Abstract:
The present invention is a method and apparatus for protecting a power supply from electrical faults. The present invention operates substantially independently of the current drawn by the load. In addition, the present invention includes a time delay circuitry for preventing false detection of ground faults when the power source is connecting to the load. In a preferred embodiment, the apparatus of the present invention includes a control circuitry for connecting the power supply to the load. The apparatus also preferably includes a sensor circuitry for detecting electrical faults, including ground, transient, and arc faults, and triggering the control circuitry to disconnect the power source from the electrical faults when electrical faults are detected. Thus, the present invention can protect wiring and load connections from improper operation and fire hazards that may be caused by electrical faults. Finally, the apparatus preferably includes a fault protection condition indicator to indicate whether the circuit breaker circuitry is working properly.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a continuation of application Ser. No. 10/076,177, filed on Feb. 13, 2002, now U.S. Pat. No. 6,650,516, which is a continuation of application Ser. No. 09/670,842, filed Sep. 27, 2000, now abandoned, which is a continuation-in-part of application Ser. No. 09/603,069, filed on Jun. 26, 2000 now U.S. Pat. No. 6,671,144. 

   FIELD OF THE INVENTION 
   The present invention relates generally to a circuit breaker circuitry for protecting a power source from electrical faults. 
   BACKGROUND OF THE INVENTION 
   Many devices known in the art are useful for protecting power sources from electrical faults. There are at least three types of electrical faults: a ground fault, a transient fault, and an arc fault. A ground fault occurs when a grounded conductor comes into contact with electrical circuitry, causing an excessive current flow in that circuitry. A transient fault occurs when a grounded conductor briefly comes into contact with an electrical circuitry, causing a temporary excessive current flow in that circuitry. As a result of the excessive current drawn by ground and transient faults, power supplies can become overloaded, and the load that a power supply is meant to power ends up receiving little or no current. An arc fault occurs when an arc is struck between two conductors that are not in physical contact but are close to each other. An arc can produce high temperatures in its vicinity, which can create a fire hazard. 
   Existing devices for protecting power sources from electrical faults use thermal sensors, magnetic sensors, and/or current sensors to detect electrical faults. For these devices, it is necessary to select and calibrate their sensors to accommodate the current drawn by the load for proper operation, making the existing fault protection devices load dependent. The process of selecting and calibrating particular sensors to the current drawn by the load is time consuming and expensive. Furthermore, these sensors must be recalibrated when the current drawn by the load changes significantly or if a different load is used. 
   Accordingly, there exists a need for an electrical fault detection and protection device that operates independently of the load so that no calibration of the sensor is needed and is cost-effective to construct. 
   SUMMARY 
   A circuit breaker circuitry in accordance with the present invention operates independently of the load to which a power source is connected. In addition, the preferred circuit breaker circuitry includes a time delay circuitry to prevent false detection of electrical faults resulting from current spikes that may occur when connecting the power supply to the load. 
   Preferably, the circuit breaker circuitry comprises a control circuitry that connects a power source to its load. The control circuitry disconnects the power source from the rest of the circuitry when an electrical fault is detected. 
   Preferably, the circuit breaker circuitry also comprises a sensor circuitry that detects electrical faults by monitoring the voltage drop across the control circuitry. When an electrical fault occurs in the circuit, a large current is drawn causing a significant potential drop across the control circuitry. The potential drop is in turn detected by the sensor circuitry. If an electrical fault threatens to interfere with the proper operation of the power supply, the sensor circuitry causes the control circuitry to disconnect the power source from the electrical faults, thus protecting the power source. 
   After the electrical fault has passed or is removed and a circuit breaker circuitry is reset, either manually or automatically, power returns to the control circuitry and the connection between the power source and the load is restored. Preferably, the time delay circuitry delays the activation of the sensor circuitry. This delay functions to shield the sensor circuitry from any current spikes that may occur when connecting the power source to the load and prevents false detection of electrical faults. 
   Preferably, the circuit breaker circuitry also includes a fault protection condition indicator for indicating whether the circuit breaker circuitry is working properly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of an embodiment of the present invention that protects against ground faults; 
       FIG. 2  is a schematic of an embodiment of the present invention that protects against ground faults including a power switching time delay relay; 
       FIG. 3  depicts the temporal relationship between a current spike caused by connecting a power supply to its load compared to the time delay caused by the time delay circuitry; 
       FIG. 4  depicts a detailed schematic of an alternate embodiment of the present invention that protects against ground faults including a ground switching time delay relay; 
       FIG. 5  is a schematic of an embodiment according of the present invention that works with AC signals; 
       FIG. 6A  depicts an AC signal from a AC generator; 
       FIG. 6B  depicts the AC signal of  FIG. 6A  after the signal passes through the control relay; 
       FIG. 6C  depicts the difference in AC signals of  FIG. 6A  and  FIG. 6B ; 
       FIG. 6D  depicts a portion of the AC signal of  FIG. 6C  in further detail; 
       FIG. 7  is a block diagram of an embodiment of the present invention that protects against transient, arc, and ground faults; 
       FIG. 8  is a schematic of an embodiment of the present invention that protects against transient, arc, and ground faults; and 
       FIG. 9  is a schematic of a circuitry for powering various parts of a helicopter including a circuit breaker circuitry in accordance with an embodiment of the present invention that protects against ground faults. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates a circuit breaker circuitry in accordance with the present invention that protects against ground faults. It includes a control circuitry  100 , a sensor circuitry  400 , and a time delay circuitry  500 . Control circuitry  100  connects power source  200  to load  300 . Sensor circuitry  400  causes control circuitry  100  to isolate power source  200  from circuit breaker circuitry  10  when sensor circuitry  400  detects a electrical fault. When the electrical fault is removed and the control circuitry  100  is reset, control circuitry  100  reconnects power source  200  to circuit breaker circuitry  10 . While control circuitry  100  is being reset or when control circuitry  100  initially connects power source  200  to its load, a current spike may occur as a result of connecting load  300  to power source  200 . Time delay circuitry  500  isolates sensor circuitry  400  from this current spike to prevent false electrical fault detection. Control circuitry  100 , sensor circuitry  400 , and time delay circuitry  500  are connected in such a way that circuit breaker circuitry  10  operates independently of load  300 , as will be illustrated by the preferred embodiments below. 
   A schematic of an embodiment of the present invention is shown in  FIG. 2 . In this embodiment, control circuitry  100  includes a control relay  102  and circuit breaker  104 . Although various relays and circuit breakers may be used, the preferred control relay  102  and circuit breaker  104  are the Cutler Hammer SM150D2 relay and the Klixon 7277-2-½ circuit breaker respectively. Control relay  102  includes control coil  106 , control armature  108 , resistive contacts  110 , and time delay circuitry switch  112 . Control armature  108  connects power source  200  to load  300  when it engages resistive contacts  110 . Although biased away from resistive contacts  110 , control armature  108  engages resistive contacts  110  when control coil  106  creates a magnetic field that pulls control armature  108  to resistive contacts  110 . Similarly, time delay switch  112 , which is biased to engage an open circuit, connects to time delay circuitry power supply  508  when control coil  106 &#39;s magnetic field pulls time delay switch  112  to time delay circuitry power supply  508 , powering time delay relay  502 . Circuit breaker  104  connects power source  200  to control coil  106  to supply control coil  106  with the necessary current to create its magnetic field. Circuit breaker  104  also connects power source  200  to time delay relay  502  and sensor diode  402 . 
   Sensor circuitry  400  (see  FIG. 1 ) includes a sensor diode  402  (see  FIG. 2 ) that monitors the voltage drop across control relay  102  at points A and B. Although various diodes may be used, a preferred sensor diode  402  is the Motorola 1N4005 diode. Sensor diode  402  connects to point A on one terminal via sensor circuitry switch  506  and circuit breaker  104 . Sensor diode  402  connects to point B directly on the other terminal. Sensor diode  402  is biased to allow current to flow from point A to point B, but it will only allow current to flow through when the voltage drop across control relay  102  is greater than sensor diode  402 &#39;s forward voltage, typically 0.6 volts. Since resistive contacts  110  have very low resistance, the voltage drop across control relay  102  exceeds sensor diode  402 &#39;s forward voltage only when a high current is drawn from power source  200 , which occurs when there is a ground fault. When sensor diode  402  allows current to flow through it, that same current flows through circuit breaker  104 , causing circuit breaker  104  to overload and become an open circuit. 
   Also shown in  FIG. 2 , time delay circuitry  500  (see  FIG. 1 ) includes a time delay relay  502 , a time delay circuitry power supply  508 , a fault protection diode  510 , and a fault protection condition indicator  514 . Although various time delay relays may be used, the preferred time delay relay  502  is the NCC L1F-00010-562 time delay relay. Time delay relay  502  includes a timing resistor  516 , a timing circuit  518 , a time delay coil  504 , and a sensor circuitry switch  506 . Timing resistor  516  and timing circuit  518  operate together to delay switching of sensor circuitry switch  506  when time delay relay  502  is activated. The resistance value of timing resistor  516  determines the length of the time delay. In the NCC L1F-00010-562 time delay relay, the period of time delay may be varied from 10 ms to 10 s. 
   Sensor circuitry switch  506  connects sensor diode  402  to circuit breaker  104  when sensor circuitry switch  506  engages sensor diode  402 . Although biased to connect to fault protection diode  510 , sensor circuitry switch  506  connects to sensor diode  402  under the force of the magnetic field created by time delay coil  504 . Time delay circuitry power supply  508 , which is connected to control relay  102 , provides time delay coil  504  with the necessary current to generate its magnetic field. Fault protection diode  510  is biased to conduct current from the power source  200  to fault protection indicator  514  in the event that control relay  102  connects power source  200  to load  300  while time delay relay  520  fails to activate. 
   In operation, the preferred embodiment of  FIG. 2  functions as follows. When no ground fault is detected, control armature  108 , which is in engagement with resistive contacts  110  under the force of control coil  106 &#39;s magnetic field, connects power source  200  to load  300 . Power source  200  supplies the necessary current via circuit breaker  104  to the control coil  106  for generating the magnetic field. Control coil  106 &#39;s magnetic field also engages time delay circuit switch  112  with time delay relay power supply  508 , supplying power to time delay relay  502 . 
   Sensor diode  402  monitors the voltage drop across control relay  102  via points A and B. Sensor diode  402  is in voltage contact with point A on one terminal via sensory circuitry switch  506  and circuit breaker  104  and is directly connected to point B on the other terminal. Sensor circuitry switch  506  is held in contact with sensor diode  402  by time delay coil  504 &#39;s magnetic field. Time delay circuitry power supply  508  provides the necessary current to time delay coil  504  via time delay circuit switch  112  to generate the magnetic field. 
   The voltage drop across points A and B is caused by resistive contacts  110  of control relay  102 . Normally, load  300  does not draw enough current from power source  200  to cause enough voltage drop across points A and B to activate sensor diode  402 , which typically requires a forward voltage of 0.6 volts for activation. However, when a ground fault occurs, the ground fault draws a high quantity of current from power source  200 , causing the voltage drop across resistive contacts  110  and, consequently, the voltage drop across points A and B to exceed the forward voltage of sensor diode  402 . In alternate embodiments, sensor diode  402  can be made more sensitive to current drawn by a ground fault by using a diode with a lower forward voltage rating. Sensor diode  402  can also be made more sensitive to current drawn by a ground fault by placing a shunt resistor in series with resistive contacts  110  between points A and B so as to raise the potential drop across points A and B. As a result of exceeding its forward voltage, sensor diode  402  becomes active and begins to conduct current from power source  200  to the ground fault through circuit breaker  104 . 
   Circuit breaker  104  responds to the surge in current by opening the circuit, disconnecting power source  200  from control coil  106 . Without current from power source  200 , control coil  106  loses its magnetic field, releasing control armature  108  from resistive contacts  110 . As a result, power source  200  is isolated from the ground fault as well as most of the circuit breaker circuitry  10 . The loss of magnetic field in the control relay  102  also releases time delay circuitry switch  112  disconnecting time delay relay  502  from time delay circuitry power supply  508 . Consequently, time delay coil  504  also loses its magnetic field, disconnecting sensor circuitry switch  506  from sensor diode  402 . 
   At this point, power source  200  is isolated from the ground fault and time delay relay  502  is without power. In order to reactivate the circuit breaker circuitry  10  and allow current to again flow from power source  200  to load  300 , the ground fault needs to be removed and the circuit breaker  104  needs to be manually reset. 
   After circuit breaker  104  is reset (typically manually), power source  200  restores current to control coil  106 , generating a magnetic field in control relay  102 . The magnetic field engages control armature  108  and time delay circuit switch  112  to resistive contacts  110  and time delay circuitry power supply  508  respectively. As a result, power source  200  is again connected to load  300  and time delay relay  502  is activated. 
   When control armature  108  connects power source  200  to load  300 , a current spike may occur which results in a temporary high potential drop across points A and B that may falsely activate sensor diode  402 . Time delay relay  502  functions to isolate sensor diode  402  from effects of the current spike by connecting sensor diode  402  to point A only after enough time has passed for the current spike to subside. The period of time delay is determined by timing resistor  516  and timing circuit  518 .  FIG. 3  illustrates the current spike as a function of time in relation to the time delay created by time delay relay  502 . 
   If, during the process of-resetting circuit breaker circuitry  10 , sensor circuitry switch  506  fails to engage the sensor diode  402 , fault protection diode  510  is activated, conducting current from the power source  200  to the fault protection condition indicator  514 . Fault protection condition indicator  514  then warns of improper resetting of the circuit breaker circuitry  10 . If, however, sensor circuitry switch  506  properly connects to sensor diode  402 , fault protection condition indicator  514  indicates proper operation and circuit breaker circuitry  10  resumes normal conditions, where control relay  102  connects power source  200  to the load  300  and sensor diode  402  monitors the voltage drop across points A and B. 
   In an alternate preferred embodiment illustrated in  FIG. 4 , time delay relay  502  can be ground switching rather than power switching, as was described above. In the ground switching embodiment, time delay circuitry power supply  508  connects to time delay relay coil  504  via time delay coil switch  510 , and ground  512  is connected to control relay  102 . 
   Operation of the alternate preferred embodiment depicted in  FIG. 4  is similar to the operation of the preferred embodiment of  FIG. 2 . They differ only in the following two ways. First, when circuit breaker  104  becomes an open circuit in response to a ground fault and, consequently, control coil  106  loses its magnetic field, time delay switch  112  switches from ground  512  to an open circuit rather than from the time delay circuitry power supply  508  to open circuit as in the power switching relay embodiment above. Second, when circuit breaker  104  is manually reset, time delay relay  502  initially draws current from power source  200  rather than from time delay circuitry power supply  508  as in the power switching relay embodiment above. Only after the time delay caused by timing resistor  516  and timing circuit  518  does time delay coil  504  generate a magnetic field to pull time delay coil switch  510  to engage time delay circuitry power supply  508 , powering time delay relay  502  in steady state. 
   The preferred embodiment can also be modified to operate with AC signals. One such embodiment is shown in  FIG. 5 . The preferred circuitry depicted in  FIG. 5  is similar to the one depicted in  FIG. 2 ; the differences exist only in the components used. Specifically, relay  114  is an AC relay rather than a DC relay. In addition, power source is an AC power source  204 , and the load is an AC load  304 . 
   Operationally, the AC embodiment of  FIG. 5  functions similarly to the DC embodiment of  FIG. 2 . The only difference is that an AC power source  204  powers control coil  106  and an AC signal activates sensor diode  402 .  FIG. 6A  depicts the AC signal seen at point A, which is the signal from AC power source  204 .  FIG. 6B  depicts the signal seen at point B, which is the AC signal seen at point A reduced by voltage drop across resistive contacts  110 .  FIG. 6C  depicts the difference between the two AC signals. If a ground fault occurs, the voltage difference between points A and B becomes large enough to activate sensor diode  402 . Tis condition is depicted in  FIG. 6D , where the positive peak of the AC signal exceeds the forward voltage of sensor diode  402 , causing the sensor diode  402  to activate and conduct current through circuit breaker  104 . Consequently, circuit breaker  104  becomes an open circuit. 
   In the above AC embodiment, due to the polarity of sensor diode  402 , sensor diode  402  can only be tripped during the positive portion of the AC signal from power source  200 . In an alternate embodiment, a second sensor diode may be added in parallel but in an opposite polarity to sensor diode  402 , so that the second sensor diode can be tripped in the same manner as sensor diode  402  but during the negative portion of the AC signal from power source  200 . In essence, with the second sensor diode, the AC embodiment is able to perform full-wave detection rather than half-wave detection. 
   While the above embodiments detect ground faults and protect power source from the ground faults, these embodiments can be modified to detect transient and arc faults in addition to ground faults and protect the power source from all three electrical faults.  FIG. 7  illustrates the transient, arc, and ground fault circuit breaker circuitry  20 . 
   As illustrated in  FIG. 7 , transient, arc, and ground fault circuit breaker circuitry  20  in accordance with the present invention includes a control circuitry  100 , a time delay circuitry  500 , a sensor circuitry  600 , a counting circuitry  700 , and a triggering circuitry  800 . Control circuitry  100  and time delay circuitry  500  are the same control circuitry and time delay circuitry described in connection with  FIG. 1 . Sensor circuitry  600  detects arc and transient electrical faults in addition to ground faults. If a ground fault is detected, sensor circuitry  600  signals control circuitry  100  to disconnect power source  200 . If transient or arc faults are detected, sensor circuitry  600  signals counting circuitry  700  to count transient or arc fault occurrences. If frequent transient or arc fault occurrences are detected, indicating a possible fire hazard and threat to proper operation of power source  200 , counting circuitry  700  signals triggering circuitry  800  to trigger control circuitry  100  to disconnect power source  200 . 
   A schematic of transient, arc, and ground fault circuit breaker circuitry  20  in accordance with an embodiment of the present invention is shown in  FIG. 8 . Sensor circuitry  600  includes an optocoupler emitting diode  602 , an optocoupler detecting diode  604 , and an AND gate  606 . Counting circuitry  700  includes a counter  702  and a reset timer  704 . Triggering circuitry  800  includes a trigger relay  802 . Trigger relay  802 , in turn, includes a trigger circuitry coil  804  and a switch  806 . 
   One terminal of optocoupler emitting diode  602  connects to point A through circuit breaker  104  and sensor circuitry switch  506  and the other terminal connects directly to point B. When activated, optocoupler emitting diode  602  is biased to allow current to flow from point A to point B and, in addition, emits an electromagnetic wave which can be detected by optocoupler detecting diode  604 . 
   One terminal of optocoupler detecting diode  604  connects to time delay circuitry power supply  508  through control relay  102  and the other terminal connects to input C of AND gate  606 . Optocoupler detecting diode  604  becomes active when it detects electromagnetic waves emitted by optocoupler emitting diode  602 . When activated, optocoupler detecting diode  604  is biased to allow current to flow from time delay circuitry power supply  508  to input C of AND gate  604 . Input D of AND gate  606  connects to the time delay circuitry power supply  508  through control relay  102 . Therefore, when optocoupler detecting diode  406  is active, both AND gate  606 &#39;s inputs are connected to time delay circuitry power supply  508 , which causes AND gate  606  to output a high signal. 
   The output of AND gate  606  connects to the input of counter  702 , and indicates whether a transient or arc fault has been detected by sensor circuitry  600 . Reset timer  704  connects to counter  702  so that it can periodically reset counter  702 . The output of counter  702  connects to trigger circuitry relay coil  804  of trigger relay  802 . Finally, switch  806  of trigger relay  802  connects circuit breaker  104  to ground when it is under magnetic force created by trigger circuitry relay coil  804 . 
   In operation, when a transient or arc fault occurs, it draws an unusually large current that flows across resistive contacts  110  of control relay  102 . This current causes a voltage drop across points A and B that may be large enough to exceed the forward voltage of optocoupler emitting diode  602 , activating optocoupler emitting diode  602 . The forward voltage of optocoupler emitting diode  602  is typically 1.5 volts. When it is activated, optocoupler emitting diode  602  conducts current from point A to point B through circuit breaker  104  and emits an electromagnetic wave which optocoupler detecting diode  604  is able to detect. Although current flows across circuit breaker  104  while optocoupler emitting diode  602  is active, due to the temporary nature of transient and arc faults, optocoupler emitting diode  602  does not stay active long enough to allow current to flow across circuit breaker  104  for a sufficient period of time to overload it. 
   When optocoupler detecting diode  604  detects the electromagnetic wave emitted by optocoupler emitting diode  602 , optocoupler detecting diode  604  is activated, connecting time delay circuitry power supply  508  to input C of AND gate  606 . With both inputs now connected to time delay circuitry power supply  508 , the output of AND gate  604  toggles from a low signal to a high signal. 
   When transient or arc fault disappears, optocoupler diodes  602 ,  604  become inactive. As a result, input C of AND gate  606  is no longer connected to time delay circuitry power supply  508 , causing the output of AND gate  606  to toggle back to a low signal. The result is that AND gate  606  outputs a non-zero signal, such as a square wave, for each transient or arc fault that occurs in the circuit. Counter  702  receives this signal from AND gate  606  and accordingly increases its count of transient or arc fault occurrences by one. In this fashion, counter  702  is able to keep a running count of the number of transient or arc fault occurrences. 
   Reset timer  704  periodically resets counter  702  to start over and begin counting from zero. For example, reset timer  704  may reset counter  702  at periodic time interval T. This in turn causes counter  702  to count the number of transient and/or arc faults that occurs within time period T. For example, if the time interval T is set to 500 milliseconds and the predetermined number of faults is set to three, if three faults are detected within a 500 milliseconds interval, the output of counter  702  will toggle from a low signal to a high signal. 
   The high signal from counter  702  supplies current to sensor circuitry coil  804  of sensor circuitry relay  802 . The current from counter  702  allows sensor coil  804  to generate a magnetic field that pulls switch  806  in contact with circuit breaker  104 , grounding power supply  200  through circuit breaker  104 . Circuit breaker  104  overloads and opens due to the rush of current from power supply  200 , which in turn results in the isolation of power source  200  as described in connection with  FIG. 2 . 
   When ground faults occur rather than transient or arc faults, a ground fault always lasts long enough to activate optocoupler  602  and draw current through circuit breaker  104  for a sufficient time period to overload circuit breaker  104 . 
   Like circuit breaker circuitry  10  ( FIGS. 1 and 2 ), when circuit breaker circuitry  20  is reset, time delay circuitry  500  delays connection of sensor circuitry  600  to control circuitry  100  in order to isolate sensor circuitry  600  from any current spikes resulting from connecting power source  200  to load  300 . Isolation of sensor circuitry  600  from current spikes prevents false detection of electrical faults. 
   Importantly, circuit breaker circuitry  10  in accordance with the disclosed embodiments, operates independently of load  300 ; that is, nothing in circuit breaker circuitry  10  is required to be calibrated to a particular load  300  in order for it to operate properly. In a typical relay, resistive contacts  110  have resistance on the order of 0.0003 Ohms. In order to activate sensor diode  402 , which typically requires a forward voltage of 0.6 volts, the current drawn would have to be on the order of 2000 Amps. Even with power source  200  supplying a high voltage of about 200 volts, any mechanism that can activate the sensor diode would have to have less than 0.1 Ohms resistance. Since load  300  would have a much larger resistance than 0.1 Ohms, the voltage drop across points A and B caused by load  300  is negligible to sensor diode  400  such that, without having to specially calibrate a typical relay or diode, circuit breaker circuitry  10  can be connected to most any load  300  and operate properly. 
   Circuit breaker circuitry  20  similarly operates independently of load  300 . Again, in a typical relay, resistive contacts  110  have resistance on the order of 0.0003 Ohms. In order to activate optocoupler emitting diode  602 , which typically requires a forward voltage of 1.5 volts, the current drawn would have to be on the order of 6000 Amps. Even with power source  200  supplying a high voltage of, for example, about 150 volts, any mechanism that can activate sensor diode would have to have less than 0.025 Ohms resistance. Since load  300  would have much larger resistance than 0.025 Ohms, voltage drop across points A and B caused by load  300  is negligible to optocoupler emitting diode  602  such that, without having to specially calibrate a typical relay or diode, circuit breaker circuitry  20  can be connected to most any load  300  and operate properly. 
   Circuit breaker circuitries  10 ,  20 , as described above, may be integrated into the circuit depicted in  FIG. 9  which is used for powering various parts of a helicopter. Circuit breaker circuitries  10 ,  20  are designated by 2K 6 , 2K 5 , 2K 10 , 2K 16 , and 2K 15  in the schematic. These circuit breaker circuitries act to protect power sources from electrical faults. It should be noted that circuit breaker circuitry  10 ,  20  can also be employed in circuits powering various parts of an airplane or any other types of aircraft, as well as numerous other applications, both for aviation and non-aviation. In general, the present invention can be used wherever circuit breaker circuitry is typically used. 
   The disclosed embodiments can be modified by a person skilled in the art without deviating from the scope of the present invention. For example, time delay relay  502  may be replaced with a logic circuit that can isolate sensor circuitry  400  or  600  from current spikes that may occur when connecting power source  200  to load  300 . 
   While the invention has been described in conjunction with specific embodiments, it is evident that numerous alternatives, modifications, and variations will be apparent to those skilled in the art in the light of forgoing descriptions. The scope of this invention is defined only by the following claims.