US2253719A

US2253719A - Circuit interrupting means

Info

Publication number: US2253719A
Application number: US266991A
Authority: US
Inventors: George F Mcmahon
Original assignee: Schweitzer & Conrad Inc
Current assignee: Schweitzer & Conrad Inc
Priority date: 1939-04-10
Filing date: 1939-04-10
Publication date: 1941-08-26
Anticipated expiration: 1958-08-26

Description

y Aug. 2s, 1941.

G. F. McMAHoN v 2,253,719 CIRCUIT INTERRUPTING MEANS Fil ed April 10, 1939` 5 Sheets-Sheet' l @y @if /6 .ff/,14 p

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G. F. McMAHoN 2,253,719`

CIRCUIT INTERRUPTING MEANS Aug; 26, 1941* Filed April 10, 1939 3 SheetS-Sheet 2 Jima/VZW Aus. 26, 1941. i G, F. MC'MAHON j 2,253,719

- CIRCUIT INTERRUPTING MEVANS` Patented Aug. 26, 1941 2,253,119 cincmr iN'rEnnUr'riNG MEANS l George F. McMahon, Chicago,

Schweitzer & Conrad, Inc., Chicago,

poration of Delaware Application April 10, 1939, Serial No. 266,99]

54 Claims.

This invention relates, generally, to new and improved materials for use with electrical apparatus and for flame proofing purposes, and it has particular relation to the L.composition and use of such materials for insulation and arc extinguishing purposes in circuit interrupters of both the fusible element and separable contact type.

When an electric circuit is opened by a circuit interrupter, the arc that is formed should be promptly extinguished. Various methods and means have been proposed for effecting arc extinction. It is common practice now to provide material along the arc path which will evolve an arc extinguishing medium due to the heat of the arc that will assist in one way or another in effecting its extinction. Usually the arc extinguishing material is tubular in form or is provided with a bore from the inner surface of which the arc extinguishing medium is evolved in the form of gas or vapor. Many of the materials that have been proposed for this purpose are unsatisfactory for'one reason or another, or they are not as eiilcient as is the class of arc extinguishing materials disclosed herein.

A material, to be suitable for arc extinguishing purposes, should have the following characteristics:

(l) Non-inflammable and stable under normal operating conditions;

(2) Non-corrosive to metals and other materials with which it is associated;

(3) Non-poisonous;

(4) High dielectric qualities both before and after arc extinction;

(5) Evolution of a sufficient quantity of gas or vapor to effect satisfactory arc extinction and which gas or vapor is non-poisonous and will not support combustion;

(6) Little or no carbonization of the surface acted upon by the arc, and no deposition of carbon on the associa-ted parts of the circuit interrupting apparatus.

In order to facilitate a more complete understanding of these various characteristics, a brief discussion of each of them will be set forth. It will be understood that it is preferable to employ a single material which possesses all of these desirable characteristics, so that the construction of the circuit interrupter can be as simple as possible for a given set of operating conditions.

Under normal operating conditions in a fuse or circuit interrupter of the separable contact type, certain of the parts are subjected to relatively high temperatures. Consequently, the ma- Ill., assignor to Ill., a corterials adjacent such high temperature conditions, and particularly those which are employed for arc extinguishing purposes, should be noninflammable. Likewise they should be stable so that they will not deteriorate even though they are subjected to comparatively high operating temperatures over long periods of time. 1f the material is unstable and deteriorates, it ordinarily would not be capable of performing properly its arc extinguishing function when finally called upon to do so.

Since circuit. interrupting apparatus is cornposed of metallic parts and insulating material, it is, of course, desirable that any material which is employed for arc extinguishing purposes be incapable of corroding the associated 'metallic and insulating parts.

The material that is used for arc extinguishing purposes should be non-poisonous, since it must be handled by workmen in the manufacturing establishment, and possibly by repair men and operators in the field.

The class of electrical apparatus to which the present invention is directed is ordinarily operable at relatively high voltages, i. e., 1000 volts and upwards. When these voltages are employed, the material that is used for arc extinguishing purposes should have relatively high dielectric properties. It should be of this character under normal operating conditions in order to maintain the parts in proper insulated relationship. After the arc is extinguished, it should still retain its high dielectric properties, so that there is little or no likelihood of leakage across it which might result 1 in dangerous conditions on a circuit that otherwise was considered to be deenergized.

In order to effect efiicient arc extinction, the arc extinguishing material that is employed should be capable of evolving a sufficient quantity of gas or vapor due to the heat of the arc that will be capable of extinguishing the same by providing a deionized space at current zero, and also provide a blast action which tends to sweep the conducting materials out of the arc space. Of course, such gas or vapor should be non-poisonous, so that there is no likelihood of injury to a person coming in contact with it. The gas or vapor should not be capable of supporting combustion, and should be non-conducting, so that the presence thereof will tend to extinguish the arc and prevent its striking on metallic parts in the vicinity of the device or restriking. The gas or vapor that is evolved should create very little pressure in order to avoid the occurrence of destructive pressures in the device.

A chief cause of the lowering ot the dielectric properties of the arc extinguishing material is the carbonization of its surface after it has been acted upon by the arc. For eillcient arc extinguishing purposes, therefore, a material should be employed which, preferably, does not carbonize on its surface under the heat of the arc. Further, in order to maintain the insulating qualities of the device, there should be no deposition of carbon on the various parts which would be likely to form creepage paths over the surface thereof.

In view of the foregoing, an object of the invention, generally stated, is to provide an arc extinguishing material which possesses all of the foregoing desirable characteristics.

A further object of the invention is to provide an arc extinguishing material having a large percentage (about 5G%) comprising water of crystallization which is evolved as water vapor due to the heat of an arc.

Still another object of the invention is to provide a material for use in electrical apparatus that not only is capable of evolving an arc extinguishing medium due to the heat of an arc, but also possesses adhesive properties which permit it to be formed or compacted into a rigid member Without requiring the use of another binding agent and which enable it to impregnate fibrous or other materials likewise without requiring a binding agent.

A still further object of the invention is to prom vide an arc extinguishing material that is relatively insoluble in water and which is capable oi thoroughly impregnating fibrous material, such as illter paper (cellulosic organic material), fiber glass, and asbestos (inorganic materials), and binding their bers together.

An object of the invention is to provide an improved method of manufacturing insulating material'for use with electrical apparatus and having arc extinguishing properties.

Still another object of the invention is to provide a new composition of matter having flame proof and high electrical resistance characteristics, and a method for manufacturing the same.

A further object of the'inventlon is to provide a fibrous material capable of withstanding relatively high temperatures (red heat) without carbonization. Asbestos is a rial for this purpose.

Still another object of the invention is to improve the dielectric properties of asbestos by impregnating it with magnesium borate.

A still further object of the invention is to so construct a fuse link that its operation is substantially independent of the diameter of the expulsion tube or housing in which it may be used.

A still further object of the invention is to increase the arc extinguishing properties of an expulsion fuse tube.

Other objects of the invention will, in part, be obvious, and in part appear hereinafter.

The invention, accordingly, is disclosed in the embodiments thereof shown in the accompanying drawings, and it comprises the features oi construction, combination o! elements, arrangement of parts, and novel steps which Will be exemplitled in the construction and process hereinafter set forth, and the scope of the application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of the invention, reference may be had to the following detailed description.

suitable fibrous matef CIE taken in connection with the accompanying drawings in which:

Figures 1, 2, 3 and 4 are longitudinal sectional views of fuse links employing the arc extinguishing material of the present invention in various respects;

Figure 5 is a longitudinal sectional view of a spring type of fuse link positioned in an expulsion tube, the sleeve of the fuse link and the expulsion tube being constructed in accordance with the present invention;

Figure 6 is a longitudinal sectional view of another form of fuse link than that shown in Figure 4, positioned inside of an expulsion fuse tube, the fuse link being biased by an external spring which likewise causes movement of the expulsion tube;

Figure 7 is a longitudinal sectional view of a heavy duty fuse type of circuit interrupter employing the arc extinguishing material of the present invention; and

Figure B is a longitudinal sectional view of a separable contact type of circuit interruptor in which the arc extinguishing material of the present invention is employed.

Referring now particularly to Figure l of the drawings, it will be observed that the reference character l0 designates, generally, a replaceable fuse link of a type that is now well known in the art. The fuse link I0 comprises fusible and strain elements il and I2 which are secured at their ends to terminals I3 and I4. The terminal I3 is provided with a threaded stud I5 onto which an adapter I E is threaded. The stud I5 and the adapter I6, or the stud I5 alone, provide for connection to one line terminal, while a ilexible lead Il, secured to the terminal I4, provides for connection to the other line terminal.

Now, it is desirable to-surround the fusible means, comprising the fusible and strain elements il and I2, with a material that is adapted to evolve an arc extinguishing medium due to the heat of an `are formed between the terminals I3 and M on blowing of the fusible and strain elements i I and I2 which will assist in quickly and efllciently extinguishing the arc. For this purpose, a sleeve I8, having these properties, as will be presently described, is provided around the fusible and strain elements II and I2 in telescopic relation with the terminals I3 andA i4. It will be observed that the terminal I3 is provided `with a knurled portion I9 over which the upper end of the sleeve I 8 is forced, and whereby relative rotation between the terminal I3 and the sleeve I8 is prevented. The upper end of the sleeve I8 is crimped into a groove 20 that is formed in the terminal I3. If desired, a retaining ring may be provided around the outside of the upper end of the sleeve I8 for holding it securely in the groove 2U.

It has been the practice in the past to form the tube or sleeve I 8 of fiber. While this material is capable of evolving a limited amount of an arc extinguishing medium due to the heat of an arc, it is not entirely satisfactory. It does not evolve a suiiicient quantity of arc extinguishing medium. Under low current operation, i. e., a few amperes to several hundred amperes, the expulsive effect is not sufficient to entirely sweep out the layer of carbonized material that is caused by the heat of the arc. As a result the inner surface of the liber tubes or sleeves of the prior art may, in some cases, provide a relatively low resistance path for leakage current to iiow over.

According to the present invention, the tube or sleeve I8 is formed of fibrous material such as paper, although it may be formed of asbestos. In the case of paper, it is preferable to use filter paper or alpha cellulose which are practically pure cellulose. Preferably the fibrous material is impregnated with a material which has all of the desirable characteristics enumerated hereinbefore.

Magnesium borate has been found to have all of these characteristics and'to be capable of use not only as an impregnant, but also as a solid arc extinguishing material, either in powder form or formed into a tube as will be described hereinafter.

Magnesium borate is generally considered to have eight molecules of Water of crystallization,

in which 56.7% of its weight comprises Water of crystallization. Magnesium borate can also be prepared in a form which has six molecules of water of crystallization, in which case 49.5% of its weight comprises Water of crystallization. This amount of water of crystallization is appreciably more than that found in boric acid which has 43.6% by weight of water of crystallization. The use .of boric acid as an arc extinguishing material is disclosed in Patent 2,077,282, to Strom et al. Magnesium hydroxide has only 30.8% by weight of Water of crystallization. This material is disclosed as an arc extinguishing material in the copending application of McMahon and Ramsey, Serial No. 62,118, filedFebruary 3, 1936, now Patent No. 2,183,751.

Magnesium borate possesses all of the desirable characteristics outlined hereinbefore and, because of its relatively high water content (about 50% or more), it is capable of evolving a relatively great amount of Water vapor for arc extinguishing purposes.

Magnesium borate constitutes an alkaline earth compound. In its water soluble form, the solution has a hydrogen ion concentration or pH value of about 8. At this stage the borate is in the crystalloidal or incompletely formed crystal state. If allowed to stand for a time, crystals are produced which are slightly soluble in cold water and insoluble in hot water. If the crystalloidal solution is allowed to evaporate, a transparent film is formed. Under ordinary operating conditions, it is non-corrosive and is relatively nonpoisonous in either the solid form or vaporized form. Not only is it non-inflammable, but also, the evolved arc extinguishing mediumr being water vapor is also non-inflammable. Since the arc extinguishing medium comprises water vapor, comparatively low pressures' are generated on the occurrence f an arc.

Crystalloidal magnesium borate has adhesive and varnish-like properties and it is well suited i for impregnating fibrous materials such as paper,

cloth, asbestos, etc. When these materials are impregnated with magnesium borate, they are substantially flame proof. In addition, they possess excellent arc extinguishing properties and have the appearance of ceramic or porcelain-like bodies. l

The sleeve or tube I8 may be formed of several layers of paper, for example filter paper, that has been impregnated with magnesium borate. Preferably the tube I8 is formed by rolling a relatively thin sheet of paper that has been impregnated with magnesium borate to the desired shape and size. The paper may first be dipped into a crystalloidal solution of magnesium borate and "then wound under pressure on a mandrel. After the tube has thus been formed, it is allowed to dry in air until the laps or layers of the paper are stuck together. Since magnesium borate is inherently adhesive, the use of an additional binding agent, which would be undesirable from a cost standpoint as Well as possibly introducing undesirable effects on the arc extinguishing characteristcs, is not required. Preferably, the dry tube is further impregnated or dipped into a magnesium borate crystalloidal solution, redried and allowed to crystallize several times. In some cases where it is desired to make relatively thick walled tubing, the impregnation should be carried out in a vacuum and pressure process. In order to hasten drying, the impregpated tube can be baked in the atmosphere at low temperature or under a vacuum. As the borate crystallizes .within the fiber structure of the paper, both strength and hardness are imparted thereto as the fibers are cemented and bonded together. A good grade of filter paper will absorb as much as or more of its Weight of magnesium borate, and this will remain intact in the paper with its Water of crystallization. The tubes may be vacuum dried to remove excess water and improve the insulating qualities with no harm being done to them.`

If it is desired to water-proof the impregnated fiber tube, the outer surface can be coated with varnish. In doing this, care should be taken to apply the varnish to the outer surface only, since it is inflammable and, if applied to the inner surface, would promote flame and 'carbonization Instead of forming the sleeve or tube I8 of paper or asbestos, it may be formedby an extruson process. For this purpose wood flour, asbestos flour, paper pulp, siliceous, carbonaceous or other finely divided material are first impregnated or mixed thoroughly with crystalloidal magnesium borate. 'I'he resulting plastic mass is extruded by suitable extruding dies into the desired size and shape of tubing.

Generally, the foregoing steps may be employed for the manufacture of boards, sheets, etc., having a base of asbestos, paper, or other material. Such material is first suitably impregnated with magnesium borate and then is pressed into the desired shape and form with or without the application of heat. Alternatively, the material may be in the form of flour which is mixed with the magnesium borate and then pressed into the desired shape and form and allowed to age until the maximum strength is obtained.

In some cases it is desirable to provide a fibrous material that is capable of withstanding relatively high temperatures, for example red heat, with no resulting carbonization. For this purpose, asbestos can be impregnated with magnesium borate. When subjected to such high temperatures, even though the water is removed thereby, still the asbestos retains substantially its original shape and strength due to the presence of the borate. I

Not only is asbestos made more resistant to high temperature, but also, by impregnation with magnesium borate, its electrical insulating qualities are greatly improved. y

Magnesium borate differs greatly from a great many inorganic insulating compounds in that it alone has adhesive properties which are unusual.

In Figure 2 of the drawings there is shown, generally, at 2| a fuse link that is somewhat similar in construction to that of the fuse link illustrated in Figures 2 and 3 of Patent No. 2,091,453, to Ramsey. The fuse link 2| comprises relatively

infusible terminals

22 and 23 which are interconnected by a .fusible element 24, such as a silver wire, and a strain element 25, such as a nickel-chromium wire. Surrounding the fusible and strain wires is a filling 26 of arc extinguishing material within a sleeve 21 of suitable insulating material such as paper. A pin 23 extending through the terminal 22 and through the filling 23 of are extinguishing material and the sleeve 21 serves to hold the same in place.

'Ihe filling 26 of arc extinguishing material is formed l'by making a mixture of wood flour or asbestos flour and an aqueous solution of magneslum borate and pouring it into the sleeve 21 with a wedge through the center and allowing it to set. After the mixture dries or sets, due to the crystallization of the borate, the wedge is removed and through the opening left thereby the terminal 22 is slipped to a fusible and strain elements surrounded by the filling 26 of arc extinguishing material, as shown. 'Ihe pin 28 is then inserted.

In Figure 3 of the drawings, a replaceable fuse link I is shown that is generally similar to the fuse link I 0 of Figure 1. The lower terminal I4' is slightly different in construction. If desired, the sleeve or tube I3 may be formed of fiber, 'as in the prior art, or it may be formed of fibrous material impregnated with magnesium borate as described hereinbefore.

Within the sleeve or a sleeve of woven fiber nated with magnesium strain elements II and impregnated fiber glass Still another form of fuse link is illustrated at I0" in Figure 4 of the drawings. The fuse link Ii" is generally similar to the fuse link IIJ of Figure l. The terminals I3 and I4 are slightly different, and the sleeve or tube I8" is slightly longer than the sleeve I 8. It may be formed of ilber, as in the prior art, or may be formed of impregnated fibrous material as described. Within the tube or sleeve I3 and between the terminais I3 and I4" there is a filling of magnesiumI borate powder 30 which embeds both the fusible element II and the strain element I2.

In Figure o1' the drawings, a circuit interrupter, designated generally at 3|, of the expulsion type, is illustrated. It comprises a fuse tube or housing 32 having terminals 33 and 34 at its ends. It will be understood that the terminals 33 and 34 are adapted to be mounted in suitable fuse clips which form the line terminais.

The fuse tube or housing 32 is provided with a liner 33 that is formed preferably of magnesium borate. or paper, or other fibrous material impregnated with magnesium borate. The tube or housing 32 itself may be formed of "a phenolic condensation product or glass. presence of the magnesium boratein theliner 33, the arc extinguishing properties and expulsive effects of the expulsion type circuit inter- 24 and 25 are fully tube I3 there is provided glass 29 that is impregborate. The fusible and I2 are surrounded by this sleeve.

rupter 3| are considerably improved over the prior art constructions.

The fuse tube or housing 32 with the liner 35 may be constructed by first preparing the liner 33 in the manner described for the manufacture of the tube or sleeve Il for the fuse link Il of position where the Because of the Figure 1. After the liner 35 has been properly formed, the tube or housing 32 may be formed thereon by winding around it paper that has been impregnated with a phenolic condensation product or varnish. Another method of construction is to completely fill a tube or housing 32 formed of a phenolic condensation product or glass with wood pulp impregnated with magnesium borate. After the inserted material has thoroughly dried, it is bored out to provide the desired longitudinal aperture therethrough.

Within the fuse tube or housing 32 there is provided a replaceable fuse link, shown generally at Il. The fuse link 3l may be of any of the so-called Universal" type of fuse links now found on the market, or it may be the type of fuse link shown in Figures 1, 3 and 4 hereof. The particular fuse link 38 illustrated in Figure 4, however, is constructed in accordance with the disclosure in the lcopending application of Lindell, Serial No. 70,280, filed March 23, 1936. It

comprises a terminal 33 having a threaded stud portion 40 upon which a cap 4I is threaded. The cap 4I ls held in place against the terminal 33 by means of a cap 42. A fusible element 43 interconnects the terminal 33 and another terminal 44. A corona shield 43 is integrally formed with the terminal 44, as shown. A flexible lead 48 is connected to the terminal 44 and extends out of the lower end of the fuse tube or housing 32 where it is connected to the lower terminal 34 by means of a screw 41 cooperating with a washer 43. A coll tension spring 43 serves to tension the fusible element 43 and to bias the terminal 44 downwardly. 'I'he upper end of the spring 43 is secured to the terminal '44, while its lower end ls secured to a fitting 30 that is deformed onto the flexible lead 48. Another fitting 5I is deformed onto the flexible lead 46, and it bears against an anchor plate 52 that rests upon the lower end of a sleeve 'or tube 33 which surrounds the spring 43 and fusible element 43 and is crimped at its other end as indicated at I4 on the terminal 3l and bears against a flange integrally formed therewith.

Preferably. the sleeve or tube I3 is formed of fibrous material, such as paper, impregnated with magnesium borate, as described hereinbefore for the tube or sleeve I l forming a part of the fuse link I0 of Fiure 1.

It has been found that win a fuse link, such as the fuse link 33, is provided with a sleeve 33 impregnated with an arc extinguishing material such as magnesium borate, it may be employed in an expulsion fuse tube of the prior art, having a fiber liner, with satisfactory results. Ordinarily, when fuse links of the prior art are employed in expulsion fuse tubes having ber liners, the life of the latter is relatively short due to the deposition of carbon on the surface. However, when a fuse link is employed having a tube or sleeve formed oi' fibrous nated with magnesium borate, posit is not formed and the life of such expulsion tubes is materially prolonged. Accordingly, it is within the scope of the present invention to provide fuse links of the type shown in Figures 1, 2, 3, 4 and 5 in expulsion fuse tubes having fiber liners.`

In Figure 6 of the drawings, a portion of a drop-out fuse device incorporating the present invention is illustrated. 'I'he fuse device, shown generally at 30, is constructed along the lines oi' the fuse device shown in the copending application of Ramsey, dell and Van Ryan, Serial No. 115,690, filed December 14. 1936. The fuse device 80 is intended to be mounted on a box formed of insulating material, such as porcelain. that is customarily mounted on the cross-arm of a pole supporting an electric power line. Since the box for housing the fuse device 80 forms no part of the present invention, a showing thereof is omitted herein.

The fuse device 60 comprises a fuse tube or housing 6|, formed of insulating material such as a phenolic condensation product, and it is slidably mounted in a sleeve 62 that is secured by suitable means to a door or cover 63 that is formed of insulating material, such as a phenolic condensation product. Because of space limitations, the operating eye for the door or cover 63 has been omitted from the showing in the drawing. The door 83 is provided with an apertured guide portion 64 through which the fuse tube or housing 6| can slide. At its upper end the fuse tube or housing 6| is provided with a terminal clip 65 for detachable connection to a.

cooperating stationary contact member on the rear wall of the box. Likewise, Ithe sleeve 62 is provided with a contact clip 66 which is arranged to have contact engagement with a cooperating contact member also positioned on the rear wall o f the box.

A liner 69 is provided inside of the fuse tube or housing 6|, and it is preferably formed of fibrous material, such as paper, thoroughly impregnated with magnesium borate. Its action, when subjected to the heat of an arc, will be as described hereinbefore.

A fuse link, shown generally at 10, is positionedv within the fuse tube or housing 6|. The fuse link 10 is similar in construction to the fuse link I" shown in Figure 4 of the drawings. However, the lling of powdered magnesium borate 30 is omitted. The fuse link 10 is provided with the sleeve I8" which, as previously described, is preferably formed' of rolled paper impregnated with magnesium borate.i It has been found that, when the sleeve I8" is formed as described, the liner 69, if formed of liber in accordance with the prior art, has a much longer lifedue to the fact that its surface is not so readily carbonized.

As shown in Figure 6, the fuse link 10 is provided with a flexible lead l1 that extends out of the lower end of the fuse tube or housing 6| and over a flipper 1| that is pivoted at 12 to the sleeve 62. The free end of the flexible lead |1 is secured in a terminal clamp assembly 13 so that it is in good 'electrical Contact with the sleeve 62. At the lower end of the tube or housing 6| there is provided a collar 14 having an arm 15 extending therefrom for engagement with the upper side of the flipper 1| close to its axis of rotation at 12. A coil compression spring 16 between the upper side of the collar 14 and a shoulder 11 of the sleeve 62 serves to bias the fuse tube or housing 6| downwardly. This downward movement is restrained by the fuse link 10 acting through the flexible lead I1, iiipper 1|, and arm 15.

In Figure '7 of the drawings, a circuit interrupter is illustrated, generally, at 80 which is constructed generally along the lines of one of the circuit interrupters shown in the patent of McMahon and Ramsey, referred to herein. The circuit interrupter 80 is provided with a tubular housing 8|, preferably formed of glass, having at its

ends terminals

82 and 83 that are secured n,

thereto by cement.

At one end of the housing 8| there is provided a replaceable fuse cartridge, designated of the terminal 90.

generally at 84. 'I'he cartridge 84 is provided with a shell 85, formed preferably of a phenolic condensation product and having at its upper end a cylindrical terminal 86 which interfits with and engages the terminal 82. A sleeve 81 depends from the shell 85 and serves to protect the inner surface of the glass housing 8| from the effects of arcs formed on operation of the circuit interrupter. A fusible element 88 in the form of a coil of silver wire is provided, one end being positioned in a groove 89 in the terminal 86, the edges being peened over to provide mechanical and electrical engagement therewith, while the other end is electrically and mechanically connected to a tubular movable terminal 90 by being positioned in a longitudinal slot 9| therein, the edges of which are peened over. The tubular terminal 90 is movable within the bore 92 of a body 93 of solid arc extinguishing material.

The body 93 of solid arc extinguishing material is preferably formed of magnesium borate. 'I'he magnesium borate in powder form is compacted to the shapel shown. Instead of using pure magnesium borate, a composition of comminuted fibrous material impregnated with magnesium borate may be employed. When an arc acts upon the surface of the bore 92, an arc extinguishing medium, comprising water vapor, is evolved therefrom and acts, as previously indicated, to assist in extinguishing the arc by blast action which helps to remove conducting materials from the arc space and to deionize it at current zero. The upper end of the mass 93 of arc extinguishing material is flared outwardly as indicated at 94 to provide an arcing chamber. A nut 95 threaded into the lower end of the shell 85 serves to hold the mass 93 of solid arc extinguishing material in place,

Within the hollow terminal 90 there is provided a sleeve 99 of insulating material having a bore |00 therein. The sleeve 99 may b e formed of fiber, or it may be formed of paper impregnated with magnesium borate, or it may be extruded as previously described. Within the bore |00 in'the sleeve 99, there is provided a strain element |0| in the form of a high strength wire, the lower end |02 of which is looped around a strain wire nut |03 threaded into the lower end The upper end |04 of the strain wire |0| is looped over a crosspin |05 that rests upon the terminal 85. The end of the strain wire |0| that is looped over the cross-pin |05 is brought back into the bore |00 of the sleeve 99 and is secured, as by welding, to the main portion of the strain wire |0|, as indicated at- |06. Obviously, this construction is such that the section |01 of the strain wire |0| will be :fused first, thereby forming the arc at the lower end of the bore |00 1n the sleeve 99.

The cartridge 84 is held in place by means of a clamp nut |08 that is threaded, as shown, into the terminal 82. A disc |09, preferably formed of mica and transparent, is provided underneath the clamp nut |08 for preventing the entrance of extraneous material.

A stud ||2 is threaded into the lower end of the terminal 90, and it, in turn, is threaded into a spring and cable fastener ||3. Flexible leads ||4 are provided for interconnecting the spring and cable fastener ||3 with another spring and cable fastener ||5 that is secured, as shown, to the terminal 83. A coil tension spring I6 is connected at its ends, as shown, to the spring and cable fasteners ||3 and '||5, and serves to bias the terminal 90 for movement through the bore 92 in the mass terial.

Referring now particularly to Figure 8 of the drawings, a circuit interrupter shown, generally, at of the separable contact type, is illustrated. The circuit interrupter |20 is constructed along the lines of the circuit interrupter shown in Conrad Patent No. 1,336,069, as modified by the construction shown in the patent of McMahon and Ramsey, and referred to hereinbefore.

Now, in order to extinguish the arcs that are drawn on operation of the circuit interrupter |20, and particularly the arc that is drawn between the contact surface 25 of the terminal stud |25 and the contact fingers |32, a mass |46 of arc extinguishing material is provided. It is positioned within a shell |41, preferably formed oi' a phenolic condensation'product, that is secured by means of pins |48 to the terminal |24, as shown. A retainer nut |49, threaded into the lower end of the shell |41, serves to hold the mass |43 of arc extinguishing material in position.

The mass |46 of arc extinguishing material is preferably formed of magnesium borate that has been compacted from the powder form into the generally cylindrical form shown, providing a bore |50 therein. It can also be formed of finely comminuted iibrous material, such as asbestos, or cellulosic material, like paper, Wood pulp, etc., impregnated with magnesium borate, the resulting mass being formed into the shape shown.

93 of solid arc extinguishing maformed preferably of fiber. The mass |5| oi' arc extinguishing material is formed o1' magnesium borate or impregnated iibrous material as de scribed for the mass |46. It is provided with an inner bore |53 through which the rod |33 moves.

However, when the circuit interrupter i20 is called upon to interrupt a relatively large current Ilow. such as takes place under short circuit conditions, an arc will restrike between the contact fingers |32 and the contact surface HB. In such case, there will be two arcs-one inside the bore |50, and the other inside the bore |53. The heat from these arcs will evolve an arc extinguishing medium which. as described, will assist in extinguishing them.

Since it is obvious that certain further changes may be made in the above constructions, and different embodiments of the invention may be made Without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed as new is:

1. In electrical apparatus, a conductor from which an arc may be drawn, and a quantity of magnesium berate along the path of the arc from which an arc extinguishing medium is evolved due to the heat of the arc sufficient to extinguish the same.

2. In electrical apparatus, a conductor from which an arc may be drawn, and insulating means impregnated with magnesium berate in such position as to have a surface acted upon by the are from which surface an arc extinguishing medium is evolved due to the heat oi the arc sutlicient to extinguish the same.

3. An electric circuit interrupter comprising, in combination, means between which an arc is formed on interruption of the circuit, and means including magnesium borate disposed along the path of the are and adapted to evolve an arc extinguishing medium due to the heat of the arc.

4. An electric circuit interrupter comprising, in combination, separable terminals between which an arc is drawn on operation of the device, and insulating means disposed in such position as to surround and confine the arc and including a quantity of magnesium berate sumcient to evolve a medium due to the heat of the arc for extinguishing the same.

5. An electric circuit interruptor comprising, :in combination, separable terminals between which an arc is drawn on operation of the device, and a tubular member o1' fibrous insulating material impregnated with magnesium borate surrounding and confining the arc from the inner surface of which an arc extinguishing medium is evolved due to the heat of the arc suflicient to extinguish the same.

6. An electric circuit interrupter comprising, in combination, separable lterminals between which an arc is drawn on operation of the device, and a tubular member of organic insulating material impregnated with magnesium borate surrounding and confining the arc from the inner surface of which an arc extinguishing medium is evolved due to the heat of the arc sufficient to extinguish the same.

7. An electric circuit interrupter comprising, in combination, separable terminals between which an are is drawn on operation of the device, and a tubular member of cellulosic material impregnated with magnesium borate surrounding and confining the arc from the inner surface of which an `arc extinguishing medium is evolved due to the heat of the arc sufiicient to extinguish the same.

8. An electric circuit interrupter comprising, in combination, separable terminals between which an arc is drawn on operation of the dematerial by dipping it into a bath of inorganic arc extinguishing material, forming the impregnated sheet into a tube, and drying the tube.

18. Method of manufacturing an insulating sleeve having are extinguishing properties for use with electrical apparatus which comprises, impregnating a sheet of insulating material with arc extinguishing material, forming the impregnated sheet into a tube, and impregnating the tube with arc extinguishing material.

19. Method of manufacturing an insulating sleeve having arc extinguishing properties for vice, and a, tubular member of fibrous inorganic insulating material disposed in such position as to surround and confine the arc and impregnated with a quantity of magnesium borate suiiicient to evolve an arc extinguishing medium due to the heat of the arc for extinguishing the same.

9. An electric circuit interrupter comprising, in combination, separable terminals between which an arc is drawn on operation of .the device, and a tubular member of asbestos disposed in such position as to surround and confine the arc and impregnated with a quantity of magnesium borate suiiicient to evolve an arc extinguishing medium due to the heat of the arc for extinguishing the tame.A

10. A fuse link comprising, in combination, a pair of terminals interconnected by fusible means,v and a sleeve surrounding said fusible means and formed of nely divided fibrous material impregnated with magnesium borate.

11. A fuse link comprising, in combination, a pair of terminals interconnected by fusible means, and a sleeve surrounding said fusible means and formed of asbestos nour impregnated with magnesium borate.

12. In a fuse link, a rolled paper tube surrounding the fusible means and impregnated with magnesium borate.

13. In a fuse link, a rolled paper ltube surrounding the fusible means and impregnated with an inorganic arc extinguishing material having adhesive characteristics.

14. In a. fuse link, a tube of cellulosic material surrounding the fusible means and impregnated with magnesium borate.

15. An electric circuit interrupter comprising, in combination, means between which an arc is formed on opening of the circuit, and a tubular insulating member comprising rolled paper impregnated with magnesium borate.

16. An insulating sleeve for electrical apparause with electrical apparatus which comprises, impregnating a sheet of cellulosic material by dipping it into a solution.. of magnesium borate, rolling the impregnated sheet into a tube, and re-impregnating the tube by dipping it into a solution of magnesium borate.

20. Method of manufacturing an insulating sleeve having arc extinguishing properties foruse with electrical apparatuswhich comprises, irn-v pregnating a sheet of cellulosic material by(dipping it into a solution of magnesium borate, rolling the impregnated sheet into a tube, successively dipping the tube into a solution of magnesium borate, drying the tube after each immersion, and applying a water proofing layer to the outside surface of the tube.

21. A fuse link comprising, in combination, a pair of conductors interconnected by fusible means, a sleeve yof insulation surrounding said fusible means, and a quantity of magnesium borate within said sleevel embedding said fusible means. 4

22. A fuse link comprising, in combination, a pair of conductors interconnected by fusible means, a sleeve of insulation surrounding said fusible means, and a liner of fiber glass impreg- A nated with magnesium borate within said sleeve surrounding said fusible means.

23. A fuse vlink comprising, in combination, a pair of conductors interconnected by fusible means, a sleeve of insulation surrounding said fusible means, and a quantity of magnesium borate in powder form within said sleeve embedding said fusible means.

24. An expulsion fuse tube having its inner surface at least formed principally by a magnesium compound capable of evolving an arc extinguishing medium due to the heat of an arc sumcient to extinguish the same. y

25. An expulsion fuse tube having its inner surface at least formed principally by magnesium borate for evolving water vapor due to the heat of an arc sufficient to extinguish the same.

26. An expulsion fuse tube having a liner of fibrous insulating material impregnated with a magnesium compound capable of evolving an arc extinguishing medium due to the heat of an arc sufflcient to extinguish the same.

27. An expulsion fuse tube having a liner of fibrous insulating material impregnated with magnesium borate for evolving water vapor due to the heatof an arc sufficient to extinguish the tus upon theinner surface of which an' arc may vact comprising a tubular body of cellulosic material impregnated with magnesiumborateband having its outer surface covered with water proof material.

17. Method of manufacturing an insulating sleeve having arc extinguishing properties which comprises, impregnatlng a sheet of cellulosic same.

28. A circuit interrupter comprising, in combination, a fuse tube, a fuse-link within said fuse tube, and a sleeve of fibrous. insulating material surrounding .the fusible means of said fuse link, said sleeve being impregnated with a magnesium compound capable of evolving an arc extinguishing medium due to the hea-t of an arc suiiicient to extinguish the same. l

29. A circuit interrupter comprising, in combination, a fuse tube, a fuse link within said fuse tube, and a sleeve of fibrous insulating material surrounding the fusible means of said fuse link,

said sleeve being impregnated with magnesium borate for evolving water vapor due to the heat of an arc suilicient to extinguish the same.

30. A circuit interrupter comprising, in combination, an expulsion fuse tube having its inner surface at least formed principally by a magnesium compound capable of evolving an arc extinguishing medium due to the heat of an arc, and a fuse link within said fuse tube having a sleeve of fibrous insulating material impregnated with an inorganic arc extinguishing material surrounding the fusible means of said fuse link.

31. A circuit interrupter comprising, in combination, an expulsion fuse tube having its inner surface at least formed of magnesium borate for evolving water vapor due to the heat of an arc, and a fuse link within said fuse tube having a sleeve of fibrous insulating material impregnated with a magnesium compound capable of evolving an arc extinguishing medium due to the heat of an arc surrounding the fusible means of said fuse link.

32. An electric circuit interrupter comprising, in combination, means between which an arc is formed on opening of the circuit, and a tubular body of solid arc extinguishing material surrounding and confining the arc drawn between said means, said tubular body comprising magnesium borate.

33. An electric circuit interrupter comprising, in combination, means comprising a body of magnesium borate providing a bore, and a pair of arcing terminals one being stationarily mounted at one end of said bore and the other being mov,- able therethrough whereby an arc drawn therebetween plays upon the inner surface of said bore and evolves water vapor therefrom due t the heat of the arc sufficient to extinguish the same.

34. An electric circuit interrupter comprising, in combination, means comprising a body of magnesium borate providing a bore, a pair of arcing terminals one being stationarily mounted at one end of said bore and the other being movable therethrough, and fusible means interconnecting said arcing terminals and restraining movement of said other terminal, said fusible means being adapted to blow on the occurrence of a predetermined overload whereupon said other terminal is released and an arc is formed between said terminals which plays upon the inner surface of said bore and evolves water vapor therefrom due to its heat sufiicient to extinguish the same.

35. An electric circuit interrupter comprising, in combination, means comprising a body of magnesium borate providing a bore. and a pair of normally engaged switch members one being stationarily mounted at one end of said bore and the other being movable therethrough whereby an arc drawn therebetween plays upon the inner surface of said bore and evolves water vapor therefrom due to the heat of the arc sufficient to extinguish the same.

36. For use in a circuit interrupter of the class described an arc extinguishing material containing more than 44% by weight of water of crystallization.

37. An electric circuit interrupter comprising, in combination, separable terminals between which an arc is drawn on operation of the device, and a tubular member of fibrous insulating material impregnated with an adhesive inorganic arc extinguishing material capable of binding the fibers of said insulating material together and adapted to evolve an arc extinguishing medium due to the heat of the arc sufficient to extinguish the same.

38. As a new composition of matter having flame proof and high electrical resistance characteristics, fibrous material impregnated with an adhesive magnesium compound.M

39. As a new composition of matter having flame proof and high electrical resistance characteristics, fibrous material impregnated with an alkaline-earth borate solution.

40. vAs a new composition of matter having flame proof and high electrical resistance characteristics, fibrous material impregnated with mangesium borate.

4l. Method of flame proofing fibrous material which comprises impregnating the same with an adhesive magnesium compound.

42. Method of flame proofing organic fibrous material which comprises impregnating the same with magnesium borate.

43. Method of flame proofing paper which comprises impregnating the same with an adhesive alkaline-earth borate solution.

44. Method of producing a formed high electrlcal resistance non-inflammable body which comprises: mixing or impregnating fibrous or other materials with an adhesive alkaline-earth borate solution, and comprising, drying and aging the resulting product with or without the application oi' heat to impart strength and rigidity to the same.

45. As a new composition of matter a cement or plastic body containing magnesium borate.

46. A fuse link comprising, in combination, a pair of conductors interconnected by fusible means, a sleeve of insulation containing magnesium borate surrounding said fusible means, and means holding said sleeve to one of said conductors, the other conductor -belng free to move out of said sleeve on blowing of said fusible means.

47. A fuse link comprising, in combination, a pair of conductors interconnected by fusible means, an outer sleeve of insulation surrounding said fusible means, and a sleeve `of insulation containing magnesium borate within said outer sleeve.

48. A fuse link comprising, in combination, a pair of conductors interconnected by fusible means, an outer sleeve of insulation surrounding said fusible means, a. sleeve of insulation containing magnesium borate within said outer sleeve, and means for holding said sleeves to one 0f said conductors, the other conductor being free to move out of said sleeves on blowing of said fusible means.

49. A fuse link comprising, in combination, a pair of conductors interconnected by fusible means, an outer sleeve of insulation surrounding said fusible means, a sleeve of insulation containing magnesium borate within said outer sleeve, and a pin extending through said sleeves and into one of said conductors for preventing relative movement therebetween, the other conductor being free to move out of said sleeves on blowing of said fusible means.

50. An electric circuit interruptor comprising, in combination, means between which an arc is formed on opening of the circuit, and an insulating structure surrounding and confining the arc space having a lining including magnesium borate and an outer housing therefor including a thermosetting resin.

5l. An electric circuit interruptor comprising,

in combination, means between which an arc is formed Ion opening of the circuit, and an insulating structure surrounding and confining the arc space having a lining formed by paper treated with magnesium borate and an out'er housing formed by paper treated with a thermosetting resin.

52. An electric circuit interrupter comprising, in combination` means ,between which an arc is formed on opening of the circuit, and an insuiating structure surrounding and confining the arc space having a. lining formed by a rolled,

paper tube impregnated with magnesium borate and an outer housing formed by a. rolled GEORGE F. MCMAHON.