Abstract:
A leakage current detection and interruption (LCDI) device, for use as a safety device for a cable connecting, a power source with a load. The LCDI having a safety circuit that senses the presence of an arcing condition between one of the conducting lines and a metal sheath, and in response thereto, opens at least one of the conducting lines between the power supply and the load. The structure of the LCDI circuit card assembly incorporates a load input cavity having fire retardant materials surrounding the load input terminals, and further includes a contact actuator which encases the switch or contact arm at the source input section of the LCDI.

Description:
BACKGROUND 
     1. Field of Use 
     The present invention relates generally to electrical safety devices and more particularly to a Leakage Detection and Interruption (LCDI) device having ignition containment features. 
     2. Description of Prior Art 
     Conventional electrical appliances typically receive alternating current (AC) power from a power supply, such as an electrical outlet, through a pair of conducting lines. The pair of conducting lines, often referred to as the line and neutral conductors, enable the electrical appliance, or load, to receive the current necessary to operate. 
     A power cable typically comprises at least two conducting lines through which current travels from the power source to the load. Specifically, a power cable typically comprises a power line and a neutral line. A metal sheath can be used to surround the power line and the neutral line in order to provide the power cable with arc sensing capabilities. 
     The connection of an electrical appliance to a power supply through a pair of conducting lines can create a number of potentially dangerous conditions. In particular, there exists the risk of ground fault and grounded neutral conditions in the conducting lines. A ground fault condition occurs when there is an imbalance between the currents flowing in the power and neutral lines. A grounded neutral condition occurs when the neutral line is grounded at the load. 
     Ground fault circuit interrupters are well known in the an and are commonly used to protect against ground fault and grounded neutral conditions. A ground fault circuit interrupter (GFCI) typically comprises a differential transformer with opposed primary windings, one primary winding being associated with the power line and the other primary winding being associated with the neutral line. If a ground fault condition should occur on the load side of the GFCI, the two primary windings will no longer cancel, thereby producing a flux flow in the core of the differential transformer. This resultant flux flow is detected by a secondary winding wrapped around the differential transformer core. In response thereto, the secondary winding produces a trip signal which, in turn, serves to open at least one of the conducting lines between the power supply and the load, thereby eliminating the dangerous condition. 
     While GFCI circuits of the type described above are well known and widely used in commerce to protect against ground fault and grounded neutral, conditions, it should be noted that a power cable is susceptible to other types of hazardous conditions which are not protected against by a conventional GFCI circuit. As an example, it has been found that one type of arcing condition can occur between one of the conducting lines and the metal sheath which surrounds the conducting lines. It should be noted that the presence of this type of arcing condition between either the power line and the metal sheath or the neutral line and the metal sheath can result in a fire or other dangerous condition. 
     When an electrical spark jumps between two conductors or from one conductor to ground the spark represents an electrical discharge through the air and is objectionable because beat is produced as a byproduct of this unintentional “arcing” path. Such arcing faults are a leading cause of electrical fires. Arcing faults can occur in the same places that ground faults can occur—in fact, a ground fault would be called an arcing fault if it resulted in an electrical discharge, or spark, across an air gap. Arc fault detection is typically accomplished by monitoring the electrical current flow into a load and comparing the profile of this current flow to a characteristic “signature&#39; that arcing faults will exhibit it is known for ALCI enclosures to “burn up” during an internal fire or ignition creating extreme hazards and dangerous conditions. 
     In U.S. Pat. No. 7,525,777, to Aromin, V, incorporated herein by reference for all it discloses, new and improved safety circuits for a power cables are disclosed. The power cable includes two or more conducting lines and a metal sheath surrounding the conducting lines. The safety circuits sense the presence of an arcing condition between one of the conducting lines and the metal sheath, and in response thereto, opens at least one of the conducting lines between the power supply and the load. 
     Although a variety of safety circuits are available to shut down an ALCI is response to hazardous arcing conditions there is a need for an ALCI that can contain “burn up” during an internal fire through the use of fire retardant materials and structure located on the circuit assembly. 
     BRIEF SUMMARY 
     The foregoing and other problems are overcome, and other advantages are realized, in accordance with the presently preferred embodiments of these teachings. In accordance with one embodiment of the invention a Leakage Current Detection and Interruption Device (LCDI) with Ignition Containment features is disclosed. 
     The structure of the LCDI circuit card assembly incorporates a load input cavity having fire retardant materials surrounding the load input terminals, and further includes a contact actuator which encases the switch or contact arm at the source input section of the LCDI. Further, the particular placement of components on the circuit card assembly is to maximize the fire containment features of the LCDI. The circuit card assembly incorporates either 120 Volt, 240 Volt 15 Amp, or 240 Volt 20 Amp source input conductors. 
     Components and circuit traces mounted and or adhered to the LCDI Circuit Card assembly are configured to minimize packaging density while simultaneously maximizing distances between component and circuit traces to conform to required safety standards, e.g., UL840, to prevent electric arcing, and dielectric breakdown. A safety circuit for a power cable is included and disposed on the circuit assembly which includes two or more conducting lines and a metal sheath surrounding the conducting lines. 
     The safety circuit senses the presence of an arcing condition between one of the conducting lines and the metal sheath, and in response thereto, opens at least one of the conducting lines between the power supply and the load. The safety circuit and circuit card assembly may be mass produced, has a minimal number of parts, and can be easily assembled. 
     The safety circuit is for use with a power cable, said power cable connecting a power source with a load, said power cable comprising a power line, a neutral line and a metal sheath which surrounds the power line and the neutral line, said safety circuit comprising a circuit breaker comprising a first switch located in one of said lines between the power source and the load, said switch having a first position in which the power source in its associated line is connected to the load and a second position in which the power source in its associated line is not connected to the load, a circuit opening, device for setting said switch in either its first position or its second position, said circuit opening device being operable in either a first state or a second state, said circuit opening device setting said switch in its first position when in its first state and said circuit opening device setting said switch in its second position when in its second state, a first silicon controlled rectifier (SCR) for detecting the presence of an arcing condition between one of said lines and the metal sheath, said first SCR setting said circuit opening device at its second state upon detecting the presence of an arcing condition between one of said lines and the metal sheath. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic circuit diagram of an embodiment of a safety circuit used in the Leakage Current Detection and Interruption Device (LCDI) of the present invention; 
         FIG. 2  is another schematic circuit diagram of an embodiment of a safety circuit used in the LCDI of the present invention; 
         FIG. 3  is another schematic circuit diagram of an embodiment of a safety circuit used in the LCDI of the present invention; 
         FIG. 4  is another schematic circuit diagram an embodiment of a safety circuit used in the LCDI of the present invention; 
         FIG. 5  is a perspective top view of an LCDI enclosure employing the principles of subject invention; 
         FIG. 6  is a perspective bottom view of an LCDI enclosure with 240 Volt 20 Amp source conductors employing the principles of subject invention; 
         FIG. 7  is a perspective bottom view of an LCDI enclosure with 240 Volt 15 Amp source conductors employing the principles of subject invention; 
         FIG. 8  is a perspective bottom view of an LCDI enclosure with 120 Volt source conductors employing the principles of subject invention; 
         FIGS. 9 through 13  illustrate a circuit assembly for an LCDI employing the principles of subject invention; 
         FIG. 11A  illustrates an exploded view of  FIG. 11 ; 
         FIG. 14  illustrates a circuit card assembly mounted in a bottom LCDI housing employing the principles of subject invention; 
         FIGS. 15 and 16  illustrate a circuit card assembly having a connected load input cable employing the principles of subject invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1  there is shown a first embodiment of a safety circuit constructed according to the teachings of the present invention, the safety circuit being represented generally by reference numeral  1011 . Safety circuit  1011  is designed principally for use as a safety device for a power cable P which connects a power source (i.e., a line) to a load, said power cable P including a power line L, a neutral line N, and a ground line G. Each of the power and neutral lines L and N is wrapped with a metal sheath or other similar type of shielded wrapping. 
     The metal sheaths of the power and neutral lines L and N are, in turn, twisted together so as to effectively form a single metal sheath S 1  which surrounds power line L and neutral line N. Ground line G remains electrically isolated from power line L and neutral line N. 
     As will be discussed in detail below, safety circuit  1011  interrupts the flow of current through power line L and neutral line N extending between the power source and the load when an arcing condition occurs either between power line L and metal sheath S or between neutral line N and metal sheath S 1 . As can be appreciated, the presence of an arcing condition either between power line L and metal sheath S or between neutral line N and metal sheath S can result in a fire or other dangerous condition. 
     Safety circuit  1011  comprises a circuit breaker  13  which selectively opens and closes power line L and neutral line N. Circuit breaker  13  includes a first normally-closed switch K 1  which is located in power line L between the power source and the load. Circuit breaker  13  also includes a second normally-dosed, switch K 2  which is located in neutral line N between the power source and the load. Switches K 1  and K 2  can be positioned in either of two connective positions. Specifically, switches K 1  and K 2  can be positioned in either a first, or closed, position or a second, or open, position. With switches K 1  and K 2  disposed in their closed position, which is the opposite position as illustrated in  FIG. 1 , current is able to flow from the power source to the load. With switches K 1  and K 2  disposed in their open position, which is illustrated in  FIG. 1 , current is unable to flow from the power source to the load. 
     A metal-oxide varistor MOV 1  protects against voltage surges in power and neutral conducting lines L and H. Metal-oxide varistor MOV 1  preferably has a model number of Z151 and includes a first terminal  61  and a second terminal  63 . First terminal  61  of metal-oxide varistor MOV 1  is connected to power line L and second terminal  63  of metal-oxide varistor MOV 1  is connected to neutral line N. 
     A solenoid SOL is ganged to the circuit breaker contacts of switches K 1  and K 2  and is responsible for selectively controlling the connective position of switches K 1  and K 2 . Specifically, when solenoid SOL is de-energized, switches K 1  and K 2  remain in their closed positions. However, when solenoid SOL is energized, solenoid SOL moves and maintains switches K 1  and K 2  into their open positions. Solenoid SOL includes a winding  15  which includes a first end  17  and a second end  19 , second end  19  being connected to power line L. It should be noted that safety circuit  1011  is not limited to the use of solenoid SOL to selectively move and maintain the connective position of switches K 1  and K 2 . Rather, it is to be understood that solenoid SOL could be replaced with alternative types of circuit opening devices which are well known in the art without departing from the spirit of the present invention. 
     A first silicon controlled rectifier SCR 1  acts to detect the presence of an arcing condition between the power line L and the metal sheath S 1  and to switch solenoid SOL from its de-energized state to its energized state upon detecting the presence of the arcing condition between the power line L and the metal sheath S. First silicon controlled rectifier SCR 1  preferably has a model number of ECI03B and includes an anode  21 , a cathode  23  and a gate  25 . 
     Diode bridge  1013  comprises four diodes D 91 , D 92 , D 93  and D 94 , each diode preferably having a model number of IN4004. Diode D 91  includes an anode  1015  connected to cathode  23  of silicon controlled rectifier SCR 1  and a cathode  1017  connected to first end  17  of solenoid SOL. Diode D 92  includes an anode  1019  connected to cathode  1017  of diode D 91  and a cathode  1021  connected to anode  21  of silicon controlled rectifier SCR 1 . Diode D 93  includes an anode  1023  connected to neutral line N at the power source and a cathode  1025  connected to anode  21  of silicon controlled rectifier SCR 1 . Diode D 94  includes an anode  1027  connected to cathode  23  of silicon controlled rectifier SCR 1  and a cathode  1029  connected to neutral line N at the power source. 
     In use, diode bridge  1013  in safety circuit  1011  acts to detect the presence of an arcing, condition between neutral line N and metal sheath S 1  and to switch solenoid SOL from its de-energized state to its energized state upon detecting the presence of the arcing condition between neutral line N and metal sheath S 1 . Voltage dropping resistor R 21  preferably has a value of approximately 15 Kohms. Diode  022  is preferably model number of IN4148. Capacitor C 21  preferably has a value of approximately 0.22 uF. A pair of nuisance tripping resistors R 22  and R 23  preferably have a value of approximately 330 ohms. Resistor R 22  is connected in parallel with capacitor C 21  and protection diode D 22 , with one of its terminals connected to gate  25  of first rectifier SCR 1 . In use, resistor R 22  serves to reduce the likelihood of nuisance tripping in rectifiers SCR 1  and diode bridge  1013 . 
     An indicator circuit  213  is included connecting power line L to neutral line N at a location between sheath S 1  and circuit breaker  13 . Indicator circuit  213  comprises a light emitting diode (LED) D 25 , a current limiting resistor R 24  and a protection diode D 26  which are connected in Series. Preferably, current limiting resistor R 24  has a value of approximately 33 Kohms and protection diode D 26  has a model number of IN4004. In use, indicator circuit  213  serves to provide a visual indication (i.e., a light) when power is being applied to the load. 
     A test circuit  215  is included in safety circuit  1011 , test circuit  215  connecting power line L (at a location between sheath S 1  and circuit breaker  13 ) to R 21 . Test circuit  215  comprises a test switch TEST and a resistor R 25  which are connected in series. Preferably, resistor R 25  has a value of approximately 33 Kohms. In use, test circuit  215  allows the user to test whether safety circuit  1011  is operating properly. 
     In use, safety circuit  1011  functions in the following manner. In the absence of arcing conditions, switches K 1  and K 2  are disposed in their normally-closed positions, thereby enabling AC power to pass from the power source to the load through power and neutral lines L and N. Upon the presence of an arcing condition between power line L and metal sheath S, leakage voltage travels from metal sheath S and passes through resistor R 21 , resistor R 21  dropping the leakage voltage to an acceptable level. 
     Diode bridge  1013  in safety circuit  1011  acts to detect the presence of an arcing condition between neutral line N and metal sheath S 1  and to switch solenoid SOL from its de-energized state to its energized state upon detecting: the presence of the arcing condition between neutral line N and metal sheath S 1 . 
     A first silicon controlled rectifier SCR 1  acts to detect the presence of an arcing condition between the power line L and the metal sheath S 1  and to switch solenoid SOL from its de-energized state to its energized state upon detecting the presence of the arcing condition between the power line L and the metal sheath S 1 . 
     It should be noted that safety circuit  1011  differs from conventional electrical safety devices in that fireguard  1011  does not comprise a differential transformer rendering the fireguard circuit  1011  more compact in size and less expensive to manufacture than conventional electrical safety devices which utilize a differential transformer. 
     Referring now  FIG. 2 , there is shown a second embodiment of a safety circuit constructed according to the teachings of the present invention, the safety circuit being represented generally by reference numeral  1111 . Safety circuit  1111  is identical in all respects with safety circuit  1011  with one notable exception: the power connections for solenoid SOL and the sensing circuitry are derived from the output side the load) rather than from the input side (i.e., the power source). Specifically, second end  19  of winding  15  for solenoid SOL is connected to power line L at a location between sheath S 1  and circuit breaker  13 . In addition, anode  1023  of diode D 93  and cathode  1029  of diode D 94  are connected to neutral line N at a location between sheath S 1  and circuit. breaker  13 . 
     Referring now  FIG. 3 , there is shown a third embodiment of a safety circuit constructed according to the teachings of the present invention, the safety circuit being represented generally by reference numeral  1211  Safety circuit  1211  is substantially similar in construction to safety circuit  1011 . The principal distinction between safety circuit  1211  and safety circuit  1011  is that, in safety circuit  1211 , solenoid SOL is connected directly to silicon controlled rectifier SCR 1  whereas, in safety circuit  1011 , solenoid SOL is connected indirectly to silicon controlled rectifier SCR 1  through diode bridge  1013 . Specifically, in safety circuit  1211 , first end  17  of the winding for solenoid SOL is connected to anode  21  of silicon controlled rectifier SCR 1  and second end  19  of the winding for solenoid SOL is connected to cathode  1021  of diode D 92 . Furthermore, diode bridge  1013  is directly connected to the input side (i.e., the power source) of power line L and neutral line N, with anode  1019  of diode D 92  connected to power line L at the power source and anode  1023  of diode D 93  connected to neutral line N at the power source. 
     Referring now  FIG. 4 , there is shown a fourth embodiment of a safety circuit constructed according to the teachings of the present invention, the fireguard circuit being represented generally by reference numeral  1311 . Safety circuit  1311  is identical in all respects with safety circuit  1211  with one notable exception: the power connections for diode bridge  1013  are derived from the output side (i.e., the load) rather than from the input side (i.e., the power source). Specifically, anode  1019  of diode D 92  is connected to power line L at its output side and anode  1023  of diode D 93  is connected to neutral line N at its output side. 
       FIGS. 5-8  illustrate the external housings used to encase the circuit card assemblies  20  illustrated in  FIGS. 9-16 . External Housing  10  includes bottom cover  10 A, a top cover  10 B, and a wire cover  10 C. As illustrated in  FIGS. 6-8 , the LCDI of the present invention is adaptable to support a variety of source input prong assemblies including  240   20 A prongs  12 ,  240   15  A prongs  14 , and 120 Volt prongs  16 . 
       FIG. 9  illustrates a circuit card assembly  20  having a top side  20 A, a bottom side  20 B, a load input section  25  and a source input section  27 , the load input section  25  and source input section  27  positioned at opposite ends of circuit board  21 . Referring to  FIG. 10  and  FIG. 14  a Load Input section  25  includes a cavity  30 , positioned on circuit board  21 , formed by sidewalk,  30 A, top wall  30 B, and bottom wall  30 C. Cavity  30  serves as a containment barrier for arcing conditions occurring either between power line L and metal sheath S 1  or between neutral line N and metal sheath S 1  that could result in a fire or other dangerous condition. Referring to  FIG. 1-4 , Cavity  30  encases load input conductors terminals L, N, and G, and sheathing S 1 . Cavity  30  can be made from any suitable fire retardant material having material properties with flame ratings in accordance with Underwriters Laboratories (UL) 94 flame rating data. In the preferred embodiment, suitable materials such as phenolic and VALOX manufactured by SABIC Corp. are utilized. 
     In the preferred embodiment, MOV  50  is mounted on bottom side  20 B on the surface of bottom wall  30 C. Movable contact arms  60  extend from a first load contact end  60 A located within cavity  30 , thru bottom wall  30 C, and extending to a second source contact end  60 B ( FIG. 11 ,  FIG. 12 ) located at the source input section  27 . A ground conductor  65  extends from a first load contact end  65 A, thin bottom wall  30 C, and extending to a second source contact end  65 B located at the source input section  27 . 
     Movable contact arms  60  are resiliently flexible and include at the source input section  27 , an actuating member  70 , and latch  72  to reciprocate second source contact end  60 B. Referring to  FIG. 11 , source contact prong assembly  12  includes line and Neutral conductors having an outlet end  12 A and a circuit end  12 B. Actuating member  70  includes a cavity  70 A positioned on circuit board  21  for isolation and containment of both source contact prong  12  circuit end  12 B and movable contact arm  60  source contact end  60 B. Cavity  70 A provides containment of arcing conditions occurring either between power line L and metal sheath S or between neutral line N and metal sheath S that could result in a fire or other dangerous condition. Referring to Circuits  1 - 4 , cavity  70 A contains switches K 1  and K 2 . Cavity  70 A can be made from any suitable fire retardant material having material properties with flame ratings in accordance with the Underwriters Laboratories (UL) 94 flame rating data. In the preferred embodiment, suitable materials such as phenolic and VALOX manufactured by SABIC Corp. are utilized. 
     Referring to  FIG. 14 , circuit card assembly  20  is fitted in bottom cover  10 A. Bottom cover  10 A includes openings for the passage and securement of source contact prongs  12  thereby ensuring a fixed placement of circuit end  12 B within cavity  70 A, and further ensures the fixed placement of ground conductor  65 . Referring to  FIG. 11A , Cavity  70 A includes sidewalls  70 B and a top wall  70 C. When fitted in bottom cover  10 A, top wall  70 C isolates movable contact arm  60  source contact end  60 B from contacting the interior of bottom cover  10 A. 
     Referring to  FIGS. 15 and 16 , load input cable  80  includes a power line  80 A, a neutral line  80 B, and a metal sheath  80 C line that forms a single metal sheath S 1  which surrounds power line L and neutral line N. Ground line  65  remains electrically isolated from power line  80 A and neutral line  80 B.  FIG. 16  further illustrates the removal of wire cover  10 C for easy access and quick connection of load types. 
     The embodiments shown of the present invention are intended to be merely exemplary and those skilled in the art shall be able to make numerous variations and modifications to it without departing from the spirit of the present invention. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims.