US2183751A - Circuit interrupter - Google Patents

Description

Dec. 19, 1939.

cs. F. M MAHON ET AL CIRCUIT INTERRUPTER 4 Sheets-Sheet 1 Filed Feb. 3, 1936 fiamseg/ 3 o 5 w 8 w a lll llll w x a k h 7 P w m J 6 V 1 G. F. M MAHON ET AL Dec. 19, 1939.

' CIRCUIT INTERRUPTER Filed Feb. 3, 1936 4 Sheets-Sheet 3 IHIIIII WMIMi 0 iii 3 8 a 7 1 l r d an Allan Dec. 19, 1939. cs. F. MCMAHON ET AL CIRCUIT INTERRUPTER Filed Feb. 5. 1936 4 Sheets-Sheet 4 1. I M E Q \\\\\\\\\\\\\\\\\\\\\w Nm v INA/811E115 Gear 2 F Mfl/ZZO/i Al ai? (227288 and ' Patentcd Dec. 19, 1939 r CIRCUIT INTERRUPTER George, F. McMahon,

Evanston,

Chicago, and Allan Ramsey, Ill., assignors to Schweitzer & Conrad, Inc., Chicago, 111., a corporation of Delaware Application February 3, 1936, Serial No. 62,118

88 Claims.

Our invention relates to circuit interrupters suitable for high tension power circuits.

The chief object of the present invention is to provide an improved circuit interrupter of the type employing a solid material from which there is evolved a gaseous medium serving to extinguish the arc whereby to interrupt the current flow, and which medium also serves to prevent reestablishment of the are after it is extinguished. The gaseous medium preferably is utilized to produce a blast directed into the space between the terminals.

The production of a circuit interrupter fulfilling such object presents two main difficulties. 15 First, there is the problem of securing positive circuit interruption of arcs occasioned by overloads which are of. low current values. The second is the provision of a suitable material and organization which, while permitting positive circuit interruption on overloads, will not limit too greatly the capacity of the device for interrupting large currents.

Our invention may be embodied in a wide variety of forms. An essential in all forms is creating discontinuity of the normal conductive path. This results in an arc. The extinguishing of this arc and preventing its reestablishment presents the fundamental requirement, whether the apparatus be a fuse, or a switch, or other apparatus. We show herein both a switch and a fuse embodying the basic features of the present invention. The circuit interrupter and particularly the fuse herein disclosed is a development in part of the so-called ejector cutout shown in Conrad 35 Reissue Patent No. 17,612, of March 4, 1930. The circuit breaker herein disclosed is of the one shot type disclosed 1,836,069, of April 6, 1920. The ejector cutout employed a spring-tensioned fuse link consisting of a strain wire paralleled by a fusible conductor, both being surrounded by a cork, and which link was housed in an open-ended fiber tube. The cork furnishes a under the action of the arc, is decomposed by heat to furnish a gas that serves to put out the arc and prevent its reestablishment. The bore of the fiber tube directs the evolved gases and vapors under all conditions of operation and serves under so heavy current operation as a material from which the heat of the are, by destructive distillation, drives off arc extinguishing gases. This device thus provided the advantage of the evolution of gas for producing the desired pressure of gas and 55 the so-called blast or expulsion action. In mechanical structureit offered a simple and effective device. This arrangement with the cork free to move out of the end of the tube when only light gas pressure developed in back of it, at times caused a low current arc. which should have in Conrad Patent No.

reduced bore of material which,

been interrupted in the cork, to transfer to the lower tube ferrule and be extended in the relatively large bore of the tube. which was'relatively slow and feeble in-evolving gas on low currents.

When a heavy current is to be interrupted, the cork is blown out of tube almost instantly, and does little or nothing toward interrupting circuit. The gas evolved from the tube lining, at a rapid rate, is the arc extinguishing medium.

The present invention involves the principle of the retreating terminal in an arcing tube supplied with a specially provided solid material suitable to evolve gases. It utilizes the two-bore principle of the ejector cutout for the two ranges of current flow. In the preferred form of the invention, the strain wire and fuse wire are disposed in separate bores.

Circuit interrupters, and particularly fuses for the service for which the present invention is particularly applicable, are called upon to interrupt the circuit chiefly under two general conditions. The first is known as overload, and it involves a flow of current in excess of the current rating of the fuse and persisting for a longer period of time'than the fuse is intended to remain intact under such conditions according to its predetermined time-current characteristic. This condition produces an arc of low energy release in the device and, consequently, unless specific provision is made, inadequate gas evolution is likely to occur. The second condition is that of low impedance fault condition where a great flow current results. This is often termed short circuit condition. The flow 'of current produces a violent release of energy with a consequent violent evolution of gas, producing a blast action which insures a satisfactory ability'to extinguish the arc. The same conditions are encountered in a switch or circuit breaker.

A device of the character herein disclosed is generally designed with reference to the maximum flow of current which it is intended to interrupt. If the current should exceed this maximum'rating, the pressure of the evolved gases may be dangerous to the integrity of the structure. When less than the rated maximum occurs, the tendency is for the gas evolution to be less violent and less effective. Hence, unless special provisions are made to meet the situation, an overload current may produce insuflicient gas evolution to produce the necessary extinguishment of the, arc. One of the particular features of the present invention is the organization of the device to accomplish extinguishing of the are under all conditions of current flow under which it may be called upon to operate, and particularly in the case of a fuse under all conditions of current flow which cause melting of the fusible element.

An electric fuse is a protective device. As such,

it should be accurately responsive to the conditions for which it is intended to become active. Furthermore, such accuracy and responsiveness should be stable and permanent. It should be so designed and constructed as to operate in accordance with some certain predetermined time-current characteristic. It must carry full rated load without damage and Without impairment or change of its predetermined characteristics. Also, it must be capable of taking transient overloads without operation and without changing its predetermined characteristics.

Fuse conductors of the type usually employed, operating at elevated temperatures, are peculiarly subject to chemical attacks by oxygen or other reagents in the atmosphere or other surrounding medium. When the fusible element assembly stands under spring tension, the conditions produced by heating or by corrosion, or by both, are highly adverse. According to the present invention, we employ as the fusible element a silver, or silver alloy wire which is substantially free of chemical attack by oxygen or other usual reagents present in the atmosphere or in a fuse housing of fuses of this type. Also, we employ, as a chemical arc extinguishing medium, a substance such as magnesium hydrate, boric acid, or the like, which, as solids or powders, when compressed or molded, will possess good mechanical properties and which will deliver, under the action of the are, a vapor or other gaseous medium favorable to are extinction and the surface of which material, following circuit interruption at current zero, regains its insulating properties at a greater rate than the recovery of the system voltage.

It is an object of the present invention to provide blast producing means suitable in form and composition and properly organized in correlation with the other parts of the circuit interrupter to provide satisfactory operation throughout all values of current flow to be interrupted.

The above and such additional substances as are herein disclosed do not, when used in a fuse, cause corrosion of the fuse wire, and being subjected to the normal operating temperature of the silver fuse, will not deteriorate.

To avoid the effect of the spring tension upon the rather soft metal of the current sensitive element, and particularly when the same is at an elevated temperature, we employ as a strain wire a high tensile strength wire of a higher electrical resistance than silver, which strain Wire is also highly resistant to chemical attack and retains its properties under rated current flow and will not melt or lose its tensile strength until after the fuse wire is melted in the operation of the device.

The strain wire and current sensitive wire cooperate in a novel manner herein in acting as two I parallel fuses of different current carrying capacities and different resistances. The fuse wire itself first melts and throws the current through the strain wire which, for a very brief period,

carries the full flow of current during overload operation. Any are which would tend to be formed by the silver fuse wire is put out by the effect of the parallel path through the strain wire. The strain wire then parts and releases the spring terminal and produces elongation of the arc, together with the desired blast action.

Optionally the strain wire may be so constructed that it will continue to maintain the arc, particularly under low current operation, so as to allow increase of the gap at the melted'silver fuse before extinguishing of the arc at the strain wire occurs. This tends to establish the arc definitely at the severed ends of the strain wire, particularly under low current are conditions, and is desirable particularly where, as in certain forms of the present invention, the strain wire is disposed in a separate bore and subjected to an individual blast action to extinguish the arc therein. Also, the strain wire may be normally out of the circuit and connected into the circuit only by the increase of potential across the terminals of the silver wire upon melting, or by the effect of ionized, gases, as by introducing a gap in the circuit of the strain wire. This may be done by insulating the strain wire at the suspending pin.

If the rise of voltage is such as to cause the arc to be reestablished between the terminals of the fuse element in a separate bore or in an enlarged bore, the arc extinguishing material available there will provide the blast for extinguishing the arc and preventing reestablishment. In addition to the purely blast action the pressure of the gaseous medium may also be utilized in the action of arc extinguishing. Also, chemical action of the evolved medium with the metallic or other constituents of the material by which the arc is sustained or chemical reactions initiated by the arc to evolve the gaseous arc extinguishing medium may be employed.

A feature of the present invention is the construction and organization of the strain wire to insure blowing thereof in the corresponding bore at a point remote from the outlet so as to secure the desired blast action for overload operation. A further feature is the arrangement of the fuse wire so it will form its interruption adjacent 1 the outlet of the bore with which it cooperates to put out a heavy current arc, particularly to prevent too violent action on heavy current operation.

A further general object of the invention is to provide, in a device of the present type, a novel and useful disposition of the arc establishing means and the cooperating arc extinguishing material in order, in the case of a fuse, to promote stability of the components during normal load current conditions and. in any form of device to promote effectiveness during interrupting action. A further object is the provision of novel are extinguishing materials for fuses of this type.

A further object is the provision of a refill unit so organized as to facilitate refilling of the device in the field, to prepare it for another circuit interrupting operation.

A further object of the invention is to improve the operation of circuit interrupters of this general type Now in order to acquaint those skilled in the art with the manner of constructingand operating a device embodying our invention we shall describe, in connection with the accompanying drawings, a specific embodiment in which our invention appears.

In the drawings:

Figure 1 is a longitudinal vertical section of a fuse embodying our invention;'

Figure 2 is an isometric view of the upper ferrule showing the integral chuck jaws;

Figure 3 is a side elevational view of the operating parts of the fuse, including the refill unit;

Figure 4 is a longitudinal section through the insulating sleeve and liner for the refill unit shown in Figure 3;

Figure 5 is a side elevational view of one form of plunger or arcing terminal and connected fuse which forms also the strain wire;

Figure 6 is a fragmentary sectional view showing a detail of the connection between the movable plunger or arcing terminal and the associated refill unit;

Figure 7 is a cross-sectional view taken on the line 1-1 of Figure 6;

Figure 8 is a longitudinal vertical section through a modified form of fuse;

Figure 9 is a longitudinal section on an enlarged scale of the refill unit shown in Figure 8;

Figure 10 is a longitudinal vertical section through another modified form of fuse of our invention;

Figure 11 shows a modified form of strain wire;

Figure 12 is a side elevational view with the upper part in longitudinal section showing a circuit breaker embodying our invention;

Figure 13 is a longitudinal sectional view of the upper part of a modified form of circuit breaker; and

Figure 14 is\a fragmentary longitudinal section through a modified form of refill unit.

The fuse device shown in Figure 1 comprises two main parts, namely, first, the housing, which in the housing. The manner in which this is accomplished will appear more clearly hereinafter but it may be pointed out here that the refill unit is mechanically and electrically coupled to the ferrule 2 by the chuck or compression coupling 1 at the upper end of Figure 1. The opposite end of the refill unit is coupled by a screw coupling to the upper end of the spring and cable assembly 5 and the lower end of the spring and cable assembly is coupled to the plug 6 by a similar screw coupling.

The glass sleeve I has cemented upon its lower end ferrule 3, which ferrule is made of brass, bronze or the like, provided with a bore of great enough size to pass the refill unit 4 therethrough.

This bore is provided with internal screw threads 8 and with these screw threads is adapted to cooperate the threaded external surface 9 of plug The plug 6 is provided with a pair of saw cuts Ill-l0 for the application of a suitable wrench or the like to draw the plug tight upon the screw threads or to loosen the same.

The plug 6 has an integral threaded stud I 2 which threads into the corresponding threaded opening in a disc member l3. The disc member I3 is exteriorly provided with a helical groove, into which groove are threaded the lower convulutions I 4 of the helical tension spring IS. The disc or spring anchor I3 is provided with a relatively deepgroove on its back side to receive a fiat ring l6 thereinto. The disc or spring anchor- I3 is drilled parallel to its axis to provide three holes to receive the lower ends of'the flexible strands l8 and also to provide three holes for the clamping screws I! which extend into and thread into the clamping ring l6. The ends of the flexible leads or cables l8 are passed through the corresponding holes and preferably are bent over within the groove which-receives the ring I6, and these bent-over ends are clamped by the ring l6 through the medium of the screws ll.

The ends of the leads l8 may be bushed out and tinned after being passed through the holes in the spring anchor l3 and then clamped by the ring l6, but it is not desirable to rely solely on tinning or soldering to provide the electrical connection.

The plug 6 is provided with an overhanging rim or flange l9 to provide a substantially tight joint or fit endwise of the ferrule 3.

The upper ferrule 2 is shown in isometric view in Figure 2. It comprises a cylindrical portion provided with a suitable counterbore at 20 for receiving the upper end of a glass tube. or sleeve I. A suitable alloy or other cementitious material is employed to make a mechanical and preferably, but not necessarily, fluid-tight joint between the upper end of the glass sleeve and the ferrule 2. The lower ferrule 3 is similarly mounted upon the lower end of the glass sleeve l.,

Both of these ferrules 2 and 3 are slabbed off at their sides to provide fiat parallel faces such as 23 shown in Figure 2 for engagement with mounting jaws for supporting the device. Obviously, the exterior of the ferrules 2 and 3 may be otherwise shaped or fitted for engagement with mounting jaws and/or trunnions or similar connectors to put the fuse in an electric circuit and to hold the same mechanically in place.

Preferably in mounting this fuse the discharge end is directed downwardly. This is optional.

The upper end of the ferrule 2 has integral cone clutch jaws 24 formed thereupon and a collet or cone nut 25 has an internally threaded portion cooperating with the threads 26 and a tapered or conical chucking surface at 21 which, when the nut is drawn tight on the threads,

.forces the spring fingers 24 radially towards the center or axis to produce a clutching action, Since the ferrule 2 is made of cast brass or bronze, it provides the necessary spring action within the required limits. By unscrewing the collet or nut 25, the spring fingers 24 tend to spring outwardly into the original position.

The refill unit 4 comprises an outer fixed heavy sleeve 28 which may be made of fiber, but which preferably is made of fiber paper impregnated with Bakelite and rolled into a sleeve and cured. At the upper end, as shown in Figure 1, the hollow brass terminal member 29 embraces and is pinned upon the upper end of the outer sleeve 28. This tubular terminal member 29 is reduced in thickness and threaded at its outer end, as indicated at 30, to receive the internally threaded ring 32. This ring 32 serves as an annular shoulder or catch for engaging the upper ends of the spring fingers 24. The ring 32 may be unscrewed to release the refill unit in case it is desired to remove the refill unit, in the initial or unfused condition. from the housing in which it may be mounted. The bronze cross pin 33 is passed through a diametrical opening in the upper end of the tubular terminal member 29 and the ring 32 closes the ends of the opening in which it lies. The outer end of the tubular terminal member 29 is counterbored to provide a shoulder upon which rests a mica closure disc 34. This disc might be made of any other suitable material either metal or insulation. Mica may be utilized because of its transparency. It closes the terminal against the entry of extraneous material but is not absolutely tight.

Preferably, the fuse is mounted with this end and the plug 31 is preferably made of brass.

in external diameter and a thin sleeve 35 of fiber or fiber treated with Bakelite slips over said reduced end and is pinned as indicated at 36. This serves as a protection for the glass sleeve I. The glass sleeve l permits of convenient inspection and shows whether the device has operated.

The lower end of the bore of the tube 28 is threaded to receive an apertured brass plug 31. The plug 31 has a central hole through the same, the upper end of which is circular at 38 and the lower end 39 of which hole is hexagonal so as to receive the hexagonal portion 40 of the terminal plunger 42. Thus, by the interfitting hexagonal opening in the plug 39 and the hexagonal surface of the lower end of the plunger 42, the plunger is free to be withdrawn when released at its upper end, but the parts normally are non-rotatable and non-separable so long as the strain wire is intact.

The lower end of the plunger 42 is provided with a threaded stud 43 which is threaded into a spring anchor member 44 which, in all essential respects, is like the lower spring anchor member I3 heretofore described. In other words, the spring and cable assembly unit has the same construction at each end.

The thin fiber sleeve 35 extends down over a portion of the spring and cable assembly and serves, when the fuse blows, to keep metallic particles and vapors which might be blown through the clearance about the plunger from directly striking the glass. Such deposits are then removed when the blown refill unit is removed.

The plunger 42 is preferably made of copper Immediately above the plug 31 and within the sleeve 28 is a liner or tube 45 of a compressed powder forming an arc extinguishing material.

This material may be any one of a number of substances which we have discovered to be suitable in this form and in this organization, but we prefer magnesium hydroxide which, under the influence of the arc yields an excellent medium for a blast to extinguish the are. It is a relatively cheap material giving off an effective medium at not too great a pressure for the satisfactory operation of the device.

's.We may employ for this material boric acid which also serves very well in the present construction. There are a number of other materials, which we shall discuss later in more detail, suitable for this service.

The upper end of the plunger 42 is reduced in diameter to receive telescopically the lower end of the fiber sleeve 46. The plunger 42 is held normally in position by the strain wire 41 which is' formed of a nickel-chromium alloy obtainable on the market as Nichrome or Chromel. 'Ifhis wire is of single thickness at the central portion and is formed of double thickness at the top and bottom by looping back the ends and welding the ends to the body of the wire so as to form two loops for attachment of the wire to the plunger and to a cross pin 48 mounted in the tubular terminal 29, respectively. The lower end of the wire 41 is held in a bore 49 formed in the upper end of the copper plunger 42 by means of a end in order to make certain that the single wire section falls well within the fiber tube 46. so that rent.

. can be screwed down tight.

the initial formation of an are at the strain wire will be down in the tube so that an adequate blast will be secured.

A silver or silver alloy fuse wire 52 at its lower end is attached to the copper plunger 42, as follows: A slot or keyway is sawed into the outer surface of the upper end of the plunger, the wire 52 has its end laid thereinto, and the edges of the slot are then battered or riveted over the silver Wire to form a good mechanical and electrical connection extending along a fairly good length of the wire so as to secure excellent conductivity. At its upper end the silver wire 52 is extended diagonally or radially through a drilled hole in the tubular terminal 29 and the walls of the hole are distorted as by means of a prick punch or the like to pinch the walls of the brass terminal 29 upon the lateral surfaces of the end of the wire. The silver wire 52 lies within the fiber sleeve 46 closely adjacent to but out of contact with the strain wire 41. The silver wire is not under mechanical tension from the spring l5, but the strain wire 41 is.

At its upper end the bore of the fiber tube 46 is plugged with an asbestos plug or the like for the purpose of holding within the fiber sleeve 46 the filling 53 of arc extinguishing material which completely fills the available space within the fiber tube 46. Thus both the strain wire and the silver fuse wire 52 are in contact with arc extinguishing material which, in the present construction, is a powder filling within the said sleeve 46. The plunger 42 is just enough smaller than the bore of the liner of arc extinguishing material 45 to provide satisfactory mechanical clearance. Likewise, the sleeve 46 is of substantially the same outer diameter as the bore of the said liner 45. The fiber tube 46 may be utilized for this purpose without any filler. Optionally it may be impregnated with a suitable material.

The upper end of the bore of the liner 45 may be flared outwardly to provide a clearance extending substantially from the upper end of the copper terminal towards the open end of the liner 45 to permit lateral rupture of the fiber tube 46 more easily and freely in the case of large cur- In either form, light current operation expels the contents of the fiber tube 46. Heavy current operation may destroy or expel the fiber tube 46.

The housing member comprising the glass sleeve and the ferrules may be provided with the operating parts by dropping the refill unit, with spring and cable assembly 5 and plug 6 connected thereto, through the opening in the ferrule 3. Due to the longitudinal contraction of the spring 15 the upper end of the refill unit 4 will not reach the chuck 1 and therefore the plug 6 This closes the lower end of the fuse housing. Then a hook-like instrument similar to a button hook is inserted into the open end of the ferrule 2 and engages the bronze pin 33 at the notch in the center, whereupon the refill unit 4 may be pulled upward to tension the spring I 5. The nut 25 being backed off to allow the spring fingers to spring outward at this time, permits the upper end of the refill unit 4, with the ring 32 upon the upper end thereof, to be pulled through the spring fingers 24, whereupon the spring fingers catch back of the ring 32 and prevent retraction. Thereupon the nut or collet 25 is tightened to grip the tubular terminal 29 mechanically and electrically. The fuse is thereby charged. In refilling, the operation is substantially the same, namely, that the plug 6 is unscrewed, the collet or nut 25 is loosened, and the upper end of the used refill unit is pulled out in the upward direction as viewed in Figure 1. Then, when the used plunger 42 is removed, the spring and cable unit may be coupled, by threading, to a new refill unit and the entire assembly then brought together as above in interrupting current is as follows: Assume that the device is standing under normal current load; the fuse wire 52 will be at a fairly high temperature, well below its melting point, but if the current exceeds the rated value for a predetermined length of time, melting of the silver fuse wire will occur. The resistance of the strain wire 41 is very much higher than that of the silver wire and normally practically no current flows through it. If desired, the pin 50 or the pin 48 may be wrapped with insulation or made of insulation so as to definitely take the strain wire 4'! out' of the circuit and require it to be brought into the circuit only when the fuse'wire 52 blows. This insures that the silver wire will be blown and dissipated to form a gap and a resulting are before the current is caused to jump the gap and pass through the strain wire. If the strain wire is connected in parallel, the rise of current will blow and dissipate the silver fuse wire before the strain wire melts and forms an arc The heat of the fuse Wire 52 under load is not slulicient to cause decomposition of the material 53 in the sleeve 46. Different compositions of arc extinguishing material may be used in the sleeve 46 and in the main sleeve 28, due to the differences in temperature to which the two are normally subjected in service. The material disposed in the sleeve 46 may be of different characteristics from that of the liner 45.. Thus, for example, the filling 53 in the sleeve 46 may be limestone or the like. The'material inthe liner 45 may be of magnesium hydroxide, aluminum hydroxide, chromic hydroxide, or other metallic hydrates, or boric acid or similar materials, which substances tend to decompose at temperatures which may not be much removed from the running temperatures of the silver fuse 52 under rated load. Metallic hydrates are preferable to boric acid for the higher running temperatures.

For fuses of very low current rating the entire normal current flow may proceed through this strain wire without a parallel silver wire at all. That is to say, a nickel chromium fuse link 55 may form the sole connection between the plunger 56 and the tubular terminal member 29 and pin 48. In that event, it is not necessary to have the fusible section of the link 55 disposed as low in the liner 45 of arc extinguishing material as is shown in-Figure l.

The link 55 shown in Figure is formed of a nickel chromium wire looped at the upper end and having the loose end welded parallel to the main body of the link at the upper end. At the lower end, the wire is passed through the transverse hole 5'! in the upper end of the plunger 56 and is looped back and welded to the main body of the link. At its lower end, the plunger 56 is provided with the threaded stud 43 to make a coupling with the spring anchor 44. It is also provided with a cross pin 58 which is adapted to lie This is an optional feature,

in a transverse slot in the plug 31 to prevent turning of the plunger with respect to the plug 31 and sleeve 28, as will be described in connection with the form of fuse shown in Figures 8 and 10. The bore of the liner 45 and the diameter of the plunger 42 will be varied in accordance with the maximum rating of the device. That is to say a smaller plunger, and hence a smaller bore,-may be employed where the maximum interrupting capacity is less and these parts are made larger where the maximum interrupting capacity in amperes is to be larger.

In Figure 3 I have shown a modified form of refill unit which may be employed in the same fuse housing as shown in Figure 1. In this construction, the outer heavy sleeve 28, the thin Bakelite sleeve extension 35, and the upper tubular terminal member 29 with the removable threaded ring 32, are substantially the same as struction as shown in connection with Figure 1,

but the upper end of its bore is flared out at 59 to provide a chamber in which the silver fuse element 66 is disposed. In this case, the plunger 62 is hollow throughout the major part of its length, and in the bore thereof there is disposed a fiber tube 63 which is designed to coact with the are formed upon melting of the strain wire 64. The strain wire in this case is provided at each end with a loop or bight, the upper end being anchored by the pin 48 to the tubular terminal 29. The lower end of the tube and the stem are provided with a cross-drilling to receive the pin 65, this pin having a reduced extension 66 which passes through the loop at the lower end of the strain wire 64 and has its outer end riveted at 61 to hold the cross pin firmly in place. The strain wire is thus made of double thickness by the ends which are bent back and welded to the main portion of the wire except along the portion 68, where the wire is of a single strand. The tendency, therefore when heated by excess current, is first to melt or yield at this single strand portion 68 which is disposed down in the fiber tube 63.

The fiber tube 63 extends for a short distance 10. The outer end of the fuse wire 60 is extended through a drilled diagonal hole the walls of which are collapsed upon the end of the fuse wire to make good electrical and mechanical connection.

The cross-pin 65 in the lower end of the plunger 62 lies in a transverse slot in the brass plug 31. The solid end of the plunger 62 closes both the bore in the said plunger and the bore of the fiber tube 63.

The outer end of the tubular terminal member 29 is here shown as provided with transverse drilled openings for receiving a bail-like instrument for pulling the refill into place. Obviously, a cross-pin or other instrument for this purpose, as shown in Figure 1, may be substituted. The removable plug or disc 34 closes the assembly against the entry of extraneous matter. It is blown out upon operation of the fuse.

In the operation of the present fuse employing the refill shown in Figure 3, an overload will first melt the silver element 60 and then cause melting of the strain wire at the single strand portion the inner end of 88 which is well down in the fiber tube 88. This fiber tube yields an arc extinguishing gas under the influence of the arc and produces a blast which blows the remains of the strain wire 64 outwardly, if of suflicient violence, but under any circumstance is sufficiently effective to put out the are even under low overloads. At the same time the plunger 62 is retracted by the spring, increasing the gap at the point where the silver element has melted and also the gap produced by melting of the strain wire. The are, therefore, after being extinguished is not reestablished.

On heavy current operation the silver fuse and the strain wire will melt substantially simultaneously, although there is a tendency for the silver fuse to go out first and the strain wire to keep the are from reforming at the silver wire until the strain wire has parted and formed an arc.

The arc will tend to either reform or to persist at the gap in the silver fuse wire, that is, between the outer end of the plunger 62 and the tubular terminal 29, although it is quickly put out in the arcing tube 63 after the strain wire melts and produces an arc and blast therein. The movement of the plunger away from the open end tends to extend the are in the bore between the fiber tube extension 69 and the bore of the liner 45. This are, therefore, is brought in fairly close relation to both the arc extinguishing material in the sleeve 45 and in thev extension of the fiber tube 68. The result is a suitable evolution of gas, largely steam, from the arc extinguishing material in the liner 45, and carbon monoxide, hydrogen, and some water vapor from the fiber extension 68. This blast is effective to extinguish the arc and to prevent its restriking'after passing through current zero.

The strain wire 84 may take the form shown in Fig. 11, where the end 5| of the wire that forms the lower loop is extended beyond the single strand portion 68. Melting at 68 allows the strain wire to part and release the plunger 62 so that the gap at the ends of the silver wire 8|) v is increased to a point where the are, once extinguished, will not be reestablished. The overlap of part 5| with the double strand portion maintains the current flow at this point long enough to allow the separation of the terminals of the main fuse 60 as above described. The strain wire 84 may be employed with a gap, as by an insulated layer on one of the supporting pins such as 48 or 65. The extension 5| is of low enough carrying power that in the case of a heavy current operation it will promptly be melted and the arc in the small bore extinguished ahead of that in the large bore.

In Figure 4 we have shown the fiber tube 83a as counterbored to receive a liner 13 of a suitable arc extinguishing material, such as magnesium hydroxide or the like, for cooperation with the arc formed upon melting of the reduced section 68 of the strain wire. This dry arc extinguishing material 13 may be packed in loosely to fill the entire space in the bore, or may be formed as a compressed self-sustaining sleeve. Also, we pro vide an external cylindrical body 15 of arc extinguishing material between the silver fuse element 80 and the projecting end of the fiber tube. This body 15 may be made of fiber or any of the arc extinguishing materials herein disclosed. The body 13 may be made up of rings or sections, as illustrated in Figure 14.

In Figures 8 and 9, we have illustrated a modified form of fuse embodying a disposition of strain wire and fusible link similar to the arrangement shown in Figure 3, but in which the refill unit is inserted from the discharge end of the housing.

In this construction, the upper ferrule 18, mounted on the upper end of the sleeve of glass I, is provided with a threaded counterbore l9 terminating in a shoulder 80 upon which the flange 82 of the refill unit is adapted to be seated. This flange 82 is preferably an integral part of the tubular 'terminal member 28a mounted on the upper end of the outer Bakelite sleeve 28 that surrounds the liner 45 of arc extinguishing material. The Bakelite tube 35 which forms the extension of the heavy tube 28 surrounds the spring l5 as in the modification heretofore described. The lower ferrule 83, which is fastened upon the opposite end of the glass sleeve I, has a central opening through the end thereof for receiving a stud 84, which stud is formed as an extension of the lower spring anchor member Hi. The stud 84 is provided with a central axial socket 85 which is threaded to receive a rod by which the spring I5 is tensioned after the refill unit and the spring and cable assembly coupled to it are introduced into the upper end of the housing.

The stud 84 is provided with a cross pin 88, the projecting ends of which enter slots forming extensions of the hole in the bottom of the end wall of ferrule 83 to prevent turning of the stem 84. The pin 86 is shown as spaced from the bottom spring anchor I3 by a distance less than the thickness of the bottom wall of cap 83. A plain nut 81 screws down on the stud 84 to clamp the anchor 13 against the inside bottom wall of the cap 83,

The tubular terminal 29a carries a cross pin 48 upon which is suspended, through the strain wire 84, the movable hollow plunger 82 containing the fiber liner 63. The fiber liner 83 has the extending portion 69 disposed above the upper end of the metal part of the plunger 62. The silver wire 68, which is fastened at its inner or lower end, as shown in Figure 9, to the plunger 62, has its upper or outer end secured in the metal of the annular flange 82 by being passed through a drilled hole, the walls of which are then collapsed upon the end of the wire. plunger 62 passes through the brass plug 31 which has a cross notch for receiving the pin 88 to key or pin the plunger tothe sleeve 28 so that the spring and cable assembly may be coupled to the plunger and sleeve portion on the threads 89 of the stud member 90, which stud member is threaded into the lower end of the tubular plunger 82 to close the same and to provide a mechanical coupling between the spring and cable assembly and said plunger.

An anchorage for the lower end of the strain wire 84 is provided by a plug 92 which is drilled to receive the two legs of the loop 83 by which the strain wire is anchored to said plug 82. The extending end. of the loop is brought parallel to the main body of the strain wire and welded thereto as heretofore described.

A thin removable disc 94, which may be made of mica or bakelized fiber, is held by its margins under a threaded ring 95 which is provided with a suitable wrench slot 98. Mica is transparent, resilient, and unaffected by heat or by the action of the weather, and is particularly suitable. The disc 94 is adapted to be readily blown out upon pressure being generated inside the housing.

The operation of'the form of fuse shown in Figures 8 and 9 is substantially the same as that escribed in connection with Figure 3. The chief At its lower end the in the cross-slot in the plug v3'I.

difference between the two forms is in the method of assembly or refilling. It' is to be observed that the refill unit is introduced from the discharge end of the housing, the flange 82 resting upon the stationary shoulder 88. Then a threaded rod is introduced through the opening in the bottom of ferrule 83 and threaded into the socket 85, whereupon the stud 84 with its keying pins 86 may be drawn through the opening and the spring I5 thereby tensioned, the nut 81 being threaded over the rod and tightened. Thereupon the disc 94 is laid over the open end of the refill unit and the threaded ring 95 is fastened down.

The pin 48 may be releasable by the blast or it may be fixed permanently in position, as in the construction shown in Figures 1 and Ii. The margins of the disc 84 may be clamped against the circular shoulder if desired, so that a fairly tight joint is produced. At the opposite end a substantially tight joint is secured around the stud 84 by the nut 81. An additional cap nut (not shown) may screw on the stud 84 to form a tight joint. Obviously, the stud 84 may be held in place in various other ways.

The form of plunger shown in Figure 5 may be employed in this form for low ampere rating. Likewise, the form of plunger in which arc extinguishing material .is disposed within the fiber tube 83a, as shown in Figure 4, may be'employed in the device of Figures 8 and 9.

The fuse of Figure 18 employs the method of reloading of the fuse of Figures 8 and 9 and it shows the disposition of the silver fuse wire and the strain wire substantially the same as that disclosed in Figure 1. The tubular terminal 29 mounted upon the outer Bakelite sleeve 28 has a cross-pin 48 upon which is suspended the upper loop of the strain wire 52. The upper end of the silver wire 41 is extended through an opening formed radially in the flange 82. The lower end of the strain wire 52 is suspended on a crosspin 58 passing transversely through the upper end of the plunger 42. The lower end of the silver wire 41 is laid in a slot or extended in a drilled hole and clamped therein by battering over or deforming the side walls of the opening. The thin fiber sleeve 48 is mounted upon the upper end of the plunger 42 and lies between the two fusible conductors and the liner 45 of arc extinguishing material.

The space within the sleeve 48 and-surrounding the fusible conductors 52 and 41 may be filled with a suitable are extinguishable material or an inert filler, as desired. The lower end of the plunger 42 is keyed by means of the pin 58 lying The lower end of the plunger 42 is provided with a threaded stud 43 by which it is coupled to the upper spring anchor 44. The lower spring anchor I3 has the extending stud 84 with the threaded axial socket 85 as described in connection with Figure 8 for extending the spring I5 and bringing the stud 84 through the opening in the lower ferrule 83. The threaded ring 85 rests upon the flange 82. The outer end of the tubular terminal member 29 is provided with a shoulder upon which rests the mica disc 34. This disc is held in place by a spring snap ring 91. This form of fuse is assembled as described in connection with Figures 8 and 9 and its mode of operation is substantially that as described in connection with Figure 1.

The sleeve or liner 45 may be made of sections or rings and these rings may be made of different material. The innermost rings may be made of a material which is more easily decomposed and the outer ones of material which requires higher temperature to produce decomposition.

In Figure 14, I have shown a fragmentary longitudinal section through the relatively stationary part of the refill unit wherein the outer fiber sleeve 28 having the upper metal terminal pinned thereto at the upper end and the threaded ring 31 inserted at the lower end carries rings of arc extinguishing material of different characteristics. The uppermost funnel-shaped ring I88 which defines the arcing chamber 59 for the silver fuse wire as shown in Figures 3, 8 and 9 lies at the top of a stack of rings of which the outer rings I83 are of a solid arc extinguishing material such as aluminum hydroxide and the innermost or facing rings I82 are formed of a different solid material which may be, for example, magnesium hydroxide. The rings I82 and I83 are held in place between the ring I88 of fiber or other are extinguishing material at the upper end and the threaded metal ring or bushing 31 at the lower end. A suitable plunger, such as shown in any of the forms of 'fuse herein illustrated may be employed in conjunction with the cartridge assembly shown in Figure 14.

Obviously, the details of any of these forms may be modified or interchanged, as will be apparent to anyone skilled in the art.

Figure 12 shows a "one-shot circuit breaker of the general type disclosed in Conrad Patent No. 1,336,069, of April 6, 1920. Such a device may be employed as a normal connecting link between a line and apparatus to be protected, or between two parts of an electric circuit, or it may be brought into circuit for the purpose of interrupting current flow in a-line under load conditions. While the device is shown as adapted to be operated manually by a tension member I88, operating a trip bell crank lever I82, it .will be understood by reference to the aforesaid patent that automatic operation may be provided if desired. The device comprises a tubular sleeve I83. of insulation which'may be, and preferably is, fiber impregnated with a suitable synthetic resin or the like. Upon the upper end, as illustrated in Figure 12, there is mounted a ferrule I84 provided with an extending portion threaded internally as indicated at I 85 for receiving a threaded metallic terminal I88 having a hexagonal head I81. The ferrule I84 may similarly have ,a hexagonal portion I88, so that a wrench may be applied, if desired, for securing the two parts together. The ferrule I84 at the upper end and a similar ferrule I89 at the lower end may be provided with slabbed-oif portions for providing a fiat surface at each side adapted to be embraced by spring jaws. The lower ferrule I89 has a cloclosure having a central longitudinal bore through which extends the operating rod 'II2.

The rod has a button H3 at the lower end for closing the contacts, later to be described. It also has a notch I I4 adapted to be engaged by the bolt H5. The bolt H5 is guided in a frame member I I8 secured onto the end member I I8. A compression spring III bearing against a flange II8 tends to thrust the bolt I I5 into the notch H4. The releasing lever I82 comprises a. bell crank lever, one armof which II9 engages the pin I28 in the bolt II5 for release of the rod H2. The rod I I2 has secured to the upper end thereof a movable terminal member I22 which is pinned to the rod by the pin I23. A tension spring I24 is connected at its upper end to the movable head I22, and at its lowerend to the stationary head H0. A pair of flexible conductors I connect the movable head I22 to the stationary head I I0, thereby shunting the spring I24. The movable head I22 has a tubular extension I 26 which is slotted at its upper end as indicated to provide contact fingers I21 adapted to engage and embrace a terminal stud member I28. This terminal member I28 has a central bore I29 extending throughout its full length. At its upper end the member I28 has a threaded stud of reduced diameter threaded into the central portion I30 of the fitting I06. The fitting I06 which is threaded into the open end of the ferrule I04 receives the upper end of a sleeve of insulating fiber I32. The

I metallic terminal fitting I06 and the sleeve I 32 are secured together against displacement by pins I33 or the like. The sleeve I32 is provided with a liner 45 of suitable arc extinguishing material, the bore of which fits fairly closely, but with suitable clearance, the external surface of the hollow plunger I26. At its lower end the sleeve I32 receives a threaded ring I34 which holds the liner 45 in place. The terminal stud I28 has its lower end reduced in diameter at I35, and the upper end of a fiber or other insulating sleeve I36 embraces the portion I35. lower end of the tube I36 is provided with a flared ring I31 which may be of metal or fiber, the flare being for the purpose of guiding the upper end of the concentric terminal member I38 that is secured at its lower end to the head I22. Within the inner tube I36 there is provided a lining I39 of arc extinguishing material of suitable character, or, if desired, a fiber tube, from the walls of which an arc may produce gases, may be employed to fairly closely embrace the central plunger rod I30.

The plunger rod I38, at its lower end, is threaded intothe head I22. At its upper end it is slit, as indicated, to provide resilient contact fingers I40 engaging the bore I29 of the terminal stud I28. The upper metallic fitting or ferrule I06 is provided with openings I42 to permit the escape of gases formed in the concentric bore or annular space in which the hollow terminal mem-: ber I 26 moves.

It will be observed that the spring fingers I21 of the tubular terminal member I26 overlap a relatively short distance on the free surface of the stud I28, whereas the contact fingers I 40 of the central plunger rod I30 extend Within the bore of the metallic stud member I28 a substantially greater distance. The object of this provision is to cause the spring fingers I21 to leave the terminal stud I20 and produce an are at this point,

or to be in position to do so before the spring fingers I40 leave the lower end of the bore of the metallic terminal stud I20. The conduction'of current between the movable plungers I26-J38 occurs mainly through the spring fingers I21 and the external surface of the stud I20. The conductivity of these parts is such that very little current needs to pass through the central rod I38 and its spring fingers I40 to the bore of the terminal member I28.

When the device is operated as by pulling up on the tension member I00, the bolt H5 is withdrawn from the notch H4, and a tension spring I24 retracts the movable system comprising the concentric tubular member I26 and a central terminal rod I38. The movable system traveling downwardly under the influence of the spring first separates the spring fingers I21 from the external surface of the stud I28. Except in the case of very heavy current, an arc will not be formed at the ends of the spring fingers I21 when they first leave the surface of the stud I20, because the central rod I38 bearing against the bore of the extension I35 prevents the formation of an are by conducting the current through said rod I30 and contact member I20. Thus the tubular terminal I26 is permitted to be separated from the stud I20 to interpose a gap. Upon further movement, the spring fingers I40 of the rod I 38 leave the lower end of the bore of the stud I20, thereby producing an arc. The are immediately acts upon a lining I39 of arc extinguishing material forming the walls of the bore surrounding the rod I30, creating a violent blast of arc extinguishing material out through the bore I29 to atmosphere, or to a condenser if the same is utilized. If the current fiow to be interrupted is relatively light, an arc may not be formed between the spring fingers I 21 and the surface of the stud I28 in the hollow annular space embraced on the outside by the liner 45 and defined on the inside by the fiber sleeve I36. If,

however, the current flow to be interrupted is heavy, interruption of the are at the contact portions I40-I28 may be followed by striking of an are between the fingers I21 of the tubular plunger, and the surface of the stud I 28. Here the arc is confined in a narrow annular space and, asthe movable system retreats under the action of the spring I24, sufficient gas will be evolved to drive out the products of the arc, and at the next current zero, or at a subsequent current zero, prevent reestablishment of the arc.

The small bore in which the plunger I38 moves is capable of producing sufflcient action of the arc upon the arc extinguishing material, even on low current flow, to insure that any are established in the bore will be promptly extinguished and not reestablished.

The arc between the main contacts which is extended in the annular space between are extinguishing material 45, on the outside, and the fiber sleeve I36 on the inside, will, in the case of a heavy current flow, evolve sufficient gas to drive the products of the arc out through the end of the bore by way of openings I42 and substitute a suitable dielectric medium through which the potential will be unable to establish an arc after cyclical current zero.

It will be observed that in Figure 12 both arcs are formed at the upper end of the respective bores. 1

In Figure 13 we have shown a structure in which the are formed in the inner bore is initiated at the inner end of the inner bore, while the arc initiated in the outer bore is so initiated at the outer end of the bore. In Figure 13, the stationary contact member I45 is in the form of an annular cylindrical part having a threaded portion of reduced diameter I46 threaded into an opening in the upper wall of the stationary conductor I06 that threads into the upper end of the ferrule I04. The member I06 has the depending sleeve of insulation I32 closed at the lower end by the externally threaded ring I34. A liner 45 of arc extinguishing material is disposed within the sleeve I32 and above the closure ring I 34. In the present construction, the movable head I22 which is attached to the rod H2 is provided with a hollow bore which defines a tubular portion I26 and below the bore of portion I26 there is a bore of smaller diameter concentric with the larger bore, this smaller bore I41 being adapted to receive the spring fingers I48 of the central rod I49 which at its upper end is connected to the stationary member I06 and to the stationary cylindrical contact member I45. The rod I49 at its upper end is provided with a head I50 to limit its inward motion. The upper end of the rod I49 is slotted at I52 to provide a resilient contact portion where the rod extends through the head of the cylindrical contact member. I45. The head of the contact I45 is provided with vent openings I53 for the escape of gases from both bores.

The tubular plunger I26 carries a liner of fiber I54 or other suitable arc extinguishing'material, the bore of which liner I54 receives the central rod I49. The tubular plunger I25 is slotted at its upper end to provide the spring fingers I21, but these fingers, contact on their outer faceswith the inner face of the stationary cylindrical terminal contact I45. These spring fingers I2'I are sufiiciently spaced from the surface of the liner I54 to provide the desired play to secure contact with the member I45.

The operation of the device shown in Figure 13 is as follows:

Upon tripping of the holding member, the spring I24 retracts the movable system, the tubular contact plunger I26 and its liner I54 of arc extinguishing material. Thereupon the spring fingers I27 separate from and leave the stationary contact I45 to interpose a gap between these parts. Thereafter the spring fingers I48 of the central rod I49 leave the end of the bore I41 in the metallic head I 22, and an arc is formed within the bore of the fiber liner I54. If the current value is low, no arc will be established between the spring fingers I21 and the tubular terminal I45, and continued separation of the parts results in extending the length of the are from the central bore that is within the sleeve I54 until suflicient gas is evolved to produce the desired arc extinguishing effect, namely, of interposing a dielectric medium which at cyclical current zero will notbe broken down by the system voltage.

If, however, the current fiow which is to be interrupted is heavy, an arc may initially be formed between the spring fingers I2! and the stationary contact I45, or if not initially formed, may be formed as soon as the arc in the central bore is interrupted. In the event that an arc is thus established in the larger bore, it will be drawn in contact with the inner surface of the liner 45, whereby suflicient gas may be evolved for the extinguishment of the arc.

The interrupting capacity of the small bore,

that is, its ability to extinguish an are which is,

formed therein, is considerably greater than that of the outer bore, because of the violent blast which is produced due to the small diameter of the bore and consequently the closer proximity of the active surface to that of the arc, and also to the choking efiect, that is, greater ratio of length to cross l section than that of the larger bore. Since the rod I49 is frictionally held in the contact member I45 only by the resiliency oithe slotted end I52, the generation of sumcient pressure in the bore of the liner I54 will drive the rod I49 outwardly while the head I22 and the liner I54 are being drawn inwardly by the spring I24. The are formed between the spring fingers I48 and the head I22 within the bore of the liner I54 is thereby quickly extinguished medium in the restricted bore.

Thus in Figure 12 or Figure 13, the tendency is normally to establish the arc in a small bore and to extinguish it. If the current flow is low, this may result in complete interruption. If the current flow to be interrupted is too high, the arc may reestablish itselfin the outer bore or in both bores. If established in both bores, it is interrupted in the inner bore and in the outer bore. Due to the greater violence of action in the inner'bore, it is possible that the arc may persist longer in the outer bore than it does in the inner bore.

In each of the forms shown in Figures 12 and 3, the'stationary unit may be renewed by unscrewing the fittings IIlIi on the threads inside the ferrule I04, and a new contact and arc extinguishing tube and liner substituted. In each case, the removable unit contains two contact portions and the moving system comprises two cooperating contact portions. Also, the unit in each case carries the outer liner of arc extinguishing material bore, whereas in Figure 13 the movable system carries the means which provides the inner bore.

The circuit interrupter of our invention is adapted to be employed inconnection with a cooling and condensing chamber for producing a wholly enclosed device. Thus, in any of the forms here shown, the discharge end of the housmedium has been found to be suitable for our,

purposes. It is stable; has a crystalline form; it can be compressed or compacted into a solid, self-supporting body. It will retain its shape when so compacted by pressure, being unaffected by moisture of the atmosphere or other influences. It is substantially insoluble in water at 100 C., and is only slightly soluble in water atlower temperatures. It is not afl'ected by the vapor evolved, and hence the surface does not become pasty when it is subjected to the blast of steam which is evolved. The material in compacted form has a high dielectric strength, the fiashover per inch being of the order of 16,000 volts. It has a high percentage by weight of water in the molecule, namely, approximately 30.9%. The material is stable and unaffected by temperatures around 100 C. to 115 C., or less. Hence, it is quite suitable to be used in a fuse in conjunction with a silver fuse wire operated at its full rated load current. The decomposition temperature of this'material is around 200 C. The pressure produced by the arc in the fuses shown in Figures 1,to 10 and in circuit breakers of Figs. 12 and 13 is sufliclently low to provide excellent arc extinguishing properties without developing destructive pressures.

The oxide which results from decomposition of the material has a very high resistance, and has a melting point of approximately 2800 C.

The general properties of this material are material to be employed in the present device and indevices of similar character.

We have discovered. that metallic hydrates, particularly of the lighter metals, arelsuitable In Figure 12. the removable unit carries the member which provides the inner therefore such as to constitute it an excellent for our purpose. They give oifwater vapor, but only at relatively high temperatures and in general leave residues of excellent insulating properties. Specifically, as a sub-class of metallic hydrates, metallic hydroxides constitute a class of suitable materials. These hydroxides yield water from the chemical composition of the molecule, but only at relatively high temperatures, being quite stable compounds. After decomposition they leave oxides of high melting point and relatively good stability. This will be apparent from the fact that the union of oxygen with the metals, particularly the lighter metals, produces stable compounds which can be broken down only under high temperatures.

Of these hydroxides, the alkaline metal groups are very stable. Hence; for stability, it is desirable to employ hydroxides of the metals of the lighter or more nearly alkaline character.

Suitable examples of metallic hydrates, that is,

. chemical compounds carrying constituents of water as a part of the chemical composition, or carrying water as water crystallization, which we have found, under investigation, to be suitable From the above it will be seen that we provide materials which give off the desired constituent at widely varying temperatures. These materials may be employed for gas evolution, for are extinguishing purposes in structures other than the specific forms herein shown. Their different characteristics may be selected to suit the particular purpose.

We find that suitable mixtures of the above mentioned are extinguishing materials may be employed to yield the desired arc extinguishing vapor or gas at the desired temperatures in accordance with the design under consideration; that is to'say, for designs in which the temperature of the fuse wire and its surroundings are fairly high, a suitable selection of arc extinguishing material or mixture of materials 'may be employed, whereas, where the arc extinguishing material is either more remote or otherwise less subject to the temperatufi of the heat of normal operatiomas may be the case in a circuit breaker, a different material may be employed, or a mixture of materials may be employed which will evolve the desired gas at a lower temperature.

-We do not intend to be limited to the details shown and described, as modifications and variations will immediately suggest themselves to those skilled in the art.

We claim:

1. In a circuit interrupter, relatively separable terminals between whicha pair of arcs is adapted to be drawn in parallel, and are extinguishing means providing two concentric bores each being adapted to contain and extinguish one of the arcs.

2. In a circuit interrupter, relatively separable terminals, said terminals having means for initiating two arcs in parallel, and arc extinguishing means providing two concentric bores in which said arcs are individually elongated and extinguished by relative separation of the terminals.

3. In a circuit interrupter, relatively separable terminals, are extinguishing means associaated with said terminals providing two concentric bores, means for initiating an arc at one end of one bore and means for initiating another arc at the opposite end of the other bore.

4. In a circuit interrupter, relatively separable terminals, are extinguishing means associated with said terminals providing two concentrid bores closed at one end and open at the other, means for initiating an are at the inner end of the inner bore, and means for initiating another arc at the outer end of the outer bore.

5. A fuse device comprising a tubular housing and a removabie operating unit comprising a filler, said housing having an annular seat at one end and a catch at the other, said filler comprising a generally cylindrical element with a plug for said seat at one end and a terminal member having a shoulder for said catch at the other and comprising a spring adapted to be put under tension when the filler is put in place, said filler comprising a movable f'use terminal connected to said spring, and a fuse element connecting said movable fuse terminal and said terminal member.

6. In a fuse device, the combination of a tubular housing comprising a sleeve of insulation having a tubular fitting on each end, the opening through the first fitting being of larger effective diameter than the opening through the second fitting, an extensible spring link for connecting said fittings, said link having a terminal at one end providing a shoulder, said terminal being adapted to be passed through both fittings and to be caught on the edges of the opening through the second fitting, and a second terminal comprising a shoulder at the other end of the' link adapted to be held against passing through the opening in the first fitting.

'1. The combination with claim 6 of screw threaded means for binding the terminals of said extensible spring link to said fittings respectively.

8. In a fuse device, the combination of a tubular housing comprising a ferrule at each end, an extensible spring link having a spring and having terminals for cooperating with said ferrules, the first terminal and the first ferrule having cooperating threads for closing the ferrule and anchoring the said first terminal, the second ferrule having spring fingers and the second terminal having a shoulder which is adapted to be engaged by the spring fingers when the second terminal is drawn through the second ferrule.

9. In a fuse device, the combination of a tubular housing comprising a ferrule fixed at each end, an extensible spring fuse link having a first terminal comprising a plug adapted to be releasably coupled to the first ferrule to connect with and to close the same, and having a second terminal comprising a ring with an external annular shoulder, said second ferrule having detent means adapted to drop back of the annular shoulder when said spring link is extended, said second terminal having quick detachable means internally thereof for engagement by an extending tool to extend said spring and to bring said annular shoulder beyond said detent means.

10. The combination with claim 9 wherein a sleeve of insulation is supported at one end in said ring, a lining of arc extinguishing material supported inside said sleeve, a plunger connected at one end to said spring extending inside said lining and a fusible link connecting said plunger and said ring.

11. In a fuse the combination of a, sleeve of insulation having a metal ring mounted on one end, a transverse pin in said ring, a lining of arc extinguishing material in said sleeve, a plungersubstantially filling the bore of the lining, a high tensile strength wire of high melting point connecting said plunger and said pin.

12. The combination with claim 11 of a tube of insu'ation surrounding said wire.

13. The combination with claim 11 of means permitting endwise travel of the plunger with respect to said sleeve, but preventing turning of said plunger and sleeve relative to each other.

14. A fuse refill unit comprising a sleeve of in-. sulation having a metal ring at one end, a thin tubular spring housing forming an extension at the other end, a sleeve of arc extinguishing ma;- terial in said first sleeve, an apertured plug lying at the second mentioned end of said sleeves,

the aperture having a non-circular portion, a"

plunger having a threaded coupling at one end, and a non-circular portion adjacent said coupling lying in said non-circular portion of the aperture to prevent relative rotation, said plunger extending into the bore of said second sleeve, an anchor member on said ring providing an axial v seat, and an axially disposed strain wire con-.

necting the adjacent end of the plunger and said seat;

15. The combination with claim 14 of a fiber sleeve surrounding said strain wire and carried by said plunger.

16. The combination with claim 14 of a sleeve of insulation surrounding said strain wire and carried by said plunger, and a packing of arc extinguishing material in said latter sleeve surrounding said strain wire. L

1'7. A renewable spring unit for fuses, comprising a. pair of circular discs, a spring having its end coils threaded upon the periphery of said discs, each disc having an annular groove on its outer face, apertures through the disc in register with the grooves, flexible conductors connecting said discs and having their ends projecting through said apertures, a ring fastened in said groove for-clamping said ends, and a central threaded socket in each disc.

- 18. In a device of the class described, the combination of a sleeve of insulation, a ferrule for said sleeve, said ferrule having cone chuck jaws 7 extending from the end thereof, a threaded chuck nut for contracting said jaws toward the axis of the ferrule, and a circuit interrupter unit having a terminal adapted to be engaged by said jaws for mechanical and electrical connection.

19. The combination of claim 18 wherein the cone chuck jaws are integral extensions of the ferrule, the unit terminal has an annular shoulder for engaging the ends of the jaws, and spring means pulling on the terminal to hold the shoulder and jaws in temporary engagement.

20. In a circuit interrupter, a tubular housing comprising the combination of a sleeve, a ferrule having a threaded coupling at one end for receiving one terminal of replaceable fuse link means, and a ferrule having a screw chuckterminal at the other for receiving the other terminal of said replaceable fuse link means.

21. A circuit interrupter housing comprising a sleeve of insulation, a ferrulefixed on one end of the sleeve, saidferrule having a threaded coupling portion for receiving one terminal of replaceable fuse link means, and a ferrule fixed on the other end of the sleeve and having a compression coupling for receiving the other terminal of said replaceable fuse link means.

22. The combination with claim 21 of a refill unit of generally cylindrical form having one terminal provided with a cooperating threaded coupling member for quick attachment to the first ferrule and a tubular terminal adapted to be clamped by said compression member of the second ferrule.

23. A fuse refill assembly comprising a terminal, a sleeve of insulation bearing a tubular terminal, a liner'of arc extinguishing material, a plunger disposed in said liner, a fusible conductor connecting said plunger and said tubular termi-; nal, a sleeve of insulation embracing said fusible conductor and lying within said liner, and a spring connecting said plunger and said terminal.

24. The combination of claim 23 wherein the said fusible conductor comprises a high tensile strength strain wire disposed axially of said plunger and said tubular terminal and has a portion of minimum section disposed within said last named sleeve of insulation.

25. A refill for a fuse comprising an outer heavy 25 sleeve of insulation, a tubular terminal on one end of the sleeve, a liner of arc extinguishing material in the sleeve and having a central bore, a plunger disposed in said bore, said plunger having a threaded coupling at its outer end, a non-. rotatable but axially slidable connection between said sleeve and said plunger, an axially disposed strain wire connecting the plunger and the tubular terminal, a fusible conductor connecting the plunger and the tubular terminal, a sleeve of insulation surrounding the strain wire and are extinguishing material in said last named sleeve.

26. The refill of claim 25 with-a sleeveof insulation extending beyond the coupling end of the plunger.

27. In a fuse device, the combination of fuse terminals, a fusible conductor forming a current sensitive element connected between said terminals,-a spring for separating said terminals, one of said terminals comprising a plunger, arc extinguishing material providing a main bore in which said plunger is adapted to be" moved by said spring, a strain wire connecting the terminals to prevent their separation, and means surrounding said strain wire and providingan individual bore therefor.

28. In a fuse device, the combination of fuse terminals, a fusible conductor forming a current sensitive element connected between said terminals, a spring for separating said terminals, one of said terminals. comprising a plunger, are extinguishing material providing a main bore in which said plunger is adapted to be moved by said spring, a strain wire connecting the termi- 60 nals to prevent their separation, means surrounding said strain wire and'providing an individual bore therefor, and a body of are extinguishing material lining the bore individual to said strain wire.

29. In a fuse device, the combination of fuse terminals, a fusible conductor forming a current sensitive element connected between said terminals, a spring for separating said terminals, one of said terminals comprising a plunger, arc extin- 70 guishing material providing a main bore in which said plunger is adapted to be moved by said spring,

a strain wire connecting the terminals to preventtheir separation, and' means surrounding said strain wire and providing an individual bore r therefor, said fusible conductor being d sposed adjacent the outer end of said main bore to cause a gap at that point upon melting and said strain wire being organized to melt adjacent the inner end of its individual bore.

30. In a circuit interrupter, means for drawing an are including a pair of separable terminals, and a substantially rigid body of solid arc extinguishing material having a longitudinal bore in which the arc is drawn on movement of one of said terminals therethrough, said are extinguishing material comprising a metallichydrate.

31. In a circuit interrupter, means for drawing an are including a pair of separable terminals, and a substantially rigid body of solid arc extinguishing material having a longitudinal bore in which the arc is drawn on movement of one of said terminals therethrough, said arc extinguishing material including a quantity of magnesium hydroxide.

32. In a circuit interrupter, the combination of a pair of concentric cylindrical stationary arcing terminals, a movable member having a pair of concentric cylindrical portions cooperating with said stationary arcing term nals to establish two arcs in parallel a spring for moving said movable member away from said arcing terminals, and means comprising a renewable unit carrying said stationary arcing terminals for providing two concentric bores the walls of which provide arc extinguishing material.

33. In a circuit interrupter, in combination, a pair of oppositely. movable rod-like terminals between which an arc is drawn, and a tubular insulating member having a restricted bore through which one of said terminals moves and in which the arc is drawn and extinguished.

34. In a circuit interrupter, in combination, support means, a rod-like material releasably carried by said support means, a movable terminal between which and said rod-like terminal an arc is drawn, means biasing said movable terminal away from said rod-like terminal, and a tubular insulating member having a restricted bore through which said rod-like terminal is expelled and released from said support member as a result of pressure generated within said bore by the arc.

35. In a circuit interrupter, in combination, support means, a rod-like terminal releasably carried by said support means, a movable terminal between which and said rod-like terminal an arc is drawn, means biasing said movable terminal away from said rod-like terminal, and a fiber member carried by said movable terminal and having a restricted bore through which said rodlike terminal is expelled and released from said support member as a result of pressure generated by evolution of arc extinguishing fluid from said fiber member by the heat of the are.

36. A renewable circuit interrupter comprising, in combination, a tubular insulating housing, tubular terminals at the ends of said housing,a replaceable circuit interrupting device insertable through one of said tubular terminals and secured at one end thereto by means the final angular position of which is indeterminate, and means arranged and adapted to clamp the other end of said replaceable circuit interrupting device to the other tubular terminal in any angular position in which it may be positioned.

37. In a fuse device, in combination, a pair of separable fuse terminals, a pair of fusible elements interconnecting said fuse terminals, a tubular member having a relatively large bore closed at one end and open at the other and adapted to assist in extinguishing large current arcs, and'a tubular member having a relatively small bore closed at one end and open at the other and adapted to assist in extinguishing small current arcs, one of said fusible conductors being located adjacent the open end of said large bore and the other being located adjacent the closed end of said small bore.

38. In a fuse device, in combination, a pair of separable fuse terminals, a pair of fusible elements interconnecting said fuse terminals, a tubular member having a relatively large bore closed at one end and open at the other and adapted to assist in extinguishing large current arcs, a tubular member having a relatively small bore closed at one end and open at the other and adapted to assist in extinguishing small current arcs, one of said fusible conductors being located adjacent the open end of said large bore and the other being located adjacent the closed end of said small bore, and reenforcing means surrounding said tubular member having a relatively small bore at its closed end for preventing rupture thereof by the pressure generated as a result of the are drawn therein.

39. A terminal for a fuse comprising a rod having an axial bore, a fiber sleeve in said bore, said sleeve projecting beyond the end of said bore, a body of solid arc extinguishing material surrounding the projecting end of said sleeve and having the same external diameter as said rod, and means for anchoring a fuse wire to the end of the terminal externally of the sleeve.

40. The combination with a tubular body of a solid arc extinguishing material of a relatively stationary terminal at the open end of the tubular body, a plunger extending into the opposite end of the bore of said body, a fusible strain wire coupling said terminal and said plunger, said strain wire having a portion of minimum conductivity disposed within said tubular body remote from said open end.

41. In a device of the class described, a pair of terminals, means for separating the terminals, a pair of links having fusible sections connected in parallel between said terminals, a pair of tubes having surfaces adapted under the action of the arcs produced therein to evolve a gaseous arc extinguishing medium,- said tubes having outlets at one end, said links being disposed with the fusible section of one in one tube near the outlet and the fusible section of the other in the other tube remote from the outlet.

42. The combination of claim 41 wherein the tubes are concentric and the fusible link in the inner tube constitutes a strain wire under tension.

43. In a, device of the class described, a pair of fusible elementsof different current carrying capacity connected in parallel, tubular means provided with an arc extinguishing material for cooperation with the arc produced by melting of the element of greater capacity, and tubular means provided with an arc extinguishing material for cooperation with the are produced by melting of the element of less capacity, the arc extinguishing material of one of the tubular means decomposing at a higher temperature than.

that at which the other material decomposes.

4a. In a device of the class describedfa silver fuse wire, a tubular housing for said fuse wire having magnesium hydroxide in position to be decomposed by the are formed upon melting of said wire, but not decomposed by the passage of full load current through the fuse wire.

45. In a device of the class described, a relatively stationary terminal, a movable plunger terminal, a spring for retracting the second terminal, a fuse wire connecting said terminals electrically, a tubular body of arc extinguishing material, the movable plunger terminal being adapted to be retracted along the bore of said tubular body, a strain wire for connecting said terminals mechanically, and a fiber sleeve carried by the movable plunger and surrounding the strain wire.

46. A movable terminal for a fuse comprising a metal rod having a longitudinal bore, a sleeve of insulation disposed in said bore and projecting from the end thereof, the projecting end of said sleeve being of substantially greater outside diameter than that of the portion disposed within the bore of the terminal, and means for anchoring a strain wire within said sleeve.

4'7. A terminal for a fuse comprising a rod having an axial bore, a sleeve of insulation therein, said sleeve projecting beyond the end of the bore, means for anchoring a strain wire to the terminal within the sleeve, and means for anchoring a fuse wire to the end of the terminal externally ,of the sleeve.

' 48. For use in a circuit interrupter of the class described, an arc extinguishing material comprising a metallic hydrate.

49. For use in a circuit interrupter of the class described, for are extinguishing purposes, a quantity of magnesium hydroxide.

50. A strain wire for a fuse comprising a length of refractory metal wire having a long loop at one end, with the free end of the long loop fastened to the main part of the wire and having a short loop with the free end of the short loop fastened to the main part of the wire, leaving a short section of single strand intermediate said loops and near the short loop.

51. The strain wire of claim 50 wherein the free end of one of the loops overlaps but is free from the single strand section.

52. In a device of the class described, a tubular housing open at one end and, having a first terminal adjacent said open end and having a second terminal, means disposed in said housing adjacent said open end providing two concentric bores the walls of which constitute arc extinguishing material, and means for forming and extending an arc in each of said bores, said last named means comprising a plunger and spring means in the housing for retracting said plunger.

53. In a circuit interrupter, the combination of a pair of stationary arcing-terminals, a movarc is formed in one bore in advance of forming the arc in the other bore.

55. The combination of claim 53 wherein one of said bore defining walls is moved with the,

movable member.

56. In a device of the class described, an as-' sembly for supplying arc extinguishing gas to an are formed between two terminals comprising a main sleeve of insulation having a metal terminal at its upper end and containing concentric layers of arc extinguishing material of different evolving characteristics.

57.111 combination, a sleeve of insulation bearing a hollow metal ferrule at its outer end, an apertured bushing disposed in the lower end, and a liner of arc extinguishing material within the sleeve, said liner having an inner facing of arc extinguishing material of a different character from that of the liner.

58. In combination, an outer sleeve of insulating material having a metal ferrule comprising an arcing terminal at its upper end, an apertured retaining member for the lower end, a ring of solid arc extinguishing material having a flared opening disposed adjacent the metal ferrule and concentric rings of arc extinguishing material disposed in the sleeve between said first named ring and said closure.

59. In an expulsion fuse of the class described comprising a fusible link and havinga tubular discharge opening for gases, a-mica disk disposed in said tubular discharge passageway, said disc being sufficiently transparent to permit inspection of the fusible link and being expellable by the gases generated upon blowing of the link.

60. In a fuse of the class described, a tubular metal terminal providing a discharge passageway, solid arc extinguishing material disposed adjacent said .discharge passageway, a fusible link associated with said are extinguishing material adjacent said discharge passageway, and a thin mica disc disposed in said discharge passageway transversely thereof and being removable by internal pressure when the link is fused.

61. In a fuse of the character described, a rodlike terminal having a quick detachable coupling at one end and having a transverse opening therethrough at the other end, and slots extending from the transverse opening, and a strain wire extending through said transverse opening and lying in said slots whereby the strain wire is confined within the diameter of the terminal.

62. In a renewable spring unit for circuit breakers, a cylindrical head having a helical groove on its external surface and having an annular, groove in one end face, apertures through the head communicating with the groove, flexible conductors projecting through said apertures and having their ends disposed in the groove, and a ring clamped in said groove upon the ends of said flexible conductors.

63. In a circuit interrupter, tubular means of insulating material for defining the outer wall of an arc passage; a second tubular means disposed within said first tubular means for defining the inner wall of said arc passage and for defining the outer wall of a second arc passage; and parallel circuit means for establishing an are having a portion in each of said are passages during the operation of said interrupter; a substantial portion of the surfaces defining said arc passages including a solid material that is capable of evolving considerable quantities of an are extinguishing gas when placed in proximity to an electric arc.

64. In an expulsion type circuit interrupter; a pair of concentric tubes for defining the walls of two are passages, one of which is defined by the inner surface of the smaller tube and the other of which is defined by the space between said concentric tubes; means for closing one end 65. In an expulsion type circuit interrupter; a pair of concentric tubes for defining the walls of two are passages, one of which is defined by the I inner surface of the smaller tube and the other I portion of the surfaces which define said are passages being formed of a solid material which evolves considerable quantities of an arc extinguishing gas when placed in proximity to an electric arc.

66. In a circuit interrupter, in combination, a pair of tubular members one within the other in spaced relation providing a pair of arcing chambers having inner surfaces formed by solid arc extinguishing material from which an arc extinguishing medium is evolved by the heat of an arc formed therein, means closing one end of each tubular member while the other end of each is open, and circuit means in each chamber adapted to form an are under predetermined operating conditions, said circuit means being in parallel circuit relation, relatively small current arcs being more readily extinguished in one arcing chamber and relatively large current arcs being more readily extinguished in the other arcing chamber.

67; Ina circuit interrupter, in combination, a pair of tubular members one within the other in spaced relation providing a pair of arcing chambers having inner surfaces formed by solid arc extinguishing material from which an are extinguishing medium is evolved by the heat of an arc formed therein, means closing corresponding ends of said tubular members while the other ends remain open, and fusible means of different current carrying capacity in each arcing chamber, said fusible means being in parallel circuit relation, the opposite walls'of one arcing chamber being relatively close together for extinguishing ,one bore and relatively large current arcs being extinguished in the other bore.

69. In a: circuit interrupter, relatively separable terminals, arc extinguishing means associated with said terminals providing two concentric bores one of which provides a passage of greaterwidth for the arc than the other, and parallel circuit means for initiating an arc first in the bore providing the passage of greater width and then in the other bore. 7

70. In a circuit interrupter, relatively separable terminals, are extinguishing means associated with said terminals providing two concentric with said terminals providing two concentric bores one of which provides a passage of greater width for the arc than the other and each of which is open at one end and substantially 'closed at the other end at least during the arc extinguishing period, and parallel circuit means for initiating the arc first in the bore providing the passage of greater width and then in the other bore.

72. In a circuit interrupter, relatively separable terminals, arc extinguishing means associated with said terminals providing two concentric bores one of which provides a passage of greater width for the arc than the other, each of said bores having a solid material therealong which gives off gas when acted upon by an arc, and parallel circuit means for initiating an arc first in the bore providing the passage of greater width and then in the other bore.

'73. In a circuit interrupter, means of insulating material for defining the wall of a first arc passage, means of insulatinglmaterial within said first arc passage for defining the wall of asecond arc passage, parallel circuit means for establishing an arc in each of said are passages, one of said arc passages being so narrow that arcs of small current magnitude are readily extinguished therein and the other of said are passages being so wide as to accommodate arcs of large current magnitude, and said means for establishing the are causing the arc to be first established in the wide arc passage.

74. In an expulsion circuit interrupter, means of insulating material for defining the wall of a first arc passage, means of insulating material within said first arc passage for defining a second arc passage, parallel circuit means for estab lishing an arc in each of said are passages, each of said are passages having included in its wall a material which gives oil" gas when acted upon by an arc and being open at one end at least-when the arc is being extinguished therein to permit a blast of gas to fiow through the arc, and one of said are passages being so narrow that arcs of small current magnitude intimately contact its wall and the other of said passages being of suflicient width to accommodate arcs of high current magnitude without destructive pressures being formed.

'75. In an expulsion circuit interrupter, means of insulating material for defining the wall of a first arc passage, means of insulating material within said first arc passage for defining a second arc passage, parallel circuit means for establishing an arc in each of said are passages, each of said are passages having included in its wall a material which gives oil gas when acted upon by an arc and being open at one end at least when the arc is being extinguished therein to permit a blast of gas to flow through the arc, and one of said arc passages being so narrow that arcs of small current magnitude intimately contact its wall and the other of said passages being of sufilcient width to accommodate arcs of high current magnitude without destructive pressures being formed, and said means for establishing the are causing the arc to be first established in the passage for arcs of high current magnitude.

76. In circuit interrupting apparatus, in combination, arc extinguishing material providing main and auxiliary bores having respectively large and small cross-sectional areas, stationary terminal means at one end of said bores, and main and auxiliary relatively infusible terminals in said main and auxiliary bores respectively substantially filling the same and adapted on being moved away from said stationary terminal means to draw an arc first in an auxiliary bore means in said auxiliary bore for relieving said fusible element of the biasing force of said spring means, said strain means being arranged and adapted to be released on blowing of said fusible element to permit relative movement between said plunger and said are extinguishing material. I 78. In a fuse device, in combination, are extinguishing material providing a main bore and an auxiliary bore, a terminal adjacent one end of said bores, a terminal movable through said main bore, a fusible element interconnecting said terminals, and strain means in said auxiliary bore also interconnecting said terminals and relieving said fusible element of stress tending to separate said terminals.

79. A renewable circuit interrupter comprising, in combination, a tubular insulating housing, a replaceable circuit interrupting device adapted to be inserted through one end of said housing with one end of the device thereat in any angular position, and means arranged and adapted to hold the other end of said device at the other end of said housing in any angular position in which it may be positioned.

80. A renewable circuit interrupter comprising, in combination, a tubular insulating housing, a replaceable circuit interrupting device insertable through one end of said housing and including a fuse cartridge attached to a spring having means at its free end cooperating with said one end of said housing for holding the same thereat, and means at the other end of said housing automatically interfitting with said fuse cartridge when it is drawn to .a predetermined position through said housing for latching the same thereat.

81. A renewable circuit interrupter comprising, in combination, a tubular insulating housing, a replaceable circuit interrupting device insertable through one end of said housing and including a fuse cartridge attached to a. spring having means at its free end cooperating with said one end of said housing for holding the same thereat, means at the other end of said housing automatically interfitting with said fusecartridge when it is drawn to a predetermined position through said housing for latching the same thereat, and means adapted to be manually operated for releasing the automatic latching means to permit removal of said fuse cartridge from said housing.

82. A renewable circuit interrupter comprising, in combination, a tubular insulating housing, tubular terminals at the ends of said housing, a replaceable circuit interrupting device insertable through one of said tubular terminals including a fuse cartridge attached to a tension spring having means at its free end cooperating with said one terminal for holding it thereat, and means carried by the other tubular terminal for automatically interlocking with said fuse cartridge when it is drawn therepast to hold the same in a predetermined position in said housing.

83. A renewable circuit interrupter comprising, in combination, a tubular insulating housing, tubular terminals at the ends of said housing, a replaceable circuit interrupting device insertable through one of said tubular terminals including a fuse cartridge attached to a tension spring having means at its free end cooperating with said one terminal for holding it thereat, means carried by the other tubular terminal for automatically interlocking with said fuse cartridge when it is drawn therepast to hold the same in a predetermined position in said housing, and manually operable means disposed externally of said other tubular terminal for releasing the automatic interlocking means to permit removal of said fuse cartridge from said housing.

84. In electrical apparatus, a conductor from which an arc may be drawn, and a carbon free inorganic magnesium compound containing at least 30.9% by weight of water positioned along the path of the arc from which an arc extinguishing medium is evolved due to the heat of the are sufficient to extinguish the same.

85. Circuit interrupting means comprising, in combination, means between which an arc is formed, and insulating means surrounding and confining the are including a magnesium compound.

86. Circuit interrupting means comprising, in combination, means between which an arc is formed, and insulating means surrounding and confining the arc and having the surface impinged upon by the arc formed by a magnesium compound containing about 30% or more by weight of water.

87. Circuit interrupting means comprising, in combination, means between which an arc is formed, and insulating means surrounding and confining the arc and having the surface impinged upon by the are formed by an inorganic magnesium compound substantially insoluble in water and containing about 30% or more by weight of water.

88. In a circuit interrupter, in combination, a pair of tubular members one within the other in spaced relation providing a pair of arcing chambers having inner surfaces formed by solid arc extinguishing material from which an are extinguishing medium is evolved by the heat of an are formed therein, means closing one end of each tubular member while the other end of each is open, and means in each chamber adapted to form an arc finder predetermined operating conditions, relatively small current arcs being more readily extinguished in one arcing chamber and relatively large current arcs being more readily extinguished in the other arcing chamber, said tubular members being of substantially the same length so that the arcing chambers provided thereby are substantially coextensive whereby a maximum eifective area of arc extinguishing material is exposed to the arcs formed therein requiring a minimum of space.

GEORGE F. McMAHON. ALLAN RAMSEY.

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