US2789169A

US2789169A - Electric switch mechanism

Info

Publication number: US2789169A
Application number: US521696A
Authority: US
Inventors: Harold A Duvall; Charles G Esler
Original assignee: Square D Co
Current assignee: Schneider Electric USA Inc
Priority date: 1955-07-13
Filing date: 1955-07-13
Publication date: 1957-04-16
Anticipated expiration: 1974-04-16

Description

April 1957 H. A. DUVALL ETAL 2,789,169

ELECTRIC SWITCH MECHANISM 4 Sheets-Sheet 2 Filed July 15, 1955 April ,1957 H. A. DUVALL ETAL 2,789,169

ELECTRIC swrrcn MECHANISM 4 Shee ts-Sheet 5 r m? M HE; T 7 1 5 z N Filed July 13, 1955 .IIIIII April 1957 H. A. DUVALL ETAL 2,789,169

ELECTRIC SWITCH MECHANISM 4 Sheets-Sheet 4 Filed July 15, 1955 7 7 S T a ma; W r ,E% to a m d 4 @w/ 1 0 6 ,0 9 -L m .O

United States Patent ELECTRIC SWITCH MECHANISM Harold A. Duvall, Pasadena, and Charles G. Esler,

Arcadia, Calif., assignors to Square D Company, Detroit, Mich a corporation of Michigan Application July 13, 1955, Serial No. 521,696

10 Claims. (Cl. 200-56) This invention relates generally to switched fuse cabinets and more particularly to the operating, closing and switching mechanisms of a fused electrical switch.

One object of the invention is a dead front hinged cover switching device for a fuse'panelboard.

Another object of the present invention is a novel overcenter operating mechanism for an enclosed fused switching device.

A further object of the present'invention is an operating mechanism mounted on a hinged cover for an enclosed switching device adapted to be incorporated into a fuse panelboard in which the movable contacts of the switching device remain in the body of the device and the operating'mechanism and external operator are movable with the hinged cover.

A further object of the present invention is a plug-in type distribution device including fuse holding means and switching means for opening and closing circuits" through the device and in which the fuse holding means and the switching means are contained within the device enclosure and the operating mechanism and the external operator therefor are movable with relation thereto with a hinged cover for the enclosure.

A further object of the present invention is a switching device adapted to be incorporated into a fuse panelboard having movable bridging contacts and external operating mechanism in which the bridging contacts are rectilinearly movable within the device and the external operating mechanism is rotatable to effect the contact movement and in which an overcenter mechanism is provided intermediate the operator and'the contacts for accomplishing the conversion of movements.

A further object of the present invention is the provision of an operating mechanism with a'reversible external operator for an enclosed switching device adapted to be incorporated into a fuse panelboard whereby the device may be oriented in either of two directions and the external operator alone may be reversed with respect to the device so as to maintain a uniformity of appearance of several devices regardlessof orientation when incorporated into a panelboard.

Other objects and features of the invention will be readily apparent to those skilled in the art from the following specification and appended drawings illustrating a certain preferred embodiment of the invention in which:

Figure 1 is a front elevational view of the switching device of the present invention shown in one of two alternative alignments.

Figure 2 is a sectional View taken along the lines 11-11 of Figure 1.

Figure 3 is a sectional View taken along the lines iii-III of Figure 1.

Figure 4 is a sectional view taken along the lines 1V-1V of Figure 3.

Figure 5 is an elevation and partial section'view of the operating mechanism of the present invention taken along the lines VV of Figure 3.

Figure 6 is a front elevational view of the switching device of the present invention with the device positioned in a second of two alternative positions and with the external 0 erating mechanism shown in its reversed position;

Referring'now to Figure l of the drawings illustrating the switching device of the present invention shown gen erally at it} and comprising a folded sheet metal enclosure 12' and cover 14 hinged at 16 to an end plate 18 secured to the side enclosure 12 at one end thereof. The end plate 18 is provided with an extending flange 20 and a similar flange 22 is provided at the opposite end of the device to provide'niounting areas for the positioning of the device in a distribution panelboard as shown in the copending application of Ralph H. Kingdon, S. N. 555,- 639, filed December 27, 1955, for Electrical Panelboard, and assigned to this same assignee. Generally centrally of the pivoted cover 14 is an external operator 24 rotatably supported on an escutcheon plate 26 and adapted to pass through the cover 14, as will be described hereinafter, to operate the operating mechanism of the switching, device of the present invention. The escutcheon plate 26 is secured to the cover 14 by suitable screws 25 and, as will be described hereinafter, is reversible on the cover 14 to allow the device and the handle to be aligned in either of the two alternative positions. A conventional spring biased hook lock 27 is secured to the inside side wall of the enclosure 12, in a manner not herein illustrated, and'passes through a slot 28 in the cover 14 to provide hooking and locking means for the cover in its closed position. The cover is also provided with a circular cutout hole 29 through which access may be had to a second cover locking mechanism, to be more fully described hereinafter, to permit opening movement of the cover while-the switching device is retained in its on position.

As illustrated in Figures 2, 3 and 4, the switching device of the present invention incorporates an assembly of a plurality of insulating blocks establishing spaced barriers and operating cutouts within which a suitable plurality of fuses and switching members may be'supported and operated to accomplish switching and distribution of electrical energy through the device. The insulating base portions of the device constitute a contact base assembly 30, a contact cover assembly 32, and a fuse base assembly 34. The contact base assembly 36 is supported by suitable screws 36 and 37 which pass also, respectively, through the fuse base assembly 32 and the contact base cover assembly 34 to secure the insulating devices to a bottom plate 38 fixed by suitable screws 39 passing through the plate 38 and cooperating with a threaded bent over portion of bracket 40 suitably secured to the side plates 12 of the device as by means such as welding.

Referring now to Figure 2 wherein the contact base assembly 30 is shown as provided with a plurality of parallel recesses 42, and 46, separated by insulating barriers 43 and 4S, and establishing parallel operating channels for a like plurality of bridging contacts 47, 48 and 49 which are respectively secured to insulating blocks 51, 52 and 53'shown in Figure 4 by suitable screws such as 54. To the opposite ends of the insulating blocks 51, 52 and 53, a pair of operating hooks 55 are secured as by' molding with the blocks 51, 52 and 53 so as to be permanently and securely fixed thereto. Each of the bridging contacts 47, 48 and 49 is provided with extending legs'56 and 57 which are individually adapted to cooperate with spring jaw clips 58' and 59 so as to electrically bridge the contacts and complete a circuit therethrough as will be more completely described hereinafter.

An operating bail 60' extends through the cutout slots maintained. The interior surface of the contact base 7 assembly 30 is cut out at the edges at 67 and the central insulating barriers 43 and 45 are terminated generally centrally of the length of the contact base assembly to establish a generally arcuate operating area for the bail 60 and the side levers 64.

To the exterior of the switching device and to the outer base portion of the contact base assembly 30, a suitable plurality of spring jaw connectors 71 are secured with their associated bus connectors 72 of varying lengths so that the connectors 71'are disposed for the accommodation of isolated phases of a multiphase source and to one end of these conductors 72 folded over terminal straps 74 are secured as by studs 76. The folded over terminal straps 74 extend inwardly into the contact base assembly with a leg 78 at the extreme end of which are secured as by suitable rivets and conventional biasing members the spring jawed contacts 59.

Supported on the inside surface of the contact base assembly 30 is the previously mentioned contact base cover assembly 32 having an insulating base portion 80 and separating barriers 82. Between the insulating barriers 82 are supported a suitable plurality of spring fuse clips 84 on folded terminal conductors 85 secured to the base 80 of the contact base cover assembly by suitable screws at 86. Also secured to the terminal conductor 85 byscrews 86 is an extending folded over terminal strap 87 passing through the base of the contact base cover assembly 32 and into the aligned recess in the contact base assembly 30 and at the extended end thereof there is secured thereto, as by suitable rivets and biasing springs the spring jaw clips 58, previously mentioned.

At the opposite end of the contact base assembly and to the interior surface thereof, the previously mentioned fuse base assembly 34 is secured as by the previously mentioned screw 36 and a similar screw 35 at the opposite end thereof. The fuse base assembly comprises an insulating base 90 and spacing insulation barriers 92 between which are supported a suitable plurality of spring fuse clips 94 on terminal straps 95 secured to the insulating base 90 by suitable screws 96. There may also be secured to the spring jaw fuse clips 94 and terminal strap 95 a suitable plurality of lugs 97 to which may be secured the conductors leading to the load devices to be controlled by the fused switching device of the present invention. It is to be understood that the end or the side walls of the enclosure will be provided with cutout or knockout openings through which the conductors to the load may pass.

To the inner surface of the hinged cover 14 of the switching device of the present invention the operating mechanism for the movable bridging contacts 47, 48 and '49, just described, is supported so that it may be pivotally moved with the cover to permit access to the interior mechanism of the device. The operating mechanism for the bridging contacts constitutes an external manual operator 24 and the internal overcenter snap-acting operating mechanism as shown in Figure 5 and generally designated 101. The external operator 24 is provided with a central shaft 102 extending through the escutcheon plate 26 and terminating inside of the hinged cover 14.

to the interior surface of the cover 14, the pan 107 being secured as by screws 111 to the channels 109. Slidably supported within the pan 107 and between the pan and the cover 14 is a slide member 112 having a central cutout portion at 113 and folded over cam riders 114 at the edges of the cutout 113. The cam roller on the cam member 103 moved by the operator 24 is positioned within the cutout 113 and is adapted to operate against the cam surface 114 to move the slide member 112 between the pan 107 and the cover 14 along the cutouts provided in the channel members 109. The slide member 112 is provided with an extension 115 having secured thereto by suitable means a bearing pin 116 about which a pair of

spring guides

117 and 118 are positioned and held in place by means such as a cotter pin 119. Surrounding the

spring guides

117 and 118 are a pair of springs 121 operating against shoulders of the spring guides near their pivoted ends and at the opposite ends against turned up shoulders 122 of a pair of pivoted toggle brackets 123 pivotally supported on the pan 107 by peened over rivets 124 so as to be rotatably supported for toggling action of the over-center spring mechanism. It should be readily apparent that as the cam roller 105 is arcuately moved by the external operator 24 in contacting the cam surfaces 114 to reciprocate the slide member 112 between its two limits, as defined by the cutout channels in the channel members 109 at limits at one end and at the other end a limit by rib 145, that the extending portion will move through the overcenter position for the springs 121 so that, having passed through the overcenter position, the springs 121 will exert their biasing force to maintain the slide member 112 in an oppositely limited position against limits 110 from that indicated in Figure 5.

An insulation barrier 124 is positioned between the operating mechanism 101 and the contact cover assembly 32 and the contact base cover assembly 34 and is supported by suitable rivets 125 on the inner surface of the pan 107.

The reciprocating movement of the slide member 112 is transmitted to the operating lever 64 for the bridging contacts 47, 48 and 49 through the engagement of the operating end of the lever 64 in cutout slots 131 of side extensions 132 of the slide member 112. As the slide member 112 is moved between its limits within the channel 109 and between the pan 107 and the cover 14, the operating lever 64 is reciprocated to transfer reciprv eating motion to the bridging contacts 47, 43 and 49 through its engagement with the hook shaped brackets 55. This reciprocating motion is effected with a snap-action due to the overcenter operation of the springs 121 to effect a both rapid and forceful movement of the bridging contacts into engagement with the spring contacts 58 and 59 so as to complete the circuit from the sources at spring clips 71 through the bridging contacts to the fuse clip 84 and thus through the fusing device, not herein shown, but normally positioned between the fuse clips 84 and 94 so as to provide at the lugs 97 the necessary energization for a connected load device.

A lever lock mechanism is provided on one side of the enclosure 12 adjacent to the operating end 130 of lever 64 for insuring that the bridging contacts 47, 48 and 49 will not accidentally be moved to a position to bridge the contacts 53 and 59 when the cover 14 is opened. For this purpose a locking lever 68 is pivotally supported on the side of the enclosure by a suitable rivet in the enc1o sure side as shown at 69. The locking lever 68 is spring biased by a resilient spring wire 70 operating at one end against the lip of the enclosure side and passes around the rivet 69 to operate, at its other end, against a notch in the lever so as to normally bias the locking lever 68 in a clockwise direction as viewed in Figure 3. The lever is further provided with a bent over shoulder at 73 aligned for cooperation with an extending arm 100 on ensures inside surface of the paniIO'iso that as thecover' is closed, the armwill engagelthe shoulder 73 torotate the locking lever 68 counter-clockwise about the rivet 69 and against the bias of'the spring 70.

The end of the locking lever'fi opposite to the shouldered end 73 is adapted to engage a'pressed out stop 75 on the operating lever 64. in its freeunre'stricted position. That is, when'the cover 14 is opened, the locking lever 68 will rotate into aligned position with the stop 75' being limited in its clockwise rotation under the bias of spring 7% by the engagement of the end of the locking lever near the shoulder 73 with the lip of the enclosure in this locking-position, the lever 64 maynot be rotated to slide the bridging contacts '47, 43 and d9 except by release of the locking lever With the cover 14 closed, the locking lever 63 will be removedfrom locking alignment and the levers 64 may be operated in their normal fashion.

The operating mechanism for the fused switching device is further provided with acover latching mechanism adjacent to the end of the operating mechanism which moves away from the sides of the enclosure 12 in opening movement of the cover 14. The latching mechanism constitutes a spring biased latch 135 pivotally supported on a rivet 136 on the pan 107 for rotatable movement.

The latch 135 is formed into a substantially U shape with i legs 137 and 138 disposed respectively adjacent to the cover 14 and the pan 167. Leg 133 ofthelatch 135, at its extremity, is formed into a latching surface 139, and is disposed for engagement with surface 1410f the end surface of the sides of the enclosure 12 so as to latch under the surface l il andprevent opening'movement of the cover 14. Opposite to the latching surface 139, on the leg 13%, a spring guiding shoulder 142 is formed with a pressed out guide 143 so as to act both asa guide and a shoulder for a biasing spring 144 acting at one end against the shoulder 1.42 and at the opposite end against a stationary rib 1 55 of the pan 107. A portion of the rib 1145 is bent over to form a guide 146 for that end for the biasing spring 144. Under unrestricted operation of the latch 135, the spring 144 will bias the latching surface 139 of the latch 135 into engaged position with the surface 141 of the enclosure for the switching device so that with the cover closed and with the latch .139 in 'engagement with the surface 141, the cover 14 may not normally be opened. To permit Opening of the cover 1 while the latching surface 139 is in engageable position with the latching surface 141, a latch release means is accessible through an opening 29 in the cover 14. Coaxial with the rivet 136, the leg 137 of the latch 135 is provided with a screwdriver type accommodating slot 147 which may be engaged by a screwdriver blade or similar instrument passing through the cover 14. With this accommodation, the cover 14 may be opened even though the latch 139 is in normal engagement position with the latch surface 141 by inserting a screwdriver or similar instrument through the hole 29 to engage the slot 147 and then rotating the latch 135 to remove the latching surface 139 from its engagement with the latching surface 141.

Figure illustrates the operating mechanism for the switching device of the present invention in its contacts open position, and illustrates the slide 112 in its limited position for this condition. The slide 112 is provided with an extending arm 151 which, in the position illustrated in Figure 5, extends through a folded over slot in the rib 145 at 152. The extending arm 151 is aligned to engage the bight portion of the latch 135 to rotate the latch in a counter-clockwise direction against the bias of spring 144. to remove the latch end 13? from its engaged position with the latching surface 141 of the end barrier of the side plates 22 of the enclosure, so that when the switch mechanism is in the open circuit or off condition, the cover 14 may be readily opened with release of the conventional latch 27 from engagement with the slot 28 as illustrated in Figure 1 of the drawings.

ltishouldbeeapparent that with the coverin the open sposition not herein illustrated, the external operator 24 'may be manipulatedto move the operating mechanism :to either its on or off positiom'however, when the cover is-returned-to-its enclosing position, the operating mechanism=mustbe returnedtoithe position of the in ternalIswitchingmechanisms as established by the position of the extending :arm 130 of the switch lever 64. If the operating mechanism is in a non-conforming position with extending'arm 130-of theoperating lever 64, the covermay not :be closed due to the restricting non-alignment of.theasidexextensions 132 of the slide 112 with the extending arm130of the operating lever 64.

Figure 6 illustrates the device of the present invention in a reversed mounting position with the escutcheon plate 26 in a reversedposition with respect tothe cover 14 of the device. The construction of the opening 113 in the slide member'112andfthe construction of the operating cam rolleris such that the reversal of the escutcheon plate '26 with coincident'reversal of operating lever 24 will return the operating cam roller 105 to its alignment rality of :theseswitchingdevices are employed, adjacent or alternate switching devices may be reversed within the panelboard topermit distribution of the load conductors to either sideof the panelboard thereby reducing both the congestedcondition of wiring gutters and permitting the employmentof narrower gutters by thedistribution of the load conductors. The-reversal of the unit within the panelboard with coincident reversal of the escutcheon plate and operating handle maintains the systematic alignmentofathe escutcheonplates with merely the reversal .of the operating handle from one side to the other of the cover. If alternate or adjacent units are reversed, the nameplate andload designations generally affixed to the escutcheon plate willbemaintained in their proper alignment and the adjacent operating handles will merely have reversed alignment for'their oil and on conditions.

The operation 'of'the switching device of the present invention is considered to be readily apparent from the description and operative analysis of the various coirponents of the device'hereinbefore presented. It should beunderstoodthat the device illustrated in the drawings is merely descriptive of one of many varieties dictated by both voltage and current ratings for the device illustrated'and while only onepreferred embodiment of the invention -has been illustrated herein, it should be under stood that'further variations will be readily apparent to those :skilled .inthe art and that the invention herein shouldi'not be 'limitedto'the specific disclosure shown but'should be given'its broadest possible interpretation withinithe'terms ofthe following claims:

"What is claimed is:

1. An. electric switch comprising an enclosure, a hinged cover for said enclosure, insulating means supported within said enclosure, line contacts supported within said insulating. means,load contacts supported within said insulating .means, bridging contacts adapted to bridge said 'line and load contacts, said bridgingcontacts being supportedwithin said enclosure for slidable movement within said insulating means, means withinsaid enclosure for slidably moving'saidbridging contacts, and means supported .on said coverifor operating said means for movingzsaid' bridging contacts.

2. .An electric switchcomprising an enclosure, a hinged cover for .said enclosure, insulating means supported r 7 said insulating means, bridging contacts adapted to bridge said line and load contacts, said bridging contacts being supported within said enclosure for slidable movement within said insulating means, lever means pivotally supported on said enclosure for slidably moving said bridging contacts, and snap acting operating means supported on said cover and engageable with said lever means for eifecting movement of said lever means to move said bridging contacts.

3. An electric switch comprising an enclosure, a hinged cover. for said enclosure, insulating means supported within said enclosure, line contacts supported within said insulating means, load contacts supported within said insulating means, bridging contacts adapted to bridge said line and load contacts, said bridging contacts being supported Within said enclosure for slidable movement within said insulating means, lever means pivotally supported on the said enclosure for slidably moving said bridging contacts, means supported on said cover for effecting movement of said lever means including a member slidably movable contiguous to said cover, overcenter spring means biasing said member to either of two alternative positions and causing movement from one to the other of said positions to be with a rapid snap action, and means on said member engageable with said lever means for effecting movement of said lever means with a snap action to move said bridging contacts.

4. An electric switch comprising an enclosure, a hinged cover for said enclosure, insulating means supported within said enclosure, line contacts supported within said insulating means, load contacts supported within said insulating means, bridging contacts adapted to bridge said line and load contacts, said bridging contacts being supported within said enclosure for slidable movement within said insulating means, lever means pivotally supported on said enclosure for slidably moving said bridging contacts, operating means supported on said cover for said lever means including channel members fixed to said cover, a pan member fixed to said channel members, said pan member being spaced from said cover to provide an operating area therebetween, a slide member supported by said pan member and slidable between said pan and said cover in said operating area, overcenter spring means biasing said slide member to either of two alternative positions and causing movement from one to the other of said positions to be with a rapid snap action, means on said slide member engageable with said lever means for effecting movement of said lever means with a snap action to move said bridging contacts, and an external manual operator for maniplating said slide member.

5. An electric switch comprising an enclosure, a hinged cover for said enclosure, insulating means supported within said enclosure, line contacts supported within said insulating means, load contacts supported within said insulating means, bridging contacts adapted to bridge said line and load contacts, said bridging contacts being supported within said enclosure for slidable movement within said insulating means, lever means pivotally sup ported on said enclosure for slidably moving said bridging contacts, operating means supported on said cover for said lever means including channel members fixed to said cover, a pan member fixed to said channel members, said pan member being spaced from said cover to provide an operating area therebetween, a slide member supported by said pan member and slidable between said pan and said cover in said operating area, overcenter spring means biasing said slide member to either of two alternative positions and causing movement from one to the other of said positions to be with a rapid snap action, portions of said slide member being cut out generally centrally therof, folded edges of said central cut-out defining cam riders on said slide, an external operator, a cam roller fixed to said operator adjacent to the innersurface of said cover,.said roller .extending into said central cut-out and being engageable with said cam riders to effect movement of said slide member with manipulation of said external operator, and means on said slide member engageable with said lever means for effecting movement of said lever means with a snap action to move said bridging contacts.

6. An electric switch comprising an enclosure, a hinged cover for said enclosure, insulating means supported within said enclosure, line contacts supported within said insulating means, load contacts supported within said insulating means, bridging contacts adapted to bridge said line and load contacts, said bridging contacts being supported within said enclosure for slidable movement within said insulating means, lever means pivotally supported on said enclosure for slidably moving said bridging contacts, operating means supported on said cover for said lever means including channel members fixed to said cover, a pan member fixed to said channel members, said pan member being spaced from said cover to provide an operating area therebetween, a slide member supported by said pan member and slidable between said pan and said cover in said operating area, an overcenter spring means biasing said slide member to either of two alternative positions and causing movement from one to the other of said positions to be with a rapid snap action, means on said slide member engageable with said lever means for effecting movement of said lever means with a snap action to move said bridging contacts, means for latching said cover to said enclosure and means operated by said slide member for releasing said latch means, and an external manual operator for manipulating said slide member.

7. An electric switch comprising an enclosure, a hinged cover for said enclosure, insulating means supported within said enclosure, line contacts supported within said in sulating means, load contacts supported within said insulating means, bridging contacts adapted to bridge said line and load contacts, said bridging contacts being supported within said enclosure for slidable movement within said insulating means, lever means pivotally supported on said enclosure for slidably moving said bridgin contacts, operating means supported on said cover, a pan member fixed to said channel members, said pan member being spaced from said cover to provide an operating area therebetween, a slide member supported by said pan member and slidable between said pan and said cover in said operating area, overcenter spring means biasing said slide member to either of two alternative positions and causing movement from one to the other of said positions to be with a rapid snap action, means on said slide member engageable with said lever means for effecting movement of said lever means with a snap action to move said bridging contacts, means for latching said lever means in contacts open position when said cover is open and means operated by said pan member for releasing said latch when said cover is closed, and an external manual operator for manipulating said slide member.

8. An electric switch comprising an enclosure, a hinged cover for sald enclosure, insulating members supported within said enclosure, line and load contacts supported within said insulating members and bridging contacts supported within said insulating means and adapted to bridge said line and load contacts, an operating mechanism for manipulating said bridging contacts into engaged and disengaged position with said contacts, an external operator for said operating mechanism, said switch being adapted to be supported in either of two alternative orientations, and said external operator being reversible with respect to said switch to maintain a uniformity of alignment thereof regardless of the orientation of said switch.

9. An electric switch comprising an enclosure, a hinged cover for said enclosure, insulating members supported within said enclosure, line and load contacts supported within said insulating members and bridging contacts supported within said insulating means and adapted to bridge said line and load contacts, an operating mechanism for manipulating said bridging contacts into engaged and disengaged position with said contacts, an external opertor for said operating mechanism, an escutcheon plate on the exterior surface of said cover for supporting said operator, said switch being adapted to be supported in either of two alternative orientations, and said escutcheon plate being reversible with respect to said switch on reversed orientation of said switch to maintain a uniformity of alignment of said escutcheon plate and external operator regardless of orientation of said switch.

10. An electric switch comprising an enclosure, a hinged cover for said enclosure, insulating means supported within said enclosure, line contacts supported within said insulating means, load contacts supported within said insulating means, bridging contacts adapted to bridge said line and load contacts, said bridging contacts being supported within said enclosure for slidable movement within said insulating means, lever means pivotally supported on said enclosure for slidably moving said bridging contacts,

10 means supported on said cover for effecting movement of said lever means including a member slidably movable contiguous to said cover, portions of said member being cut out generally centrally thereof and defining a rectangular cam area, an external operator, a cam roller fixed to said operator adjacent to the inner surface of said cover, said roller extending into said rectangular cam area and being engageable therewith to effect movement of said slide member with manipulation of said external operator.

References Cited in the tile of this patent UNITED STATES PATENTS 1,561,248 Krantz Nov. 10, 1925 2,315,420 Harrington Mar. 30, 1943 2,536,522 Wilson Jan. 2, 1951 2,674,666 Stieglitz Apr. 6, 1954 2,695,934 Wills Nov. 30, 1954 FOREIGN PATENTS 105,187 Australia Sept. 15, 1938