US3733571A

US3733571A - Switch control

Info

Publication number: US3733571A
Application number: US00212201A
Authority: US
Inventors: S Budlane; D Stoll
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1971-12-27
Filing date: 1971-12-27
Publication date: 1973-05-15
Anticipated expiration: 1990-05-15
Also published as: FR2166045A1; DE2261816A1; GB1415179A; IT972528B; AU464788B2; AU4910072A; JPS4872622A

Abstract

A switch control is disclosed comprising a frame to which first and second contacts are mounted. An electrically conductive pendant arm adapted to move when electrically heated is also mounted to the frame. A third contact is mounted on the pendant arm in position to make and break contact with the first contact upon movement of the pendant arm relative to the first contact. A fourth contact is mounted on the pendant arm in position to make and break contact with the second contact upon movement of the second contact with respect to the pendant arm. Stop means are also mounted to the pendant arm for limiting movement of the second contact with respect to the fourth contact. The various switch contacts are adapted for suitable connection to motor start and run windings and to a source of electric current.

Description

United States Patent 1 Budlane et al.

[111 3,733,571 May 15,1973

[ SWITCH CONTROL [73] Assignee: General Electric Company, Fort Wayne, Ind.

22 Filed: Dec. 27, 1971 21 Appl. No.: 212,201

Primary ExaminerBernard A. Gilheany Assistant Examiner-F. E. Bell A ttorney-J ohn M. Stoudt et al.

[57] ABSTRACT A switch control is disclosed comprising a frame to which first and second contacts are mounted. An electrically conductive pendant arm adapted to move when electrically heated is also mounted to the frame. A third contact is mounted on the pendant arm in position to make and break contact with the first contact upon movement of the pendant arm relative to the first contact. A fourth contact is mounted on the pendant arm in position to make and break contact with the second contact upon movement of the second contact with respect to the pendant arm. Stop means are also mounted to the pendant arm for limiting movement of the second contact with respect to the fourth contact. The various switch contacts are adapted for suitable connection to motor start and run windings and to a source of electric current.

13 Claims, 12 Drawing Figures FIG! PATHHEUHAY 1 51975 SHEET 1 OF 3 FIGZ INVENTOR. S TANLEY J. BUDLANE, NALD H. STOLLI Q yum @4 A T TORNEY.

PATENIEU HAY I 5 I975 SHEET FIGS? FIGII INVENTOR.

8 TA NL E Y J BUDLANE,

DONALD r-r. STOLL BY ATTORNEY.

BACKGROUND OF THE INVENTION This invention relates generally to switch controls, and particularly to switch controls for electric motors of the type having independent motor start and motor run windings.

Electric motors having motor start and motor run windings require means for controlling the flow of electric current through each of the windings. Heretofore, such control has typically been provided by the combined means of an electromagnetic motor start relay and an overload switch. The electromagnetic motor start relay has ordinarily comprised a magnetic actuating plunger mounted for axial movement within an electric coil which coil is electrically coupled with the motor run windings. To start the motor the motor run windings are connected to a source of electric current causing an initial high current surge to flow through the run windings and the motor startrelay'coil coupled thereto. The magnetic flux thereby created in the relay moves the magnetic actuating plunger which movement closes adjacent switch contacts serially connected to the motor start windings. The motor start windings are thusly energized which action rapidly reduces the current flow through the motor run winding as the motor rotor is accelerated due to the accompanying increase in back E.M.F. With less current being drawn by the run windings less current is also drawn by the relay coil which reduces the level of magnetic flux therein causing the actuating plunger to return towards its unenergized position by gravity, spring bias orthe like and thereby open the motor start'contacts.

The independent motor overload switch has typically comprised a bimetallic element of such shape as a disc. In some configurations the bimetallic element is electrically resistant and is itself coupled with the'motor run windings. In other configurations an electric heating element is mounted on the bimetallic element and cow pled with the run windings rather than the bimetallic element itself being so coupled. One switch contact is mounted on the bimetallic element adjacent a mating switch contact mounted to an adjacent frame member. With either configuration heat generated by a flow of electric current through the overload switch causes the bimetallic element to move sufficiently to effect separation of the switch contacts thereby de-energizing the motor run windings to which they are serially connected. I

Having two independent components the justdescribed electric motor switch control of the prior art has occupied substantial space and been rather costly to install. The relay component being electromagnetic it itself has also been costly. In addition, its operational time has been less than desirable for many motors. Alleviation of these problems is thus highly desirable.

Accordingly, it is a general object of the present invention to provide an improved switch control.

More specifically, it is an object of the present invention to provide an improved switch control for electric motors of the type having motor start and motor run windings.

Another object of the invention is to provide relatively compact, integral control means for energizing and de-energizing electric motors having motor start and motor run windings.

Another object of the present invention is to provide relatively inexpensive control means for energizing and de-energizing electric motors having motor start and motor run windings.

Yet another object of the invention is to provide switch control means for de-energizing start windings of an electric motor after having been energized for but a very brief period.

Another'object of the invention is to provide control means for energizing and de-energizing electric motors having motor start and motor run winds which control means is substantially orientation insensitive with respect-to gravity.

SUMMARY OF THE INVENTION In one embodiment of the invention an electric motor switch control is provided comprising a frame, a first contact mounted to the frame and adapted to be connected to a motor start winding, and a second contact movably mounted to the frame and adapted to be connected to a motor run winding. An electrically conductive pendant arm adapted to move when electrically heated is also provided. The pendant arm is mounted to the frame and adapted to be connected to a source of electric current. A third contact is mounted on the pendant arm in position to make and break contact with the first contactupon movement of the pendant arm relative to the first contact. A fourth contact is mounted on the pendant arm in position to make and break contact with the second contact upon movement of the second contact with respect to the pendant arm. Stop means are also mounted to the pendant arm for limiting movement of the second contact with respect to the fourth contact.

In another embodiment of the invention an electric motor switch control is provided comprising a frame, a first contact mounted to the frame and adapted to be connected to a motor start winding, and a second contact movably mounted to the frame and adapted to be connected to a source of electric current. An electrically conductive pendant arm adapted to move when electrically heated is also provided. The pendant arm is mounted to the frame and adapted to be connected to a motor run winding. A third contact is mounted on the pendant arm in position to make and break contact with the first contact upon movement of the pendant arm relative to the first contact. A fourth contact is mounted on the pendant arm in position to make and break contact with the second contact upon movement of the second contact with respect to the pendant arm. Stop means are also mounted to the pendant arm for limiting movement of the second contact with respect to the fourth contact.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of a switch embodying one form of the present invention with a protective cover removed for purposes of illustration;

FIG. 2 is a side view in elevation of the switch shown in FIG. 1 with all switch contacts in closed position;

FIG. 3 is a fragmentary side view in elevation of the switch shown in FIG. 1 with all switch contacts in open position;

FIG. 4 is a fragmentary side view in elevation of the switch shown in FIG. 1 with one set of switch contacts in closed position and with another set of switch contacts in open position;

FIG. 5 is an end view in elevation of the switch shown in FIG. 1;

FIG. 6 is a side view in elevation of a switch embodyin g another form of the present invention with a protective cover removed for purposes of illustration;

FIG. 7 is a bottom view of the switch shown in FIG. 6.

FIG. 8 is a front end view of the switch shown in FIG.

FIG. 9 is a top view of the switch shown in FIG. 6;

FIG. 10 is a view in elevation of the other side of the switch shown in FIG. 6 with the protective cover not removed;

FIG. 11 is a circuit diagram schematically illustrating the switch shown in FIGS. 1-5, here designated as S electrically connected to an electric motor; and

FIG. 12 is a circuit diagram schematically illustrating the switch shown in FIGS. 6-10, here designated as S electrically connected to an electric motor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in more detail to the drawings there is shown in FIGS. l-5 a switch control for an electric motor having start and run windings. The switch control comprises dielectric frame member 10 upon which terminal 12 is mounted. Metallic spacer 14 overlays terminal 12 with a thin insulating strip 16 sandwiched therebetween to electrically isolate terminal 12 from the metallic spacer. Dielectric block 18 overlays spacer 14. The terminal, spacer insulating strip and dielectric block are fastened rigidly together by screws 20 and nuts 22.

One end of outer legs 24 of a three legged thermally responsive actuating element are fixed by such means as welding to metallic spacer 14. One end of center leg 26 of the actuating element is similarly secured to terminal 12. The unsecured ends of the three legs are integrally joined together by three legged element bridge portion 24' upon which is mounted double contact 28.

To the bottom of frame member 10 is secured terminal 30 by means of screw 32 threaded through an aperture in the frame member and upon the end of which screw is mounted motor start contact 34. Nut 36 is run up the threads of screw 32 both to secure terminal 30 rigidly to the frame member and to fix the position of motor start contact 34 relatively to the frame member.

To the top of dielectric block 18 between screws 20 is mounted terminal 38 by means of screw 40 which screw extends through terminals 12 and 38, block 18, metallic spacer l4, insulating strip 16 and frame member' 10. The aperture in terminal 12 and spacer 14 is of greater diameter than that of screw 40 whereby the screw may pass therethrough in spaced relation to the aperture defining walls and thereby prevent electric contact from being made thereinbetween. One end of leaf spring 42 is secured as by welding to terminal 38 while to the other end is similarly secured the proximal end of pendant arm 44. To the distal end of the pendant arm is secured arm extension 46 to which is mounted motor run contact 48. One end of toggle spring 50 is 1 held to an end of arm extension 46 by means of an exturn rigidly secured to frame member 10 by screws 54. In the position shown in FIGS. 1 and 2 toggle spring 50 spring biases pendant arm 44 and motor run contact 48 mounted thereto against double contact 28 and it in turn against motor start contact 34. The toggle spring biases the pendant arm in the opposite direction and motor run contact 48 away from double contact 28 if the arm is raised away from motor start contact 34 beyond a predetermined over center snap position as by movement of the three legged element away from the motor start contact. This is the switch condition shown in FIG. 4.

For operation terminal 30 may be coupled to a motor start winding, terminal 38 to a motor run winding, and terminal 12 to a source of electric current through suitable power on and off switch means as shown in FIG. 11. Upon closure of the

power switch contacts

28, 34 and 48 will normally be in the closed position illustrated in FIG. 2 whereby both the motor start and motor run windings will be energized. Electric current will pass through center leg 26 of the three legged element'causing it to heat and rapidly assume temperatures elevated above those of outer legs 24. This temperature differential between the center and outer legs, coupled with the vertical offset of the end of the center leg proximal terminal 12 relative to the ends of the outer legs proximal spacer 14, cause the three legged element to pivot. Bridge portion 24' of the three legged element accordingly moves upwardly away from frame member 10 causing double contact 28 rapidly to break from motor start contact 34. This action terminates the flow of current to the motor start windings.

In moving upwardly away from frame member 10 and motor start contact 34 the three legged element forces pendant arm 44 also upwardly insomuch as the top surface of double contact 28 mounted to the three legged element engages the bottom surface of motor run contact 48 as viewed in FIG. 2. This movement is in opposition to the bias provided by spring 42. In the event the motor run winding load is within a predetermined limit the current passing through center leg 26 heats the leg sufficiently to insure that a substantial gap exists between double contact 28 and motor start contact 34. However, as seen by reference to FIG. 4, this gap will not be so great as to position pendant arm 44, forced upwardly by the movement of the three legged element, above and over center snap position provided by toggle spring 50. Should the motor malfunction however and the motor run winding load exceed the aforementioned predetermined level, current through center leg 26 will increase causing bridge portion 24' to move upwardly further away from frame member 10. This excessive current flow forces pendant arm 44 above the over center point at which toggle spring 50 snaps the pendant arm upwardly abruptly opening

contacts

28 and 48. In this position, which is that shown in FIG. 3, both the motor start and motor run windings are de-energized. Flow of electric current through center leg 26 accordingly terminates thereby causing it to cool and move downwardly towards frame member 10. As the three legged element moves downwardly dielectric stop 53 attached thereto engages pendant arm 44 if not already having done so in arresting the snap movement thereof. Continued downward movement of the three legged element thus forces pendant arm 44 downwardly until its over center snap position is again reached beyond which point toggle spring 50 snaps the dog, forces motor run contact 48 into engagement with double contact 28 and it in turn into engagement with motor start contact 34 as the force of the toggle spring overcomes the positional stability of the three legged element. In this manner the switch is reset and the motor start and run windings are once again energized.

If desired, the just described switch may be used in controlling devices other than motors. Particular utility may, for example, be found for the specific embodiment just described in numerous circuits requiring both operative and overload protective switch means. And, of course, modified versions thereof may be had to satisfy special needs. Ambient temperature sensitivity may be provided, for example, through the use of bimetal for pivot 52. The bimetal itself may, of course, comprise more than two dissimilar layers of metal, if desired.

To provide more freedom of choice in material selection for the three legged element a heater wire may be mounted in electrical insulation form, but in thermal contact with, center leg 26. This provides means for utilizing more flexible three legged elements. Two single, independent contacts maybe substituted for double contact 28. For specific applications where automatic reset is not desired a manual reset may be substituted for the reset functionally provided by the three legged element, pendant arm 44 and dielectric stop 53.

FIGS. 6-l0 illustrate another embodiment of the present invention. Here, female terminal 60, which is adapted to be connected to motor run windings, is mounted to dielectric frame member 62. One end of flexible ribbon heater 64 is connected to conductive link 63 which link is electrically connected to terminal 60. A portion of the heater ribbon intermediate its ends is mounted to center leg 66 by a dielectric adhesive placing this portion in thermal contact but in electrical insulation with the center leg. The other end of the ribbon heater is both mechanically and electrically secured to bridge portion 68 of the three legged element. This bridge portion integrally joins a distal end of center leg 66 with the distal ends of two outer legs 70 of the three legged element. The proximal leg ends of the three legged element are secured to a spacer, not shown, which in turn is secured to dielectric frame projection 72 by rivets 74.

To dielectric frame member 62 is also mounted female terminal 78. Conductive support 80 is also mounted to the frame member and electrically connected to terminal 78 which terminal is adapted to be connected to a motor start winding. The proximal end of flexible, conductive pendant arm 82 is mounted to support arm 80. Motor start contact 84 is mounted to the distal end of flexible, pendant arm 82 in contact with double contact 86 which double contact is mounted to bridge portion 68 of the three legged element.

To dielectric frame projection 72 is also mounted a bifurcated, flexible conductive pendant arm 76 having an integral bridge portion 77 linking the distal ends of the bifurcated arm. Contact 88 is mounted to one side of arm bridge portion 77 in contact with double contact 86. A thin sheet of insulation 89 overlays the other side of the bridge portion. One end of bimetallic pivot 90 is also mounted to dielectric frame projection 72. To tab 92, which integrally projects from the other end of the bimetallic pivot, is secured one end of toggle spring 95. The other end of the toggle spring is secured to tab 96 which integrally projects from arm bridge portion 77.

Male terminal 98 is mounted to dielectric frame pro- 5 jection 72 in electrical contact with bifurcated pendant arm 76 and contact 88. This male terminal projects from the switch proper where it is accessible for electrical connection with a source of electric current. A second male terminal 99 is merely connected to female terminal 100.

A backing plate 102, which is an integral extension of terminal 98, is secured to dielectric frame projection 72 with bimetallic pivot and bifurcated pendant arm 76 sandwiched therebetween. Pendant arm 76, pivot 90 and backing plate 102 are welded together. Adjustment screw 105 is threaded through the backing plate into contact with pivot 90. Adjustment screw 107 is similarly threaded through support arm 80 into contact with flexible pendant arm 82. Bracket 108 is mounted to bridge portion 68 of the three legged element adjacent but in spaced relation about bridge portion 77 of pendant arm 76. An adjustable stop screw 110 is threaded through the bracket.

Although the basic operation is the same there are several distinguishing features of the embodiment shown in FIGS. 6-10 over that previously described which should be particularly noted. For example, pendant arm 44 in the former case is metallic whereas in the later embodiment pivot 90 is bimetallic with the layer of lower thermal expansion disposed facing the three legged element and the layer of higher thermal expansion facing backing plate 102. With this bimetallic construction the current required to cause separation of contact 88 from double contact 86 will decrease as ambient temperature increases. In the former embodiment motor start contact 34 was rigidly mounted to frame member 10 whereas in the latter described embodiment motor start contact 84 is flexibly mounted to the frame member. This configuration causes motor start contact 84 to engage double contact 86 and to build up mating contact force therebetween prior to engagement of motor run contact 88 with double contact 86 while the switch cools following separation of the three contacts. This in turn causes the motor run windings to be energizing only after motor start windings have been energized during switch recycling. It should also be noted that the circuitry in the two embodiments differ somewhat. In the former example both motor start and motor run winding current flows through center leg 26 of the three legged element causing it to heat and the element to pivot. In the latter example however only current from the motor run winding flows through ribbon heater 64. This is due to the fact that double contact 86 is connected to motor run windings in the latter described embodiment whereas double contact 28 is connected to a source of electric current in the formerly described embodiment. In addition, in the latter case an auxiliary heater is employed whereas in the former case the center leg itself functions as the heater.

It should be understood that the two described embodiments are merely illustrative of principals of the present invention. Many other modifications may, of course, be made thereto without departing from the spirit and scope of the invention as set forth in the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A switch control for an electric motor h aving start and run windings comprising a motor start contact, a movable double contact adapted to make and break contact with said motor start contact and to be electrically connected to a source of electric current, a motor run contact adapted to be electrically connected to the motor run winding and to make and break contact with said double contact, thermally responsive actuating means including an electrically conductive pendant arm to which said double contact is mounted for moving said double contact away from said motor start contact upon heating, snap acting toggle spring means mechanically coupled with said motor run contact to spring bias said motor run contact against said double contact when said pendant arm is below a predetermined temperature and to snap said motor run contact rapidly away from said double contact when said pendant arm is above said predetermined temperature, and stop means mounted to said pendant arm for limiting snap movement of said motor run contact away from said double contact.

2. A switch control in accordance with claim 1 wherein said electrically conductive pendant arm includes three mutually spaced legs and wherein said thermally responsive actuating means includes an electric heater mounted to one of said mutually spaced legs.

3. An electric motor switch control comprising a frame, a first contact mounted to said frame and adapted to be connected to a motor start winding, a second contact movably mounted to said frame and adapted to be connected to a motor run winding, an electrically conductive pendant arm adapted to move when electrically heated, said pendant arm being mounted to said frame and adapted to be connected to a source of electric current, said pendant arm comprising two arm end portions, three substantially parallel arm leg portions interconnecting said two arm end portions, and means for elevating the temperature of at least one of said leg portions with respect to the other of said leg portions, a third contact mounted on said pendant arm in position to make and break contact with said first contact upon movement of said pendant arm relative to said first contact, a fourth contact mounted on said pendant arm in position to make and break contact with said second contact upon movement of said second contact with respect to said pendant arm, and stop means mounted to said pendant arm for limiting movement of said second contact with respect to said fourth contact.

4. A switch comprising a frame, a first terminal mounted to said frame, a second terminal mounted to said frame, a third terminal mounted to said frame, a first contact electrically coupled with said first terminal, an electrically conductive flexible arm mounted to said frame and electrically coupled with said second terminal, a second contact mounted to said flexible arm, toggle spring means coupled to said flexible arm, a thermally responsive pendant arm mounted to said frame and electrically coupled with said third terminal, said pendant arm having a third contact mounted thereto to make and break contact with said first contact and having a fourth contact mounted thereto to said flexible arm towards said first contact as said thermally responsive pendant arm moves towards said first contact when cooled.

5. A switch in accordance with claim 4 wherein said thermally responsive pendant arm comprises a proximal end portion mounted to said frame, a distal end portion to which said'third and fourth contacts are mounted, and three spacially separated leg portions interconnecting said proximal and distal ends.

6. A switch in accordance with claim 5 including means for electrically elevating the temperature of at least one of said legs with respect to the other of said legs to cause said distal end portion to move with respect to said proximal end portion.

7. A switch control for an electric motor having start and run windings comprising a motor start contact adapted to be electrically coupled to the motor start winding, a motor run contact adapted to be electrically coupled to the motor run winding, a double contact adapted to be electrically coupled to a source of electric current, thermally responsive actuating means including an electrically conductive pendant arm upon which said double contact is mounted, said pendant arm being adapted to move along a predetermined path to make and break contact between said double contact and said motor start contact, snap acting toggle spring means mechanically coupled with said motor run contact to spring bias said motor run contact against said double contact when said pendant arm is located along a first portion of said predetermined path and to spring bias said motor run contact away from said double contact when said pendant arm is located along a second portion of said predetermined path, contact between said motor run contact and said double contact being broken when said pendant arm is located along said second portion of said predetermined path.

8. A switch control in accordance with claim 7 wherein said pendant arm comprises three spaced leg portions, and wherein said thermally responsive actuating means includes an electric heater mounted to one of said three spaced leg portions.

9. A switch control in accordance with claim 7 comprising a second electrically conductive pendant arm upon which said motor run contact is mounted and a dielectric stop mounted to said pendant arm upon which said double contact is mounted to limit movement between said pendant arm upon which said double contact is mounted and said second pendant arm upon which said motor run contact is mounted.

10. A switch control for an electric motor having start and run windings comprising a first contact adapted to be electrically connected to the motor start winding, a movable double contact adapted to make and break contact with said first contact and to be electrically connected to the motor run windings, a second contact adapted to be electrically connected to a source of electric current and to make and break contact with said double contact, thermally responsive actuating means including an electrically conductive pendant arm for moving said double contact away from said motor start contact upon heating, snap acting toggle spring means mechanically coupled with said motor run contact to spring bias said motor run contact against said double contact when said thermally responsive actuating means pendant arm is below a predetermined temperature and to snap said motor run contact rapidly away from said double contact when said thermally responsive actuating means pendant arm is above said predetermined temperature, and stop means mounted to said pendant arm for limiting snap movement of said motor run contact away from said double contact.

11. A switch control in accordance with claim 10 wherein said electrically conductive pendant arm includes three mutually spaced legs and wherein said thermally responsive actuating means includes an electric heater mounted to one of said mutually spaced legs.

12. A switch control in accordance with claim 10 comprising a flexible pendant arm to which said first contact is mounted.

13. An electric motor switch control comprising a frame, a first contact mounted to said frame and adapted to be connected to a motor start winding, a

second contact movably mounted to said frame and adapted to be connected to a source of electric current, an electrically conductive pendant arm adapted to move when electrically heated, said pendant arm being mounted to said frame and adapted to be connected to a motor run winding, said pendant arm comprising two arm end portions, three substantially parallel arm leg portions interconnecting said two arm end portions, and means for elevating the temperature of at least one of said leg portions with respect to the other of said leg portions, a third contact mounted on said pendant arm in position to make and break contact with said first contact upon movement of said pendant arm relative to said first contact, a fourth contact mounted on said pendant arm in position to make and break contact with said second contact upon movement of said second contact with respect to said pendant arm, and stop means mounted to said pendant arm for limiting movement of said second contact with respect to said fourth contact.

Claims

1. A switch control for an electric motor having start and run windings comprising a motor start contact, a movable double contact adapted to make and break contact with said motor start contact and to be electrically connected to a source of electric current, a motor run contact adapted to be electrically connected to the motor run winding and to make and break contact with said double contact, thermally responsive actuating means including an electrically conductive pendant arm to which said double contact is mounted for moving said double contact away from said motor start contact upon heating, snap acting toggle spring means mechanically coupled with said motor run contact to spring bias said motor run contact against said double contact when said pendant arm is below a predetermined temperature and to snap said motor run contact rapidly away from said double contact when said pendant arm is above said predetermined temperature, and stop means mounted to said pendant arm for limiting snap movement of said motor run contact away from said double contact.

4. A switch comprising a frame, a first terminal mounted to said frame, a second terminal mounted to said frame, a third terminal mounted to said frame, a first contact electrically coupled with said first terminal, an electrically conductive flexible arm mounted to said frame and electrically coupled with said second terminal, a second contact mounted to said flexible arm, toggle spring means coupled to said flexible arm, a thermally responsive pendant arm mounted to said frame and electrically coupled with said third terminal, said pendant arm having a third contact mounted thereto to make and break contact with said first contact and having a fourth contact mounted thereto to make and break contact with said second contact, at least a portion of said thermally responsive pendant arm being adapted to move with respect to said first contact when heated, and a trip dog mounted to said thermally responsive pendant arm to engage and move said flexible arm towards said first contact as said thermally responsive pendant arm moves towards said first contact when cooled.

5. A switch in accordance with claim 4 wherein said thermally responsive pendant arm comprises a proximal end portion mounted to said frame, a distal end portion to which said third and fourth contacts are mounted, and three spacially separated leg portions interconnecting said proximal and distal ends.

13. An electric motor switch control comprising a frame, a first contact mounted to said frame and adapted to be connected to a motor start winding, a second contact movably mounted to said frame and adapted to be connected to a source of electric current, an electrically conductive pendant arm adapted to move when electrically heated, said pendant arm being mounted to said frame and adapted to be connected to a motor run winding, said pendant arm comprising two arm end portions, three substantially parallel arm leg portions interconnecting said two arm end portions, and means for elevating the temperature of at least one of said leg portions with respect to the other of said leg portions, a third contact mounted on said pendant arm in position to make and break contact with said first contact upon movement of said pendant arm relative to said first contact, a fourth contact mounted on said pendant arm in position to make and break contact with said second contact upon movement of said second contact with respect to said pendant arm, and stop means mounted to said pendant arm for limiting movement of said second contact with respect to said fourth contact.