STANDARD SIZE APPARATUS TO DETECT ARC FAILURES AND GROUND FAILURES IN CIRCUITS
OF ELECTRICAL POWER RAMALES DE
MULTIPLE WIRES
Background of the Invention Field of the Invention This invention relates to an apparatus for providing protection in multiple-wire branch circuits of electric power distribution systems and, in particular, to two-pole circuit breakers that share a common neutral, for provide protection for arc faults and ground faults in such circuits, which are capable of mounting in two standard, adjacent 3/4 inch slots of a load center panel. Background Information Branch circuits in power distribution systems often share a common neutral conductor to reduce the required wiring. Such multiple wire branch circuits are often referred to as "quadrangular"
(home runs). Quad runs are allowed as long as the two line drivers are energized by separate phases of 120 volts from a single-phase, center-tip transformer, to avoid overloading the neutral conductor. This simultaneous disconnection of both ungrounded conductors can be achieved with two-pole disconnect circuit breakers, two simple poles, with a handle clamp, or a two-pole circuit breaker. Presently, such multiple wire branch circuits can be provided with protection against short circuits and overcurrent by means of the single-pole circuit breakers moored or the two-pole circuit breaker. Only a two-pole circuit breaker can also provide protection against ground faults along with the addition of a common ground fault detector. Ground fault protection can be either personal protection or equipment protection. Recently there has been an increased interest in providing protection against arc faults. Arc faults are intermittent, high impedance faults that can be caused, for example, by worn insulation, loose connections, broken conductors, and the like. Due to their intermittent nature and high impedance, they do not generate currents of sufficient instantaneous magnitude or sufficient average current to trigger the thermo-magnetic triggering device that provides protection against short circuits and overcurrent. Various types of arc fault detectors have been proposed, but except for the circuit described in U.S. Patent Application No. 08 / 939,263, filed September 29, 1997 (attorney's file 97-PDC-312) , such detectors have not been adapted to multiple wire branches that use a common ground. There is an additional need for an arc fault circuit breaker in a two-pole design with a shared neutral for application in common domestic load centers, which employ standard face panels with 3/4 inch slots. The state of the art has taught the use of multi-pole circuit breaker designs, such as those of U.S. Patent Nos. 5,483,211, filed January 9, 1996, and 5,453,723, filed September 26, 1995, where the electronic trip circuits are housed in separate compartments of the thermo-magnetic trip units and span several circuit breaker slots in a load center. However, none of these arrangements is adequate for a quadrangular configuration. In this way, the state of the art evidences the additional need for an arc fault circuit breaker in a two-pole design, with a shared neutral for application in common domestic load centers, which employ standard face panels with grooves of 3/4 of an inch SUMMARY OF THE INVENTION These and other needs are met by the invention, which is directed to an apparatus for detecting faults in multiple-wire branch circuits, that is, capable of to fit within 3/4 inch slot panels of standard load centers. It includes a two-pole circuit breaker (providing standard protection in the circuit) having a first pole connected to interrupt current in the first line conductor and a second pole connected to interrupt current simultaneously in the second line conductor. The apparatus further includes fault detection circuitry which includes a first arc fault detector connected to detect arc currents between the first line and neutral conductor or ground and to generate a trip signal in response thereto., and a ground fault detector connected to detect ground faults between each of the line and ground conductors. The apparatus also includes a conventional thermo-magnetic trip mechanism and means that respond to each of the trip signals to trip the two-pole circuit breaker. Preferably, the thermo-magnetic trip unit for both poles is maintained within a standard 3/4 inch circuit breaker box, having a face designed to protrude through the standard 3/4 inch slots the load center panels. The electronic processing circuits for the earth fault detection and arc fault circuits are maintained within a standard 3/4 inch housing that meets the first housing on its side so that the two housings are aligned and connected at their junction in a way that allows them to protrude through adjacent slots in the load center panel. In one embodiment, circuit breaker switches protrude through the face of the first housing, while the trip indicator and dual trip test button protrude through the face of the second housing. Desirably, electrical shielding is provided at the interface between the first and second housings. These, together with other objects and advantages that will be subsequently apparent, reside in the details of construction and operation as will be more fully described and claimed hereinafter, reference being made to the accompanying drawings, which form a part hereof. BRIEF DESCRIPTION OF THE DRAWINGS The preceding aspects will be more fully appreciated in view of an illustrative example thereof, taken in conjunction with the accompanying drawing, in which: Figure 1 is a top perspective view of a circuit breaker housing. circuit constructed in accordance with this invention. Description of the Preferred Embodiment Form Figure 1 illustrates a circuit breaker housing 10 constructed in accordance with this invention. The housing 10 forms two interior compartments 12 and 14. Each of the compartments 12 and 14 is sized to be substantially equivalent in volume and design to a standard 3/4 inch circuit breaker housing. The compartment 12 houses a thermo-magnetic trip mechanism of the circuit breaker, which is well known in the art. The thermomagnetic firing mechanism includes separate thermo-magnetic firing sets for each pole, which are tied together by means of a common firing bar. Each pole can be reset using the switch levers 16 and 18, which are connected by means of a handle link 17 so that both poles are simultaneously reset. Where a common neutral conductor is used, it is important that both poles are disconnected simultaneously. Although not shown, a male pin is provided under each of the housings 12 and 14 to connect the live side of the line, respectively, for phases A and B. A female pin is also provided on the underside of the breaker and aligned to connect to the line ground on the rear panel of the load center. The load wiring of phase A is connected to terminal 24 and the load wiring of phase B is connected to terminal 26; both terminals being positioned at the periphery of the housing 12. The second compartment 14 houses the electronics for the ground fault detection circuit and the arc fault detection circuit. The electronics and operation of the fault detection circuits can be better appreciated by reference to U.S. patent application Serial No. 08 / 939,263, pending (attorney's file 97-PDC-312). Preferably, electrical shielding is provided between the housings 12 and 14 so that arcing occurring within the compartment 12 does not affect the electronics housed in the compartment 14. A dual test button 22 protrudes through the face of the compartment 14 to test the earth fault and / or arc fault detection circuits. In addition, a trip indicator is provided on the face of the compartment 14. Both the compartment 12 and the compartment 14, respectively, have a raised portion on its face, which fits through the slot in the load center panel. A recess 32 is provided between the two raised faces 28 and 30 to seat the cross member extending between the slots in the load center panel. In this manner, the housing of this invention allows a two-pole circuit breaker that employs a shared neutral and having arc fault and earth fault trip capability to be seated within a standard 3/4 inch circuit breaker panel. , so as to allow to shield the electronics of the arcs generated within the portion of the thermo-magnetic trigger mechanism in the housing. Although specific embodiments of the invention have been described in detail, those skilled in the art will appreciate that various modifications and alternatives to those details may be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are intended to be illustrative only and not limiting as to the scope of the invention, to which the full scope of the appended claims and any and all equivalents thereof must be given.