Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Reexamination Certificate
1999-09-13
2003-05-06
Leja, Ronald W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
C361S049000, C340S649000, C340S652000
Reexamination Certificate
active
06560079
DESCRIPTION:
20 —Plug
21 —Ground prong on plug
22 —Electrical outlet
23 —Neutral prong on plug
24 —Hot conductor
25 —Hot prong on plug
26 —Neutral conductor
28 —Ground conductor
29 —Earth ground
30 —Load
32 —Appliance housing
34 —Control circuit
36 —Triac
37 —Sensitive gate triac
38 —Triac gate
39 —SCR gate
40 —Resistor
41 —Desensitizing resistor
42 —MT 1 terminal of triac
43 —Cathode of SCR
44 —MT 2 terminal of triac
45 —Anode of SCR
46 —Low current switch
47 —Silicon controlled rectifier
48 —Limiting resistor
49 —NPN transistor
50 —Neon indicator lamp
51 —PNP transistor
52 —Low current/low voltage switch
53 —Steering diode
54 —Back to back zener diodes
55 —Steering diode
56 —Current dead zone
57 —Ground current limiting resistor
58 —Diac
60 —Hot prong
62 —Neutral prong
64 —Ground prong
66 —Hot side triac
68 —Diac
70 —Charge capacitor
72 —Steering diodes
74 —NPN Darlington
76 —PNP Darlington
78 —Resistor
80 —Voltage divider
82 —Conductor
84 —Conductor
86 —Hot to ground fault
88 —Hot to neutral fault
90 —Load to ground fault
92 —Node
FIG. 1 portrays a block diagram of the ground detection circuitry. A plug 20 has three prongs 21 , 23 , 25 on one side that insert into an electrical outlet 22 . By convention, these prongs are configured to correspond to either the ungrounded conductor 24 (also known as the “hot” conductor), the grounded conductor 26 (also known as the “neutral” conductor) or the ground conductor 28 , which, when plug 20 is inserted into outlet 22 , should be electrically connected to earth ground 29 . This connection to earth ground 29 may be at the outlet 22 or at a remotely located distribution panel, transformer, or other location. The load 30 represents an appliance load, for example, the heater coil in an electric heater, the light bulb filament in an electric light, or the motor in a pump. The load 30 may be optionally surrounded by a grounded appliance housing 32 . A control circuit 34 is connected in electrical series between the load 30 and the neutral conductor 26 . The control circuit 34 also makes a connection to the ground conductor 28 . The control circuit 34 serves to monitor the connection to ground through the ground conductor 28 . When this connection is broken, the control circuit responds by inhibiting the flow of electrical current out of the load 30 and to the neutral conductor 26 thereby forcing the appliance into an off condition.
FIG. 2 depicts a specific embodiment of the ground detect circuit. In its simplest embodiment, the control 34 consists of a triac 36 electrically connected at the MT 1 terminal 42 to the load 30 and from the MT 2 terminal 44 to the neutral conductor 26 . A triac is a type of thyristor which may be thought of as a latching electrical switch. When the magnitude of the voltage potential at the triac gate 38 exceeds the magnitude of the voltage potential at the MT 1 terminal 42 by more than some characteristic gate turn-on voltage, the triac 36 turns on, allowing electrical current to flow from the load 30 to the neutral conductor 26 . Once the triac 36 is triggered into a conducting state, it continues to conduct electrical current as long as current magnitude is above some minimum threshhold known as the holding current. In this case, the triac 36 is said to be latched and continues to conduct even in the absence of a gate stimulus. If the triac 36 is in a nonconducting state, and the voltage potential at the triac gate 38 remains below the gate turn-on voltage, then the triac 36 will remain in a nonconducting state and little or no electrical current will flow from the load 30 into the neutral conductor 26 . A resistor 40 may be used to connect between the ground conductor 28 and the triac gate 38 . This serves to limit current flow to ground to that amount sufficient to turn on the triac 36 without drawing excessive currents that might damage the triac 36 or exceed accepted standards for ground current.
In a proper
REFERENCES:
patent: 3697808 (1972-10-01), Lee
patent: 3809961 (1974-05-01), Kershaw
patent: 3996496 (1976-12-01), Volk
patent: 4068276 (1978-01-01), Pintell
patent: 4598331 (1986-07-01), Legatti
patent: 4649454 (1987-03-01), Winterton et al.
patent: 4931893 (1990-06-01), Glennon et al.
patent: 5844759 (1998-12-01), Hirsh et al.
patent: 5943198 (1999-08-01), Hirsh et al.
patent: 5973896 (1999-10-01), Hirsh et al.
patent: 0 154 450 (1985-09-01), None
Hirsh Stanley S.
Nemir David C.
Leja Ronald W.
Myers Jeffrey D.
Peacock Myers & Adams P.C.
X-L Synergy
LandOfFree
Ground loss detection for electrical appliances does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ground loss detection for electrical appliances, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ground loss detection for electrical appliances will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3052490