US3368052A

US3368052A - Combined butt and finger contact

Info

Publication number: US3368052A
Application number: US593479A
Authority: US
Inventors: Jensen Otto
Original assignee: ITE Circuit Breaker Co
Current assignee: ABB Inc USA; ITE Circuit Breaker Co
Priority date: 1966-11-10
Filing date: 1966-11-10
Publication date: 1968-02-06
Anticipated expiration: 1985-02-06

Description

Feb. 6, 1968 o. JENSEN I COMBINED BUTT AND FINGER CONTACT 4 Sheets-Sheet 1 Filed Nov. 10, 1966 4 Sheets-Sheet 2 Feb. 6, 1968 o. JENSEN COMBINED BU' IT AND FINGER CONTACT Filed Nov. 10, 1966 .Q a W V vxivkuwvx 6 n I II wiwku km g Q Q MN MN \N R N\ E O. JENSN COMBINED BUTT AND FINGER CONTACT Feb 6, i fifi Filagi Nov. 10, 1966 Feb. 6, 1968 o. JENSEN 3,363,052

COMBINED BUTT AND FINGER CONTACT 4 Sheets-Sheet 4.

Filed Nov. 10, 1966 QNE United States Patent 3,368,052 COMBINED BUTT AND FINGER CONTACT Otto Jensen, Malvern, Pa, assignor to l-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Nov. 10, 1966, Ser. No. 593,479 6 Claims. (Cl. 200-166) ABSTRACT OF THE DISCLOSURE A contact structure particularly useful for circuit breakers is formed with a combined butt and jaw structure where cooperating contacts engage on abutting surfaces, which surfaces are subjected to arcing during closing and opening of the contacts. The butt-contact of the stationary contact is slidably engaged along its sides to opposing jaw-contacts with the movable contact continuing to move inwardly and driving the stationary butt-contact inwardly of the jaw-contacts after engagement of the butt-contacts. The continued movement of the stationary contact moves the sides thereof into jaw-contact type engagement with the sides of the jaw-contacts of the stationary contact. The spacing of the stationary jaws are equal to the width of the movable contact so that there is no bounce of the jaw-contacts with the major current flow path occurring through the jaw-contact after the butt-contact portions have absorbed the major burden of any arcing.

This invention relates to a contact structure, and more specifically relates to a novel combined butt and jawcontact structure for use with circuit interrupters wherein a butt-contact portion is provided for absorbing the major portion of the arcing duty during opening and closing of the contacts, while the movable contact and stationary jaw-contacts conduct the major current flow through the contacts when the contacts are closed.

Electrical contacts commonly used in circuit breaker switches and conductors are normally either of the butttype in which the contact surface is normal to the line of travel of the movable contact, or of the jaw-type in which the contact surfaces are parallel to the line of travel of the movable contact. These contacting surfaces are subject to deterioration due to pre-arcing and contact bouncing during closing and due to metal evaporation during the opening of the contacts.

In the butt-type of contact arrangement, contact pressure required for effective current transfer at the contact surface is obtained by suitable compression springs. The inertia of the moving parts and the elasticity of the springs constitute an oscillating mechanical system that is set in oscillation when the mating contacts meet at high speed. These oscillations are damped by friction, but while they last, they cause momentary reduction in contact pressure and in some cases actual contact separation after they meet. When the contacts close on even relatively light current, this bouncing results in melting and welding at the contact surfaces which progressively continues until the contact surfaces are destroyed. In addition to the contact erosion caused .by contact bounce, as described above, contacts are subject to prearcing during closing where, once the contacts reach a predetermined distance from one another with a sufficient voltage across the contact, an arc will be formed until the contact surfaces meet. Clearly, during opening of the contacts while the contacts carry current, there will be arcing and metal evaporation which additionally causes contact erosion.

Similar problems cause contact erosion in the usual type of jaw-type contact where a blade is forcibly inserted between two jaws with a spring biasing means applied to the two jaws tending to force them toward one another. The jaws and their springs thus constitute an oscillating Patented Feb. 6, 1968 mechanical system which is subject to bouncing as in the case of the butt-type contact whereby contact surface erosion is again caused due to contact bouncing, prearcing during closing, and arcing during opening.

In accordance with the present invention, a novel arrangement is formed which incorporates the principles of both the butt and jaw-type contact arrangements which avoids the harmful effects of bouncing and restricts contact erosion to contact surfaces which are used only for opening and closing the circuit while preventing erosion of the contact surfaces used for normal current conduction through the contacts.

In accordance with the invention, a set of jaw contacts are provided which are spaced from one another by a distance equal to .the width of a movable blade contact. A sliding follower type contact, having the same width as the blade contact, is then interposed between the set of jaw-contacts, and the sides of the sliding follower are in sliding contact with the sides of the jaw-contacts. The sliding follower is then outwardly biased toward buttcontact engagement with the movable contact, but is movable against the force of its bias into the direction of movement of the movable blade contact when the blade contact moves to its engaged position. The jaws are held closed on both the contact follower and the blade by suitable springs that supply the pressure required for effective contact.

When the contact is open, the end of the follower extends out beyond the ends of the jaw. Upon closing, the forward end of the movable blade contact initially engages the forward edge of the follower in butt-contact fashion. All arcing due to the contact closing and bouncing between the blade and the follower will then occur between the butt surfaces of the blade and follower which are normal to the direction of motion of the blade. A current path is then initially set up from the blade to the follower and then laterally through the stationary jaws which engage the sides of the follower. As the closing motion of the blade continues, the follower is pushed inwardly of the jaws and the blade is inserted between the jaws. Since a current path has already been established between the blade and the follower, as the blade moves between the jaws, there will be no arcing between the side surfaces of the blade and the coopenating side surfaces of the jaw so that these surfaces will be clean and free of erosion due to arcing. Major current flow now proceeds through the clean side contact surfaces of the jaw-contact portion of the arrangement. Note that no bouncing will occur at the jaw fingers, since the blade has the same width as the spacing between the jaw-contacts.

During opening, as the blade moves out from the jaws, the follower, being biased by a suitable biasing means, moves out with the blade and maintains electrical buttcontact with the moving blade. When the blade is entirely outside the jaws, the current path will be from the jaws to the follower and from the follower butt-contact surface that which could be efficiently obtained by the engagement of the single blade and single set of jaw-contacts, additional parallel-connected blades and jaw-contacts could be provided. While these additional sets could also incorporate the follower contact for initially engaging and finally disengaging the contact blade, it has been found unnecessary to provide the follower for the other parallel contacts since all engagement and disengagement arcing can occur on a-single follower and blade even though there are a plurality of parallel contacts.

Another advantage obtained with the novel contact arrangement of the invention is that where there are parallel connected contacts, only the contact adapted with the follower arcing need be contained within an arcing extinguished arc chute. The other main contacts in parallel with the arcing contact arrangement may then be disposed outside of the arc chute where they will be subject to better cooling while the arc chute, being narrower than one containing all of the contacts, will be more efiicient, and a higher magnetic field can be established through the limited arcing area.

Accordingly, a primary object of this invention is to provide a novel contact structure in which the main current carrying surfaces are not subject to erosion due to arcing.

Another object of this invention is to provide a novel circuit breaker contact configuration which incorporates the principles of both a jaw-contact system and a buttcontact system with only one of the contact systems being subject to arcing.

A still further object of this invention is to provide a novel jaw-contact arrangement which is provided with an additional butt-contact system which initially closes a circuit, and is the final contact element to separate during circuit breaker interruption whereby the cooperating jawcontact surfaces are maintained substantially free of erosion due to arcing.

Still another object of this invention is to provide a novel combined butt and jaw-contact arrangement for circuit breakers which can incorporate a plurality of parallel connected jaw-type contact systems with at least a single combined butt and jaw-contact system which supports all arcing duty during opening and closing of the system.

A still further object of this invention is to provide a novel combined butt and jaw-contact arrangement for circuit breakers which can incorporate a plurality of parallel connected jaw-type contact systems with at least a single combined butt and jaw-contact system which supports all arcing duty during opening and closing of the system where a narrow highly efiicient arc chute is provided only for the arcing contact element with the other main contacts disposed externally of the arc chute.

These and other objects of this invention will become apparent from the following description when taken in connection with the drawings, in which:

, FIGURE 1 is a side plan view of the stationary contact of a combined jaw and butt-contact arrangement made in accordance with the invention.

FIGURE 2 is a side view of FIGURE 1 as seen from the left-hand side of FIGURE 1.

FIGURE 3 is a cross-sectional view of FIGURE 1, taken across the section line 33 in FIGURE 1, which illustrates the stationary combined butt and jaw-contact arrangement with the blade contact in the disengaged position.

FIGURE 4 is similar to FIGURE 3 and illustrates the arrangement with the blade contact in the engaged position, with the butt-contact driven backwardly against the force of its outwardly biasing springs.

FIGURE 5 is a side plan view of a second embodiment of the combined blade and jaw-contact of the invention which is adapted especially for use as the arcing contact of a contact array.

FIGURE 6 is a side view of FIGURE 5 when seen from the left-hand side of FIGURE 5.

FIGURE 7 is a cross-sectional view of FIGURE 5 taken across the section line 77 in FIGURE 5.

FIGURE 8 is atop view of FIGURE 5.

FIGURE 9 is a perspective diagram of the contacts of a single pole for a circuit interrupter, which contacts incorporate the present invention, wherein the main con- 4 tacting section is of the type illustrated in FIGURES 5 through 8, while the main current carrying contacts include at least one contact of the type shown in FIGURES 1 through 4.

FIGURE 10 schematically illustrates a contact array constructed in accordance with the invention where only one of the contacts adapted to support arcing is provided with an arc chute.

Referring first to FIGURES 1 through 4, there is illustrated therein a main conductive support plate 20 which can form one terminal 21 in an electrical circuit which is to be interrupted. The terminal 20 has an extending boss 22 which carries the right-hand end of

conductive contact strips

23 and 24. Two elongated

conductive spacers

25 and 26 are spaced along the outer surfaces of

conductive strips

23 and 24 and

second contact strips

27 and 28 have their right-hand ends located

adjacent spacers

25 and 26. Aligned openings are then placed in the righthand ends of

members

27, 35, 23, 22, 24, 26 and 28, which receive a clamped bolt 30, which is terminated by a suitable washer 31 and nut 32 whereby the

conductive strips

23, 24, 27 and 28 are securely clamped mechanically and electrically to boss 22 of conductive strip plate 20. The left-hand end of

conductive strips

23, 24, 27 and 28 are then held in position by means of a hollow conductive tube 4-0, the ends of which are peencd over, as illustrated, on washers 41 and 42.

Suitable spring washers

43 and 44 are interposed between

conductive strips

23 and 27 and between

conductive strips

24 and 28, respectively, thereby tending to bias

strips

23 and 24 inwardly and toward one another. The ends of

strips

27 and 28 are then inwardly turned and shown as inwardly turned

sections

50 and 51 and are then reentrantly bent outwardly so that the interior surface of

end portions

52 and 53, respectively, are coplanar with the interior surfaces of

strips

23 and 24.

The

spring washers

43 and 44 would normally deflect strips 23 and 24 toward one another. However, the follower butt-contact 60 is interposed between strips 23 and 24 (and effectively between

sections

52 and 53 of contact strips 27 and 28) whereby the follower contact 60 is slidably interposed between the contact strips and engages the contact strips along the interior surfaces thereof. Note that in FIGURE 3 the left-hand end of follower contact 60 protrudes slightly beyond the ends of

conductive strip portions

52 and 53 The follower contact 60 has the shape shown in FIG- URE 1 whereby it is provided with a generally V-shaped groove 61 which permits motion of contact 60 to the right without interference with the conductive tube 40. A spring biasing structure is then provided to normally bias the base of V-shaped groove 61 of follower 60 into a stop position engagement with tube 40. This spring biasing system includes an elongated rod 62 which is secured to the right-hand end of follower contact 60 in any desired manner. By way of example, the follower contact 60 may have a vertical slot 63 therein which permits the contact to be slightly spread apart with the end of rod 62 in serted into a suitable drilled opening entering slot 63 with these members suitably fastened together as 'by welding, or threading, or the like. Note, however, the opposing top and

bottom surfaces

64 and 65 of the follower 60 should be as closely parallel as possible. The rod 62 then extends backwardly through an opening 70, which passes through boss 22, and plate 20, and terminates in a pistonshaped end 73 which seats against the biasing compression spring 74 contained in a spring-containing tube 75. As shown in FIGURES 1, 3 and 4, two identical spring containers 75 and 76 are provided where the container 76 will receive a second rod similar to rod 62 which also engages the contact follower 60 in a manner identical to that described for rod 62 in FIGURES 3 and 4.

The manner in which the spring containers 75 and 76 are held to the main support plate 20 is best shown in FIGURES 3 and 4 for container '75 wherein the plate 20 is provided with a chamber 80 which has a plate 81 bolted to extend partly across the opening of the chamber. Container 76 then has an outwardly flanged end which is captured beneath the interior of plate 81 whereby the container 75 (as well as the container 76) are flexibly held to the support plate 20 by the spring biasing force of spring '74.

The foregoing structure then defines the stationary combined jaw and butt-contact of the invention with the follower 60 serving as the butt-contact and the contact springs 23, 24, 27 and 28 serving as the jaw-contact. The

springs

43 and 44 bias the sides of

spring

23 and 24 into jaw-type sliding engagement with the sides of follower 60, while the securement of

strips

27 and 28 by tube 40' cause the engagement of

contact strip sections

52 and 53 in jaw-type sliding engagement with follower 60.

The movable blade contact, which then cooperates with this arrangement, is shown in FIGURES 3 and 4 as the moving blade 90 which is connected to some suitable operating mechanism 91 which moves the blade 953 in the direction illustrated by the arrows. The movable blade 90 may then be connected to a second terminal 92 with the contact structure opening and closing a circuit connected between

terminals

21 and 92. The blade 99 then has a width identical to the width of contact follower 6%) with the operating mechanism 91 moving blade 90 from the open position illustrated in FIGURE 3, to the closed position illustrated in FIGURE 4.

When moving to the closed position, the contact blade 90 will initially engage contact follower 60 in butt-contact fashion along the butt surfaces 93 and 94 of

contacts

90 and 60, respectively. The arcing due to pre-arcing and contact bounce will then occur mainly between

surfaces

93 and 94 with the contact erosion due to such arcing occurring on these surfaces. Current transfer during this initial period will then be from terminal 92 to blade 90 through the contact interface of

surfaces

93 and 94, the contact follower 60, and from the side surfaces 64 and 65 of contact follower 69 to the

conductive strips

23, 24, 27 and 2S, and thence to the main contact support 20 of the terminal 21. As the blade 90 continues to move inwardly toward its fully engaged position, it will initially move between the opposing sliding surfaces of

contact segments

52 and 53 without arcing, since a current connection has already been established between

surfaces

93 and 94. Thus, the blade 93 will eventually interpose itself between the side surfaces of

segments

52 and 53 and eventually between the opposing surfaces of contact strips 23 and 24 (again without arcing), whereupon a major current conduction path is established from blade 90 through its side surfaces 95 and 96, directly to the side surfaces of the contact blade strips 23, 24, 27 and 28. Note that this major current conduction is taken through clean surface areas which are not eroded by arcing during closing or opening, since all arcing has taken place between the opposing bu-tt surfaces 93 and 94.

During opening of the contact and going from the position of FIGURE 4 to the position of FIGURE 3, the contact blade slides with respect to the opposing surfaces of contact strips 23, 24, 27 and 28 without arcing since a current path remains through the butt-contact interface of

surfaces

93 and 94. Note that compression spring 74 moves contact follower 60 along with blade contact 90 as the blade contact is removed so that this butt current connection is retained. Once the follower contact 69 reaches the position of FIGURE 3, the continued movement of blade contact 90 to the left causes the final contact separation so that any arcing which now occurs is contained between the

interfaces

93 and 94 with the sliding butt and jaw-contact surfaces of both the blade contact 90 and strips 23, 24, 27 and 28 being kept clean and free of erosion.

FIGURES through 8 illustrate a second embodiment of the invention for a contact particularly well adapted to be the main arcing contact of any array of contacts in .a circuit interrupter. The structure of FIGURES 5 6 through 8 is generally similar in organization to that of FIGURES 1 through 4, but is provided only with a single biasing spring for the contact follower and a single pair of contact strips which form the jaw-contact portion of the interrupter. In addition, an arcing plate is provided for use with the contact follower.

Referring now to FIGURES 5 through 8, the main sup port for the stationary contact is comprised of a contact plate which carries an arcing contact plate 111, having the standard type of arcing horn 112 and a pair of L-shaped

conductive strips

113 and 114 which form the jaw-contact portion of the arrangement. All of these components are secured together by

bolts

115 and 116, as illustrated. The spacing of

conductive strips

113 and 114 is then fixed by the conductive tube which is peened over on

washers

121 and 122, as shown. A contact follower is then slidably disposed in sliding contact with the interior surfaces of strips 113 and 11 4 and contains a groove 131 (FIGURE 5) which receives tube 120 at the bottom thereof to serve as a stop for the maximum left-hand travel of the follower 130. Note that the appropriate contact pressure for good contact engagement between the opposing surfaces of contact follower 130 and

conductive strips

113 and 114 is obtained by the appropriate spacing of the ends of tube 120 which are peened over washers .121 and 122, as illustrated in FIGURE 7.

A spring biasing means for normally holding the contact follower 130 in its left-handmost position is then provided which includes the single rod having an enlarged head 141 terminated in spring-containing tube 142 which carries the compression spring 143. Tube 142 may then be connected to the main conductive support 110 in any desired manner as, for example, shown in FIGURES 3 and 4 for the case of tube 75. The stationary contact structure illustrated in FIGURES 5 through 8 will then cooperate with a movable blade contact (not shown) which operates in an identical manner to that described for FIGURES 3 and 4. Thus, all contact arcing will take place from the contact blade to the butt-contact surface 145 of contact follower 130 with the circuit continuing through the side surface engagement of the contact follower 130 in the jaw-contact type arrangement with

conductive strips

113 and 114. As the blade contact then drives the contact follower 130 backwardly and moves between

conductive strips

113 and 114, a jaw-type contact will then be established between the contact blade and the opposing surfaces of

conductive strips

113 and 114 in the manner previously described in FIGURES 1 through 4.

FIGURE 9 illustrates in perspective view an arrangement whereby a plurality of separate contact segments are arranged in accordance with the invention for obtaining a contact system wherein arcing is confined to buttcontact surfaces, while current flow is carried through clean surfaces in a jaw-contact type arrangement. In FIGURE 9, a stationary contact assemblage is provided which comprises a main support plate 151 which has a rearwardly extending terminal 152 which is to be connected to suitable circuit means. Suitable bosses extending from support plates 151, such as boss 152, mounts three

contact sections

153, 154 and where contact section 153 is identical to the arrangement shown in FIGURES 1 through 4, while

contact sections

154 and 155 are substantially identical to the arrangement of FIG- URES 1 through 4, except that the contact follower structure is eliminated. A similar arrangement is provided behind the

assemblies

153, 154 and 155 and comprises three additional assemblies 156, 157 and 158 which are pairs of opposing contacts each identical in construction to the

assemblies

154 and 155. That is to say, each of assemblies 156, 157 and 158 is identical to the arrangement of FIGURES 1 through 4 except that the contact follower structure has been removed. Note that for the the

rearwardly extending tubes

159 and 160 would cor- 7 respond identically to tubes 75 and 76 in FIGURE 1 and carry the biasing springs for biasing the contact follower 161 of FIGURE 9 outwardly.

In the arrangement of FIGURE 9, the elongated contact strips of assemblies 153 through 158 which serve as jaw-contacts all terminate in a common plane perpendicular to the direction of their elongation. The single contact follower 161, which is provided for the assemblage, then protrudes beyond this plane.

A main arcing contact arrangement is also provided in FIGURE 9, shown as the arcing contact arrangement 170, which is bolted to plate 151. The arrangement for the arcing contact 170 is identical in construction to that shown in FIGURES through 8, with the end of the contact strips protruding slightly beyond the plane of the ends of jaw-type contact strips for contact assemblies 153 through 158, while its contact follower 171 extends even further beyond this plane.

This entire stationary contact assembly then cooperates with the movable contact blade 180 which can, for example, be pivoted about a pivot 181 and driven by a suitable operating mechanism. The contact blade 180 is then composed of two blade sections 182 and 183- and a central arcing contact blade section 184. When the blade 180 moves into engagement with the contact assemblages 153 through 158 and arcing contact 1'70, blade portion 180 will initially engage follower 171 so that closing arcing occurs between the front butt surface 185 and blade portion 184 and the front butt surface of follower 171. As the blade 180 continues to rotate toward its fully engaged position, follower 171 will be driven backwardly and blade portions 182 and 183 will be inserted between the opposing jaw-type contact strips of contact assemblies 152454455456-157-158, respectively. Note that the blade 182 will initially engage follower 161 with all subsequent arcing which has not been prevented by the engagement of blade portion 184 and contact portion 170 being confined between the abutting surfaces of follower contact 161 and the corresponding abutting surface of blade 182. The main current conductive path which is eventually established, however, will be through the side surfaces of

blade portions

182, 183 and 184 and their respective stationary contact portions 153 through 158 and 170. Thus, main current conduction always occurs through clean, uneroded contact surfaces while all arcing due to opening and closing of the contacts will cause erosion only of the abutting surfaces of contact followers 161 and 171 and the respective abutting portions of

blade portions

182 and 184.

FIGURE schematically illustrates the electrical connection between various contacts constructed in accordance with the invention and the manner in which only one of the contacts responsible for arcing conditions can be contained within an arc chute. This permits the use of a narrower arc chute which thereby permits an increased magnetic field strength, and permits mounting of the parallel contacts outside of the arc chute.

FIGURE 10 shows three parallel connected contacts which are stationarily mounted, including contact assemblies 200, 201 and 202. Contacts 200 and 201 are main contacts where contact 200 is constructed in the manner described in FIGURES 1 through 4 and contains jawcontacts 203, 204, 205 and 206. A sliding butt-type contact 207 slides within the jaw-contacts 203 through 206 and is biased to the left by the biasing means 208. The center contact 201 is constructed similarly to contact 200 except that it has no provision for the follower type contact 207. Contact 201 is comprised of the jaw-contact members 210 through 213 with each of the contact segments connected electrically to each of the contact segments of contact 200. The arcing contact 202 is then constructed in the manner described in FIGURES 4 through 8 and comprises the jaw-

contact segments

215 and 216 which carry follower contact 217 which is biased at the left by the biasing spring 218. A movable contact blade having

blade sections

219, 220 and 221 carried ona common movable arm 222 then moves into and out of engagement with the contacts 200 through 202 by the common operation mechanism 230. The movable contact arm 222 is then connected to a terminal 231 while all of the contact segments of contacts 200, 201 and 202 are connected to the common terminal 232. FIGURE 10 then illustrates an important aspect of the invention, in that it permits the use of an arc chute, schematically illustrated by dotted lines 240, to cooperate with only one of the contacts adapted for arcing such as contact 202 in FIGURE 10. The remaining contacts, such as contacts 200 and 201 may then be positioned externally of the arc chute since these contacts are not subject to arcing duty, since arcing duty will be absorbed by the butt surface contact sections of follower contact 217 and blade contact 221. Therefore, the contacts mounted exteriorly of the arc chute can now be subject to improved cooling not affected by the surrounding confines of the standard are chute.

Although this invention has been described with respect to its preferred embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in the art, and it is preferred, therefore, that the scope of the invention be limited not by the specific disclosure herein, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A cooperating contact structure comprising a first blade-type contact, and a second combined butt and jawcontact; said first contact movable into and out of contact with said second contact and having a first contact surface disposed generally normal to the direction of travel of said first contact and at least one side surface disposed generally parallel to the direction of motion of said first contact; said second contact comprising a conductive jaw-contact having a contact surface disposed generally parallel to the direction of travel of said first contact and a movable follower contact member; said movable follower contact member having a first surface normal to the direction of motion of said first contact and engageable with said first contact surface of said first contact, and having a second contact surface in sliding contact with said contact surface of said conductive jaw-contact; said second contact surface of said first contact slidably engaging said contact surface of said conductive jaw-contact when said first and second contacts are engaged; biasing means connected to said movable follower contact member for normally moving an end portion of said movable follower contact member containing its said first contact surface beyond the end of said conductive jaw-contact and beyond all the conductive parts of said second contact; said first contact movable into engagement with said second contact in a sequence whereby said first contact surface of said first contact engages said first contact surface of said movable follower contact member, and said second contact surface of said first contact thereafter engages said contact surface of said conductive jaw-contact, moving said movable follower contact member rearwardly against the force of said biasing means in sliding contact with said contact surface of said conductive jaw-contact; said second contact surface of said movable follower contact member remaining in sliding contact with said contact surface of said conductive jaw-contact throughout said sequence for maintaining constant pressure of said contact surface of said conductive jaw-contact on said second contact surface of said first contact.

2. The structure as set forth in claim 1 which includes second biasing means biasing said second surface of said movable follower contact member into engagement with said surface of said conductive jaw-contact.

3. The structure as set forth in claim 2 wherein said second contact surface of said first contact comprises opposing parallel surfaces of a conductive body, and wherein said contact surface of said conductive jaw-contact comprises opposing parallel surfaces of first and second extending conductive members, and wherein said second conductive surface of said movable follower contact member comprises opposing parallel surfaces; said movable follower contact member interposed between said first and second extending conductive members.

4. The structure as set forth in claim 3 wherein the spacing between said opposing parallel surfaces of said first contact is equal to the spacing between said opposing surfaces of said movable follower contact member.

5. The device as set forth in claim 1 which further includes a parallel connected cooperating contact structure substantially identical, respectively, to said first contact and at least said conductive jaw-contact portion of said second contact; the ends of said conductive jaw-contacts lying in a generally common plane; said normal surfaces of said first contacts lying in a generally common plane.

6. The device as set forth in claim 5 which further includes arc chute means; said are chute means enclosing said first and second contacts; said further parallel connected cooperating contact structure disposed exteriorly of said are chute.

References Cited UNITED STATES PATENTS 2,426,387 8/1947 Caswell 20()---146 2,455,998 12/ 1948 Hoye 200146 ROBERT K. SCHAEFER, Primary Examiner.

H. O. JONES, Assistant Examiner.