BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a remotely controlled power disconnect circuit which provides a ground fault and prevents power from being applied to an electrical outlet in the event the electrical neutral is lost, the load is shorte or some other unsafe condition arises. 2. Description of the Prior Art

In prior art electrical power systems for a dwelling, 12 VAC or 240 VAC power is supplied to the electrical outlets arranged throughout the home. The load on respective circui including one or more outlets is monitored at a junction box, and a relay is "tripped" so as to disconnect the power to the circuit in the event that an excessive current is drawn by t circuit. Such an excessive current is drawn, for example, when there is a short in a device plugged into an outlet or too many appliances are connected to the circuit. The "tripping" of the relay prevents further supply of electrica power to the circuit so as to ^• prevent perpetuation of the unsafe condition by causing a fire or an electrical shock.

A power disconnect circuit of the type just described m be depicted in simplified form as shown in FIGURE 1. In particular, a ground fault detector, which may comprise a transformer coil, may be used to detect external impedances applied to the power line circuit connected to a particular relay at the junction box, and as described above, applicati of power to the circuit may be controlled remotely by openin the relay to disconnect the "hot" line when excessive impedances are measured. In other words, the relay is close during normal operation (i.e., as long as a large external impedance is not detected) , but when a large external impedance is detected, the relay is opened so as to shut-off power supply to the circuit. Such a technique is known as universal ground fault protection.

Such a system functions quite well in typical dwellings as long as a large external impedance or ground fault on a particular circuit may be detected by the ground fault detector. However, such a system does not prevent the 120 V power from being applied to unused outlets unless the whole power circuit is disconnected. As a result, instances of electric shock may still occur as when a child sticks a meta object such as a fork into an electrical outlet, for example Accordingly, the prior art arrangement is potentially dangerous.

SUMMARY OF THE INVENTION The present invention overcomes this problem of the pri art in a cost effective manner by way of an electrical circu disposed at each electrical outlet which cooperates with a centrally located processing unit (central controller) to disconnect the AC power from its associated outlet unless an appliance is plugged into that outlet. Also, in the event an open neutral conductor for the power line feeding the outlet or a short in the appliance or switch supplying AC power to the outlet, the circuit of the invention provides ground fault and prevents the further application of AC pow until the faulty condition is remedied. In particular, the circuit of the invention enables remote control application AC power to an outlet by remotely controlling the condition a local relay connected to the "hot" AC power line at each outlet. In other words, the relay at a particular outlet i opened until an appliance is plugged into the outlet.

The present invention is particularly useful with a centralized power control system of the type taught by MacFadyen et al in U.S. Patent Application Serial No. 07/126,794, the disclosure of which is hereby incorporated reference. MacFadyen et al disclose a system which control the supply of AC power as well as communication signals to each electrical outlet. When used in such an arrangement, circuit of the present invention includes a communications/ relay control circuit which receives a signal from a centra

controller which provides overall power supply control to th dwelling. For example, the central controller determines whether AC power should be applied to a particular electric cutlet to power a load, and if so, the communications/relay control circuit closes the relay at the appropriate outlet as to energize the load.

The circuit of the invention also includes a power detector which detects whether AC power is actually being applied to the load. In the event that the power detector detects that power is being applied to the load in the abse of a power "ON" signal from the central controller, the circuit of the present invention determines that an "unsafe" condition is present, and a ground fault is applied across electrical outlet. The communications/relay control circui also may then instruct the central controller to shut-off A power to that particular electrical outlet by activating th ground fault circuit interrupter. When the occupier of the dwelling becomes aware of the problem at that particular outlet, he or she may take appropriate action (i.e., unplug the appliance plugged into that outlet) and reset the groun ault circuit interrupter by way *of the central controller. On the other hand, a circuit breaker or device that has tripped or been turned OFF manually must be reset or turned manually.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features of the invention will become more readily apparent upon consideration of the following detailed disclosure in conjunction with the drawings, of which:

FIGURE 1 is a simplified diagram of a universal ground fault detector of the prior art;

FIGURE 2 is a generalized functional diagram of an embodiment of a remote sensing power disconnect circuit in accordance with the invention; and

FIGURE 3 is a detailed schematic diagram of a preferre embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The remote sensing power disconnect circuit of the invention will be described in detail with reference to FIGURES 2 and 3. The invention therein shown and described below provides ON/OFF control of 120 and 240 VAC appliances and other fixed-in-place loads. These are loads which are supplied in accordance with the invention by dedicated branc circuit wiring which places no additional loads on the circuit. For purposes of the description below, these appliances and loads will be simply referred to as "loads".

The present invention may be used in conjunction with a integrated power and communications system of the type set forth by MacFadyen et al in U.S. Patent Application No. 07/126,794, whereby an appliance has its power and communications controlled from a central controller. In suc a system, the power of the remotely controlled appliance is turned ON or OFF by sending appropriate control signals over branch channel to the remote control device address, and similarly, the remotely controlled appliance may communicate with the central controller if the appliance is equipped to so. As shown in Figure 2, for example, communications betwe the appliance and the central controller may be routed via communication/relay control circuit 2. The present invention utilizes this communications feature of the integrated system taught by MacFadyen et al t enable power to be disconnected from a load by a remote controller without requiring a central relay and control wir to the relay. An ON/OFF status indicator may be located on the central controller itself, and local means will allow th power at that outlet to be turned OFF. The circuit of the invention performs this latter function and will now be described with reference to Figures 2 and 3.

The circuit of the present invention solves the proble of the prior art by providing a ground fault circuit interrupter (GFCI) to disconnect the load when an error condition is detected. The GFCI may then be reset by the u

so as to turn ON the AC power once the fault has been corrected. This may be controlled by the central controlle of the power distribution system so as to allow lower cost switching elements to be used downstream in a circuit provi at each outlet. However, the circuit of the invention, provided at each outlet, is designed to assure that the pow to the outlet will be disconnected should the lower cost (a less power consuming) semiconductor switch fail, thus not compromising electrical safety. As shown in Figure 2, the circuit of the invention includes a communications/relay control circuit 2 for controlling semiconductor switch SW1, a power detector (sensor) 4 for detecting whether AC power is being applied the outlet 10, and a logic circuit 6 for applying a ground fault across resistor R by closing switch SW2 when the logi circuit 6 determines that a fault condition exists. During operation, communications/relay control circuit 2 informs t communications control system that 120 VAC power should be applied to outlet 10 when an appliance (load) is plugged i the outlet 10. The communications control system then instructs communications/relay controller 2 to close switc SW1 so that the 120 VAC power may be applied to the outlet Power detector 4 measures whether power is being applied t the outlet 10, and when the switch SW1 is closed, power detector 4 determines that power is being applied to the outlet. Therefore, during normal operation the power dete 4 and communications/relay controller 2 both indicate that outlet is energized and no fault condition exists.

However, in the event of a fault condition the circui the invention takes necessary precautions to prevent the occurrence of fire or electrical shock and the like by disconnecting power to the outlet containing the fault condition. The power interrupting feature of the embodime of FIGURE 2 is performed by logic circuit 6. Logic circui compares the output signal of communications/relay control circuit 2 to the detected output of power detector 4 to determine whether power is being applied to the load in th

absence of a signal from the communications control system apply power to the outlet. When the signals do not coincid logic circuit 6 determines that a fault condition has occurred, and logic circuit 6 outputs a signal to close swi SW2, thereby applying a ground fault across resistor R so a to ground the AC power applied to the outlet 10. Moreover, upon detection of such a fault condition, the communications/relay control circuit 2 may send a fault sig to the communications control system to make certain that a power to the outlet 10 is shut-off by the ground fault circ interrupter. The circuit may then be reset manually by the user once the fault condition has been eliminated.

A further embodiment of the present invention is shown Figure 3. As shown, a load is plugged into an outlet so as be connected to the neutral, ground and 120 VAC power lines However, as in the first embodiment, power is not supplied the load unless semiconductor switch SW1 is closed. Semiconductor switch SW1 is controlled by opto-coupler and control circuit Q, in response to low voltage DC "ON" or "O signals from the communications control system as applied across resistor Rl. Power detector and logic circuit 12 is connected across the power lines and functions to prevent t application of AC power to the outlet unless the load is plugged therein and no fault condition exists. Power detector and logic circuit 12 is comprised of a switching diode or triac switch SCR1 which is responsive to lost neutral detector comprised of a zener diode VR1 and an opto-coupler Q2. The power detector and logic circuit also includes an AC power switch failure detector comprised of resistor R4, diode CR1, opto-coupler Q2, resistor R2 and ze diode VRl. R5 is a gate resistor on SCR1 that keeps the leakage currents from turning on SCRl, while capacitor Cl serves to filter voltage spikes that could turn on SCRl. T operation of the power detector and logic circuit shown in Figure 3 will now be described.

When ^either a "live" AC line will not turn-off, or whe neutral conductor in the same circuit opens and disables th

normal disconnect means, the power detector and logic circ of the invention detects the problem and activates the swi SCRl to produce a ground fault when a threshold is exceede The ground fault interrupter (GFCI) in the central control will then disconnect the AC power to that outlet.

During normal operation, the diode switch SCRl is connected from the AC (hot) to ground in series with resis R3 but does not conduct. When an unsafe condition arises as a lost neutral conductor or switch short in switch SW1, SCRl starts to conduct and causes a half wave, 35 ma groun fault current to flow therethrough, and the branch circuit breaker is thus caused to open so that no power is deliver to the load. The occupant of the home may then manually r the breaker once the electrical safety problem has been corrected.

The lost neutral sensor circuit functions by measurin threshold level which is determined by the characteristics zener diode VR1. When the neutral conductor opens, the op coupler Q2 will no longer clamp the voltage at the junctio diode CR1 and zener diode VR1 to ground, and the voltage w thus rise until it exceeds the threshold of the zener diod VR1, which by way of example, may be 19 volts. The curren then generated by the hot conductor will flow across the series combination of resistor R4, diode.CR1, zener diode and resistor R5 and charge capacitor Cl and turn-on switch

SCRl. This causes the current to flow through resistor R3 diode SCRl to ground to thereby apply a ground fault. The ground fault circuit interrupter will prevent the applicat of AC power to the outlet. The circuit of the present invention may also functio detect AC power switch failures (i.e., failures of switch SW1) . In normal operation, when the AC switch SW1 is "ON" opto-coupler Q2 is turned ON by a positive voltage across resistor R2 from the central controller and causes the vol at the junction of zener diode VRl and diode CR1 to be approximately 0 volts, keeping VRl from conducting and fro turning "ON" the diode switch SCRl. However, when the swi

SWl fails duo to a shorted device or a welded contact (whe switch SWl is a relay) , opto-coupler Q2 will turn OFF, the causing the voltage at the CR1 - VRl node to rise until di CR1 begins to conduct so as to turn ON diode switch SCRl. before, once switch SCRl starts to conduct, a ground fault generated.

The invention thus enables one to disconnect a branch circuit because of a problem such as a fire or because a l appliance has malfunctioned and human intervention is requ to repair or remove the faulty device. Moreover, since ea outlet only receives power when it has been detected that load is plugged into the outlet, the circuit of the presen invention makes the electrical outlets in a home particula safe in that high AC voltages are not applied to the electrical outlets in the absence of a load. Such safety improved further by the use of "intelligent" appliances wh identify themselves to the central controller before power applied to the corresponding outlet.

The circuit of the invention thus monitors the outlet indicates when AC power will not turn off either because o welded relay contact, a malfunction.of the control circuit a shorted semiconductor switch. Moreover, the monitoring circuit may determine that a neutral wire is open and appropriately produce a trip condition in the power source necessary. The simple circuit of the invention thus provi a convenient, remote control, low-cost disconnect circuit use with a low-current ground fault circuit interrupter.

Although the invention has been described in connect with a sample embodiment, it should be understood that the invention is not limited to such an embodiment. For examp a more sophisticated logic circuit may be placed at each electrical outlet in order to control the outlet in respon to a series of power control commands from the communicati control system. Accordingly, the present invention is intended to cover all further alternatives, modifications equivalents as may be included within the scope and spirit the invention as defined by the appended claims.