Electricity: electrical systems and devices – Safety and protection of systems and devices
Reexamination Certificate
2002-09-24
2004-12-07
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
C361S042000, C361S072000, C361S115000
Reexamination Certificate
active
06829123
ABSTRACT:
BACKGROUND OF THE INVENTION TECHNOLOGY
FIELD OF THE INVENTION
The present invention relates to a safety system and method in a device for the protection of people and property, and more specifically when a potentially harmful event and/or undesirable conditions occur in an electrical device, e.g., an electrical appliance, the system and method of the present invention will de-energize power, lock-out access and/or alarm on the harmful event. Such undesirable conditions may include among others, undesirable leakage currents from the power source causing electrical shock potential on metal parts of the device, fire within or on the device, too high of a temperature, a pressure deviating too far from normal, the presence of smoke or particulate matter or, the presence or absence of light or of a light opaque member within the device.
The safety system and method of the present invention provides additional protection, not provided by prior systems, for electrical appliances and tools. In addition to providing protection from electrical leakage currents, and protecting a user from the hazard of electrical shock, it includes additional sensors for detecting and providing protection from undesirable events such as for example but not limited to flames, smoke, excessively high temperatures, and/or abnormal pressures in the device. Upon detection of the undesirable event, an alarm may be actuated and/or access to an affected area of the device blocked or locked-out so that harm to a device user or exasperation of the undesirable condition does not occur.
More particularly it relates to an enhancement of appliance leakage current interrupters (ALCIs) and equipment leakage current interrupters (ELCIs), to provide additional protection to a leakage current protected electrical device. More generally, it relates to an enhancement of any Leakage Current Protection Device as set forth in Underwriters Laboratories, Inc. Reference Standard UL943A, which includes not only ALCIs and ELCIs, but also immersion detection circuit interrupters (IDCIs). Whenever the term GFCI or ground fault circuit interrupter is used herein, it is intended in the broader sense of any leakage current protection device, where applicable.
More particularly it relates to protection of personal proximate to and users of the device by preventing access to the area of the device where the undesirable or harmful condition is occurring. It further prevents worsening the undesirable or harmful condition, e.g., allowing more oxygen to feed the fire, spread of the fire to adjacent flammable materials, release of excess pressure that could be harmful to people close to the device, release of smoke and/or toxic fumes to the surrounding area.
BRIEF SUMMARY OF THE INVENTION
In accordance with this invention, the protection provided against leakage currents and arcing (generally referred to as arcing currents herein), either separate from or in connection with a GFCI, to an electrical device power delivery cord, is extended to the electrical device which is connected to a power supply through the power delivery cord. The extended protection encompasses not only leakage currents and arcing, but also other undesirable conditions which may occur in the electrical device. Typical of the electrical devices which may be protected in accordance with this invention are electric heaters, air purifiers, room air conditioners, water distillers, and such kitchen appliances as toasters, toaster ovens, bread makers, and coffee makers. The extended protection upon detection of unsafe or undesirable conditions indicated by abnormal light or source of light, temperature or pressure conditions, or the presence of flame or smoke will result in disconnecting the electrical device form its power source.
Further in accordance with this invention, protection is provided against potentially dangerous access to the undesirable or harmful event by latching or locking an area, volume or compartment of the device from being inadvertently opened during the occurrence of the undesirable or harmful event.
Further in accordance with this invention, an alarm may be activated so as to alert personnel to the occurrence of the undesirable or harmful event.
One embodiment of the protection system and method of this invention is for use with two wire electrical devices such as an appliance or tool, which receives electrical power through a power cord, which includes an unshielded power line, and an unshielded neutral line. As described in co-pending application Ser. No. 08/682,957, entitled: “Electrical System With Arc Protection”, which application is hereby incorporated by reference herein for all purposes, a sensing lead, substantially electrically isolated from the power and neutral lines and the electrical load of the appliance, is provided in the power cord. A sensing lead integrity checking device, such as a neon glow tube or a switch, may be connected between the sensing lead and the power line. The integrity checking device connects the power line to the neutral line through the sensing lead. The impedance of the integrity checking device is increased by substantial additional resistance, so that the current flow is very small, well below the predetermined magnitude that would initiate response of the arcing current protection arrangement. Thus, although the integrity checking device does provide a connection between the sensing lead and the power line, the power line and the sensing lead are only connected for a brief integrity checking period through a switch, or the total impedance between the power line and the sensing lead is so high that, for practical purposes of the arcing current protection arrangement, the sensing lead is isolated from the power line and the appliance or tool load.
A rectifier, such as a diode rectifier circuit, may be connected between the power line and the neutral line to provide DC power to a circuit opening device, such as a solenoid which actuates normally closed contacts in the power line. In most situations, it is also desirable to open the neutral line. In such situations, a second pair of normally closed contacts in the neutral line are actuated by the solenoid.
Energization of the solenoid coil may be controlled by a suitable switching device, such as a silicon controlled rectifier (SCR) having the anode-cathode circuit connected in series with the solenoid coil. The gate of the SCR coil may be connected to the cathode through a suitable resistance that will bias the SCR to a conducting state when current flow of a pre-determined magnitude passes through the resistance, thus providing a current responsive arrangement. The sensing lead is also be connected to the gate of the silicon controlled rectifier, usually through a limiting resistor. Of course, with a different type of circuit opening device, the sensing lead would be connected to the control circuitry therefor.
When an arcing current above a predetermined magnitude is produced on the sensing lead, such as by detecting an arc resulting from a breakdown of the insulation separating the power line and the neutral line, the SCR will be gated to a conducting state and the solenoid will be energized to open the power line and, usually, the neutral line as well. Typically the leakage current detection level is set between a range of 250 microamperes and 5 milliamperes.
In accordance with this invention the sensing lead is electrically connected to the metal housing or frame of the electrical device. If there is a dielectric or insulation failure between the metal housing or frame and the power or neutral line, and a leakage current, tracking or arcing occurs with respect to the metal housing or frame of the electrical device, it will flow through the sensing lead to cause the SCR or other suitable switching device to be gated to a conducting state. Thus, the solenoid will be actuated by energization or de-energization, depending on the circuit configuration, to open the power line and usually, the neutral line as well. This embodiment of the arcing current protection arra
Campbell Les
Guptill Brian
Legatti Raymond H.
Baker & Botts L.L.P.
HP Intellectual Corporation
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