Electricity: electrical systems and devices – Safety and protection of systems and devices – Transient responsive
Reexamination Certificate
1999-03-10
2001-08-28
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Transient responsive
C361S118000, C361S042000
Reexamination Certificate
active
06282075
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to surge suppressors for protecting AC power lines, coaxial transmission lines and communication lines from overvoltage conditions using a virtual ground rather than 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 plugs. The electronic equipment, which also has a three prong AC plug, 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 plug.
While newly-built homes and buildings have AC outlets which carry a separate ground wire and accept three prong AC plugs, older homes and buildings have AC outlets which only accept two prong AC plugs. Therefore, plug in secondary surge arrestors currently being marketed (which have three prong AC 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 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 plugs.
SUMMARY OF THE INVENTION
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 plugs. The surge suppressor of the present invention provides such overvoltage protection by creating a “virtual ground”, i.e., a return path to the two wire AC power source through which voltage surges appearing on coaxial transmission lines and/or communication lines may be directed. The present invention fills the need for a surge suppressor which protects electrical equipment having three prong AC plugs and which can be used in homes and buildings equipped with AC outlets which will only accept two prong AC plugs.
REFERENCES:
patent: 6023400 (2000-02-01), Nevo
Jackson Stephen W.
Morgan & Finnegan L.L.P.
TII Industries Inc.
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