US2493316A - Electrical cutout - Google Patents

Description

5 Sheets-Skaai 2 Jan. 3, 1950 w. c. scHuL-rz nncrnrcn. cu'rou'r Filed lamb 6, 1946 Jan'. a, 195o w. Q. Smm 2,493,316

ELECTRICAL CUTOUT Filed Ilarch 6, 1946 5 Sheets-Sheet 4 A g4 Mhz a ou@ IN V EN TOR. W/ZI/M 0. Jil/MIZ Jan. 3,1950 w. o. cHuL-rt 2,493,3l6

ELECTRICAL cuToUT Filed Hatch 6, 1946 5 Sheets-Shea?, 5

'ai VA 1 .I

Patented Jan. 3, 1950 UNITED sTATEs PATENT OFFICE ELECTRICAL CUTOUT William 0. Schultz, South Milwaukee, Wis., as-

signor to Line Material Company, Milwaukee, Wis., a corporation of Delaware Application March .6, 1946, Serial No. 652,323

6 Claims. (Cl. 20G-114) This invention relates to electrical cut-outs and is particularly directed to oil fuse cut-outs.

Objects of this invention are to provide a housed type of oil fuse cut-out which is so constructed that it will automatically open the circuit on overload and which may be opened manually under load and which is arranged to insure the immediate extinction of any arc that may be formed, either due to automatic or manual opening of the circuit.

Further objects are to provide an oil fuse cutout which is equipped with a housing in which are located concentric cylinders formed of insulating material with stationary contacts carried on the inner side of the inner cylinder, with the cylinders open at their upper and lower ends and with the incoming leads positioned between the cylinders, thus aiording a high degree of protection.

Further objects are to provide an oil fuse cutout in which a housing is provided with an open upper end through which a combined switch element and fuse carrier is adapted to be inserted in only one position corresponding to.

j member pivoted on the housing and provided with means for locking the cover to the housing, the yoke being so arranged that it coacts with manually operable means to prevent operation of the switch when the yoke is rocked downwardly to allow removal of the cover, the co-` action of the combined switch element and fuse carrier and the housing being such as to prevent removal of the combined switch element and fuse carrier unless the parts are in open switch position.

Further objects are to provide a novel form of throw-out mechanism 'in which a floating lever assembly is employed and is spring urged in a manner to tension a fuse link when in circuit closed position and to throw out any remaining portions of the fuse link on rupture thereof and which coacts with the stationary contacts in a manner to provide a heavy yielding contact pressure between the floating lever assembly and the stationary contacts.

Further objects are to provide a fuse link throw-out construction for an oil switch which is so made that no tension is imposed on the fuse link when the switch is in switch open position, but is arranged to tension the fuse link when the switch is in closed position.

'A further specific object of this invention is to provide a novel manner of mounting the stationary contacts so that they are rmly and Securely mounted on the innermost part of two concentric insulating cylinders with the lead re- 2 ceiving portion of the contacts located between the cylinders.

Further objects are to provide an oil fuse cutout construction in which a very short fuse link is employed, in which there is no chance of any portion of the fuse link dropping downwardly after rupture of the fuse link, in which a short relatively heavy liber or other insulating tubular member is provided for the fuse link and is carried in an insulating rotary combined switch element and fuse carrier, in which the tubular member which receives the fuse is open at both ends and is relatively short and insures extinction of the arc by the expulsion of the oil and gases from both ends of the tube while at the same time preventing the building up of excessive pressure within the tube.

Further objects are to provide a construction in which extreme rigidity and strength is obtained for the several parts of the device, in which the concentric insulating cylinders are securely held in a positive and rigid manner to the housing, in which adequate means are provided i'or protecting the tie bolts or other members that hold the concentric tubular cylinders in place, and in which there is no chance of the arc striking from any of the contacts to any of the metal portions of the housing or other parts of the apparatus.

Embodlments of the invention are shown in the accompanying drawings, in which:

Figure 1 is a vertical sectional view on the line l-l of Figure 3, however, showing the yoke in its normal or vertical position.

Figure 2 is a sectional view on the line 2 2 of Figure 3 and similarly to Figure 1 showing the yoke in its normal vertical position.

Figure 3 is a sectional view on the line 3-3 of Figure 1, however, showing the yoke rocked downwardly to its horizontal position.

Figure 4 is a sectional view on the line 4 3 of Figure 1.

Figure 5 is a sectional view on the line 5 5 of Figure 1.

Figure '6 is an enlarged fragmentary sectional view of the lower portion of the combined switch element and fuse carrier showing the parts in the position they occupy when in switch open position and when the fuse link is not ruptured.

Figure 7 is a view corresponding to Figure 6, however, showing the parts in the positionthey occupy in switch closed position.

Figure 8 is a view corresponding to Figure rl showing theposition of the parts after rupture of the fuse link.

Figure 9 is a view corresponding to Figure '1 showing a further form of combined switch element and fuse carrier showing the parts in the position they occupy when the switch is in closed ,stationary contacts I8 as position and when the fuse link is not ruptured.

Figure 10 is a face view of the movable contact assembly.

Figure 11 is a view corresponding to Figure 9 showing the parts in the position they occupy when the switch is in switch open position.

Figure 12 is a view corresponding to Figure 9 showing the switch in closed position and showing the position that the parts occupy when the fuse has been ruptured.

Referring to the drawings. it will be seen that the electrical cut-out comprises a casing having a lower portion I, a bottom portion 2 and an upper portion 3. The upper portion is provided with a circular opening l and with a laterally and downwardly the leads or conductors 6 extend, such conductors projecting through suitable insulating bushings 1. It is preferable to at least partially lill the portion l with an insulating sealing compound indicated at I. The housing is adapted to be filled with oil or other suitable insulating liquid to approximately the level indicated by the dotted line 9 in Figure 2, a suitable plug I Il being provided. The casing is equipped with any suitable means such as the feet I I, whereby it may be attached to a suitable support, not shown.

A pair of concentric insulating cylinders are positioned within` the housing. The innermost cylinder is indicated by the reference character I2 and the outermost cylinder by the reference character I 3. These cylinders are spaced apart and are open at their upper and lower ends. The upper ends of the cylinders bear against three or more inwardly projecting lugs Il and are held against such lugs by means of tie bolts I5. The tie bolts or elongated screws I5 are provided at their lower ends with downwardly extending insulating sheath-like members I6 which have reduced portions I1 located in the space between the concentric cylinders I2 and I3 as shown most clearlyin Figure 1. Thus the tie bolts are housed for the major part of their length jointly by the concentric cylinders and bythe sheath or insulating thimbles I6.

A pair of diametrically opposed stationary contacts Il are positioned on the inner side of the innermost cylinder, as shown most clearly in Figures 2 and 5. These stationary contacts I8 are secured in place by means of screws I9 which extend from the outer side of the innermost insulating cylinder I2 into the stationary contacts I8. The stationary contacts I8, it will be noted, are extended in one direction and may be abruptly cut oil' in the other direction, as shown in Figure 5, so as to permit the free riding of the movable contacts over the extended portion of the will appear hereinafter. 'I'he extended portions or reduced portions of the stationary contacts I8 are indicated by the reference character 2l,v in Figure 5.

A further point to be'noted in connection with the stationary contacts is that they are provided with outwardly and upwardly projecting extended portions arranged to receive the leads or conductors i. These lead receiving portions of the stationary contacts Il are indicated by the reference characters 2|, in Figures 2 and 5.

It will be seen from the description thus far siven that the stationary contacts are mounted on the inner side of the innermost insulating cylinders and have integral projecting portions extending upwardly into the space between the concentric cylinders I2 and I 3, see Figure 2, which portions receive the leads l. From the extending portion 5 through which y'tangular lips I2 4 above description it will be seen that the leads 6 are housed for the portion thereof adjacent the stationary contacts in the space between the concentric cylinders and consequently there is no chance of any arc reaching the leads. Further it is to be understood from reference to Figure 2,

lower poring.

The component parts I, ing are held together by The tie rods 24 2, and 3 of the casmeans of tie rods 2l. are all located externally of the lower portion I of the casing and are threaded into the upper portion I thereof, as shown most clearly in Figure 4. It is preferable to provide a gasket 25 between the portion I and the portion 3 of the casing and to weld the bottom 2 to the lower portion I of the casing.

The upper portion l of the casing, as has been previously described, is provided with a circular opening 4. This opening has relatively large rectangular notches 26 formed at diametricaily opposite points, as shown in stop pins 29 and Il, as shown in Figure 4, to deilne the amount of rotation allowed the combined fuse carrier and movable switch element which which constitutes the rotor portion of the device.

The movable contacts are carried by a rotor indicated generally at 3|. 'I'his rotor is formed of insulating material and is adapted to be normally centrally located with reference to the concentric cylnders I2 and I3. It has an upper metal portion 32 and is provided with a relatively large rib 33 and a relatively smaller rib 34, see Figures 1 and 2, which are adapted to respectively pass through the notches 2l and 21, see Figure 4. The rotor is also provided with an upwardly projecting shaft 35 which passes through a packing gland composed of the packing 26 and the compression nut 31 carried by a head or cover 38 which is adapted to close the upper opening 4 in the casing, see Figures 1 and 2. Preferably, a gasket 39 is carried by the head 38 so as to seal against the upper edge of the casing when the head is forced downwardly by means hereinafter described. The upper end of the shaft is journaled in an overhanging portion 40 of the head 38 and is provided with a handle receiving socket member or hub II rigid with the shaft 35.

It is to be noted from Figures l, 2, and 4 that the upper portion 32 of the rotor is provided with diametrically opposed outwardly projecting substantially rectangular lips 42 which are adapted to pass through the rectangular openings 26, see Figure 4, when the rotor is inserted into the casing. When the rotor is in place, these recride beneath shouldered portions or overhanging portions 43 of the casing and thus prevent withdrawal of the rotor in all positions except when the lugs or ears I2 are in alignment with the notches 2G. When the ears 42 are in alignment with the notch 2t the rotor is in switch open position and when the rotor has been rocked through degrees to the position shown in Figures 1, 2, and 4, the rotor is in switch closed position.

Further it is to be noted from Figure 1 that the upper portion 32 of the rotor is provided with a pair of upstanding ears Il which aid in centeringtherotorwhileitisbeingmoved toitsnal position during insertion and prior to the time thatthe head 33' of they rotor.v assembly is clamped tightly against the casing 3 in a manner hereinafter to appear. The movable contacts of the rotor assembly are shown most clearly in Figures 6, '7, and 8 and comprise a pair of'oating levers 45 on opposite sides of the rotor. These iloating levers are provided with contact portions 45 adapted to engage the stationary contacts I8 when the rotor is rocked to switch closed position, as shown in Figure 7 for instance. The floating levers 45 carry at` their lower ends fuse link receiving means consisting of the threaded studs 41 rigid with the levers 45 and provided with thumb nuts 48 for clamping the ends of the fuse link, indicated generally by the reference character 49, in place. The iioating levers are carried by means of a pair of outwardly spring pressed supporting levers 50 pivotally supported from the rotor in brackets l, secured to the rotor by means of screws 52, the screws 52 being 1ocated in recesses 53 formed in the rotor. The supporting levers 5|) are pivoted to the floating levers at the free ends of the levers 5|) by means of pivot pins 54. They are provided with upper ends 55 which are adapted to engage stops 53 formed integrally with the brackets 5I when the contacts 45 of the floating levers 45 are not in engagement with the stationary contacts-IB, see Figure 6. Springs 51 are loosely coiled about the pivot pins 53 of the supportingv levers 50 and urge the lower ends of the supporting levers towards outward rocking motion, thus tending to carry the pivot pins 54 of the floating levers 45 outwardly. The floating levers are provided with bearing portions 59 adjacent their lower ends arranged to contact with portions of the rotor 3| to limit the inward position of the lower ends of the levers 45.

The fuse link'indioated generally at 49 is, as

stated, very short in its total length.l It is pro-I vided at one end with a rigid metal member 50 which is hook-shaped, as may be seen from Figure 1. At its other end it is provided with a flexible leader 6|. 'Ihe leader 5I and the rigid member 60 are adapted to be clamped in place on the levers 45 by means of the thumb nuts 48. The

intermediate portion of the fuse link has a very short fusible section 62 and a strain wire 63. The fusible section of the fuse link is housed within a fiber tube 64 carried by the rotor 3| and extending transversely of the rotor. 'I'he rotor 3| is preferably of oil impregnated wood, whereas f the fuse tube 54 is preferably formed of fiber to aid in the extinction of the arc upon rupture of the fuselink in a well known manner. However, it is obviousthatthe materials oi which the fuse tube 64 and the rotor 3l are composed may be varied if desired.

It is to be noted that the fuse tube 64 is an expulsion fuse tube and is open at both ends so as to allow expulsion of oil and gas from both ends of the tube on rupture of the fuse link on overload. It is apparent, therefore, that this device can withstand extremely heavy overloads without generating excessive pressure within the short expulsion fuse tube 64.

When the switch is in open position, the movable contacts occupy the position'shown in Figure 6. When the lswitchis in closed'position, the

movable contacts occupy the position shown in Figure v'7. It will be seen that vthe contact portions 48 of the floating levers 45'are pressed against the stationary contacts I8 and thus secre a high contact pressure at the same time the fuse link is tensioned. In the event an overload occurs, the fuse link is ruptured and the noating levers rock to the position shown inv Fig- 5 ure 8, extracting any remaining portion ofthe fuse link and assisting in clearing thecircuit. In addition to this, there is an expulsion action. The oil and generated gases are expelled from the expulsion tube 64 and further assist' in extinguishing the resulting arc.

'It is to be noted particularly that when the switch is in open position the parts occupy the positions shown in Figure 6 and there is no tension on the fuse link. However, when the switch is rocked to closed position, the parts occupy the positions shown'in Figure 7 andthe fuse link is placed under tension.

The switch may also be manually opened under load as the break occurs beneath the oil level and the arc is quickly extinguished. This manual opening of the switch is secured by rotating the rotor 3l about its axis.

Attention is now directed to Figures 1, 2, and 3. It will be seen that the portion 3 of the casing is provided with a pair of upstanding ears or lugs 65 which carry pivot pins or screws 66. These pivot members 66 have reduced portions 51 on which the arms of a bail or yoke member 58 are pivotally mounted. This yoke is provided with a downwardly extending flange 69 which is arranged to contact with the upper portion 40 of the head 38, see Figure 1, when an attempt is made to rock the yoke or bail member 68 in a clockwise direction as viewed in Figure l. However, the bail may be rocked in a counter-clockwise direction, as viewed in Figure 1. When the bail'or yoke is in vertical position a pressure screw is arranged to be screwed down to force the head or cover portion 38 into tight, sealing relation with the portion 3 ofthe casing. When the parts are in this position with the bail vertical, it is clear that the operating handle 1| may be inserted into the handle receiving hub portion 4| and the switch may be moved manually to either open or closed position by rotating the rotor 3l. However, when the bail or yoke 68 is rocked downwardly into the dotted line position shown in Figure 1 and the full line position shown in Figure 3, it is clear that the two upstanding ears or portions 12 formed integrally with the yoke 6B prevent the insertion of the handle 'Il vinto the handle receiving socket 4| in either switch open or switch closedA position and consequently it is impossible to operate the switch when the bail -is in its horizontal position, as shown in full lines in Figure 3 or in dotted lines in Figure 1.

Further it is to be noted from reference to Figures l, 2, and 4 that the combined rotor and fusecarrier cannot be removed from the casing, although the bail 68 may be rocked downwardly to its horizontal position, as long as the switch is in closed position as the lugs 42 arelocked beneath the shouldered portions 43 of the casing 55 and 'consequently preclude the removal of the rotor. When it is desired to remove the rotor it is necessary to first rock the switch to switch open position so that the lugs 42 are in alignment with the rectangular notches 26. vThere- 70 after the handle is removed, the pressure screw 10 is loosened and the bail 68 is rocked to its horizontal position. The rotor may be lifted directly upwardly from the casing. It may be refused and reinserted into the casing. However, 'I5 the switch cannot be rotated to switch closed p0- 7 sition as one of the ears 12 is in front of the handle receiving portion 4|, see Figure 3. It is necessary to rock the bail to its vertical position before the handle can be inserted in the handle receiving portion 4|. Consequently, there is no danger of the operator closing the switch until.

the lbail has been rocked to its vertical position. The natural procedure, therefore, consists of the rocking of the bail to its vertical position at which time the pressure screw 10 is again tightened to rmly hold the head 38 in sealing rela-i tion to the casing. Thereafter, the handle 'Il is inserted in the handle receiving portion 4| and the switch is rocked to switch closed position.

It is obvious that, if desired, the casing may be completely sealed from communication with the outside air as has been shown in thedrawings. The casing is provided with a pair of removable screw plugs 18. see Figure 3. One or both of these screw plugs may be removed and a cushioning chamber or cushioning chambers may be screwed into the resulting opening. In place of this a suitable vent pipe or vent pipes may replace one or both of the screw plugs 13, respectively. Inasmuch as both of these features, namely, the vent pipe and the cushioning chamber are old in the art, such construction has not been shown.

Referring to Figures 9 through 12 it will be seen that this form of the invention is very similar in principle to that previously described and operates in very much the same way as that previously described. The movable contacts are indicated by the reference character 14 and are carried by theheavy spring members 15. Preferably the spring members are slotted as indicated at 'I8 in Figure 10. The iloatingthrowout levers of the movable contact assemblies are indicated by the reference character 11 and are pivoted as indicated at 18 on the ears 19 carried by springs 8U. The springs 80 and 15 are held in place by means of the screws 52. The floating pivoted levers 11 are provided with screws 8| and with'thumb nuts 82 which serve to-clamp o pposite ends of the fuse link. It is to be noted that a flexible conducting braid 83 is held beneath the heads 14 of the movable contacts and beneath the heads of the screws 8| so as to afford excellent electrical connection between the movable contacts 14 and the throw-out levers 11. This braid may be formed of a strip looped about the head of the screw 8| and having its ends clamped beneath the heads 14 of the movable contacts. The intermediate portion of the braid 88 is overlapped and 11, see Figure 10. The floating throw-out levers 11 are provided with rounded upper ends 85 which bear against the inner side of the main contact springs 15.

The fuse link may be'constructed as previously described and extends through Vthe tube 64. When the fuse link ruptures on overload any remaining portion thereof is pulled out or thrown out as previously described. Also the expulsion action and the extinguishing action due to the oil takes place as previously described.

It is to be noted from Figure 11 that when the switch is in open position that there is no stress onvthe fuse link. 'I'he springs 15 and 80 move outwardly to the position shown in Figure 1l. However, when vthe switch is moved to closed position as shown in Figure 9 the contacts 14 are forced inwardly and move the upper ends passes through an opening 84 in the corresponding throw-out lever when the switch is rocked to 88 of the iloating throw-out levers 1l inwardly. This moves the pivot points 18 of the throw-out levers 11 inwardly and moves the springs 84 inwardly and thus tensions the fuse link. Upon rupture of the fuse link the parts assume the position shown in Figure 12 and it will be seen that rrn contact between the movable contacts and the stationary contacts is maintained although the springs have moved outwardly and have consequently caused the throw-out levers 11 to pull out or throw out any remaining portion of the fuse link.

It will be seen that a novel type of electrical cut-out construction of the \oil fuse type has been provided by this invention which may be manually opened under load or which may be automatically opened under load with the assurance that any resulting arc will be quickly extinguished.

Further it is obvious that the device is wholly safe in use as it is impossible for the operator to either open or close the switch when the bail or yoke is in horizontal position. Access to the handle receiving portion can be had only when the bail is in its vertical position. In addition to this, the combined rotor andfuse carrier can be inserted in only one position and when moved to switch closed position it cannot be lifted from the casing although the bail may be in horizontal position. Thus a full degree of safety is provided for the operator. It is also clear` that the novel arrangement of concentric insulating cylinders, the innermost of which carries the stationaryl contacts, provides for the free circulation of oil upon rupture of the fuse link or manual opening of the circuit, as these cylinders are open at their top and bottom.- In addition to this, the peculiar relation between the arrangement of the leads and the concentric insulating cylinders protects the leads. It is to be noted that the total length of the fuse link between the lower ends of the floating levers or thro -out levers is less than the distance from either of these levers tothe bottom of the casing. Thus it is clear that there is no chance of any dangling portion of the fuse link shorting to the bottom of the casing when the fuse link is ruptured on overload.

It will be seen further that the device is easy to operate as no pressure is imparted to the vertical shaft of the rotor by the pressure screw of the yoke or bail portion.

It is to be noted particularly that in both forms of the invention when the switch is in open position, the fuse link is not tensioned. However, closed position the fuse link is placed out action on the ture on overload.

Although this inventionhas been described in considerable detail. it is to be understood that fuse link in the event of rupysuch description is intended as illustrative rather under tension and the parts are in position to execute the throw-out or pullincluding outwardly spring urged contacts arranged to engage and disengage said stationary contacts when said rotor is turned to a rst or a second position, and a fuse link elec*rica1ly connecting said movable contact assemblies, said movable contact assemblies having means arranged to tension said fuse link when said rotor is turned to said first position and to relieve said tension when said rotor is turned to said second position.

2. An oil switch construction comprising a casing adapted to contain oil, a pair of stationary contacts located within said casing below the level of the oil, a rotor revolubly supported within said casing and having a pair of movable contacts arranged to engage and disengage said stationary contacts when said rotor is rotated to a iirst or a second position, respectively, an expulsion fuse tube of insulating material carried by and extending transversely of said rotor and open at both ends and located below the level of the oil, a fuse link located within said fuse tube and electrically connecting said movable contacts, and spring urged throw-out means on opposite sides of said rotor for tensioning said fuse link and arranged to throw out any remaining portion of said fuse link on rupture due to overload.

3. A switch construction comprising a casing, a pair of stationary contacts located within said casing, a rotor revolubly supported within said casing, an expulsion fuse tube oi' insulating material extending transversely of said rotor and open at both ends, combined movable contact and throw-out means located on opposite sides of said rotor and each including a supporting lever pivoted .on said rotor and having a free end, spring means urging said free end outwardly, a floating lever pivoted intermediate its ends to the free end o! said supporting lever and having one end constituting a contact end and arranged to engage the corresponding stationary contact when said rotor is rotated to switch closed position and having the other end provided with means for receiving a fuse link and constituting a fuse link receiving end, and a fuse link extending through said fuse tube and having its ends attached to the said fuse link receiving ends of the floating levers, each of said throw-out levers being arranged to tension said fuse link when said switch is in closed position and'being arranged to relieve the tension on said fuse link when said switch is in open position.

4. A switch construction comprising a casing, a pair o! stationary contacts located within said casing, a rotor revolubly supported within said casing, an expulsion fuse tube of insulating material extending transversely of said rotor and open at both ends, combined movable contact and throw-out means located on opposite sides of said rotor' vand each including a supporting lever pivoted on said rotor and having a' free end, spring means urging said tree end outwardly, a iloatlng lever pivoted intermediate its ends to the free end of said supporting lever and having one end constituting a contact end and arranged to engage the corresponding stationary contact when said rotor is rotated to switch closed position and having the other end provided with means lor receiving a luso link and constituting aniselinkrecelvlngendnndatuselinkextendinsthrwghsaidiusetubeandhavingitsends attached to the said fuse link receiving ends of the floating levers, said fuse tube being short and said fuse link having a short fusible section located wholly within said fuse tube.

5. A switch construction comprising a casing, a pair of stationary contacts located within said casing, a rotor revolubly supported within said casing, an expulsion fuse tube of insulating material extending transversely of said rotor and open at both ends, combined movable contact and throw-out means located on opposite sides of said rotor and each including a supporting lever pivoted on said rotor and having a free end, spring means urging said free end outwardly, a floating lever pivoted intermediate its ends to the free end of said supporting lever and having one end constituting a contact end and arranged to engage the corresponding stationary contact when said rotor is rotated to switch closed position and having the other end provided with means for receiving a fuse link and constituting a fuse link receiving end, and a fuse link extend-v ing through said fuse tube and having its ends attached to the said fuse link receiving ends of the floating levers, said fuse tube being relatively short as compared with its diameter and said fuse link having a short fusible section and a rigid end portion at one end and a ilexible leader at the other end arranged for attachment to the fuse link receiving ends of the respective floating levers.

6. An oil switch comprising a casing adapted to contain oil, insulating means carried by said casing and having a portion projecting into the oil, stationary contacts carried by said insulating means, an linsulating rotor revolubly supported within said casing and located between said stationary contacts, a fuse tube extending transversely through said rotor, a fuse link extending through said fuse tube, movable contacts carried by said-rotor for engaging and disengaging said stationary contacts when `said rotor is turned to switch open and switch closed positions, spring means for urging said movable contacts outwardly, iloating throw-out levers pivoted intermediate their ends, said fuse link being attached to one end of each of said iloating levers, the other end of each of said levers bearing against said stationary contacts, and

= separate and distinct spring means urging the intermediate portions of said floating levers outwardly, whereby said fuse link is-tensioned only when said switch is in closed position.

WILLIAM O. SCHULTZ.

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

UNITED STATES PATENTS Number Name Date Y 891,306 Van Valkenburg June 23, 1906 1,203,316 Downes Oct. 31, 1916 1,248,090 Downes Nov. 27, 191'? 1,740,699 Murray Dec. 24, 1929 1,950,199 Tritle Mar. 6, 1934 1,953,812 Lincks et al. Apr. 3, 1934l 1,972,958 Steinmayer et al. Sept 11, 1934 1,980,506 Steinmayer et al. Nov. 13, 1934 2,161,427 Papp June 6, 1939 2,250,210 Smith, Jr. July 22, 1941

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