members including a pair ofspaced apart contact members for engagement with said contact fingers therebetween, silver inserts in said switch members forming the contact/ engaging portions therebetween, and means extending transversely through said contact fingers for limiting movement thereof to positions slightly within the path of relative movement of said switch members.

7. A switch comprising,` in combination, a pair of switch members mounted for relative movement to open and closer an electric circuit, one of said members including a pair of spaced apart Contact fingers, the other of said members including a pair of spaced apart contact members for engagement with said contact fingers therebetween, spring means biasing said contact iingers apart, and stop means extending transversely through said contact iingers for limiting movement thereof apart.

8. A switch comprising, in combination, a pair of spaced apart blades guided for movement in parallel paths, a prestressed bifurcated 'stationary contact member the branches of which individually engage the inner surfaces of said blades when they are moved to the switch closing position, -the contact engaging portions being limited to a small area of each branch of said bifurcated contact members and corresponding areas on said blades, silver insertsl in said blades and branches forming the contact engaging portions in said small areas, and stop means extending transversely through said branches for limiting movement of said silver inserts carried thereby to positions slightly within said paths of said blades.

9. A switch comprising, in combination, a pair of spaced apart blades guided for movement in parallel paths, a bifurcated stationary contact. member the branches of which individually engage the inner surfaces of said blades when they are moved to the switch closing position, resilient means for biasing said branches into engagement with said blades, and stop means extending transversely through said branches for limiting movement thereof apart.

10. A switch comprising, in combination, a pair of switch members mounted for relative movement to open and close an electric circuit, one of said members including a pair of spaced apart bifurcated contact fingers, the other of said members including a pair of spaced apart contact members for engagement with said contact lingers therebetween, resilient means for biasing said contact fingers into engagement with said contact members, and stop means extending transverselythrough said branches for limiting movement thereof apart.. l

l1. A switch comprising, in combination, a pair of spaced apart blades guided for movement in parallel paths, a bifurcated stationary contact member having bifurcated branches for individually engaging the inner surfaces of said blades when they are moved -to the switch closing position, resilient means for biasing said bifurcated branches into engagement with said,

blades, and stop means extending transversely through said branches for limiting movement thereof apart.

12. In combination for a switch having relatively movable switch members for closing an electric circuit, a pair of bifurcated prestressed spaced apart contact lingers disposed to be carried by one of said switch members for engagement with the other switch member, the contact engaging portions lbeing limited to a small area of each branch of each of said bifurcated contact members and corresponding small areas on said movable switch members, and means extending transversely through said fingers for limiting movement thereof apart.

13. In combination for a switch having relatively movable switch members for closing an electric circuit, a pair of prestressed spaced apart contact fingers disposed to be carried at one end by one of said switch members for engagement near the other end with the other switch member and having aligned apertures at said other end, and stop means slidably mounted in at least one of said apertures and extending transversely through said apertures for limiting movement apart of said ngers.

14. In combination for a. switch having relatively movable switch members for closing an electric circuit, a pair of spaced apart contact fingers disposed to be carried at one end by one of said switch members and having aligned apertures near the otherend, means intermediate the ends of. said fingers and extending outwardly therefrom to form small area contact engaging portions with said other switch member, a coil spring disposed `coaxially with said apertures for biasing said fingers apart, and stop means slidably mounted in said apertures and having headed ends for limiting the movement apart of said ngers to position said contact engaging portions slightly within the path of relative movement of said switch members.

15. In combination for a switch having relatively movable switch members for closing an electric circuit, a pair of spaced apart contact ngers disposed to be carried at one end by one of said switch members and having aligned apertures near the other end, contact means intermediate the ends of said iingers and extending outwardly therefrom to form small area. contact engaging portions ,with said other switch member, a. coil spring disposed coaxially with said apertures for biasing said fingers apart, and a spacer having neck portions at each end slidably mounted in said apertures and having headed outer end portions to limit the movement apart of said fingers to position said contact means slightly within the path of relative movement of said switch members, the diameter of the central portion of said spacer being slightly less than the internal diameter of said spring.

16. In combination for a switch having relatively movable switch members for closing an electric circuit, a pair of spaced apart contact fingers disposed tobe carried at one end by one of said switch members and having centrallyl located aligned apertures near the other end, each of said ngers having slots extending from said 'apertured end toward said other end, contact .means in each section formed by said slots to provide small area contact engaging portions with said other switch member, a coil spring disposed coaxially with said apertures for biasing said fingers apart, and stop means slidably mounted in said apertures and having headed ends forv limiting the movement apart of said fingers to position said contact means slightly within the path of relative movement of 'said switch members.

17. In combination for a switch having relatively movable switch members for closing an electric circuit, a pair of spaced apart contact fingers disposed to be carried at oneend by one of said switch members and having centrally located aligned apertures near the other end, each of said fingers having slots extending from said apertured end toward said other end, contact means in each section formed by said slots to provide small area contact engaging portions with said other switch member, a coil spring disposed path coaxially with said apertures for biasing said lingers apart, an inwardly extending ridge on each of said sections providing the sole engagement with the ends of said spring whereby substantially point engagement is provided between said spring and said sections, and stop means slidably mounted in said apertures and having headed ends for limiting the movement apart of said fingers to position said contact means slightly within the path of relative movement of said switch members.

18. In combination for a switch having relatively movable switch members for closing an electric circuit, a pair of spaced apart contact ngers disposed to be carried at one end by one of said switch members and having centrally located aligned aperturesfnear the other end, each of said fingers having slots extending from said apertured end toward said other end, contact means in each section formed by said slots to provide small area contact engaging portions with said other switch member, a coil spring disposed coaxially with said apertures for biasing said fingers apart, an inwardly extending ridge on each of said sections providing the sole engagement with therends of said spring whereby substantially point engagement is provided between said spring and said sections, and a spacer having neck portions at each end slidably mounted in said apertures and having headed outer end portions to limit the movement apart of said fingers to position said contact means slightly'within the of relative movement of said switch members, the diameter of the central portion of said spacer being slightly less than the internal diameter of said spring.

19. A terminal member for an electric circuit comprising, in combination, a substantially U- shaped contact member having aligned apertures centrally disposed near the ends of its branches, each branch having a longitudinal slot through its aperture forming two sections in each branch, contact means in each section to provide a small area contact engaging portion, a coil spring disposed coaxially with said apertures for biasing said ends apart, a transverse ridge extending inwardly from each section in alignment with said apertures and providing the sole engagement with the ends of said spring whereby substantially` point engagement is provided between said spring and said sections, and stop means slidably mounted in said apertures and having headed ends for limiting the movement apart of said branches.

20. A terminal member for. an electric circuit comprising, in combination, a substantially U- shaped contact member having aligned apertures centrally disposed near the ends of its branches, each branch having a longitudinal slot through its aperture forming two sections in each branch, contact means in each section to provide a small area contact engaging portion, a coil spring disposed coaxially with said apertures for biasing said ends apart, a transverse ridge extending inwardly from each section in alignment with said apertures and providing the sole engagement with4 the ends of said spring whereby substantially point engagement is provided between said spring andsaid sections, and a spacer having neck portions at each end slidably mounted in said apertures and having headed outer end portions to limit the movement apart of said branches, the diameter of the central portion of said spacer being slightly less than the internal diameter of said spring.

21. In combination for a switch having relatively movable switch members for closing an electric circuit, a pair of spaced apart contact ngers disposed to be carried by one of lsaid switch members and having downturned flexible end portions for contact engagement with the other switch member, bracket means interfltting with said'contact ngers, resilient means reacting against said bracket means for biasing said end portions into contact engagement with said other switch member, and stop means forA limiting the movement of said end portions to positions slightly within the path of relative movement of said switch members.

22. A switch comprising, in combination, an arm guided for movement in substantially a predetermined .plane, a pair of spaced apart stationary contact ngers having downturned flexible end portions for contact engagement with said arm, bracket means intertting with said contact fingers, resilent means reacting against said bracket means for biasing said end portions into contact engagement with said arm, and stop meansfor limiting the movement of said end portions to positions slightly within the path of said arm.

23. A switch comprising, in combination, an arm guided for movement in substantially a predetermined plane, va pair of spaced apart stationary contact iingers having inturned exible end portions for contact engagement with said arm therebetween, a bracket intertting with said contact fingers, resilient means reacting against said bracket for biasing said end portions toward each other, and stop means for limiting the movement of said end portions to positions slightly within the path of said arm whereby said resilent means is prestressed.

24. A contact member comprising, in combination, a pair of spaced apart contact iingers having downturned flexible end portions for engagement with a relatively movable cooperating contact member, bracket means intertting with said contact fingers, resilient means reacting against said-bracket means tor biasing said ex- K ible ends in opposite directions, and stop means for limiting the movement of said end portions to positions -slightly within the path of relative movement of said contact members whereby said resilient means is prestressed.

25. A contact member comprising, in combination, a pair of spaced apart contact lingers having inturned flexible \end portions for engagement with a relatively movable cooperating contact member therebetween, a bracket intertting with' said contact ngers, a spring-individual to each end portion and reacting against said bracket for biasing it into engagement with said movable contact member, and stop means for limiting the movement of said end portions to positions slightly within the path of relative movement ofwithin said contact member, a coil spring interposed between each branch of said bracket and each inturned end portion for biasing the latter toward each other, and stop means carried by said bracket for limiting the movement oi said movable cooperating contact member therebetween, a substantially U-shaped bracket secured 10 within said contact member, a coil spring interposed between each branch of said bracket and each inturned end portion for biasing the latter toward each other, and stop means extending through the free ends of said flexible end portions for limiting the movement thereof to positions slightly within the path of relative movement of said contact members whereby said ends are free to oat between the arms of said U-shaped bracket.

ALLAN RAMSEY.

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