US2209848A - Automatic circuit breaker - Google Patents

Description

July 30, 1940. v SACHS 2,209,848

AUTOMATIC CIRCUIT BREAKER Filed Feb. 27, 1939 Invent 0r c/bsgpfz Sachs Patented July 30, 1940 UNITED STATES PATENT OFFlC Joseph Sachs, West Hartford, Com, asslgnor to Colts Patent Fire Arms Manufacturing Company, Hartford, Conn., a corporation of Connecticut Application February 27, 1939, Serial No. 258,700

19 Claims.

This invention relates to a circuit breaker of the general type disclosed in my reissued Patent No. 20,018 and in my Patent No. 1,811,970, each entitled Automatic'circuit breaker. The general object of the present invention is to provide a circuit breaker of the type disclosed having two separate movable contact members at least one of which moves to open and close the circuit for ordinary switching purposes, one of the said members being movable independently of the other to break the circuit upon the attainment of excess current conditions therein. In accordance with the invention, one of the contact members is manually operable and provided with at least one contact and the other contact member is biased for independent circuit opening movement and is provided with at least one contact which, when in closed-circuit position, engages with the corresponding contact of the first contact member. When both members are in closed-circuit positions one of the movable contacts also engages with a corresponding stationary contact, the circuit thus extendingthrough all three contacts.

For ordinary switching purposes at least one contact member is moved and preferably the two contact members move in unison, the contact of one of the members being disengaged from and engaged with one of the other contacts; but upon the attainment of excess current conditions the member other than that connected with the manually operable means is released from the remaining member and moves independently thereof to open-circuit position, its movable contact being disengaged from at least one of the other contacts.

In the accompanying drawing I have illustrated one suitable embodiment of the invention, but it will be understood that the drawing is intended for illustrative purposes only and is not to be construed as defining or limiting the scope of the invention, theclaims forming a part of this specification being relied upon for that purpose.

Of the drawing:

F g. 1 is a front view of a circuit breaker embodying the invention, the front cover being omitted. The movable parts are shown in closedcircuit positions.

Fig. 2 is a side view of the circuit breaker as shown in Fig. 1, the front cover being included.

Fig. 3 is a bottom view of the circuit breaker as shown in Fig. 1.

Fig. 4 is a vertical sectional view taken along the line 4-4 of Fig. 1, but showing the movable parts in open-circuit positions.

Fig. 5 is a view similar to Fig. 4, but showing the parts in the positions which they assume when the circuit is opened automatically.

Referring to the drawing, I and 2 represent two transversely spaced parallel insulating plates which constitute the main framework of the cir-. cuit breaker. These plates are mounted upon or connected with a main rear base 3 and for this purpose there are provided near the top and bottom ends ofthe plates two transversely extending brackets. 4 and 5 having forward projecting ears 4* and 5 to which the plates I and 2 are riveted. Plates 6 and I are brazed or otherwise connected with the brackets 4 and 5 at the rear thereof and screws 8 and 9 extend forward through plates 6 and I and the brackets 4 and 5 to hold the said brackets and also the plates I and 2 in fixed relationship with the base. At the front of the plates I and 2 is a cover plate I0 held in place by screws II II which are threaded into angle brackets I2, I2 carried by the plates I and 2. The base 3 is provided with holes 3, 3 for receiving screws by which the base may be secured to the rear wall of anenclosing casing or to any other suitable support.

The circuit breaker is provided with at least one stationary contact and preferably two separate contacts constituting a pair. As shown, there are two contacts I3 and carried respectively by the side plates I and 2. Each of these contactshas a head at the inner side of the corresponding side plate and has a shank which projects through a circular hole in the plate. Connected with the respective contacts are conductors I5 and I6 which resiliently hold the contacts and tend to move them inward. The resilient conductor I5 is held by a rivet II extending through the plate I and this rivet also engages a. conductor I8 which electrically connects the conductor IS with the bracket 4, the connection with the bracket being effected by means of a rivet IS. A nut 20 on the screw 8 cooperates with the bracket 4 to constitute a wire terminal. It will be apparent that electrical connection is established from the ter. minal 20 through the bracket 4, the conductor I8 and the conductor 1 5 to the stationary contact I3.

The resilient conductor I 5 is held by a rivet 2I which directly engages the bracket 5. A nut 22 on the screw 9 cooperates with the bracket 5 to constitute a wire terminal. Electrical connection is established from the wire terminal 22 through the bracket 5 and the conductor I6 and the stationary contact I4.

Two separately movable contact members are provided and in the construction shown, these are positioned between the two main frame moving pivotally. The contact members are 5 supported on a transverse pivot pin 28 which extends transversely between the two side platesl and -2. Thesaid contact members preferably comprise insulating plates and as shown each of them comprises two separate plates spaced apart transversely. One of the members which I will designate as the-first contact member, is operable under manual control and is provided with at least one and preferably two contacts or contact faces, the said contacts or contact faces being electrically connected with each other. The other member which I will designate as the second contact member has one and preferably two contact elements or contacts each adapted when the circuit is closed to engage the corresponding contact face on the first contact member and also the corresponding stationary contact.

In the construction as shown, there are four parallel insulating plates 24. 25, 25 and 21 all mounted on the before mentioned transverse pivot pin 23 and held in proper spaced relationship by bushings on the pin. The plates 25 and 21 constituting a portion of the second contact member are movable in planes between the stationary contacts l3 and I4, and the plates 24 and 25 constituting a portion of the first contact member are movable in planes between the planes of the plates 25 and 21.

I The first contact member is movable under manual control. As shown, there is an operating member or handle 28 which is mounted on the pin 23 betweenthe plates 24 and 25, the handle or operating member having hubs with square or otherwise non-circular end portions 28 which project into similarly shaped openings in the plates 24 and 25 so that the operating member and the plates move in unison. The front portion of the handle or operating member projects through a. suitable opening in the front cover II. The plates are provided with fiat portions such as 25', 25' at angles to each other which are engaged by a bifurcated spring 25 carried by a bracket 30 which extends transversely between theside plates l and 2. This spring by reason of its engagement with the fiat portions of the side plates serves to hold the first contact member either in the closed-circuit position as shown in Figs. 2 and 5 or in the open-circuit position as shown in Fig. 4. Movement of the first contact member in the clockwise direction is limited by the stop pin 3| extending transversely between the side plates l and 2, and

-movement of the first contact member in the counter-clockwise direction is limited by the stop pin 22 extending transversely between the side plates I and 2.

- The plates 24 and 25 of the first contact member are connected with each other and held in proper relationship not only by the operating member as already described but also by a transverse spacing rod 33 and by a transverse insulating bar 24. The plates 24 and 25 carry two movable contacts 35 and 35 each of which has a circular head at the outer side of the corresponding plate and a smaller shank which ex tends through a. hole in the plate. Each shank is flattened at one side and the hole is correspondingly shaped to receive the flattened shank to prevent rotation thereof.

The plates 25 and 21, constituting a portion .correspondingly shaped holes in the respective plates. The two plates '24 and 25 of the first contact member are notched or recessed at 24,

25 to provide clearance for the cross bar 31, The two plates 25 and 21 respectively carry movable contacts 35 and II which are shown as being U-shaped pieces of metal each of which extends through the corresponding plate to provide contact faces at both sides thereof. While each of the contacts 35 and 25 is shown as comprising a single metallic element, it will be understood that this is not essential so long as there-are two contact faces electrically; connected with each other. Springs 40 and 4| surround the bushings on the pin 23 and engage the plates 25' and 21 and also the-main side plates I and 2. These springs servevto bias the second contact member for movement in the clockwise or circuit-opening direction.

The first and second contact members are separately movable but preferably they are normally mechanically connected with each other for movement in unison, the connection being electro-responsively releasable so that the second contact member can be released from the] first upon the attainment of excess current conditions in the circuit I prefer to provide a thermally responsive bi-metallic element which serves as a part of the mechanical connection, and this may advantageously be a U-shaped bi-metallic strip or latch 42 carried by the first contact member and electrically connected between the contacts 25 and 36. The U-shaped bl-nietallic latch 42 has the end portions of its legs connected respectively with the shanks of the contacts 35 and 38. Rivets 42 and 44 extend through the contact shanks and through the legs of the U-shaped latch and also through the transverse insulating bar 24 to hold all of these parts in fixed relationship. Cooperating with the latch 42 is a retaining element 45 which projects from the cross bar 31 of the second contact member, this being in such position as to normally engage the latch 42 as shown in Fig. 2. The retaining element 45 is' beveled to facilitate re-engagement with the latch 42 after the parts have been disengaged.

Figs. 1, 2 and 3 show the movable parts of the circuit breaker in their normal closed-circuit positions. Electrical connection is established from the stationary contact t 7 through the movable contact 38 to the movable the contact 35 the circuit extends through the bi-metallic latch 42 to the contact 36. From the contact 35 the circuit extends through the movable contact 39 to the stationary contact l4.

By means of the operating member or handle 25, one movable contact member is movable to disengage each movable contact thereon from or engage it with its immediately adjacent contact and thus open or close the circuit. The other movable contact member is movable independently of the member first mentioned upon the attainment of abnormal current conditions in the circuit, the circuit in this instance being opened by the disengagement of one movable contact from the other.

Preferably the two contact members are normally mechanically connected by means of the latch 42 and the retaining element 45 so that they can move in unison under the control of the operating ntact 35. From member or handle 2|. when the handle is moved from the closed-circuit position shown in Fig. 2 to the open-circuit position shown in Fig. 4. the two contact members move together, movement oi the second contact member being caused by the engagement of the plates 28 and II with the cross bar 31 at the upper edges of the notches hand I". In this way the movable contacts 3| and a are separated from the stationary contacts it and I4 thus breaking the circuit at two places.

I In the event of an overload or excess current conditions in the circuit, the bi-metallic latch 42 is heated and deflected, moving forward as shown in Fig. 2 so as to disengage itself from the retaining element Ii. Thereupon the second con: tact member, being no longer held by the latch II, is moved by the springs ll and ll to its opencircuit position as shown in Fig. 5. During such movement the first contact member remains in its normal closed-circuit position and the movable contacts 38 and 39 are disengaged not only from the stationary contacts I! and H but also from the contacts 35 and 36 of the first contact member. In this way the circuitis broken in four p es After automatic breaking of the circuit, reclosing is eifected by first moving the handle and the first contact member to open-circuit positions as shown in Fig. 4, thus eifecting reengagement of the bi-metallic latch 42 with the retaining element l5. Then the handle and both contact members can be moved to their closed-circuit positions as shown in Fig. 2.

What I claim is:

1. In an automatic circuit breaker, the combination of a stationary contact, two movable contact members each having a movable contact, the two movable contacts engaging each other when in closed-circuit positions and one of them engaging the stationary contact so that the circuit extends through all three contacts, manually operable means for moving one movable contact member to disengage one of the two movable contacts from or engage it with at least one of the other two contacts and thus open or close the circuit, and electro-responsive means acting upon the attainment of abnormal current conditions in the circuit to cause automatic movement of the other movable contact member to disengage the movable contact thereof from at least one of the other two contacts, the last said movable contact member moving independently of the first said movable contact member upon electrorespons'ive action and thus opening the circuit independently of the said manually operable means.

2. In an automatic circuit breaker, the combination of a stationary contact, a movable contact member having a movable contact, a second movable contact member having a movable contact which engages the contact of the first contact member when both members are in closedcircuit positions and which also engages the stationary contact so that the circuit extends through all three contacts, manually operable means for moving the first said movable contact member to disengage one of the two movable contacts from or engage it with at least one of the other two contacts and thus open or close the circuit, and electro-responsive means acting upon the attainment of abnormal current conditions in the circuit to cause automatic movement of the second said movable contact member to disengage the movable contact thereof from both of the other two contacts, the second said movable contact member moving independently of the first said movable contact member upon electro-responsive action and thus opening the circuit independently oi the said manually operable means. 3. In an automatic circuit breaker, the combination of a pair 01' separate stationary contacts, two movable contact members each having a pair of separate movable contacts, the movable contacts of one member being electrically connected with each other and respectively engaging the movable contacts of the other member whenboth members are in closed-circuit positions and the contacts of the last mentioned member also respectively engaging the two stationary contacts so that the circuit extends through all six contacts, manually operable means for moving one movable contact member to disengage the movable contacts of one pair from or engage them with movable contacts of at least one of the Other pairs and thus open or close the circuit in at least two -places, and electro-responsive means acting upon the attainment of abnormal current conditions in the circuit to cause automatic movement of the other movable contact member to disengage the movable contacts thereof from the contacts of at least one of the other pairs so as to open the circuit in at least two places, the last said movable contact member moving independently of the first said movable contact member upon electro-responsive action and thus opening the circuit independently of the said manually operable means. 4. In an automatic circuit breaker, the combination of a pair of separate stationary contacts,

. a movable contact member having a pair of electrically connected movable contacts, a second movable contact member having a pair of separate movable contacts which respectively engage the contacts of the first contact member when both members are in closed-circuit positions and which also respectively engage the stationary contacts so that the circuit extends through all six contacts, manually operable means for moving the first said movable contact member to disengage the movable contacts of one pair from or engage them with the movable contacts of at least one of the other pairs and thus open or close the circuit in at least two places, and electroresponsive means acting upon the attainment of abnormal current conditions in the circuit to cause automatic movement of the second said movable contact member to disengage the movable contacts thereof i'rom the contacts of both of the other pairs so as to open the circuit in four places, the second said movable contact member moving independently of the first said movable contact member upon electro-responsive action and thus opening the circuit independently of the said manually operable means.

5. The combination in an automatic circuit breaker of a stationary contact, two movable contact members normally movable in unison and each having a movable contact, the two movable contacts normally engaging each other and one of them engaging the stationary contact when the contact members are in closed-circuit positions, manually operable means for moving the two contact members in unison to disengage the movable contact of one of them from or engage it with the stationary contact and thus open or close the circuit, and electro-responsive means acting upon the attainment of abnormal current conditions in the circuit to cause automatic movement of one movable contact member independently of the other and independently of the manually operable means thus disengaging the movable contact. of one member from the movable contact oi the other member and thereby opening the circuit a 8. The combination in an automatic circuit P breaker, 01' a stationary contact, a movable contact member having a movable contact. a second contact member normally movable in unison with the first contact member and having a movable contact which normally engages the movable con "I tact of thefirst member and which also engages the stationary contact when the two contact members are in closed-circuit positions, manually operable means for moving both of the contact members in unison to open and close the circuit ll by disengaging the second movable contact from or engaging it with the stationary contact, and electro-responsive meansacting upon the attainment of abnormal current conditions in the air-- cuit and causing the automatic movement of the second contact member independently of the first contact member and independently of the manually operable means thus opening the circuit in two places by disengaging the second movable contact from the stationary contact and also from 7 85 the first movable contact.

7. The combination in an automatic circuit breaker 01' a pair of separate stationary contacts, two movable contact members normally movable in unison and each having a pair of movable 80 contacts, the two movable contacts of one member being electrically connected and being normally in engagement respectively with the two movable contacts of the other member and the two movable contacts of the last mentioned member respectively engaging the two stationary contacts when the contact members are in closedcircuit positions, manually operable means for moving the two contact members in unison to disengage the movable contacts of the last mentioned member from or engage them with the respective stationary contacts and thus open or close the circuit in two places, and electro-responsive means ,acting upon the attainment of abnormal current conditions in the circuit to cause automatic movement of one movable contact member independently of the other and independently of the manually operable means thus disengaging the movable contact of one member from the movable contact of the other member and thereby opening 50 the circuit in at least two places.

8. The combination in an automatic circuit breaker, 01 a pair of separate stationary contacts,

a movable contact member having a pair of electrically connected movable contacts, a second contact member normally movable in unison with the first contact member and having a pair of movable contacts which normally respectively engage the movable contacts of the first member and which also respectively engage the-stationary contacts when the two contact members are in closed-circuit positions so that the circuit extends through all six contacts, manually operable means for moving both of the contact members in unison to disengage the movable contacts of the second member from or engage them with the respective stationary contacts and .thus open or close the circuit in two places, and electro-responsive means acting upon the attainment of abnormal circuit conditions and causing the automatic movement of the second contact member independently of the first contact member and independently of the manually operable means thus,

disengaging the two movable contacts of the second member irom the two stationary contacts and also from the two movable contacts of a,aoo,e4a 4 the first member so as to open the circuit in four places.

9. In an automatic circuit breaker, vthe combination of a stationary contact, two movable contact members each having a movable contact, 5 the two movable contacts normally engaging each other and one of them engaging the stationary contact when the contact members are in closedcircuit positions, manually operable means connected with one contact member for movingit, and a movable electro-responsive releasable mechanical connection normally enabling the last mentioned contact member'to move the other member in unison therewith with the two movable contacts In engagement with each other the circuit being opened and closed by the disengagement oi' one movable contacttrom or engagement with the stationary contact, the said mechanical connection between the two members being automatically released upon the attainment oi excess current conditions in the circuit so as to permit the contact member other thanthat with which the manually operable means is connected to automatically move to open-circuit position independently of the remaining member thus disengaging one movable contact i'rom the other movable contact to open the circuit.

10. In an automatic circuit breaker, the combination of a stationary contact, a contact member movable under manual control and having a contact, a second contact member movable in unison with the first contact member but biased for circuit-opening movement independently thereof, the said second member having a contact element which engages the stationary contact and also the contact of the first member when both contactmembers are in closed-circuit positions, and a movable electro-responsively releasable mechanical connection normally enabling the first contact memberto move the second in unison therewith to thereby cause the contact element of the second. member to disengage and engage the stationary contact for ordinary switching purposes, the said mechanical connection between the two members being automatically released upon the attainment of excess current conditions in the circuit so as to permit the second member to automatically move to opencircuit position independently of the first member thus disengaging the contact element of the second member from the stationary contact and also from the contact \of the first contact member.

11. In an automatic circuit breaker, the combination of a stationary contact, a contact mem- .ber movable under manual control and having a contact, a second contact member movable in tact member and normally engaging the second contact member to enable the first member to move the second in unison therewith to thereby cause the contact element of the second member to disengage and engage the stationary contact for ordinary switching purposes, the said bimetallic latch being arranged to be heated and deflected upon the attainment of excess current conditions in the circuit so as to disengage the second contact member and permit the latter to automatically move to open-circuit position independll ently of the first member thus disengaging the contact element of the second member from the stationary contact and also from the contact of the first contact member.

12. In an automatic circuit breaker, the combination of a stationary contact, a contact member pivotally movable under manual control and having a contact, a second contact member pivotally movable in unison with the first contact member but blamed for pivotal circuit-opening movement independently thereof, the said second member having a contact element which engages the stationary contact and also the contact of the first member-when both contact members are in closed-circuit positions; and a movable electro-responsively releasable mechanical connection normally enabling the first contact member to pivotally move the second in unison therewith to thereby cause the contact element of the second member to disengage and engage the stationary contact for ordinary switching purposes, the said mechanical connection between the two members being automatically released upon the attainment of excess current conditions in the circuit so as to permit the second member to automatically move to open-circuit position independently of the first member thus disengaging the contact element of the second member from the stationary contact and also from the contact of the first contact member.

13. In an automatic circuit breaker, the combination of a stationary contact, a pivotally movable handle, a contact member connected with the handle and pivotally movable coaxially therewith and having a contact, a second contact member pivotally movable coaxially with the first contact member and in unison therewith but biased for circuit-opening pivotal movement independently thereof, the said second member having a contact element which engages the stationary contact and also the contact of the first member when both contact members are in closed-circuit positions, and a movable electro-responsively releasable mechanical connection normally enabling the first contact member to pivotally move the second in unison therewith to thereby cause the contact element of the second member to disengage and engage the stationary contact for ordinary switching purposes, the said mechanical connection between the two members being automatically released upon the attainment of excess current conditions in the circuit so as to permit the second member to automatically move to open-circuit position independently of the handle and of/ the first member thus disengaging the contact element of the second member from the stationary contact and also from the contact of the first contact member.

14. In an automatic circuit breaker, the combination of a pair of separate stationary contacts, two movable contact members each having a pair of movable contacts, the two movable contacts of one member being electrically connected and being normally in engagement respectively with the two movable contacts of the other member and the two movable. contacts of the last mentioned member respectively engaging the two stationary contacts whenthe contact members are in closed-circuit positions, manually operable means connected with one contact member for moving it, and a movable electro-responsively releasable mechanical connection normally enabling the last mentioned contact member to move the other member in unison therewith with the two movable contacts in engagement with each other the circuit being opened and closed by the dis-" en agement of the two movable contacts of one member from or engagement with the respective stationary contacts, the said mechanical connection between the two members being automatically released upon the attainment of excess current condition in the circuit so as to permit the contact member other than that with which the manually operable means is connected to automatically move to open-circuit position independently of the other said member thus disengaging the two movable contacts of one member from the two movable contacts of the other member to open. the circuit.

15. In an automatic circuit breaker, the combination of two stationary contacts, a contact I, member movable under manual control and having two contact faces, a second contact member movable in unison with the first contact member but biased for circuit-opening movement independently thereof, the said second member having two contact elements which respectively engage the corresponding stationary contacts and also the corresponding contact faces of the first member when both contact members are in closed-circuit positions, and a movable electroresponsively releasablemechanical connection normally enabling the first contact member to move the second in unison therewith to thereby cause the respective contact elements of the 4 second member to disengage and engage the corresponding stationary contacts for ordinary switching pw'poses, the said mechanical connection between the two members be g automatically released upon the attainment excess current conditions in the circuit so as to permit the second member to automatically move to open-circuit position independently of the first member thus disengaging the respective contact elements of' the second member from the corresponding stationary contacts and also from the corresponding contact faces of the first contact member.

16. In an automatic circuit breaker, the combination of two stationary contacts, a contact member movable under manual control and having two separate contacts, a second contact member movable in unison with the first contact member but biased for circuit-opening movement independently thereof, the said second member having two contactelements which respectively engage the corresponding stationary contacts and also the corresponding contacts of the first member when both contact members are in closedcircuit positions, and a releasable mechanical connection normally enabling the first contact member to move the second in unison therewith to thereby cause the respective contact elements of the second member to disengage and engage the corresponding stationary contacts for ordinary switching purposes, the said mechanical connection including an electro-responsive device which is carried by the first contact member and electrically connected between the two con-' tacts thereof and which is automatically released upon the attainment of excess current conditions in the circuit so as to permit the second member to automatically move to open-circuit position independently of the first member thus disengaging the respective contact elements of the second member from the corresponding stationary contacts and also from the corresponding contacts of the first contact member.

1'7. In an automatic circuit breaker, the combination of two stationary contacts, a contact member movable under manual control between J open-circuit and closed-circuit positions and having two separate contacts, a second contact member movable in imison with the first contact member but biased for circuit-opening move-.

ii ment independently thereof, the said second member having two contact elements which respectively engage the corresponding stationary contacts'and also the corresponding contacts of the first member when both contact members are 10 in closed-circuit positions, and a bi-metallic latch which is carried by the first contact member and electrically connected between the two contacts thereof and which normally engages the second of the first member thus 'disengaging the r'espec-- I tive contact elements of the second member from the corresponding stationary contacts and also from the corresponding contact faces of the first contact member.

18. In an automatic circuit breaker, the combination of two transversely spaced stationary contacts, two movable contact members one movable under manual control and the other movable in unison with the first but biased for circuitopening movement independently thereof, the

* said second member comprising two transversely spaced plates in planes between the stationary contacts and each having a contact element adapted to engage the corresponding stationary contact and the said first member comprising 40 two transversely spaced plates in planes between the planes of the plates of the second contact member and each having a contact normally engaging the corresponding contact element of the second contact member, and a releasable mechanical connection normally enabling the first contact member to move the second in unison therewith to thereby cause the respective contact elements of the second member to disengage and engage thecorrespondlng stationary contacts for ordinary switching purposes, the said mechanical connection including an electro-responsive device which is positioned between the plates of the first contact member and electrically connected between the two contacts thereof and which is operated upon the attainment of excess current 5 conditions in the circuit so as to release the second member and thereby permit it to automatically moveto open-circuit position independently of the first member thus disengaging the respective contact elements of the second member from the corresponding stationary contacts and also from the corresponding contactsof the first con tact member. 19. In an automatic circuit breaker, the combination of two transversely spaced stationary 15 contacts, two pivotally movable contact members one movable under manual control and the other movable in unison with the first but biased for circuit-opening movement independently thereof, the said second member comprising two transversely spaced plates in planes between the sta-- tionary contacts and each having a contact element adapted to engage the corresponding stationary contact and also comprising a transverse cross bar between the plates and the said first member comprising two transversely spaced plates in planes between the planes of the plates of the second contact member and each having a contact normally engaging the corresponding contact element of the second contact member, and a bi-metallic latch which-is positioned between the plates of the first contact member and electrically connected between the two contacts thereof and which normally engages the cross bar of the second contact member to enable the first contact member to move the second in unison therewith to thereby cause the respective contact elements of the second member to disengage and engage the corresponding stationary contacts for ordinary switching purposes, the said latch being 49 heated and deflected upon the attainment of excess current conditions in the circuit so as to release the secondmember and thereby permit it to automatically move pivotally to open-circuit position independently'of the first member thus disengaging the respective contact elements of the second member from the corresponding stationary contacts and also from the corresponding contacts of the first contact member.

JOSEPH sacns.

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