Fire detection and projection circuit and device

Abstract

An early warning fire detection system utilizes a ground fault protected circuit fed through a conventional ground fault circuit interrupter (GFCI) as a vehicle for detecting elevated temperature conditions indicating a fire or incipient fire. Thermal detectors located at strategically-located convenience outlets powered by a ground fault protected circuit or circuits individually operate in response to a predetermined high temperature condition to produce a controlled ground fault, either on the line or the neutral side of the associated circuit, thereby precipitating circuit interrupting operation of the GFCI unit. An alarm associated with the protected circuits is activated in response to the circuit interrupting operation of any of the GFCI units.

Description

BACKGROUND OF THE INVENTION

It is well known that one of the major causes of accidental death, personal injury and property damage in the United States is fire.

Despite the dramatic seriousness of this problem, early warning fire detection systems have not been widely adopted. Typical systems require running low voltage wiring throughout a building or residence linking the various remotely located detectors to a central station. The equipment, and particularly the installation, is quite expensive, even prohibitively so to the average homeowner. Recently developed wireless systems, though less expensive than the wired systems, due to their economy of installation, are nevertheless not sufficiently low in cost as to have gained widespread acceptance and use by the average homeowner.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide an early warning, hazardous condition detection system which is inexpensive both in terms of equipment and installation.

Another object of the invention is to provide a fire detection system of the above character which utilizes existing electrical wiring in homes and buildings.

A further object of the invention is to provide a system of the above character which combines the function of fire detection and warning with the function of ground fault protection, i.e., shock protection, by utilizing currently available ultra-sensitive ground fault circuit interrupter (GFCI) units.

Still another object of the invention is to provide an electrical receptacle or alternatively a plug-in module electrically connecting a hazardous condition detector into a ground fault protected power distribution circuit.

The invention accordingly comprises the features of construction, combinations of elements, and arrangements of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided an early warning, hazardous condition detection system which is created simply by the appropriate electrical connection of a suitable condition responsive detector in a ground fault protected electrical power distribution circuit. If the distribution circuit is not ground fault protected, the invention is created by the inclusion therein of a ground fault sensor module alone or in conjunction with a circuit breaker module to constitute a ground fault circuit interrupter (GFCI), and a condition responsive detector.

In one form of the invention, the detector is situated at various strategically-located convenience outlets fed by the ground fault protected circuit. The detector is electrically connected between either the line side or, more preferably, the neutral side -- when the ground fault sensor has faulted neutral response capability -- of the power circuit and ground and responds to the existence of the hazardous condition to create a controlled fault condition to which the ground fault sensor is sensitive. The sensor, in responding to the detector imposed ground fault, may interrupt the circuit and/or activate an alarm.

In an alternative embodiment, the detector is incorporated in a pronged module for plug-in electrical contacting engagement with the receptacle at the convenience outlet, pursuant to electrically connecting the detector into the ground fault protected circuit.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in conjunction with the accompanying drawing in which:

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram of a portion of an electrical power distribution system incorporating the early warning fire detection system of the invention;

FIGS. 2 and 3 are schematic diagrams of alternative embodiments of a thermally responsive detector utilized in FIG. 1; and

FIG. 4 is a perspective view, partially in diagrammatic form, of a plug-in module for electrically connecting a thermally responsive element into the power distribution system of FIG. 1.

Like reference numerals refer to like parts throughout the several views of the drawing.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the detection system of the invention is shown incorporated in an electrical power distribution system such as is used in a typical residence or building and including a power control panel or load center, generally indicated at 10. The load center 10 ordinarily includes a generally rectangular metallic box, indicated at 11, with terminals 12, 14 and 16 used for connection to a neutral conductor 18, and phase conductors 20 and 22, respectively, emanating from a source 23. This is intended to represent a typical electrical feed arrangement, especially for a residence. It will be understood that the particular power source arrangement shown is merely exemplary. Any convenient or available power source may be utilized in various arrangements, such, for example, as utilizing only one phase conductor and the neutral conductor, or a 3-phase system including three phase conductors together with a neutral conductor.

The neutral terminal 12 is connected by means of a conductor 24 to a neutral bar 26, and, in the installation shown, the neutral bar is also connected to ground, indicated at 27, as is the load center box 11. The terminals 14 and 16 are connected by means of a 2-pole circuit breaker 28 to main power supply bus bars 30 and 32, respectively. Connected to each bus bar are conventional circuit breakers 40.

For the purposes of simplification, only one power distribution circuit will be described in connection with FIG. 1. It will be understood, however, that a number of such circuits emanate from load center 10.

Still referring to FIG. 1, reference numeral 42 generally indicates a ground fault circuit interrupter (GFCI) unit having the capability of responding to a ground faulted neutral, as well as a ground faulted line. A suitable GFCI is marketed by the General Electric Company under the trademark CB3. For a description of the operation of such units, reference is made to U.S. Pat. No. 3,611,035. Power is taken from bus 32 through interrupter contacts 44 and supplied by an internal connection 45 to the branch conductor 46 of a 3-wire conductor, commonly indicated at 47. Neutral connection to the source is effected by conductor 48 from the neutral bus 26 to the GFCI unit 42 and thence via an internal connection 49 to a neutral wire 50 of conductor 47. An equipment ground wire 51, included in conductor 47, is connected to an equipment ground bus 52 which is grounded to the load center metallic enclosure 11.

The GFCI line and neutral internal connections 45 and 49 are inductively associated as primary windings of differential current transformer 54, while the neutral connection is inductively associated as a secondary winding of a transformer 56. The secondary winding of transformer 54 and the primary winding of transformer 56 are connected to an electronic module 58 which operates to energize a trip coil 60, in the event of a predetermined current imbalance in line and neutral connections 45 and 49. For a ground fault on line conductor 46, the current imbalance arises from leakage current to ground which bypasses neutral conductor 50 and neutral connection 49. For a ground fault on the neutral conductor, the current imbalance in transformer 54 is created by the action of transformer 56 in inducing a current in the neutral circuit which effectively becomes a short circuited secondary winding when grounded at any point downstream from load center 10.

A load outlet 62, serviced by conductor 47, includes a metallic housing or enclosure 63. In cases where the housing is made of insulation, a conductive element (not shown) is added which functions electrically in the same manner. It will be appreciated that the conductor 47 services additional outlets and other forms of load outlets connected downstream.

For purposes of illustration, outlet 62 comprises a duplex receptacle 62a shown mounted in outlet housing 63 and as including two 3-prong sockets 64, each including line contacts 64a, neutral contacts 64b, and ground contacts 64c, all of the plug-in, prong-acceptance type. Line contacts 64a are connected in common to line conductor 46 by connection 66, while neutral contacts 64B are connected in common to neutral conductor 50 by connection 68. The ground contacts 64c are connected in common by connection 70 to ground conductor 51. This ground connection is also made to the metallic housing 63 of outlet 62 as indicated at 72.

The wiring installation thus far described may be considered as conventional in accordance with present requirements of the National Electrical Code for a ground fault protected circuit.

In accordance with the invention, a hazardous condition responsive detector 74, such as a thermal detector, is adapted to or incorporated in the receptacle 62a. This thermal detector may take any number of forms so long as it is capable of abruptly and substantially reducing its electrical impedance upon experiencing a thermal condition above an appropriate temperature threshold. Examples of suitable thermal detectors are a simple bimetallic switch, illustrated at 74b in FIG. 3, and a solid state device such as a negative temperature coefficient (NTC) thermistor, illustrated at 74a in FIG. 2. Other forms of detectors and detector circuits manifesting the requisite electrical response to elevated temperature conditions will readily occur to those skilled in the art.

As seen in FIG. 1, the detector 74 is situated in the outlet enclosure 63 and is electrically connected between the neutral connection 68 and the ground connection 70 so as to be imposed across the neutral conductor 50 and the ground conductor 51 running between the receptacle 62 and the load center 10. As the temperature within the receptacle, due to a faulty electrical connection, or in the room where the receptacle is located, due to a fire, rises to a predetermined dangerous level, the impedance of detector 74 goes from a high impedance to a low impedance, simulating a ground fault on the neutral conductor 50. The GFCI unit 42 senses the resulting current imbalance in the line and neutral conductors and energizes the trip coil 60 to open the breaker contacts 44. A suitable alarm, such as illustrated at 80, may be connected across the line and neutral conductors to be activated to emit an alarm upon the removal of power therefrom. The alarm may be battery powered, powered from either of the main buses 30, 32, or from an external auxiliary source. It will be appreciated that other techniques for producing an alarm signal in response to circuit interruption by the GFCI unit 42 may also be employed. It is also to be noted that if the high temperature condition arose from electrical overheating of the receptacle 62 itself, circuit interruption by the GFCI unit will alleviate the situation before an actual fire is started.

Rather than situate the detector 74 within the receptacle box 63, a separate 3-prong adapter 82, illustrated in FIG. 4, may be utilized to accommodate the detector. In this embodiment of the invention, the detector is incorporated in the adapter body 84 and electrically connected between the ground contact prong 86 and the neutral contact prong 88. A line contact prong 90 is blank or may be omitted altogether. It is seen that when the adapter 82 is plugged into one of the receptacle sockets 64, the requisite connection of the detector 74 across the neutral and ground conductors is achieved. Moreover, rather than in a separate adapter, the detector may be incorporated in a molded plug adapted to the end of an appliance cord, or the like.

It will be appreciated that the objects of the invention may be achieved by connecting the detector 74 across line conductor 46 and equipment ground conductor 51 so as to provide a current leakage path to ground when the temperature rises to a dangerous level. In this arrangement a current limiting resistor should be connected in series with the detector. However, Underwriters Laboratory and the various electrical Codes frown on the practice of imposing a fault on the line side of a power circuit for any purpose, consequently simulating a ground fault on the neutral side, as herein illustrated, is seen to be the better approach to practicing the present invention.

The invention has been described operating in conjunction with a GFCI unit since there is a current trend to require such units at least on some of the circuits in a residence where shock hazards are most common. Thus, locating the detector 74 in load outlets serviced by such ground fault protected circuits provides fire detection capability in addition to shock protection at minimal additional cost. It will be appreciated that instead of using a GFCI unit, per se, the "tickler coil" feature provided by transformer 56 may be utilized to sense a ground faulted neutral conductor, as simulated by detector 74, and signal an electronic module, which, in turn, activates an alarm directly without effecting circuit interruption or activates a shunt trip associated with the circuit breaker in the affected circuit or the main circuit breaker 28 in load center 10. Such circuit interruption may also be accompanied by the activation of an alarm.

While the present invention has been described utilizing thermal detectors, it will be appreciated that other types of abnormal or hazardous condition detectors, such as smoke, unauthorized intrusion, gas, etc., detectors may be utilized.

It will thus be seen that objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Claims

Having described our invention, what we claim as new and desire to secure

1. An abnormal condition detection system using conventional building electrical power distribution circuits which include a line conductor, a neutral conductor and a continuous, conductive ground circuit extending from a load center to various distributed load outlets, wherein the neutral conductor is connected to the ground circuit at a location in the vicinity of the load center, said system comprising, in combination:

A. means associated with the line and neutral conductors at a location intermediate the location of neutral conductor ground circuit connection and the load outlets for sensing a ground fault on either conductor;

B. an abnormal condition responsive detector located in the vicinity of one of the load outlets and electrically connected between the neutral conductor and the ground circuit,

1. said detector exhibiting a normally high electrical impedance until the condition to which said detector is sensitive reaches a predetermined degree of abnormality, whereupon said detector exhibits a low impedance sufficient to simulate a ground fault on the neutral conductor of sufficient magnitude to produce a response by said sensing means; and

C. means responsive to said response of said sensing means for manifesting

2. The system defined in claim 1, wherein said detector is located in a

3. For use in a power distribution circuit protected by a ground fault circuit interrupter unit, an abnormal condition responsive detector adapted for location at a condition monitoring site and for electrical connection between the neutral side of the distribution circuit and ground, said detector having a normally high impedance until the condition to which the detector is sensitive reaches a predetermined degree of abnormality, whereupon said detector exhibits a low impedance sufficient to simulate a ground fault on the neutral side of the distribution circuit of sufficient magnitude to produce a response by the ground fault circuit

4. The invention defined in claim 3 wherein said detector is incorporated in an adapter and electrically connected between two conductive prongs carried by said adapter, whereupon plugging said adapter into an outlet socket serviced by the distribution circuit, said detector is electrically connected, via said prongs, between the neutral side of the circuit and

5. The invention defined in claim 3, wherein said detector is incorporated in a plug receptacle and electrically connected between contacts thereof

6. For use in a power distribution circuit for distributing electrical power from a load center to a plurality of load outlets, wherein the distribution circuit is equipped with means for sensing a ground fault condition existing on the neutral side thereof, the combination of an abnormal condition responsive detector adapted for electrical connection between the neutral side of the distribution circuit and ground at a location proximate one of the load outlets serviced thereby, said detector exhibiting a normally high electrical impedance until the condition to which said detector is sensitive reaches a predetermined degree of abnormality, whereupon said detector exhibits a low impedance sufficient to simulate a ground fault on the neutral side of the circuit of sufficient magnitude to produce a response by said sensing means; and alarm means adapted for actuation in response to the response of said sensing means to manifest the existence of the abnormal condition.