US2197200A - Switch - Google Patents

Description

April 16, 1940. c. J. WERNER SWITCH Filed Oct. 21, 1936 2.Sheets-Sheet l April 16 1940. c. J.- WERNER SWITCH Filed Oct. 21, 1936 2 Sheets-Sheet 2 Ina uuztlom W Insulation Patented Apr. 18, 1940 UNITED STATESLPATENT OFFICE- SWITCH Werner, Dayton, Ohio, assignor to General 'Motors Corporation, Detroit, Mich, a corporation of Delaware Application October 21, 1936, Serial No. 106,723 x 20 Claim.

This invention relates to a thermal responsive switch, and more particularly to such a switch adapted toprotect an energytranslating device from damage due to overheating.

An object of this invention is to provide a switch for protecting an energy translating device from overheating, which switch can be easily and cheaply manufactured and which cannot have the purpose thereof defeated by the user by u securing the actuating member in some fixed position. This object is accomplished by providing a switch structure comprising a small= number of inexpensive parts, including a thermal responsive latch, that are easyto' assemble l. and by so constructing and arranging theparts that the switch actuating member holds the' switch contacts apart while force is applied thereto to actuate the contacts, whereupon the con tacts engage upon release of the force-applied to the actuating member and whereupon one of the'contact members is free of the actuating member upon such release of the pressure applied thereto, so that when the thermal responsive latch releases the said one contact member, the contacts are disengaged irrespective of the position of the acuating member.

Another object of this invention is to provide a thermal responsive switch for protecting an energy translating device, which switch is adapted a to receive heat from the energy translating device by virtue of being mounted in heat ,receiving ,relation, therewith and which is adapted to be -provided with 'means adaptable to the energy translating device and the protection desired foradditionally influencing the operation of the switch. This object is accomplished by providing a thermal responsive locking structure that is adapted to have a heating element such'as a resistance wire associated therewith and/or a heat conducting element for/conducting heat from apart of the energy translating device to the thermal responsive locking structure.-

Further objectsand advantages of the present invention will be apparent from the following de-' scription, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown. In the drawings: I Fig. 1 is a fragmentary view of 'a dynamo electric machine equipped with one form,of thermal protective device embodying the present invention, said device belngbroken away to show the interior thereof. The heater element has been omitted for the sake of clearness. r j .i 'igs. 2, 3 and 4 are views of the thermal protective device minus-its heater element, with parts thereof shown in different positions of operation. These views show the device with the cover removed and looking in the direction of arrow 2 ,of Fig. 1.

invention different in some details from that shown in Fig. '1. a

Fig. 5 is a view taken in the direction of arrow '5 of Fig. 4 inverted, however, and with the heater element attached.

arrow 6 of Fig. 5.

I Fig. 7 is a sectional view on the line l 'l of mg 5 Y Fig, 8 is a sectional view taken on line 8-8 of Fig. 1 and turned through an angle of 90.

Figs. 9 and 10 are perspective views of a modifled form of switch embodying the present invention and indicateone operating position ofthe switch parts as viewed from substantially opposite sides of the switch. a

' Figs. 11 and 12 are also perspective views of the r apart Fig. 6 is a view taken in the direction of the Figs. -2, 3 and 4 show a form of the l2 has. slots i6 and I8 in one end thereof in which a resilient switch arms 20 and 22 respectively areanchored. Connebtoriugs 24 and 26 that are preferably integral with the switch arms 20 and 22 respectively, extend outwardly from the housing i2 for making electricalconnections to the switch arms. .The switch arms 20 and 22 extend into the housing i2, out of contact with the walls thereof, and have contacts 28 and 30 respectively mounted thereon in alignment for engagement.

The switch arms 20 and 22 are normally biased to positions, substantially as indicated inFlg. 2, such that the contacts 2-8- and '30 are out of engagement. The switch arm 20 is preferably longer than the switch arm 22, sothat it extends beyond the end of the switch arm 22; the switch arm 20 having a pawl 32 provided thereon, preferably by bending the end of the arm 20 in substantially the form of a hook. The switch arms 20 and 22 have lugs 34 and 36 respectively on the sides thereof which are preferablyintermediate the ends of the switch arms. Resilient reinforcleaf springs 36 and 46, preferably made of spring steel and that are substantially the same shape as the switch arms 26 and 22 respectively, but somewhat shorter than the switch arms, extend along one side of those portions of the switch arms that are subject to iiexure, and are anchored inthe slots I6 and I8 in the end of the housing. These leaf springs 38 and 46 have lugs 4I and 43 thereon that correspond to and are in alignment with the lugs 34 and 36 on the switch arms. The switch arms 26 and 22 and the reinforcing strips 36 and 46 each have lugs such as those indicated at 42 and 46 thereon which fit into cooperating recesses 44 and 41 respectively in the housing I2 to aid in the anchoring of the switch arms and reinforcing springs.

A tubular stud 46 extends through the housing I2 and fits an opening 46 in one wall of the housing. A ratchet wheel 66 is rotatably mounted on the stud 46, and is normally held stationary with respect to the stud by a layer of solder or other similar bonding material at 62 intermediate the stud and ratchet wheel, which fusible material fuses or melts at a temperature abnormal to the energy translating device with which the switch is used. The stud 46 and ratchet wheel 56 are located in position for latching engagement with the pawl 32 when the switch arm 26 is flexed toward the switch arm 22. Figs. 1 to 7 inclusive indicate the preferable form of switch for use when it is desirable to have the switch responsive to current flow through a winding of the energy transferring device with which it is used. A resistance wire heater element 64 has one end anchored in an opening 56 at one end of the stud, and extends substantially axially through the hollow stud. This heater element 64 is connected into the circuit of the energy translating device by a connecting lead 51 which is electrically connected to the end of the stud 46 and preferably soldered thereto, as at 56, and is also connected to the connector lug 24 by soldering, as at 66. In the Figs. 1 to 4 the heater element 54 has not been included for the purpose of simplifying the drawings. This heater, however, is shown in Figs. 5, 6 and 7.

In a modified form of the switch, such as that shown in Figs. 1 and 8, where it is desired to have the switch responsive to the temperature of the windings of the energy translating device for which it is used and to omit the heater element 54, an angular plate 62 of heat-conducting material, such as copper, preferably has the stud 46 extruded from one side thereof and integral therewith to provide high heat conductivity from the plate to the stud. This plate 62 extends along one side of the-housing and is preferably mounted against the winding of the energy translating device, substantially as indicated in Fig. 1, for conducting heat from the winding to the stud. In either case, the stud preferably extends through an opening 66 in the cover I4 and is riveted over, as at 66, to hold one end of the cover I4 in place. Y A manually operable actuating member I6 extends through an opening I2 in the housing I2.

This actuating member 16 has openings I4 and 76 therein, into which the lugs 64 and 36 re-' spectively, extend. In order to have trip-free operation of the switch, the opening I4 is preferably larger than the opening'16. That is. these openings are preferably of such size and so spaced that when force is applied to the actuating member I6 which moves that actuating member and the switch arm 26 to the left, as viewed in Figs. 2, 3 and 4 the contacts 26 and 66 are held apart by virtue of the spacing of the surfaces 16 and I5 of the openings I4 and 16 respectively, and the normal bias of the switch arms 26 and 22 and substantially as illustrated in Fig. 3. Further, when the pawl 62 engages the ratchet 66 to hold the switch arm 26 in a flexed position, the switch arm 22 biases the actuating member to the right as viewed in Fig. 3, so that when the pressure on the actuating member III is released, the bis of the switch arm 22 against the surface I6 effectsmovement of the actuating memberfin the direction of the bias, which movement effects engagement of the contacts. This movement of the actuating member that occurs responsive to the bias-of the switch arm 22 to effect engagement of the contacts provides a space between the surface I6 of the opening I4 and the lug 64, substantially as indicated in Fig. 4. Hence, when the fusible material that holds the ratchet wheel 66 stationary with respect to the stud 46 melts, and the contacts 26 and 36 are engaged, the switch arm 26 is free of the actuating member I6, so that the bias of the switch arm 26 turns the ratchet wheel 66 on the stud 46 to release the pawl 62 from the ratchet wheel 66 and eifect disengagement of the contacts 26 and 36.

As previously explained, the stud 46 is riveted at 66 to hold one end of the lid I4 in place. The other end of the lid is held by a rivet or other suitable fastening means I6 that extends through an opening 66 in the housing l2 and through an opening 62 in the lid I4 and which is riveted at 63.

As illustrated in Fig. 1, the switch is adapted to be mounted-in heat receiving relation to an energy translating device 64 having a frame or housing 66 and an end head 66. The switch I6 is secured or tied therein in such a position that the heat conducting plate 62 is against the end turns 61 of the windings of the energy translating device and the actuating member I6 extends outwardly through an opening 66 in the end head. Theactuating member is thus accessible from the cut side of the energy translating device for manual resetting of the switch to contact closed position. A bezel 96 is preferably provided around the opening 66.

It is understood that when desirable for use with a particular form or type of energy translating device, the heat conducting plate 62 can be used in conjunction with a heating element such as 54. heating element 54 is preferably mounted within the housing of an energy translating device in such a position that it is influenced by heat from the energy translating device.

With particular reference to Figs. 9 to 13 inclusive, similar reference numerals refer to similar parts. In this form of switch, a base I66 of any suitable insulation material, has switch arms I62 and I64 secured thereto by rivets I66 and I68 respectively, or other suitable fastening means. The ends of the switch arms I62 and I64 that are secured to the base I66 are preferably separated, and the switch arms preferably extend angularly toward each other so that the free ends thereof are near one another. An angular contact member III having a contact portion II2 that extends toward the switch arm I64 is secured to an end portion II4 of the switch arm I62 by a rivet H6 or other suitable fastening means. The portion II4 of the switch arm However, a switch incorporating the I02 is angularly disposed with respect to the rest of the switch arm. A stud H is secured to an angularly disposed end I of the switch arm I04 by riveting the end of the stud at I22. A shoulder I24 on the stud II8 engages the side of the portion I20 of the switch arm I04 opposite the riveted portion I22 of the stud. The

stud H8 is preferably hollow, and has a contact support I26 secured in an opening, I28 in the end portion I30 of the stud opposite the riveted end thereof, so that the contact support I26 extends through the hollow stud substantially coaxially therewith and projects from the end thereof. This contact support I26v is made of resistance material and provides a heating element when it is desired to have the stud heated in accordance with the current flow through the switch. If such heating is not desired, the stud is made of a material of higher conductivity. A contact I32, preferably having a substantially circular contact surface is secured to the projecting end of the contact support I26 in alignment for engagement with the contact H2. The switch arms I02 and I04 are preferably inherently resilient and are so biased that the contacts H2 and I32 are normally out of engagement.

A ratchet wheel I34 is rotatably mounted on the outer surface of the stud H8. and is normally bonded to the stud and held in a fixed position relative thereto by a layer of fusible material I36 that is preferably intermediate to the stud H0 and the ratchet wheel I34. This fusible material, such as solder, melts at a temperature abnormal for the device with which the switch is used, and which the switch protects. An arm I38 which is preferably integral with the switch arm I04 is bent at the end thereof to provide a pawl I40 which engages the ratchet wheel I34 to hold the switch arm I04 in a flexed position such that the contacts H2 and I32 are engaged. The arm I38 is preferably integral with the switch I04 so that the switch arm I04 and the arm I38 cannot turn relative to each other to effect disengagement of 'the pawl from the ratchet wheel due to causes such as vibration. When the fusible material is melted by excessive heat, the normal bias of the switch arm I04 effects a turning movement of the ratchet wheel I34 on the stud H8 and a consequent release of the ratchet wheel from the pawl I40, whereupon the switch arms assume positions substantially as indicated in Figs. 9 and 10.

A manually operable actuating member I42 is slidably mounted adjacent the switch arms I02 and I04 in a suitable support such as that indicated at I44 which may be the end frame of a dynamo electric machine. The actuating member I42 is movable toward or away from the switch arms I02 and I04, and has a flange portion I46 which acts as a stop to prevent the actuating member from coming out of the support I44 and is sufficiently large to engage both of the switch arms I02 and I04. 1

Upon movement of the actuating member I42 toward the switch arms I02 and I04, and the continued movement thereof in that direction, the flange I46 engages the arms I02 and I04 to effect movement of both of the arms against the normal bias thereof The arm I04 is thus moved to such a position that the pawl I40 engages the ratchet wheel I34 to prevent return movement of the switch arm I 04. By virtue ofthe differences in distances between the contacts H2 and I32 and the parts of the arms I02 and I04 respectively which engage the flange I44, the contacts 2 and I32 are held apart as long as sufficient force isapplied to the actuating member I42 to overcome the bias of the arm I02. That is, by movement of the actuating member I42 which effects engagement of the ratchet wheel I34 with the pawl I40, the switch arm I02 moves to a position such as that indicated in solid lines in Fig. 11. Upon release of the pressure upon the actuating member I42, so that the contact arm l02 moves the actuating member in the direction of the bias of that arm, the arm I02 and actuating member I42 return to a position such as that indicated by the dot-and-dash lines in Fig. 11; whereupon the contacts engage as indicated in Fig. 12. When the contacts are in engagement, there is suflicient space between the switch arm I04 and the flange I46 that the arm I04 is free of the actuating member and disengagement of the contacts will follow a release of the ratchet wheel from the pawl,

Both of the forms of the switches disclosed herein are similar in principle and operation; and both are adapted to be mounted in heat receiving relation to an energy translating device, such as a dynamo electric machine, so that the' fusible material that normally holds the ratchet wheel in place is melted by excessive heat from the energy translating device. That is, each of the switches is adapted to be mounted, for instance, within the end frame of the motor, so that the actuating member extends thru the switch cannot be defeated by tying or sec'ur-' ing the actuating member in any position. Sufficient force applied to the actuating member of either of the forms holds the contacts apart. When sufficient force is applied to the actuating member, one switch arm, in each case, is, locked I in a substantially fixed position by engagement of the pawl and ratchet wheel while the contacts are held apart. pawl and ratchet wheel, the release of the force applied to the actuating member permits a return movement of the actuating member and one of the switch arms by virtue of the bias of that latter mentioned switch arm. until tliecontacts engage. The portion of the actuating member which engages the locked switch arm having moved away from the locked switch arm during After the engagement of the the return movement effected by the bias of the other switch arm, a clearance is provided between the locked switch arm and the actuating member which is sufficient to permit separation of the contacts upon release of the pawl from the ratch et wheel. It is thus clear that securing the actuating member in some positions will hold the conit is to be understood that other forms might be adopted, all coming within the scope of the claims device; means engaging the ratchet wheel to hold the arms in contact engaged position against the normal biasing force of the arms; a manually operable actuating member for moving one of the arms to contact engaged position, said actuating member holding the arms apart so that the contacts cannot engage while manual force is applied thereto.

2. A thermal responsive switch for the protection of an energy translating device comprising, in combination, a base; a pair of switch arms each having one end anchored to the base and each having a contact thereon in alignment for engagement with the contact on the other arm, said arms being normally biased to positions such that the contacts are disengaged; a locking element; means movably supporting the locking element, said locking element being normally held stationary by a material that is fusible at an abnormal temperature of the energy translating device; means engaging the locking element and adapted to hold the arms in contact eng ged p sition against the normal biasing force oi. the arms; a manually operable actuating member for effecting engagement of the last mentioned means with the locking element, said actuating member holding the arms apart during movement toward engagement of said locking element with the last mentioned means and until said actuating elementis effectively released, one of said arms being free to move from the contact engaged position upon release of said means from the locking element even when the actuating element is held in any position which permits engagement of the contacts.

3. A thermal responsive switch for the protection of an energy translating device comprising, in combination, a base; a pair of switch arms each having one end anchored to the base and each having a contact thereon in alignment for engagement with the contact on the other arm, said arms being normally biased to positions such that the contacts are disengaged; a stud in heat receiving. relation with the energy translating device, a ratchet wheel mounted on said stud and adapted to rotate with respect thereto, said ratchet wheel being normally prevented from rotation with respect to the stud by a layer of material intermediate the stud and ratchet wheel that is fusible at an abnormal temperature; a pawl adapted to engage the ratchet wheel to hold one of the arms against movement in the direction of the normal bias thereof; a manually operable actuating member for moving the said one of the arms to eilfect engagement of the pawl and ratchet wheel, said actuating member holding the arms apart while force is applied thereto sufficient to overcome the bias of one or both of said arms, said contacts engaging upon release of the actuating member, and said contacts breaking upon fusing of said material and resulting release of'said one of the arms regardless of the position of the actuating member within the limits of movement thereof which permit engagement of the contacts.

4. A thermal responsive switch for the protection of an energy translating device comprising, in combination, a base;' a pair of switch arms each having one end anchored to the base and each having a contact thereon in alignment 1 for engagement with the contact on the other 7 arm, said arms being normally biased to positions such that the contacts are disengaged; a stud in heat receiving relation with the energy translating device, a ratchet wheel mounted on 1 said stud and adapted to rotate with respect thereto, said ratchet wheel being normally pres vented from rotation with respect to the stud wheel, said-actuating member holding the arms I apart while force is applied thereto suiiicient to overcome the bias of one or both or said arms, said contacts engaging upon release of the actuating member, and said contacts breaking upon fusing of said material and the resulting 112- I lease of said one of the arms regardless of the position of the actuating member within the limits oi movement thereof which permit engagement or the contacts.

5. A thermal responsive switch for the protec- 4 tion of 'an energy translating device comprising, in combination, a base; a pair of switch arms each having oneend anchored to the base and each having a contact thereon in alignment for engagement with the contact on the other arm,

said arms being normally biased to positions such that the contacts are disengaged; a stud in heat receiving relation with the energy translating device, a ratchet wheel mounted on said stud and adapted to rotate with respect there- I to, said ratchet wheel being normally prevented from rotation with respect to the stud by a layer of material intermediate the stud and ratchet wheel that is fusible at an abnormal temperature; a heating element comprising a resistance wire for imparting heat to the stud in addition to that received from the energy translating device, by virtue of being in heat receiving relation therewith, a pawl adapted to engage the ratchet wheel to hold one of the arms against movement in the direction or the normal bias thereof; a manually operable actuating member for moving the said one of the arms to eii'ect engagement of the pawl and ratchet wheel, said actuating member holding the arms apart while 1 force is applied thereto suiiicient to overcome the bias of one or both or said arms, said contacts engaging upon release of the actuating member, and said contacts breaking upon fusing of said material and the resulting release 7 of said one oi the arms regardless of the position of the actuating member within the limits of movement thereof which permit engagement of the contacts.

6. A thermal responsive switch for the protection of an energy translating device comprising, in combination, a base; a pair of switch arms each having one end anchored to the base and each having a contact thereon in alignment for engagement with the contact on the other am, said arms being normally biased to positions such that the contacts are disengaged; a stud secured to the base; a locking element movably mounted on the stud and normally held in one position by a layer of fusible material intermediate the stud and locking element; one of said arms having a pawl thereon adapted to engage the locking element to hold the arm againstmovement in the direction of the biasing force of the arm; a manually operable actuating member for effecting engagement of the pawl and locking element to hold the contacts in engaged position, said actuating member engaging both of the arms to hold them apart during movement in the direction effecting engagement of the pawl and locking element; the other of said arms being biased to effect engagement of the contacts upon release of the actuating member, the said one of said arms being free of the actuating member to move upon release of the pawl when the contacts are engaged.

7. A thermal responsive switch for the protection of an energy translating device comprising in combination, a base; a first switch arm anchored at one end and having a contact mounted near the other end thereof; a second switch arm anchored at one end and having a contact mounted near the other end thereof, said contacts being in alignment for engagement and said arms being normally biased to positions such that the contacts are out of engagement; a stud; a ratchet wheel rotatably mounted on the stud and normally bonded to the stud by a layer of fusible material; means engaging the ratchet wheel to hold the first switch arm against the normal bias thereof, the

being free of the actuating member upon engagement of the contacts.

8. A thermal responsive switch for the protection of an energy translating device comprising in combination, a base; a first switch arm anchored at one end and having a contact mounted near the other end thereof; a second switch arm anchored at one end and having a contact mounted near the other end thereof, said contacts being in alignment for engagement and said arms being normally biased to positions such that the contacts are out of engagement; a stud secured to the base; a ratchet wheel rotatably mounted on the stud and normally bonded to-the stud by a layer of fusible material; a pawl on the end of the first arm adapted to engage the ratchet wheel to hold the first switch arm against the normal bias thereof; the second switch arm being biased to effect engagement of the contacts when the pawl engages 'the ratchet wheel; a manually operable actuating member adapted to move the first arm to a position of engagement of the pawl with the ratchet, said actuating member engaging the second arm during movement of the first arm toward engagement of the pawl with the ratchet to hold said arms apart, said second arm being biased to effect engagement of the contacts upon release of the actuating member, said first arm being free of the actuating member when the contacts are engaged.

9. A thermal responsive switch for protecting an energy translating device from damage due to excessive heat comprising, in combination, a base; a first switch arm anchored at one end and having a contact mounted at the other end thereof; a second switch arm anchored at one end and having a contact mounted at the other end thereof in alignment for engagement with the contact on the first arm, said arms being normally biased to positions such that the contacts are out of engagement; a stud secured to one of the arms; a ratchet wheel rotatably mounted on the stud and normally bonded to the stud by a layer of material that is fusible at an excessive temperature of the device; means engaging the ratchet wheel to hold the said one switch arm against the normal.

bias thereof and in a position such that said contacts are biased into engagement; a manually operable actuating member adapted to effect ening an energy translating device from damage due to excessive heat comprising, in combination, a base; a first switch arm anchored at one end and having a contact mounted at the other end thereof; a second switch arm anchored at one end and having acontact mounted at the other end thereof in alignment for engagement with the contact on the first arm, said arms being normally-biased to positions such that the contacts are out of engagement; a stud secured to the first arm; a ratchet wheel rotatably mounted on the stud and normally bonded in a fixed position by a layer of material that is fusible at an excessive temperature of the device; a pawl adjacent the first arm for engaging the ratchet to hold the first arm against the normal bias thereof and in a position that the second arm biases the contacts into engagement; a manually operable actuating member adapted to effect engagement of the. ratchet with said pawl, said arms and actuating member being so constructed and arranged that the contacts are held apart by force exerted upon the actuating member, said first arm being free to move with respect to the actuating member to effect disengagement of the contacts when the saidmaterial fuses at an excessive temperature.

11. In a thermal responsive switch, asubassembly comprising, in combination, a resilient of the switch arm, a ratchet mounted on the stud and adapted to rotate with respect thereto, said ratchet being normally prevented from rotation .withrespect to the stud by a layer of material intermediate the stud and ratchet that is fusible at abnormal temperature, an arm integral with the substantially stationary portion of the switch arm and having a pawl thereon adapted to engage the ratchet to hold the switch arm against the normal bias thereof. 13. In a thermally operated switch, a pair of resilient contact arms normally biased to open circuit position, a thermally responsive ratchet mounted on one of said arms and adapted to latch the other arm theretoso that the latched arm forms a closed circuit, said thermally responsive ratchet upon obtaining a predetermined temperature releasing the arms so that they may assume an open circuit position.

14. In a thermally operated switch, a pair of resilient contact arms biased to open circuit position, a thermally responsive ratchet carried by one of said arms, latching means adapted to engage the ratchet so that the contact arms are held in closed circuit position, said ratchet upon obtaining a predetermined temperature disengaging from said means and releasing the arms so that the arms assume an open circuit position.

15. In a thermally'operated switch, a pair of resilient contactarms biased to open circuit position, a thermally responsive ratchet carried by one of said arms, latching means adapted to engage the ratchet so that the contact arms are held in closed circuit position, said ratchet upon obtaining a predetermined temperature disen-' gaging from said means and releasing the arms so that'the arms assume an open circuit position, and means for resetting the arms in closed circuit position after release.

16. In a thermal responsive switch, a spring terminal member, and a spring contact member. said members being normally biased to open circuit position, thermal means carried by the terminal member including a portion adapted to engage the contact member and to latch the contact member and the terminal member in closed circuit position, said thermal means being adapted to release said members so that they may assume an open circuit position upon the attainment of a predetermined temperature, and an operating member for resetting said contact member and said terminal member in closed circuit position, said operating member being adapted to open circuit the contact member and the terminal member at will when said members are in latched relation.

17. In a thermally operated switch, a pair of resilient contact arms normally biased to open circuit position, thermally responsive means carried by one of said arms and adapted to latch the other arm thereto so that the biased arms form a closed circuit, said means upon obtaining a predetermined temperature releasing the arms so that they may assume open circuit position.

18. A circuit breaker comprising two cooperating' contact blades normally biased to circuit open position; an actuator engaging both of said blades and adapted to move both blades simultaneously out of normal position while maintaining them separated; a detent; thermal means carried by the one blade and adapted to engage the detent to retain said one blade in actuated position, said means being adapted also to release the said one blade at a predetermined temperature; and means on the second blade for engaging the retained blade when the actuator is released.

19. A circuit breaker comprising two flexible contact blades normally biased to circuit open position; a detent formed integrally with one of said blades; a thermally responsive ratchet carried by the second blade and adapted to engage the detent to retain said second blade in an actuated position below a predetermined temperature; and an actuator adapted to engage both of said blades and to move both blades simultaneously while holding them separated, the said one blade being adapted to engage the retained second blade only when the actuator is released after being operated.

20. A circuit breaker comprising two flexible contact arms normally biased to circuit open position; an actuator, engaging said arms and adapted to move both simultaneously out of normal position while maintaining them separated, and thermal means on one of said arms adapted to engage a portion of the other arm to provide ior engagement of both of said arms when the actuator is released.

CALVIN J.

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