ARC FAULT CIRCUIT INTERRUPTER WITH PLUG-ON NEUTRAL CONTACT CLIP SPRING

BACKGROUND OF THE INVENTION Field of the Invention

[0001] The invention relates generally to circuit interrupters and, more particularly, to arc fault circuit interrupters including a neutral connector.

Background Information

[0002] Circuit interrupters include, for example, circuit breakers, contactors, motor starters, motor controllers, other load controllers, and receptacles having a trip mechanism. Circuit breakers are generally old and well known in the art. Examples of circuit breakers are disclosed in U.S. Pat. Nos. 5,260,676 and 5,293,522.

[0003] Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal which is heated and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism which opens separable contacts of the circuit breaker to interrupt current flow in the protected power system. The trip device also includes an armature which, when attracted by the sizable magnetic forces generated by a short circuit or fault condition, also unlatches, or trips, the spring powered operating mechanism.

[0004] Recently, there has been considerable interest in also providing protection against arc faults. Arc faults are intermittent high impedance faults which can be caused, for instance, by worn insulation between adjacent conductors, by exposed ends between broken conductors, by faulty connections, and in other situations where conducting elements are in close proximity. Because of their intermittent and high impedance nature, arc faults do not generate currents of either sufficient instantaneous magnitude or sufficient average RMS current to trip the conventional circuit interrupter. Even so, the arcs can cause damage or start a fire if they occur near combustible material. It is not practical to simply lower the instantaneous current trip

level on conventional circuit breakers, as there are many typical loads which draw similar currents and would, therefore, cause nuisance trips. Consequently, separate electrical circuits have been developed for responding to arc faults. See, for example, U.S. Pat. Nos. 5,224,006 and 5,691,869.

[0005] Figure 1 shows an arc fault circuit interrupter (AFCI), such as a single pole miniature circuit breaker 1. Circuit breaker 1 includes several terminals/leads which are connectable to various parts of an electrical circuit. For example, terminals 3 (load line) and 4 (load neutral) are structured to electrically connect circuit breaker 1 to a load (not shown). Terminal 5 (as is best seen in Figure 2A) is structured to electrically connect the circuit breaker 1 to a source line conductor (not shown) of a power distribution system. Additionally, a pigtail 2 is structured to electrically connect the circuit breaker 1 to a source neutral conductor (not shown) from the power distribution system.

[0006] Figures 2 and 2A show the circuit breaker 1 installed in a loadcenter 6. Loadcenter 6 includes, without limitation, a neutral bar 7 and a backplate 21. The backplate 21 has a number of notched rails 22 thereon. It should be apparent that loadcenter 6 may have other components which, in the instant example, have been omitted for clarity.

[0007] The neutral bar 7 is a rectangular conductive bar having a number of threaded apertures 8. Each aperture 8 may have a screw 9 associated therewith. Typically, the neutral bar 7 is connected to the source neutral conductor (not shown) from the power distribution system. As illustrated in Figures 2 and 2 A, the free end 2a (Figure 1) of pigtail 2 is inserted into one of the threaded apertures 8 and secured therein with an associated screw 9.

[0008] The backplate 21 typically carries one or more line busses (not shown), each of which is connected to a source line conductor (not shown) of the power distribution system. Accordingly, when circuit breaker 1 is mounted on the notched rail 22 of the backplate 21 (for example, as best seen in Figure 2A), the terminal 5 is structured to electrically connect with one of these line busses (not shown).

[0009] There are several disadvantages related to the use of an arc fault circuit breaker 1 having a pigtail 2. For example, extra cost is incurred to manufacture the arc fault circuit breaker 1 because the other end of the pigtail 2 (not shown) must be electrically connected to the AFCI circuitry within the circuit breaker 1. Typically, a brazing/welding process is used to join the end of the pigtail 2 to the AFCI circuitry. Additionally, installation of the circuit breaker 1 requires an electrician to connect the free end 2a of the pigtail 2 to the neutral bar 7. As a result, the time needed to install the circuit breaker 1 and the possibility of human error (e.g., the pigtail end 2a not being connected correctly) increases. Furthermore, the interior of the loadcenter 6 becomes cluttered as a result of plural pigtails 2 being routed from plural circuit breakers to the neutral bar 7.

[0010] Thus, a need exists for an improved AFCI which eliminates these and other problems.

SUMMARY OF THE INVENTION

[0011] These needs and others are met by embodiments of the invention, which are directed to a circuit interrupter comprising a housing, separable contacts mounted within the housing, an operating mechanism structured to open the separable contacts when actuated, a trip assembly comprising an arc fault trip mechanism structured to generate a trip signal in response to detecting an arc fault, the trip assembly structured to actuate the operating mechanism in response to the trip signal, and a contact clip spring structured to mechanically couple and electrically connect the circuit interrupter to a neutral bar, wherein the contact clip spring is in electrical communication with the arc fault trip mechanism.

[0012] As another aspect of the invention, a circuit interrupter comprises a first terminal structured to electrically connect the circuit interrupter with a line conductor, a second terminal electrically connectable to a load conductor, separable contacts electrically connected between the first terminal and the second terminal, a trip assembly comprising an arc fault trip mechanism structured to generate a trip signal in response to detecting an arc fault, an operating mechanism structured to open the separable contacts in response to the trip signal, a contact clip spring structured to mechanically and electrically connect the circuit interrupter to a neutral bar, the

contact clip spring being in electrical communication with the arc fault trip mechanism, the neutral bar being in electrical communication with a neutral conductor, and a third terminal electrically connectable to a load neutral conductor, the third terminal being in electrical communication with the contact clip spring and the arc fault detector.

[0013] As another aspect of the invention, a circuit interrupter structured for use within an enclosure having a line bus electrically connectable to a source line conductor and a neutral bar electrically connectable to a source neutral conductor comprises a housing, separable contacts mounted within the housing, a trip assembly comprising an arc fault trip mechanism structured to generate a trip signal in response to detecting an arc fault, an operating mechanism structured to open the separable contacts when actuated in response to the trip signal, a contact clip spring structured to mechanically couple and electrically connect the circuit interrupter to the neutral bar, the contact clip spring being electrically connected to the arc fault trip mechanism, and a terminal structured to electrically connect the circuit interrupter to the line bus, the terminal being electrically connected to one of the separable contacts.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:

[0015] Figure 1 is an isometric view of an arc fault circuit breaker. [0016] Figure 2 is a simplified vertical elevation view of a loadcenter in which the arc fault circuit breaker of Figure 1 is installed.

[0017] Figure 2A is a cross-sectional view along lines 2A - 2A shown in Figure 2. [0018] Figure 3 is an isometric view of an arc fault circuit breaker according to an embodiment of the invention.

[0019] Figure 4 is a simplified vertical elevation view of a loadcenter in which the arc fault circuit breaker of Figure 3 is installed.

[0020] Figure 4A is a cross-sectional view along lines 4A - 4A of Figure 4. [0021] Figure 5 is a block diagram in schematic form of the circuit breaker of Figure 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS [0022] Directional phrases used herein, such as, for example, left, right, clockwise, counterclockwise, top, bottom, up, down, and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.

[0023] As employed herein, the term "number" shall mean one or more than one and the singular form of "a", "an", and "the" include plural referents unless the context clearly indicates otherwise.

[0024] As employed herein, the statement that two or more parts are "connected" or "coupled" together shall mean that the parts are joined together either directly or joined together through one or more intermediate parts. Further, as employed herein, the statement that two or more parts are "attached" shall mean that the parts are joined together directly.

[0025] Figure 3 shows an arc fault circuit interrupter (AFCI), such as circuit breaker 10. Circuit breaker 10 includes a housing 11 which is assembled from a number of molded sections composed of an electrically insulating material (as is well known). The housing 11 contains therein an arc fault detection trip mechanism 45 which, referring briefly to Figure 5, includes, for example and without limitation, an arc fault detector (AFD) 32, a silicon controlled rectifier (SCR) 35, a trip solenoid 36, a resistor 37, a capacitor 38, and a test circuit 39. Returning to Figure 1, a molded handle 16 projects from the housing 11 for manually opening and closing the circuit breaker 10 as is well known. Although not required, the circuit breaker 10 also includes a test push button 17, as described in U.S. Patent No. 5,982,593 and which is hereby incorporated by reference.

[0026] Circuit breaker 10 also includes several terminals/leads which are mechanically and/or electrically connectable to various parts of a power circuit. For example, at one end of the housing 11, terminal 12 is provided to electrically connect circuit breaker 10 to a load line conductor 42 (Figure 5) and terminal 13 is provided to electrically connect circuit breaker 10 to a load neutral conductor 43 (Figure 5). Terminal 14 (as best seen in Figure 4A) is structured to electrically connect the circuit breaker 10 to a source line conductor 25 (Figure 5) from a power source such as a

power distribution system (not shown). A contact clip spring (e.g., without limitation, made of spring steel; made of stainless steel; made of a suitable conductor that also provides a spring force) 15, located at the end of the housing 11 opposite the terminal 14, is structured to electrically connect the circuit breaker 10 to a source neutral conductor 26 (Figure 5) of the power distribution system (not shown). [0027] Referring to Figures 4 and 4A, the circuit breaker 10 is installed in a loadcenter 20. Loadcenter 20 includes, without limitation, backplate 21 having a number of notched rails 22 thereon. Loadcenter 20 also includes a neutral bar 23 which is structured to mechanically couple and electrically connect to circuit breaker 10. Loadcenter 20 may also include a neutral bar 7 as previously discussed. As seen in Figures 4 and 4A, neutral bar 23 is electrically connected to neutral bar 7 via conductive strap 40. It should be apparent that loadcenter 20 may have other components which, in the instant example, have been omitted for clarity. Additionally, although shown installed in a loadcenter 20, it should be apparent that circuit breaker 10 may be installed in other enclosures (e.g., panelboard; motor control center; power outlet panel; disconnect; switchboard; switchgear; etc.) adapted to receive circuit breaker 10 therein.

[0028] The neutral bar 7 and the neutral bar 23 are rectangular conductive bars, each having a number of threaded apertures 8. Each aperture 8 may have a screw 9 associated therewith. In the current embodiment, the neutral bar 7 is electrically connected to the source neutral conductor 26 (Figure 5) from the power distribution system (not shown) and, as mentioned above, neutral bar 23 is electrically connected to neutral bar 7 (and thus electrically connected to the source neutral conductor 26) via conductive strap 40. Alternatively, the neutral bar 23 may be directly electrically connected to the source neutral conductor 26. Although two neutral bars 7,23 are shown in Figure 4, preferably, a single inboard neutral bar (e.g., 23) is employed that accepts both the plug neutral connection (e.g., contact clip spring 15) from a circuit breaker, such as 10, and conventional screw terminations, such as 9, from returns or other non-arc fault circuits.

[0029] The backplate 21 typically carries one or more line busses (not shown), each of which is electrically connected to a source line conductor 25 (Figure 5) of the

power distribution system (not shown). The line busses may include a number of line stabs (not shown) which are structured to mechanically couple to terminal 14 and thereby electrically connect terminal 14 to the source line conductor 25. More specifically, when circuit breaker 10 is mounted on the notched rail 22 of the backplate 21 (for example, as best seen in Figure 4A), the terminal 14 electrically connects with one of these line busses.

[0030] Neutral bar 23 is positioned such that, when notched rail 22 is suitably aligned, neutral bar 23 is mechanically engaged by (i.e., coupled to), and is electrically connected with, contact clip spring 15.

[0031] As best seen in Figure 4 A, the contact clip spring 15 is structured to "snap over" the neutral bar 23 such that the interior surfaces of the contact clip spring 15 are sufficiently joined (both electrically and mechanically) to the outer surfaces of the neutral bar 23. In the exemplary embodiment, the contact clip spring 15 is constructed from a flat, strap-type conductor which is bent to the desired shape (e.g., bent in a shape that readily couples to neutral bar 23). Although the exemplary embodiment is discussed in the context of a specific contact clip spring 15, it should be apparent that other arrangements may be employed. Accordingly, as used herein, the term "contact clip spring" is intended to refer to any arrangement which both electrically connects and mechanically couples the circuit breaker 10 to a line neutral conductor 26 (e.g., via neutral bar 23) and thereby eliminates the pigtail connection.

[0032] Another conductor (e.g., made of any suitable conductor; made of brass; made of copper) 44 (Figure 5) electrically connects the contact clip spring 15 to the arc fault trip mechanism 45 within the housing 11 of circuit breaker 10 thereby eliminating the need for a pigtail connection in the exemplary embodiment. As a result, the cost of manufacturing the circuit breaker 10, the time needed to install the circuit breaker 10, and the possibility of human error occurring during installation are decreased. Furthermore, because pigtails are eliminated, the interior of the loadcenter 20 is less cluttered when circuit breaker 10 is installed therein. Although both of the contact clip spring 15 and conductor 44 are shown, it will be appreciated that they may be combined in a single component.

[0033] As shown in Figure 5, the circuit breaker 10 is a component within an electric power system 24 which has, without limitation, source line conductor 25, source neutral conductor 26, load line conductor 42, and load neutral conductor 43. More specifically, terminal 14 is electrically connected to source line conductor 25 (for example, via a line bus with a number of line stabs as discussed above) and contact clip spring 15 is electrically connected to source neutral conductor 26 (for example, via the neutral bar 23 as discussed above). Terminal 12 is electrically connected to load line conductor 42 and terminal 13 is electrically connected to load neutral conductor 43.

[0034] The circuit breaker 10 includes separable contacts 27 which are mounted in the housing 11, at least one of which is electrically connected to the source line conductor 25. The separable contacts 27 are opened and closed by an operating mechanism 28. In addition to being operated manually by the handle 16 (as shown in Figure 3), the operating mechanism 28 can also be actuated to open the separable contacts 27 by a trip assembly 29 in response to predetermined current conditions. [0035] The trip assembly 29 includes the conventional bimetal 30 which is heated by persistent overcurrents and bends to actuate the operating mechanism 28 to open the separable contacts 27. An armature 31 in the trip assembly 29 is attracted by the large magnetic force generated by very high overcurrents to also actuate the operating mechanism 28 and provide an instantaneous trip function. Separable contacts 27 and bimetal 30, without limitation, form a circuit path 41 between terminal 14 and terminal 12.

[0036] The trip assembly 29 of the circuit breaker 10 also includes the arc fault trip mechanism 45 which, in the exemplary embodiment (and as discussed above), includes arc fault detector (AFD) 32, silicon controlled rectifier (SCR) 35, trip solenoid 36, resistor 37, capacitor 38, and test circuit 39. The AFD 32 may be, for instance, of the type which detects the step increases in current which occur each time an arc is struck, although other types of arc fault detectors could also be used. Suitable arc fault detectors are disclosed, for instance, in U.S. Pat. No. 5,224,006, with a preferred type described in U.S. Pat. No. 5,691,869, both of which are hereby incorporated by reference herein.

[0037] The AFD 32 senses the current in the electric power system 24 by monitoring the voltage across a resistive element (e.g., without limitation, the bimetal 30) in the same conductive path through the lead 33 to sense an arc fault condition. As described in U.S. Pat. No. 5,691,869, the AFD 32 includes circuitry which generates a pulse in response to each step change in current. The pulse signal is integrated with the result of the integration being attenuated over time. When the time attenuated accumulation of the pulses reaches a selected level, the AFD 32 generates at its output an arc fault trip signal 34 which is active in response to the arc fault. In turn, the signal 34 is employed to actuate the operating mechanism 28 and open the separable contacts 27 in response to the arc fault.

[0038] More specifically, the trip signal 34 turns silicon controlled rectifier (SCR) 35 on and energizes the trip solenoid 36, thereby actuating the operating mechanism 28 to open the separable contacts 27 in response to the arc fault. Resistor 37 in series with the coil of the solenoid 36 limits the coil current and capacitor 38 protects the gate of the SCR 35 from voltage spikes and false tripping due to noise. [0039] The arc fault detector 32 has a test circuit 39 associated therewith. The arc fault test circuit 39 is enabled in response to test push button (PB) 17 for testing the AFD 32. Under test operation, if the AFD 32 is operating properly, then it generates the trip signal 34 when the associated test circuit 39 is enabled. [0040] The arc fault test circuit 39, when enabled, provides test signals to the AFD 32 to simulate an arc fault condition by mimicking arc faults in the electric power system 24 and, thereby, testing operation of the AFD 32. The test circuit 39 preferably includes a low frequency relaxation oscillator and a coupling circuit for coupling a pulse signal generated by the relaxation oscillator to the AFD 32. [0041] While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.