Note: Descriptions are shown in the official language in which they were submitted.
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Ground fault circuit interrupting (GFCI) devices
have recently been developed in ratings suitable for imple~
; mentation in residential circuits. These GFCI devices typically
include, in addition to ground fault protection, overload and
short circuit protection. ~11 of these protective ~eatures
are packaged in a molded case comparable in size to a con-
ventional circuit breaker, such that GFCI devices can be
accommodated in existing circuit breaker load centers.
Ground fault protection is afforded by a so-called
"module" which energizes a trip solenoid to initiate circuit
interruption. To provide adequate protection in terms of
preventing personal injury, the GFCI module must respond to
high impedence line to ground faults where the fault current
is quite small, e.g., 5 to 6 milliamps. Fault currents in
excess of 5 to 6 milliamps flowing through the body for even
a short duration can produce harmful and even fatal conse-
quences~
A GFCI module basically includes a current sensor,
a signal processor and an electronic switch. The current
sensor is in the form of a differential current transformer
which responds to a current im~alance in the line and neutral
conductors of the distribution circuit, as is occasioned by
leakage current flowing from the line conductor through a
fault to ground and back to the source over a circuit path
other than the neutral conductor. The transformer response
to this current imbalance or differential is amplified by
the signal processor pursuant to ~riggering the electronic
- switch, typically a silicon controlled rectifier, and therby
complete an energization circuit for the trip solenoid~ With
the extremely low signal levels involved, the signal processor
must be relatively sophisticated in design and include
provisions for rejecting electrical noise in order to provide
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reasonable immunity to nuisance tripping.
In addition to tripping in the event of a line to
ground fault GFCI devices are required to trip in the event
of a low impedance ground fault on the neutral conductor.
This is done to guard against the possible desensitizing
effect that a neutral ground fault has on the current sensor.
That is, should the line and neutral conductors both experience
ground faults, some of the current flowing through the line-
ground fault could return to the source through the neutral-
ground fault and the neutral conductor. The current differ~
ential seen by the current sensor would not therefore be a
true measure of the ground fault current magnitude, and the
GFCI device would not trip even though the fault current
exceeded the 5-6 milliamp trip level~ To also sense a neutral
ground ~ault, the module is further typically equipped with a
second transformer which is energized to induce an imbalancing
current flow in the neutral conductor of sufficient magni-
tude to precipitate a ground fault trip function ln the event
the neutral conductor experiences a ground fault.
It will be appreciated that assembly of the comp-
onent parts of a GFCI module having all of these requisite
capabilities into a compact package of small physical size
is an exacting task which contributes significantly to the -~
overall manufacturing cost of GFCI devices, such as GFCI
circuit breakers.
It is accordingly an object of the present inven-
tion to provide a GFCI device having an improved module -
incorporated therein.
Another object is to provide a GFCI module designed
to facilitate assembly of its component parts into a compact
package of small physical size.
Yet another object is to provide a GFCI m~dule of
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the above character wherein the assemblage of its component
;` parts is maintained without resorting to potting.
A further object is to provide a GFCI module of the
above character with improved shielding against RF noise
which could precipitate nufsance tripping of the GFCI device.
Other objects of the invention will become appar
ent from the following detailed description and claims.
In accordance with the present invention, there
is provided a ground fault circuit interrupting (GFCI)
device, such as a circuit breaker, which incorporates an
improved module facilitating assembly of the component
parts thereof. The module includes magnetics and electronics,
mounted on a circuit board, is accommodated in one compart-
ment of the shell. The shell is structurally adapted to
provide a resilient latch for retaining the electronics
positioned in its compartment. The magnetics consists of a
differential current transformer and a neutral oscillator
transformer, each accommodated in separate shell compartments.
The shell is provided with resilient means for engaging the
transformers upon insertion in their respective compartments,
retaining them in position for subsequent assembly operations.
The core apertures of the two transformers, retained in their -
respective shell compartments, are aligned such as to accom-
modate the insertion therethrough of single turn winding
elements. Intermediate the transformer compartments, the
shell is formed to provide a bounded opening through which
the winding elements also pass, thereby effectively locking
the magnetics in place.
An additional feature of the invention, the differ-
ential transformer, is encompassed by a cup-shaped conductive
magnetic shield to prevent RF noise and external magnetic
fields from being coupled into the secondary winding thereof.
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The invention accordingly comprises the ~eatures
of construction, combination of elements, and arrangement
of parts which will be exemplified in the construction here- .
inafter set forth, and the scope of the invention will be indi- ::
cated in the claims. :
For a fuller understanding of the nature and objects
of the invention, reference should be had to the following
detailed description taken in connection with the accom- ~ :
panying drawings, in which~
FIGURE 1 is a side elevational view of a GFCI
circuit breaker, with cover removed to expose a GFCI modulq
embodying the present invention; ~ -
FIGURE 2 is a one side elevational view of the - : :
module shell with the electronics and magnetics removed;
FIGURE 3 is a sectional view taken along line 3-3
of FIGURE 2; ~ ~:
FIGURE 4 is an opposite side elevational view of the
GFCI module shell with magnetics in place;
FIGURE 5 is a sectional view taken along line 5-5
of FIGURE 4; .
FIGURE 6 is a sectional view taken along line 6-6 ~-
of FIGURE 4; .
FIGURE 7 is a sectional view taken along line 7-7
of FIGURE 4; and
FIGURE 8 is a sectional view taken along line 8-8
of FIGURE 4.
Like reference numerals refer to corresponding parts
throughout the several views of the drawings.
The present invention is illustrated as being
embodied in a ground fault circuit interrupting (GFCI) circuit
breaker of the type disclosed in U. S, patent no 3,789,268,
dated January 29, 1974, assigned to the assignee of the instant
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application. As seen from the disclosure of this
patent, the GFCI circuit breaker is housed in an
insulative case consisting of two case sections and
a cover. One of these case sections houses the circuit
breaker proper which includes separable contacts, an
operating mechanism and a trip mechanism, all of which
may be of conventional circuit breaker design such as
shown, for example in U.S. Patent No. 3,464,040, dated
August 26, 1969, also assigned to the assignee of
the present application.
The other case section, together with
the cover, enclosed those components devoted to
providing the ground fault protective function. The
major one of these components is a GFCI module, which
is generally indicated at 12 in FIGURE 1 herein.
This GFCI module includes a shell 14 for accommodating
the electronics and magnetics, respectively generally
indicated at 16 and 18. Also included in this
section of the GFCI circuit breaker case 10 is a
trip solenoid 20 which is selectively energized under
the control of the module 12 to initiate a ground
fault trip function. More specifically, a trip
solenoid plunger 22 engages one end of a link 24
extending into the circuit breaker section of case 10.
Thus, upon energization of the trip solenoid, its
plunger is attracted to move the link into tripping
engagement with a latch (not
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shown), thereby releasing the circuit breaker operating
mechanism to initiate circuit interruption.
Still referring to FIGURE 1, power for the GFCI
electronics 16, mounted on a printed circuit board 26, is
obtained from a conductive post 28 via lead 30, trip solenoid
20, and lead 32. Post 28 extends laterally into the circuit
breaker section of the case 10 where it is electrically con- ~ -nected to the load side of the separable contacts (not shown). ~ -
Also electrically connected to post 28 is a conductor 34
which conveys line current through the magnetics portion of
the GFCI module 12. The other end of this conductor is
soldered to a strap 36 which extends laterally into the cir-
cuit breaker section of the case 10 to the line side load ~ -
terminal of the GFCI circuit breaker. A conductive braid
38 encompasses the conductor 34 for excursion throuqh the
magnetics 18. One end of braid 38 is connected to one end of ~ -
a pigtail conductor 40, whose other end, upon installation of
the GFCI circuit breaker, is connected to a neutral bus (not
shown) of a circuit breaker load center. The other end of
braid 38 is connected to a strap 42 included in a neutral
side load terminal, generally indicated at 44, of the GFCI -
circuit breaker. A lead 46 from the electronics 16 to
braid 38 completes the module connections for energization
from the distribution circuit for which grounded fault
protection is afforded. -
Still referring to FIGU~E 1, to verify the oper-
ability of the GFCI circuit breaker, a test switch 47 is
connected between strap 36, electrically common to the load
side line terminal, and the module electronics 16 by leads
48 and 50. The electronics includes a suitably valued
resistor (not shown) electrically connected in series between
leads 46 and 50, such that closure of the test switch 47
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1~48~00
simulates a ground leakage current of the prescribed trip
level, e.g., 5 milliamperes, in response to which the GFCI ~ -
circuit breaker should trip.
Turning to FIGURES 2 and 3, insulative shell 14,
molded in plastic in a generally tray-like configuration, is
formed with a continuous sidewall 58. Ledges 60a, 60b and 60c,
molded with the compartment sidewall 58 support the printed
circuit board 26 in spaced relation to the compartment
floor, as best seen in FIGURE 3, so as to afford clearance
for the electronic components mounted to the circuit board.
Molded rib 62, seen in FIGURE 2, together with the compart- -
ment sidewall 58 served to locate the position of the electronics
in compartment 54. As best seen in FIGURE 3, a tab 64,
molded in the free edge of sidewall 58, together with an
integrally formed resilient latching finger 66, then serve
to retain the once located electronics 16 in compartment 54.
In assembly, one edge of printed circuit board 26 is first
caught under tab 64 and the opposite edge is caught under a
latch sur~ace 66a formed in the termination of resilient
finger 66. To facilitate assembly, the termination of
resilient finger 66 is provided with an angular surface 66b
which is engaged by the edge portion of the printed circuit
board 26 as the electronics is pressed into place to cam the
barbed termination of finger 66 to the left as seen in phantom
in FIGURE 3. When the edge of the circuit board clears
latching surface 66a, the finger 66 springs back to its normal
erect orientation with its latching surface then engaging the
circuit board. It is thus seen that circuit board 26 is
trapped between tab 64, finger 66, and ledges 60a,;60b, 60c
for positive retention in compartment 54, without the neces-
sity for the application of a potting material. The elimina-
tion of potting not only reduces direct manufacturing costs,
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1~4~
but also renders the salvaging of the electronics 16 from
otherwise defective modules economically practicable.
To accommodate the GFCI magnetics 18, shell 14 is
formed to provide a pair of compartments 70 and 72, as seen
in FIGURE 4. These compartments are open to the reverse
side of the module shell 14 frcm the opening to electronics
compartment 54. Compartment 72 accommodates a differential
current transformer, generally indicated at 74, for sensing
a current imbalance in condu~tor 34 and braid 38 which, in
application, carry the currents in the line and neutral sides,
respectively, of the distribution circuit. As seen in the
sectional view of FIGURE 5, the differential transformer
includes a toroidal core 76, on which is wound a multi-turn
secondary winding 78. The wound core is mounted coaxially
on a spool 80 equipped at one end with an annular flange 80a.
According to a feature of the present invention, a magnetically
and electrically conductive, cup-shaped shield 82 surrounds
the wound core to prevent the coupling of external magnetic
fields and RF noise into the transformer secondary winding
78. Conductor 34 and braided conductor 38 are passed through
an axial bore 80b in spool 80 to constitute separate, single-
turn primary windings for the differential current transformer
74. While conductors 34 and 38 are in coaxial relationship
during the single pass through the differential current
transformer simply to conserve space, it will be appreciated
that these conductors can be in side-by-side relation. In
order to provide a lower profile, a portion of the floor for
compartment 72 is removed, as indicated at 72a in FIGURES 1
and 2, to provide an opening accommodating the lower peripheral
portion of the differential current transformer. To support
and position the differential current transformer 74 in
compartment 72, shield 82 is provided with an axially extending
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annular collar 82a which seats in a semi-circular depression
72b formed in one endwall of compartment 72. At the other
end of the differential current transformer, spool 80 extends
beyond the termination of shield 82 so as to rest in another
semi-circular depression 72c formed in the opposite compart-
ment endwall. At one or more locations, collar 82a of shield
82 so as to rest in another semi-circular depression 72c
formed in the opposite compartment endwall. At one or more
locations, collar 82a of shield 82 is dimpled, as indicated
at 82b in FIGURE 5, so as to insure electrical contacting
engagement with braided conductor 38. Thus RF noise voltage
intercepted by shield 82 is conducted to ground via the
braided conductor 38 and the neutral side of the electrical
source, which, according to conventional practice is grounded
at the load center.
As seen in FIGURES 4 and 8, the compartment endwall
is integrally formed to provide, on each side of depression
72b, a resilient finger 84 upstanding in a wall recess 85.
Each finger carries a protuberance 84a which resiliently
engages shield 82 so as to frictionally retain transformer
74 in compartment 72.
The other magnetics compartment 70 in shell 14
accommodates a neutral excitation transformer, generally
indicated at 90. As seen in FIGURE 5, this transformer
includes a toroidal core 92 on which is wound a multi-turn
primary winding 94. The wound core is mounted on a spool
96 provided with an annular flange 98 at one end. The lower
peripheral portion of flange 90 rests on the floor 70a of
compartment 70, while the other end of spool 96 extends
beyond the wound core to rest on a semi-circular depression
70c provided in the end wall common to compartments 70 and
72.
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The neutral excitation transformer 90 is detained
in its compartment by a pair of resilient tabs 100 molded
into the endwall 70b of compartment 70. As seen in FIGURES
4 and 7, each tab 100 is carrisd on a narrow wall segment
101 which is separated from the main endwall 70b by a
rectangular through-slot 102. The lower end of wall segment
101 is not joined to the floor 70a of compartment 70 so as
to enhance flexibility. When the neutral transformer 90
is inserted in its compartment 70, the tabs 100 press against
the spool flange 98 to retain the transformer in its compart-
ment until the conductors 34 and 38 are inserted through the
spool bores in a subsequent assembly step.
According to a feature of the invention the common
wall between compartments 70 and 72 is molded to provide an
arch 106 (FIGURE 6) itermediate the semi-circular depressions
70c and 72c. The material for arch 100 is taken from the
common endwall, as evidenced by the slot 108 therein (FIGURE
5). It is thus seen that upon insertion of the conductors
34 and 38 through the axial bores in transformer spools 96 and
80, the magnetics are locked into their respective compart-
ments 70 and 72 by the bounded aperture defined by arch 106
and flanking depressions 70c and 72c. Endw~ll 70b is provided
with a semi-circular depression 70d to accommodate conductors
34 and 38. -
Referring to FIGURES 3 and 5, a portion of the floor
56 of compartment 54 is removed, as is a portion of the wall
common to the electronics and magnetics compartments, so as
to provide an opening 110 admitting a series of leads for
electrically interconnecting the electronics and the magnetics.
The leads from the electronics are lodged in notches 111 formed ~-
in the edge of the common wall at the opening~ To facilitate
this interconnectiont the shell 1~ is formed with a plurality
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~486~0
of wells 112 (FIGURE 6) into which are press fitted terminals
114 to which the leads from the electronics and the leads
from the magnetics are commonly soldered. As shown in
FIGURE 2, shell 14 is integrally formed with a laterally ex-
tending bracket 116 which is suitably notched to receive
conductor 30 running from the post 28 to solenoid 20
(FIGURE 1). The retention of conductor 30 in this bracket
notch serves to hold the solenoid essentially in its position
against the module 12 during assembly into case 10 and the
making of the electrical connection of conductor 30 to
post 28.
It will thus be seen that the objects set forth
above, among those made apparent in the preceding description
are effi~iently attained and, since certain changes may be
made in the above construction without departing from the
scope of the invention, it is intended that all matter con-
tained in the above description or shown in the accompanying
drawings shall be interpreted as illustrative and not in a
limiting sense.
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