US2470301A

US2470301A - Combination electric switch and circuit breaker

Info

Publication number: US2470301A
Application number: US658895A
Authority: US
Inventors: Stephen S Grady
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-04-02
Filing date: 1946-04-02
Publication date: 1949-05-17
Anticipated expiration: 1966-05-17

Description

May 17, 1949. s. s. GRADY COMBINATION ELECTBIC SWITCH AND CIRCUIT BREAKER Filed April 2, 1946 3 Sheets-Sheet l y 1949. s. s. GRADY 2,470,301

COMBINATION ELECTRIC SWITCH AND CIRCUIT BREAKER Filed April 2, 1946 3 Sheets-Sheet 2 Will/III! May 17, 1949. s. s. GRADY COMBINATION ELECTRIC SWITCH AND CIRCUIT BREAKER Filed April 2, 1946 5 Sheets-Sheet 3 Patented May 1 7, 1949 OFFICE COMBINATION ELECTRIC SWITCH ANT CIRCUIT BREAKER- Stephen S. Grady, New York, N. Y. Application April 2, 1946, Serial No. 658,895 4 Claims. (01. 175-294) This invention relates to electric switches in general, and more especially to combination electric switches and circuit breakers.

Among the objects of the present invention it is aimed to provide an improved combination electric switch and circuit breaker such as used in power stations and the like whereby at will the circuit may be interrupted of a three phase circuit by mere movement of a handle, and which circuit in turn will be interrupted by an overload in any conductor of the three phase circuit without materially actuating the handle if at all.

It is still another object of the'present invention to provide an improved combination electric switch and circuit breaker for controlling a three phase circuit whereby the circuit may be manually interrupted by actuation of a handle and in turn also interrupted in case of an overload in any one or more of the conductors of the three phase circuit without actuating the handle so that an attendant may be eifectively protected against injury should he be holding, or be in the path of movement of, the handle at the time the circuit is interrupted by an overload, which circuit breaker may be set in anticipation of an overload interruption after which the handle may be actuated into and out of current interrupting position without affecting the overload circuit breaking mechanism.

It is still another object of the present invention to provide an improved combination electric switch and circuit breaker which includes a handle for manually actuating an interposer to interrupt the circuit at will, a fuse interposed in the conductor when the circuit is established, and an electric circuit breaker for automatically actuating the interposer to interrupt the current when the fuse has been blown or destroyed, which fuse will predetermine the maximum load to be carried, and which will short circuit the circuit breaking mechanism so that the circuit breaking mechanism may be sensitive to a very low amperage not in any way related to the maximum load to be carried by the conductor.

It is still another object of the present invention to provide an improved combination electric switch and circuit breaker for a three phase circuit including an interposer operatively connected to a manually operated handle to actuate the interposer to interrupt the circuit at will, a

circuit breaker operatively connected to actuate said interposer in case of an overload, means for operatively connecting said manually operated handle to set said circuit breaker in anticipation of an overload, and a plurality of ammeters,

one for each conductor of the three phase circuit which can be readily inspected by the attendant to determine the relative flow of current in the three conductors of the three phase circuit.

- With combination electric switches and circuit breakers, especially for light control stations or power plants where three conductors are associated in three phase circuits, a single switch has been extensively used simultaneously to interrupt or establish the circuit through the three conductors. While good practice requires that the flow through all conductors be maintained substantially equal to one another, it is practically impossible to maintain the load equal in all three conductors. Consequently, if the fuses for the three conductors have been selected to carry a predetermined load, obviously when an overload occurs the critical point is not reached in all three conductors at the same time, but generally reached in one conductor first. In view of the foregoing, it is an object of the present invention to provide a combination switch and circuit breaker to interrupt the current in all three condutors whenever an overload occurs in any one of them so that the attendant or operating engineer will not by inadvertence be injured by the current flowing through the electrode of which the fuse has not been blown.

It is still another object of the present invention to provide a door which cannot be opened to gain access to the switch until the current in all three conductors has been effectively interrupted, when the switch used is made in accordance with the combination electric switch and circuit breaker of the present invention and the switch is used with the three conductors of a three phase circuit.

It is still another object of the present invention to provide an improved electric switch and circuit breaker for the three conductors of a three phase circuit associated with an ammeter and an electro-magnet for each conductor for initiating the actuation of the circuit breaker when any of the three fuses, due to an overload, is blown in which the circuit through the electro-magnet is not established unless the needle of the ammeter registers zero which will occur momentarily when the fuse for any conductor is blown due to an overload, the energizing of the electro-magnet initiating the actuation of the circuit breaker for all three conductors. as a result of which arrange-' ment, the electro-magnet is definitely protected against injury in case of an overload and in turn a fuse responsive to a predetermined critical point corresponding to a predetermined overload 3 can be selected without regard to leakage through the electro-magnet.

These and other features, capabilities and advantages of the invention will appear from the subjoined detail description of one specific embodiment thereof illustrated in the accompanying drawings, in which Fig. 1 is a fragmental front elevation of a casing to house a plurality of combination switches and circuit breakers made according to the present invention.

Fig. 2 is a front elevation of a combination electric switch and circuit breaker typical of one unit partly in section.

Fig. 3 is a section on the line 3-3 of Fig. 2.

Fig. 4 is a fragmental enlarged section on the line 4--4 of Fig. 2.

Figs. 5, 6 and '7 are fragmental sections similar to the section shown in Fig. 1, showing successive positions of the main actuating means, but on a smaller scale than that shown in Fig. 4.

Fig. 8 is a section on the line 8-8 of Fig. 3.

Fig. 9 is a perspective with parts broken away of the interposer.

Fig. 10 is a fragmental perspective of one portion of a unit.

In the embodiment shown, see Fig. 1, there is illustrated a succession of switch housings l, 2 and 3, only three being shown in this instance, illustrating in a general way the position of these housings in a control room for a plant in which the housing I may house or encase the combination electric switch and circuit breaker of one three phase unit, the housin 2 of another three phase unit, and the housing 3 of still a third three phase unit. Access to the electric switch is afforded through the door 4 pivotally connected at its lower end, in the present instance, and provided with a latch 5 at its upper end for anchoring the door 4 in place. The door 4 has a window 6 which may be equipped with a sheet of glass to facilitate inspecting the

ammeters

8 and 9, but bar tampering with the same when the door 4 is in closed position. The door 4 is also provided with two slots l and H to clear the outer ends I2 of the actuating plates I3 and also the extensions 4 for the handle l5. These slots 0 and H are just large enough to clear the extensions I4 when current is interrupted, that is, when the extensions M are shown in the position illustrated in Fig. 5, but bar the opening of the door 4 when the extensions l4 are in the raised position or circuit making position, that shown in Fig. 3. In this way, the attendant will be assured that the current is interrupted before he opens the housing.

In the housing I, which is typical of any number of housings, such as 2 and 3, there are provided two supporting metal bars or angle irons H and M6 to which are secured the bars I1 and I8 composed of a suitable insulating material, see Figs. 2 and 3, across which bars I1 and I8 are secured the cross bars l9 and 20 composed of a suitable insulating material. The bars I1 and 8 are preferably spaced from one another as shown in Fig. 2, and the bars l9 and 20 preferably extend beyond the bars I! and Hi to form three spaced supporting areas. In the present instance, between the bars l1 and I8 and the cross bar l9, there are secured the bus bars 2|, 22 and 23 which are provided in the present instance with the brackets 24, 25 and 26 at their upper ends to receive the

electrodes

21, 28 and 29, respectively, and to the outer face of the cross bar l9 there are secured the upper ends of 4 the flexible laminated

contact members

30, 3| and 32 and extending down from the-upper ends of the

flexible members

30, 3| and 32 there are provided the

bus bars

33, 34 and 35, respectively, which in turn are spaced from the upper ends of the

bus bars

36, 31 and 38, respectively, mounted on the insulated base plates 39, 40 and 4|, respectively. extending up between the cross bar 20 and the bus bars 36, 3'1 and 38, respectively. The

bus bars

36, 31 and 38, however, are preferably secured to the cross bar 20 by screws or bolts which extend through the flanges of the

brackets

42, 43 and 44, respectively, and the adjacent base plates 39, 40 and 4|, respectively, to which

brackets

42, 43 and 44 in turn are connected the

electrodes

45, 46 and 41, respectively.

It is of course obvious that the present invention is applicable to a combination switch and circuit breaker for a single conductor as well as a plurality of conductors without departing from the general spirit of the invention, although the application of the present invention to the three conductors of a three phase circuit presents features peculiar to a three phase circuit and distinguishable from a switch associated with a single conductor.

It is of course also obvious, Fig. 10, that the electrode 21 and electrode 45 are associated with the bracket 24, bus bar 2|, flexible contact 30, bus bar 33, insulated plate 39, bus bar 36 and bracket 42, that the electrode 28 in turn, Fig. 3, is associated with the electrode 46 through the bracket 25, bus bar 22, flexible contact 3|, bus bar 34, insulated plate 40, bus bar 31 and bracket 43, and that the conductor 29, Fig. 2, is associated with the conductor 4'! through the bracket 26, bus bar 23, flexible conductor 32, Fig. 8, bus bar 35, insulated plate 4|, bus bar 38, Fig. 2, and bracket 44.

The bus bar 33 and bus bar 36 are connected by the fuse plate 46, the bus bar 34 in turn is connected to the bus bar 3'! by the fuse plate 49, and the bus bar 35 is connected to the bus bar 38 by the fuse plate 50. These

fuses

48, 49 and 50 are of course selected to blow or fuse, in the conventional way, when a predetermined load is reached. If the normal load of the several conductors is below 1000 amperes, then obviously the .fuses 48, 49 and 50 would be selected to blow when a load of approximately 1100 amperes is reached.

For interrupting the circuit in any one of the conductors there is provided an interposer 5| which is operable either by the handle l5 manually to interrupt or establish the current, or else automatically operated whenever any one of the

fuses

48, 49 or 50 is blown or broken.- The interposer 5|, Fig. 9, in the present instance, consists essentially of a plate of insulated material common to all three conductors. The plate, in the present instance, has recessed

cheeks

52, 53 and 54 adjacent the

openings

55, 56 and 51, respectively. This plate 5| in actual practice is positioned so that either the

cheek plates

52, 53 and 54 are interposed between the bus bars 2|, 22 and 23, and

flexible conductors

30, 3| and 32, respectively, to interrupt the current passing from the bus bars 2|, 22 and 23 to the

flexible conductors

30, 3| and 32, respectively, or else positioned so that the

openings

55, 56 and 51 register, see Fig. 10, with the ends of the bus bars 2|, 22 and 23 and

flexible conductors

30, 3| and 32, respectively. to establish a circuit or contact between the bus bars 2|, 22 and 23, and

flexible conductors

30, 3| and 32, respectively. In order to efiect an intimate engagement between the bus bars 2|, 22 and 23 and the

flexible conductors

30, 3| and 32, re-

the rollers 8|. These

spring arms

58 and 59, see' particularly Fig. 3, engage the outer faces of the bus bar and flexible conductor, such as the bus bar 22 and flexible conductor 3|, to press the same into intimate engagement with one another when the interposer is elevated into the circuit making position shown in Fig. 3.

The mechanism whereby the handle I5 may be manipulated manually to actuate the interposer 5| to establish and interrupt the circuit will now be described.

The handle I5, as aforesaid, is mounted on the extensions II of the plates I3. Since both plates I3 are identical to one another, a description and explanation of the plate I3 cooperating with the slot II alone will be undertaken and suiiice for both of them. In Fig. 4, this plate I3 is mounted on the pin 62 journalled in the plate 63, secured to the cross bars I9 and 20. This plate I3 has an arcuate slot 64 concentric to the pin 62. This plate I3 has a pin 65 in the projection 66 and an opening 61 near the recess 68. The recess 68, and more particularly the shoulder 69 of the recess 68, is adapted to cooperate with the pin III on the plate 63 to determine the lowest position of the plate I3. In this lowest position when the cover 4 is removed, the opening 6! receives the pin II formed on the spring arm I2 secured to the plate 63 so that the pin II extends through the opening I3 in the plate 63 into the opening 6'! in the plate I3. When the plate I3 is actuated into the position shown in Fig. 5, where the pin II registers with the opening 61, then if the door 4 is opened, it will clear the spring arm I2 and permit the arm I2 to project the pin II into the opening 61 in the plate I3. When the pin is so projected into the opening 61 in the plate I3, it will anchor the plate I3 and its companion plate I3 from movement about its pivot 62, and not again to establish the circuit interrupted by the interposer plate 5| until the spring arm I2 has been deflected to withdraw the pin II from the opening 61 when the plates I3 will be free again to raise the interposer plate 5| into the circuit making position illustrated in Fig. 4, where the

openings

55, 56 and 5! register with the free ends of the bus bars 2|, 22, 23 and the free ends of the

flexible contacts

38, 3| and 32, respectively.

In order to enable the plates I3 to move the interposer plate 5|, each of the plates I3 is operatively connected to a link II which link is provided with a slot I5 slidably mounted on the pin I6 extending from the plate 63 through the arcuate slot 64 in the plate I3. The link I I has a finger 1! extending into an opening I8 in the interposer plate 5|. The interposer plate 5| is provided with two openings I8 for the finger II of each of the links I4. Each link 14 is indirectly actuated by a plate I3 due to the spring I9 connected to the pin 88 on the plate I3, the other end of which spring I8 is connected to the pin 8| on the finger I1. Preferably in the interest of assembly, the plate I3 and link I4 are disposed on one side of a. plate 63 and the spring I9 is disposed on the other side of the plate 63, the pin 88 extending beyond the front free edge of the plate 63 and the pin 8| extending through the recess 82 in the plate 63 and in the present instance just forwardly of the interposer plate 5|. The spring I8,

plate I3 and link N form a toggle, as a result of which, when the plate I3 is moved into the position shown in Fig. 5, about its pin 62, the spring 78 will swing the link I4 into the position shown in Fig. 5. On the other hand, when the plate I3 is moved into the position shown in Fig. 4 from the position shown in Fig. 5, where the pin 88 of the spring I8 moves upwardly relative to the pin I6 on which the link I4 is slidably mounted, the spring I9 will actuate the link I4 upwardly into the position shown in Fig. 4. For actuating the link II in case of a short circuit, the coil spring 83 wound around the pin 84, secured to the plate 63 is provided. one end of the coil spring being biased against the stop 85 formed in the plate 63, the other free end 86 of which having a lip 81 to cooperate with the latch bar 88 fixedly mounted on the shaft 88. The latch bar or plate 88 on the shaft 88 is biased into the position shown in Fig. 4 by the spring 38 shown in Fig. 2, secured to the shaft 88, wound around the same, and with one end yieldable in engagement with the pin 9| extending from one of the plates 63 nearer to the left hand side of the unit. The link I I has an arm 82 extending from one end thereof, and provided with a pin 93 to cooperate with the finger 86 of the spring 83. The plate I3, see Fig. 4, is also provided with a pin 94, normally engaging the edge 95 of the link I4, and positioned to enter the recess 96 in the link 14 adjacent the slot I5.

In practice, when an overload occurs, the latch 88 is rocked with its shaft 88 so that the latch 88 clears the lip 81 and allows the finger 86 of the spring 83 to strike the pin 93 of the link 18. Initially, this lateral movement of the link 14 will cause the link I4 to slide on the pin I6 so that the pin I8 enters the front end of the slot I5, when the recess 98 will register with the pin 94, and due to the continuing urge of the spring arm 86 will cause the link II to move into the position shown in Fig. 6, where the pin 94 registers with the recess 86, and then urge the link II into the position shown in Fig. 7, carrying with it the interposer plate 5| into circuit breaking position. In order to restore the lip 8! in biased position on the latch plate 88, the handle I5 of the plate I3 may then be depressed when the plate I3 will cause its pin 65, see Figs. 7 and 5, to engage the arm 86 of the spring 83 and deflect it to pass the latch 88, until the lip 81 again rests on the front end of the latch 88 as shown in Figs.

'5 and 4.

In this depressed position of the handle I5, however, the interposer plate 5| will still be in circuit breaking position. At this time, however, as aforesaid, when the cross piece of the handle I5 is removed, the slots I 0 and II will clear the extensions I4 of the plates I3 and allow the door 4 to be opened. Immediately, however, that the door is opened, the pin II of the spring I2 will snap into the opening 61 of one of the plates I3 and anchor the plates I3 against further actuation thereby protecting the attendant from injury should he accidentally attempt to move the plates I3 into circuit making position. In other words, the locking of the plates I3 in this circuit breaking position will require the attendant to defleet the spring arm I2 and thereby bring to his attention the fact, if he is acquainted with the switch, that the switch in such anchored position is in circuit breaking position and may only be moved into circuit making position when the spring arm 12 is deflected.

After an overload has actuated the interposer plate 5| into the position shown in Fig. '7, and

the plates I3 have been moved-into the position shown in Fig. 5, to reset the spring-arm 86 on the latch plate 88, the position shown in Fig. 5, and the door 4 has been opened, the fuses which may have been blown may be restored while the circuit is still broken, thereupon the door 4 again closed and then only the handle I5 raised into the position shown in Fig. 4, again to establish the circuit.

From the foregoing, it will appear that with two plates I3 each provided with a spring 88 and a link 14 operatively connected to the interposer plate 5I, the handle I5 may be actuated manually to establish and interrupt the circuit. In other words, disregarding the latch 88 and its circuit breaker association, when the spring arm 86 rests on the latch 88, if the handle I5 is elevated into the position shown in Fig. 3, the interposer 5| will assume the position shown in Fig. 4 when the circuit will be established, and in turn when the handle I5 is depressed so that the plates I3 assume the position shown in Fig. 5, the interposer 5I will descend into circuit breaking position, all without affecting the position of the spring arm 86 on the latch 88.

The operation of the latch 88 will now be described. The latch 88, as aforesaid, is mounted on the shaft 89, which in the present instance has three arms 91, one for each electro-magnet 98 mounted on the bus bars 33, 34 and 35 but insulated therefrom by the insulated plates 99. The arms 91 preferably have formed at their ends a piece of soft iron I to facilitate magnetic action on the same by the electro-magnets 98 when energized. The electro-magnets 98 are insulated from the bus bars 33, 34 and 35, and consequently when circuits are established through the bus bars 33, 34 and 35 for normal operation, the electro-magnets 98 will not be energized. Preferably above the electro-magnets 98, the bus bars 33, 34 and 35 are provided with the ammeters IOI. These ammeters IOI, each consist essentially of a plate I02 having a main section I03 and an auxiliary section I04 extending parallel to the section I03, but spaced therefrom by the web I05. The section I04 is shorter than the section I05 to afford access to the fastening screws for the section I03 and to provide an area for graduation marks which are disposed in an arcuate line to aline with the path of movement with the free end of the needle I06, all as shown and more fully described in my co-pending application, Serial No. 606,368, filed July 21, 1945, now Patent No. 2,430,465. The ammeters IOI in the present instance, however, are distinguished from the ammeters disclosed in my aforesaid copending application in that the zero position of the needle I06 coincides with the position of the needle I06 where it engages the pin I01 insulated from a

bus bar

33, 34, 35 by the insulated jacket I08. The pin I 01 of each ammeter I III is connected with an eIectro-magnet by the conductor I 09. The electro-magnet in turn is connected with a

bus bar

38, 31, 38 by a conductor IIO.

From the foregoing, it will thus appear that when a

fuse

48, 49 or 50 is blown or fused to interrupt the current between a pair of bus bars 33-36, 34-31, or 35-38, then the current will be momentarily interrupted in such circuit and cause the needle I06 to drop into position where it will engage the pin I01. Since the needle I06 is electrically connected to a

bus bar

33, 34, 35 immediately that the needle I06 strikes the pin I01, the current will momentarily rush from the needle I06 through the electro-magnet 98 to energize the same, in turn to attract the armature I00 and rock the shaft 89 in turn to swing the latch plates 88 clear of the fingers 81 when the arms 86 of the springs 83 will strike the pins 93 as aforesaid, so that from the position shown in Fig. 4, the links 14 will first assume the position shown in Fig. 6 and then move into the position shown in Fig. 7 where as aforesaid they will have actuated the interposer plate 5i into circuit breaking position.

From the foregoing it will be seen that due to this positioning of the ammeters IN, the full charge during normal operation will always flow through the respective fuses 48, 49 and 50 and no leakage of current will be deflected through the electro-magnets 98. Still furthermore, since the energization of electro-magnets' 98 will only require a momentary contact of a needle I06 with a pin I01 to rock the shaft 89, the overload current can never develop full amperage when passing through the electro-magnets 98, and consequently the electro-ma-gnets will at all times b fully protected against injury.

From the foregoing, it will also appear that the recesses 96 receiving the pins 94 of-the plates I3 will allow the links 14 to actuate the interposer plate 5| without materially afiecting, if.at all, the position of the plates I3, so that if an attendant should be standin next to the handle I5 when an overload is registered to actuate the circuit breaker, he can, under no circumstances. be injureddue to movement of the handle I5 when the circuit breaks.

Preferably the plates I3 and associated links 14 and partitions 63 are spaced from the circuit breaker mechanism, including the electro-magnets 98 and fuses 48, 49 and 50 by the partitions I08 composed of insulated material extending from the front face of the interposer plate 5i. Preferably also, the partitions I09 composed of insulated material extending from the rear face of the interposer plate 5I insulate the fingers 11 of the links 14 from the bus bars 2|, 22 and 23, so that each conductor unit, includin electrodes 21-45, 28-46, and 29-41 are insulated from one another effectively to prevent any arcing between the adjacent conductor units.

It is obvious that various changes and modifications may be made to the details of construction without departing from the general spirit of the invention as set forth in theappended claims.

It is, of course, obvious that the electro-magnets 98 instead of being connected to the pins I01 by the conductors I 09 could be directly connected to the bus bar 33 without departing from the general spirit of the invention in which case, however, leakage could not be effectively barred as is the case when the electro-magnets 98 are connected to the pins I01.

I claim:

1. In a circuit breaker for two conductors, the combination of a first bus bar for one conductor, a second bus bar, a contact connected to said second bus bar with its free end normally engaging said first bus bar, a third bus bar connected to the other conductor, means including a fuse for connecting the second bus bar to said third bus bar, an interposer slidably mounted between said first bus bar and contact, a lever operatively connected to said interposer, a spring biased in inoperative position and when released operatively associated to actuate said lever in turn to actuate said interposer into circuit breaking position, a latch for anchoring said spring in biased position, an electro-magnet positioned when energized to actuate said latch to release said spring, an ammeter including a pivotally mounted needle electrically connected to said second bus bar to record the amperage of the current flow when said fuse is intact, a pin insulated from said ammeter, a conductor connecting said pin to said electro-magnet, and a second conductor connecting said electro-magnet to said third bus bar, said needle engaging said pin when the current is interrupted by the blowing of said fuse, in turn momentarily to establish a circuit after the fuse is blown between said ammeter and said third bus bar thereby to energize said electromagnet in turn to actuate said latch.

2. In a circuit breaker for a three phase circuit having three pairs of conductors, a first bus bar and a second bus bar for one conductor of each pair, a contact for each of said pairs of conductors and connected to its associated second bus bar with its free end normally in engagement with its associated first bus bar, a third bus bar for the other conductor of each pair, a fuse connecting each associated second bus bar with its associated third bus bar, an interposer common to all three pairs of conductors slidably mounted between said first bus bars and said contacts, an actuating device including links operatively connected to said interposer, springs for actuating said links into circuit breaking position, a latch for anchoring said springs in inoperative position, an ammeter including a needle for each pair of conductors electrically connected to its associated second bus bar and in position to record the amperage of the circuit passing through a pair of conductors when its associated fuse is intact, a pin for each ammeter insulated from the same, an electro-magnet for each ammeter, a conductor connecting each pin to one of said electro-magnets, a second conductor connecting each electro-magnet to its associated third bus bar, the needle of each ammeter when the current of its associated circuit has been interrupted by the blowing of a fuse receding to zero and engaging the pin momentarily to reestablish the circuit through its associated pair of conductors, a shaft for said latch, armatures on said shaft, one for each electro-magnet to be attracted by an electro-magnet when energized to release said latch to free said springs to actuate said interposer whereby the blowing of a fuse associated with any pair of conductors will initially interrupt the circuit by said interposer through all three pairs of conductors.

3. In a circuit breaker for two conductors, the combination of a first bus bar for one conductor. a second bus bar, a contact connected to said second bus bar with its free end normally engaging said first bus bar, a third bus bar connected to the other conductor, means including a fuse for connecting the second bus bar to said third bus bar, a second means for interrupting the passage of current from said first bus bar to said contact, a lever operatively connected to said second means, a spring biased in inoperative position and when released operatively associated to actuate said lever in turn to actuate said second means into circuit breaking position, a latch for anchoring said spring in biased position, an electro-magnet positioned when energized to actuate said latch to release said spring, an ammeter including a needle electrically connected to said second bus bar, a pin insulated from said mmeter, said needle being deflected from said pin by the current flow when said fuse is intact, a conductor connecting said pin to said electromagnet, and a second conductor connecting said electro-magnet to said third bus bar, said needle engaging said pin when the current is interrupted by the blowing of said fuse, in turn momentarily to establish a circuit, after the fuse is blown, between said ammeter and said third bus bar thereby to energize said electro-magnet in turn to actuate said latch.

4. In a circuit breaker for a three phase circuit having three pairs of conductors, a first bus bar and a second bus bar for one conductor of each pair, a contact connected to its associated second bus bar with its free end normally in engagement with its associated first bus bar, a third bus bar for the other conductor of each pair, a fuse connecting its associated second bus bar with its associated third bus bar, a means common to all three pairs of conductors for'interrupting the passage of the current between their first bus bars and their contacts, an actuating device including links operatively connected to said means, springs for actuating said links into circuit breaking position, a latch for anchoring said springs in inoperative position, an ammeter including a pivotally mounted needle for each pair of conductors electrically connected to its associated second bus bar responsive to the amperage of the circuit passing through a pair of conductors when its associated fuse is intact, a pin for each ammeter insulated from the same, said needle being deflected from said pin when its associated fuse is intact, an electro-magnet for each ammeter, a conductor connecting each pin to one of said electro-magnets, a second conductor connecting each electro-magnet to its associated third bus bar, the needle of each ammeter when the'current of its associated circuit has been interrupted by the blowing of a fuse swinging into engagement with its associated pin momentarily to re-establish this circuit through its associated pair of conductors, a shaft for said latch, armatures on said shaft, one for each electro-magnet to be attracted by an electro-magnet when energized to release said latch to free said springs to actuate said means whereby the blowing of a fuse associated with any pair of conductors will initially interrupt the circuit by said means through all three pairs of conductors.

STEPHEN s. GRADY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED s'rA'rEs PATENTS