RECEPTACLE PROVIDING
SUSTAINED EXCESSIVE VOLTAGE PROTECTION
BACKGROUND OF THE INVENTION
Field of the Invention
This invention pertains generally to electrical switching apparatus and,
mre particularly, to receptacles.
Background Information
Receptacles are outlet circuit interrupters, which are intended to be
installed at a branch circuit outlet, such as an outlet box, in order to provide, for
example, arc fault and/or ground fault protection of loads.
Known receptacles typically include both a reset button and a test
button. The reset button is used to activate a reset cycle, which attempts to reestablish
electrical continuity between input and output conductive paths or conductors. While
the reset button is depressed, reset contacts are closed to complete a test circuit, in
order that a test cycle is activated. The test button also activates the test cycle, which
tests the operation of the circuit interrupting mechanism.
Known 120 VRMS ground fault and/or arc fault receptacles are designed
to survive the application of 240 VRMS, without tripping or without being damaged.
However, if any one or more 120 VRMS loads are downstream and/or are electrically
connected to the receptacle, then such loads will most likely be damaged or destroyed
by a sustained 240 VRMS overvoltage condition.
Sustained overvoltage conditions can result from a loss of the neutral
electrical connection at the upstream utility, load center or circuit breaker. Sustained
overvoltage conditions can also occur from certain utility faults. For example, if the
neutral is "lost" (e.g., due to an electrical problem; due to a "white" neutral wire being
disconnected from the power bus) in a single-pole, two-pole or three-phase power
system, then the nominal 120 VRMS line-to-neutral voltage may rise to 208 or 240
VRMS, thereby causing the line-to-neutral MOV(s) in the receptacle to fail (i.e., due to
an excessive voltage condition of sufficient duration).
U.S. Patent No. 6,671,150 discloses overvoltage protection in a circuit
breaker by employing an analog circuit (e.g., an MOV; a sidac; a circuit including a

diode, a zener diode and two resistors) to detect an excessive voltage condition
through a trip coil and responsively energize such trip coil.
There is room for improvement in electrical switching apparatus, such
as receptacles.
SUMMARY OF THE INVENTION
These needs and others are met by the present invention, which
provides a receptacle that protects a power circuit from a sustained excessive voltage
condition.
In accordance with one aspect of the invention, a receptacle for a
power circuit comprises: a receptacle housing; a line conductor structured to receive a
voltage including one of a nominal voltage and an excessive voltage, which is greater
than the nominal voltage; a load conductor; at least one neutral conductor; at least one
set of separable contacts, one set of the at least one set of separable contacts being
electrically connected between the line conductor and the load conductor; an
operating mechanism structured to open and close the at least one set of separable
contacts; and a trip mechanism cooperating with the operating mechanism to trip open
the at least one set of separable contacts, the trip mechanism comprising: a first circuit
structured to detect a first trip condition associated with the power circuit and to
responsively actuate the operating mechanism to trip open the at least one set of
separable contacts, and a second circuit structured to detect an excessive voltage
condition between the at least one neutral conductor and the line conductor or the load
conductor and to responsively actuate the operating mechanism to trip open the at
least one set of separable contacts.
The line conductor or the load conductor may include the received
voltage; the second circuit may comprise a voltage sensor structured to sense the
received voltage of the line conductor or the load conductor and a processor
structured to determine if the sensed received voltage is greater than a predetermined
value for greater than a predetermined time and to responsively actuate the operating
mechanism to trip open the at least one set of separable contacts, in order to protect a
load downstream of the load conductor from the excessive voltage condition.
The received voltage of the line conductor may be an alternating
current vcltage including a plurality of line cycles; the processor may be structured to

determine one of an integrated half cycle peak voltage, an average voltage and an
RMS voltage from the sensed received voltage; the predetermined value may be one
of an integrated voltage value, an average voltage value and an RMS voltage value;
and the predetermined time may be at least the duration of at least one of the line
cycles.
As another aspect of the invention, a receptacle for a power circuit
comprises; a receptacle housing; a line conductor structured to receive a voltage
including one of a nominal voltage and an excessive voltage, which is greater than the
nominal voltage; a load conductor; at least one neutral conductor; at least one set of
separable contacts, one set of the at least one set of separable contacts being
electrically connected between the line conductor and the load conductor; an
operating mechanism structured to open and close the at least one set of separable
contacts; a first circuit structured to detect a first trip condition associated with the
power circuit and to responsively actuate the operating mechanism to trip open the at
least one set of separable contacts, and a second circuit structured to detect a sustained
excessive voltage condition between the at least one neutral conductor and the line
conductor or the load conductor and to responsively actuate the operating mechanism
to trip open the at least one set of separable contacts.
BRIEF DESCRIPTION OF THE DRAWINGS
A full understanding of the invention can be gained from the following
description of the preferred embodiments when read in conjunction with the
accompanying drawings in which:
Figure 1 is a block diagram of a receptacle in accordance with the
present invention.
Figure 2 is a flowchart of a routine executed by the processor of Figure
1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is described in association with an arc fault /
ground fault receptacle, although the invention is applicable to a wide range of
receptacles.
Referring to Figure 1, a receptacle 2 for a power circuit 4 includes a
receptacle housing 6, a line conductor, such as terminal 8, structured to receive a

voltage 10 including one of a nominal voltage and an excessive voltage, which is
greater than the nominal voltage, a load terminal 12, and one or more neutral
terminals, such as 14 and/or 16. One or two sets of separable contacts 18,20 are
provided. One set 18 of the separable contacts is electrically connected between the
line terminal 8 and the load terminal 12. Another set 20 of the separable contacts may
be electrically connected between the neutral terminal 14 and the load neutral terminal
16. An operating mechanism 22 is structured to open and close the separable contacts
18,20. A trip mechanism 24 cooperates with the operating mechanism 22 to trip open
the separable contacts 18,20. The trip mechanism 24 includes a first circuit 26
structured to detect a first trip condition associated with the power circuit 4 and to
responsively actuate the operating mechanism 22 to trip open the separable contacts
18,20, and a second circuit 28 structured to detect an excessive voltage condition
between the load neutral terminal 16 (or the neutral terminal 14) and the line terminal
8 or the load terminal 12 and to responsively actuate the operating mechanism 22 to
trip open the separable contacts 18,20.
Example 1
The example trip mechanism 24 includes a microcontroller 30, a power
supply 32, a signal conditioning circuit 33 and a trip solenoid 34. The microcontroller
30 includes an analog-to-digital converter (ADC) circuit 36 and a microprocessor 38
having a firmware routine 40. The ADC circuit 36 includes a plurality of sensors,
such as ADC inputs 42,44,46,48 for sensing voltages respectively corresponding to
the line terminal 8 (line), the load terminal 12 (load), a test button 50 (test) and one or
more ground terminals 52,54. The ADC circuit 36 further includes a plurality of
sensors, such as ADC inputs 56 and 58,60, for sensing voltages corresponding to a
neutral shunt 62 (current) and the two inputs (sense) from a ground fault current
transformer 64, respectively. The microcontroller 30 and the various voltages are
referenced to a circuit ground (circuit_ground) on the load neutral side of the neutral
shunt 62 at node 66.
The neutral shunt 62 includes a voltage (current) corresponding to
current flowing through the separable contacts 20. The ADC input 56 senses that
voltage (current) and provides that sensed voltage for step 76 of Figure 2, as will be
discussed.

The current transformer 64 includes a signal corresponding to the
difference between current flowing through the separable contacts 18 and the load
terminal 12 and current flowing through the separable contacts 20 and the load neutral
terminal 16. The ADC inputs 58,60 sense this voltage and provide the corresponding
value for step 76 of Figure 2.
Example 2
Referring to Figure 2, the firmware routine 40 is shown. After starting
at 70, a timer (e.g., hardware; firmware) value is set to zero at 72. Next, at 74, the
microprocessor 38 reads and suitably processes the various voltages corresponding to
the ADC inputs 42,44,46,48,56,58,60. Then, at 76, arc fauk / ground fault trip logic is
executed to process the current value associated with the ADC input 56 and the two
sense inputs from the ground fault current transformer 64 at ADC inputs 58,60.
Under arc fault or ground fault trip conditions, the microprocessor 38 sets a digital
output 77, which provides a TRIP signal to the trip solenoid 34, in order to trip open
the separable contacts 18,20. Next, at 78, it is determined if the line voltage
associated with the ADC input 42 or the load voltage associated with the ADC input
44 is greater than a predetermined value. If not, then there is an absence of an
excessive voltage condition and execution resumes at 74. Otherwise, there is an
excessive voltage condition and, at 80, it is determined if the timer (e.g., hardware;
firmware) was started. If not, then at 82, the timer is started. Otherwise, or after 82, it
is determined if the timer value is greater than a predetermined time. If not, then
execution resumes at 78. On the other hand, if the timer value is greater than the
predetermined time, then there has been a sustained excessive voltage condition (e.g.,
the load voltage with respect to the neutral voltage (circuit_ground); the line voltage
with respect to the neutral voltage (circuit_ground)) of suitable time and magnitude.
Hence, under such sustained excessive voltage condition, at 86, the microprocessor 38
sets the digital output 77, which provides the TRIP signal to the trip solenoid 34, in
order to trip open the separable contacts 18,20. The microprocessor 38 and the
firmware routine even steps 78-86, thus, provide the microprocessor-based electronic
overvoltage protection circuit 28, while the microprocessor 38 and the firmware
routine step 76 provide the microprocessor-based electronic arc fault / ground fault
protection circuit 26. Both of step 76 (in the event of an arc fault or ground fault) and

step 86 actuate the operating mechanism 22 by issuing the trip signal through digital
output 77 to the trip solenoid 34, in order to trip open the separable contacts 18,20 and
protect a load (not shown) downstream of the load terminal 12 from the sustained
excessive voltage condition.
Example 3
The received voltage 10 of the line terminal 8 may be an alternating
currem: voltage including a plurality of line cycles. At step 74, the microprocessor
routine 40 may be structured to determine one of an integrated half cycle peak
voltage, an average voltage and an RMS voltage from the sensed received voltage of
ADC input 42.
Example 4
At step 78, the predetermined value may be one of an integrated
voltage value, an average voltage value, and an RMS voltage value (e.g., without
limitation, about 150 VRMS). At step 84, the predetermined time may be at least the
duration of at least one of the line cycles (e.g., without limitation, about 16.67 ms at
60 Hz). Thus, if a sustained excessive voltage above a predetermined threshold for a
predetermined time is detected, then the receptacle 2 opens one or both sets of
separable contacts 18,20 to disconnect any attached load(s) or downstream loads from
the source of the excessive voltage.
Example 5
The protection circuit 26 may be, for example, one or both of an arc
fault protection circuit and a ground fault protection circuit. Non-limiting examples
of arc fault detectors are disclosed, for instance, in U.S. Patent No. 5,224,006, with a
preferred type described in U.S. Patent No. 5,691,869, which is hereby incorporated
by reference herein. Non-limiting examples of ground fault detectors are disclosed in
U.S. Patent Nos. 5,293,522; 5,260,676; 4,081,852; and 3,736,468, which are hereby
incorporated by reference herein.
Example 6
Although step 78 may employ one or both of the line voltage and the
load voltage, preferably, at least the line voltage is sensed for determining a normal,
non-excessive voltage condition, or an excessive voltage condition.

Example 7
As is conventional, the operating mechanism 22 preferably includes a
suitable reset mechanism, such as RESET button 88, structured to mechanically close
the separable contacts 18,20.
Example 8
As is conventional, the trip mechanism 24 preferably includes a
suitable test mechanism, such as TEST button 50, structured to initiate one or both of
an arc fault protection test and a ground fault protection test. If the test signal at ADC
input 46 is active, then suitable signals (not shown) are sent to the control circuit 90 to
apply simulated fault signals (not shown) to test the arc fault / ground fault protection.
For example, the test button 50 can test the dual function arc fault and ground fault
trip logic 76 as disclosed in U.S. Patent No. 5,982,593, which is hereby incorporated
by reference herein.
Example 9
Although two sets of separable contacts 18,20 are shown, the
receptacle 2 may include a single set of separable contacts (e.g., separable contacts 18
electrically connected between the line and load terminals 8,12).
Example 10
The receptacle 2 preferably includes a suitable indication circuit 92
structured to indicate different fault conditions. For example, the circuit 92 includes a
first LED 94 driven by microprocessor output 95 and a second LED 96 driven by
microprocessor output 97.
Example 11
Further to Example 10, the LED 96 is red and is structured to indicate
at least one of the excessive voltage condition, the arc fault trip condition and the
ground fault trip condition, while the LED 94 is green, and when illuminated,
indicates a normal receptacle condition with no fault.

Example 12
Further to Example 10, the LED 96, when illuminated, is structured to
indicate the arc fault trip condition and the LED 94, vv'hen illuminated, is structured to
indicate the ground fault trip condition.
Example 13
Further to Example 12, one of the LEDs 94,96, such as 94, may be
structured to indicate the excessive voltage condition by flashing a corresponding
pattern, and to indicate one of the arc fault trip condition and the ground fault trip
condition by being solidly illuminated.
Example 14
Further to Example 12, both of the LEDs 94,96, when illuminated,
may be structured to indicate the excessive voltage condition.
Example 15
The power supply 32 is preferably powered from both (e.g., through
one or more auctioneering diodes (not shown) of the load terminal 12 and the line
terminal 8, in order to protect downstream load(s) under normal and reverse fed
conditions. Alternatively, the power supply 32 may be powered from at least one of
the terminals 8,12.
Example 16
As shown in Figure 1, an MOV 100 may be disposed between the load
terminal 12 and the load-neutral terminal 16, in order to provide transient voltage
protection.
The disclosed receptacle 2 advantageously provides automatic
electronic overvoltage protection by sensing line and/or load voltage(s) with respect
to a suitable circuit ground reference (e.g., a neutral voltage). If the sustained sensed
voltage (e.g., integrated half cycle peak, average, RMS) is above a predetermined
value (e.g., without limitation, 150 VRMS) for a predetermined time (e.g., without
limitation, one line cycle; a plurality of cycles; a suitable time), then the downstream
load(s) are disconnected from the source of the overvoltage.
While specific embodiments of the invention have been described in
detail, it will be appreciated by those skilled in the art that various modifications and

alternatives to those details could be developed in light of the overall teachings of the
disclosure. Accordingly, the particular arrangements disclosed are meant to be
illustrative only and not limiting as to the scope of the invention which is to be given
the full breadth of the claims appended and any and all equivalents thereof.

What is Claimed is:
1. A receptacle (2) for a power circuit (4), said receptacle
comprising:
a receptacle housing (6);
a line conductor (8) structured to receive a voltage (10)
including one of a nominal voltage and an excessive voltage, which is greater than
said nominal voltage;
a load conductor (12);
at least one neutral conductor (14,16);
at least one set of separable contacts (18,20), one set
(18) of said at least one set of separable contacts being electrically connected between
said line conductor and said load conductor;
an operating mechanism (22) structured to open and
close said at least one set of separable contacts; and
a trip mechanism (24) cooperating with said operating
mechanism to trip open said at least one set of separable contacts, said trip mechanism
comprising:
a first circuit (38,26,56,62) structured to detect a
first trip condition associated with said power circuit and to responsively actuate said
operating mechanism to trip open said at least one set of separable contacts, and
a second circuit (38,28,42,44) structured to
detect an excessive voltage condition between said at least one neutral conductor and
said line conductor or said load conductor and to responsively actuate said operating
mechanism to trip open said at least one set of separable contacts.
2. The receptacle (2) of Claim 1 wherein said line conductor or
said load conductor includes said received voltage; wherein said second circuit
comprises a voltage sensor (42,44) structured to sense the received voltage of said line
conductor or said load conductor and a processor (38) structured to determine if said
sensed received voltage is greater than a predetermined value for greater than a
predetermined time and to responsively actuate said operating mechanism to trip open
said at least one set of separable contacts, in order to protect a load downstream of
said load conductor from said excessive voltage condition.

3. The receptacle (2) of Claim 2 wherein the received voltage of
said line conductor is an alternating current voltage including a plurality of line
cycles; wherein said processor is structured to determine one of an integrated half
cycle peak voltage, an average voltage and an RMS voltage from said sensed received
voltage; wherein said predetermined value is one of an integrated voltage value, an
average voltage value and an RMS voltage value; and wherein said predetermined
time is at least the duration of at least one of said line cycles.
4. The receptacle (2) of Claim 1 wherein said second circuit
comprises a voltage sensor (44) structured to sense a voltage between said load
conductor and said at least one neutral conductor to detect said excessive voltage
condition.
5. The receptacle (2) of Claim 1 wherein said second circuit
comprises a voltage sensor (42) structured to sense a voltage between said line
conductor and said at least one neutral conductor and a processor (38) structured to
compare said sensed voltage to a predetermined value to detect an absence of said
excessive voltage condition.
6. The receptacle (2) of Claim 1 wherein said first circuit is an arc
fault protection circuit (26).
7. The receptacle (2) of Claim 6 wherein said second circuit
comprises a voltage sensor (56) and a shunt (62) electrically connected in series with
said one set of said at least one set of separable contacts, said shunt including a
voltage corresponding to current flowing through said one set of said at least one set
of separable contacts, said voltage sensor being structured to sense said voltage
corresponding to current flowing through said one set of said at least one set of
separable contact and provide said sensed voltage to said arc fault protection circuit.
8. The receptacle (2) of Claim 1 wherein said first circuit is a
ground fault protection circuit (26).
9. The receptacle (2) of Claim 8 wherein said second circuit
comprises a voltage sensor (58,60) and a current transformer (64) operatively
associated with said one set of said at least one set of separable contacts, said current
transformer including a signal corresponding to a difference between current flowing
through said one set of said at least one set of separable contacts and current flowing

through said at least one neutral conductor, said voltage sensor being structured to
sense the signal of said current transformer and provide said sensed signal to said
ground fault protection circuit.
10. The receptacle (2) of Claim 1 wherein said operating
mechanism comprises a reset mechanism (88) structured to mechanically close said at
least one set of separable contacts.
11. The receptacle (2) of Claim 1 wherein said first circuit
comprises at least one of an arc fault protection circuit (26) and a ground fault
protection circuit (26).
12. The receptacle (2) of Claim I wherein said at least one set of
separable contacts includes a first set of separable contacts (18) and a second set of
separable contacts (20); wherein said at least one neutral conductor includes a neutral
conductor (14) and a load neutral conductor (16); wherein said first set of separable
contacts is electrically connected between said line conductor and said load
conductor; and wherein said second set of separable contacts is electrically connected
between said neutral conductor and said load neutral conductor.
13. The receptacle (2) of Claim 1 wherein said first circuit
comprises an arc fault trip circuit (26) structured to trip open said at least one set of
separable contacts in response to an arc fault trip condition, and a ground fault trip
circuit (26) structured to trip open said at least one set of separable contacts in
response to a ground fault trip condition.
14. The receptacle (2) of Claim 13 wherein said trip mechanism
further comprises at least one indicator (92) structured to indicate at least one of said
excessive voltage condition, said arc fault trip condition and said ground fault trip
condition.
15. The receptacle (2) of Claim 14 wherein said at least one
indicator includes a first indicator (96) structured to indicate said arc fault trip
condition and a second indicator (94) structured to indicate said ground fault trip
condition.
16. The receptacle (2) of Claim 14 wherein said at least one
indicator is a single indicator (94) structured to indicate said excessive voltage

condition by flashing a pattern, and to indicate at least one of said arc fault trip
condition and said ground fault trip condition by being solidly illuminated.
17. The receptacle (2) of Claim 1 wherein said trip mechanism
further comprises a power supply (32) powered from at least one of said line
conductor and said load conductor.
18. A receptacle (2) for a power circuit (4), said receptacle
comprising:
a receptacle housing (6);
a line conductor (8) structured to receive a voltage (10)
including one of a nominal voltage and an excessive voltage, which is greater than
said nominal voltage;
a load conductor (12);
at least one neutral conductor (14,16);
at least one set of separable contacts (18,20), one set of
said at least one set of separable contacts being electrically connected between said
line conductor and said load conductor;
an operating mechanism (22) structured to open and
close said at least one set of separable contacts;
a first circuit (38,26,56,62) structured to detect a first
trip condition associated with said power circuit and to responsively actuate said
operating mechanism to trip open said at least one set of separable contacts, and
a second circuit (38,28,42,44) structured to detect a
sustained excessive voltage condition between said at least one neutral conductor and
said line conductor or said load conductor and to responsively actuate said operating
mechanism to trip open said at least one set of separable contacts.
19. The receptacle (2) of Claim 18 wherein at least one of said line
conductor and said load conductor includes said received voltage; wherein said
second circuit comprises a voltage sensor (42,44) structured to sense said received
voltage and a processor (38) structured to determine if said sensed received voltage is
greater than a predetermined value for greater than a predetermined time and to
responsively actuate said operating mechanism to trip open said at least one set of

separable contacts, in order to protect a load downstream of said load conductor from
said sustained excessive voltage condition.
20. The receptacle (2) of Claim 19 wherein the received voltage of
said line conductor is an alternating current voltage including a plurality of line
cycles; wherein said processor is structured to automatically determine one of an
integrated half cycle peak voltage, an average voltage and an RMS voltage from said
sensed received voltage; wherein said predetermined value is one of an integrated
voltage value, an average voltage value and an RMS voltage value; and wherein said
predetermined time is at least the duration of at least one of said line cycles.

A receptacle for a power circuit includes a receptacle housing, a line
terminal structured to receive a voltage including one of a nominal voltage and a
greater excessive voltage, a load terminal, a neutral terminal, a load neutral terminal,
separable contacts electrically connected between the line and load terminals, an
operating mechanism structured to open and close the separable contacts, and a trip
mechanism cooperating with the operating mechanism to trip open the separable
contacts. The trip mechanism includes a trip circuit structured to detect a first trip
condition associated with the power circuit and to responsively actuate the operating
mechanism to trip open the separable contacts. The trip mechanism also includes an
overvoltage circuit structured to detect a sustained excessive voltage condition
between the at least one neutral terminal and the line or the load terminals and to
responsively actuate the operating mechanism to trip open the separable contacts.