U.S. patent number 3,864,649 [Application Number 05/452,956] was granted by the patent office on 1975-02-04 for electrical safety device with improved trip mechanism.
This patent grant is currently assigned to The Rucker Company. Invention is credited to Richard C. Doyle.
United States Patent |
3,864,649 |
Doyle |
February 4, 1975 |
Electrical safety device with improved trip mechanism
Abstract
Electrical safety device for controlling the flow of current in
a conductor and interrupting the flow in the event of a
predetermined current such as an excessive current or ground fault
current.
Inventors: |
Doyle; Richard C. (Benicia,
CA) |
Assignee: |
The Rucker Company (Concord,
CA)
|
Family
ID: |
27375743 |
Appl.
No.: |
05/452,956 |
Filed: |
March 20, 1974 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
271988 |
Jul 14, 1972 |
|
|
|
|
141151 |
May 7, 1971 |
|
|
|
|
87713 |
Nov 9, 1970 |
|
|
|
|
Current U.S.
Class: |
335/21;
200/DIG.42; 335/173; 335/18; 335/166 |
Current CPC
Class: |
H01H
71/505 (20130101); H01R 13/7135 (20130101); H01H
83/04 (20130101); H02H 3/33 (20130101); H01H
2071/506 (20130101); H01H 2083/045 (20130101); Y10S
200/42 (20130101); H01H 71/501 (20130101) |
Current International
Class: |
H01H
71/50 (20060101); H01H 83/00 (20060101); H01H
71/10 (20060101); H01H 83/04 (20060101); H02H
3/33 (20060101); H02H 3/32 (20060101); H01R
13/70 (20060101); H01R 13/713 (20060101); H01h
073/02 () |
Field of
Search: |
;335/18,26,172,173,192,194,82,38,15,16,21,25,174,200,166
;337/168,170 ;200/DIG.42 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Broome; Harold
Attorney, Agent or Firm: Flehr, Hohbach, Test, Albritton
& Herbert
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This is a division of copending application Ser. No. 271,988, filed
July 14, 1972, which was a continuation-in-part of then pending
application Ser. No. 141,151, filed May 7, 1971, now abandoned,
which was a continuation-in-part of then pending application Ser.
No. 87,713, filed Nov. 9, 1970, now abandoned.
Claims
I claim:
1. In an electrical safety device for controlling the flow of
current in a conductor and interrupting the flow in the event of a
predetermined current: first and second contacts for making and
breaking a circuit with the conductor, a floating contact arm
having the first contact mounted thereon and movable relative to
the second contact, a latch member releasably engaging the contact
arm at a point spaced from the first contact, resilient means
engaging the contact arm between the first contact and the latch
member for urging contacts together when the latch member is
engaging the contact arm, said resilient means serving to pivot the
arm about the contacts to provide rocking movement between the
contacts when the latch member is disengaged from the arm, means
for disengaging the latch member from the contact arm in response
to the predetermined current, and a fulcrum member positioned for
engaging the contact arm between the first contact and the
resilient means when the arm has pivoted a predetermined distance
about the contacts and thereafter cooperating with the resilient
means to separate the contacts.
2. The electrical safety device of claim 1 wherein the means for
disengaging the latch member includes an operating coil.
3. The electrical safety device of claim 1 further including a
manually operable reset member engaging the contact arm for
exerting a force on said arm generally opposite to the force of the
resilient means to return the arm to a position in which said arm
can be engaged by the latch member.
4. The electrical safety device of claim 3 further including a
resilient member urging the latch member into position for engaging
the contact arm.
5. The electrical safety device of claim 3 wherein the means for
disengaging the latch member is adapted for holding the latch
member out of engagement with the contact arm as long as the
condition producing the predetermined current is present.
Description
SUMMARY AND OBJECTS OF THE INVENTION
This invention pertains to an electrical safety device for
controlling the flow of current in a conductor and interrupting the
flow in the event of a predetermined current such as an
overcurrent, a short circuit or a ground fault current. The device
includes a set of contacts movable between open and closed
poaisitons for controlling the flow of current in the conductor, a
floating contact arm carrying one of the contacts, a latch member
releasably engaging the arm member, and resilient means engaging
the arm member between the contact carried thereby and the latch
member for urging the contacts together when the latch member is
engaging the contact arm. The resilient means also serves to urge
the contact arm to pivot about the contacts to provide a rocking
movement between the contacts when the latch member is disengaged
from the contact arm. A fulcrum member is positioned for engaging
the contact arm between the contact carried thereby and the
resilient means when the arm has pivoted a predetermined distance
about the contacts and thereafter cooperating with the resilient
means to separate the contacts.
It is in general an object of the invention to provide a new and
improved electrical safety device for controlling the flow of
current in a conductor and interrupting the flow in the event of a
predetermined condition in the current.
Another object of the invention is to provide an electrical safety
device of the above character having an improved trip
mechanism.
Additional objects and features of the invention will be apparent
from the following description in which the preferred embodiments
are set forth in detail in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of one embodiment of an electrical safety
device incorporating the invention.
FIG. 2 is a front elevational view of one embodiment of an electric
receptacle assembly with ground fault protection incorporating the
invention.
FIG. 3 is a side elevational view, partially sectioned, of the
receptacle assembly illustrated in FIG. 2.
FIG. 4 is a bottom plan view, partially sectioned, of the
receptacle assembly illustrated in FIG. 2.
FIG. 5 is a cross-sectional view taken along line 5--5 in FIG.
4.
FIG. 6 is a cross-sectional view taken along line 6--6 in FIG.
3.
FIG. 7-10 are fragmentary cross-sectional views illustrating the
operation of the trip mechanism of the receptacle assembly shown in
FIGS. 2-6.
FIG. 11 is a front elevational view of a second embodiment of an
electric receptacle assembly with ground fault protection
incorporating the invention.
FIG. 12 is a cross-sectional view taken along line 12--12 in FIG.
11.
FIGS. 13-15 are fragmentary cross-sectional views illustrating the
operation of the trip mechanism of the receptacle assembly shown in
FIGS. 11 and 12.
FIG. 16 is a cross-sectional view taken along line 16--16 in FIG.
13.
FIG. 17 is a wiring diagram of the receptacle assembly of FIGS.
11-16.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the drawing, the invention is illustrated in connection with a
single phase, two wire system consisting of an A.C. source 15, an
ungrounded line conductor L and a ground neutral conductor N. The
neutral conductor N is connected to ground at its source end.
Although illustrated as a direct connection, the ground return does
not have to have a resistance of zero ohms. The invention will
operate satisfactorily with a resistance as large as approximately
2000 ohms in the ground return.
The safety device illustrated in FIG. 1 is a receptacle assembly
having socket means 16, interrupter contacts 17 connected for
controlling the flow of current between the conductors L and N and
the socket means 16, ground fault detector means 18, and operating
means 19 for opening the contacts 17 when a ground fault is sensed
by the detecting means 18. Reset means 21 is provided for closing
the contacts 17 after a ground fault has been corrected.
The socket means 16 provides means for delivering electrical energy
from the conductors of the distribution system to an electrical
appliance such as the load 22. In the preferred embodiment, this
socket means is a conventional three prong socket having a line
terminal 23 for connection to the line conductor, a neutral
terminal 24 for connection to the neutral terminal, and a ground
terminal 26 which is connected to ground. The load 22 typicall
includes a line cord or service cord 27 which includes a connecting
plug 28 having a plurality of current carrying prongs 29. The
socket means 16 is adapted for receiving the plug 28 in such manner
that the prongs 29 contact the terminals therein.
In one preferred embodiment, the ground fault detecting means 18 is
of the flux storage type which is disclosed in U.S. Pat. No.
3,614,533, issued Oct. 19, 1971. This means includes a differential
transformer 31 having a toroidal core 32, single turn primary
windings 33 and 34 connected in series with the line and neutral
conductors and passing through the toroidal core, and a secondary
winding 36 consisting of a plurality of turns wound on the core.
Under normal conditions, that is in the absence of a ground fault,
the currents in the primary windings 33 and 34 are balances,
producing a zero net flux in the core 32 and a zero output voltage
across the secondary winding 36. Upon the occurence of a ground
fault, the currents in the primary windings 33 and 34 are no longer
equal, a non-zero net magnetic flux is produced in the core 32, and
a fault signal is induced in the secondary winding 36. As is
described more fully in the referenced copending application, this
fault signal is applied to one or more reactor cores where it is
stored in the form of a flux signal. The stored flux signal is read
out of the reactor cores by means of a pulsating signal and after
suitable conditioning, such as amplification, is applied to the
operating means 19 for actuating the contacts 17. The portion of
the ground fault responsive means other than the differential
transformer 31 is represented by the block 37 in FIG. 1. This
portion is conveniently constructed in a small package such as an
integrated circuit, and if desired, it can include means for
protecting against undesired grounding of the neutral conductor at
or near the load, as described in U.S. Pat. No. 3,611,035, issued
Oct. 5, 1971, and in U.S. Pat. No. 3,506,906, issued Apr. 14, 1970.
Alternatively, the ground fault detecting means 18 can be of the
modulating type disclosed in U.S. Pat. No. 3,597,656, issued Aug.
3, 1971.
As is described more fully hereinafter, the operating means 19
includes a trip coil connected for energization by the ground fault
responsive means, together with mechanical linkage for opening the
contacts when the trip coil is energized.
Means is provided for testing the operating of the ground fault
protector. This means includes a resistor 38 and a switch 39
connected in series between the line and neutral conductors on
opposite sides of the differential transformer.
As illustrated in FIGS. 2-6, the receptacle assembly is adapted to
be mounted in a standard receptacle wiring box 41 of the duplex
type. Boxes of this type are on the order of 4 inches long, 2
inches wide and 2 inches deep, and they are commonly used for
housing single socket and/or switch assemblies. Box 41 is
illustrated as being mounted in a recessed area formed in a
building wall 42. A cover plate member 43 is mounted on the outer
surface of the wall 42 over the recessed area and provides means
for enclosing the box 41. The box 41 is typically fabricated of an
electrically conductive metal, and the cover plate is typically
fabricated of an insulative material such as plastic.
The receptacle assembly includes a housing 44 which is mounted
inside the standard box 41. This housing is generally rectangular
in shape and is fabricated of an insulative material such as
Bakelite. The remaining components of the receptacle assembly are
mounted within the housing 44. This housing is open at the top and
is formed to include arc discharge openings 46 in proximity to the
electrical contacts which are mounted therein. The housing 44 is
mounted to the box 41 by means of a mounting plate 47. This plate
is formed to include mounting tabs 48 which engage ear portions 49
on the insulative housing 44. The mounting plate is secured to the
metal box by means of screws 51, and the cover plate 43 is attached
to the mounting plate by means of screws 52.
A generally planar rectangular base member 56 is mounted within the
housing 44 and rests upon ledges 57 which are formed in the side
walls of the housing. Conventional socket assemblies 58, 59 are
mounted on the upper side of this base member proximate the ends
thereof. Each of these socket assemblies includes a line terminal
23, a netural terminal 24, and a ground terminal 26 for receiving
the connecting prongs of a plug such as the plug 28. The line
terminals of the two socket assemblies are connected together by
means of a conductor 61 disposed in a recess in the upper surface
of the base member, and the neutral terminals are connected
together by means of a conductor 62 which is disposed in a recess
formed in the bottom surface of the base member. The ground
terminals are connected together by means of a conductor 63 which
is also disposed in a recess formed in the bottom surface of the
base member. Thus, as will be apparent to those familiar with the
art, the two socket assemblies are connected electrically in
parallel.
The differential transformer 31 and remainder of the ground fault
responsive means 37 are mounted in the space between the base
member 56 and the bottom wall of the insulative housing.
The contacts 17 and operating means 19 are mounted on the top side
of the base member between the socket assemblies 58 and 59. Two
sets of contacts are provided, one for interrupting the flow of
current in the line conductor and the other for interrupting the
flow of current in the neutral conductor. Each of these sets of
contacts includes a fixed upper contact 66 and a movable lower
contact 67. An insulative mounting post 68 is mounted to the base
member 56 intermediate the two sets of contacts. The upper contacts
in the two sets are carried by rigid conductors 69 which are
supported at one end by the insulative post 68 and are connected at
their other ends to the line and neutral terminals of the socket
assemblies. Thus, one of the conductors 69 connects one of the
upper terminals 66 to the neutral terminal of the socket assembly
58, and the other conductor 69 connects the other upper contact to
the line terminal of the socket assembly 59. Flexible conductive
pigtails 71 are connected to the movable contacts in the two sets,
and these pigtails pass through the toroidal core of the
differential transformer to form single turn primary windings. The
pigtails also pass through openings formed in the bottom wall of
the insulative housing and are connected to the line and neutral
conductors by conventional connectors, such as wire nuts 72, in the
space between the insulative housing and the standard outlet box. A
third pigtail 73 is connected to the ground conductor 63 and passes
through an opening in the insulative housing for connection to a
grounded conductor 74 by means of a wire nut 72. Alternatively, if
desired, the flexible pigtails 71 can be terminated at wiring posts
mounted on the base member 56, and the connections to the wire nuts
can be completed with conventional insulated wire such as -4
stranded copper wire. In this alternative arrangement, the
insulated wires, rather than the flexible pigtails, pass through
the differential transformer core and the openings in the
housing.
The movable contacts 67 are carried by a contact arm member 76
which is fabricated of an insulative material. This member is
generally T-shaped, with the contacts being mounted on the upper
surface of the cross bar portion. A roller 77 is pivotally mounted
in a notch formed in the base portion of this member. As is
discussed hereinafter, means is provided for rotating the arm
member 76 to move the contacts between open and closed
positions.
The operating means includes a supporting framework which is also
mounted on the upper side of the base member between the socket
assemblies. This framework includes a base portion 81, a vertically
extending back wall 82, vertically extending side walls 83 and a
front wall 84. A solenoid 86 is mounted in the space between the
front, back and side walls. This solenoid includes a trip coil 87
which is adapted for connection to the ground fault responsive
means by conductors 88, and it also includes a plunger member 89
movable between advanced and retracted positions in accordance with
the energization of the trip coil. The supporting framework can
serve as part of the magnetic circuit for operating the solenoid
plunger and is preferable fabricated of a good magnetic material
such as a mild steel.
An upper pivot rod 91 and a lower pivot rod 92 extend horizontally
between the side walls 83. A latch member 93 is pivotally mounted
at one end on the upper pivot rod 91 and releasably engages the
contact arm roller 77 at its other end. The latch member is linked
to the armature member 89 by means of a connecting pin 94. A latch
spring 96 is provided for urging the latch forward into engagement
with the contact arm roller 77.
A generally U-shaped resilient member 97 is mounted on the lower
pivot rod 92 and engages the contact arm member 76 intermediate the
contacts 67 and the roller 77. This resilient member urges the
lower contacts 67 up against the latch member 93. The post 68 is
formed to include a fulcrum portion 98 in proximity to the upper
surface of the arm member 76 intermediate the contacts 67 and the
resilient member 97.
Means is provided for resetting the operating means and moving the
contacts to their closed position following the correction of a
ground fault. This means includes a generally cylindrical member
101 which is slidably mounted in a vertically extending bore 102
formed in the post 68. The lower extremity of the member 101
engages the upper surface of the arm member 76 at a location
intermediate the resilient means 97 and the lower contacts 67, thus
providing means for applying a force to the contact arm generally
opposite to the force applied by the resilient means 97. The
cylindrical member 101 extends through an opening 103 in the cover
plate 43 and through an opening 104 in the mounting plate 47. This
member is movable between extended and retracted positions, and a
light spring 106 is provided for holding it in its retracted
position. A colored band 107 is provided on the member in such
position that it is visible only when the member is in its extended
position. As will appear hereinafter, the operation of the reset
means is such that the contacts cannot be manually closed by it
while a ground fault is present.
The resistor 38 is mounted in a vertical bore in the post 68. In
one terminal of this resistor is connected to the neutral pigtail
on the source side of the differential transformer. In one
presently preferred embodiment, this connection is made by means of
an insulated wire which passes through the differential transformer
core and then is connected to the neutral wiring post on the base
member. The other resistor lead 111 is cut off close to the
resistor and disposed in proximity to a resilient contact member
112 which is connected to the upper contact 66 connected to the
line terminals of the sockets. An insulative test button 113
engates the contact member 112 and passes through an opening 116 in
the frame member 47. This button extends part of the way through an
opening 114 in the cover plate 43 and is accessible from outside
the cover plate by means of a small or pointed instrument. Being
recessed, however, it is not likely to be accidentally
depressed.
Operation and use of the electrical safety device can now be
described briefly. Initially, let is be assumed that an electrical
appliance has been connected to one of the sockets and that the
system is operating normally, that there is no ground fault. In
this condition, the trip coil 87 is deenergized, and the resilient
member 96 urges the latch member 93 forward into engagement with
the roller 77 of the contact arm member 76. The resilient member 97
urges the contact arm member upward, holding the contacts in their
closed position. The reset member 101 is urged downward against the
contact arm member by the spring 106, and it remains in its
retracted position with the colored band 107 concealed by the cover
plate 43.
Upon the occurrence of a ground fault, or when the test button 113
is depressed, as illustrated in FIG. 7, the trip coil 87 is
energized. This moves the solenoid plunger member 89 to its
retracted position, drawing the latch member 93 out of engagement
with the contact arm member roller 77. In this condition, the
contacts 66 and 67 function as a fulcrum, and the resilient member
97 moves the roller end of the contact arm in an upward direction,
producing a rocking action at the contacts. This rocking action has
been found to be very desirable since it tends to break any contact
welds which may have formed between the contacts. The rocking
action continues until the contact arm engages the fulcrum portion
98 of the post 68. At this point, the center of rotation shifts
from the contacts to the fulcrum portion 98, and the contacts are
separated. As the contact arm rotates, it pushes the reset member
101 upward to its extended position, exposing the band of color 107
to provide a visible indication of the occurrence of the ground
fault. The rotational movement of the contact arm continues until
its contact end engages the upper surface of the base member 56.
The assembly is shown in its fully tripped position in FIG. 8.
In order to reset the operating means and close the contacts, the
reset member 101 is manually depressed. This exerts a force on the
contact arm member opposite to the force exerted by the resilient
member 97. The contact arm now pivots around the contact end which
is engaging the upper surface of the base member 56, and the roller
end moves downward. The resilient member 96 moves the latch member
93 back into position for engaging the roller 77. As long as the
reset member 101 is depressed, the contacts will remain open, as is
best seen in FIG. 9. When the reset means is released, the contact
arm 76 moves upward until the roller engages the latch member 93.
Thereafter, the contact arm rotates about the roller, with the
contact ends thereof moving upward until the contacts are in their
closed position. Thereafter, the device will again be in the normal
operating conditions illustrated in FIG. 6.
It is to be noted that the protective operation of the device
cannot be defeated by the reset means. As long as the reset member
101 is depressed, the contacts will remain open. When the trip coil
87 is connected to remain energized throughout the ground fault,
the unit cannot be reset until the ground fault is removed since
the solenoid armature 89 will be in its retracted position,
preventing the latch member 93 from engaging the roller 77. If the
trip coil is deenergized by the ground fault, the device will trip
immediately if an attempt is made to reset it during the
continuance of the ground fault.
The receptacle assembly shown in FIGS. 11-17 includes a housing
assembly 121 which is preferably fabricated of an insulative
material. A cover plate 122 is mounted on the housing assembly by
means of a mounting plate 123, and the entire assembly is mounted
in a standard duplex box 124. The housing assembly includes a
raised portion 121a which extends through a generally rectangular
opening 122a in the cover plate. A pair of three conductor outlets
126 and 127, a reset button 128, and a test button 129 are all
mounted in the raised portion of a housing assembly and accessible
from the outer side of the cover plate. The line, neutral and
ground terminals of outlets 126 and 127 are connected electrically
and parallel by conductors 131-133.
The flow of current to conductors 131 and 132 and, hence, to
outlets 126 and 127 is controlled by a contact assembly 134. This
assembly includes two sets of contacts, one for the line conductor
and the other for the neutral conductor. Each set includes a fixed
contact 136 and a movable contact 137, with the fixed contacts
being connected to the line and neutral terminals of the outlets.
The movable contacts are mounted on a contact arm 138 and connected
to flexible pigtails 139 which are connected to the protected line
and neutral conductors. Conductor 133 is connected to ground by a
third pigtail 141.
Contact arm 138 is fabricated of an insulative material, and it is
generally T-shaped. Contacts 137 are mounted on the cross bar
portion of the arm, and the other end of the arm is releasably
engaged by a latch 142 which forms a part of a clapper type
solenoid assembly 143. This assembly includes a trip coil 144 and
the latch or clapper 142. The coil is mounted on a generally
U-shaped bracket 146, and the clapper is pivotally mounted on a
pivot rod 147 which extends between the arms of the U-shaped
bracket. A spring 148, carried by rod 147, engages the central
portion of arm 138 and urges the arm in an upward direction, as
viewed in FIG. 12. A latch spring 149 urges latch or clapper 142
toward the latching position shown in FIG. 12.
The operation of solenoid assembly 143 is controlled by a ground
fault sensing module 151 which is mounted on the lower portion of
housing assembly 121. In the preferred embodiment, the module
contains the circuit shown in FIG. 19 which, as disclosed in
copending application Ser. No. 141,297, filed May 7, 1971, can be
constructed in a compact modular form. The module includes a window
152 through which the line and neutral pigtails 139 pass to form
the single turn primary windings of a differential transformer. One
end of solenoid coil 144 is connected to the module by a lead 153,
and the other end of the coil is connected to a switch contact 154
which is normally engaged by a movable contact 156. A second
movable contact 157 engages contact 156 when test button 129 is
depressed. One lead 158a of a resistor 158 is connected to contact
157, and the other lead 158b of this resistor is connected to the
line conductor through fixed interrupter contact 136.
Reset button 128 is movable between extended and retracted
positions, and a spring 161 urges the button toward its retracted
position, as illustrated in FIG. 12. The button is provided with an
indicator band 128a which can be seen from the outer side of the
cover plate only when the button is in its extended position. When
the button is in its retracted position, the lower portion of the
button extends somewhat below a shoulder 162 formed by the housing
assembly.
Operation and use of the receptacle assembly shown in FIGS. 11-17
can now be described. Initially, let it be assumed that an
electrical appliance has been connected to one of the outlets and
that the system is operating normally, that is, there is no ground
fault. In this condition, solenoid coil 144 is deenergized, and
latch spring 149 urges latch or clapper 142 into engagement with
the end of contact arm 138. Spring 148 urges the contact arm
upward, holding the contacts in their closed position. Reset button
128 is urged downward against the contact arm by spring 161, and it
remains in its retracted position with indicator band 128a
concealed by cover plate 122.
If test button 129 is depressed, as illustrated in FIG. 13, contact
157 engages contact 156, connecting resistor 158 between the line
and neutral conductors on opposite sides of ground fault sensing
module 151, creating an imbalance in the currents in the protected
conductors. The module energizes solenoid 153 in response to this
imbalance, as it would in the event of a ground fault, and latch
142 is drawn out of engagement with contact arm 138. In this
condition, contacts 136 and 137 function as a fulcrum, and spring
148 moves the free end of the contact arm in an upward direction,
producing a rocking action at the contacts. This action continues
until the contact arm engages the shoulder portion 162 of the
housing assembly. At this point, the center of rotation shifts from
the contacts to the shoulder portion, and the contacts are
separated, as illustrated in FIG. 4. As the free end of the contact
arm moves upward, it engages contact 156, moving this contact out
of engagement with contact 154 to deenergize solenoid coil 144. It
will be noted that interrupter contacts 136 and 137 separate before
contact 156 is moved, thereby assuring interruption of the current
in the protected conductor before the solenoid coil is deenergized.
When the coil is deenergized, spring 149 urges latch 142 to back
into position for engaging the free end of the contact arm when the
arm is reset to close the contacts. With the contacts open, contact
arm 138 moves reset button 128 to its extended position, exposing
indicator band 128a.
After the ground fault has been corrected, the assembly can be
reset by depressing reset button 128, as indicated in FIG. 15.
Depressing the button moves the free end of the contact arm
downward into latching engagement with latch 142. When the button
is released, spring 148 will move the other end of the contact arm
upwardly, closing contacts 136 and 137. It will be that when the
reset button is first depressed, the free end of contact arm 138
releases contact 156 which then moves back into contact with
contact 154, completing the circuit to solenoid coil 144. Thus, if
someone attempts to reset the assembly before a ground fault is
corrected, the unit will trip again immediately upon the closing of
the contacts 136 and 137.
It is apparent from the foregoing that a new and improved
electrical safety device has been provided. While only the
presently preferred embodiments have been described, as will be
apparent to those familiar with the art, certain changes and
modifications can be made without departing from the scope of the
invention as defined by the following claims.
* * * * *