US2247815A - Plural break circuit interrupter - Google Patents

Description

July 1, 1941. K. A. LOHAUSEN PLURAL BREAK CIRCUIT INTERRUPTER Filed Nov. 7, 1958 s m a a W H w w n e S u a h o L A H a K ili - Patented July 1, 194 1 z.24'i, s1s PLURAL BREAK cmcurr m'rcnaur'raa Karl A. Lohausen, Oberachoneweide, Germany,

asaignor to General Electric Company. a corporation of New York )3 Application November '7, 1938, Serial No. $319,395 In Germany November 13,1837

19 Claims.

The present invention relates to circuit interrupters, and has for a general object the provision oi improvementsin circuit interrupters employing a plurality of serially connected circuit interrupting points for producing a plurality of serially related breaks in a circuit to be interrupted, with means operable responsively to initial break at a first one of the interrupting points for ef-' fecting a break at a subsequent interrupting'point and for producing pressure discharge of arc quenching medium at such subsequent point.

One of the more specific objects of the invention is the provision of an improved circuit interrupter such as referred to above, wherein an initial break at an interrupting point including a fusible element, causes a subsequent serially connected break, or breaks, at an interrupting point, or points, including mechanically separable contacts.

As is well known, there is now available a. wide selection of fusible solders by means of which there can be produced so called "solder point 1 uses having practically any desired melting characteristics, However, such solder point iuses as heretofore constructed have had important drawbacks from the standpoints, among others, of mechanical construction requirements and 0peraticnal characteristics under certain circuit conditions, particularly in high voltage applications. It is another object of the present invention to provide a circuit interrupter combining the feature of plural serially related breaks with the feature of solder point fusing in a manner to secure the attendant advantages of both features without the heretofore encountered disadvantage oi these features. 1

It is a further object of the invention to provide a circuit interrupter capable of producing a multiplicity of serially related breaks in succession. or cascade, with discharge of arc quenching medium at each 01' the breaks, following the initial break, under suflicient pressure and in sufllcient quantity to insure effective are interruption at each of the breaks.

A still further object of the invention is the provision oi a circuit interrupter having means for producing multiple serially related breaks under certain excess current conditions, such as overloads, with additional interrupting means for producing interruption with current limiting action under short circuit condtlons.

These and other objects as well as the details of that which I consider to be my invention will be more clearly understood from the following description and the claims appended thereto,

taken in conjunction with the accompanying drawing in which are illustrated two exemplary embodiments of my invention. In the drawing, Fig. 1 shows a construction employing only two circuit interrupting points; Fig. 2 shows a construction employing a multiplicity of interrupting points; Fig. 3 represents a cross-sectional view along the lines 3-3 of Fig. 2; and Fig. 4 illustratesa modification of the Fig. 2 construction.

Referring to Fig. 1 of the drawing, the interrupting device shown therein is provided with an enclosed casing which comprises in the main an elongated tube ill of fibrous or other suitable insulating material, a ferrule i i screw threaded. on the lower end of the tube, a terminal formic or sleeve i2 secured intermediate the ends of th; tube, and a terminal cap I3 screw threaded or. the upp r end of the tube, Within the upper end of the bore of the tube is disposed a hollow tubular metal bushing or sleeve i4. Intermediate the ends of the bore there is disposed an annular contact 15 which is secured in place and electrically connected with ferrule H by means of screws 48 or the like, and the lower portion cf which contact is provided with an arcing ring H. An insulating lining 2B, comprised of urea resin or other suitable material capable of ca veloping arc quenching gas and of becoming electrically non-conductive under the influence of the heat of an arc, is applied to the inner wall of tube ill intermediate sleeve H and contact i5, while the inner wall of the tube below contact 15 is provided with a lining 2! of any suitable arc resisting insulating material, such, for example, as hard rubber.

Longitudinally slidable within the bore of tube I0 is a conducting rod 22 the lower end of which supports a round contact 23 normally surrounded casing with screw threads for engagement by a clamping nut 21. The end of cap I3 is flexible and resilient, and tension normally is imposed on rod 22, terminal 26, and solder junction 25 by screwing clamping nut 21 downwardly until the end of cap I3 is sprung inwardly. Thus the biasing force of the inwardly sprung end of the terminal cap tends to pull upwardly on the plunger, comprised of terminal 28, junction 25 and rod 22, while contact 23 is in firm abutment with an inwardly projecting flange 23 adjacent the upper end of stationary contact ring l5.

The solder junction between rod 22 and terminal 26 is tightly surrounded by a sheath 2! which is readily frangible upon rupture of the junction and which is illustrated as being comprised of a felted material impregnated with any suitable substance capable of producing large quantities of arc quenching gas upon subjection thereof to the heat of an arc. However, this sheath may if desired be made of a single self-supporting gas producing material such as an urea resin.

Upon fusion of solder junction 25, due to flow of excess current between terminal ferrule l2 and terminal cap l3, terminal 26 is separated rapidly from terminal 24 due to springing out of the inwardly sprung end of cap l3, thereby insuring rupture of the junction between terminals 24 and 26 for arcing therebetween. This arcing causes large quantities of arc quenching gas to be developed by sheath 29 and a high pressure therefore is developed within the upper end of the bore of tube i0, since the flange 30 on terminal 26 tightly closes the Opening in the end of sleeve I4 when terminal 26 is impelled upwardly. The pressure within the tube, which if desired may be aided by some form of spring means (not shown) then causes downward movement of rod 22 to separate contact 23 from contact i5. Due to the rapid separation of terminals 24 and 26 and the inertia of rod 22 and contact 23, a substantial interval elapses subsequent to rupture of junction 25 and before separation of contact 23 from contact l5. This interval insures development of a high pressure and a considerable quantity of gas within the upper end of tube In so that when contact 23 finally moves down to the point of separation from contact I5, a large quantity of arc quenching gas is discharged at high pressure between the separating contacts so as effectively to extinguish arcs formed between the two contacts. The development of the arc quenching gas by sheath 29 is supplemented by lining 20 and also by a sheath 3|, of urea resin or other suitable insulating gas producing material, which is applied to the outer surface of rod 22. This latter sheath, 3|, serves not only to supplement the gas development but also to prevent back arcing between contact I and rod 22. It is to be noted that sleeve I4 and contact l5 each extends a considerable distance in the direction of move ment of rod 22. As a result.of this expedient arcing at the upper end of rod 22 is limited to short arcs between terminal 24 and sleeve |4 up to the instant of separation of contact 23 from contact l5, whereby the energy of arcing is kept small.

At the lower end of tube l6 there is provided a gas filter which preferably is comprised of a multiplicity of closely spaced radially extending plates 32 which are attached to lower ferrule These plates permit the expulsion of gas from the lower open end of the tube while cooling the gas and preventing expulsion of solid particles- The upper portions of the plates are formed and arranged to guide contact 23 on rod 22 into a catch member or socket 33 supported centrally of the plates. This socket is provided with a shock absorber 34 of resilient material, such as rubber, for breaking the force of impact of the plunger. The lower end of the socket is provided with a screw threaded closure 35 which may be removed readily for removal of plunger 22, 23, and also for removal of terminal 26 subsequent to unscrewing of clamping nut 21. A replacement unit, comprising a contact 23, rod 22, solder joint 25, and terminal 26 may then be inserted into the tube through the opening in socket 33 and the new unit secured in place by clamping nut 21.

In the embodiment of Fig. 2, there are pro-' vided six serially connected circuit-interrupting points, although more or less may be provided if desired. As in the embodiment of Fig. l, the interrupting point first to be broken comprises a terminal 40 on the upper end of a conducting rod 4| and a terminal 42 joined to terminal 40 by fusible solder 43. Terminal 42- is spring-biased outwardly by means of engagement of clamping nut 44 with the inwardly sprung end of a terminal cap 45 mounted on the upper end of elongated tube 46 which is comprised of fibrous or other suitable insulating and pressure resistant material. The annular stationary contacts 41, 48, 49, 50 and 5| of the subsequent interrupting points are secured in spaced relationship within the bore of tube 46 by means of screws 52. Movable contacts 53, 54, 55, 56 and 51, which are arranged for engagement respectively with stationary contacts 41, 46, 49, 50 and 5|, form parts of a longitudinally movable plunger of which rod 4| and terminal 46 also form parts. This plunger includes also insulating rods which serve to maintain contact 53 in insulated spaced relation to contact 54 and contact 55 in insulated spaced relation to contact 56. Electrically conductive rods 6| of the plunger serve to maintain contacts 54 and 56 in conductive spaced relation to contacts 55 and 51 respectively. As in the previously described embodiment, the supporting rods of the plunger are provided with sheaths of a suitable material, such as urea resin, capable of producing arc quenching gas and becoming non-conductive upon subjection thereof to heat of an arc. The sheaths on conducting rods 4| and 6| serve to prevent back arcing while the sheaths on non-conducting rods 50 serve to prevent carbonization. A lining 66 of similar material is applied to the inner walls of the tube intermediate the terminals and contacts. Also the lower inner end of the tube is provided with rubber or other material 61 having good insulating and heat-resisting characteristics. and a plunger catching element 33 of the form previously described are supported by a terminal ferrule 68 secured to the lower end of tube 46.

In the simplest form of the embodiment of Fig. 2, which form is illustrated in the partial view of Fig. 4, stationary contacts 41 and 4| are electrically interconnected by means of a conductor 10 separate from the movable plunger and secured to the outer surface of tube 44 by means of screws 52, although this conductor may be disposed in any other suitable location if desired, and stationary contacts 49 and 56 are similarly interconnected. If the arrangement of Fig. 4 is employed the circuit normally extends serially from upper terminal cap 45 through terminal 42, solder junction 43, terminal 40, rod 4|, contacts 53 and 41, conductor 10, contacts 44 and 54, rod 6|, contacts 55 and 49, a second conductor 10, contacts 50 and 56, the second rod 6|, and contacts 51 and 5| to lower terminal ferrule 63.

With the construction as just described, initiation of the interrupting action by rupture of solder junction 43 with resultant production of A gas filter, comprising plates 32,

.arc quenching gas under pressure, and initiation of downward movement of the plunger, take place in the same manner as described hereinbefore in connection with the embodiment of Fig. 1, and the plunger, after completion of the interrupting operation, is caught by the socket 88. However, the downward movement of the plunger results in a multiplicity of breaks due to separation of the contacts at the respective circuit interrupting points. The contacts at all of the in terrupting points may be arranged to separate simultaneously to produce simultaneous breaks. However, it is preferable to arrange the contacts in some manner so as to produce successive or cascade breaks. One means of accomplishing this is shown in Flgs.'2 and '4 wherein, with some exaggeration for clarity, it will be noted that the top of the movable contact of each succeeding interrupting point is displaced a slight bit farther upwardly from the bottom of its cooperating stationary contact than is the top of the movable contact of the immediately preceding interrupting point from the bottom of its cooperating stationary contact. Thus, the break at the third interrupting point, involving separation of the top of contact 54 from the bottom of contact 48, takes place a slight interval after separation of the top of contact 53 from the bottom of contact 41 at the second point, while the top of contact 55 separates from the bottom of contact 40 at the fourth point a slight interval after separation of contact 54 from contact ll at the third point, and so on for each succeeding point of interruption. As a result of this arrangement. it is insured that when the contacts at eachof the interrupting points separate, there has been built up previously in the preceding portion of the fuse tube bore a suiiicient pressure and quantity of arc quenching gas to insure effective extinction of the arcs formed upon separation of th contacts.

An important advantage of the constructions as liereinbefore described, particularly that of Fig. 2,.modified as shown in Fig. 4, is that the fusion of a single solder point is effective, after a time interval which may be adjusted as desired within limits, to produce either simultaneousiy or in cascade practically any number of circuit breaks with insurance of suflicient pressure and quantity of arc extinguishing gas to effect proper extinction of arcs at all of the interrupting points.

The basic construction of the embodiment of Figs. 2 and 4 lends itself very well to the provision of auxiliary circuit interrupting means for taking care of extreme excess current conditions. such as short circuits, while permitting the solder spot and the contacts of the multiple interrupting points with the expulsion action within tube II to interrupt excess current of lesser magnitude such as on overloads. This idea may be carried out as illustrated in Fig. 2 by substituting a current limiting fuse device for the conductors 16 constructed of material having the proper insulating andheat resisting characteristics; However, it is preferable to wind the fusible conductors l8 spirally on annular members 16 of star-shaped form, such as shown in Fig. ,3,

, mounted on tube 48, and constructed of high heat through the contacts of the multiplicity of interrupting points. The terminal cap and the terminal ferrule ll, respectively on the upper and lower ends of tube 65, are provided with flanged skirts Bil-which serve to support an outer cylindrical casing ll of glass, porcelain or other suitable material. Within this casing and embedding the wires II is a body of granular inert refractory insulating material such as sand or pulverized quartz. It is essential, of course, that the spacings between the current limiting fuse units on tube 46, be sufficient to insure proper insulation in view of the voltage drop between the units. The number and-lengths of wires I! are determined by the voltage and current to which they are likely to be subjected in installations for.

which the circuit interrupter is designed. Furthermore, the current limiting fuse units should beso designed with relation to the characteriswhile these latter units will effectively interrupt of Fig. 4. Such a current limiting fuse device may be employed in the form of a separate unit,

with stationary contacts 48 and 80, respectively,

by means of fusible elements in the form of one or more relativelyflnc wires l5, which may be wound spirally directly on tube 46 if this tube be high short circuit currents either without melting of the solder spot or in such a manner. that the current limiting fuse units will, in efiect, unload the multiple break expulsion part of the circuit interrupter. As is well known, the current limiting fuse units operate on the basis of extremely fast dissipation of heat and vapors from the fusible conductors through the surrounding body of inert material, and"such units are effective upon short circuit to limit the current to a value which is only a fraction of that which the system is capable of producing.

From the foregoing it will be apparent that the present invention is not limited to the details 1 of the embodiments herein described and illustrated and that various modifications thereof will occur to those skilled in the art. It is intended, therefore, that such modifications as do not depart .from the true spirit and scope of the invention shall be covered by the appended claims.

What I claim as new and. desire to secure by Letters Patent of'the United States:

1. In a circuit interrupter. a casing, means therein providing a plurality of serially connected inten'llP l-M points for producing serially related breaks in a circuit, the first of said points to be broken comprising a pair of relatively movable terminals Joined by a fusible element, other of said points comprising mechanically separable contacts, means operative to sheet rapid relative movement apart of said terminals to rupture the Junction therebetween upon fusion of said fusible element, means responsive to mi e between said terminals for producing gaseous 'u'c quenching to be broken comprising a pair of terminals, each supported for movement relative to the other, and a fusible element joining the terminals, other of said points comprising mechanically separable contacts, spring means operative to effect rapid movement apart of said terminals to rupture the junction therebetween upon fusion of said fusible element, means responsive to arcing between the terminals for producing gaseous arc quenching medium, and means operative upon rupture of said junction for effecting permanent separation of said contacts an appreciable interval after rupture of said junction and for producing discharge of said medium under pressure between said contacts.

3. In a circuit interrupter, a casing, means therein providing a plurality of serially connected interrupting points for producing serially related breaks in a circuit, the first of said points to be broken comprising a pair of relatively movable terminals joined by a fusible element, other of said points comprising mechanically separable contacts, said casing having a terminal cap with a resilient flexible portion engaging one of said terminals and normally sprung inwardly, means cooperative with said inwardly sprung cap portion normally to tension the junction between said terminals, said inwardly sprung portion being operative to eflect rapid relative movement apart of the terminals to rupture the junction therebetween upon fusion of said fusible element, means responsive to arcing between the for producing serially related breaks in a circuit, the first of said points to be broken comprising a pair of relatively movable terminals joined by fusible solder, other of said points comprising mechanically separable contacts, means operative to eifect rapid relative movement apart of said terminals to rupture the junction therebetween upon fusion of said solder,

means responsive to arcing between the terminals for producing arc guenching medium, and means operative upon rupture of said junction to eflect separation of said contacts and discharge of said medium under pressure between the contacts.

5. In a circuit interrupter, a casing, means therein providing a plurality of serially connected interrupting points for producing serially related breaks in a circuit, the first of said points to be broken comprising a pair of relatively movable terminals joined by fusible solder, other of said points comprising mechanically separable contacts, spring means operative upon fusion of said solder junction to efiect rapid relative movement apart of said terminals for arcing therebetween, means responsive to such arcing for producing arc-quenching medium under pressure in said casing, and means responsive to pressure in the casing for eflecting separation of said contacts and discharge of said medium between the contacts.

6. In a circuit interrupter, a casing, means providing a plurality of serially connected interrupting points for producing serially related breaks in a circuit, the first of said points to be broken comprising a pair of relatively movable terminals joined by fusible means, one of which terminals is supported and spring biased for rapid movement away from the other of the terminals upon fusion of said fusible means, thereby to produce arcing between the terminals, said other terminal being disposed on one end of a conducting rod longitudinally movable in said casing, the other end of which rod supports a contact normally engaged by a stationary contact supported by said casing, and means operative responsively to rupture of said junction and arcing thereat for efi'ecting longitudinal movement of said rod to separate said contacts and for discharging arc-quenching medium under pressure between the contacts.

7. In a circuit interrupter, a casing, means providing a plurality of serially connected interrupting points for producing serially related breaks in a circuit, the first of said points to be broken comprising a pair of relatively movable terminals joined by fusible means, one of said terminals being supported on one end of a conducting rod longitudinally movable in said casing and the other end of which rod supports a contact engaging a stationary contact supported by the casing, means operative upon fusion of the junction between said terminals to effect relative movement apart oithe terminals for arcing therebetween, a sheathing on said rod comprised of material capable of giving off arc-quenching medium upon subjection thereof to the heat of an arc, and means operative responsively to rupture of said junction and arcing thereat for effecting movement of said rod to separate said contacts and for discharging said medium under pressure between the contacts.

8. In a circuit interrupter, a casing, means providing a plurality of serially connected interrupting points for producing serially related breaks in a circuit, the first of said points to be broken comprising a pair of relatively movable terminals joined by fusible means, one of said terminals being supported on one end of a conducting rod longitudinally movable in said casing and the other end of which rod supports a contact engaging a stationary contact supported by the casing, means operative upon fusion of the junction between said terminals to effect relative movement apart of the terminals for arcing therebetween, said casing having wall portions in relatively closely spaced surrounding relationship to said rod and lined with material capable of giving off arc-quenchingmedium and becom ing non-conducting upon subjection of said material to the heat of an arc, and means operative responsively to rupture of said junction and arcing thereat for effecting movement of said rod to separate said contacts and for discharging said medium under pressure between said contacts.

9. In a circuit interrupter, a casing, means providing a plurality of serially connected interrupting points for producing'serially related breaks in a circuit, the first of said points to be broken comprising a pair of relatively movable terminals joined by fusible solder, one of said terminals being supported on one end of a conducting rod longitudinally movable in said casing and the said interrupting points comprising a stationary other end of which rod supports a contact engaging a stationary contact supported by the casing. means operative upon fusion of said solder Junction to effect relative movement apart of said terminals for arcing therebetween, a sheathing closely surrounding saidssolder junction and comprised of readily frangible material capable of giving 011- arc-quenching medium upon subiection of the material to arcing, and means operative responsively to rupture of said junction and arcing thereat for effecting movement of said rod to separate said contacts and for discharging said medium under pressure between said contacts. 4 l

10. In a circuit interrupter, a casing, a rod longitudinally movable in the casing, a pair of relatively movable terminals Joined by fusible means and one of which is supported by the casing while the other is supported by said rod, a pair of cooperative contacts one of which is stationarily supported by the casing in insulated spaced relation to said one terminal, and the other of which contacts is supported by said rod in spaced conductive relation with said other terminal, said one stationary contact having substantial extent in the direction of movement of said rod, means operative upon fusion of the junction between said terminals to effect relative movement apart, of the terminals for arcing therebetween, means operative responsively to rupture of said Junction and arcing thereat for effecting movement of said rod to separate said contacts and for producing discharge of arc-quenching medium under pressure between the contacts, and a metal sleeve supported by said casing in conductive relation with the casing supported one of said terminals and in closely surrounding spaced relation to the rod supported one of said terminals, which sleeve has substantial extent in the direction of movement of said rod to provide for relatively short arcing between the sleeve and said rod supported terminal substantially up to the instant ofseparation of said contacts.

11. In a circuit interrupter of the expulsion type, a tubular casing having a discharge openin: at one end, a plunger longitudinally movable in the casing, means providing a plurality of contact supported by the casing and a cooperating movable contact supported by said plunger in spaced conductive relation to said one terminal,

means operative upon fusion of the junction between said terminals to effect relative movement apart of the terminals for arcing therebetween, means operative responsively to rupture of said junction and arcing thereat for effecting movement of said plunger toward said one end of the casing to separate said contacts and for producing pressure discharge of arc-quenching gas between the contacts, and socket means adjacent said one end of the casing operative to catch said plunger while permitting expulsion of gases from said opening, which said socket means includes a closure element removable to provide for replacement of plungers in said casing.

13. In a circuit interrupter, a casing, means therein providing at least three serially connected interrupting points for producing serially related breaks in a circuit, the one of said points to be broken first comprising a pair of terminals joined by fusible means and one of which terminals is supported on a plunger arranged for movement in said casing, the second and third of said interrupting points each including' a pair of mechanloally separable contacts, one of which contactsof each pair is supported lay-the casing and the other of which contactsvof each pair is supported by the plunger, means to efl'ect movement of the plunger to separate the contacts of said second and third points in response to rupture of said fusible Junction, and means to cause pressure discharge of arc quenching medium between the separating contacts at said second and third points in response to arcing between the terminals at said first point.

serially connected interrupting points for producing serially related breaks in a circuit, the.

first of said points to be broken comprising a pair of relatively movable terminals joined by fusible means, other of said interrupting points comprising a stationary contact supported by said casing and a cooperating movable contact supported by said plunger, means operative upon fusion of said fusible means to eii'ect relative movement apart oi said terminals for arcing therebetween, means operative responsively to rupture of the Junction between the terminals and arcing thereat for effecting movement of said plunger toward said one end of said casing to separate said contacts and for producing pressure discharge of arc quenching gas between the contacts, and socket means adjacent said one end of the casing operative to catch said plunger while permitting expul- 14. In a circuit interrupter, a casing, means therein providing at least three serially connected interrupting points for producing serially related breaks in a circuit, the one of said points to be broken first comprising a pair of terminals Joined by fusible means and one of which terminals is supported on a plunger arranged for movement in said casing, the second and third of said interrupting points each including a pair of mechanically separable contacts, one of which contacts of each pair is supported by the'casing and the other of which contacts of each pair is supported by the plunger, means to eifect movement of the plunger to separate the contacts of said second and third points in response to rupture of said fusible Junction, and means to cause pressure discharge of arc quenching medium between the separating contacts at said second and third points in response to arcing between the terminals at said first point, the contacts at said second point being arranged to separate a slight interval after rupture of said junction and the contacts at said third point being arranged to separate a slight interval after separation of the contacts at the second point.

15. In a circuit interrupter,'means providing at least three serially connected interrupting points for producing serially related breaks in a circuit,

- the one of said points to be broken first comprisly movable terminals iolnedby fusible means, one

of which terminals is supported by a plunger a longitudinally movable in said anothcrof 7:!

ing a pair. of terminals joined by fusible means, the secondand third of said points each comprising a movable contact in mechanically separable engagement with a stationary contact, one of said terminals and the movable contacts of the second and third points being carried by a common movable support, said terminals being electrically connected with the contacts of said second point by a conductive portion of saidmovable support while the contacts of the second point are connected with the contacts of the third point by conductive means separate from said movable support, means to effect movement of said support to separate the contacts of the second and third points in response to rupture of the fusible junction at said first point, and means to cause pressure discharge of arc quenching medium between the separating contacts of the second and third points in response to arcing between the terminals at said first point.

16. In a circuit interrupter, means providing at leastthree serially connected interrupting points for producing serially related breaks in a circuit, the one of said points to be broken first comprising a pair of terminals joined by fusible means, the second and third of said points each comprising a movable contact in mechanically separable engagement with a stationary contact, one of said terminals and the movable contacts of the second and third points being carried by a common movable support, said terminals being electrically connected with the contacts of said second point by a conductive portion of said movable support while the contacts of the second point are connected with the contacts of the third point by conductive means separate from said movable support, said last mentioned conductive means including an auxiliary circuit interrupting device having operational characteristics differing from those of the fusiblev means of said first interrupting point, means to effect movement of said support to separate the contacts of the second and third points in response to rupture of the fusible junction at said first point, and means to cause pressure discharge of arc quenching medium between the separating contacts of the second and third points in response to arcing be tween the terminals at said first point.

17. In a circuit interrupter, an insulating cas-.

ing, means providing at least three serially con nected interrupting points for producing serially related breaks in a circuit, the one of said points to be broken first comprising a pair of terminals joined by fusible means, the second and third of said points each including a movable contact in mechanically separable engagement with a stationary contact, one of said terminals and the movable contacts of said second and third points being supported by a movable plunger in said casing with said one terminal electrically con nected with the movable contact of said second point by a conductive portion of the plunger, the other of said terminals and the stationary contacts of the second and third points being supported by said casing with the stationary contacts of the second and third points electrically connected by conductive means separate from said plunger, means to effect movement of the plunger to separate the contacts of the second and third points in response to rupture of the fusible junction at said first point, and means to cause pressure discharge of arc quenching medium between the separating contacts in response to arcing at said first point.

18. In a circuit interrupter, an insulating casing, means providing at least three serially connected interrupting points for producing serially related breaks in a circuit the one of said points to be broken first comprising a pair of terminals joined by fusible means, the second and third of said points each including a movable contact in mechanically separable engagement with a stationary contact, one of said terminals and the movable contacts of said second and third points being supported by a movable plunger in said casing with said one terminal electrically connected with the movable contact of said second point by a conductive portion of the plunger, the other of said terminals and the stationary contacts of the second and third points being sup ported by said casing with the stationary con tacts of the second and third points electrically connected by conductive means separate from said plunger, said last mentioned conducting means including a fusible conductor wound spirally on a portion of said casing and embedded in a body of inert arc quenching material surrounding said portion of the casing, means to efiect movement of the plunger to separate the contacts of the second and third points in response to rupture of the fusible junction at said first point, and means to cause pressure dis charge of arc quenching medium between the separating contacts in response to arcing at said first point.

19. In a circuit interrupter, an insulating casinghaving at least an outer portion thereof comprised of high heat resisting material and formed with a generally star-shaped cross-sectional contour, means providing at least three serially connected interrupting points for producing serially related breaks in a circuit, the one of said points to be broken first comprising a pair of terminals joined by fusible means, the second and third of said points each including a movable contact in mechanicallyseparable engagement with a stationary contact, one of said terminals and the movable contacts of said second and third points being supported by a movable plunger in said casing with said one terminal electrically connected with the movable contact of said second point by a conductive portion of the plunger, the other of said terminals and the stationary contacts of the second and third points being sup ported by said casing with the stationary contacts of the second and third points electrically connected by conductive means separate from said plunger, which said last mentioned conductive means includes a fusible conductor wound spirally on said star-shaped portion of the casing and embedded in a body of granular arc quenching material surrounding said portion of the casing, means to effect movement of the plunger to separate the contacts of the second and third points in response to rupture of the fusible junction at said first point, and means to causepressure discharge of arc quenching medium between the separating contacts in response to arcing at said first point.

KARL A. LOHAUSEN.

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