US2813952A

US2813952A - Bayonet type circuit interrupter

Info

Publication number: US2813952A
Application number: US465922A
Authority: US
Inventors: Charles H Baker; John J Mikos
Original assignee: S&C Electric Co
Current assignee: S&C Electric Co
Priority date: 1954-11-01
Filing date: 1954-11-01
Publication date: 1957-11-19
Anticipated expiration: 1974-11-19

Description

Nov. 19, 1957 c. H. BAKER ET Al. 2,813,952

BAYONET TYPE CIRCUIT INTERRUPTER Filed NOV. 1, 1954 4 Sheets-Sheet l Nqv. 19, 1957 c, H. BAKER ETAL 2,813,952

BAYONET TYPE `CIRCUIT INTERRUPTER Filed NOV. l, 1954 4 Sheets-Sheet 2 75 y A @Zaki/@1% VBy Nov. 19, 1957 c.I H. BAKER ET AL BAYONET TYPE CIRCUET INTERRUPTER FiledV Nov. i, 1954 A4 Sheets-Sheet 3 @5' f 17 di i 45 40 #if L' J6 l J/ 49 2/ 50 Nov. 19, 1957 C, H. BAKER ET AL BAYONET TYPE CIRCUIT INTERRUPTER 4 Sheets-Sheet 4 Filed NOV. l, 1954 NVENTOR5 /O (/za//Y f3 nAYoNnT TYPE CIRCUIT rNrEnnUPrER Charles H. Baker, Arlington Heights, and .lohn I. Mikes,

Highland Park, Ill., assignors to S & C Electric Coinpany, Chicago, Ill., a corporation of Delaware Application November 1, 1954, Serial No. 465,922 22 Claims. (Cl. 20G- 127) This invention relates, generally, to bayonet type circuit interrupters, and it has particular relation to fuse cutouts capable of interrupting load current. It constitutes an improvement over the cutout construction shown in Lindell et al. Patent No. 2,591,949, issued April 8, 1952, and Triplett Patent No. 2,316,470 issued April 13, 1943, both assigned to the assignee of this application. This application is a continuation-in-part of application Serial No. 406,531, filed January 27, 1954, now abandoned.

The Lindell et al. patent above referred to shows a bayonet type cutout and it comprises a tubular insulating housing which is adapted to be mounted in an upright position and is provided with annular line contacts at the upper and lower ends. A bayonet member in the form of a fuse tube having terminals at its ends is arranged to be inserted in the tubular insulating housing in such position that these terminals engage the line contacts. Within the fuse tube is a replaceable fuse link that generally comprises fusible and strain elements that are connected at one end to a terminal which, in turn, is connected to the upper terminal of the fuse tube. The other ends of the fusible and strain elements are connected by a flexible lead to the lower terminal of the fuse tube. A small insulating sleeve surrounds the fusible and strain elements. Between the line contacts in the tubular insulating housing is a large sleeve which is formed of insulating material, such as libre. In the event that the cutout is subjected to an overload or to a short circuit, the fusible and strain elements within the fuse link melt and the fuse link terminals are separated to draw and extinguish the arc incident to the operation either within the sleeve of the fuse link or within the fuse tube itself.

In some instances it is necessary to withdraw the bayonet member or fuse tube from the tubular insulating housing in order to deenergize the circuit in which the cutout is connected. When this operation takes place, it is usually accomplished with load current flowing through the cutout, this load current, of course, being within the normal range of current that is intended to be conducted by the cutout. When the fuse tube is withdrawn from the tubular insulating housing, arcs are drawn between the terminals at the ends of the fuse tube and the annular contacts at the ends of the tubular insulating housing. The arc drawn between the lower fuse tube terminal and the lower annular line contact is drawn within the large insulating sleeve. This sleeve protects the inner surface of the tubular insulating housing from the heat of the arc.

When the large insulating sleeve is formed of libre or Fire methylmethacrylate resin certain operating diculties may arise. The fibre sleeve, when subjected to rain, sleet or snow in the absence of the bayonet member, is likely to become warped. The sleeve of methylmethacrylate resin, while impervious to moisture, may become deformed as a result of being subjected to heat resulting from operating the cutout for a long time under overload insufficient to cause the fusible element to blow. In both cases the distortion is likely to interfere with the subsequent insertion and removal of the bayonet member.

The Triplett patent, Figure 8 shows a bayonet type circuit interrupter construction that is generally similar to that shown in the Lindell et al. patent except that the terminals of the bayonet member are interconnected by a metallic rod. The device then has no overcurrent operating characteristics but functions as a disconnecting switch and can be used to open the circuit manually.

Among the objects of this invention are: To provide for attaching a trailer of insulating material to the lower terminal of the bayonet element or fuse tube of the cutout described in the above patents for improving the ability of the device to interrupt load current or moderate overload current but not short circuit current, when the bayonet element is withdrawn from the housing containing the line contacts by causing the arc to come into more intimate contact with the inner surface of the large insulating sleeve; to accomplish the attachment of the trailer to the lower terminal in such manner that operation of the device for automatically interrupting the circuit under overload and short circuit conditions is not interfered with; to provide an articulated connection between the lower terminal and the trailer to permit the trailer to center itself with respect to the lower line Contact and the large diameter insulating sleeve thereabove and with respect to the arc drawn between the lower terminal and the lower contact of the tubular insulating housing; to prevent static discharge from the parts forming the articulated coupling between the trailer and the lower terminal of the fuse tube when the latter is energized at high voltage; to attach the trailer to the lower terminal in such manner as to accommodate various types of fuse links and in particular for use with a fuse link having an indicator projecting from the lower end of the fuse tube and tubular insulating housing; to construct the trailer in such manner that pressure generated thereabove when the cutout is closed on a fault can be readily relieved without injury to the cutout housing and contacts; to attach the trailer to the lower terminal in such fashion that there is no interference with the withdrawal of the bayonet member resulting from overlapping with the trailer of the flexible lead and terminal portions of the blown fuse link; and to employ for the large insulating sleeve a material that is unlikely to be deformed by moisture or the heat to which it is subjected and which will cooperate with the material forming the trailer to evolve an arc extinguishing medium and leave a minimum of conducting material on the surfaces of the sleeve and trailer.

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

This invention is disclosed in the embodiments thereof shown in the accompanying drawings, and it comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the constructions hereinafter set forth and the scope of the 3 application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of this invention, reference can be had to the following detailed description, taken together with the accompanying drawings, wherein:

Figure 1 is a view, in side elevation, of a fuse cutout in which the present invention is embodied;

Figures 2A and 2B, taken together, the former placed above the latter, show, at an enlarged scale, a longitudinal cross-sectional View of the cutout illustrated in Figure l;

Figure 3 is a longitudinal sectional view of the lower end of the fuse tube and trailerattached thereto with the remains of a blown fuse link held in anI alternate position but prevented from dropping out of the cutout;

Figure 4 is a vertical sectional view, taken generally along the line 4-4 of Figure 2B andillustrating the manner in which the fuse link with the indicator is held against the lower end of the threaded portion, depending from the lower fuse tube terminal;

Figure 5 is a view, partly in longitudinal section, and partly in side elevation illustrating the manner in which the trailer of the present invention can bel employed with a different type of fuse link',

in section, showingV the details of construction of thel articulated connection for the trailer, the trailer sleeve being shown slightly cocked to illustrate the articulated connection;

Figure 7 is a view, similar to Figure 6, but showing a modied form of the ar 'culated connection for use with a trailer adapted to be employed in a fuse cutout having an ampere rating greater than the fuse cutout for which the trailer illustrated in the preceding gures yis used;

Figure 8 is a top plan view of a split ring that is employed in the construction shown in Figure 7;

Figure 9 is a top plan view of an anti-static spring ernployed in the construction shown in Figure 7;

Figure 10 is a view, in side elevation, of the spring shown in Figure 9 and showing how the spring is dished;

Figure 11 is a top plan view of the retaining ring that is employed in the construction shown in Figure 7;

Figure 12 is a top plan view of the snap ring that is employed in the construction shown in Figure 7;

Figure 13 is aview, in side elevation, showing the present invention embodied in a bayonet element for a disconnecting type of circuit interrupter;

Figure 14 is a view, similar to Figure 2B, showing another modification of the trailer arranged so that the` flexible lead and terminal of a blown fuse link do not interfere with the withdrawal of the bayonet member to which the trailer is attached;

Figure l5 is a vertical sectional view taken generally along the line 15-15 of Figure 14;

Figure 16 is a side elevational view of the trailer construction shown in Figure 14, certain parts being broken away to illustrate more clearly certain details of construction; and

Figure 17 is a horizontal sectional View taken generally along the line 1717 of Figure 16.

Referring now particularly to Figure l of the drawings, it will be observed that the reference character 11B designates a wood cross arm that may be surrounded by a sectional clamp 11 to which a bracket 12 is secured. The bracket 12 may be clamped by bolts 13 to support a fuse cutout of the bayonet type, illustrated generally at 14. The fuse cutout 14- may be of the construction described in the Lindell et al. patent above referred to. Accordingly, only a general description thereof will be set forth herein. The fuse cutout 14 includes a tubular insulating housing 15 that ordinarily is formed of wet process porcelain and is arranged to be positionedin a generally upright lposition as shown. An insulating handle 16 is located at the top of the housing 15 for closing the same and also for attachment to the bayonet element to be described presently.

In Figures 2A and 2B of the drawings, the internal details of construction of the fuse cutout 14 are shown more clearly. It will be noted that upper and lower cylindrical line contacts 17 and 18 are secured near the respective ends of the insulating housing 15. It will be understood that these line contacts 17 and 1S are arranged to be connected to the electric power circuit in which the cutout is to be used. An internally threaded insert 19 is secured to the underside of the insulating handle 16 for attachment tothe upper end of a bayonet member `or fuse tube that is shown, generally, at 20. The fuse tube 2t) has upper and lower

fuse tube terminals

21 and 22 at its respective ends. As shown these fuse tube terminals are arranged to engage, respectively, the upper and lower line contacts 17 and 18. ln addition, the upper fuse tube terminal 21 is threaded into the insert 19. In this manner the bayonet member or fuse tube 2@ and the insulating handle 16 provide a unitary structure.

The fuse tube 20 is arranged to receive different types of fuse links for interconnecting the

terminals

21 and 22, and, in turn, the line contacts 17 and 18. ln the embodiment illustrated in Figures 2A and 2B of the drawings, a spring and cable assembly, shown generally at 23, is inserted in the upper end of the fuse tube 2G and this assembly has a threaded terminal 24 at its lower end for receiving a fuse link that is shown, generally, at 25. T he fuse link 25 includes a fuse link terminal 26 that is threaded into the terminal 24 and has depending therefrom a-strain wire 27 and a fusible element 28. At their lower ends the strain wire 27 and fusible element 28 are connected to a fuse link terminal 29 which has a sleeve portion 3'() that is secured atone end of a exible lead 31. Surrounding the strain wire 27 and fusible clement 28 is az fuse link sleeve 32 which is secured to the fuse link terminal 26. At the lower end of the flexible lead 31 is a terminal fitting 33 which has secured thereto an indicator 34 in the form of a rodl of insulating material. lt is pointed out that the fuse link 25 including the indicator 34 may be constructed as shown in McMahon Patent No. 2,253,720, issued August 26, 1941, and assigned to the assignee of this application; The terminal fitting 33 with the indicator 34 attached thereto is arranged to enter a split threaded portion S that depends from the lower fuse tube terminal 22. 'The split threaded portion 35 is illustrated and described in more detail in Schultheiss Patent No. 2,531,949, issued November 28, 1950, and assigned to the assignee of this application. It will be noted that the terminal ii'tting 33V has a shoulder 36 which bears against the lower end of the split threaded portion 35.

Located within the tubular insulating housing 15 and positioned above the lower line contact 13 is an insulating sleeve 37"that may be formed of libre. The purpose of this sleeve is to prevent any arc drawn between the lower fuse tube terminal 22 and the lower cylindrical linek Contact 18 from impinging on theV inner surface of the porcelain housing 15 and causing damage thereto.

The construction of the fuse cutout 14 thus far described is known in the prior art. The present invention has to do particularly with means for confining the are drawn within the insulating sleeve 37 when the handle 16 and `fuse tube Ztl are withdrawn from the tubular insulating housing 1S'and with the material of which the sleeve 37 is composed.

With the cutout construction thus far described, when the fuse link 2S blows on the occurrence of anoverload or short circuit, thev spring and cable assembly 23 withdraws the terminal 24 upwardly into the fuse tube 2h together with the fuse link terminal 26 and possibly the fuse link sleeve 32 unless it is completely ruptured. The

remaining portions of the strain wire 271and fusible element'28 are shown in Figure 3 where it will be observed the fuse link terminal 29 and parts attached thereto have dropped downwardly. Normally these parts including the indicator 34 will drop to the ground. It is thus possible to detect by the absence of the indicator 34 that the cutout 14 has operated and that the fuse link 25 therein should be replaced.

In accordance with this invention, provision is made for conning the arc drawn within the insulating sleeve 37 by a trailer that is shown, generally, at 40 and is removably attached to the split threaded portion of the lower fuse tube terminal 22. In attaching the trailer 4@ to the lower fuse tube terminal 22, care must be taken that there is no interference with the normal operation of the fuse cutout 14 under overload or short circuit conditions. It will be observed that the split threaded portion 35 is oset slightly from the vertical axis of the fuse tube 20. Because of this olfset relation and the necessity for having the trailer of such an outside diameter that it tits closely within the insulating sleeve 37 and, because it must be inserted axially through the line contacts 17 and 18, provision is made, as described hereinafter, for an articulated connection between the trailer 40 and the lower fuse tube terminal 22. A further design limitation is that the attachment of the trailer 40 to the fuse tube terminal 22 should be such that fuse links other than those having a terminal fitting similar to the terminal fitting 33 can be employed in the cutout 14. A still further design limitation resides in the necessity for avoiding the presence of any loose metallic connections which would be likely to give rise to a static discharge when the cutout 14 is energized at high voltage.

The details of construction of the trailer 40 are shown more clearly in Figures 3 and 6 of the drawings. lt will be observed that it includes a trailer sleeve 41 that is formed of suitable insulating material, such as methylmethacrylate resin or other insulating material, which, when subjected to the heat of an arc, will evolve an arc extinguishing medium. For reasons which appear hereinafter the sleeve 41 is formed preferably of this particular resin. The diameter of the trailer sleeve 41 is such that it lits fairly closely within the insulating sleeve 37 so as to confine the arc drawn between the lower line contact 18 and the lower fuse tube terminal 22 and cause the same to come into intimate contact engagement with the inner surface of the sleeve 37 and the outer surface of the trailer sleeve 41. The trailer sleeve 41 has a hollow lower portion 42 for telescoping over the indicator 34 when a fuse link of this type is employed. At the upper end of the hollow lower portion 42 is a radially, inwardly extending shoulder 43 above which there is a cavity 44 into which a lower cylindrical portion 45 of a metallic coupling member, shown generally at 46, is positioned. The coupling member 46, preferably formed of brass, and by a screw-machine operation, has a head portion 47 in the form of a nut with internal threads 48 for threading on the split threaded portion 35 of the lower fuse tube terminal 22.

At the lower end of the cylindrical portion is a radially extending shoulder 49, the diameter of which is slightly less than the internal diameter of the cavity 44. Reacting against the shoulder 49 is a metallic spring washer 50 that is split radially at 51 to facilitate assembly over the shoulder 49. The spring washer Sil bears against the underside of a metallic retaining ring 52 that is formed preferably of brass and is radially split at 53 so that it too can be assembled over the shoulder 49 with its upper side located underneath a split metallic snap ring 54 that cooperates with an annular groove 55 in the upper end of the cavity 44.

In order to assemble the coupling member 46 with the trailer sleeve 41, the split snap ring 54, retaining ring 52 and the spring Washer 5t) are applied to the cylindrical portion 45 in the order named. Then the cylindrical portion 45 is inserted into the cavity 44 and the ring 54 is snapped into position. Since the metallic spring washer 50 bears against the radial shoulder 49 of the metallic coupling member 46 and also against the underside of the retaining ring 52 to urge it into contact with the metallic snap ring 54, they are retained in mutual contact engagement and there is a continuous circuit between these various metallic parts. There is then no likelihood that there will be a static discharge from any of these parts as might be the case if the metallic spring washer 50, which may be termed an anti-static spring washer, were not employed.

The interconection between the metallic coupling member 46 and the trailer sleeve 41 is such that the latter telescopes over the former and the connection is effected wholly within the cavity 44.

By providing the relatively loose yet spring urged interconnection between the coupling member 46 and the trailer sleeve 41, there is a limited degree of relative movement therebetween so that the connection can be termed an articulated connection. As shown in Figure 6, the longitudinal axis of the coupling member 46 is indicated at 56 while the longitudinal axis of the trailer sleeve 41 is indicated at 57. This illustrates that the trailer sleeve 41 can be cocked to a slight extent with respect to the coupling member 46. Not only does this freedom of movement of the trailer sleeve 41 with respect to the coupling member 46 and the lower fuse tube terminal 22 facilitate the insertion of the fuse tube 20 into the housing 15 but also the trailer sleeve 41 can be moved by the arc within the insulating sleeve 37 so as to effect a random positioning thereof. lf the trailer sleeve 41 were attached rigidly to the lower fuse tube terminal 22, it would always assume the same position with respect to the insulating sleeve 37, making it likely that the arc always would be drawn along the trailer sleeve 41 at the same location. Such a rigid construction would tend to cause burning of the contact 18 and terminal 22 and erosion of the sleeve 37 and trailer sleeve 41 at o-ne point or along one line rather than random location and thus would shorten the operating life of the fuse cutout 14.

As pointed out hereinbefore when the bayonet member or fuse tube 2t), with the trailer 40 is attached thereto, is withdrawn through the housing 15 to separate the lower fuse tube terminal 22 from the lower line contact 1S While the fuse cutout 14 is carrying load current, an arc is drawn within the insulating sleeve 37. This arc is confined within the sleeve 37 by the trailer sleeve 41. The material of which the sleeve 37 is formed is important. For the reasons above set forth libre or methylmethacrylate resin, while satisfactory from an arc extinguishing standpoint, are subject to distortion. Accordingly, the sleeve 37 is formed preferably of nylon which does not absorb moisture and warp, as does libre, and which has dimensional stability at temperatures higher than does methylrnethacrylate resin. While the evolution of arc extinguishing gas from nylon is less than from methylmethacrylate resin, the combination of the trailer sleeve 41 of this resin with a sleeve 37 of nylon provides highly satisfactory results from the standpoint of arc extinction and at the same time the mechanical advantages above outlined are obtained. Since the trailer sleeve 41 is normally located outside the housing 15, is unaffected by heat generated on operation of the cutout 14 under overload insutiicient to blow the fuse link 2S which would be likely to damage the sleeve 3'7 if it were formed of methyimethacrylate resin. The use of such a sleeve 41 is highly desirable since it evolves a large quantity of gas when subjected to the heat of an arc and promotes a scavenging action over its surface and the inner surface of the sleeve 37 to the end that there is a minimum of conducting residue on these surfaces and the breakdown strength remains high.

ln Figure 5 of the drawings, there is shown the fuse link 25 with the exible lead 31 extending between the branches of the split threaded portion 35 and to the rear A 7 of the depending portion of the lower fuse tube terminal 22. The indicator 34 is not employed in this construction, nor is the spring and cable assembly 23 used.

'Rather the fuse link 25 is positioned in the upper end of the fuse tube as shown. With a view to clamping the flexible lead 3l securely in contact engagement with the lower fuse tube terminal 22, the upper surface of lthe head portion 47 has annular ribs 58 formed therein Vthe sleeve 41, may be formed of insulating material, such as methylmethacrylate resin. lt too has a hollow portion 62 for receiving the indicator 34 if a fuse link employing the same is used. There is a radially, inwardly extending shoulder 63 near the upper end of the trailer sleeve 6l and a cavity 64 thereabove for receiving a cylindrical portion 65 of a metallic coupling member 66. It has a head portion 67 in the form of a nut that is internally threaded at 68 for threading on a split threaded portion of a fuse cutout similar to the split threaded portion previously described. At the lower end of the cylindrical portion 65, there is an annular groove 69 for receiving a split ring 76 that is split radially, as indicated at 71. It will be understood that the ring 70 provides a shoulder at the lower end of the cylindrical portion against which a dished anti-static annular spring 72 reacts. As shown in Figures 9 and l0, the spring 72 is in the form of an annulus and is dished or curved to assume the position when unstressed as shown in Figure l0. The spring 72 bears against the split ring '70 and against the underside of a metallic retaining ring 73 which, as shown in Figure ll, is in the form of an annulus. The spring 72 urges the retaining ring 73 upwardly against a snap ring 74, Figure 12, which is located within an annular groove 75 near the upper end of the cavity 64. Annular ribs 76 are formed in the upper surface of the head portion 67 for clamping a flexible lead as previously described.

Prior to positioning the cylindrical portion 65 in the 'cavity 64, the snap ring 74 is placed thereon. Then the retaining ring 73, which has an internal diameter slightly greater than a radially extending ange 77 at the lower end of the cylindrical portion 65 is positioned thereon. Then the spring 72 which also has an internal diameter slightly greater than the external diameter of the flange 77 is positioned on the cylindrical po-rtion 65. Finally the split ring is snapped over the ange 77 and assumes a position within the groove 69 to form a shoulder aganist which the spring 72 can react. The complete assembly is inserted in the cavity 64 and the ring 74 is snapped into place where the retaining ring 73 is held in contact engagement therewith by the spring 72 which also bears against the upper surface of the split ring 70. As before, the spring 72 holds these Various metallic parts in contact engagement so that there is a complete circuit from the coupling member 66 to the snap ring '74. There are -no loose parts which could separate due to vibration and cause a static discharge likely to interfere with radio reception when the cutout is energized at high voltage.

The trailer 60 also has an articulated connection to the cutout. This is illustrated by the relative positions of the axis 78 of the coupling member 66 and the axis 79 of the trailer sleeve 6l. Thus it is possible to cock the trailer sleeve 6l slightly in order to facilitate insertion of the bayonet member into the insulating housing and also to centralize the trailer sleeve 61 within the sleeve above the lower line contact and cause random positioning of 8 the arc which is drawn when the fuse cutout is operated to interrupt the circuit when it is carrying load current.

With the coupling member 66 threaded onto a split threaded portion of the lowerterminal of the fuse -tube and a fuse link of the type illustrated inlFigure 3 employed, when the fuse link has blown,-the sleeve portion 30, while permitting the indicator 34 to drop down to an alternate position through the `trailer sleeve 61, is prevented by the head portion `67 from dropping to the ground as otherwise would be the case if the coupling member 66 were not employed. However, `bythe changed position of the indicator 34 Vwith respect to the trailer sleeve 6l, it is possible to determine that the fuse cutout has operated and that the fuse link should Vbe replaced.

In some instances, it is desirable to employ the tubular insulating housing lo' with its upper and lower line contacts 17 and l in conjunction with a disconnecting switch blade instead of employing thebayonet member or fuse tube 20 having a replaceable fuse link 25 therein. Thisalternate device used solely for disconnecting purposes is illustrated in Figure -l3 where a bayonet switch blade member is illustrated, generally, at. The switch blade 89 is formed of good conducting material, such as copper-in contradistinction to the fuse tube Ztl which is formed of insulating material. At its upper end the switch blade 8) is provided with an upper switch blade terminal 3l which is generally similar to the upper fuse tube terminal 2l, previously described. Its outer configuration is the same so that it can be threaded into the insulating handle i6 at its upper end and can interiit with theupper'line contact 17 in the tubular insulating housing 15. At its lower end the switch blade 30 has a lower switch blade terminal 82 which is generally similar to the lower fuse tube terminal 22, in that it is arranged to engage the lower line contact 18.

The lowermost portion of the lower switch blade terminal 82 has a boss 83 extending therefrom, and it is threaded for receiving the head portion or nut 47 of the trailer 40 which has been described previously. The trailer sleeve 41 is in articulated relation with respect to the head portion or nut 47 and thus the insertion of the blade St) into the housing l5 is facilitated. When the switch blade is withdrawn from the housing l5 and an arc is drawn between the lower switch blade terminal S2 and the lower line contact 86, it is confined between the outer surface of the trailer sleeve 41 and the inner surface of the insulating sleeve 37 in the manner described previously and for the purposes hereinbefore outlined.

It is pointed out that the insulating housing l5 equipped with the bayonet switch blade Sil has a current carrying capacity which is about twice the current carrying capacity of the device when the fuse tube 20 is employed with the fuse link 2S. However, it would not be feasible to interrupt such a magnitude of load current by withdrawing the bayonet switch blade 86 unless the trailer 4i? were ernployed.

The fuse cutout 14 is intended to interrupt automatically the circuit in the event that a predetermined overload or a short circuit occurs thereon. Under certain circumstances of load interruption the sleeve portion 30 of the fuse link 25, instead of dropping to the position shown in Figure 3, may be expelled with sufficient force so that it swings downwardly past the lower end of the lower fuse tube terminal 22 to the position shown in Figure i4. If the trailer 4) or 60 is employed under these conditions, the terminal Sil may wedge between the upper end of the trailer or dll the lower cylindrical line contact 18 in such manner as to interfere with the withdrawal of the bayonet member 2Q. In order to overcome this possible ditiiculty the trailer construction as shown, generally, at 90 in Figures 14, l5, 16 and l7 can be employed.

It will be observed that the trailer 96 includes a hollow stem 91 that is formed preferably of nylon or other insulating material which is relatively strong. Articulated 9 with the hollow stem 90 is a trailer sleeve 92 that is formed preferably of methylmethacrylate resin as are the

trailer sleeves

41 and 61 referred to hereinbefore.

At its upper end the hollow stem 91 is provided with a nut 93 carrying threads 94 for engaging the threads on the split threaded portion 35 of the lower fuse tube terminal 22. The nut 93 is provided with depending

flanges

95 and 96 which telescope over the upper end 97 of the hollow stem 91 which is reduced in thickness as shown. The outer surface of the upper end 97 is provided with a groove 98 into which a portion 99 of the depending ange 96 can be deformed. This construction essentially makes the nut 93 integral with the hollow stem 91 at its upper end.

It will be observed that the diameter of the hollow stem 91 is substantially less than the outside diameter of the trailer sleeve 92. The sum of the outside diameter of the hollow stem 91 and of the diameter of the sleeve portion 30 is les-s than the inside diameter of the lower cylindrical line contact 18. Thus, when the terminal 30 is expelled so as to occupy the position illustrated in Figure 14, it does not interfere with the withdrawal of the bayonet member or fuse tube 20 from the tubular insulating housing to permit refusing of the cutout 14.

At the same time that provision is made for accommodating the Isleeve portion 30 of the fuse link terminal 29 the diameter of the trailer sleeve 92 is such that it approaches the internal diameter of the insulating sleeve 37 within the porcelain housing 15 which, as previously indicated, is formed preferably of nylon to maintain dimensional stability.

The trailer sleeve 92 is maintained inseparable from the hollow stem 91 by providing the latter with an enlarged lower end 102 which has an upper shoulder 103 that is arranged to engage a downwardly facing shoulder 104 formed on the underside of a reduced diameter upper end 105 of the sleeve 92. It will be understood that the trailer sleeve 92 is freely slidable on the hollow stem 91 and that the latter is inserted in the former prior to the assembly of the nut 93 on the upper end as described previously. The upper end 105 of the trailer sleeve 92 is beveled as indicated at 106 in order to facilitate entry into the lower cylindrical line contact 18 and into the insulating sleeve 37.

Since the diameter of the enlarged lower end 102 is such with respect to the inside diameter of the trailer sleeve 92 that the latter freely moves on the former, it will be obvious that the trailer sleeve 92 is exbly connected to the hollow stem 91 which is rigidly connected by the nut 93 to the lower fuse tube terminal 22. Thus there is a limited amount of relative movement between the trailer sleeve 92 and the lower fuse tube terminal 22 which facilitates the movement of the latter through the

fuse tube terminals

21 and 22 and through the insulating sleeve 37.

It is entirely possible that the short circuit which may have caused the blowing of the fuse link 25 will not have been removed by the time that the operator decides to reclose the circuit after the bayonet member or fuse tube has been refused with an unblown fuse link. Under these circumstances when the operator attempts to restore service by closing the cutout 14 on insertion of the refused bayonet member or fuse tube 20 therein, the circuit will be closed under such conditions that the short circuit will be reestablished momentarily. This will take place as soon as the lower fuse tube terminal 22 engages the lower cylindrical line contact 18 and `before the operator will have had a chance to restore the bayonet member or fuse tube 20 to the fully closed position. The fuse link 25 blows and instantly large amounts of gas are release". Pressure is built up within the housing 15 since the dis-- charge lower end of the fuse tube 20 is well above the lower end of this housing. When the

trailer

41 or 61, previously described, is employed under these circumstances it lls completely the lower cylindrical contact 18 and, as a result, substantial pressure may be generated at the lower end of the porcelain housing 15. Such operation may be of suflicient severity as to expel the lower line contact 18 from the porcelain housing 15 or to break olf the lower end of the latter.

With a view to relieving the pressure that otherwise would be built up under these conditions and at the same time providing for restricting the arc that is drawn Within the insulating sleeve 37 when the bayonet member or fuse tube 20 is removed under load, the outer surface of the trailer sleeve 92 is provided with several longitudinal grooves or iiutes 107.

When the cutout 14 is operated to interrupt load current and the trailer sleeve 92 is used, the arc between the lower line contact 18 and the lower fuse tube terminal 22 is initiated at random at any point around the trailer sleeve 92 and it will be moved into any one of the several grooves or utes 107 as the result of gas flow under pressure. The arc Will be extinguished in that particular groove. At the same time, while the grooves or flutes 107 together are of suflicient depth to relieve the gas pressure which is generated when the cutout 14 is closed on a short circuit, they are of such size that individually they do not open the cross-sectional path for the load current arc which is drawn when the bayonet member or fuse tube 20 is withdrawn for interrupting the circuit under load suiciently to reduce the load current interrupting ability of the device. As pointed out the longitudinal grooves or flutes 107 provide a sufficient cross-section of escape passageway to relieve the gas pressure attendant upon inadvertent closure of the fuse cutout 14 on an existing fault to a sufficient extent that there is no likelihood of damage to the cutout 14.

As shown the lower end of the trailer sleeve 92 is beveled as indicated at 108 to facilitate the entry of the trailer 92 into the upper end of the insulating sleeve 37 and into the upper end of the lower cylindrical contact line 18 as well as initial entry into the upper end of the upper cylindrical line contacts 17.

In the drawings the

trailers

40 and 90 are shown in the positions occupied thereby both before and after the blowing of the fuse link 25'. As pointed out hereinbefore, the

trailers

40, 60 and 90 are employed to assist in extinguishing the arc that is drawn on separation of the lower fuse tube terminal 22 from the lower line contact 18 when the bayonet member or fuse tube 20 is withdrawn from the housing 15 while the fuse cutout 14 is carrying load current. The arc thus drawn is confined between the inner surface of the insulating sleeve 37 and the outer surface of the

trailers

40, 60 and 90. However, the construction of these trailers and their application to the lower fuse tube terminal 22 are such that they do not interfere with the insertion or removal of the bayonet member or fuse tube 20 nor with the blowing of the fuse link 25.

Since certain further changes can be made in the foregoing constructions and different embodiments of the invention can be made Without departing from the spirit and scope thereof, it is intended that all matter shown in the accompanying drawings and described hereinbefore shall be interpreted as illustrative and not in a limiting sense.

What is claimed as new is:

l. A circuit interrupter comprising, in combination, a tubular insulating housing having internal terminal members near its ends, a bayonet member insertable into and removable endwise from said housing and having spaced interconnected terminals for engaging said internal terminal members respectively, and a trailer connected to the terminal of said bayonet member that trails when the same is removed from said housing, said trailer including an elongated sleeve of insulation and coupling means inseparably and exibly connecting one end of the same to the trailing terminal of said bayonet member whereby there is limited relative movement therebetween and they move conjointly when said bayonet member is withdrawn through said housing where the arc is confined between theinside thereof and the outer surface of said'sleeve of insulation.

2. A circuit interrupter comprising, in combination, a tubular insulating housing having internal terminal members near its ends, a bayonet member insertable into and removable endwise from said housing and having spaced terminals for engaging said internal terminal members respectively, one of said terminals on said bayonet member constituting a trailing terminal when the same is withdrawn from said housing, means within said bayonet member interconnecting said terminals including a fuse link having a rod-like indicator projecting therefrom and from the end of said bayonet member that trails when the same is removed from said housing at which time when the interrupter is opened under load an arc is drawn between the trailing member and the associated terminal member, said trailing terminal having a threaded portion, and a trailer connected to said trailing terminal including a sleeve of insulation telescoped over said indicator and allowing movement of the same endwise therethrough, threaded coupling means threaded on said threaded portion of said trailing terminal, and means flexibly connecting said sleeve to said coupling means whereby there is limited relative movement permitted between said sleeve and said trailing terminal when said bayonet member is drawn through said housing and the arc is confined betwen the inside thereof and the outside or" said sleeve of insulation.

3. A trailer for an energized terminal of the bayonet portion of a bayonet type circuit interrupter comprising, in combination, an elongated insulating member, an electrical terminal connection including a plurality of metallic parts connected to one end of said elongated insulating member for connecting said insulating member in articulated relation to said terminal, and resilient means cooperating with said coupling means and said insulating member to maintain the former static free when connected to the energized terminal.

4. A trailer for an energized terminal of the bayonet portion of a bayonet type circuit interrupter comprising, in combination, an elongated insulating member, and an electrical terminal connection including a plurality of loosely arranged metallic parts for interconnecting one end of said insulating member and said terminal in articulated relation, one of said metallic parts being a resilient member cooperating with the other metallic parts to maintain them in spring pressed contact and thereby static free.

5. A bayonet type circuit interrupter comprising, in combination, a tubular insulating housing having cylindrical terminal assemblies near the ends, a bayonet member having terminals near its ends for insertion in and removal from said housing with its terminals engaging said terminal assemblies, the terminal rst introduced into and last withdrawn from said housing having an externally threaded portion, an elongated insulating member having a cavity at one end, an elongated metallic coupling member internally threaded at one end for threading on said threaded portion with the other end loosely telescoped within said cavity, and retaining means disposed wholly within said cavity and operatively interconnecting said insulating member and said coupling member.

6. A trailer for an externally threaded terminal of the bayonet portion of a bayonet type circuit interruptor comprising, in combination, an elongated insulating member having a cavity at one end having an annular groove adjacent the outer end, an elongated metallic coupling member internally threaded at one end for threading on said threaded terminal with the other end loosely telescoped within said cavity, flange means extending radially outwardly from the inner end of said coupling member, a metallic snap ring in said groove, and an annular metallic retaining member surrounding said coupling 12 member and interposed between said ange means and said snap ring to prevent withdrawal of said coupling member from said cavity.

7. A trailer for an externally threaded terminal of the bayonet portion of a bayonet type circuit interrupter comprising, in combination, an elongated insulating mem- -ber having a cavity at one end having an annular groove adjacent the outer end, an elongated metallic coupling member internally threaded at one end for threading on said threaded terminal with the other end loosely telescoped within said cavity, ange means extending radially outwardly from the inner end of said coupling member, a metallic snap ring in said groove, an annular metallic retaining member surrounding said coupling member and interposed between said flange means and snap ring to prevent withdrawal of said coupling member from said cavity, and an annular spring member within said cavity and cooperating with said coupling member, retaining member and snap ring to maintain the same in contact engagement.

8. A trailer for an externally threaded terminal of the bayonet portion of a bayonet type circuit interrupter comprising, in combination, an elongated insulating member having a cavity at one end having an annular groove adjacent the outer end, an elongated metallic coupling member internally threaded at one end for threading on said threaded terminal with the other end loosely telescoped within said cavity, flange means extending radially outwardly from the inner end of said coupling member, a metallic snap ring in said groove, a radially split annular metallic retaining member surrounding said coupling member and interposed between Said flange means and said snap ring to prevent withdrawal of said coupling member from said cavity, and a radially split annular spring member `disposed between said ange means and said retaining member to maintain a continuous circuit through said metallic members to said snap r1ng.

9. A trailer for an externally threaded terminal of the bayonet portion of a bayonet type circuit interrupter comprising, in combination, an elongated insulating member having a cavity at one end having an annular groove adjacent the outer end, an elongated metallic coupling member internally threaded at one end for threading on said threaded terminal with the other end loosely telescoped within said cavity and having an annular groove near the inner end, a split metallic ring in said annular groove in said coupling member extending radially outwardly therefrom, a metallic snap ring in said annular groove in said cavity, and a metallic retaining member in the form of an annulus surrounding said coupling member and interposed between said split metallic ring and said snap ring to prevent withdrawal of said coupling member from said cavity.

l0. A trailer for an externally threaded terminal of the bayonet portion of a bayonet type circuit interrupter comprising, in combination, an elongated insulating member having a cavity at one end having an annular groove adjacent the outer end, an elongated metallic coupling member internally threaded at one end for threading on said threaded terminal with the other end loosely telescoped within said cavity and having an annular groove near the inner end, a split metallic ring in said annular groove in said coupling member extending radially outwardly therefrom, a metallic snap ring in said annular groove in said cavity, a metallic retaining member in the form of an annulus surrounding said coupling member and interposed between said split metallic ring and said snap ring to prevent withdrawal of said coupling member from said cavity, and a dished metallic spring member in the form of an annulus surrounding said coupling member and disposed between said split metallic ring and Said metallic retaining member and reacting against the former to urge the latter into contact engagement with said snap ring whereby a continuous circuit is maintained between said coupling member and said snap ring.

11. A bayonet type circuit interrupter comprising, in combination, a tubular insulating housing having cylindrical terminal assemblies near the ends, a bayonet member having terminals near its ends for insertion in and removal from said housing with its terminals engaging said terminal assemblies, detachable means for attachment to said terminal on said bayonet member first introduced into and last withdrawn from said housing, a stem of insulating material secured at one end to said detachable means, a trailer sleeve of insulating material telescoped over the other end of said stem, and cooperating means between said stem and sleeve for preventing separation thereof.

12. A bayonet type circuit interrupter comprising, in combination, a tubular insulating housing having cylindrical terminal assemblies near the ends, a bayonet member having terminals near its ends for insertion in and removal from said housing with its terminals engaging said terminal assemblies, detachable means for attachment to said terminal on said bayonet member first introduced into and last withdrawn from said housing, a stem of insulating material secured at one end to said detachable means, a trailer sleeve of insulating material telescoped over the other end of said stem, and cooperating means between said stem and sleeve for preventing separation thereof, said trailer sleeve having one or more lengthwise extending grooves in its outer surface to facilitate the escape of gas thereover.

13. A bayonet type circuit interrupter comprising, in combination, a tubular insulating housing having cylindrical terminal assemblies near the ends, a bayonet member having terminals near its ends for insertion in and removal from said housing with its terminals engaging said terminal assemblies, detachable means for attachment to said terminal on said bayonet member first introduced into and last withdrawn from said housing, a stem of insulating material secured at one end to said detachable means, and having an enlarged portion at the other end, and a trailer sleeve of insulating material telescoped over said other end of said stem and having a reduced diameter portion cooperating with said enlarged portion to prevent separation of said sleeve from said stem.

14. The invention as set forth in claim 13 wherein the stem as formed of nylon, the trailer sleeve is formed of methylmethacrylate resin and the outer surface of the latter has one or more lengthwise extending grooves to facilitate the escape of gas thereover.

15. A circuit interrupter comprising, in combination, a tubular insulating housing for mounting in a generally upright position, upper and lower cylindrical `line contacts in aligned spaced relation within said housing, an insulating sleeve between said line contacts, a bayonet member for insertion in said housing and said sleeve and having upper and lower terminals for engaging said upper and lower line contacts respectively, attaching means on said lower terminal, a fuse link within said bayonet member interconnecting said terminals and having a flexible lead connected to a fuse link terminal portion likely to be expelled on operation of the interrupter, detachable means on said attaching means, a stem of insulating material depending from said detachable means, the outside diameter of said stem and the diameter of said fuse link terminal portion together being less than the diameter of said line contacts whereby said stern and fuse link terminal portion can be withdrawn therethrough when alongside each other, and a trailer sleeve of insulating material telescoped over and flexibly connected to the lower end of said stem whereby there is limited relative movement between said trailer sleeve and said lower terminal of said bayonet member when the latter is withdrawn through said tubular insulating housing to interrupt the How of load current and the resulting arc drawn between said lower line contact and said lower terminal is confined between said insulating sleeve and said trailer sleeve.

16. The invention as set forth in claim 15 wherein the trailer sleeve has one or more lengthwise extending grooves in its outer surface to facilitate the escape of gas generated by the heat of the arc acting on the inner surface of the insulating sleeve between the line contacts and said outer surface of said trailer sleeve.

17. The invention as set forth in claim 15 wherein the insulating sleeve between the line contacts is formed of nylon and the trailer sleeve is formed of methylmethacrylate resin.

18. A bayonet type circuit interrupter comprising, in combination, a tubular insulating housing having cylindrical terminal assemblies near the ends, a tubular insulating member within said housing between said terminal assemblies, a bayonet member having terminals near its ends for insertion in and removal from said housing through said tubular insulating member with its terminals engaging said terminal assemblies, an elongated sleeve of insulation of such diameter as to permit passage through said tubular insulating member and said terminal assemblies and constituting an endwise extension of said bayonet member, and coupling means connected to the terminal of said bayonet member first introduced into and last withdrawn from said housing including means inseparably and iiexibly connecting said sleeve at one end to said terminal whereby there is limited relative movement between said sleeve and said terminal and the former moves conjointly with the latter when it is drawn through said tubular insulating member where the arc is conned between the inner surface of said tubular insulating member and the outer surface of said sleeve of insulation.

19, The invention as set forth in claim 18 wherein the bayonet member is a fuse tube and the terminals at its ends are interconnected by a fuse link.

20. The invention as set forth in claim 18 wherein the bayonet member is a switch blade and the terminals at its ends are interconnected thereby.

21. A circuit interrupter comprising, in combination, a tubular insulating member from the inner surface of which an arc extinguishing medium is evolved due to the heat of an arc, a circuit terminal at one end of said tubular insulatingimember, a terminal in circuit closed position in engagement with said circuit terminal and movable into said tubular insulating member out of engagement with said circuit terminal accompanied by the drawing of an arc therebetween within said tubular insulating member, and a trailer formed of a material capable of evolving an arc extinguishing medium due to the heat of the arc and movable with said terminal into said tubular insulating member, said trailer having a relatively close t with said tubular insulating member and having a plurality of lengthwise extending grooves for relieving pressure incident to the evolution of arc extinguishing medium and permitting random positioning of the arc during successive operations.

22. A circuit interrupter comprising, in combination, a tubular insulating housing having internal terminal members near its ends, a bayonet member insertable into and removable endwise from said housing and having spaced terminals for engaging said internal terminal members respectively, one of said terminals on said bayonet member constituting a trailing terminal when the same is withdrawn from said housing, means within said bayonet member interconnecting said terminals including a fuse link having a rod-like indicator projecting therefrom and from the end of said bayonet member that trails when the same is removed from said housing at which time when the interrupter is opened under load an arc is drawn between the trailing terminal and the associated terminal References Cited in the le of this patent UNTED STATES PATENTS 738,503 Waters Sept. 8, 1903 15 Gapp Sept. 13, Mueller July 29, Steinmayer Mar. 25, Ramsey Ian. 24, Triplett Apr. 13, Froland Jan. 13, YSchneider May 31, Schneider Feb. 14,