Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Reexamination Certificate
1999-04-26
2001-04-03
Ballato, Josie (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
C361S049000, C361S117000
Reexamination Certificate
active
06212048
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to combination/circuit interrupter/overvoltage protection apparatus for protecting AC power lines, coaxial transmission lines and communication lines from overvoltage conditions without the use of a separate ground conductor.
2. Discussion of the Related Art
Today many homes and buildings use sensitive electronic equipment such as home entertainment centers with expensive audio/visual equipment, personal computers, modems, printers, copiers, facsimile machines and telephone answering machines. This sensitive electronic equipment is connected to the outside world by AC power lines, coaxial transmission lines (both cable TV, satellite dish antennas and broadband internet connections) and communication lines (telephone, facsimile and high speed data). Because the electronic equipment is expensive, there is a need to protect the equipment from voltage surges occurring on the AC power lines, the coaxial transmission lines and the communication lines.
To fill this need a number of companies have developed plug in secondary surge suppressors which are designed to plug into AC wall outlets which carry a separate ground conductor and which accept three prong AC power plugs. The electronic equipment, which also has three prong AC power plugs, is then plugged into the secondary surge suppressor. Some plug in secondary surge suppressors currently available also provide overvoltage protection for coaxial transmission lines and/or communication lines. See, for example, Cawley U.S. Pat. No. 4,438,477 issued Mar. 20, 1984, which discloses a plug in secondary surge suppressor which protects both AC power lines and communication lines from overvoltage conditions using the ground obtained from the AC outlet by means of a three prong AC power plug.
While newly-built homes and buildings have AC outlets which carry a separate ground wire and accept three prong AC power plugs, older homes and buildings have AC outlets which only accept two prong AC power plugs. Therefore, plug in secondary surge arrestors currently being marketed (which have three prong AC power plugs and use the ground from the AC outlet to provide overvoltage protection) cannot be used in older homes and buildings with AC outlets which only accept two prong AC power plugs. A need therefore exists for a plug in secondary surge suppressor which can be used with AC outlets which only accept two prong AC power plugs.
While many homes today have ground fault circuit interrupters (GFCIs), those devices are only found in areas where water or moisture is present. GFCIs are current sensing devices and are tripped when a current imbalance is detected, generaly for a substantial period of time (up to 25 milliseconds) compared to the time a voltage transient exists (tens of microseconds). GFCIs do not respond to overvoltage conditions and do not protect against overvoltage condidtions. Indeed, GFCIs may be damaged by overvoltage conditions.
SUMMARY OF THE INVENTION
The preferred embodiment of the present invention provides a plug in secondary surge suppressor which utilizes a two wire AC power source (no separate ground wire) to protect electrical equipment having three prong AC power plugs. The preferred embodiment of the present invention employs a GFCI in combination with an AC overvoltage protection circuit and a “virtual ground”, i.e., a return path to the two wire AC power source through which voltage surges may be directed. The present invention fills the need for a surge suppressor which protects electrical equipment having three prong AC power plugs and which can be used in homes and buildings equipped with AC outlets which will only accept two prong AC power plugs.
The subject matter which I regard as my invention is more particularly pointed out in the claims at the end of the specification. The invention, including its method of operation and its numerous advantages, may best be understood by reference to the following description taken in conjunction with the accompanying drawings wherein like reference numerals refer to like compounds.
REFERENCES:
patent: 4023071 (1977-05-01), Fussell
patent: 4025822 (1977-05-01), Hughes et al.
patent: 4438477 (1984-03-01), Cawley
patent: 4807083 (1989-02-01), Austin
patent: 4903161 (1990-02-01), Huber et al.
patent: 5566056 (1996-10-01), Chaudhry
patent: 5654857 (1997-08-01), Gershen
patent: 5844764 (1998-12-01), Meyerhoefer et al.
Ballato Josie
Huynh Kim
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