Patent Application
20110115585
The present invention relates to multi-pole circuit breakers that use shared components to reduce cost and size.
Miniature circuit breakers sold today are usually 1 or 2 pole units, in either 15 or 20 amp configurations (although units with additional poles and other amperages also exist), and can include electronics to provide arcing fault (“AFI”) and/or ground fault (“GFI”) protection. These circuit breakers are typically sold and packaged as single units, thus requiring stocking of each individual type or version in stores or in warehouses. There is an increasing need for multi-pole circuit breaker assemblies, particularly for residential applications, and thus there is a need for alternatives to the use of multiple 1-pole and/or 2-pole circuit breakers.
The present disclosure provides a multi-pole circuit breaker comprising a single main housing containing multiple circuit breakers for protecting multiple branch circuits. Each of the circuit breakers comprises a single line terminal for receiving electrical current from a utility line, a plurality of load terminals for supplying electrical current from the single line terminal to a plurality of branch circuits via load lines, and a plurality of neutral terminals for receiving electrical current returned from the branch circuits via neutral lines. Line conductors inside the main housing connect the line terminal to the plurality of load terminals. Sensors inside the main housing generate signals representing characteristics of the electrical current flow in the branch circuits, and a signal processor uses the signals generated by the sensors for detecting fault conditions in the branch circuits and generating trip signals in response to the detection of fault conditions. A single tripping mechanism between the line terminal and the load terminals receives the trip signals and interrupts the flow of current to the branch circuits in response to a trip signal.
As used herein, the term “circuit breaker” refers to a device that uses a single tripping mechanism to control the flow of current to two or more branch circuits.
In one implementation, a single ground fault sensor is coupled to conductors located inside the main housing and to the load terminals and neutral terminals for the plurality of branch circuits, for producing a signal representing an imbalance in the current flow in the load and neutral lines for a plurality of branch circuits, and a separate current sensor coupled to each of the branch circuits produces a separate current signal representing characteristics of the current flow in each branch circuit. A single signal processor receives signals from all the ground fault and current sensors to detect the occurrence of a ground fault, overloads or an arcing fault in any of the plurality of branch circuits. If desired, voltages and other operating conditions may also be monitored and used to control the tripping operations.
The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which:
Although the invention will be described in connection with certain preferred embodiments, it will be understood that the invention is not limited to those particular embodiments. On the contrary, the invention is intended to cover all alternatives, modifications, and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims.
Turning now to the drawings and referring first to
Inside the housing 10, the two neutral lines associated with each circuit breaker are joined to a single neutral conductor 17 (see
The front of the housing 10 forms a pair of shallow recesses for receiving a pair of face plate labels 21 and 22. Included in the face plate labels are circuit traces and electronic components such as the push-to-test (PTT) buttons 14a-14d and LEDs 24a-24d, which may be used to indicate the trip status of each of the four circuit breakers. The labels 21 and/or 22 may include a dome switch (not shown) for each pole position. The LEDs 24a-24d may be illuminated to show the cause of a breaker trip (e.g., overload, ground fault, arcing fault, or the use of a PTT button) or to indicate which of the branch circuits associated with a common breaker caused the tripping of that breaker. For example, an LED may be illuminated continuously or intermittently in one or more colors to indicate which branch circuit caused the tripping of a given breaker.
From the movable contact carrier 31, the line conductor 34 conducts the current through a single ground fault sensor 40 that is common to both branch circuits, and then the bifurcated portions 34a and 34b conduct current through a pair of parallel arcing fault or current sensors 41 and 42 to the two load terminals 15a and 15b. The current path them proceeds from the load terminals 15a and 15b to the field loads by means of field wiring (not shown).
After the current has gone through the field loads, it returns to the circuit breaker via neutral wires (not shown) which are connected to the neutral terminals 16a, 16b, and is then carried by the single neutral conductor 17 through the ground fault sensor 40 to the common neutral conductor 18 for all the neutral wires in the housing 10. The conductor 18 exits the housing 10 and forms the neutral pigtail 20. Since multiple poles are combined into one housing, only the one common neutral pigtail 20 (or other standard connector) is needed outside the housing, which further reduces the cost of the assembly.
The illustrative circuit breaker includes an actuating mechanism that opens and closes the contacts 32 and 33. For the open position, the movable contact carrier 31 is rotated away from the stationary contact 32, causing the movable contact 33 to separate from the stationary contact 32. When the contacts 32 and 33 separate, current no longer flows from the line terminal 13a to the load terminals 15a and 15b. The circuit breaker may be tripped open in any of several ways, including manual control or in response to an abnormal condition such as a short circuit, an overload, arcing fault or ground fault.
The movable contact carrier 31 may be moved between the open and closed positions by a user manually moving the handle 12a to the right or left, respectively, causing corresponding movement of the upper end of the movable contact carrier 31 to the left or right of a pivot point. A spring 35 is connected at one end to trip lever 50 and at another end to the bottom of the movable contact carrier 31. When the upper end of the movable contact carrier 31 is left of the pivot point, the spring 35 biases the bottom of the movable contact carrier 31 to the open position. Conversely, when the upper end of the movable contact carrier 31 is right of the pivot point, the spring 35 biases the bottom of the movable contact carrier 31 to the closed position.
In the closed position, the trip lever 50 is latched by engagement with an armature 51. The trip lever 50 is pivotally mounted about a pivot at one end. The other end of the trip lever 40 is seated in a latched position on the armature 51. The spring 35 connects the trip lever 40 to the movable contact carrier 31, and biases the movable contact 33 against the stationary contact 32. To trip the breaker, a solenoid 52 is energized to move the armature 51 to unlatch the trip lever 50. The trip lever 50 then swings clockwise to its tripped position, carrying the upper end of the spring 35 to the opposite side of its dead center position. The spring 35 rotates the movable contact carrier 31 from the closed circuit position to the open circuit position, separating the movable contact 33 from the stationary contact 32.
The circuit breaker is provided with circuitry 53 to trip the breaker in response to an arcing fault, ground fault or overload. The trip circuitry 53, which typically includes signal processing circuitry (usually in the form of a signal processor), is formed on a printed wiring assembly (PWA, which is a printed circuit board having multiple components mounted on it) 54 mounted within the housing 10. When the circuitry detects any of these abnormal conditions, it generates a trip signal to energize the solenoid 52.
To detect the occurrence of a ground fault when the contacts 32 and 33 are closed, the ground fault sensor 40 detects any difference between the currents in the line conductor 34 and the neutral conductor 17 and provides a signal representing any such difference to the trip circuitry 53. The neutral conductor 17 and the line conductor 34 are both routed through the ground fault sensor 40 to permit sensing of any such imbalance of current flow in the line and neutral conductors. If the imbalance exceeds the trip level of the ground fault detection circuitry, the trip circuitry 53 sends a trip signal to energize the solenoid 52 to trip the circuit breaker.
One example of a ground fault detection circuit is described in U.S. Pat. No. 7,193,827, and an improved sensor utilizing that circuit is described in copending application Ser. No. 12/267,750 filed Nov. 10, 2008, both of which are assigned to the assignee of the present invention and are incorporated herein by reference in their entirety. The detection circuit described in U.S. Pat. No. 7,193,827 detects both ground faults and grounded neutrals with only a single current sensor.
To detect the occurrence of an arcing fault when the contacts 32 and 33 are closed, the bifurcated portions 34a and 34b of the line conductor 34 pass through the arcing fault or current sensors 41 and 42 to monitor the currents supplied to the two branch circuits via the load terminals 15a and 15b. Signals from the sensors 41 and 42, preferably representing the respective rates-of-change of the currents, are supplied to the trip circuitry 53 mounted on the printed circuit board. The arcing fault detection circuitry in the trip circuitry 53 analyzes the signal for characteristics of an arcing fault. If the arcing fault detection circuitry detects the presence of an arcing fault, it sends a trip signal to energize the solenoid 52 to trip the circuit breaker.
The patterns of the fluctuations in the signals produced by the arcing fault or current sensors 41 and 42 indicate whether the associated branch circuits are in normal operating condition or an arcing fault condition. Examples of suitable arcing fault sensors and arcing fault detection circuitry or signal processors are described in U.S. Pat. Nos. 6,259,996, 7,151,656, 7,068,480, 7,136,265, 7,253,637 and 7,345,860, owned by the assignee of the present invention, which are incorporated herein by reference in their entirety.
To detect the occurrence of an overload when the contacts 32 and 33 are closed, an overload detection portion of the trip circuitry 53 samples the current flowing through the line conductor 34. The overload detection circuitry analyzes the current samples for characteristics of an overload, and if an overload is detected, the trip circuitry 53 sends a trip signal to energize the solenoid 52 to trip the circuit breaker in the same fashion as described above. Overload detection circuitry typically simulates the bimetal deflection of traditional circuit breakers, as described in U.S. Pat. No. 5,136,457, assigned to the assignee of the present invention and incorporated herein by reference in its entirety. To simulate bimetal deflection, the overload circuitry accumulates the squared values of current samples taken from the line conductor 34. The sum of the squared values of that current is proportional to the accumulated heat in the tripping system. The overcurrent circuitry decrements logarithmically the accumulated square of the current to account for the rate of heat lost due to the temperature of the power system conductors being above ambient temperature. When the accumulating value exceeds a predetermined threshold representing the maximum allowed heat content of the system, the trip circuitry 53 sends a trip signal to energize the solenoid 52 to trip the circuit breaker.
To produce a faster trip when the current in the load line increases significantly, such as in the case of a short circuit, the line conductor 34 is wrapped around (two turns) the frame 54 of the tripping solenoid 52 to induce a magnetic loop (see
The neutral wires from the branch circuits are connected to the neutral terminals 16a and 16b that have a common connector plate 75 connected to the neutral conductor 17 that passes through the ground fault sensor 40 to a common neutral bar 70 that receives the neutral wires from all the branch circuits.
While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.
