US2337889A - Electric circuit breaker - Google Patents

Description

1943- w. c. HARLOW ET AL 2,337,889

ELECTRIC CIRCUIT BREAKER Filed May 29, 1942 2 Sheets-Sheet 1 M wmm W wmm amaa n w ram v n oa 0 50m tH W t mm n. D

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Dec. 28, 1943. w.' G. HARLOW ET AL ELECTRIC C IRCUIT BREAKER Filed May 29, 1942 2 Sheets-Sheet 2 /IIIIIIIIIIIII/I co /=5)? WOOL 6A5 PRODUCING /N5ULAT/0N (FIBER ETC.)

Inventors:

Harlow, George A. Healis,

Winton G Edwin A. Williams Jr,

Their Attorney.

Patented Dec. 28, 1943 um'rso STATES PATENT orrica ELECTRIC CIRCUIT BREAKER Winton G. Harlow. Chatham Village, and George A. Healis and Edwin A. Williams, Jr., Lansdowne,Pa., asslgnors to General Electric Company, a corporation of New York Application May 29, 1942, Serial No. 445,054

7 18 Claims. (Cl. 200-146) electrically eflicient, durable and weatherproof and has large current interrupting capacity without exxternal evidence of arcing.

Our invention will be more fully set forth in the following description referring to the accompanying drawings, and the features "of novelty which characterize our invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawings, Fig. 1 is an elevational view, partly in section. of a load-break switch embodying the present invention in the closed circuit position thereof; Fig. 2 is a similar view showing the device in the partly open circuit position prior tothe final disconnecting operation; Fig. 3 is an enlarged sectional end view of the interrupting unit of Figs. 1 and 2; Fig. 3a is a sectional plan View taken along the section line 3a,3a of Fig. 3; Fig. 4 is a detailed plan view of terminal and contact structure taken along the section line 4-4 of Fig. 1; Fig. 5 is 2. diagrammatic illustration of the operation of the interrupting contacts; Fig. 6 is a view similar to Fig, 1 showing a modified form of the breaker gas venting arrangement; and Fig. 7 is a detail view, enlarged, taken along the section line '|-'l of Fig. 6.

The circuit breaker of the load-break, switch type illustrated by way of example, comprises, referring first to Fig. 1, two relatively fixed spaced conducting terminals I and 2 which are suitably mounted on an insulating supporting panel 3. The terminals, to which the power line conductors (not shown) are electrically connected, are adapted to be bridged by a main current-carry ing blade structure 4 that is pivotally mounted at 5 on the lower terminal I. The upper terminal 2 is provided with contact structure at 6 arranged to be engaged by the blade 4. The

terminals l and 2 (including the associated contacts) and the blade i normally constitute the main power circuit for the breaker.

For the purpose of extinguishing arcing when the breaker is opened on load, the main blade 4 carries an arc extinguishing device I. that is so mounted on the blade as to be automatically controlled thereby. The device I constitutes astructural unit including an insulating housing 8 for enclosing relatively movable arcing contacts 9-4 H and ll-lZ. These arcing contacts are composed of a suitable arc-resisting metal, such as tungsten impregnated with copper, and are adapted to form two breaks in series in an interrupting circuit between the terminals l and 2. This interrupting circuit also includes a movable disconnecting contact I3 mounted on the interrupting unit I and controlled thereby so as'to separate from the terminal structure at 2 only after opening of the main current-carrying blade 4 and separation of the arcing contacts 9I0 and lll2.

Before describing in detail the structural arrangement of the complete circuit breaker, the essential steps in the operation thereof will be briefiy described. When the main blade is closed ed to engage and release the blade hook-ring M,

from the blade latch l4. As the blade swings open, the disconnecting contact l3 at first remains in the closed position and the power current is transferred without arcingto the interrupting circuit including the arcing contacts 9-H] and H-i2.

After predetermined opening movement of the blade 4, the interrupting device I is then operated, so as to open the arcing contacts for interrupting within the insulating housing 8 the power current now traversing the interrupting circuit. Opening of the interrupting circuit is then followed by opening movement of the disconnecting contact l3. The disconnecting contact is finally spring biased toward the blade as illustrated by the dotted line position of Fig. 1. This biasing operation also recloses the arcing contacts. This final disconnecting operation introduces a suitable air gap between the movable contact structure and the upper terminal 2.

When the breaker is closed the interrupting circuit is completed first, i.'e., when the disconnecting contact l3 makes electrical contact at the terminal 2. With the power current flowing through the interrupting circuit, the main blade 5 can now be closed without burning or arcing at the current-carrying surfaces.

The interrupting unit 1 isconveniently mounted on the main blade 4 between a pair of spaced conductingstri ps constituting the blade as best illustrated by Fig. 3. The insulating housing 8 of the unit, which is formed by halves of molded insulating material clamped together, supports the arcing contacts I and I2 and the movable disconnecting contact I3. Within the insulating housing, there is mounted for rotative movement a rotor I that supports the inner arcing contacts 9 and II previously referred to. The rotor I5 is likewise formed by halves of molded in-. sulating material suitably clamped together. The arcing contacts 9 and II are roller-like members which are mounted on pinsin conducting bracket-like contact supports 9' and Il respectively. The conicts 9 and ii are biased into normal contact making engagement with the housing contacts by a compression spring I6, and are electricallly connected (through the roller pins and contact supports) by a flexible conducting braid 61. This rotor contact assembly is suitably mounted centrally of the rotor within a space formed by grooves in the rotor halves.

As best shown by Fig. 3, the rotor i5 is provided with a pair of stub shafts I8 having squared portions at I8 embedded as inserts in the molded material of the rotor. The stub shafts I8 are journaled in the two side members of the main blade 4 so as to provide the main rotatable support for obtaining proper operation of the rotor I5 as the main blade is opened, there is provided a gear arrangement between the enclosing housing 8, the blade 4, and the rotor I5 Briefly, this gear arrangement causes, after initial separation of the main blade movement inopposite directions between the housing and the rotor, i. e., referring to Fig. 2, as the housing 8 is rotated counterclockwise on the blade 4 due to holding engagement of the disconnecting contact I3 at the terminal 2, the' rotor I5 is rotated clockwise thereby introducing two breaks inseries in the interrupting circuit.

The specific gear arrangement for accomplishing this comprises, referring first to Fig. 1, an internal gear segment I9 carried by the housing 8, a pinion 20 in mesh with said gear segment and a spur gear 23 in mesh with said pinion. The spur gear is mounted on the squared portion I8 of one of the stub shafts I8. The pinion 20 is mounted on a pin 2| on a supporting bracket 22 that is secured at 22' to the main blade structure (see Fig. 3).

From the foregoing, it will be apparent that relative counterclockwise movement of the hous ing 8 from its normal position shown in Fig. 1 due to opening movement of the main blade causes clockwise movement of the rotor I5 through the relatively fixed pinion 20.

This operation is shown diagrammatically by Fig. 5 which indicates a vertical axis of the arcing contacts when the switch is in the closed circuit position. During the interrupting operatior'neach break is lengthened due to two factors, namely, 1) the counterclockwise rotation of the housing 8 anditscontacts, and (2) the clockwise rotation of the rotor and its contacts. It is apparent that this relative movement of the housing and the rotor in opposite directions results in a. greater separating break-distance. Also, since the break-distances are along arcuate paths, thereby providing breakdown gaps of greater length than in the case of straight line breaks,

4 from its contact, relative rotational.

the interrupting unit on the blade. For

the apparatus can be more compact for a given voltage rating.

In the specific example shown, the housing 8 just prior to release and separation of the disconnecting contact I 3 is rotated 35 counterclockwise from the original contact axis, and the rotor moves clockwise through an angle of approximately 84. This makes a total separating break of 119" for each break which is amply suflicient not only for interrupting heavy load current arcs but also for preventing reestablishment of arcing. Although, as illustrated by Fig. 5, the movable arcing contacts are spaced when in the open circuit position but 61 from the housing contacts of the opposite pair; .this isolating distance is quite sufiicient since the insulating surfaces through this angle are relatively cool and of high dielectric strength since they have not been in contact with the arc proper.

When the arcing contacts have been fully separated in the manner above described, continued opening movement of the main blade causes separating movement of the disconnecting contact I3 from the contact-latch arrangement shown in Fig. 4. The disconnecting contact I3 bears in wiping contact engagement on a spring contact finger 25 suitably connected to the upper terminal structure 2, this wipe being sufficient to permit initial separation of the main blade prior to opening of the arcing contacts. For the purpose of holding the disconnecting contacts I3 and 25 in engagement during'the arc interrupting operation, a latch member 26 pivotally mounted on the terminal structure at 21 is spring-biased at 28 so as to hold the disconnecting contact against its coacting contact. The latch 26 near its free end is provided with a shoulder 26 adapted to be engaged by the rod contact I3 after an initial wiping movement along the contact 25. This initial movement corresponds to the initial opening movement of the main blade 4. When the contact I3 engages the shoulder 26' it is temporarily restrained and further opening movement of the main blade causes relative movement of the housing and rotor contacts in the manner above described to interrupt the circuit.

Continued clockwise movement of the main blade, referring to Fig. 2, lowers the disconnecting contact I3 out of engagement with the shoulder 26'. The interrupting unit 'I is now free of the stationary termnal structure at 2. When this takes place, the housing 8 carrying the disconnecting contact I3 is rotated clockwise by a spiral biasing spring 29 (Fig. 3) having its inner end connected at 38 to one of the stub shafts I8 and the outer end at 3| to the housing 8. The spring 29,'which is flexed when the disconnecting contact I3 is restrained by the latch 26 as the blade 4 is initially opened, therefore restores the housing and the contact structure to their original relative position with respect to the main blade 4 as illustrated by the dotted line position of Fig. 1. A buffer member 4' on the blade serves also to position the disconnecting contact.

When the circuit breaker is closed by counterclockwise movement of the blade assembly, the disconnecting contact I3 first engages the camming surface 26 of the latch 26 so as to move the latch to one side against the bias of its spring (see Fig. 4). As the contact I3 moves into sliding engagement with the contact 25 the latch snaps behind it. Since the arcing contacts in the unit I are also closed, the power circuit is complete through the interrupting circuit and the main blade can now engage the main fixed contacts at 6 without arcing.

The specific arc extinguishing structure and the conducting path through the housing 8 will now be described. The rotor I .is journaled in the housing 8 by means of hub-like insulating extensions 32 of the rotor and is spaced at the outer periphery thereof from the housing so as to form a narrow arc chamber of arcuate shape. This arc chamber is formed between two concentriand 34 which are secured respectively to the housing and the rotor. These cylinders are slightly spaced as illustrated so that. the are drawn at .the two breaks is confined to a narrow restricted breaker attendant is not subiected to danger and the dielectric strength of the isolating gap is not impaired. Highly heated arc gases in the vicinity of high voltage apparatus may cause voltage break-down with serious results. In disposing of these gases, we provide means for both cooling the gases and for mufiiing the sharp report incident to are interruption in addition to directing the gases in harmless directions.

To this end, referring first to Fig. 3, the lower arc chamber space at the contacts |l-|2 communicates through apertures in the cylinder 33 with passages 35 leading to the exterior of the unit through a tube 36 filled with a porous heatabsorbing material 31, such as copper wool. The are gases can flow from the passages 35 into the tube by way of slots 36', as clearly shown in Fig. 2, so as to be directed laterally in opposite directions from the tube 36 at the lower end of the housing.

This gas cooling device also has another function in that it provides a conducting path from the housing contact I2 to the main blade 4. The contact i2 is mounted on a conducting block 35', in which the passages 35 are formed, and which is clamped between the halves of the housing 8. This conducting block 35' is in turn electrically connected to one side member of the blade 4 by a resilient conducting strip 38. The strip 38 is connected at 39 to the conducting block and is spring-biased at 40 into sliding conducting engagement at 4| with the blade 4.

The upper housin contact In is connected to the disconnecting contact l3 by a conducting tube 42. The tube 42, whichis suitably secured at its upper end as illustrated to the disconnecting contact has attached thereto at its lower end the contact ID. This end of the tube isrexpanded to form a gas passage 43 communicating through alined apertures in the cylinder 33 with the arc space. This passage is conveniently formed by slotting the tube 42 at opposite sides to form tongue-like members 42 that are bent outwardly in opposite directions as illustrated. The tube 42, as in the previous case, contains copper wool or the like 31 for cooling the arc gases and mufliing the arc interruption. The exhaust end of the venting passag includes slots 44 at the cally disposed cylinders of insulating material 33 upper part of the tube communicating with an annular space 45 in the insulating housing that terminates finally, after reversal in direction, in lateral vent openings 46 as best shown in Figs. 2 and 3a. It will therefore be seen that the arc gases are directed laterally and away from the upper terminal 2 after passing through the cooler and mufiier. Breakdown of the disconnecting or isolating gap is therefore efiectively guarded against.

It will also be noted that this arrangement of the gas venting passages provides substantially weather-proof protection for the unit for outdoor use since there is little possibility of rain being driven into the unit by reason of the inverted U-shape venting passage. Th lower downwardly directed venting passage beneath the housing is also substantially weather-proof. For completing the weather-proof protection, a cover plate 41 is provided for the housing recess in which the spiral spring 29 is mounted and a similar cover plate 48 is provided for the recess in the opposite side in which the gearing l9 20-23is located. K

A further operating consideration in outdoor use is that of ice accumulation on the terminals. By reason of the angular prying action of the disconnecting contact i3 as it is initially operated by the blade, the ice is easily broken at this point so that there is no difliculty in obtaining complete disconnection after the interrupting operation.

The molded material of the housing 8 and rotor 15 has both high dielectric strength and rugged physical characteristics. For the purpose of further increasing the dielectric strength of the space between housing and rotor, the parts are preferably corrugated as shown at 49 for increasing the length of the creepage path.

A very practical advantage of the circuit breaker and disconnecting unit above described resides in its compactness. This compactness is made possible by mounting the comparatively short disconnecting contact together with the interrupting unit on an intermediate part of the main blade for rotary movement while at the same time providing maximum disconnecting distance in the open circuit position (Fig. 1).

There is shown by Figs. 6 and 7 a modified form of the gas venting arrangement for the interrupting unit. In this design the arc gases are also cooled and directed laterally away from the upper terminal 2. In addition to this, the arc gases are so directed from the arc chamber to the venting passages that a cross-blast or expulsion effect on the arc is obtained. This has been .found to result in improved arc interrupting ability.

Referring now to Fig. 6 which illustrates in general the interrupting unit I of Figs. 1 and 2, the insulating housing 8 is provided at its upper and lower sides with gas exhaust passages 50 and 5|, respectively, leading from the arc chambers of the two sets of interrupting contacts so as to exhaust in lateral directions from the housing. As best shown by Fig. '7 which illustrates the upper passage, the housing 8 also has formed therein grooves 52 leading laterally from one side of the narrow arc chamber 53 around the corresponding ends of the fibre cylinders 33 and 34 to the exhaust passage 50. Accordingly the arc gases are expelled laterally of the arc chamber 7 toward one side (the opposite side being closed) as indicated by the flow-direction arrows so that a high velocity cross-blast efiect is obtained at the arc. As indicated by Fig. 6, the arc is subjected to this cross-blast action shortly after separation of the contacts while the arc is still short.

The hot arc gases are suitably cooled by a muilling and cooling device 54 mounted in the exhaust end of passage 50. The device 54 may comprise, for example, stacked corrugated copper sheets disposed edgewise to gas flow, or the like, for freely venting the arc gases while cooling them.

Since the lower exhaust passage 5| is arranged substantially the same as passage 50, further detail description thereof is unnecessary as simi lar reference numerals indicate similar structures.

It shouldbe understood that our invention not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the spirit of our invention.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. An electric circuit breaker comprising a pair of relatively fixed terminals, a main current carrying blade structure arranged electrically to bridge said terminals, and an arc extinguishing unit comprising relatively rotatable members mounted on and carried by said blade, a plurality of relatively movable arcing contacts carried by said relatively rotatable members and arranged electrically in an interrupting circuit between said terminals, said unit being controlled by movement of said blade for causing relative ro-' tative circuit controlling movement of the aforesaid arcing contacts.

2. An electric circuit breaker 'of the load-break switch type comprising a pair of relatively fixed terminals, a main current carrying blade structure arranged electrically to bridge said terminals, an arc extinguishing unit comprising a pair of relatively rotatable members, a plurality of relatively movable arcing contacts carried by said rotatable members and mounted for rotative movement on said blade and included in an interrupting circuit between said terminals, said unit being controlled by movement of said blade for interrupting the circuit at said arcing contacts after initial opening movement of said blade.

3. An electric circuit breaker comprising a pair of relatively fixed terminals, a main current carrying blade structure pivotally mounted at one of said terminals and arranged electrically to engage the other of said terminals, an arc extinguishing unit comprising a pair of relatively rotatable members, a plurality of relatively movable arcing contacts also arranged electrically in an interrupting circuit between said terminals. said arcing contacts being supported on said relatively rotatable members, said unit being mounted on said blade intermediate its ends and including contact operating means for said arcing contacts controlled by pivotal movement of said blade for causing separate rotative movement of the arcing contacts subsequent to separation of said blade from said other of said terminals.

4. An electric circuit breaker comprising a pair of relatively fixed terminals, a main current carying blade structure arranged electrically to bridge said terminals, an arc extinguishing unit carried by said blade having relatively movable arcing contacts also arranged electrically in an interrupting circuit between said terminals, said unit including two coacting rotatable contact controlling members operable in site directions by and in accordance with movement of said blade for controlling and interrupting the circuit in said unit after initial opening movement of said blade.

5. An electric circuit breaker of the loadbreak switch type comprising a pair of relatively fixed terminals, a main current carrying blade structure arranged electrically to bridge said terminals, an arc extinguishing unit carried by said blade having relatively rotatable insulating mem bers carrying arcing contacts also arranged electrically in an interrupting circuit between said terminals, one of said insulating members also having a disconnecting contact connected in series with said arcing contacts and arranged to be in engagement with one of said terminals during relative rotation of said insulating members and arcing contactsand to separate from said one of said terminals subsequent to interruption of arcing within said unit.

6. An electric circuit breaker comprising a pair of relatively fixed terminals, a main current carrying blade structure pivotally mounted at one of said terminals and arranged electrically to engage the other of said terminals, an arc extinguishing unit rotatably mounted on said blade having a relatively movable housing and rotor each carrying arcing contacts arranged to be connected in an interrupting circuit between said terminals, means interconnecting said housing, rotor and blade for controlling said contacts in accordance with the operation of said blade, said unit also including a disconnecting contact connected in series with said arcing contacts and arranged to be in engagement with said other of said terminals 'for carrying the load current after initial opening of said blade, said disconnecting contact being controlled by said blade to separate from said other of said terminals subsequent to circuit interruption by the arcing contacts of said unit.

7. An electric circuit breaker comprising a pair of relatively fixed terminals, a main cur'rent carrying blade structure, arranged electrically to bridge said terminals, an arc extinguishing unit mounted on and carried by said blade comprising an insulating housing, an insulating rotor in said housing, coacting arcing contacts carried by said housing and rotor, means for mounting said housing and rotor with respect to said blade so that both said housing and rotor are rotatable with respect to each other and with respect to said blade, a disconnecting contact carried by said unit arranged to be in series with said arcing contacts and to engage one of said terminals thereby forming an interrupting circuit for the main power current, and means operatively relating said blade to said unit so that after predetermined initial opening movementof said blade the power current is transferred to said interrupting circuit and said rotor and housing are relatively rotated to cause separation of said arcing contacts so that-the circuit is interrupted within said housing, continued opening movement of said blade causing said disconnecting contact to be disengaged from the aforesaid terminal to provide a disconnecting gap in the circuit.

8. An electric circuit breaker comprising a pair of relatively fixed terminals, a main current carrying blade structure arranged electrically to bridge said terminals, an arc extinguishing unit mounted on and carried by said bl e comprising an insulating housing, an insulating rotor in said housing, coacting arcing contacts car-- ried by said housing and rotor respectively, means for rotatably mounting said housing and rotor on said blade, a disconnecting contact carried by said unit arranged to be connected in series with said arcing contacts and to engage one of said terminals thereby forming an interrupting circuit for the main power current, and gear means operatively interconnecting said blade, housing and rotor so that after initial opening movement of said blade, said rotor and housing are rotated relative to each other to cause separation of said arcing contacts and interruption of the circuit within said housing, continued opening movement of said blade causing said disconnecting contact to be disengaged from the aforesaid terminal so that it can move therefrom to provide a disconnecting gap in the circuit.

9. An electric circuit breaker comprising a pair of relatively fixed terminals, a main current carrying blade structure arranged electrically to bridge said terminals, an arc extinguishing unit mounted on and carried by said blade comprising an insulating housing, an insulating rotor in said housing, coacting arcing contacts carried by said housing and rotor respectively, insulating gas-producing structure mounted on said housing and rotor respectively adjacent to the periphery of said rotor and spaced to form a restricted, arcuate arc extinguishing chamber,

means for rotatably mounting said housing and rotor on said blade for controlling said arcing contacts, a disconnecting contact controlled by said unit arranged to be connected in series with said arcing contacts and to engage one of said terminals thereby forming an interrupting cir- 10. An electric circuit breaker having a mov-.

able main current-carrying blade and an arc extinguishing unit controlled and carried by said blade comprising an' insulating housing, an insulating rotor member mounted within said housing, coactingarcing contacts carried by said housing and rotor member respectively arranged so that rotative movement of said member relative to said housing in response to predetermined operation of said blade causes circuit controlling operation of said contacts, and means forming a narrow arcuate shaped arc chamber between said rotor member and housing comprising spaced. and substantially concentrically arranged arcuate strips composed of gas emitting material mounted on said housingand rotor member .respectively.

11. An electric circuit breaker having a movable main current-carrying blade and an arc extinguishing unit controlled and carried by said blade comprising an insulating housing, an in sulating rotor member mounted within said housbetween said rotor member and housing comprising spaced and substantially concentrically arranged cylinders composed of gas emitting material mounted on said housing and rotor member respectively, the are formed between said contacts being extinguished between said cylinders by the gases released.

12. An electric circuit breaker comprising an insulating housing, an insulating rotor member mounted within said housing, coacting arcing contacts carried by said housing and rotor member respectively arranged so that rotative movement of said member relative to said housing causes circuit controlling operation of said contacts, means forming a narrow arc chamber between said rotor member and housing comprising spaced walls of gas emitting material on said housing and rotor member respectively, said chamber being closed at one side, and means for directing gases released from said walls during arcing laterally from said chamber at the opposite sidethereof so that the arc in said chamber is subjected to cross-blast extinguishing action.

13. An electric circuit breaker comprising an insulating housing, an insulating rotor member mounted within said housing, coacting arcing contacts carried by said housing and rotor member respectively arranged so that angular rotative movement of said member relative to said housing causes circuit controlling operation of said contacts, means forming a narrow arcuate shaped arc chamber between said rotor member and housing, and means for increasing creepage distance at opposite sides of said arc chamber between said contacts in the open circuit position including corrugations formed both on the insulating side walls of said rotor member and on the adjacent inner side walls of said housing.

14. An electric circuit breaker comprising a pair of relatively fixed terminals, a main current carrying blade arranged electrically to bridge said terminals, an arc extinguishing unit mounts ed on and carried by said blade, said unit comprising an insulating housing rotatably mounted on said blade, an insulating rotor mounted within said housing, coacting arcing contacts carried by said housing and rotor respectively arranged to be in an interrupting circuit between said terminals, and a gear train interconnecting said blade, housing and rotor for controlling said arcing contacts in accordance with the operation of said blade for insuring interruption of the circuit at said arcing contacts within said housing.

15. An electric circuit breaker comprising a pair of relatively fixed terminals, an are extinguishing unit included in an interrupting circuit between said terminals, said unit comprising a disconnecting contact arranged to coact with one of said terminals, an insulating housing, an insulating rotor mounted for angular movement within said housing, coacting arcing contacts carried by said housing and rotor respectively arranged to be in series with said disconnecting contact in said interrupting circuit, means for controlling said unitfor insuring interruption of the circuit at said arcing contacts within said housing prior to separation of said disconnecting contact from its terminal, and resetting spring means operatively interrelating said disconnecting contact and arcing contacts biased so as to move said disconnecting contact to an isolating position and to reclose said arcing contacts subsequent-to said circuit interruption, the circuit thereby being made at said disconnecting contact and. its terminal in the next closing operation.

16. An electric circuit breaker comprising a pair of relatively fixed terminals, a pivoted main current carrying blade arranged electrically to bridge said terminals, an arc extinguishing unit including a pair of relatively rotatable members and a disconnecting contact materially shorter than said blade arranged to coact with one of said terminals mounted on and carried by said blade at an intermediate part thereof, said unit comprising coacting arcing contacts arranged to be in an interrupting circuit in series with said disconnecting contact between said terminals, means for controlling said unit in accordance with the operation of said blade for insuring interruption of the circuit'at said arcing contacts prior to separation of said disconnecting contact from its terminal, and means for biasing said disconnecting contact towards said blade so that both said blade and said disconnecting contact are materially spaced from the aforesaid terminal in the open isolating position.

17. An electric circuit breaker comprising a pair of relatively fixed terminals, a main current carrying blade arranged electrically to bridge said terminals, an arc extinguishing unit rotatably mounted on and carried by said blade, said unit comprising a disconnecting-contact and co acting arcing contacts arranged to be connected in series in an interrupting circuit between said terminals, said disconnecting contact being in wiping electrical contact with respect to one of said terminals, means for controlling said unit in accordance with the operation of said blade so that said blade can move to open position during the wiping contact engagement of said disconnecting contact thereby transferring the power current to said interrupting circuit, and means for opening said arcing contacts subsequent to opening of said blade and during said wiping engagement for insuring interruption of the circuit at said arcing contacts.

18. An electric circuit breaker comprising a pair of relatively fixed terminals, a pivoted main current carrying blade arranged to make and break contact with one of said terminals and electrically to bridge said terminals, an are extinguishing unit rotatably mounted on and carried by said blade, said unit comprising a disconnecting contact and coacting arcing contacts arranged to be connected in series in an interrupting circuit between said terminals, said disconnecting contact being in wiping electrical contact with respect to said one of said terminals, means for controlling said unit in accordance with the operation of said blade 50 that said blade can move to open position during the wiping contact engagement of said disconnecting contact thereby transferring the power current to said interrupting circuit, means for temporarily restraining said disconnecting contact in engagement with the aforesaid terminal, means for causing opening of said arcing contacts when said disconnecting contact is restrained in response to further opening movement of said blade for insuring interruption of the circuit of said arcing contacts, further opening movement of said blade causing said disconnecting contact to be disengaged from the aforesaid terminal, and biasing means for thereupon moving said disconnecting contact away from the aforesaid terminal toward isolating position.

WINTON G. HARLOW. GEORGE A. HEALIS. EDWIN A. WILLIAMS, JR.

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