US2214471A

US2214471A - Circuit breaker

Info

Publication number: US2214471A
Application number: US216708A
Authority: US
Inventors: Leon R Ludwig; Merl E Horn
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1938-06-30
Filing date: 1938-06-30
Publication date: 1940-09-10
Anticipated expiration: 1957-09-10
Also published as: DE759249C; CH214010A; NL62088C; FR855804A

Description

Sept. '10, 1940- L. R. LUDWIG E'r AL I- CIRCUIT BREAKER 4 sheet-sheet 2 Filed June so, 193e INVENTRTS' Leon l? ludwzglAmfd Meri E. Horn.' x Y f lvn-roRNV a m 4 t u T.. Kimm@ mmm. l I N 2, Q www m WUH m s )1.1. /A 4 7m@ ww /JM M um m n m m w, wu m U U J M d I e R c m L W, L M 1, W S w @WM i m. N n www Sept. l0, 1940.

L. R. LUDWIG ET AL CIRCUIT BREAKER Filed June 30, 1938 4 Sheets-Sheet 4.

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INVENTORS H. Lucwi WITNESSES:

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Mer! @I R/ATTORNE Patented Sept. 10, 1940 UNITED STATES PATENT OFFICE @IRUUIT BREAKER Application June 30, i938, Serial No. 216,708

2i) Claims.

The invention relates to circuit breakers in general and more particularly to contact systems for air circuit breakers.

Conventional air circuit breakers are usually provided with one or more auxiliary sets of contacts which are designed to bypass a large portion of the current for a short interval of time during circuit interruption for the purpose of minimizing burning or pitting of the main contacts. `It has been the usual practice to connect the auxiliary contacts to the main contact either by individual resilient conductors on which the contacts are y mounted, or by individual exible shunts.- The resistance and reactance of these connections are relatively high with the result that a considerable voltage drop exists across the main contacts during interruption of heavy magnitude currents. This produces undesirable arcing between the main contacts, thus o'setting to some extent the eectiveness of the auxiliary contacts. When the auxiliary contacts are mounted closer to one another and to the main contacts to reduce the resistance and reactance of the electrical coniuections,r cross-arcing between the contacts and connections takes place which in some instances causes the parts to become welded together. Also, when resilient conductors are used, it has been found that the conductors become annealed by the passage of heavy magnitude currents so that they lose much of their resiliency.

een object of the rpresent invention is the provision of a circuit breaker embodying an improved contact system which obviates the abovementioned electrical andmechanical diiiiculties, and which is simple and less expensive to manufacture than the contact systems of the prior art devices.

In air circuit breakers embodying a main movable contact of the bridging type, the magnetic eld produced by surge currents causes the bridging contact to lift off of the stationary contacts and when the voltage drop across the main contacts is large, large current arcs are drawn which damage the contacts. Attempts have been made to increase the contact pressure by increasing the strength of the biasing springs for the bridging-contact vto prevent lifting of the contact on surge currents. It was found, however, that when the strength of the biasing springs was increased an amount sufficient to prevent liftingvof the contact, the latching and tripping load of the breaker was increased beyond desirable limits.

Another object of the invention is the provision of a circuit breaker embodying amain (Cl. 20D-146) bridging contact and auxiliary contacts, in which the bridging contact is biased toward the stationary contacts by a comparatively light force which permits it to lift oi of the stationary contacts at a predetermined value of'current above the maximum rated current of the breaker, but which is low enough that any arcs which may be drawn between the bridging contact and the stationary contacts are `of such low magnitude that they will not burn or pit the contacts.

Another object of the invention is the provision of a circuit breaker-with an improved contact system which provides a minimum voltage drop between the main contacts when the current is transferred to the auxiliary contacts, and which prevents arcing between the main contacts.

Another object of the invention is the provision of an improved contact system for a circuit breaker which eliminates the necessity of providing individual exible shunts or resilient conductors for each of the auxiliary contacts.

Another object of the invention is the provision oi an/improved Contact system for a circuit breaker which utilizes a common flexible shunt for connecting the auxiliary contacts to the terminals of the breaker.

Another object of the invention is the provision of a'n improved contact system for a circuit breaker in which a single flexible shunt conductor connects all of the auxiliary contacts to their corresponding terminals and isV arranged to eiectively neutralize the magnetic forces tending to blow the auxiliary contacts apart.

Another object of the invention is the provision of an improved contact system for a circuit breaker in which the flexible shunt connections are arranged to maintain the bridging contact separated from the stationary contacts when the current exceeds a predetermined value and which at the same time prevents the magnetic force from blowing the auxiliary contacts apart until after the main contacts'are separated a predetermined safe distance.

Another object. of the invention is the provision of an improved contact system for a circuit breaker embodying rigid main and intermediate contacts which are mounted in such a manner as to provide the required contact pressure, and

to separate in the propersequence during opening of the breaker.

The novel features that are considered characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to structure and operation, together with additional objects and advantages 2 thereof wm be been understood from' the' fonowing detailed description of one embodiment thereof the breaker showing the contact means in an initial stage of a circuit opening operation when the bridging contact has :lust separated from the main stationary contacts; o

Fig. 4 is a view similar to Fig. 3 showing the relative positions of the parts at a later stage in the opening operation when one pair of the auxiliary contacts have just separated;

Fig. 5 is a view similar to Fig. 3 showing the contact means in the full open position:

' Fig. 6 is a view similarv to Fig. 3 showing the switch member in closed position and the bridging contact lifted from the stationary contacts by the magnetic force of the current;

Fig. 'I is a fragmentary front elevational view of the stationary contact means; and

Fig. 8 is a longitudinal sectional view taken through the contact means.

Referring to the drawings, and particularly to Fig. 1 thereof,hthe reference numeral designates a base of insulating material which vsupports the various parts of the circuit breaker. A pair of terminal members |43 and I5 are mounted in spaced relation on the base by means of a plurality of bolts I1, and each of the terminal membershas a plurality of blades I9 for connlfting the breaker to an external electrical circ t. o

The upper terminal I3 has a contact block 2| of rigid conducting material secured thereto. A contact block 23 also of rigid conducting material is electrically connected to the lower terminal I5 through the winding of the trip coil |24 of the breaker. 'I'he contact blocks 2| and 23 form the main stationary contacts of the circuit breaker, and their adjacent edges are beveled and have a pair of

main contact tips

25 and 21 secured thereon. The

contact tips

25 and 21 are prefer ably formed of silver or an alloy of silver and are secured to the beveled edges of the blocks 2| or 23 either by brazing or by mechanical means. The stationary contact means, including the main contacts 2| and 23, also includes auxiliary contact means comprising a platform 29d-rigid conducting material on which is mounted an intermediate contact 3| and an arcing contact 33,

the contacts 3| and 33 being secured on the front surface of the'platform 29 either by brazing or by mechanical means. The arcing contact 33. which is mounted on the upper end of the platform 29, is-preferably formed of a suitable conducting material which resists deterioration by electric arcs, and this Contact is provided with an arcing horn 35.-v

'I'he auxiliary contact platform 29, which has side walls 31 and an end wall 39 (Figs. 'T and 8), is mounted for limited bodily and tilting move-.- ment relative to the base II toward the movable contact means of the breaker by means of a transverse pin 4|, which extends through the I -side walls 31 and has its ends engaged inA elongated slots 43 provided ina pair of guide brackets 45 mounted on the base II. 'I'he platform 29 is biased away from the base I I toward the movable contact means of the breaker by three springs 41, 49'and 5|. Two of the springs 41 and 49 (Fig. 7)

are interposed between the platform 29 and the upper main contact 2| adjacent the lower comers of the platform. The third spring 5| encircles a ,guide stud 53 mounted on the base, and its outer end engages the platform 29 beneath the arcing contact 33.

A loop-shaped exible conductor 51 disposed between the side walls 31 of the platform 29 electrically connects the platform to the upper terminal I3, the ends of the conductor being secured to the. platform 29 and the terminal I3 by pairs contact means of the breaker islimited by the engagement of the ends of the pin 4I with the outer ends oitheslots 43 in the guide brackets 45. A pair of ears 6I extending from the side walls 31 adjacent the upper end of the platform are adapted to engage extensions 63 of the guide brackets 45 to limit movement of the upper end -of the, platform 29 toward the movabl contact means. An insulating bale 52 isrmounted on the Vcontact block 2| to shield the main contacts of the breaker from arcs drawn between the auxiliary contacts during circuit interruption.

The movable contact means of the circuit breaker comprises a channel-shaped contact arm 65 of conducting material, which is rigidly secured f to a pivoted switch member 61 by means of a plurality of screws 39. The contactarm car- 'ries a main contact bridging member 1I for bridging: the main contacts 2| and 23, and an auxiliary contact member 13 for engaging the auxiliary contacts 3| and 33 of the stationary contact means.

The main contact bridging member 1| is formed of rigid conducting material, such as copper or an alloy of copper, and is loosely mounted for limited movement relative to the contact arm 65 toward and away from the main contacts 2| and 23 on a pair of studs 15 carried by the contact arm 65. The free ends of the studs 15 have a pair of nuts 11 mounted thereon for limiting movement of the bridging member 1| toward the main contacts 2| and .23. A pair of coil springs 19 encircle the studs'15and are disposed between the contact arm 55 andthe bridging member 1| for biasing the bridging member toward the stationary main contacts 2| and 23 with a predetermined force. The ends of the bridging member 1I are beveled and have a pair oi contact tips 8| of silver or silver alloy secured thereon for engaging the

stationary contact tips

25 and 21.

The auxiliary contact member 13 isformed of rigid conducting material, preferably copper, and is secured to the upper end of the contact arm 65 by a pair of bolts 83. The contact member 13 has an intermediate contact 85 and an arcing contact 81 secured thereto either by brazing or by mechanical means, for engaging the intermediate and arcing contacts 3| and 33 of the stationary contact means. 'Ihe movable arcing contact 81 is preferably formed of a suitable arc resisting material similar to that of the arcing contact 33, and is provided with an arcing horn 39.

A common iiexible shunt conductor 9| elec-V trically connects the auxiliary contact member u 13 and the bridging member 1| to the main stationary contact 23. The conductor v9| has its upper end clamped between the auxiliary contact member 13 and the contact arm 65 by one of the bolts 93, and its lower end is secured to a portion of the lower main stationary contact 23 by means of bolts 93. 'I'he intermediate portion of the conductor 9| is secured at two points to the bridging member 1| by a pair of screws 95, the

lower portion of the shunt being looped over the pivot pin 99 which supports the movable switch member 61. In the case of higher current ratings, the movable bridging member 1| may be split into two parallel bridging members and the common flexible shunt 9| also split into two parallel shunt conductors, each being connected to one of the parallel bridging members. The provision oi two parallel bridging members allows them to be ventilated and cooled so that they can carry larger amounts of current and still keep within the permissible temperature rise.

'I'he switch member 61 has a yoke-shaped lower end which is pivotally mounted on the side walls of a main frame 91 by means of a pivot pin 99. The switch member is movable about its pivot axis to open and closed circuit positions to open and close the contact means of the breaker by means of an operating mechanism indicated generally at The operating mechanism |0| may be of any suitable type but is preferably similar to the mechanism which is fully described in the copending application of Walter M. Austin, Serial No. 118,588, led December 31, 1936, and assigned to the assignee of the present invention, now Patent No. 2,177,014, issued October 24, 1939. The mechanism is supported by the frame 91, and comprises in general an actuating f lever |03 pivoted on a pin carried by the frame and connected to the switch member by means of a link |01, an operating member |09 also pivoted on the pin |05, and a trip device The actuating lever |03 is normally and releasably connected to the operating member |09 for movement thereby by a pair of latches ||3 and ||5 carried by the lever |03, the latch ||3 oi which engages a roller ||1 carried bythe operating member |09. 'I'he operating member |09 is adapted to be releasably held in closed circuit position by means of a latch I I9 which releasably engages the roller ||1. The trip device comprises a pivoted trip'member |2| which is ioperable to release the latches ||5 and ||3. The trip lever is operable either manually, or by a tripping electromagnet |23 in response to predetermined conditions. 'I'he tripping electro` magnet has anenergizing winding |24 which is connected in series between the lower terminal |5 and the lower main contact block 23 so as to be traversed by the current iiowing throughthe breaker.

The switch member 61 is biased in a clockwise direction toward open circuit position by a pair of opening springs |25. When the latches ||0 and ||3 are released by the trip device A| the springs |25 move the switch ymember 91 and the actuating lever |03 to open circuit position in dependently of the position of the operating memberA |09. As the actuating lever |03 moves to open circuit position, it effects release of the latch ||9 which releases the operating member |09.

To close. the circuit breaker, the operating member |09 must be moved in a counter-clockwise directionto open position to reset the latches ||5 and k| I3 and reestablish the connection be-v tween the operating lever |09 and the actuating lever |03. 'Ihe operating lever |09 is then moved in a clockwise direction to the closed position shown to eiiect movement of the switch member 91 in a counter-clockwise direction to closed cir-= cuit position., When the operating lever |09 reaches closed position, the latch H9 reengages the roller |1 to hold the operating lever in closed position.

' Referring to the contact means of the breaker, it will be noted that when the switch member 61 i is in closed circuit position, the bridging member 1| engages the stationary main contacts 2| and 23 to establish a normal path for the current through the main contacts and the bridging member, the springs 19 maintaining a predetermined contact pressure between the contact tips 8| of the bridging member 1| and the

contact tips

25 and 21 ofthe main contacts. The intermediate and arcing contacts 90 and 81 of the auxiliary contact member 13 also engage the intermediate and arcing contacts 3| and 33 oi the contact platform 29 when the switch member is in closed circuit position. However, substan tially no current flows through the intermediate and arcing contacts because ofthe low resistance of the main current path through the main contacts 2| and 23 and the bridghg member 1|. It

base with the springs 41, 49and 5| compressed when the switch member is in closed position, and also that the bridging member 1| is near its limit of movement toward the base relative to the contact arm 65 with the springs 19 slightly compressed.

'I'he operation of the contact means is brieiiy as follows: When the switch member 91 is moved in a clockwise direction to open circuit position by the opening springs |25 following operation of the trip device the lnuts 11 on. the studs 15 engage the bridging member 1| during the initial portion of the movement and cause the bridging member 1| to vseparate from the main contacts 2| and 23 and move toward open circuit position with the contact armi 95 and the switch member 91. During the rst portion of the Vopening movement bt, the switch member 01, the

biasing'springs

41, 49 and 5| cause the auxiliary contact platform 29 to move outwardly from the base and follow the auxiliary contact member 13 to maintain the intermediate' and arcing contacts 3| and 33 of the platform in pressure engagement with the intermediate and arcing

contacts

85 and 81 of the movable auxiliary contact member 13 until the bridging member 1L has been separated a predetermined distance from the main contacts 2| and 23.

As soon as the bridging member 1| separates from the main contacts 2| and 23, the current which previously owed through the contact members 2|,23 and 1| is shunted around these contact members and iiows through an auxiliary path from the lower main contact 23 through the exible shunt conductor 9|, auxiliary contact member 13,

intermediate contacts

85 and 31|, the lower portion of the contact platform 29 an`v mediate contact 3| oi?` the contact platform 29.

` tain the arcing vthe auxiliary contact member tacts in pressure The ears 6| of the contact platform 29 are so disposed thatthey permit the upper end of the platform 29 to continue to move outwardly from the base after the pin 4| has engaged the outer ends of the slots 43 until the intermediate contact 85 has been separated a predetermined distance from the intermediate contact3| of the platform 29. The upper biasing spring 5| causes thecontact platform 29 lto rotate'in a clockwise direction about the pin 4| as an axis to maincontact 33 in pressure engage'- ment with the arcing contact 81 of the auxiliary contact member 13 until the intermediate contact 85 has been separated from the intermediate contact 3| the predetermined distance. As ,soon as the intermediate contact 85separates from the intermediate contact 3| the current which previously'owed through these con-l tacts is shunted through a second auxiliary path from the lower main contact 23 through the flexible shunt 9|, auxiliary contact member 13, arcing

contacts

81 and 33 through the contact platformi 29 and the flexible shunt conductor 51 to the upper main contact 2|.` Due to the fact that 13 and the platform 29 are of rigid 'conducting material and that-the spring 5| maintains the arcing conengagement so that their contact drop is low, the resistance and inductance of this second auxiliary path for the current is only a very small amount greater than the aux- 'iliary path through the intermediate contacts 81 and 3|. The low resistance and inductance of the auxiliary paths forthe current reduces the difference of potential between the bridging member -1| and the main contacts, and also the difference of potential between the intermediate contacts 85 that substantially little or no arcing takes place between these contact members during interruption of the circuit.

As soon as the intermediate 'contact 85 has been separated a predetermined distance `fromJ the intermediate contact 3| of the platform 29,

the stop ears 6| engage the extension 53 ofthe brackets 45, as shown in Fig. 4. The continuedopening movement of the switch member 6 1 then causes the arcing contact 81 to separate from .the arcing contact 33 of the platform 29. The full open .circuit position of the contact arm i l' and switch member is` shown in Fig. 5.

4 .When the switch-member is moved to closed circuit position,v the arcing

contactsy

81 and 33 engage and complete the circuit before the intermediate-contacts 85 and 3| are brought into engagement, and the bridging member 1| engages the main contacts 2| and 23 in the nal portion of the closing movement of the switch member after the intermediate'and arcing contacts have been brought into engagement.

It will be seenfrom the above description that the mounting of the intermediate and arcing contacts on members of rigid conducting material eliminates the necessity of providing indiand` 3| when they are separated, sol

vidual flexible or resilient conductors for the intermediate and arcing contacts and materially reduces the resistance and inductance of the auxiliary paths for the current. The mounting arrangement of the auxiliary contact platform and its biasing m'eans causes the intermediate and arcing contacts to remain in engagement until the bridging member has been separated a predetermined safe distance from the main stationary contacts, and also causes the intermediate contacts to separate before separation of the arcing contacts so that all arcing takes place between the arcing contacts of the breaker.

In order to prevent burning and pitting of the main contact surfaces by any arcs that may be drawn between the bridging member 1I and the main contacts 2| and 23 when extremely large surge currents flow through the breaker, the biasing springs 19 for the bridging member are made comparatively weak so that the force exerted thereby on`the bridgingmember 1| permits the magnetic force produced by through the main contacts 2| and 23 and the bridging member 1| to separate the bridging member 1| from the main contacts at 'a predetermined value of current in excess of the maxinium tripping current rating ofthe breaker, the predetermined value of current being low enough that any arcs that may beydrawn between the bridging member 1| and the main contacts 2|v and; 23 are of such low magnitude that they will not materially burn or pit the main contact surfaces. For example, a breaker having a rating of 600 amperes inservice might easily be subjected to short circuit or surge currents having a peak value of about 100,000 amperes. Under such conditions,l if the bridging member were separated from the main contacts at any value of current near this peak value, the arcs drawn between the bridging member and the main contacts would be of such high magnitude in spite'of the intermediate and arcing contacts being in shunt therewith that thearcs would burn or pit the main contact surfaces. According vto the present invention, in the case of a breaker having a rating of 600- amperes, the bridging member biasing springs 19 would be selected to have such a strength that they would permit the magnetic force of the current to separate the bridging member from the stationary main contacts at approximately 10,000 amperes or approximately six- .teen times normal rated current. Any arcs drawn between the bridging member and the main ,contacts at this value of current would be o1' such low magnitude that they would not materially burn or pit the main contact surfaces. The

value of current at which the springs are designed to permit lifting or blowing open of the bridging' member may be higher or lower than the approximate valuen given in the above example. For a breaker of any given current rating the lower limit ofthe current at which the bridging member is permitted to blow open must be above the normal current rating of the breaker and is limited bythe fact that the biasing springs must have sufficient strength to produce the required 1normal contact pressure so as to keep within the permissible temperature rise. 'Ihe higher the value of current at which the bridging member is allowed to blow open the greater will be the `amount of burning or pitting of the main contact surface. In determining the strength of the, biasing springs for the main bridging member which consequently determines the value of curthe current flowing rent at which the bridging member will be blown open, these two factors must be considered, and the springs should be selected of such strength that the value of current which will cause blowing open of the bridging member will be at some value intermediate the lower and upper permissible limits. This value of current may range from several times the normal current rating of the breaker up to a fraction of the maximum interrupting capacity of the breaker. From ten to twenty times the normal current rating has been found satisfactory. I

As soon as the bridging member H is separated -irom the main contacts 2| and 23 by the magnetic force of the current, the current is shunted through the flexible Ashunt conductor Si, which is connected to the auxiliary contacts, and the arrangement of this flexible shunt conductor is such that the magnetic force produced by the current iiowing therethrough maintains the bridging member 1i separated from the main contacts at all values of current in excess of the predetermined value at which the bridging member is designed to separate from the main contacts.

The looped shape of the flexible conductor 51 causes the current which flows through the conductor to produce a magnetic force whichl effectively neutralizes the magnetic forces tending to blow the auxiliary contacts apart, and assists the biasing springs to maintain the auxiliary contacts in engagement until the bridging member has been separatedapredetermined distance from the main contacts by opening movement of the switch member 61, while the bridging member 1I is separated from the main contacts by the magnetic force of the current.

An arc extinguishing structure indicated generallyat |21 is mounted on the upper portion of the base Afor extinguishing the arcs drawn between the arcing

contacts

81 and 33 during interruption of the circuit. The arc extinguishing structure 121 may be of any suitable type, but is preferably of the type fully described in the copending application of L. R. Ludwig, Serial No. 216,884, Bled July 1, 1938, and assigned to the assignee of the present invention.

While the invention has been disclosed in accordance with the provision of the patent statutes, it is to be understood that various changes in the structural details thereof may be made without departing from the spirit of the invention. It is desired, therefore, that the appended claims be given the broadest reasonable interpretation permissible in the light of the prior art.

We claim as our invention:

1. In a circuit breaker, a base, contact means on said base comprising a main contact of rigid conducting material and a member of rigid conducting material of high electrical conductivity electrically connected to said main contact and .aving spaced intermediate and arcing contacts, movable switch means for opening and closing the circuit comprising a movable main contact ofrigid conducting material for engaging the main contact on said base, a movable member of rigid conducting material electrically connected to said movable main contact and having spaced intermediate and arcing contacts for engaging the intermediate and arcing contacts on said base, and means for causing said main contacts to separate a predetermined distance before said intermediate and arcing contacts separate and for causing said arcing contacts to separate after said intermediate contacts have separated during each circuit opening operation of said switch means, said intermediate and arcing contacts being spaced a suiclent distance apart to prevent restriking of an arc between said intermediate contacts. 5

2. In a circuit interrupter, a pair of relatively movable contact means for opening and closing the circuit, each of said contact means comprising a main contact of rigid conducting material and a member of rigid conducting material of w high electrical conductivity electrically connected to said main contact and having a Vplurality of spaced metal contacts rigid with said member forming auxiliary contacts, a movable switch member for opening and closing said contact means, and means for causing said main contacts to separate a predetermined distance before said auxiliary contacts separate and for causing said auxiliary contacts to separate in a predetermined order during a circuit opening operation.

3. In a circuit breaker, a pair of separable contact means for opening and closing the circuit, each of said contact means comprising a main contact member of rigid conducting material, a member of rigid conducting material of high electrical conductivity `electrically connected to said main contact member and having a plurality of spaced metal contact portions rigid with said member forming auxiliary metal contacts, and a support for said members; one of said rigid conducting members and one of said main contactmembers being mounted for limited movement on its support and biased toward its cooperating member of the other contact means.

4. In a circuit breaker, a pair of relatively mov- 5 able contact means. for opening and closing the circuit, each of said contact means comprising a main contact of rigid conducting material, a member of rigid conducting material having a plurality of contact portions forming auxiliary contacts, and a flexible shunt conductor for electrically connecting said rigid conducting member to said main contact; means mounting and biasing one of said rigid conducting members to cause said auxiliary contacts to separate in a predetermined order after 'said main contacts have separated a predetermined distance during a circuit opening operation of the breaker, and for causing said rigid member and its auxiliary contacts to automatically self-align with the auxiliary contacts of the other contact means when said auxiliary contacts are engaged.

5. In a circuit breaker, stationary contact means comprising a main contact and a member .of rigid conducting material having a plurality of contact portions rigid with said member forming intermediate and arcing contacts, a movable switch member for opening and closing the circuit, a main contact carried by said switch member for engaging the stationary main contact, a member of rigid conducting material carried by said switch member having contact portions rigid with said member forming intermediate and arcing contacts for engaging the intermediate and ment of said switch member, and a exible shunt conductor connecting said rigid conducting member of said stationary contact means to said stationary main contact.

6. In a circuit breaker, relatively movable contact means for opening and closing the circuit, one of said contact means-comprising a main contact, an auxiliary contact platform of rigid conducting material mounted on a support for limited movement relative to the support toward and away from the other contact means, auxiliary contacts on said platform, spring means biasing said platform toward said other contact means, a bowed flexible shunt conductor disposed in back of said platform connecting said platform to said main contact, said platform having sidewalls and an end wall forming an enclosure for said shunt to protect said shunt from arcs drawn between said contact means.

7. In a circuit breaker, relatively movable main and auxiliary contacts, means for opening and closing said contacts, one of said main contacts being mounted for limited movement relative to its support toward and away from the other main contact and being biased toward said other main contact with a predetermined force, means forming a normal path for the current through said main contacts, and van auxiliary path for the current through said auxiliary contacts, the magnetic force produced by the currentin owing through said paths causing said one main contact to separate from said other main contact and to vremain separated therefrom when said current exceeds a predetermined value in excess of the maximum normal current rating of the breaker, said predetermined value of current being low enough that any arcs that may be drawn between said rnain contacts will not materially burn or pit the main contacts.

8. In a circuit breaker, relatively movable main and auxiliary contacts, means for opening and closing said contacts, one of said main contacts being mounted for limited movement toward and away from the other main contact when the breaker is closed and being biased toward said other main contact, means for causing said one main contact to separate and remain separated from said other main contact when the current jowing through said breaker exceeds a predetermined value in excess of the maximum current rating of said breaker, said predetermined value of current being low enough that any arcs drawn between said main contacts will not damage said main contacts.

- 9. In a circuit breaker, relatively movable main and auxiliary contacts, means for opening and Aclosing said contacts, one of said main contacts being mounted for limited movementtoward and away from the other main contact when the breaker is closed and being biased toward said other main contact, means for causing said 'one main'contact to separate and remain separated from said other main contact when the current flowing through said breaker exceeds a prede-'- termined value in excess of the maximum current rating of said breaker, said predetermined value of current being low enough that any arcs.

drawn between said main contacts will not dam- `age said main contacts, and means for causing said auxiliary contacts to remain in engagement until said main contacts have separated a preldetermined distance in excess of the limited movement of said one main contact.

10. In a circuit breaker, relatively movable maincontacts, relatively movable auxiliary contacts connected to said main contacts for shuntcontact from the other when the current owing g through said breaker exceeds a predetermined valuev in excess` of the current rating of said breaker and which maintain said main contact separated at all values of current in excess of said predetermined value, said predetermined value of current being low enough that any arcs drawn between said main contacts will not niaterially damage the contacts.

11. In a circuit breaker, relatively movable main contacts, relatively movable auxiliary contacts connected to said main contacts for shunting the current around said main contacts during opening of said main contacts until said main contacts have separated a predetermined distance, .means for opening and closing said contacts in a predetermined order, one of said main contacts being mounted for limited movement toward and away from the other main contact when the breaker is closed and being biased toward said other main contact, 4:and means for producing magnetic forces which separate said one main contact from said other main contact and maintain said contacts separated when the current owing through said breaker exceeds a soV `.predetermined value in excess of the current rating of said breaker and which maintain said auxiliary contacts in engagement until said main contacts have been separated a predetermined distance by an opening operation of said breaker, said predetermined value of current being low enough that any arcs which may be drawn between said main contacts will not materially damage said main contacts.

12. In a circuit breaker having a base and a pair of spaced terminals, a pair of stationary contacts on said base electrically connected to said terminals, an auxiliary contact on said base electrically connected toy one of said terminals, a movable switch member for opening and closing the circuit, said switch member having a bridging member for bridging said stationary contacts and an auxiliary contact for engaging the auxiliary contact on said base, said bridging member being mounted on said switch member for limited movement relative thereto toward and away from said stationary contacts, a spring for biasing said bridging member toward said stationary contacts, a exible shunt conductor connecting the auxiliary contact of the switch member and the vbridging member to the opposite terminal of. the breaker, said spring permitting the magnetic force of the current flowing through said stationary contacts and bridging member to separate said bridging member from said sta- -tionary contacts when the current exceeds a predetermined vaiue, and the magnetic force produced by the, current owing through said flexible shunt maintaining said bridging member separated from said stationary contacts at all values of current in excess of said predeter- 1 mined value, said predetermined value of current amarsi 7 between said bridging member and said stationary contacts will not materially damage said contacts and said member.

13. In a circuit breaker, stationary contact means comprising a main contact and an auxiliary contact, a movable switch member for opening and closing the circuit, said switch member having main andauxiliary contacts for engaging the main and auxiliary contacts of said stationary contact means, one of said main conf tacts being mounted for limited movement toward and away from the other main contact when the breaker is closed, a spring for biasing said one main contact toward said other contact with a predetermined force which permits said contact to separate from the other main contact when the current flowing through said breaker exceeds a predetermined value in excess oi the normal current rating of the breaker, said predetermined value being low enough that any arcs drawn between said main contacts will not materially damage the main contacts, a flexible shunt conductor connecting said one main movable contact and its auxiliary contact to one terminal of said breaker, said shunt actinglto main-` tain said one movable contact separated from said other main contact at all values of current in excess of said predetermined value, and means for causing said auxiliary contacts to remain engaged until said main contacts have separated a predetermined distance in excess f theiimited movement of said main contact.

i4. in a circuit breaker, stationary contact means including a pair of main contacts and an aurdiiary contact, a 'movable contact arm for opening and closing the circuit, a bridging member carried by said arm for bridging said main contacts and an auxiliary contact carried by said arm ier engaging the auxiliary contact of said stationary contact means, said bridging member being mounted for movement reiative to said contact arm toward and 'away from said stationary contact means, spring means ior biasing said bridging member toward said main contacts with a predetermined iorce, and a demble shunt conductor connecting said allary contact on said contact arm and said bridging :member to one terminal ci said breakere 1 i5. in a circuit breaker, stationary contact means' including a pair of stationary main contacts and an auxiliary contact. a movable contact arm for opening and closing the circuit, a bridging member carried by said arm and movable a limited amount relative thereto toward and away from said stationary contacts, spring means for biasing said bridging member toward said stationary contacts with a predetermined force, an auxiliary contact carried by said arm for engaging the auxiliary contact of said stationary *contact means, and a flexible shunt conductor connectingthe auxiliary contact of said contact arm and said bridging member to one terminal of said breaker, said shunt being secured to said bridging member at at least two points intermediate the ends of said bridging member.

16. In a circuit breaker, stationary contact means including a pair of spaced main contacts and a member of rigid conducting material having a plurality of contact portions forming auxiliary contacts, a movable contact arm for opening and closing the circuit, a main contact bridging member mounted on said arm for limited movement relative to said arm toward and away from said main contacts, spring means biasing said bridging member toward said main contacts, a member of rigid conducting material mounted on said arm having a plurality of contact portions forming auxiliary contacts for engaging the auxiliary contacts of said stationary contact means, a common exible shunt conductor connecting the rigid member of said contact arm and said bridging member to one of said main contacts, a second flexible shunt conductor connecting the rigid member of said stationary contact means to the other of said main contacts, means mounting the rigid member of said stationary contact means for limited movement toward the rigid member ci said contact arm and for biasing said rigid member toward the rigid member of said contact arm to cause said auxiliary contacts to separate in a predetermined order and only after said bridging member has separated a predetermined distance from said main contacts during opening of the breaker, said spring means permitting the magnetic force produced by the current owing through said main conl tacts and bridging member to separate said bridging member from said main contacts when the current exceeds a predetermined value, and said common flexible shunt maintaining said bridging member separated from said main contacts for all value, said predetermined value of current being in excess of the current rating of the breaker but low enough that any arcs drawn between said bridging member and said main contacts will not materially damage said contacts and member.

i7. 1n a circuit breaker, stationary contact means comprising a main contact and a member oi rigid conducting material having a plurality of spaced contacts rigid withsaid member forming auxiliary contacts, a movable contact means having a main contact and a plurality of auxiliary contacts for engaging the contacts of the -stationary contact means, means mounting said rigid member of the stationary contact means for limited movement toward and away from the movable contact means and spring means biasing said member toward said movable contact means, and a nezdble shunt conductor connecting said rigid member to the main stationary contact and forming a path for the current which causes the magnetic force produced by the current in flowing through said shunt to bias said rigid member toward the movable contact means.

i8. in a circuit breaker, a pair of spaced terniinals, stationary contact means comprising a pair of spaced main contacts electrically connected respectively to said terminals, and a member of rigid conducting material of high electrical conductivity adjacent one of said contacts, said member having an intermediate contact and an arcing contact rigid with said member, a movable switch member for opening and closing the circuit, a bridging contact member carried by said switch member for bridging said main contacts, said bridging member being mounted for limited movement on said switch member toward and away from said main contacts and biased toward said main contacts, a member of rigid conducting material of high electrical conductivity carried by said switch member and having intermediate and arcing contacts rigid with said member for engaging the intermediate and arcing contacts of said stationary contact means, a single iiexible shunt conductor connecting the rigid conducting member and the bridging contact member of said movable switch member to one terminal of said breaker, means for movably mounting and biasing the rigid conducting member of said stationary contact means to cause said intermediate contacts to separate after said bridgingl contact `member has separated a. predetermined distance from said main contacts and to cause said arcing contacts to separate after said intermediate contacts have separated during opening movement of said switch member, and a flexible shunt conductor connecting the rigid conducting member of said stationary contact means to the adjacent main contact.

19. In a circuit breaker, a pair of spaced terminals, stationary contact means comprising a stationary main contact connected to one of said terminals, and a member of rigid conducting material of high electrical conductivity having an intermediate contact and an arcing contact rigid with said member, a movable switch member for opening and closing the circuit, a main contact mounted for limited movement on said switch member toward and away from the stationary main contact and biased toward said stationary 'main contact, a member of rigid conducting ma- `terialiof high electrical conductivity carried by tact means to cause said, intermediate contacts to separate after said main contacts have separated a predetermined distance and to cause said arcing contacts to separate only after said intermediate contacts have separated during opening movement of said switch member, and a flexible shunt conductor connecting the rigid conducting member and the stationary main contact of said stationary contact means.

20. In a circuit-breaker, a pairof spaced ter-- intermediate and an arcing contact rigid with said member, a movable switch member for opening and closing the circuit, a main contact mounted on said switch member for limited movement relative to said switch member toward and vaway from the said stationary main contact and biased `toward said stationary main contact, a member of rigid conducting material of high electrical conductivity carried by said switch memberiand having an intermediate and an arcing contact rigid with said member for engaging the intermediate and arcing contacts of said stationary contact means, a single exible shunt conductor connecting the rigid member and main contact carried by said switch member to the other of said terminals, means movably mounting and biasing said rigid conducting member of said stationary contact means to cause said intermediate contacts to separate after said main contacts have separated a predetermined distance and to cause said arcing contacts to separate only after said intermediate contacts have separated during opening movement of said switch member, and for causing the intermediate and arcing contacts of said stationary contacts to automatically self-align with the cooperating contacts carriedl by said switch member, and a exible shunt'conductor connecting the rigid conducting member and the stationary main contact of said stationary contact means.

LEON 11..l LUDWIG.

MERLE. HORN.