US2041877A - Disconnecting switch - Google Patents

Description

May 26, 1936.7

-.J. s. THoMPsoN ET Al. 2,041,877

DI SCONNECT ING SWITCH Filed Jan. l0, 1954 4 Sheets-Sheet 1 May 26, 1936. J. s. THOMPSON ET A1.

ADISCONNECTING SWITCH 4 sheets-sheet 2 Filed Jan. l0, 1934 VVENTORIS ZZ/aww m .BY

I l l v ATTORNEY May 26 1936- J. s. THOMPSON ET Al. 2,041,877

DISCONNECTING SWITCH Filed Jan. lO, 1934 4 Sheets-Sheet 3 NVENTOBS BY 11h/v May 26, 1936- v vJ`.--5. THOMPSON ET A1. 2,041,877

DISCONNECTING SWITCH vFiled Janl. l0, 1934 4 Sheets-Sheet 4 57 P/Lg'. :ny/63 60 A M T-,54 Q

Lez

F' lng.

JNVENTORS Patented May 26, 1936 PATENT oFricE DISCONNECTING SWITCH Joseph S. Thompson, Palo Alto, and Brian E. Menzies, San Mateo, Calif., assignors to Pacino Electric Manufacturing Corporation, San Francisco, Calif., a corporation of California Application January 10, 1934, Serial No. 706,050

9 Claims.

l0 essary to sectionalize .a power transmission line,

or to open or close a branch circuit at the point v of intersection with the main line, or for the protection of any other electrical equipment that may be operated from an electrical high voltage transmission line.

Another object of the invention is to provide an improved operating means for a disconnecting switch which can bev easily and positively operated under all conditions of use.

Another object of the" invention is to provide a spring type of counterbalancing means for a-vertically movable electrical switch blade which will substantially counterbalance the blade in all its positions of operation without imparting any actuating force thereto.

A switch of the character contemplated by this invention is generally mounted in the open where it is subjected to bad weather conditions, and as a result itis necessary that the cooperating contacts of the switch be made so that they can be easily moved -into and out of engagement with each other and at the same time provide a high Contact pressure. Therefore, it is another object of the invention to provide an improved blade and an improved operating mechanism which will move the blade into and out of cooperating relation with a stationary contact and produce a positive high pressure contact between the stationary contact and the movable switch blade.

A further object o'f the invention is to provide an improved blade for an electric switch which can be easily moved into cooperating relation with a stationary clip terminal and then into high pressure engagement therewith to thus insure a good electrical contact between the parts, `when the switch is closed, without interfering with the closing movement of the switch blade.

With the above and other objects in view the invention resides in the construction, combina- 50 tion `and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims.

For a better understanding of the invention reference should be had to the accompanying 5.5 drawings, wherein there is shown by way of illustration and not of limitation a preferred embodiment thereof.

In the drawings;

Figure 1 is a side elevation of a disconnecting switch constructed in accordance with this in- E vention and mounted in an upright position,

Figure 2 is a view, similar to Figure 1, showing the switch mounted in an inverted position,

Figure 3 is an enlarged fragmentary view of the switch, illustrated in Figure 1, with parts i0 broken away and in section to show the position of the operating mechanism When the switch is in its closed position, i

Figure 4 is a plan view of the switch as shown l in Figure 3, l5

Figure 5 is a fragmentary side elevation partly in section showing the position of the operating mechanism when the switch is in its opened position,

Figure 6 is an end elevation taken from' Figure 20 5, looking to the right,

Figure '7 is an enlarged fragmentary view showing details ofthe operating mechanism, and

Figures 8, 9 and 10 are side elevations partially in section showing the details of the stationary 25 contacts and the cooperating blade portions of switches constructed in accordance with the present invention. Y

In disconnecting and high Atension switch installations, particularly where the switch is used 30.

infrequently or is placed in the open whereY it is exposed to the elements, it is desirable that the switch be so constructed that the stationary contact and the movable switch blade will engage each other with a highcontact pressure. At the 35 same time it is necessary that the high contact pressure producing means be of such a character that it will not interfere with the free closing and/or opening movements vof `the switch blade.

With the above and other requirements in view, the present invention contemplates a special form of switch blade and cooperating contact and an improved actuating mechanism therefor which means of a worm II andY a worm gear I8, tol

the switch operating mechanism I0. The sta` tionary contact I2 is mounted upon the end of an insulating post I3 and the switch blade II is pivotally mounted upon a similar insulating post I4. Disposed in spaced relation with the insulating post I4, there is an linsulatingpost I5 which is adapted to control the switch operating mechanism IU. The insulating posts I3 and I4 are rigidly secured in spaced relation upon a suitable support I6, such as the vstructural iron frame Work of a transmission tower, and the insulating post I5 is journaled upon the support I6 so that it maybe rotated about its axis, by

control the switch operating mechanism I El, as will hereinafter appear.

In Figure l of the drawings the switch is shown as mounted in an upright position above the support I6 and in Figure 2 of the drawings it is shown as suspended below the support I6. In each of these arrangements, except for the difference in a switch blade counterbalancing means which is to be described in detail hereinafter, the several elements of the switch blade and its operating mechanism are identical in form and mode of operation. v

For a more detailed description of the switch operating mechanism I and the switch blade I I, reference is now made to Figures 3, 4 and 5 of the drawings. As here shown, the switch blade II is formed of a length of copper tubing I9 carried by a supporting member 20 and at its outer end it has a stirrup like member 2| which is adapted to move into circuit establishing relation with the stationary contact I2. The supporting member 20 is pivotally mounted upon a transversely disposed shaft 22 carried by a cap 23 upon the insulating post I4. Extending through the switch blade II there is a push rod 24 which carries a contact pressure producing foot 25 at its outer end. The contact pressure producing foot 25 is disposed opposite and in spaced relationwith the end or bottom of the stirrup like member 2| so that an outwardly extending portion 26, upon the stationary contact I2, can project therebetween. The other end of the push rod 24 is conneected to a switch operating lever 2'I,v by means of a clevis 28, so that' it will operate to move the contact pressure producing foot 25 into clamping engagement with the extending portion 26, upon the stationary contact I2, after the stirrup like member 2| has 'been moved into its nal switch closed position. The switch operating lever 21 pivots about'the shaft 22 and projects upwardly through the blade supporting member 20 and has a limited free movement between spaced abutments or stops 29 and 30 carried thereby. Extending between the up- Der end the switch operating lever 2l and an operating crank arm 3|, carried by the rotatable insulating post I5, there is a link 32. This link 32 is connected at its ends to the switch operating lever 21 and to the crank arm 3| by means of two cooperating clevis members 33 and 34 and it is made adjustable in length by means of screw threads and a lock nut 35 at each end thereof.

For the purpose of holding the insulating posts I4 and I5 in properly spaced relation and preventing a lateral strain being imposed thereupon by an operation of the switch, there is a pair of spaced stay rods 36. These stay rods 36 are connected at one end to the cap 23, upon the insulating post I4, and at the other end they are secured to a. journal forming member 3l, through which extends a stub shaft that carries the crank arm 3|, at the upper end of the insulating post I5. In order to further relieve the rotatable insulating post I of strain, and particularly a twisting strain, by a turning of the crank arm 3|, there is provided a switch blade counterbalancing spring 38. The spring 38 is enclosed in a cylinder 39 which is pivotally secured to a supporting arm 43 carried by the journal forming member 3l. Projecting through the free end of the cylinder 39 and cooperating with the spring 38, there is a rod 4I having a piston like head 42. The outer end of the rod 4| is pivotally connected to an upwardly extending arm 43 carried by the supporting member 20 and, as shown in all but Figure 2 of the drawings, the spring 38 is disposed between the piston like head 42 and the free end of the cylinder 39 so that it will be compressed when the rod 4I is under tension. In Figure 2 of the drawings, because of the inverted position of the switch, the piston like head 42 is shown as located intermediate the ends o the rod 4I and the spring 38 is shown as disposed between the piston like head 42 and the pivoted end of the cylinder 39. With this latter arrangement the spring 38 will be compressed and its eilective leverage arm decreased as the switch blade I I moves downwardly into its open circuit position. The spring 38 is so constructed and disposed with respect to the axis of the shaft 22 that, in each arrangement, it will substantially counterbalance the weight of the switch blade I in all positions between its limits of movement. In other words, when the switch blade II is in the position shown in Figure 3 of the drawings, the spring 38 will exert a force upon the arm 43 suicient to counterbalance the switch blade' II and its component parts and as the switch blade II moves upwardly the leverage, provided by the arm 43 and the force exerted by the spring 38, will decrease in direct proportion to the decreasing spring load exerted by tle switch blade I I as its center of gravity moves toward the pivotal point upon the shaft 22. If the switch is mounted in an inverted position, as shown in Figure 2 of the drawings, the counterbalancing pressure exerted by the spring 38 will increase as the switch blade II moves downward and, because of the decreasing leverage action resulting from the rotation of the arm 43, it is possible to construct and arrange the spring 38 SoY that it will substantially counterbalance the Weight of the switch blade II throughout its downward and upward movements.

When the crank arm 3| is turned by rotation of the insulating post I5 to open the switch, the

portion 26 upon the stationary contact I2. When the switch operating lever 2`| engages the abutment 30 and the contact pressure producing foot 25 has been retracted, the parts will be held in A this position by a latch 44 which cooperates with a projection 45 upon the clevis 28. Under these conditions, the switch blade Il may be againI fully closed by a reverse or counter-clockwise movement of the switch operating lever 2l without any lost motion of the lever and without having to overcome any retarding force due to a frictional engagement between the switch blade vIl and the stationary contact l2, as is now the usual practice.

In Figures 6 and 7 of the drawings the latch M is shown as pivotally mounted upon the supporting member-20 and as biased into an operative position by means o f a spring 46. The latch lll has an oppositely projecting foot 4l that engages an adjustable stop d8 which will cause it to disengage the projection 45 upon the clevis 28 when the switch blade ll approaches its final circuit closing position. This will release the push rod 24 and the switch' operatingv lever 2l and permit the lever to become effective, during a nal switch closing movement of the crank arm 3|, to exert a pressure upon the push rod 2d and thus move the contact pressure producing foot 25 into contact with the extending portion 26 and clamp it against the end or bottom of the strrup like member 2l to provide a high contact pressure therebetween.

The crank arm 3l is of such alength that it will move through an arc of slightly more than 180 degrees and pass over center with respect to theA axis of the insulating post l5 to produce, in conjunction with the link 32, a toggle like action which will serve to lock or hold the switch blade l l in its closed or fully opened position.

The journal forming member 3l', at the upper end of the insulang post l5, has an outwardly projecting conductor terminal supporting boss (t9, by means of which the switch can be connected in a circuit. In order to provide a low resistance path, between the boss l and a similar terminal supporting boss v5U carried by the stationary contact l2, the stay rods 36 are made f good current conducting proportions and at their inner ends they connect with braided flexible conductors which are clamped to the underside of the supporting member 26 in good -electrical contact with the copper tubing I9 of the switch blade ll.

In Figure 8 of the drawings there is shown a modiied form of stationary contact which has a pivotally mounted extending tongue 52. The tongue 52 is carried upon an insulator cap engaging plate .53 by means of a shaft 56 and is biased in an outward direction by a spring 55 located at one side of the shaft 54. A stirrup like member 56 is here shown as having an integrally formed dome like cover 5l disposed over the tongue 52. 'Ihe outer surface of the tongue 52 is curved so that it will be moved against the action of the spring 55 as the stirrup like member 56 moves into engagement therewith and thus the contacting surfaces will be brought together with a wiping action. At the bottom of the tongue 52 there is a projection 5B which cooperates with a stop 59 upon the plate 53 to limit the outward displacement of the tongue 52 whenI the stirrup like member 56 is moved out of engagement therewith. Projecting outwardly from the plate 53 there is aponductor terminal supporting boss 60 and connected between the tongue 52 and a point closely adjacent the boss 66 there is a flexible'conductor 6| which serves to conduct the current carried by the switch from the tongue 52 directly to the switch terminal; As an additional'adjunct, the plate 53 carries a bracket 62 having a pair of flared and spaced guides 63 which are adapted to engage the switch blade I l and guide the stirrup like member 56 over the tongue 52.

In Figure 9 of the drawings there vis shown a stationary terminal, designated by the numeral 64, which is similar in every respect to the stationary contact I2, previously described, except that the upwardly extending portion thereof is provided with a recess 65 on itsY inner side at the point where the contact pressure producing foot 25 engages therewith. When a terminal of this character is used and the contact pressure producing foot 25 is moved into the recess 65 by the nal movement of the switch operating lever 2l, the switch blade Il will be securely held and locked at its outer end against any circuit opening movement. This arrangement will be found particularly desirable where the switch is mounted in an inverted position, as illustrated in Figure 2 of the drawings. y

The arrangement shown in Figure of the drawings is identical to that illustrated in Figure l of the drawings, except that a yielding connection is provided between the contact pressure producing foot and its controlling push rod. The yielding connection can be provided for in a number of dierent ways. As here shown, the switch blade H is provided with a push rod 66 having a slidably mounted Contact pressure producing foot 6l upon its end. There is a compression spring 68 interposed between the end of the push rod 66 and the contact pressure producing foot 6l. This spring 68 is made very stiii` and of a few turns so that it will come into action only during the iinal movement of the push rod 66. In order to prevent a turning of th-e Contact pressure producing foot 6l and a displacement thereof, it iis secured to the push rod 66 by a pin 69 which passes through an elongated transversely extending slot l0 `formed in the end of the push rod 66.

In Figures l, 3, 9 and 10 ofthe drawings, the stirrup like member 2l is shown as having a removable cover ll which serves to protect the switch contacts against rain, sleet, snow, or the accumulation of dirt and other foreign matter at this point.

For safety, a switch of the character contemplated by this invention will vbe mounted in an elevated position upon a pole or a structural steel tower. Therefore, some provision must be made for driving the worm ll which rotates the insulating post l5. If the switch is to be manually operated, this can be accomplished by a sprocket and downwardly depending chain arrangement that connects with the shaft upon which the worm Il is mounted, or by a downwardly extending shaft having a crank at its lower end. In this latter arrangement the downwardly extending shaft may be connected to the shaft which supports the worm Il by means of beveled gears or a universal joint. If desired, the worm ll may be connected directly to an electric motor and remotely controlled by pushbuttons or relays.

The operation of the switch, illustrated in the drawings, may be described as follows:

When the switch is in its circuit closed position, asshown in Figure 3 of the drawings, and

elockwise about the shaft 22. As the switch operating lever 21 is thus rotated, it will move the contact pressure producing foot 25 to disengage the outwardly extending portion 26 of the stationary contact I2. This initial movement of the switch operating lever 21 will release the contact pressure between the engaging contacts of the switch and permit the switch blade II to be easily moved into an open circuit position. During this movement, the switch operating lever 21 will move independently of the switch blade supporting member 20 until it reaches the abutment 38 carried thereby. After the switch operating lever 21 engages the abutment 30, upon the supporting member 29, it will operate to raise the switch blade I I by rotating the supporting member 2li about its shaft 22. As soon as the supporting member 20 has rotated upwardly a suflicient distance to carry the oppositeiy projecting foot 41, carried by the latch 44, out of engage-- ment with the adjustable stop 48, the latch 44 will be moved by the spring 46 into engagement with the projection 45, carried by the clevis 28. This will lock the contact pressure producing foot 25 in a retracted position and also secure the switch operating lever 21 against the abutment 30 until the switch blade II is again operated into its circuit closing position.

During the above movement of the switchV blade II, the spring 38 will expand and, because of its angular disposition with respect to lthe shaft 22, its effective lever arm will decrease as the switch blade II approaches a vertical position. As a result, the spring 38 will substantially counterbalance the weight ci the switch blade II and relieve the crank arm 3l of all effort, except that which will be required tov impart movement to the switch blade II. When the crank arm 3l rotates to open the switch, it will move in an arc slightly over degrees or, in other words, just over the center of the insulating post I5 and, in conjunction with the link 32, provide a toggle like action which will serve to hold the switch in its vertical position until it is again turned in an opposite direction by a rotation of 'the insulating post I5.

After the switch has been fully opened, the several parts thereof will be locked in the positions shown in Figure 5 of the drawings. When the parts are in this position, the switch can then be closed by rotating the insulating post I5 in a reverse direction. This will turn the crank arm 3| outof its over center position, so that it will operate through thelink 32 to move the switch operating lever 21 in a counter-clockwise direction and, because of the latch 44, move the supporting member 20' in the direction to carry the switch blade II downwardly into its circuit closing position. As the supporting member 20 moves downwardly, it will also bring the oppositely projecting foot 41, upon the latch 44, into engagement with the adjustable stop 4i) and thus cause the latch 44 to move `out of engagement with the projection 45 to release the push rod 24 and the switch operating lever 21, so that the latter can operate through an additional arc, independently of the supporting member 28, to force the contact pressure producing foot 25 into engagement with the outwardly extending portion 2S, on the stationary contact I2, and clamp it against the bottom of the strrup like member 2| to provide a high contact pressure therebetween.

While we have, for the sake of clearness and in order to disclose the invention so that it can be readily understood, described and illustratedv i specific devices and arrangements, it is to be understood that this invention is not limited to-the specific means disclosed, but may be embodied in other ways that will suggest themselves to persons skilled in the art. It is believed that this invention is new and it is desired to claim it so that all such changes as come within the scope of the appended claims are to be considered as part of this invention. I

Having thus described our invention, what we claim and desire to secure by Letters Patent is- 1. In a hightcnsion disconnecting switch, the combination of a stationary contact, a switch blade support mounted in spaced relation with said stationary contact, a tubular switch blade pivot-ally mounted upon said support, a contact member at the end of said switch blade adapted to move into and out of engagement withv said stationary contact, a contact pressure producing means opposite the contact member at the end of said switch blade, an operating lever journaled upon said switch blade support for moving said switch blade and its contact member into and out of engagement with said stationary contact and also operating said contact pressure producing means, an operating rod extending through said tubular switch blade and connected between said contact pressure producing means and said operating lever, a latch carried by said switcn blade support and operating upon said rod for preventing an operation of said contact pressure producing means by said lever when the switch blade is in al1-but its circuit closing position, and means in the path of movement of said switch blade ,carrying member for releasing said latch and rendering said lever operative through said rod to exert a direct force upon said contact pressure producing means to provide a high pressure contact between said stationary contact and said contact member only when the switch blade is in its circuit closing position.

2. In a disconnecting switch, the combination of a support, a switch blade carrying member plvotally mounted upon said support, a tubular switch blade carried by said member, a stationary contact disposed in spacedreiation with said support, a contact making member upon the end of said switch blade adapted to engage one side of said stationary contact, a contact pressure producing member at the end of said switch blade adapted to engage the other side of Vsaid stationary Contact and cooperate with said contact making member and to produce a high contact pressure between said contacts, an operating lever pivotally mounted upon-said support for exerting a pressure upon said pressure producing member and having a limited free travel with respect to said switch blade carrying member, an operating rod extending through said tubular switch blade and connected between said pressure producing member and said operating lever, a latch upon said switch blade carrying ember for securing said operating lever to said switch blade carrying member when it reaches one of its limits of free travel, to thereby/establish a positive switch operating connec ion between said operating lever and said syl ch blade carrying member, and means carried by said support for rendering said latch inoperative when the switch blade is in its circuit closed p0- sition and permitting said operating lever to apply direct and positive pressure through said rod and upon said contact pressure producing member after the switch blade has reached its final closed position upon said stationary contact.

3. In a disconnecting switch,v the combination of a support, a switch blade carrying member pivotally mounted upon said support,V a tubular switch blade carried by said member, a stationary contact disposed in spaced relation with said support, a contact making member disposed centrally upon the end of said tubular switch blade adapted to engage the outside of said stationary contact, an operating rod extending through said tubular switch blade, a contact pressure producing member disposed opposite and in cooperating relation with said contact making member upon the end of said operating rod and adapted to be moved against the inside of said stationary contact, an operating lever pivotally mounted upon said support'and connected to the other end of said rod for moving said pressure producing member into and out of engagement with said stationary contact, a latchupon said Vswitch blade carrying member for securing said operating lever to said switch blade carrying member to prevent a movement of said operating rod and the contact pressure producing member and also establish a positive switch operating connection independently of said rod between said operating lever and said switch blade carrying member, and means for rendering said latch inoperative when the switch blade is in its circuit closed position to permit said operating lever to apply direct 'pressure to said rod and move said contact pressure producing member against and away from said stationary contact respectively during the final switch closing and the initial switch opening movement thereof.

4; In a disconnecting switch, the combination of a pivotally mounted switch blade carryingmember, a tubular switch blade carried by said member, a stirrup like contact member at the end of said tubular switch blade, a stationary contact adapted to project into and engage the inside surface of said stirrup like contact member, a rod extending through said tubular switch blade, a contact pressure producing foot at the outer end of said rod adapted to engage said stationary contact,' a lever pivotally mounted upon the same axis with said switch blade carrying member having a limited freedom of movement with respect to said switch blade carry-- ing member for moving said rod through the tubular switch blade and causing said contact pressure producing foot to engage and disengage said stationary contact, a latching means for securing said lever to said switch blade carrying member and preventing said freedom of movement when said contact pressure producing foot is outof engagement with said stationary contact, and means for rendering said latching means inoperative when said stirrup like contact member has again moved into engagement with said stationary contact.

5. In a disconnecting switch, the combination of a support, a switch blade carrying member pivotally mounted upon said support, a tubular switch blade mounted upon said member, a stirv rup like contact member secured upon the4 end ofsaid tubular switch blade having an inside contact making surface, a stationary contact adapted to project into said stirrup like contact member and engage the inside contact making surface thereof when the tubular switch blade is in its circuit closed position, a push rod extending through said tubular switch blade having a pressure producing foot at the end thereof adapted to engage'said stationary icontact, a lever pivotally mounted upon said support for moving said switch blade carrying member and the tubular switch blade carried thereby tol open and close lthe switch, said lever having a limited movement independent of said switch blade carrying member and said tubular switch blade, whereby it can operate upon said push rod and move said pressure producing foot against said stationary contact to establish a high pressure engagement between the contactmaking surface of said stirrup like contact member and said stationary contact when the tubular switch blade is in its iinal closed position, and means for locking said lever against a movement independent of said switch blade carrying member in all but the closed position of said tubular switch blade.

6. In a disconnecting switch, the combination of a circuit controlling switch blade, a pivotal support for said switch blade about which it will move in a vertical plane, a lever means for operating said switch blade from a'circuit closing to a circuit opening position and vice versa, saidlever means havng a limited free movement independent of the switch blade at the Ainitial opening and final closing positions of the switch blade, a contact pressure producing means operable by said lever during its independent movement, spring means connected to said switch blade at a point removed from its pivotal axis and operatingindependently of said switch blade operating lever means for counterbalancing the weight of said switch blade in all its positions without exerting any operating force upon the switch blade during an operating movement thereof, whereby said switch blade will remain stationary when said lever means moves independently of the switch blade to control said pressure producing means during the Ainitial switch blade in all but the closed position of said switch blade. Y Y

'7. In a disconnecting switch of the character described, the combination of a stationary switch blade support, a blade supporting member pivotally mounted upon said stationary support, a switch blade carried by and extending outwardly from said member adapted'to move in a vertical plane and engage a spaced stationary conta'ct, a Contact pressure producing means carried by said switch blade, a` leverpivotally mounted upon said stationary support independently of said member adapted to operate said contact pressure producing means when said switch blade is in its circuit closing position, an abutment upon said pivotally mounted member against which said lever will engage when in an inoperative position with respect to said pressure producing means, and a latch carried by said member for securing said lever against said abutment when said switch blade is in all but its nal circuit closing position.

8. In a disconnecting switch of the character described, the combination of a stationary switch blade support, a blade supporting member pivotally mounted upon said stationary support, a switch blade carried\by and extending outwardly from s'aid member adapted to move in a vertical plane and engage a spaced stationary contact, a contact pressure producing means upon the contact engaging end of said switch blade, a lever pivotally mounted upon said stationary support independently of said member, an operating rod connected between said lever to said pressure producing means adapted to operate said contact pressure producing means when said lever moves independently of said switch blade, an abutment upon said pivotally mounted member against which said lever will engage when in an inoperative position with respect to said pressure producing means, anda latch carried by said member for securing said lever against said abutment when said switch blade is in all but its nal circuit closing position.

9. In a disconnecting switch of the character described, the combination of a stati'onary switch blade support, a blade supporting yoke pivotally mounted upon said stationary support, a switch blade carried by and extending outwardly from said yoke adapted to move in a vertical plane and engage a spaced stationary contact, a contact pressure producing means upon the contact engaging end of said switch blade, a lever pivotally mounted upon said stationary support independently of said yoke for opening and closing said switch blade, a rod extending from said lever to said pressure producing means adapted to operate said contact pressure producing means when said lever moves independently of said switch blade, an abutment upon said pivotally mounted yoke against which said lever will engage when in one extreme of its independent movement, and a latch carried by said yoke for securing said lever against said abutment and independent movement when said switch blade is in all but its nal circuit closing position.

JOSEPH S. THOMPSON.

BRIAN E. MENZIES.

Images