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Publication numberUS3328639 A
Publication typeGrant
Publication dateJun 27, 1967
Filing dateJul 1, 1963
Priority dateJul 1, 1963
Publication numberUS 3328639 A, US 3328639A, US-A-3328639, US3328639 A, US3328639A
InventorsGryctko Carl E
Original AssigneeIte Circuit Breaker Ltd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Circuit breaker overload sensing device
US 3328639 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

June 27, 1967 ET GRYcTKo 3,328,639

CIRCUIT BREAKER OVERLOAD SENSING DEVICE June 27. 1967 c. E. GRYc'rKo CIRCUIT BREAKER OVERLOAD SENSING DEVICE 2 Sheets-Sheet 2 Filed July l 1965 um E United States Patent O 3,328,639 CIRCUIT BREAKER OVERLUAD SENSING DEVCE Carl E. Gryctko, Haddon Heights, NJ., assigner to l-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed July 1, 1963, Ser. No. 292,050 16 Claims. (Cl. S17-4l) My invention relates to a circuit breaker overload sensing device, and more particularly to a solid-state circuit arrangement operable in conjunction with the heater element of a conventional circuit breaker to electrically trip the breaker in a manner permitting increased adjustability and reliability of operation. The solid-state circuitry arrangement may also operate in conjunction with the conventional instantaneous load sensor to electrically trip the circuit breaker responsive to either a predetermined time delayed overload condition or an instantaneous short circuit condition.

lt is well known in the circuit breaker art to trip the breaker upon the occurrence of a moderate overload condition existing for a prolonged duration, with such operation usually being provided by a circuit-connected heater element arranged to deflect a bimetallic element responsive to the thermal condition resulting from Inoderate overload. The deflection of the bimetallic element is calibrated to provide the desired tripping time characteristic according to the time duration of the particular overload condition. The deflection of such bimetallic element is then mechanically interconnected to a latch arrangement for operating the circuit breaker contacts responsive to predetermined detlection of the bimetallic element. Exactness of operation of such an arrangement requires close calibration of Vthe bimetal deflection and accurate alignment of the various mechanical members interconnected between the thermally responsive element and trip latch. Accordingly, variations in alignment between such individu-al elements adversely affects the calibration of the unit. Further, the magnetic field generated within the closely contined operating members of typical present-day circuit breakers aects the alignment and distortion of the various members, thereby varying the calibration accuracy of the tripping characteristic; with such atects being greatest for high current applications.

My invention advantageously avoids these problems by electrically tripping the circuit breaker responsive to the existence of a predetermined thermal condition, as generated by the heater element of a conventional circuit breaker unit. More specically, I provide a circuit arrangement including .a thermally responsive transducer, such as a thermistor, in heat transfer relationship with the circuit breaker heater element. Although the ensuing discussion will be directed to the use of a thermistor, it is to be understood that other thermally responsive transdncer means, such as a thermocouple, may likewise be employed.

An electrical characteristic of the thermistor element, such as resistance, varies responsive to the overload thermal condition of the heater element. The thermistor element is in circuit relationship with a soli-d state switch, such as a uni-junction transistor, to transfer the unijunction transistor between its blocking and conducting states, corresponding to a predetermined resistance variation of the thermistor element.

As a particularly advantageous aspect of my invention, the thermistor element is placed within a voltage divider network to apply a biasing signal to the emitter of the uni-junction transistor element. One of the elements of the voltage divider network is adjustable' to provide variation in the input biasing signal to the uni-junction transistor switch element corresponding to predetermined 3,328,639 Patented June 27, 1967 resistance variation of the thermistor element. Accordingly, selective adjustment of such an element, which for example may be a conventional potentiometer, permits a variati-on in the relationship between the .thermally induced resistance change -of the thermistor element and the biasing signal magnitude presented to the uni-junction transistor. Accordingly, such selective adjustment provides calibration of the overload trip sensing circuitry in a simplified and reliable manner, as contrasted to the various mechanical adjustments required in the mechanical trip arrangements of the prior art.

The output ofthe uni-junction transistor may in turn be connected to the gate input terminal of .another switching element, such as a silicon controlled rectifier, for switching said rectiiier between its blocking and conducting states responsive to the aforesaid resistance variation of the thermistor elements.

The operation of the circuit breaker is preferably provide-d by a conventional type of under voltage trip unit of the general type shown in copending U.S. patent application Ser. No. 185,328 tiled Apr. 5, 1962, entitled, Shunt Trip and Under Voltage Device, in the name of Felix E. Myers and assigned to the assignee of the instant invention and now United States Patent No. 3,175,064. The under voltage tripping relay is placed in parallel across the silicon controlled rectified device, such that when the silicon controlled rectifier is in its blocking condition the voltage applied across the under voltage relay will maintain the circuit breaker in its non-tripped position. Switching of the silicon controlled rectifier to its conducting state places a low impedance short across the under voltage coil, thereby causing the breaker to trip. Alternatively, operation of the circuit breaker may be provided by a shunt trip, saturable reactor, permanent magnet or other well known devices responsive to operation of the trip sensing circuitry of the instant invention.

As another advantageous aspect of my invention, a further switching arrangement is provided to be operable in conjunction with a conventional short circuit or instantaneous load sensing means to similarly switch another uni-junction transistor between its blocking and conducting states responsive to a predetermined instantaneous load condition. The output signals of the overload and instantaneous load sensing circuitry are presented to the gate input of the silicon controlled rectifier via isolating circuitry, thereby providing operation thereof responsive to either time-delayed thermally induced resistance variation of the thermistor element, or instantaneous load conditions above a predetermined magnitude.

It is therefore seen that the basic concept of my invention resides in electrically tripping a circuit breaker mechanism by virtue of a solid-state circuit arrangement operatively responsive to load conditions sensed by conventional circuit breaker means.

It is therefore a prima-ry object of my invention to provide an improved circuit breaker overload sensing device of increased adjustability and reliability of operation.

A further object of my invention is to provide a circuity breaker overload sensing device having a thermally responsive means in heat transfer relationship with a circuit breaker heater element, and circuit arranged to switch a solid state switching means between its blocking and conducting states.

Another object of my invention is to provide such an overload sensing device having an adjustable electrical component in circuit arrangement with the thermally responsive means and solid state switching means to permit selective calibration of the operation thereof.

An additional object of my invention is to provide overload tripping of a circuit breaker in a manner -avoiding a aaneen@ bimetallic interconnection between the overload heater element and the circuit breaker tripping mechanism.

Still a further object of my invention is to provide an electronic trip unit for a circuit breaker comprising solid state switching means electrically operative responsive to predetermined overload and instantaneous current conditions to activate a relay trip means of a conventional circuit breaker.

Those as well as other objects of my invention will readily become apparent upon a consideration of the following drawings in which:

FIGURE l is -a block diagram illustrating the basic operation of my invention in a form having both time-delayed thermal trip and instantaneous short circuit trip portions.

y FIGURE 2 is a schematic ldiagram of an electrical trip arrangement in accordance with FIGURE l.

FIGURE `3 graphically shows the operating characteristics of a typical thermistor element.

Referring to the figures, thermal overload sensor 100 and instantaneous current sensor 200 are connected intermediate line terminals 10, `20 and loa-d terminals 15, 25, in the conventional manner. Sensor unit 100 typically includes a circuit connected heater element 102, and sensor unit 200 a circuit connected current transformer 202. As will be subsequently shown, the existence of predetermined load conditions being presented to the electrical circuitry of units 100 `or 200 provides electrical output signals 150, 250l respectively. These signals are then presented to solid state switching circuit 300 via circuitry 400, the latter insuring independent operation of solid state switch 300 responsive to the generation of either signals 150 or 250. Solid state switch 300 in its conducting state presents a low impedance short circuit to the conventional circuit breaker trip coil 500, to thereby provide tripping of the circuit breaker contacts 502. As is well known, heater element 102 will be at a temperature corresponding to the time duration of overload conditions; and current transformer 202 will have an output corresponding to the instantaneous load condition, with rectifiers 206, 208 and loading resistors 210, 212 being provided to per-mit operation of the instantaneous current sensor circuitry 200 responsive to either .a positive or negative fault current.

The source voltage for operation of sensing units 100, 200 and switching circuit 300 is provided by power supply 600. The input 23 of power supply transformer 22 is preferably connected to line terminals 10, 20, with diodes 26, 28 being connected to the secondary output 24 for f-ull wave operation. Capacitors 32, 34 and resistor 30 form a low power filter arrangement to reduce the ripple of the power supply, with Zener diode 36 being provided to ensure a constant well regulated D.C. potential for oper-ation of the electrical sensing circuitry of the instant invention. The energization of transformer primary 23 is preferably shown controlled by Ian auxiliary switch 503 associated with the circuit breaker, which closes :as the circuit breaker closes, to apply the operating potential to the electrical circuitry 100, 200, 300 of my invention, with such operating potential being interrupted upon tripping of the circuit breaker contacts 502. Switch 503 may be closed manually or automatically in conjunction with the operation of circuit breaker contacts 502 to de-energize transformer primary 23 upon opening 4of circuit breaker contacts 502, with switch 503 being closed to energize power supply `600 before circuit breaker contacts 502 may be closed. It is naturally understood that a separate D.C. source could alternatively 4be provided; however, the instant arrangement of obtaining the operating voltage directly from the line source advantageously avoids the requirement for such an auxiliary supply.

Referring to the operation `of the thermal overload sensor 100, a thermistor element 104 is shown in heat transfer relationship with respect to heater element 102,

it being understood that other thermally responsive transducer means, such as a thermocouple, m-ay alternatively be employed. The electrical characteristics of thermistor element 104, such as resistance, will vary in accordance with the temperature applied thereto, in the manner typically shown in FIGURE 3. Thermistor element 104, in conjunction with variable resistor 106 and fixed resistor 108, comprises a voltage divider biasing network, the output signal of which is applied across capacitor 117 to the emitter 12-6 of uni-junction transistor switching element 125. Rectifier 116 is preferably inserted along the series circuit Varrangement of elements 104, 106 and 108 to match the temperature variations in the characteristics of the uni-junction transistor 125, to thereby provide increased uniformity of operation over temperature extremes. Resistors 112 and 114 provided in thermal overload sensor stage 100 act as loading and biasing resistors for the uni-junction transistor element 125 of that stage.

Accordingly, the variation in the resistance of thermistor element 104 will vary the magnitude of biasing signal 110 applied to thermistor 125. By proper adjustment of the voltage divider network in conjunction with the characteristics of uni-junction transistor member 125, switching between its blocking and conducting states may be effected corresponding to a predetermined temperature- `induced resistance variation of thermistor element 104,

with such temperature being selectively adjustable by varying the adjustment of variable resistor 106. As, for example, consider the case where uni-junction transistor 12S will be transferred to its forward conducting state corresponding to an applied potential of thirteen voltsV at emitter 125 and will be in its blocking state corresponding to a lesser potential.

The voltage applied to the emitter 126 is given by th relationship Consider the case where:

V126 :Vin X Vin=D.C. voltage applied to the voltage divider network (20 volts) R106=2K ohms pot R108=5.2K ohms At a thermistor temperature of 90, corresponding to normal operating conditions, its resistance will be 4K (point A); thereby provi-ding 10 volts at emitter 126.

At a thermistor temperature of about C., corresponding to the predetermined tripping point of the circuit breaker, the resistance of thermistor 104 will `be 2K (point B), thereby providing 13 volts at emitter 126, causing it to transfer to its forward conducting state.

It is` naturally seen that suitable adjustment of variable resistor 106 will provide a desired operating point suitably selected in accordance with desired tripping times in relation to the thermal response of members 102, 104 ,and the characteristics of uni-junction transistor 125.

The single phase sensing arrangement shown in FIG- URE 2 may be modified, as shown dotted, to operate as a three phase unit by the addition of the similar arrangement of members 104', 106', 108 and 116 to operate in conjunction with single uni-junction transistor storage capacitor 117, to forward bias emitter 126 re sponsive to said signal exceeding ,a predetermined magnitude and transfer uni-junction transistor to its conducting state.

Considering now the operation of the silicon controlled rectifier switching circuit 300, the plate terminal 327 is connected to the D C. potential source via loading resistor 332; the cathode terminal 328 is directly connected to the opposite terminal of the potential source; and gate terminal 326 is returned to the source via resistor 336. Diode 334 is connected across resistor 336 to prevent the gate voltage from going negative. Resistors 332, 336 are selected in relation with the energizing voltage applied to the solid state switch '300, such that silicon controlled rectifier 325 will be in its blocking condition corresponding to a zero gate signal. The application of a gating impulse corresponding to t-he conduction of uni-junction switching members 125 (or, as will be subsequently discussed7 225) permits discharge of storage capacitor 117 (or 220) to apply such a gating signal 150 (or 250) respectively, to thereby switch silicon controlled rectifier 325 to its conducting state.

In its conducting state silicon controlled rectifier 325 is essentially a low impedance short across under voltage coil 500 [of the type generally shown in the aforementioned U.S. patent application Ser. No. 185,328], such that the circuit bre-aker unit -will be immediately tripped. Accordingly, upon conduction of uni-junction transistor member 125, a signal 150 is then applied to the gate terminal 326 of silicon controlled rectifier 325, causing it to abruptly switch from its blocking to its conducting state. The conduction of silicon controlled rectifier 325 will short under voltage coil 500, thereby causing its associated circuit breaker contacts 502 to trip. Alternatively, operation of the circuit breaker may be provided b-y a shunt trip, saturable reactor, permanent magnet or other well known devices actuated responsive to operation of the trip sensing circuitry of the instant invention, with appropriate modification of the circuitry arrangement of FIGURE 2 being provided.

Reference is now made to the instantaneous current sensor unit 200 having uni-junction transistor switching means 225 operable responsive to short circuit conditions; in a manner similar to that above-described to conjunction with uni-junction transistor element 125. Uni-junction transistor 225 is switched by the input signal arrangement of adjustable resistor 214, connected to the center tap 203 of current transformer 202, with the opposite phased output terminals of current transformer 202 providing an output signal to the emitter terminal 226. Alternatively, other transducer means, such as a Hall effect generator, may be employed for instantaneous current sensing. Resistors 232, 234 are the combined loading and biasing resistors of stage 200. Rectifier 216, in series with adjustable resistor 214, operates in a manner similar to rectifier 116 of stage 100km compensate for temperature variations of uni-'junction transistor element 225. Rectifier 218, intermedi-ate the common junction 219 and the emitter 226 of uni-junction transistor 225, is inserted to prevent the instantaneous pulse from influencing the charge on capacitor 220. The circuit components are so adjusted such that a magnitude of signal 204 corresponding to an instantaneous load condition above a predetermined value will fire uni-junction transistor 225 thereby applying signal 250 to gate terminal 326 of silicon controlled rectifier 325. 'Ihe single phase sensing arrangement 200 may be modified for multiphase operation by the addition of similar .arrangements (not shown) of members 202, 206, 208, 210 and 212 -for the respective phases, connected to terminals X, Y.

Isolating capacitors 130, 230 interconnect the gating output signals 150, 250 of the uni-junction transistor elements 125, 225 to common gate terminal 326-, in a manner permitting independent opera-tion thereof. Thus, silicon controlled rectifier 325 will be switched responsive to either time delayed heating of thermistor 10'4, or a short circuit output from current transformer -2.

I have obtained satisfactory operation with the following component values being employed in the circuit 6 of FIGURE 2. It is to be understood that these values are merely representative component parameters and are not intended to limit the scope of the invention.

125, ZZS-Uni-junction transistor-2N489- 325-Silicon controlled rectifier- 2Nl77lA. 26, 28-Diode--1N321l 116, 206, 208, 216, 218, 334-Diode-1N1693. 36-Zener diode-INZSlSB.

104-50K at 25 C.

R106-Resistor--2K ohms pot.

It is therefore seen that my invention provides an improved arrangement lfor electrically operating a circuit breaker trip mechanism in a manner permitting increased ease of adjustment and calibrating accuracy over the mechanical trip arrangements of the prior art.

Although I have described preferred embodiments of my novel invention, many variations and modifications will now be obvious to those skilled in the art, and I prefer therefore to be limited not by the specific disclosure herein but only by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A circuit protective arrangement including the combination of: a circuit breaker having a heater element circuit connected to the circuit to be protected, such that said heater element develops heat in a manner operatively related to circuit current, a pair of separable contacts, and an electromagnetically actuated fault responsive means for tripping said circuit breaker, such that said contacts separate for interrupting the circuit current; and an overload sensing device, said overload sensing device comprising a thermally responsive means in heat transfer relationship with said heater element; the electrical characteristics of said thermally responsive means predeterminedly varying responsive to the temperature thereof; said thermally responsive means being circuit connected in a first circuit; a first switch means having a first and second operating condition; said first circuit presenting a first signal to said first switch means; the magnitude of said first signal varying responsive to the electrical characteristic variation of said thermally responsive means; a predetermined magnitude of said first signal effecting switching of said first switch means between said first and second operating conditions; said predetermined mag.- nitude corresponding to the temperature of said thermally responsive means exceeding a predetermined magnitude; the switching of said first switch means providing a second signal to actuate said electromagnetically actuated means and trip said circuit breaker in accordance with the predetermined temperature of said thermally responsive means.

2. A circuit protective arrangement including the combination of: a circuit breaker having a heater element circuit connected to the circuit to be protected, such that said heater element develops heat in a manner operatively related to circuit current, a pair of separable contacts, and an electromagnetically actuated fault responsive means for tripping said circuit breaker, such that said contacts separate for interrupting the circuit current; and an overload sensing device, said overload sensing device comprising a thermally responsive means in heat transfer relationship with a heater element; the electrical characteristics of said thermally responsive means predeterminedly varying responsive to the temperature thereof; said thermally responsive means being circuit connected in a first circuit; a first switch means having a first and second operating condition; said first circuit presenting afirst signal to said first switch means; the magnitude of said first signal varying responsive to the electrical characteristic variation of said thermally responsive means; a predetermined magnitude of said first signal effecting switching of said first switch means between said first and second operating conditions; said predetermined magni- 7 tude corresponding to the temperatue of said thermally responsive means exceeding a predetermined magnitude; the switching of said first switch means providing a second signal; a second switch means having a first and second operating condition; said second signal being presented to said second switch means, and switching said second switch means between its first and second operating conditions; the switching of said second switch means between said first and second operating conditions actuating said electromagnetically actuated means for tripping said circuit breaker in accordance with the predetermined temperature of said thermally responsive means.

3. A circuit protective arrangement as set forth in claim 1, wherein: said first circuit includes an adjustable circuit element; the adjustment of said circuit element selectively varying the relationship between said predetermined magnitude of said first signal and the temperature of said thermally responsive means.

4. A circuit protective arrangement as set forth in claim 1, wherein: said thermally responsive means comprises a thermistor.

5. A circuit protective arrangement as set forth in claim 3, said thermally responsive means comprising a thermistor; said adjustable circuit element comprising a variable resistor in voltage divider relationship with said thermistor; the magnitude of said first signal related to the resistance relationship of said thermistor and variable resistor.

6. A circuit protective arrangement as set forth in claim 1, said first switch means being a solid state electronically operable element.

7. A circuit protective arrangement as set forth in claim 1, said first switch means being a uni-junction transistor; said first and second conducting states corresponding to reverse and forward biasing respectively of said uni-junction transistor.

8. An overloading sensing device for a circuit breaker, said overload sensing device comprising a thermally responsive means in heat transfer relationship with a heater element; the electrical characteristics of said thermally responsive means predeterminedly varying responsive to the temperature thereof; said thermally responsive means being circuit connected in a first circuit; a first switch means having a first and second operating condition; said first circuit presenting a first signal to said first switch means; the magnitude of said first signal varying responsive to the electrical characteristic variation of said thermally responsive means; a predetermined magnitude of said first signal effecting switching of saidfirst switch means between said first and second operating conditions; said predetermined magnitu-de corresponding to the temperature of said thermally responsive means exceeding a predetermined magnitude; the switching of said first switch means providing a second signal; a second switch means having a first and second operating condition; said second signal being presented to said second switch means, and switching said second switch means between its first and second operating conditions; the switching of said second switch means between said first and second operating conditions electrically tripping a circuit breaker in accordance with the predetermined temperature of said thermally responsive means; said first and second switch means being solid-state electronically operable components; said first switch means being a uni-junction transistor; said first and second conducting states corresponding to reverse and forward biasing respectively of said uni-junction transistor; said second switch means being a silicon controlled rectifier; said second signal being a gate input to said silicon controlled rectifier.

9. An overload sensing device for a circuit breaker, said overload sensing device 4comprising a thermally responsive means in heat transfer relationship with a heater element; the electrical characteristics of said thermally responsive means predeterminedly varying responsive to the temperature thereof; said thermally responsive means being circuit connected in a first circuit; a first switch means having a first and second operating condition; said first circuit presenting a first signal to said rst switch means; the magnitude of said first signal varying responsive to the electrical characteristic variation ofV said thermally responsive means; a predetermined magnitude of said first signal effecting switching of said first switch means between said first and second operating conditions; said predetermined magnitude corresponding to the temperature of said thermally responsive means exceeding a predetermined magnitude; the switching of said first switch means providing a second signal; a second switch means having a first and second operating condition; said second signal being presented to said second switch means, and switching said second switch means between its first and second operating conditions; a third switch means in electrical circuit relationship with an instantaneous load sensing means; a third signal being presented to said third switching means proportionally responsive to instantaneous load; said third switch means having a first and second operating con-dition; a predetermined magnitude of said third signal effecting switching of said second switch means between said rst and second operating conditions; said predetermined magnitude of said third signal corresponding to instantaneous load exceeding a predetermined magnitude; the switching of said third switch means providing a fourth signal; said fourth signal being presented to said second switch means and switching said second switch means between its first and second operating conditions; the switching of said second switch means between said first and second operating conditions electrically tripping a circuit breaker in accordance with both predetermined temperature of said thermally responsive element corresponding to switching of said switch means, and predetermined instantaneous load corresponding to switching of said third switch means.

10. An overload sensing device as set forth in claim 9, further including isolating circuit-ry means for i-ndependently presented said secondV and fourth signals to said second switch means.

11. An overload sensing device as set forth in claim 9, said first, second and third switch means being solid-state electronically operable elements.

12. An overload sensing device `as set forth in claim 10; said first and third switch means being uni-junction transistors; said first and second operating conditions corresponding to reverse and forward biasing respectively of said uni-junction transistors; said secondy switch means being a silicon controlled rectifier; said second `and fourth signals being gate inputsl thereto; said isolating circuitry means being circuit connected intermediate the output terminals of said uni-junction transistors, and the gate terminal of said silicon controlled rectifier.

13. In combination with a' circuit breaker having a heater element, instantaneous load sensing means an-d relay trip means; a solid state tripping means comprising a first, second and third switching means; each of said switching means having a blocking and conducting state; a circuit arrangement including transducer means in heat transfer relationship With said heater element for applying a signal to said first switch means responsive to the temperature of said heater element; said first switch means being switched between its blocking and conducting states corresponding to said heater element being at a predetermined temperature; a circuit arrangement operatively connected to said instantaneous load sensing means for applying a signal to said third switch means responsive to instantaneous load; said third switch means being switched between its blocking and conducting states corresponding to instantaneous load being above a predetermined magnitude; the switching of said first or third switch means presenting a switching signal to said second switch means; said last-mentioned switching signal switching said second switch means between its blocking and conducting states to elect operations of said relay trip means.

14. The combination as set forth in claim 13, wherein: said relay trip means is an undervoltage coil parallel circuit connected across said second switching means, the switching of said second switch means eiecting a short circuit across said undervoltage coil.

15. The combination of an instantaneous load sensing means and relay trip means with a circuit breaker having a heater element, as set forth in claim 13; said circuit arrangement of said transducer means further including an Iadjustable circuit element in voltage divider relationship with said transducer means; the magnitude of the signal applied to said rst switch means related to the resistance relationship of said transducer means and 4adjustable circuit element, whereby the adjustment of said adjustable circuit element selectively varies the temperature of ysaid heater element corresponding to switching of said rst switch means.

10 16. The combination of an instantaneous load sensing means and relay trip means with a circuit breaker having a heater element, as set forth in claim; further including isolation circuitry means `for independently presenting the switching signals of said irst and third switching means to said second switching means.

References Cited UNITED STATES PATENTS 3,032,169() 5/ 1962 Elliot 317-13 X 3,132,287 5/1964 Yarbrough. 3,209,206 9/ 1965 Courtin 317--13 X MILTON O. HIRSHFIELD, Primmy Examiner.

I D. TRAMMELL, Assistant Examiner.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3032690 *Feb 20, 1959May 1, 1962Cutler Hammer IncThermally responsive electrical control systems
US3132287 *Mar 14, 1961May 5, 1964Ryan Aeronautical CoHigh frequency circuit breaker utilizing silicon controlled rectifiers
US3209206 *Feb 9, 1962Sep 28, 1965Westinghouse Electric CorpOvertemperature protected apparatus
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3404313 *Feb 4, 1966Oct 1, 1968Power Control CorpTemperature responsive circuit apparatus employing thermistors
US3965396 *Mar 13, 1974Jun 22, 1976Robertshaw Controls CompanyCondition responsive control circuit
EP1359655A2 *Apr 28, 2003Nov 5, 2003Eaton CorporationCircuit interrupter trip unit
Classifications
U.S. Classification361/106, 361/115
International ClassificationH02H3/08
Cooperative ClassificationH02H3/085
European ClassificationH02H3/08T