US2276555A

US2276555A - Electric switch

Info

Publication number: US2276555A
Application number: US332738A
Authority: US
Inventors: Charles H Wolf; Roy E Gearhart
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-05-01
Filing date: 1940-05-01
Publication date: 1942-03-17
Anticipated expiration: 1959-03-17

Description

C. H. WQLF ETAL =Marh 17, 1942.

ELECTRIC SWITCH Filedv lay 1, 1,940

3 Sheets-Sheet 1 Mardi 17, 1942. c, H, woLF E11-M 2,276,555

ELECTRIC swITcH l Filed May 1, 1940 5 Sheetsx--Sheat 2 /O l w 4 w- H M 95 t 1 f 0 0 i 62 //0 U /afs/ ZE /a/ w50 Z T j? 30 5 45 f 42 f 7,?

Z6 l o .26 27 wir Y? 22 74 2 t .El -llli- El?. Z2?,

l /W g 35 o l- 762- llhiip I E f/f Mg 474 I BY Fay ,5, Gear/waff EATTORNEYS' March 1], 1942. c, H WOLF ErAL 2,276,555

ELECTRIC SWITCH Filed May 1, 1940 s sheets-sheet s ATTORNEYS Patented Mar. 17, 1942 UNITED ELECTRIC SWITCH charles n. wolf and any E. Gennari, Kaum City, Mo.; said Gear-hart assignor to said Wol! Application May 1, 1940, Serial No. 332,738

(Cl. 2ML-122) 16 Claims.

This invention relates to electric switches. of the type having both automatic and manually operable means for moving a main switch blade to the open-circuit position after the said blade has been disposed in the closed-circuit position by manually operable parts disposed within easy reach of an operator.

This invention has for another aim the provision of an electric switch wherein is included manually operable means for moving the switch blade to the closed-circuit position, thermally responsive structure for automatically releasing parts of the switch so as to return the switch blade to the open-circuit position, and means permitting the movement of the switch blade back to the closed-circuit position prior to the return oil the thermally responsive structure to normal position,

A further object of the invention is to provide an electric switch ofthe foregoing character with a second manually operable means for causing the switch blade to move to the open-circuit position, which second manually operable means is effective to perform the aforesaid duty regardless of the condition or position of the thermally responsive structure.

An even further aim of the invention is to provide an electric switch with manually operable parts for moving the switch blade to the closedcircuit position and a second manually operable means for causing the switch blade to. move to the open-circuit position, said two manually operable means being interconnectible for the purpose of rendering ineffective the thermally responsive structure of the switch, until the said second manually operable means has been actuated to break the connection between the two manually operable means and to cause the switch blade to assume the open-circuit position.

Another important object of this invention is to provide a switch with means for manually moving the switch blade to the closed-circuit position, thermally responsive means including a resistance for automatically moving the switch blade to the open-circuit position, and a second manually operable means for causing the switch blade to move to the open-circuit position prior to the time the thermally responsive structure operates, said second manually operable means including a part for opening the circuit supplying energy to the resistor as it functions to return the switch blade to the open-circuit position.

A large number oi important objects are ccnternplated by this invention, such additional aims will become apparent during the following speciilcation wherein will be disclosed minor objects of the invention, all of which are embodied in the form of the invention illustrated in the accompanylng drawings wherein:

Figure 1 is a face view of an electric switch made to embody the present invention.

Fig. 2 is a front elevational view of the switch with the cover plate removed.

Fig. 3 is a side elevational view of the switch.

Fig. 4 is an elevational view of the opposite side from that shown in Fig. 3, but with the cover plate and knob removed.

Fig. 5 is a longitudinal sectional view through the switch taken on line V--V of Fig. 3.

Fig. 6 is a view similar to Fig. 5, but with the switch blade in the closed-circuit position.

Fig. 'I is a side elevational view similar to that shown in Fig. 3, but with the thermally responsive structure in the operative position.

Fig. 8 is a back elevational view of the switch.

Fig. 9 is a cross sectional view'talren on line IX--IX of Fig. 5, and looking in the direction oi' the arrows.

Fig. 10 is a similar view as that shown` in F18. 9, but with the manually operable means ior releasing tlie switch blade to the open-circuit position in the eilective condition.

Figs. 1l and l2 are fragmentary front elevational views of the switch with the face plate removed and showing the detent employed for rendering the thermally responsive structure in operative in the ineiiective and effective conditions respcctively.

Fig. 13 is a wiring diagram showing the resistor for operating the thermally responsive structure in shunt circuit; and

Fig. 14 is the wiring diagram showing the thermally responsive resistor in series circuit.

The switch parts made and assembled in accordance with the present invention, have been shown embodied in a conventional wall switch that is normally placed in the well-known outlet box, not here shown, and over which the regulation face pme le is disposed.

The frame supporting the hereinafter described parts is generally designated by the numeral Il and comprises not only the block 20 of insulating material, which is necessary to support the various conductors of current but the metallic parts that are arranged in a manner that will provide adequate and substantial support.

Switch blade 22 is carried by yoke 24 for movement to and from a position where the ends thereof are in engagement with switch points 2! aa'zasss (Figs. 3 and 7) against pin 10, thereby swinging plate Il about its axis of rotation on shaft l0, which allows yoke 24 to return to the position shown in Fig. 5 under the influence of spring 42.

Obviously, switch blade 22 will leave

switch points

26 and 28 to open the circuit.

When switch blade 22 is closed, the circuit supplying current to lamp |32, for example, is as follows: y

Wire |24, wire |44 to lamp |32, and thence back to a source of supply through wire |48,

switch points

28 and 26, through switch blade 22, and thence to the point of beginning through wire As plate 58 is moved to release yoke 24, extension 64 thereon will travel therewith and separate contact point 68 and strip 90 which opens the circuit supplying current to resistor I4 for the purpose of allowing the latter to cool and permit metal 80 to return to the normal position. .A pictorial illustration of the position of the various parts with contact point 68 and strip 90 parted, is seen in Fig. 7.

If the switch is no longer manipulated, metal 80 will cool and return to the normal position and with it arm 14 will travel to the position shown in Fig. 3. As cooling occurs, the return of arm i4 will strike pin 12 to shift plate 58 back to a position where contact point t8 and strip 90 are again in engagement.

Assuming now that it is desired to again reset the switch so that lamp |32 will burn and that such manual manipulation occurs prior to the time metal 8U returns to the normal position. Knob llii is again forced to the right and yoke 24 will move in precisely the same way as above set down, however, instead of ear 52 being held against upward movement by shoulder 5S, it will be engaged by shoulder S4 on plate 58 until arm 14 strikes pin 12; thereby releasing said ear and permitting spring 42 to snap switch 22 open. This interval of time depends entirely upon the conz dition of metal 8i! when the switch was manually moved to the on position after it had been automatically opened by the heating of metal 80. When arm 14 again moves to the normal position shown in Fig. 3, a ftion of the circuit supply ing energy to resistor fili, comprising contact point 58 and contact strip will be closed by the bringing together of said contact point i8 and said contact strip li thereby readying said portion of the circuit for the part of the cycle of operation requiring the heating of bi-rnetallic strip 80.

Assuming now that the switch in the no1-- mal position with contact blade 22 bridging switch points and 2% and that metal li has been distorted slightly, not enough to automatically trip the thermally responsive structure. The ser may manually release switch blade 22 by depressing plunger 8l. Such manipulation of this plunger acts upon lever lili to move it inwardly about |02 to force bell-crank lever loi about the axis of pin |06. Leg H will be moved against plate B and spring 82 com pressed as seen in Fig. 10. Such 'action takes place when shaft Gli moves longitudinally in its bearings. Plate 58 will immediately release 'yoke 24 and spring 42 will serve to snap the associated parts of the switch back to the opencircuit position.

When plunger 28 is depressed as just mentioned, release rod |2l is moved against contact blade 2B to force it away from pin il, thus the circuit to resistor n is opened before switch blade 22 is snapped to the open-circuit position. Spring ||2 lying behind pin lll is moved inwardly against one end of release rod |20, which slides longitudinally against contact blade Il to eilec't such circuit opening. Thus, the ability of being able to operate the switch to the open-circuit position is always available upon depr plunger Il.

It is to be remembered throughout the foregoing description, that nag |25 will always move with yoke 24 and place the appropriate word,

. i. e. "on or ofi" behind window it@ in plate il.

The switch pr may ire set so the thermally respons.. -a ture will nove the parts to the openwireuit position switch so that the lomp burn constantly, plunger s as to move spring lit rearwardly raast ringer |24 mounted directly upon shaft When the switch parts are in the normal posi'- tion, linger im positioned with i to the reduced end oi' spring il?, as seen in Fig. 2. Spring H2 is easily forced rear'eardiy by lever |00 and pin llt thereon alter 'which inaob il is moved in the direction of the arrow in Fig. 1, to dispose finger |24 in the position behind datent IIB (Fig. l2). Se depressing plunger i!! will move release rod @2t rearwardly against. contact blade 53 so as to said blade ru 8l' and 'thereby open the :unt circuit to Il. In such condition, switch blade M bridges contact points 2% and 28 to cause iamp 22 burn.

Knob 45 is held in the set position to which it has been moved by dctent H8, ling-cr |24 and shaft Il. When knob 40 is so held, signal plate |48 on shaft 3l has the portion |52, for example, disposed behind window |52 in plate |4 so as to indicate to the user that the switch is set to permanently maintain the parts thereof 'in the closed circuit position. Obviously, the thermally responsive structure will not automatically open the switch and to again move switch blade 22 to the open-circuit position, plunger Il is depressed to move detent IIS out of engagement with finger |24.

Bell-crank lever |04 will simultaneously be moved to trip yoke 24 as above made clear, and when spring H2 is permitted to again assume its normal position, release rod |24 will permit contact blade 38 to return to a place where the shunt circuit to resistor il is closed.

Throughout all of the aforesaid steps of operation, fiag |28 will move to signal the condition of the switch parte, as regards the uopen" or closed circuit positions.

When the parts oi' the switch are made as above described and illustrated in the accompanying drawings, the same may be placed in a conventional outlet box or used in any suitable housing or any location where a circuit is to be automatically or manually controlled as permitted through the employment of the parts above set down.

Resistor 83 has heretofore been indicated as being in a shunt circuit, but it is within the concepts of the invention to pi "i s. similar resistor 24| in a series circuit in the manner lllustxited diagrammaticaily in Fig. i4.

Lamp 2oz controlled 'by switch blade 224 which bridges switch points Wi and 2li. When resistor 20d is in series circuit with lamp 2.2. with switch blade 204 bridging switch points 2" and 202, contact points 2li and 2|! remain apart until resistor 204 distorts under heat to automatically bring together these said points. These points 2|. and 2|2 are analogous to

members

90 and 68 respectively, as shown in Figs. 3 and 7. The only change necessary to convert the switch illustrated, to a series circuit being the placement of contact B on the upper inclined face of extension 64.

Ii switch blade 204 is manually returned to the closed-circuit condition again before the metal in resistor returns to the normal position, closed points 2l. and 2i2 with bridged points 206 and 240, will allow lamp 202 to burn as current is passing through the following circuit without resistor being therein:

Wires 2I4, 2I6 and 2li, points 2l0 and 2|2, wires 22| and 222, switch blade 204, wire 224, lamp 202, and wire 226.

When the resistor cools and its metal returns to normal, switch points 2I0 and 2|2 will be again opened through the same mechanical action as disclosed for the control of points Il and 90.

When the switch is set for causing lamp 202 to burn until manually cut off, points 220 and 230 are locked together by detent IIS as switch blade 204 is moved to the closed-circuit position. Lamp 202 is then caused to burn until the parts are released by another manipulation of the mechanism. Under these conditions, the circuit supplying lamp 202 does not include resistor 200 and is traced as follows:

Wire 2I4, wire 232, conductor 228, point 230, wire 234, point 208, blade 204, point 20B, wire 224, lamp 202, and wire 22B.

Conductor 220 in this circuit is the same as contact blade 08 heretofore described, and point 230 is the same as pin BI. 'I'he only rearrangement necessary is to place pin 66 on the other side of blade 88 so that the two normally remain apart and so that movement of rol' |20 will close A these conductors as the switch blade is locked in the closed-circuit position.

Having thus described the invention, what is claimed as new and desired to be secured lby Letters Patent is:

l. In an electric switch of the character described, a switch blade movable to open and closed circuit positions; means for moving said switch blade with a snap action to either of said positions; manually operable parts for actuating the means for moving the switch blade to place the same in the closed position; a latch to releasably hold the switch blade in the last men tioned position; thermally responsive structure, including a resistor, for automatically releasing the latch 'to cause the switch blade to move to the open circuit position after the same has remained in the closed circuit position a period of time; a second manually operable means for releasing thc latch prior to its release automatically by the said thermally responsive structure; a shunt circuit having the resistor and a switch i ein between said second manually operable rn n: and thc shunt circuit switch whereby to open the stuurt circuit as the latch is released switcll blade to assume the open t switch of the character del blade movable to open and closed l; means for moving said switch action to either of said posig the switch blade to place the f l circuit position; a latch to cry hold the .switch blade in the last menreleer@ tioned position; thermally responsive structure for automatically releasing the latch to cause the switch blade to move to the open circuit position after the same has remained in the closed circuit position a period of time; and a second manually operable means for releasing the latch prior to its release automatically by the said thermally responsive structure, said latch being formed to hold the means for moving the switch blade in place to maintain the switch blade in the closed circuit position, upon manipulation of the first mentioned manually operable parts, after the thermally responsive structure has once automatically released the latch and before the same has returned to normal condition by cooling.

3. In an electric switch oi the character described, a switch blade movable to open and closed circuit positions; means for moving said switch blade with a snap action to either of said positions; manually operable parts for actuating the means for moving the switch blade to place the same in the closed position; a latch to releasably hold the switch blade in the last mentioned position; thermally responsive structure including a resistor for automatically releasing the latch to cause the switch blade to move to the open circuit position after the same has remained in the closed circuit position a period of time; a second manually operable means for releasing the latch prior to its release automatically by the said thermally responsive structure; a shunt circuit having the resistor and a switch therein between said second manually operable means and the shunt circuit switch whereby to open the shunt circuit as the latch is released to cause the switch blade to assume the open circuit position, said latch having a switch Contact point attached thereto and movable therewith to open and close the shunt circuit as the latch is moved.

4. In an electric switch,` oi' the character described, a switch blade movable to open and closed circuit positions; means for moving said switch blade with a snap action to either of said positions; manually operable parts for actuating the means for moving the switch blade to place the same in the closed position; a latch to releasably hold the switch blade in the last mclitloned position; thermally responsive structure including a resistor for automatically releasing the latch to cause the switch blade to move to the open circuit position alter the imc rcmained in the closed circuit position r oer time; a second manually operable me leasing the latch prior to its release auto really by the said thermally responsive structure; a shunt circuit having the resistor and a switch therein between said second manually operable means and the shunt circuit switch whereby to open the shunt circuit as the latch is released to cause the switch blade to assume the open circuit position, said latch having a switch contact point attached thereto and movable therewith to open and close the shunt circuit as the latch is moved, said switch contact point being in a position to open the shunt circuit when the thermally responsive structure has moved the latch to cause the switch blade to move to the open circuit position.

5. In an electric switch o! the character described, a switch blade movable to open and closed circuit positions; means for moving said switch blade with a snap action to either of said positions; manually operable parts for actuating the means for moving the switch blade to place the same in the closed position; a latch to releasably hold the switch blade in the last mentioned position; thermally responsive structure including a resistor for automatically releasing the latch to cause the switch blade to move to the open circuit position after the same has remained in the closed circuit position for a period of time; a second manually operable means for releasing the latch prior to its release automatically by the said thermally responsive structure; a shunt circuit having the resistor and a switch therein between said second manually operable means and the shunt circuit switch whereby to open the shunt circuit as the latch is released to cause the switch blade to assume the open circuit position, said latch having a switch contact point attached thereto and movable therewith to open and close the shuntcircuit as the latch is moved, said switch contact point .being in a position to close the shunt circuit when the thermally responsive structure is in the normal position. I

6. In an electric switch oi the character described, a switch blade movable to open and closed-circuit positions; means for moving said switch blade with a snap action to either of said positions; manually operable parts for actuating the means for moving the switch blade to place the same in the closed-circuit position; a latch to releasably hold the switch blade in the last mentioned position; thermally responsive structure including a resistor for automatically releasing the latch to cause the switch blade to move to the open-circuit position after the same has remained in the closed-circuit position a period of time; a second manually operable means for releasing the latch prior to its release automatically by the said thermallyresponsive structure; a shunt circuit having the resistor and a switch therein across the switch blade: a switch in the circuit being controlled by the said blade; and a connector between said second man-v ually operable means and the last mentioned switch whereby to open the circuit as the latch is released to cause the blade to assume the opencircuit position.

7. In an electric switch of the character de scribed, a switch blade movable to open and closed-circuit positions; means for moving said switch blade with a snap action to either of said positions; manually operable parts for actuating the means for moving the switch blade to place the same in the closed-circuit position; a latch to releasably hold the switch blade in the last mentioned position; thermally responsive structure for automatically releasing the latch to cause the switch blade to move to the open-circuit position afterl the same has remained in the closed circuit position a period of time; a second manually operable means for releasing the latch prior to its release automatically by the said thermally responsive structure; a detent independent of the said latch for retaining the switch blade in the closed-circuit position; and elements independent of the thermally responsive struc-` ture for releasing the detent at will to cause the switch blade to move to the open-circuit position.

8. In an electric switch of the character described, a switch blade movable to open and closed-circuit positions; means for moving said switch blade with a snap action to either of said positions; manually operable parts for actuating the means for moving the switch blade to place to releasably hold the switch blade in the last mentioned position; thermally responsive structure for automatically releasing the latch to cause the switch blade to move to the open-circuit position aiter the same has remained in the closed' circuit position a period ottime; a second manually operable means for releasing the latch pior to its release automatically by the said thermally responsive structure; a detent independent of the said latch for retaining the switch blade in the closed-circuit position; and elements independent of the thermally responsive structure for releasing the detent at will to cause the switch blade to move to the open-circuit position, said ,elements being disposed for release by the second manually operable means when serving to retain the switch blade in the closed-circuit position.

9. In an electric switch of, the character described, a switch blade movable to open and closed-circuit positions; means for moving said switch blade with a snap action to either of said positions; manually operable parts for actuating the means for moving the switch blade to place the same in the closed-circuit position; a latch to releasably hold the switch blade in the last mentioned position; thermally-responsive structure including a resistor for automatically releasing the latch to cause the switch blade to move to the open-circuit position after the same has remainedV in the closed-circuit position a period oi' time; a second manually operable means for releasing the latch prior to its release automatically by the said thermally-responsive structure; a shunt circuit having the resistor and a switch therein across the switch blade; a detent independent of the said latch for retaining the switch blade in the closed-circuit position; elements independent of the thermally responsive structure for releasing the detent at will to cause the switch blade to move to the open-circuit position; and a connector between the detent and the shunt circuit switch to hold the latter open when the detent is inthe operative position.

10. In an electric switch of the character described, a switch blade movable to open and closed-circuit positions; means for moving said switch blade with a snap action to either ot said positions; manually operable parts for lactuating the same in the closed-circuit position; a latch the means for moving the switch blade to place the same in the closed-circuit position; a latch to releasably hold the switch blade in the last mentioned position; thermally responsive structure including a resistor for automatically releasing the latch to cause the switch blade to move to the open-circuit position after the same has remained in the closed-circuit position a period of time; a second manually operable means for releasing the latch prior to its release automatically by thev said thermally responsive structure; a shunt circuit having the resistor and a switch therein across the switch blade; a detent independent of the said latch for retaining the switch blade in the closed-circuit position; elements independent of the thermally responsive structure for releasing the detent at will to cause the switch blade to move to the open-circuit position; anda connector between the detent and the shunt circuit switch to hold the latter open when the detent is in the operative position, said elements being disposed for release by the second manually operable means when the detent is in the operative position.

11. In an electric switch of the character described, a switch blade movable to open and closed-circuit positions; means for moving said switch blade with a snap action to either o! said positions; manually operable parts for actuating the means for moving the switch blade to place the same in the closed-circuit position; a latch to releasably hold the switch blade in the last mentioned position; thermally responsive structure including a resistor for automatically releasing the latch to cause the switch blade to move to the open-circuit position after the same has remained in the closed-circuit position a period oi' time; a second manually operable means for releasing the latch prior to its release automatically by the said thermally responsive structure; a detent independent of the latch for retaining the switch blade in the closed-circuit position; and cooperating means on both the manually operable parts and said second manually operable means respectively for positioning the detent to hold the switch blade in the closedcircuit position.

12. In an electric switch of the character described, a switch blade movable to open and closed-circuit positions; means for moving said switch blade with a snap action to either of said positions; manually operable parts for actuating the means for moving the switch blade to place the same in the closed-circuit position; a latch to releasably hold the switch blade in the last mentioned position; thermally responsive structure including a resistor for automatically releasing the latch to cause the switch blade to move to the open-circuit position after the same has remained in the closed-circuit position a period of time; a second manually operable means for releasing the latch prior to its release automatically by the said thermally responsive structure; a detent independent of the latch for retaining the switch blade in the closed-circuit position; and cooperating means on both the manually operable parts and said second manually operable means respectively for positioning the detent to hold the switch blade in the closedcircuit position, the said cooperating means being arranged to so position the detent when the second manually operable means is actuated and manually held in place until the first mentioned manually operable parts move the switch blade to the closed-circuit position.

13. In an electric switch of the character described, a switch blade movable to open and closed-circuit positions; means for moving said switch blade with a snap action to either of said positions; manually operable parts for actuating the means for moving the switch blade to place the same in the closed-circuit position; a latch to releasably hold the switch blade in the last mentioned position; thermally responsive structure including a resistor for automatically releasing the latch to cause the switch blade to move to the open-circuit position after the same has remained in the closed-circuit position a period of time; a second manually operable means for releasing the latch prior to its release automatically by the said thermally responsive structure; a detent independent of the latch for retaining the switch blade in the closed-circuit position; and cooperating means on both the manually operable parts and said second manually operable means respectively for positioning the detent to hold the switch blade in the closed-circuit position, the said cooperating means being arranged to so position the detent when the second manually operable means is actuated and manually heldin place until the tlxst mentioned manually operable parts move the switch blade to the closed-circuit position, said detent being releasable by the said second manually operable means after the detent has served to retain the switch blade in the closed-circuit position.

14. In an electric switch of the character described, a switch blade movable to open and closed-circuit positions; means for moving said switch blade with a snap action to either of said positions; manually operable parts for actuating the means for moving the switch blade to place the same in the closed-circuit position; a latch to releasably hold the switch blade in the last mentioned position; thermally responsive structure including a resistor for automatically releasing the latch to cause the switch blade to move to the open-circuit position after the same has remained in the closed-circuit position a period of time; a second manually operable means for releasing the latch prior to its release automatically by the said thermally responsive structure; a detent independent of the latch for retaining the switch blade in the closed-circuit position; and cooperating means on both the manually operable parts and said second manually operable means respectively for positioning the detent to hold the switch blade in the closedcircuit position, said detent servingr to so hold the latch inoperative whereby to render ineffective the thermally responsive structure.

15. In an electric switch of the character described, a switch blade movable to open and closed-circuit positions; means for moving said switch blade with a snap action to either of said positions; manually operable parts for actuating the means for moving the switch blade to place the samein the closed-circuit position; a latch to releasably hold the switch blade in the last mentioned position; thermally responsive structure including a resistor for automatically releasing the latch to cause the switch blade to move to the open-circuit position after the same has remained in the closed circuit position a period of time; and a second manually operable means for releasing the latch prior to its release automatically by said thermally responsive structure, said latch comprising a pivotally mounted plate, provided with a pair of shoulders, movable about its axis by the thermally responsive structure, a part on the means for moving the switch blade with a snap action engageable by one of the shoulders to hold the switch blade in the closed-circuit position, and a lever operable by the second manually operable means for moving the plate longitudinally along the axis of rotation to disengage either` of the shoulders from said part.

16. In an electric switch of the character described, a switch blade movable to open and closed-circuit positions; means for moving said switch blade with a snap action to either of said positions: manually operable parts for actuating the means for moving the switch blade to place the same in the closed-circuitI position; a latch to releasably hold the switch blade in the last mentioned position; thermally responsive structure including a resistor for automatically releasing the latch to cause the switch blade to move to the open-circuit position after the same has remained in the closed circuit position a period of time; and a second manually operable means for releasing the latch prior to its release automatically by said thermally responsive structure. said latch comprising a pivotally mounted plate, provided with a pair ot shoulders, movable about its axis by the thermally responsive structure, a part on the means for moving the switch blade with a snap action engageable by one oi the shoulders to hold the switch blade in the closed-circuit position; and a lever operable by the second manually operable means for moving the plate longitudinally along the axis of rotation to disengage either of the shoulders from said part, said resistor being in a circuit having a switch movable to the open and closed-positions by the plate as the latter swings about its axis 5 of rotation.

CHARLES H. WOLF. ROY E. GEARHART.