Circuit Breaker and Shunt Trip Apparatus Combined Within Single Pole Device

This application is related to copending application titled "Calibrationless Electric Circuit Breaker", Ser. No. 648,397 filed Sept. 7, 1984 in the name of John R. Brubaker et al, and assigned to the assignee of this application.

This invention relates to molded case circuit breakers of the type for protecting against overload current conditions in electric distribution circuits. More specifically, this invention relates to circuit breakers of the aforementioned type which have a shunt trip mechanism for operation of the circuit breaker to a tripped condition from a remote location.

It has been known to provide circuit breakers of the aforementioned type with a shunt trip apparatus for enabling the breaker to be selectively operated to its tripped condition from a remote location. The shunt trip feature is commonly provided by adding a separate molded case enclosure to the side of an existing molded case circuit breaker, the separate enclosure containing the shunt trip elements such as a solenoid and a lever system which is coupled to the circuit breaker through a handle tie or through openings in the respective side walls of the molded cases. Shunt trip circuit breakers of the narrow width residential or small commercial frame type constructed in this manner occupy two pole spaces on a panelboard to which the circuit breaker is mounted, one space being required for the circuit breaker per se and the second space being required for the shunt trip mechanism. Thus, for each shunt trip breaker device of this type utilized, one pole space for a protected branch circuit is sacrificed. U.S. Pat. Nos. 4,209,761, 3,973,230 and 3,820,046 are examples of shunt trip circuit breakers of the aforementioned type.

The aforementioned related copending application Ser. No. 648,397 filed Sept. 7, 1984 discloses a circuit breaker which utilizes a shape memory effect (SME) alloy element as a current responsive trip mechanism for responding to both high and low current level overload conditions. Such structure replaces separate thermal current sensing and latch structures and may replace magnetic current sensing structures within the circuit breaker, thereby substantially reducing the number of parts, the cost, and the occupied space within the circuit breaker housing. The SME element is also utilized advantageously to eliminate calibration operations of the circuit breaker during manufacture. In accordance with this invention, the SME element is further utilized as a shunt trip mechanism and may be readily incorporated within the same housing as the circuit breaker structure.

The invention described herein provides a molded case circuit breaker of the type which is manually operable between open and closed contact positions and automatically operable in response to overload current conditions to open the contacts, such breaker being provided with a shunt trip mechanism incorporated within the single pole molded case of the circuit breaker. More specifically, this invention provides a circuit breaker mechanism of a type suitable for use in a molded case circuit breaker embodiment having an overcenter toggle spring drive for a movable contact, an operator for controlling the toggle spring drive to manually operate the movable contact between open and closed position with respect to a stationary contact, a releasable latching member which, in its latched condition, enables the overcenter toggle spring drive and operator mechanism for manual control of the movable contact and which, in its unlatched condition, causes the overcenter toggle spring drive to move the movable contact to an open position independently of the manual operator, a current sensitive trip structure comprising a shape memory effect (SME) element for restraining the latch member in its latched condition and for releasing the same in response to predetermined current levels, and shunt trip apparatus housed within the molded case of the circuit breaker which is selectively operable from a remote location for effecting operation of the SME trip means for selectively releasing the latching member.

A more complete understanding of the invention will be had from the following description and claims when read in conjunction with the accompanying drawing.

The single FIGURE of the drawing is a schematic representation of a circuit breaker constructed in accordance with this invention.

Referring to the drawing, a circuit breaker of the residential and commercial frame molded case type such as that disclosed in U.S. Pat. No. 3,081,386 to M. F. Koenig et al, the disclosure of which is hereby incorporated in this disclosure by reference, is shown in a schematic manner. The circuit breaker comprises a molded insulating housing represented by the outline 2. A stationary contact assembly 4 is positioned within the housing at the lower left-end corner thereof, the stationary contact assembly having a terminal portion 4a projecting outwardly of the bottom of the circuit breaker housing 2 for connection with an electrical power distribution circuit and having a stationary contact element 4b secured to an internal face thereof. An operator handle 6 is journaled for rotation within the housing 2 about trunnions 6a (only one shown). Operator 6 has a flange 6b depending along the forward surface with respect to the plane of the drawing and has a similar flange disposed along the rearward surface thereof to form an open channel therebetween. A movable contact arm 8, also formed as a channel, has outwardly projecting ears 8a adjacent the upper ends of forward and rearward respective legs. The ears 8a are received within holes formed in the flanges 6b of operator 6 to pivotally support the movable contact arm from the operator handle 6. A movable contact element 8b is secured to a lower face of the movable contact arm 8 to mutually engage with contact element 4b of stationary contact assembly 4. An inverted U-shaped latch lever 10 is pivotally supported within the housing 2. Latch lever 10 has a foot portion 10a formed at the lower end of left-hand leg as viewed in the drawing which rests within a suitable support recess 2a formed in the housing to serve as the pivotal support for the latch lever 10. The bight portion of latch lever 10 is disposed between the flanges 6b of operator 6 and between the legs of movable contact arm 8. The right-hand leg of latch lever 10 is provided with a notched latching surface 10b. A helical spring 12 is connected in tension between the bight portion of latch lever 10 and the unsupported lower end of movable contact arm 8. A second helical spring 14 is connected in tension between the left-hand leg of latch lever 10 and a post 2b formed in the housing 2.

A current sensing trip member 16 is rigidly affixed to a heater strip 18 by a rivet 20 or the like. Heater 18 is electrically affixed to a conductor 22 such as by brazing, soldering, welding or the like, the conductor strip 22 being received within a pressure type wiring terminal 24 which receives a conductor from an electrical distribution circuit in which the circuit breaker is to provide overcurrent protection. The opposite end of heater strip 18 is connected to one end of a flexible braided conductor 26 which is attached by soldering, brazing or the like at its other end to the movable contact arm 8. A screw 28 serves to connect heater strip 18 and conductor 26 and to secure the heater strip 18 to the housing 2. When the circuit breaker is connected into an electrical distribution circuit such as by plugging it into a panelboard and connecting the wires of the distribution circuit thereto, a circuit will exist within the circuit breaker from terminal 24 through conductor 22, heater 18, braided conductor 26, movable contact arm 8, movable contact 8b, stationary contact 4b and stationary contact terminal 4a to the other side of the power distribution circuit.

A second flexible conductor such as wire 30 is electrically attached by welding, brazing or the like to the end of trip member 16 at a point near the engagement thereof with latch lever 10. Wire 30 is brought outside the circuit breaker housing 2 and is connected to one side of a remote control apparatus which may be a manual switch or a condition sensing switch operable upon some input, either manual, mechanical or electrical, to complete a circuit through the supply side of the distribution circuit, connector 24, conductor 22, the top portion of heater 18, and through the element 16, wire 30 and control apparatus 32 and through a current limiting resistor 34 to ground. The current limiting resistor 34 limits the amount of current drawn by this pilot control circuit.

When the current sensing trip structure 16 is in the latching position shown in the drawing, the unsupported end thereof directly engages the latching surface 10b of latch lever 10 to restrain the latch lever in the position shown. In this position, the operating mechanism for the circuit breaker is enabled whereby movable contact arm 8 is manually controllable by operator 6. Manual rotation of operator 6 to the right causes the pivotal support ears 8a of the movable contact arm 8 to move leftward across the line of action of overcenter drive spring 12, thereby causing a toggling action of the movable contact arm to separate the contacts 4b and 8b with a snap-action. The housing 2 may be provided with a suitable stop 2c for arresting the opening movement of the movable contact arm 8. Manual rotation of operator 6 from the right-hand position back to the left-hand position shown in the drawings will rotate the pivotally supported end 8a of the movable contact arm 8 back across the line of action of the overcenter drive spring 12 to cause toggling action of the free end of movable contact arm 8 to thereby cause the contacts 8b to close upon stationary contact 4b.

Although not limited thereto, the current sensing trip means 16 is preferably formed from a shape memory effect (SME) alloy. Elements made from such alloys may be formed to a shape which is to be remembered by the element, heat treated to cause the element to remember that shape, and then formed to an intermediate shape. The element 16 as shown in the drawing has a memory shape which is warped to the right as represented by the dotted lines in the drawing, and is formed as a flat member in its intermediate shape. When the element 16 is heated to a temperature above a predetermined transition range for the SME material, the element changes abruptly to its memory configuration. This change occurs with significant force, relatively rapidly and provides a large degree of movement for a relatively narrow temperature band. As described in the aforementioned related application, the element 16 is formed to have a significant amount of movement from its intermediate shape to its memory shape, such movement being considerably in excess of the amount of movement required to release the latch lever 10. By so forming the element 16, calibration of the circuit breaker at the factory during and after the assembly thereof is not required.

In the event that overload current conditions are present in the distribution circuit, such currents will generate heat in the heater strip 18 so as to cause indirect heating of the SME element 16. When heated to its transition temperature, the element 16 warps to its right-hand or dotted line position, to release the latch lever 10. Spring 12 coacting between the lower end of movable contact arm 8 and the bight of latch lever 10 moves the latch lever 10 clockwise above the support point 2a. Such movement carries the line of action of overcenter toggle spring 12 across the axis of pivotal support 8a of the movable contact arm, thereby causing the latter to toggle open with a snap-action.

The element 16 is preferably formed to be a two-way SME alloy whereby upon cooling of the element below the transition temperature it returns to the intermediate flat shape in which it is in position to engage latching surface 10b and latch the latch lever 10. Alternatively, a spring may be employed between a suitable formation in the housing 2 and the element 16 to bias the element 16 to its intermediate flat condition upon cooling thereof if the element is not otherwise formed to be a two-way element. Once the SME element is cooled and in its intermediate position, the circuit breaker may be reset by operating the handle 6 fully to the right-hand position so as to relax the spring 12 to its greatest amount whereupon the spring 14 provides a counterclockwise rotation to the latch lever 10 to cause the right-hand leg to move upward along the element 16 until latching surface 10b engages the unsupported end of the SME element 16. Movement of the operator 6 to the left will then carry the pivotally supported upper end 8a of movable contact arm 8 across the line of action of spring 12 to effect toggling of the overcenter mechanism and reclosure of the contact 8b upon stationary contact 4b.

The circuit breaker may be selectively operated to its tripped position by operation of the remote control apparatus 32 to a closed condition thereby to connect the SME element in circuit with the electric source. When so connected, current flowing through the element 16 causes direct heating thereof to cause the latter to warp to its right-hand dotted-line position thereby releasing the latch lever 10 and operating the movable contact arm 8 to the tripped position as aforedescribed. Because the SME element is directly heated by current flow in the shunt trip control circuit, much less current is required to heat the element to its transition temperature than was required of the indirect heating provided by the current flow in the distribution circuit.

The foregoing has described a preferred embodiment of an electric circuit breaker which utilizes a shape memory effect element therein as a current sensing trip means and as a shunt trip operating element. It is to be understood that this invention is susceptible of various modifications without departing from the scope of the appended claims.