Patent US3761774A successfully refreshed from Google Patents.
US3761774A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Ground fault protective apparatus
Assignee: Black and Decker Corp
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Filing: 1970-03-20
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Granted: 1973-09-25
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Expires: 1990-03-20
Abstract
Abstract Simplified apparatus for disconnecting an electric appliance from the source of current upon the occurrence of a fault to ground through the tool. The apparatus may be located within the housing of the appliance or, preferably, at the connector which is inserted into a line voltage receptacle so that the entire appliance including its power cord is protected. The apparatus includes sensing means such as a differential transformer for detecting a difference in current between the two power lines leading to the appliance, resonant circuit means for producing a signal corresponding to such a difference, and circuit interruption means controlled by a semi-conductive switch which responds to the detected signal. Rectifying means are also provided to enable the apparatus to function regardless of the direction of current through the power lines to the appliance.
Inventors
- 👤 C Laughinghouse
- 👤 W Vogelsberg
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 17:31
CPC Classifications
H; H01; H01H; H01H83/00; H01H83/14; H01H83/144; H01H13/00; H01H13/02; H01H13/04; H01H13/08; H01R; H01R13/00; H01R13/648; H02; H02H; H02H3/00; H02H3/26; H02H3/32; H02H3/33; H01R13/66; H01R13/70; H01R13/713
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
174 words
In an electric tool having an electric motor, an output shaft for providing power to a work-engaging element, switch means for controlling the application of a voltage to said motor, and a power cord including a connector comprising a pair of prongs extending from a flat exterior surface for insertion into a receptacle for connecting said tool to a source of electric current, the improvement comprising means incorporated in said tool for disconnecting said tool from said source upon the occurrence of a fault current through said tool and including means for detecting a fault current through said tool; and means responsive to said detection means for interrupting the current through said connector; said disconnecting means being included in said connector whereby faults occurring in said power cord cause said disconnecting means to operate; and reset means for said disconnecting means, said reset means comprising a mechanical latch having a reset button mounted in said flat surface whereby said reset means can only be operated when said connector has been removed from said receptacle.
Claim 2
Dependent Claim
174 words
In an electric tool having an electric motor, an output shaft for providing power to a work-engaging element, switch means for controlling the application of a voltage to said motor, and a power cord including a connector comprising a pair of prongs extending from a flat exterior surface for insertion into a receptacle for connecting said tool to a source of electric current, the improvement comprising means incorporated in said tool for disconnecting said tool from said source upon the occurrence of a fault current through said tool and including means for detecting a fault current through said tool; and means responsive to said detection means for interrupting the current through said connector; said disconnecting means being included in said connector whereby faults occurring in said power cord cause said disconnecting means to operate; and reset means for said disconnecting means, said reset means comprising a mechanical latch having a reset button mounted in said flat surface whereby said reset means can only be operated when said connector has been removed from said receptacle.
Claim 3
Dependent Claim
168 words
In an electric tool having an electric motor enclosed in a housing, an output shaft for providing power to a work-engaging element, switch means for controlling the application of a voltage to said motor, and a power cord, said cord including a connector for connecting said tool to a standard source of electric current, and a strain relief member at the point of entry thereof into said housing to control the degree of flexing of said cord; the improvement comprising a self-contained protective device incorporated in said tool for disconnecting said tool from said source upon the occurrence of a fault current through said tool, said device including means for detecting a fault current through said tool at a value substantially less than the operating current of said tool; and means responsive to said detection means for interrupting the current through said connector; said detecting means including a differential current sensing means disposed within said strain relief member to sense the net current passing through said power cord.
Claim 4
Dependent Claim
168 words
In an electric tool having an electric motor enclosed in a housing, an output shaft for providing power to a work-engaging element, switch means for controlling the application of a voltage to said motor, and a power cord, said cord including a connector for connecting said tool to a standard source of electric current, and a strain relief member at the point of entry thereof into said housing to control the degree of flexing of said cord; the improvement comprising a self-contained protective device incorporated in said tool for disconnecting said tool from said source upon the occurrence of a fault current through said tool, said device including means for detecting a fault current through said tool at a value substantially less than the operating current of said tool; and means responsive to said detection means for interrupting the current through said connector; said detecting means including a differential current sensing means disposed within said strain relief member to sense the net current passing through said power cord.
Claim 5
Dependent Claim
31 words
Apparatus as claimed in claim 2 wherein said housing includes a handle adapted to be grasped by the operator of said tool and said disconnecting means is located within said handle.
Claim 6
Dependent Claim
58 words
Apparatus as claimed in claim 2 wherein said differential sensing means comprises a toroidal core of magnetic material having a secondary winding thereon, said core being disposed in surrounding relationship to said power cord; said secondary coil being arranged to cause operation of said disconnecting means upon the occurrence of a non-zero net current within said power cord.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-09-24 | 1977-03-26 | 1977-09-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-09-24 | 1981-03-26 | 1981-09-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-09-24 | 1985-03-26 | 1985-09-25 | $7700.00 | Window Closed / Lapsed |