US2285040A - Circuit breaker - Google Patents

Description

June 2, 1942. J. w. MAY

CIRCUIT BREAKER Filed Aug. 3, 1940 2 sheets-sheefli INVENTOR W WITNESSES: $5M. 1%. m

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CIRCUIT BREAKER Patented June 2, 1942 CIRCUIT BREAKER John W. May, Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsyl- Vania Application August 3, 1940, Serial No. 350,904

15 Claims.

The invention relates to circuit interrupters, in general, and, more particularly, to a circuit breaker mechanism and tripping means therefor.

Standard types of circuit breakers usually embody a rather strongly biased releasable circuit opening member normally restrained by a latching mechanism which is adapted to be released by an electro-responsive trip device. It is desirable to provide a construction in which only a very light tripping force is required to trip the breaker. On the other hand, many circuit breakers require a strong bias on the latch for maintaining it in latching engagement to prevent the breaker from being falsely tripped by shocks or jars arising either from an outside source or from the shocks which occur when the breaker is reclosed.

As a particular example, circuit breakers used in automatic network protectors must be designed to trip on a minimum of 15 volts for the standard 2G8 volt 60 cycle network system. A further limitation is the amount of current, that the relay contacts for the shunt trip magnet will carry at normal operating voltage, amounting to approximately 15 amperes. Therefore, the shunt trip assembly designed to meet these limitations will depend largely on its size for the tripping force which it will develop. If the tripping load of the breaker is small, for example 6 to 8- ounces, a compact shunt trip' assembly can be used, but if the tripping load is one pound or more the shunt trip magnet becomes too large to meet the limited space requirements. One conventional type of circuit breaker of 225 ampere rating when used in a n twork protector requires a 2*"! ounce spring to hold the latch in latching position in order to make the breaker shock-proof on a reclosing operation. This heavy spring plus the actual breaker load on the latch has a combined eiiect of more than 20 ounces tripping load at the shunt trip plunger. This large tripping load in addition to the minimum trip voltage and limited trip current require a larger shunt trip assembly than is desired.

An object of the invention is the provision of an improved circuit breaker mechanism having a very light tripping load so that it is capable of being tripped by the application of a relatively small tripping force by the electro-responsive trip means.

Another object of the invention is the provision of a circuit breaker embodying avery compact shunt trip assembly which is capable of tripping the breaker mechanism on a minimum percentage of the normal operating voltage at a small value of current.

Another object of the invention is the provision of an improved circuit breaker construction in which thecircuit breaker mechanism is strongly held in latched position against false tripping by shocks or jars and yet which has a very light tripping load so that it is capable of being tripped by a relatively small tripping force from the electro-responsive trip means.

Another object of the invention is the provision of an improved shockproof circuit breaker which is capable of being tripped by a relatively small tripping force.

In accordance with one specific embodiment of the invention, the circuit breakerhas a latching means which is biased to latching position by a relatively weak spring, and a second strong spring is disposed between the latching mechanism and the electro-responsive trip means for strongly maintaining the latching means in latching position against false tripping, the arrangement being such that when the electro-responsive trip means is actuated to trip the breaker, only the light spring is compressed and the force of the strong spring does not have to be overcome with the result that only a light tripping force is required to trip 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 thereof, will be best understood from the following detailed description of one embodiment thereof when read in conjunction with the accompanying drawings, in which:

Figure 1 is a fragmentary sectional View of a circuit breaker embodying the features of the invention, the breaker being shown in the closedcircuit position; and

Fig 2 is a View similar to Fig. 1 showing the position of the parts the instant the breaker has been tripped by the tripping means.

The invention is illustrated as applied to a circuit breaker of a network protector wherein tripping or automatic opening of the circuit breaker is effected by the operation of a shunt trip electromagnet. The network protector may be of the type disclosed in Patent No. 1,997,697 of J. S. Parson, issued April 16, 1935, and assigned to the assignee of the present invention. The shunt trip electromagnet is adapted to be energized from across two of the phases of the secondary network and controlled by a master relay which is operated to cause tripping of the breaker in response to a reversal of direction of the electric power flow through the breaker as disclosed in the aforementioned patent.

A circuit breaker constructed in accordance with the invention and a portion of the frame of the network protector on which it is mounted are shown in the accompanying drawings. The other parts of the network protector have not been shown since they are not necessary for a complete understanding of the invention.

Referring to the drawings, the reference numeral designates a portion of the frame of the network protector. Acircuit breaker indicated generally at 1 is mounted on the frame 5 by means of a plurality of bolts 9 (only one being shown). The circuit breaker 1, with the exception of the trip device and the omission of the casing cOVer, is of the same general construction disclosed in Patent No. 2,047,739 of Harry J Lingal, issued July 14, 1936, and assigned to the assignee of the present invention.

The circuit breaker 1 is of the three pole type and comprises a base ll of molded insulating material having mounted in compartments formed therein a stationary contact 3 and a cooperating movable contact |5 for each of the three poles. The three movable contacts |5 are pivotally carried by switch arms H which are mechanically connected for simultaneous movement together to open and closed-circuit positions about a common pivot l9 by means of an insulating tie bar 2|. The central switch arm I1 is disposed between the side walls of a U- shaped frame 23 secured to the circuit breaker base II, and the frame supports the pivot pin [9 which forms the common pivot for the switch arms.

The switch arms l1 are actuated to open and closed-circuit positions by a common actuating mechanism comprising a pair of toggle links 25 and 21 pivotally connected at one end by a pin 29 to the central switch arm l1 and pivotally connected at the other end by a pin 3| to a pivoted releasable carrier lever 33. The carrier lever 33 is pivoted to the frame 23 between the side walls thereof by a pivot pin 35, and the free lower end of the carrier lever is normally engaged and held by a pivoted latch 31 of the trip device 39. A yoke-shaped actuating member 4| straddles the breaker frame 23 and is pivoted to each side wall thereof at 43. The actuating member 4| is connected by a pair of overcenter springs 45 to the knee pivot of the toggle 25--21,'

the springs being disposed on opposite sides of the toggle and the carrier lever 33 and between the side walls of the breaker frame 23. A hookshaped resetting projection 41 is formed integral with the actuating member 4| for the purpose of engaging and resetting the carrier lever 33 to latched position, when the actuating member is moved downwardly to open position to re- I set the mechanism following a tripping operation. The pivoted actuating member 4| has an operating member 49 of insulating material rigidly secured to the outer end thereof which is adapted to be engaged by an electric solenoid or motor operating mechanism (not shown) for operating the circuit breaker.

Each of the movable contacts I1 is electrically connected to one of the three lower terminals 5| of the circuit breaker by means of a conductor 53, and each stationary contact I3 is electrically connected to one of the three upper terminals (not shown) of the breaker by a conductor 55.

An arc extinguishing structure 51 of the spaced plate type is associated with the contacts of each pole of the breaker for deionizing and extinguishing arcs drawn by the contacts during interruption of the circuit.

The trip device 39 of the circuit breaker comprises, in general, the pivoted latch 31, a pivoted trip bar 59 for normally engaging and restraining the latch 31 in latching position, and a shunt trip assembly 6| including a shunt trip electromagnet 63 which is operable when energized to move the trip bar 59 to tripping position and thereby effect release of the latch 31 and carrier lever 33 to cause automatic opening of the circuit breaker.

The latch 31 is mounted for pivotal and limited sliding movement on a pivot pin 65 carried by a bracket 68 secured to an insulating trip unit base 69. The trip unit base 69 is secured to the main breaker base H by one or more bolts 10. The latch 31 has a yoke-shaped upper end, the legs of which are notched to pivotally and slidably engage the pivot pin 65, and the latch also has a curved latch projection 61 for engaging the latch end of the releasable carrier lever 33, as shown in Fig. 1. the pivot pin 65 and has one end engaging the latch 31 and its other end hooked to the bracket 69 for biasing the latch upwardly and in a counterclockwise direction to latching position. The spring 1| is relatively light as its main function is to return the pivoted latch 31 to latching position following tripping of the breaker. The latch 31 is also provided with a'projecting tail portion 13 which projects through an opening provided therefor in the trip unit base 69 and has an arcuate notch 15 formed in the lower end thereof adapted to be engaged by a roller 11 carried by the trip bar 59 to hold the latch 31 in latching position as long as the trip bar 59 is held in its normal position. The trip bar and its roller 11 thus form, in effect, an auxiliary latch for engaging and restraining the main latch 31 in latching position.

The trip bar 59 is composed of molded insulating material and is pivotally mounted on the base 69 by means of a pair of pivot pins 19 at each end which engage in brackets 8| carried on the lower side of the base 69. The trip bar 59 is biased in counterclockwise direction as viewed in the drawings to its normal or latching position by a relatively light compression spring 83 which is disposed between a projection 85 of the trip bar and the trip unit base 69 and is seated in recesses provided therefor in each.

The releasable carrier lever 33 is at all times strongly biased in a counterclockwise direction as viewed in the drawings by a component of the force of the overcenter springs 45, and this force is transmitted to the latch 31 and tends to move the latch 31 in a clockwise direction to its released position. The latch 31, however, is normally held in latching position against this force by the engagement of the roller 11 of the trip bar 59 in the arcuate recess 15 and the latching bias on the trip bar produced by the compression spring 83. The spring 83 can be made relatively light due to the mechanical advantage provided by the pivoted latch 31, since the carrier lever 13 engages the latch 31 close to the pivot axis of the latch whereas the latch roller 11 of the trip bar 59 engages the latch 31 at a point remote from the pivot-65.

The latching force on the trip bar 59 produced by the spring 83, however, is not alone A spring 1| is coiled about.

sufficient to hold the breaker actuating mechanism in latched position when the apparatus is subjected to shocks or jars such as occur when the breaker is reset and immediately thereafter when automatically reclosed by the solenoid or motor operating mechanism. Consequently the breaker may be falsely tripped by shocks or jars unless either a much stronger spring is provided for biasing the trip bar to latching position or some other means is provided for preventing false tripping of the breaker by shocks or jars. For example, with one circuit breaker actuating mechanism of the type illustrated, it has heretofore been found necessary to provide a 27 ounce latching force on the trip bar to prevent the breaker from being falsely tripped by shocks and jars which occur during resetting and reclosing of the breaker. However, if a 27 ounce spring is used to bias the trip bar to latching position the tripping load at the shunt trip magnet becomes too large to permit the use of a compact shunt trip magnet which will meet the limited space requirements and still be capable of tripping the breaker at the required minimum voltage and at the limited current avail- In accordance with the present invenable. tion the problem is overcome by providing the relatively small light springl B3, of about 6 ounce strength in the device referred to by way of example, which is sufficient under normal conditions to maintain the mechanism in latched position and by incorporating a means including a second stronger spring 81, of about 21 ounce strength between the trip'bar and the shunt trip magnet for normally opposing movement of the trip bar 59 to tripping position. The combined total force of the springs 83 and 81 is sufficient to prevent the breaker from being falsely tripped by shocks or jars, and the means including the spring 81 is arranged so that the plunger of the shunt trip magnet does not stress or overcome the spring 81 when actuated to trip the breaker.

The shunt trip assembly 6|, including the shunt trip electromagnet 63, is mounted in a vertical position on a bracket 89 which is secured to the frame 5. The shunt trip electromagnet 63 comprises a stationary core 9I, a cooperating movable core 93, and an energizing winding 95. The movable core 93 has a plunger 91 secured thereto which extends through aligned openings provided therefor in the stationary core 9| and in the horizontal portion of the bracket 89 and through a metal ferrule 99 at the top of the electromagnet. The movable core 93 is biased downwardly to unattracted position by the force of gravity and its weight is partially counterbalanced by light compression spring IOI. In the device referred to as an example, the core 93 weighs 3 ounces and the spring exerts a 2 ounce force, having a net downward bias on the core 93 of one ounce. Downward movement of core 93 is limited by the lower end plate of the electromagnet at I03.

An adjustable trip rod I is pivotally connected at one end by pivot pin I01 to a yokeshaped bracket I09 secured to the trip bar 59. The trip rod I05 is made up of two sections I08 and H0. The section I08 which has a reduced The reduced outer end of the section III] of the trip rod extends through an opening provided therefor in a laterally projecting ear III of a pivoted bell crank lever II3, the opening being of larger diameter than the reduced portion of the section IIO so as to permit a sufficient amount of pivotal movement of the bell crank lever H3. The hub II5 engages the laterally projecting ear III of the pivoted bell crank lever II3 on the trip bar side so that when the bell crank lever is rotated in a counterclockwise direction, the rod I05 is moved to the left, causing a movement of the trip bar 59 .to its tripping position. A lock nut III is provided for locking the sections I08 and H0 of the trip rod I05 in adjusted position.

The spring 81 is in the form of a helical compression spring and is mounted on the end of the reduced portion of the section lI0 of the trip rod I05 between the laterally projecting ear III and a washer II9 which is retained on the end of the rod by a cotter pin. The bell crank lever H3 is pivotally mounted on a pivot stud l2I carried by the vertical side of the bracket 89, and the lever has a forwardly projecting arm I23 provided with a laterally projecting ear I25 which is disposed over the upper end of the trip plunger 91.

A latching pawl I2! is pivotally mounted on a pivot stud I29 carried by the vertical side wall of the bracket 89, and the latching pawl is provided with an upwardly extending latch projection I31 which in the normal position of the latching pawl is disposed in interfering position under a latch projection I33 formed on the bell crank lever lI3 so as to normally prevent any substantial counterclockwise movement of the pivoted bell crank lever H3. The latching pawl I27 has a forwardly extending arm provided with a laterally disposed angle-shaped tail portion I35 which extends over and directly engages the upper end of the shunt trip plunger 91 so that when the shunt trip plunger is moved upwardly by energization of the electromagnet 63, the latching pawl I2! is rotated thereby in a counterclockwise direction. During the first part of theupward movement of the plunger the latching pawl I2! is rotated in a counterclockwise direction to engage the tail portion I35 against the lateral projection I25 of the pivoted bell crank lever II3. This movement also rotates the latching projection I3I towards the left out of the path of the latch projection I33 of the pivoted bell crank lever II3 so that the pivoted bell crank lever may be freely rotated in a counterclockwise direction. The continued upward movement of the trip plunger then causes the latching pawl I21 to rotate the pivoted bell crank lever H3 in a counterclockwise direction to effect movement of the trip bar 59 in a clockwise direction to its tripping position. During this motion only the relatively light biasing spring 83 for the trip bar 59 is compressed, the heavier spring 81 being bodily moved with the trip rod I05 to the left without stressing or compressing the spring 81. It will thus be seen that the trip plunger only has to overcome the relatively light force of the spring 83 in tripping the breaker.

The spring 81, however, normally acts to oppose movement of the trip bar 59 to tripping position by reason of the fact that the pivoted bell crank lever H3 is normally prevented from being moved in a counterclockwise direction by the latching pawl IZI. Under these conditions the total force of the two springs 83 and 81 opposes movement of the trip bar 59 to tripping position, so that the breaker is thus prevented from being falsely tripped by shocks or jars. The trip rod I05 is preferably adjusted in length so that there is a slight amount of.

clearance between the cooperating surfaces of the latch projection I33 of the bell crank lever H3 and the latch projection I3I of the latching pawl I21. Under these conditions the trip plunger in moving upwardly does not have to overcome any component of the force of the spring 81 in tripping the breaker.

The operation of the circuit breaker is briefly as follows: The circuit breaker is normally opened by moving the operating member 49 downwardly, or in a clockwise direction as viewed in the drawings, to open-circuit position. During this movement of the operating member to open position, the line of action of the overcenter springs 45 passes below the pivot pin 3|, thereby causing the toggle 252'I to be moved to the collapsed position effecting movement of the three movable contacts I5 to the open-circuit position. The circuit breaker is reclosed by moving the operating member 49 upwardly to the closed position shown in Fig. 1. During this movement, the line of action of the overcenter springs 45 passes above the pivot pin 3I and causes the toggle 25-21 to be moved to the extended position, thereby effecting movement of the three movable contacts to the closed-circuit position shown in Fig. 1.

Automatic opening of the circuit breaker is caused when the shunt trip electromagnet 63 is energized. Energization of the shunt trip electromagnet 63 causes the movable core 93 to be moved upwardly to attracted position against the stationary core 9|, thereby effecting upward movement of the trip plunger 91 carried by the movable core. During the initial part of the upward movement of the trip plunger 91, the latching pawl I2! is rotated in a counterclockwise direction to engage the pivoted bell crank lever H3 and also to move the latch projection I3I of the pawl out of the path of the latch projection I33 of the pivoted bell crank lever H3. The continued upward movement of the trip plunger then effects counterclockwise rotation of the pivoted bell crank lever I I3 and this movement is I transmitted to the trip bar 59 to cause movement of the trip bar to tripping position against the bias of the relatively light trip bar biasing spring 83. During this movement the spring 81 is moved bodily with the trip rod so that this spring is not stressed at any time during the tripping operation. The movement of the trip bar 59 to the tripping position effects release of the main pivoted latch 31 and carrier lever 33, and the carrier lever 33 is moved upwardly i. e. in a counterclockwise direction about its pivot pin 35 to the tripping or released position by the force of the overcenter springs 45. During the movement of the carrier lever 33 to its released position, the pivot pin 3I is shifted above the line of action of the overcenter springs 45 and the springs thereby cause collapse of the toggle 252'I and movement of the three movable contacts I5 to open-circuit position. As soon as the carrier lever 33 disengages the latch lever 31 during the release of the breaker, the biasing spring "II immediately returns the pivoted latch 31 to its latching position as shown in Fig. 2, and as soon as the shunt trip electromagnet 63 is deenergized the biasing spring 83 causes the return of the trip bar 59 and the pivoted bell crank lever H3 and the latching pawl I21 to the normal latching position as shown in Fig. 1.

The breaker actuating mechanism is reset after an automatic opening by downward movement of the operating member 49 to the open position. During this resetting movement of the operating member 49, the resetting projection 41 moves the releasable carrier lever 33 downwardly in a clockwise direction to return the latch end thereof to latched position in which it is engaged and held by the latch 31. The latch end of the releasable carrier lever 33 is rounded so that it acts to force the latch 31 downwardly as it passes the latch projection 31 during resetting. This downward movement of the pivoted latch 31 moves the trip bar 59 in a clockwise direction, compressing spring 83 and causing the latch projection I33 of the pivoted bell crank lever II3 to engage the latch projection I3I of the latching pawl I21, and the spring 81 is compressed. The spring 8! permits resetting of the mechanism. If the lever I23 was connected directly to the link I08 and the spring 81 omitted, the releasable lever could not be reset because the latch l3I would not permit the trip bar to be moved back by the latch 31 and hence the carrier lever could not be returned to latched position. As soon as the. latch end of the releasable carrier lever 33 clears the latch projection 61, the pivot latch 31 and the other parts return to the normal position as shown in Fig. 1. A soon as the breaker actuating mechanism has been, reset by the motor operating mechanism of the network projector, the motor operating mechanism immediately recloses the breaker by moving the operating member 49 upwardly to closed position. The shock or jars which occur during the resetting and immediate reclosing operation of the breaker will not cause false tripping of the circuit breaker by reason of the fact that the combined total force of the two springs 83 and 81 act to oppose movement of the trip bar 59 to tripping position, this force being suflicient to strongly hold the mechanism in latched position.

Although the invention has been disclosed with reference to a particular circuit breaker mechanism, it is to be understood that the broad features of the invention are equally applicable to any type of circuit breaker mechanism wherein it is desired to have a light tripping load and yet at the same time have the breaker strongly held in latched position.

While the invention has been disclosed in accordance with the provisions of the patent statutes, it is to be understood that various changes in the structural details and arrangement of parts thereof may be made without departing from some of the essential features of the invention. It is desired, therefore, that the appended claims be given the broadest reasonable construction permissible in the light of the prior art.

I claim as my invention:

1. A circuit breaker having relatively movable contacts, actuating means therefor including a member movable from one position to a second position to cause opening of said contacts, spring means disposed to normally oppose movement of said member to said second position with a predetermined force, means including an electroresponsive element not connected to said spring means operable when-actuated to first render a major portion of said predetermined force ineffective to oppose movement of said memberto said second position without overcoming said portion of the force and to then move said member to said second position against the remaining portion of said predetermined force.

2. A circuit breaker having relatively movable contacts, actuating means therefor, a member movable from one position to a second position to cause opening of said contacts, a spring biasing said member to said one position, means including a second spring normally efiective to oppose movement of said member to said second position, and means including an electro-responsive element not connected to said second spring movable to'move said member to said second position Without overcoming the force of said second spring.

3. A circuit breaker comprising relatively movable contacts, actuating means therefor, a member movable from one position to a second position to cause opening of said contacts, means including a spring disposed to oppose movement of said member to said second position, and electromagnetic means operable to cause said spring to be inefl'ective to oppose movement of said member, and to move said member to said second position without stressing said spring.

4. A circuit breaker comprising relatively movable contacts, actuating means therefor, a trip member movable from a normal position to a tripping position to cause opening of said contacts, means for normally opposing movement of said trip member to tripping position comprisin a spring connected at one end to said trip member, a blocking element normally preventing substantial movement of the other end of said spring to cause said spring to oppose movement of said trip member to tripping position, and a trip element operable in response to predetermined conditions to move said blocking member to free said other end of said spring and to apply force to said trip member to move said trip member to tripping position without stressing said spring, said trip element being engageable with but disconnected from said blocking ele ment.

5. A circuit breaker comprising relatively movable contacts, actuating means therefor, a trip member movable from a normal position to a tripping position to cause opening of said contacts, a first spring biasing said trip member to normal position, means for normally opposing movement of said trip member to tripping position comprising a second spring connected at one end to said trip member, and a latch for normally preventing substantial movement of the other end of said second spring to cause said second spring to oppose movement of said trip member to tripping position, and an electro-responsive trip element operable to move said latch to free said other end of said second spring and to apply a force to said trip member to move said trip member to tripping position without stressing said second spring,

6. A circuit breaker comprising relatively movable contacts, actuating means therefor, a member movable from a nromal position to a second position to cause opening of said contacts, means for normally opposing movement of said mem her to said second position comprising a spring connected at one end to said member, and means including an electro-responsive element having no mechanical connection to said spring movable to bodily move said spring and move said member to said second position without stressing said spring.

7. A circuit breaker comprising relatively movable contacts, actuating means therefor including a spring biased member releasable to cause opening of said contacts, latching means including a trip member having a normal position for restraining said releasable member and movable to a tripping position to effect release of said releasable member, a first spring for biasing said trip member to its normal position, means for normally opposing movement of said trip member to its tripping position comprising a second spring connected to said trip member, and an electro-responsive element, having no mechanical connection to said spring, movable to move said trip member to tripping position, said trip element in moving said trip member to tripping position efiecting bodily movement of said second spring without substantially stressing the same.

8. A circuit breaker comprising relatively movable contacts, actuating means therefor, a member movable from a normal position to a second position to cause opening of said contacts, a relatively light spring for biasing said member to its normal position, a second relatively strong spring engageable with said member, means for normally preventing substantial movement of one end of said second spring to thereby cause said spring to normally oppose movement of said member to said second position, and an electroresponsive element not connected to said last mentioned means operable to cause said last mentioned means to permit movement of said end of the second spring and to then bodily move said second spring and move said member to said second position" without substantially stressing said second spring.

9. A circuit breaker comprising relatively movable contacts, actuating means therefor, a trip member movable from a normal position to a tripping position to cause opening of said contacts, a relatively light spring for biasing said trip member to its normal position, means for normally opposing movement of said trip member toits tripping position comprising a second relatively strong spring connected at one end to said trip member, and a blocking member dissposed to normally prevent movement of the other end of said second spring, said blocking member being movable to a non-blocking position in which it permits movement of said other end of the spring, and trip means including an electro-responsive trip element operable to move said blocking member to non-blocking position to free said other end of the second spring and then move said trip member to tripping position.

10. A circuit breaker comprising relatively movable contacts, actuating means therefor, a member movable from a normal position to a second position to cause opening of said contacts, means normally opposing movement of said member to said second position comprising a spring having one end connected to said member, a pivoted lever engaging the other end of said spring, a latching pawl disposed to normally prevent substantial movement of said lever whereby said spring opposes movement of said member to said second position, and means including an electro-responsive element operable when actuated to first move said latching pawl to allow movement of said lever and to then move said member to said second position.

11. A circuit breaker comprising relatively movable contacts, actuating means therefor, a trip member movable from a normal position to a tripping position to cause opening of said contacts, a spring biasing said trip member to its normal position, a link connected at one end to said trip member, a second spring connected at one end to said link, a pivoted lever engaging the other end of said spring, said lever being movable to move said trip member to tripping position, a latching pawl disposed to normally prevent substantial movement of said pivoted lever so that said second spring thereby opposes movement of said trip member to tripping position, an electromagnet having a movable armature operable when actuated to first move said latching pawl to free said lever and then move said lever to move said trip member to tripping position without stressing said second spring.

12. A circuit breaker comprising relatively movable contacts, actuating means therefor, a trip member movable from a normal position to a tripping position to cause opening of said contacts, a spring for biasing said trip member to its normal position, an adjustable link connected at one end to said trip member, a pivoted lever having an arm engageable with an element carried by said link for moving said trip member to tripping position, said trip member being movable toward tripping position relative to said lever, a second spring connected at one end to said link and engaging said arm of said lever at its other end, a latching pawl disposed to normally prevent substantial movement of said lever to thereby cause said second spring to oppose movement of said trip member to tripping position, and an electromagnet having a movable armature operable when actuated to first move said latching pawl to free said pivoted lever and to then move said pivoted lever to actuate said trip member to tripping position without stressing said second spring, 7

13. A circuit breaker comprising relatively movable contacts, actuating means therefor, a trip member movable from one position to a tripping position to cause opening of said contacts, means normally opposing movement of said member to said second position comprising a spring having one portion engageable with said member, a blocking member having a normal position in which it prevents substantial movement'of another portion of said spring to thereby cause said spring to oppose movement of'said trip member to tripping position, said member being movable to a non-blocking position in which it permits movement of said other portion of the spring, and an electroresponsive trip element operable to move said blocking member to non-blocking position and to then move said trip member to tripping position without overcoming the force of said spring.

14. A circuit breaker comprising relatively movable contacts, actuating means therefor, a trip member movable from one position to a tripping position to cause openingof said contacts, means normally opposing movement of said member to said second position comprising a spring having one portion engageable with said member, a blocking member having a normal position in which it prevents substantial movement of another portion of said spring to thereby cause said spring to oppose movement of said trip member to tripping position, said member being movable to a non-blocking position in whichit permits movement of said other portion of the spring, and electromagnetic means operable to move said blocking member to non-blocking position and to then move said trip member to tripping position without overcoming the force of said spring.

15. A circuit breaker having relatively movable contacts, actuating mechanism therefor comprising an operating member movable to close said contacts, a spring biased member re-' leasable to cause opening of said contacts irrespective of the position of said operating member, a latch normally engaging and restraining said releasable member, said latch being movable to releasing position to release said spring biased member, means comprising a spring connected at one end to said latch for normally opposing movement of said latch to releasing position, a blocking member disconnected from said spring but having a normal position in which it prevents substantial movement of the other end of said spring to thereby cause said spring to oppose movement of said latch to releasing position, and an electroresponsive element operable to move said blocking member to non-blocking position to thereby free said other end of the spring and to then move said latch to releasing position without overcoming the force of said spring, means for resetting said spring biased releasable member to its normal latched position, said spring permitting said latch to be moved by said releasable member toward releasing position against the force of said spring during resetting of said member.

JOHN W. MAY.

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