Ground fault circuit interrupter miswiring prevention device

Details Ground fault circuit interrupter miswiring prevention device Ground fault circuit interrupter miswiring prevention device

1998-12-03

2001-06-26

Metjahic, Safet (Department: 2858)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of ground fault indication

Reexamination Certificate

active

06252407

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to ground fault circuit interrupters and more particularly relates to an apparatus for preventing the miswiring of ground fault circuit interrupter devices at the time they are installed into the electrical power system.
BACKGROUND OF THE INVENTION
Presently, electrical devices known as ground fault circuit interrupters (GFCIs) enjoy widespread use in many countries around the world, in both commercial and residential environments. In fact, in many places their use is mandatory in certain locations of residential homes such as in kitchens, baths and near pools (i.e., locations close to sources of water).
A typical GFCI incorporating a duplex receptacle provides protection for devices plugged into itself and all devices located downstream of the GFCI device. Typically GFCIs are four terminal devices, two phase or AC leads for connection to AC electrical power and two LOAD leads for connection to downstream devices. Properly wired, a GFCI provides ground fault protection to downstream devices connected to its LOAD leads and to devices plugged into the GFCI receptacle itself However, if the GFCI is reverse wired or improperly wired then downstream devices are still protected if there is a ground fault but the duplex receptacle on the GFCI is not.
A perspective view illustration of a typical prior art GFCI device
12
which incorporates a duplex receptacle within its housing is shown in FIG.
1
. The GFCI device
12
comprises a housing
14
, two receptacles
16
,
18
each comprising hot
70
,
74
, neutral
72
,
76
and ground
77
,
79
slots or contacts. Line side hot and neutral screw terminals
24
provide electrical connection points to an alternating current (AC) source. Load side hot and neutral terminals
26
provide electrical connection points for electrical devices located electrically downstream from the GFCI device
12
. Tabs
28
provide means for mounting the GFCI device
12
into a wall box. A ground screw terminal
27
is provided to facilitate connecting the GFCI device
12
to a ground wire. In addition, a TEST button
20
is used to periodically test the GFCI device
12
to insure its proper functioning. A RESET button
22
is provided to reset the GFCI device
12
after it has tripped such as after testing.
A high level schematic diagram illustrating the major components of the prior art GFCI device
12
shown in
FIG. 1
as properly wired to an AC electrical source is shown in FIG.
2
. The AC source
17
is electrically coupled to the hot (i.e., phase) and neutral line side screw terminals
24
. Electrically connected across the phase and neutral lines is the GFCI circuit
11
. GFCI circuits are well known in the art. Electrical switches
13
,
15
are placed in line with the phase and neutral lines. The electrical
13
,
15
switches may be electromechanical relays, semiconductor switches or other suitable controllable switching devices. Electrical switch or relay
13
is operative to open circuit the phase conductor and electrical switch or relay
15
is operative to open the neutral conductor in the event a ground fault is detected. On the load side of the relays
13
,
15
are the two electrical receptacles
16
,
18
. The hot contacts
70
,
74
are electrically coupled to the phase conductor and the neutral contacts
72
,
76
are electrically coupled to the neutral conductor. Ground conductors
77
,
79
are electrically coupled to the system ground. The load side phase and neutral terminals
26
provide phase and neutral lines to downstream electrical devices. A pilot light 21 shows the condition of the GFCI. Such a pilot light is shown in U.S. Pat. No. 4,412,193 issued Oct. 25, 1983. See the LED pilot light 81 in FIG.
1
.
Under normal operating conditions, relays
13
,
15
are closed and electrical current flows to both the receptacles
16
,
18
and downstream devices. In the event of a ground fault, GFCI circuitry
11
is operative to open relays
13
,
15
and prevent current from flowing to the receptacles
16
,
18
and downstream electrical devices connected to the load side terminals.
However, if the GFCI
11
is miswired (miswiring is as shown in
FIG. 3
, when the GFCI trips (i.e., detects a ground fault) electrical current is properly prevented from flowing to downstream devices via relays
13
,
15
opening but electrical power is still present at the two receptacles
16
,
18
. Power is present at the receptacles
16
,
18
in this case because the receptacles
16
,
18
are now located before the relays
13
,
15
(i.e., further upstream). Thus, in the event the GFCI
11
trips, all downstream devices are protected but the GFCI's own receptacles remain live after the GFCI
11
trips.
One reason that this problem exists is that in new construction, both the input line and downstream cables appear identical when the installer is connecting a new ground fault circuit interrupter. This is especially a problem in new construction where there is no power available in order to test which cable is leading current into the device. The problem is compounded when it is considered that most GFCIs have a test button that will trip and shut off the power when pushed to verify operations of internal functions in the GFCI. However, use of the test button does not indicate whether the built in duplex receptacle is protected. Typical users may not be aware of this. Users simply test the device after installation and verify that the unit trips upon pressing the test button by way of an audible click, for example. This gives the user a false sense that all is well. What is actually happening when the GFCI
11
is reverse wired is that the GFCI
11
disconnects power from and protects everything downstream, but does not protect the receptacle contacts of the GFCI
11
itself. The device will trip depending on the condition of internal components and irrespective of how the GFCI
11
was wired. It does not matter that the GFCI
11
was reverse wired when it was tested.
If the ground fault circuit interrupter is inadvertently powered through its LOAD terminals, the GFCI
11
will still trip normally when confronted with a ground fault and all downstream receptacles will still be protected. However, due to the internal connections, the GFCI's own receptacle terminals will still remain live after the GFCI
11
trips.
Currently, all GFCI's are being shipped with an instruction label attached over the LOAD terminals as per UL requirements. The Consumer Product Safety Commission is asking for something more substantial then simply a warning label. The warning label simply informs the installer to be careful when wiring the LOAD terminals. The label covers those terminals and must be removed if the terminals are to be used. Though this gives a better chance that the warning will be read, something more likely to ensure safety is desirable.
Therefore it is apparent that there is a need for an automatic way to sense when a GFCI is miswired and to indicate to the user an improperly wired GFCI. In addition, when the GFCI is improperly reverse wired the user needs to be alerted with an indicator that cannot be turned off until the electricity is disconnected and the GFCI is correctly wired. Although the background art has attempted to solve this problems the so called solutions have their own disadvantages and drawbacks. For example, one approach utilizes a GFCI with reverse line polarity lamp indicator to indicate proper installation of the GFCI. See, for example, U.S. Pat. No. 4,412,193 issued to Bienwald et al. on Oct. 25, 1983 and assigned to the owner of the present invention. However, a push button needs to be manually pressed in accordance with instructions in order to detect whether the GFCI is miswired. An apparent drawback with this scheme is that the test is never self initiating, i.e., automatic, since the user must always remember to follow the instructions and to actually press a button to test the GFCI. U.S. Pat. No. 5,477,412 issued to Neiger et al. on Dec. 19, 1995 and owned by th

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