US3629764A

US3629764A - Circuit breaker with external heater

Info

Publication number: US3629764A
Application number: US65100A
Authority: US
Inventors: Cleon F Frey; Myron F Melvin
Original assignee: COMEL INTERNATIONAL CORP
Current assignee: COMEL INTERNATIONAL CORP
Priority date: 1970-08-19
Filing date: 1970-08-19
Publication date: 1971-12-21
Anticipated expiration: 1988-12-21

Abstract

The invention is embodied in an overload circuit breaker or protective switch of the type in which a member responsive to an electrical overload opens the circuit through the switch by latching open the switch contacts. A resetting member, when actuated, serves to reclose the switch contacts. The circuit breaker, however, is characterized by a set of auxiliary or secondary switch contacts connected electrically in series with the primary circuit breaker contacts. The movable contact arm or blade carrying the movable auxiliary contact is segmented so that the contact it carries can be electrically connected to an electric heater wrapped about the thermally responsive operator for the main switch contacts and the arm can, nevertheless, be supported by the electrically conductive housing or chassis, as can the operator for the main switch, without adversely affecting the trip-free reset operation of the breaker.

Description

United States Patent inventors Cleon F. Frey Sebastian, Fla.; Myron I". Melvin, Indianapolis, Ind. Appl. No. 65,100 Filed Aug. 19, 1970 Patented Dec. 21, 1971 Assignee Cornel International Corporation Bayamon, P.R.

CIRCUIT BREAKER WITH EXTERNAL HEATER l Claiin, 3 Drawing Figs.

3,358,099 12/1967 Bellomayre 2,191,588 2/1940 Sattler ABSTRACT: The invention is embodied in an overload circuit breaker or protective switch of the type in which a member responsive to an electrical overload opens the circuit through the switch by latching open the switch contacts. A resetting member, when actuated, serves to reclose the switch contacts. The circuit breaker, however, is characterized by a set of auxiliary or secondary switch contacts connected electrically in series with the primary circuit breaker contacts. The movable contact arm or blade carrying the movable auxiliary contact is segmented so that the contact it carries can be electrically connected to an electric heater wrapped about the thermally responsive operator for the mainswitch contacts and the arm can, nevertheless, be supported by the electrically conductive housing or chassis, as can the operator for the main switch, without adversely affecting the trip-free reset operation of the breaker.

3] i" 251 9 27 l9 :14. 20b 311) m 2 :1;

i I E 4: 3 \Y.\ S\ \\i 20 25 204/ ls INVENTORS 5 [Zea/v F [25v a BY Mmou F MEL WA] -3- MmMLUMMf/W ATTORNEYS 1 CIRCUIT BREAKER WITH EXTERNAL HEATER BACKGROUND OF THE INVENTION Circuit breakers, adapted to open the circuit through electrical appliances or television receivers or the like upon an electrical overload are well known in the prior art. Such overload protective switches are customarily provided with the trip-free feature. This trip-free quality prevents the user of the appliance from manually retaining the circuit breaker contacts closed under overload conditions by holding or jamming the reset button in actuated position. Customarily, this reset feature is provided by arranging the reset mechanism so that the circuit breaker contacts are blocked open until the reset button is released. An example of this type of structure is dis closed in Frey U.S. Pat. No. 2,948,787.

Since rapidity of response is a primary consideration in overload protective devices of this type, of necessity the thermally responsive component, usually a bimetal blade which responds to the heat generated by an electrical current overload, must have minimum thermal inertia, that is, in the case of a bimetal blade, relatively low mass. A sensitive, rapidly responsive bimetal member of low mass, however, has a relatively low force-deflection ratio, or work output per unit temperature variation. This low work output characteristic opposes the providing of the switch structure with heavy duty contacts to permit it to carry heavy overload currents without arcing and welding of the contacts together. A portion of the danger of arcing and welding of the contact structure can be eliminated if the reclosing of the contacts, after release of the reset button, is completed while no electrical potential exists across the contacts. In conventional trip-free reset circuit overloadswitches, although the contacts are held open while the reset member is depressed, when it is released, assuming the overload has not been removed, the contacts are reclosed on the full overload current. The relatively massive, heavyduty contacts required for this type of operation require heavier bimetal thermally responsive members and rapidity of response is thus sacrificed. It is, therefore, desirable to provide an overload circuit breaker in which an auxiliary pair of contacts are in series with the primary breaker contacts. These auxiliary contacts are held open mechanically as long as the reset button is depressed to provide the breaker with the tripfree feature, the primary contacts being reclosed, with no potential across them, upon depressing of the reset button. Upon release of the reset button, the auxiliary contacts are reclosed with potential across them, however, since these auxiliary contacts, as distinguished from the primary breaker contacts, are not operated by a relatively light bimetal member, they may be of a heavy-duty, massive type without sacrificing response time of the breaker.

This structural form has the advantages referred to above, however, where an external electrical heater is used to wrap the bimetal blade, rather than the internally generated heat when current passes through the bimetal blade, circuit connection difficulties occur. The use of the external bimetal heater type of construction is desireable in some European countries, for example, where a 220 volt circuit is utilized, less current being available for heat generation in the bimetal for a given power input. The circuit difficulties referred to come about because of the necessity to have the circuit through the heater electrically isolated from the switch chassis or housing. if it is not so isolated, then the chassis, usually formed of electrically conductive metal, must include elaborate, electrically insulated pivotal mountings for both the bimetal blade and the blade operating the auxiliary contacts, otherwise the chassis would short the auxiliary contacts during resetting of the main contacts and the necessary trip-free reset would be eliminated.

SUMMARY OF THE INVENTION the present invention concept utilizes a segmented arm or blade whose auxiliary-contact carrying tip is electrically isolated from the remainder of the blade which engages, for pivotal, knife-edge support, the metal chassis or housing of the switch. The chassis does not form a portion of the circuit through the heater and the auxiliary and main set of contacts, so that the pivotally supported arms or blades for these contacts can directly engage the chassis without electrical insulating supports for the blades being required. Further, the chassis or housing, since it is not in the circuit through the assembly, does not short out the auxiliary contacts during the reset operation and the necessary trip-free reset feature is retained.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, reference numeral 10 indicates a base plate, formed of electrical insulating material, the base plate having mounted thereon a metal chassis or housing which includes a top plate 11,

end plates

12 and 13 and a side plate 14, the side plate having portions cut away as indicated. An enclosing casing, indicated in broken lines and identified generally at 15, encloses the chassis. Extending through the base 10 and mounted thereon is a conductive member having one end 16 formedto provide the stationary contact of the primary circuit breaker switch structure, the other end 17 of the conductive member extending exteriorly of the housing to provide a terminal lug.

The housing top plate is provided with an aperture 18, one margin of which receives a clip 19 formed of bimetal and arranged to deflect, upon an increase in temperature, in the direction indicated by the arrow in;FlG. 1. Supported between the lower end of the clip 19 and an appropriately notched and slotted portion of the housing end wall 12 is a tripping element 21 all or a portion of which is formed of bimetal arranged to deflect upwardly, as indicated by the arrow in FIG. 1, upon an increase in its temperature. An electric heater 20 is wrapped around the bimetal tripping element and

wires

20a and 20b connect opposite ends of the heater to the member 23 and the free end 32 of the member 31, bdth subsequently described. As will be evident from FIG. 1, the tripping element 21 is supported under elastically deforming compressive stress and when the temperature of the thermally responsive bimetal reaches a predetermined point, the tripping element will snap from its stable position shown in solid lines in FIG. 1 to its stable position shown in broken lines in FIG. 1, while'the overload current traversing the heater 20 provides the temperature a blade 23, formed at its free end to provide a movable contact 24 which cooperates with the stationary contact 16, the

contacts

24 and 16 forming the primary contacts of the circuit breaker assembly. As previously mentioned, the sidewall 14 has an extensive cut away portion, indicated at 14a in FIG. 1, and extending into this cut away portion, generally in the plane of the sidewall 14 is a member 25. The electrically conductive member 25 has a lower portion 25a which extends through the base 10 and forms a terminal lug shaped identically to the lug 17. The upper end of the member 25 is bent at a right angle to the body of the member and this flanged portion extends into the housing to form the electrical contact portion 25b.

The resetting means for returning the tripping element from its broken line position to its solid line position of FIG. 1 (such resetting operation being shown in FIG. 2) includes a reset pin 26 which is freely received within an aperture in the upper plate 11 of the housing 15 and a shoulder 26a on the pin prevents its complete withdrawal from the housing. A reduced tip portion 27 of the pin extends freely through an aperture in the top plate 11, with the shoulder 29 limiting the depth of insertion of the pin into the housing. A segmented, resilient blade 31 extends beneath the undersurface of the top plate 1 1 and extends through the aperture 18 to the exterior of the housing. The exteriorly extending portion 31a of the blade is formed in upwardly offset configuration and the tip of the blade, indicated at 31b, is reduced and extends through an accommodating slot in the adjacent portion of the top plate 11. Since the blade is resilient, the offset portion 31a is formed so that the blade is urged against the leftward margin (as viewed in FIG. 1) of the aperture 18 and into engagement with the tip 27 of the reset pin. The free end, indicated at 32 in FIG. 1, is also urged, by the resiliency of the elongated element, into engagement with the face of the flange portion 25b of the element 25. Interposed between the free end 32 and the remainder of blade 31 is a section 320 formed of electrical insulating material, this portion 32a of the blade serving t electrically isolate the free eiid 32 from the remainder of the blade 31.

The electrical circuit through the circuit breaker is shown in FIG. 3 and proceeds from the lug 17, through contacts 16-24, blade 23 and through the heater 20. The circuit then proceeds via wire b to the free end 32 of the blade 31, then through flange b and element 25 to the other terminal 25a. The flange 25b and tip 32 serve as an auxiliary set of contacts in series with primary contacts 24-16.

In operation, upon the occurrence of an overload current through the contacts 16-25, the heater 20 will cause the tripping element to snap from its solid line position of FIG. 1 into its broken line position, opening the contacts. As will be evident from FIG. 2, by depressing the reset pin 26, the engagement of the underface of the element 31 with the tripping element will displace the tripping element and snap it into its stable position in which the contacts 16-24 are closed. As will be evident from a comparison of FIGS. 1, 2 and 3, when the reset pin is depressed, the consequent elastic deformation of the element 31 separates the contact surface 32 from the contact flange 25b so that, as long as pin 26 is depressed, auxiliary contacts 25b-32 are open when the tripping element is moved from its stable position indicated at broken lines in FIG. 2 to its solid line position in which the contacts 16-24 are closed. If the reset button is held in depressed position, the

contacts

32 and 25b remain separated and there is no electrical continuity between the lugs 25:: and 17. The

primary contacts

16 and 24 are thus always reclosed under open circuit conditions and the switching structure is trip free in that the circuit through the switching device is maintained open as long as the reset button is held in actuated or depressed position. When the reset button is released the restoring force generated by the elastic deformation of the element 31 moves the reset pin 26 back to its position of FIG. 1 and brings the contact surface 32 again into engagement with the contact member 25b.

From the foregoing it will be evident that the switching device is trip free and that, even though an exterior heater (20) is utilized to warp tripping element 21 to its actuated position, because the element 31 is segmented, isolating electrically its free end 32 from that portion engaging the chassis, the metallic chassis is not part of the circuit of the device, as evident from the FIG. 3, and insulating supports need not be utilized between the chassis and the element 31 or between the chassis and tripping member 21.

We claim: 1

l. A trip-free overload circuit breaker including a housing and a primary stationary contact within the housing, a bimetal tripping element supported by the ;housing movable between two stable positions, and with a primary movable contact cooperating with the primary stationary contact and movable by the tripping element into and out of engagement with the stationary contact, an electrical heater connected in series with said primary contacts for moving said tripping element to one of its stable positions from the other upon a current overload through said contacts, a reset pin supported for movement into and out of the housing with the pin being manually movable from a deactuated position to an actuated position to displace the tripping element from said one of its stable positions to the other, a unitary means for urging said reset pin from its actuated to its deactuated position and for removing the electrical potential from across said movable and stationary contacts as said reset pin is moved into its actuated position, said means comprising a segmented resilient blade pivotally supported on the housing, the free end of said blade being electrically isolated from its supported end, an auxiliary set of contacts, one of said auxiliary contacts being carried on the free end of said segmented blade, one end of said heater being electrically connected to said free end of said blade and the opposite end of said heater being electrically connected to said primary movable contact.

Claims

1. A trip-free overload circuit breaker including a housing and a primary stationary contact within the housing, a bimetal tripping element supported by the housing movable between two stable positions, and with a primary movable contact cooperating with the primary stationary contact and movable by the tripping element into and out of engagement with the stationary contact, an electrical heater connected in series with said primary contacts for moving said tripping element to one of its stable positions from the other upon a current overload through said contacts, a reset pin supported for movement into and out of the housing with the pin being manually movable from a deactuated position to an actuated position to displace the tripping element from said one of its stable positions to the other, a unitary means for urging said reset pin from its actuated to its deactuated position and for removing the electrical potential from across said movable and stationary contacts as said reset pin is moved into its actuated position, said means comprising a segmented resilient blade pivotally supported on the housing, the free end of said blade being electrically isolated from its supported end, an auxiliary set of contacts, one of said auxiliary contacts being carried on the free end of said segmented blade, one end of said heater being electrically connected to said free end of said blade and the opposite end of said heater being electrically connected to said primary movable contact.