Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Background Prior Art
A safety hazard exists in certain forms of circuit breakers in that if the
breaker blade
contacts should fuse together, then the tripping mechanism on overload will
still respond,
typically driving the reset handle to a center position indicative of
tripping, while the breaker
still remains in a circuit-completing condition.
Systems are known, such as disclosed in U.S. Patent No. 4,794,356, which
provide
in the form of a modular accessory a position-indicating switch coupled
directly to the
movement of an electrical circuit breaker contactor and which provide sensing
conditions
indicative of the contacting condition of the breaker, thus providing means
for warning the
user that the breaker has not, in fact, been effectively tripped in the event
that the blades
have become welded shut. In this system such a switch is coupled to be
actuated directly by
movement of the contactor element itself.
Additionally, in many cases it is desirable to provide a remote-tripping
feature for a
breaker whereby a remote operator can operate the breaker to a tripped
condition. Such
mechanisms are also known, being frequently provided in modular form, and
normally utilize
a member which operates on the latching mechanism which holds the breaker in
the reset
condition. A unit which can be optionally affixed to a circuit breaker to
achieve both
functions, and requiring only a single coupling element, thereby reducing
system complexity,
would be a useful feature that has not, to the applicant's knowledge, been
thus far produced.
Summary of the Invention
According to one aspect of the invention, there is provided a surface-
mountable
accessory module for a circuit breaker having a breaker housing with a breaker
assembly
disposed therein for alternately making and breaking contact with a stationary
contact via a
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movable contactor, releasable latch means for automatically operating said
breaker assembly
to a circuit-breaking position, position-indicating means carried with said
contactor for
indicating the position of said contactor and including means responsive to a
force applied
to said position-indicating means for operating said breaker assembly to said
circuit-breaking
position, said breaker housing having an aperture for providing external
access to said
position-indicating means, said module comprising: a module housing; mounting
means
adapted for mounting said module housing to said breaker housing, said module
housing
being provided with a module housing aperture disposed to confront said
breaker housing
aperture when said module housing is mounted on said breaker housing; switch
means
disposed within said module housing and operable between first and second
switching
conditions for indicating circuit-making and circuit-breaking contactor
positions respectively;
coupling means for coupling said switch means to said position-indicating
means when said
module housing is mounted on said breaker housing to operate said switch means
to said first
switching condition when said contactor is in said circuit-making position and
to said second
switching condition when said contactor is in said circuit-breaking position,
said coupling
means including at least one coupling member disposed to pass through said
module housing
aperture; solenoid means disposed within said module housing for urging said
coupling
member to operate said breaker assembly to said circuit-breaking position when
said module
is mounted on said breaker; and connector means for making electrical
connection to said
solenoid means and said switch means.
According to another aspect of the invention, there is provided a circuit
breaker and
accessory comprising: a circuit breaker housing; a circuit breaker assembly
disposed within
said housing for alternately making and breaking contact with a stationary
contact via a
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movable contactor, said assembly including releasable latch means for
automatically operating
said breaker assembly to a circuit-breaking position, position-indicating
means carried with
said contactor for indicating the position of said contactor and including
means responsive
to a force applied to said position-indicating means for operating said
breaker assembly to
said circuit-breaking position, said breaker housing having an aperture for
providing external
access to said position-indicating means; a module housing mounted to said
breaker housing,
said module housing having a module housing aperture disposed to confront said
breaker
housing aperture; switch means disposed within said module housing and
operable between
first and second switching conditions for indicating circuit-making and
circuit-breaking
contactor positions respectively; coupling means for coupling said switch
means to said
position-indicating means when said module housing is mounted on said breaker
housing to
operate said switch means to said first switching condition when said
contactor is in said
circuit-making position and to said second switching condition when said
contactor is in said
circuit-breaking position, said coupling means including at least one coupling
member
disposed to pass through said module housing aperture; solenoid means disposed
within said
module housing for urging said coupling member to operate said breaker
assembly to said
circuit-breaking position; and connector means for making electrical
connection to said
solenoid means and said switch means.
According to another aspect of the invention, there is provided an electrical
circuit
breaker comprising: a breaker housing; a breaker assembly within said housing
for alternately
making and breaking contact with a stationary contact via a movable contactor,
said assembly
including releasable latch means for automatically operating said breaker
assembly to a
circuit-breaking position, position-indicating means carried with said
contactor for indicating
the position of said contactor and including means responsive to a force
applied to said
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position-indicating means for operating said breaker assembly to said circuit-
breaking
position, said breaker housing having an aperture for providing external
access to said
position-indicating means.
In a specific embodiment of the invention, a breaker housing can be modified
to
provide an access passage exposing a portion of the breaker blade mechanism to
external
access, and a bolt-on accessory module contains in the preferred form a rotor
coupled to a
movable coupling member configured to extend through the breaker passage to
engage a
portion of the blade mechanism. A member carried with the blade mechanism, and
preferable mounted on a trip arm carried with the blade, extends towards the
passage to
engage with the coupling member. A sensing switch within the accessory module
is engaged
by a caroming surface on the rotor so that the rotor will be moved
responsively to tripping
and resetting of the breaker blade to indicate the true contacting state of
the breaker. By
engaging the breaker blade via the trip lever of the breaker, rotation of the
rotor when the
- . . . . .. .__ . _
WO 92/0648t PCT/US9Qla5b66
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breaker. .Accordingly, a solenoid is also
provided in the module configured to
engagingly rotate the rotor in the tripping
direction. There is thus provided by means of
a single coupling element not only a sensing
of the true state of the breaker, but also
means for remotely tripping it.
Other features and advantages of the
invention will be apparent from the following
specification taken in conjunction with the
following drawings.
Brief Description of Drawings
Fig. 1 is a view of a circuit breaker
according to the invention;
Fig. 2 is a view of a unitary breaker
assemb~.y according to the invention in a con-
tacting position;
Fig. 3 is a view of the unitary breaker
assembly of Fig. 2, shown in a non-contacting
position;
Fig. 4 is a view of a cam as viewed
from behind the unitary breaker assembly of
Figs. 2 and 3;
Fig. 5 is an exploded perspective of
the circuit breaker of Fig. It
FIG. 6 is an exploded view showing an
add°on modular device assembly, a coupling
member, and a modified breaker of the present
invention;
FIG. 7 is a partially cutaway plan
view of the modular assembly shown in FIG. 6
emplaced on the breaker of FIGS. 1-6;
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FIGS. 8-11 are various views of a rotor used in the modular assembly and shown
in
FIG. 7;
FIG. 12 is a plan view of the coupling member shown in FIG. 6;
FIG. 13 is a side elevation view of a coupling member shown in FIG. 12; and
FIG. 14 is a view similar to FIGS. 2 and 3, showing the breaker assembly 40 in
the
tripped condition with the contacts welded together.
Detailed Description
While this invention is susceptible of embodiments in many different forms,
there is
shown in the drawings and will herein be described in detail, a preferred
embodiment of the
invention with an understanding that the present disclosure is to be
considered as an
exemplification of the principles of the invention and is not intended to
limit the broad aspects
of the invention to the embodiment illustrated.
A circuit breaker 10 is illustrated in Fig. 1.
An additional description of general aspects of a circuit breaker can be found
in the
following patents:
A. Westermeyer, U.S. Patent No. 4,617,540, entitled "Automatic Switch, Rail-
Mounted" ,
WO 92/06484 Pcr~us9oeosf~66
_6_
B. Westermeyer, U.S. Patent
No. 4,614,928, entitled "Automatic Switch with
an Arc Blast Field",
C. Westermeyer, U.S. Patent
NO .4,609,895, entitled 'Automatic Switch With
Integral Contact Indicator", and
D. Westermeyer, U.S. Patent
No. 4,608,546, entitled 'Aut:omatic Switch with
Impact-Armature Tripping Device".
The circuit breaker 10 has a housing 11
and includes a line terminal 12 for coupling
to a source of electricity (not shown) and a
load terminal 14 for coupling to a load,(not
shown). A current path is established between
the line terminal 12 and the load tenninal 14
which includes as elements a line conductor
16, a bimetal support 18, a bimetal thermal
element 20, a braided pigtail 22, and a blade
24 including a moveable contact 26.
Continuing from the moveable contact
26, the current path includes a stationary
contact 28, a coil 31, a load conductor 34,
and ultimately 'the load terminal 14.
The blade 24 is illustrated in Fig. 1
in a closed position, wherein the moveable
contact 26 contacts the stationary contact 28.
As discussed below with respect to Fig. 3, the
blade 24 is pivotable t0 an open position,
wherein the moveable contact 26 is spaced from
the stationary contact 28, preventing current
to flow between the moveable contact 26 and
the stationary contact 28. The stationary
contact 28 comprises a copper layer 28a
laminated to a steel layer 28b with a silver/-
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graphite composition contact 28c welded to the copper layer 28a.
The blade 24 is an element of a unitary breaker assemble generally designated
40
which controls the position of the blade 24 relative to the stationary contact
28.
The circuit breaker 10 also includes a line-side arc arresting plate 29a, a
load-side arc
arresting plate 29b and a stack of deionization plates, or arc stack, 30 which
cooperate to
break an arc formed when the circuit breaker 10 opens under load. The specific
operation
of the line- and load-side arc arresting plates 29a, b, respectively, in
conjunction with the arc
stack 30 is disclosed in greater detail in the above referenced patents.
The unitary breaker assembly 40 is illustrated in Fig. 2 with the blade 24 in
the closed
position in contact with the stationary contact 28.
The unitary breaker assembly 40 includes a first frame plate 42 which forms a
first
frame surface 42s. The first frame plate 42 includes first, second and third
upright members
43, 44, 45, respectively. A pivot pin 48 extends upwardly through a hold in
the first frame
plate 42. A trip lever 50 is mounted on the pivot pin 48 through a trip lever
opening: The
trip lever 50 includes a solenoid actuator surface 52 and a bimetal actuator
surface 54. The
blade 24 includes an elongated slot 24a for receiving the pivot pin 48. The
blade 24 further
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;~~'~:3~~5
to which a first end of a toggle spring 58 is
attached.
A latch spring 60 is disposed on the
pivot pin 48 between the trip lever 50 and the
blade 24. The latch spring 60 includes a
first end 62 which engages the first upright
member 43 and a second end 63 which engages
the solenoid actuator surface 52 of the trip
lever'S0. The latch spring 60 provides a
counter clockwise bias on the trip lever 50.
A cam 64 has an operating handle 65 and
further includes a recessed portion 66 in
which a cam spring 68 is placed, as discussed
in greater detail below with reference to
Fig. 4. A first cam spring end 69a extends
out of the recessed portion 66 and engages the
third upright member 45. A second cam spring
- end 69b is retained in the recessed portion
66. The cam spring 68 maintains a clockwise
bias of the cam 64 as viewed in Fig. 2.
A Link 70 connects the cam 64 to a pawl
72. The pawl 72 is pivotally connected to a
flag end 74 of the blade 24 by a shoulder
rivet 76.
The trip lever 50 further includes an ,
engaging surface 78 which engages the pawl 72.
When in the closed position, as illus-
trated in Fig. 2, the moveable contact 26 is
in a contacting relationship with the station-
cry contact 28. The shoulder rivet 76
operates as a fulcrum on the blade 24, causing '
the toggle spring 58 to securely maintain the
moveable contact 26 in contact with the
stationary contact 28.
WO 92/06484 FCI~/US90/05666
2~~~~~5
Referring again to Fig. 1, the blade 24
can be moved to the open position by operation
of either the bimetal thermal element 20 or by
a spring loaded rod 80 disposed within the
coil 31.
As current passes between the line
terminal 12 and the load terminal 14, it
passes through the bimetal thermal element 20.
As is'well known in the art, the current
.
causes the bimetal thermal element 20 to heat,
and the heat causes the bimetal thermal
element 20 to deflect downwardly in the
direction of arrow 82. The extent of the
deflection depends on the magnitude of the
heating of the bimetal thermal element 20, and
hence depending upon the magnitude and length
of time of the current passing between the
line terminal 12 the load terminal 14.
When the bimetal thermal element 20
deflects sufficiently, a calibration screw 84 .
engages the bimetal actuator surface 54 of the
trip lever 50, causing the trip lever 50 to
rotate clockwise about the pivot pin 48 and
against the bias of the latch spring 60, trip-
ping the circuit breaker 10, as discussed in
greater detail below.
The circuit breaker 10 can also be
tripped by the coil 31. A ferromagnetic
impeller 77 is slidably movable along the
interior axis of the coil 31, and is held in
the extended position shown in Figure d by a
biasing spring 86 urging the impeller against
a stop 79. An insulating actuating rod 80 is
similarly axially movable along the central
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_lo- aaC~~~3~~5
core of the coil 31 and extends out of the
opposite end thereof. The lengths of the rod
80 and the impeller 77 are chosen so that with
the impeller drawn up into the solenoid .
passage the rod 80 will be forced upward into
engagement with a solenoid actuator surface 52
affixed to the trip lever 50. Thus, current
passing between the line terminal 12 and the
load terminal 14 passes through the coil 31
establishing an electromagnetic field
affecting the impeller 77. When the
electromagnetic force acting an the impeller
?7 exceeds the biasing force of the solenoid
spring 86, the impeller moves upwardly to
force against the interior end of the rod 80,
forcing it to engage the solenoid actuator
surface 52, causing the trip lever 50 to
rotate clockwise, tripping the circuit breaker
10, as discussed below.
Referring again to Fig. 2, when either
the bimetal thermal element 20 or the rod 80
cause the trip lever 50 to rotate clockwise,
the engaging surface 78 of the trip lever 50 '
moves away from engagement with the pawl 72.
When the engaging surface 78 moves away from
engagement with the pawl 72, biasing from the
handle spring 68 causes the cam 64 to rotate
clockwise. As the cam 64 rotates clockwise,
the cam 64 pulls downwardly upon the link 70,
causing the pawl 72 to rotate counter clock-
wise about the shoulder rivet 76.
As illustrated in Fig. 3, when the pawl
72 is released from engagement with the
engaging surface 78, the blade 24 moves
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downwardly at its left side, causing the pivot
pin 48 to engage the upper surface of the
elongated hole 24, which operates.as a
floating point. The pivot pin 48 then
operates as a fulcrum about which the blade
24
rotates, causing the toggle spring 58 to move
.
the moveable contact 26 away from the sta-
tionary contact 28, thus opening the circuit.
In the event that the operating handle
65 is locked in the upward or on, position,
and either bimetal thermal element 20 or the
rod 80 causes the trip lever 50 to rotate
' clockwise, the link 70, which is under
compression between the cam 64 and the pawl
72, causes the pawl 72 to rotate clockwise
about the shoulder rivet 76, again releasing
the engaging surface 78 from engagement with
the pawl 72. When the engaging surface 78 no
longer engages the pawl 72, the blade 24
lowers, again causing the pivot pin 48 to
operate as a fulcrum about which the blade 24
rotates, permitting the toggle spring 58 to
again move the moveable contact 26 away from
the stationary contact 28.
The cam 64 is shown from its reverse
side in Fig. 4 to better illustrate the
recessed portion 66 and the cam spring 68:
The handle spring 68 is centered on a
cam axis 88. The second cam spring end 69b is
held against a wall 66a of the recessed
portion 66. The first cam spring end 69a is
held against the third upright member 45 under
tension. The tension in the cam spring 68
WO 92/0644 PCT/US9U/05666
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biases the cam 64 and the operating handle 65
in the downward position.
The circuit breaker l0 is illustrated
- ~m an exploded perspective view in Fig. 5.
~ The first, second and third upright members
43, 44, 45.of the first frame plate 42
terminate with connecting tabs 43a, 44a, 45a,
respectively. A second frame plate 89 forms a
second frame surface 89s which includes
l0 corresponding tab receiving openings 43b,
44b,45b. The tab receiving openings 43b, 44b,
45b, receive and provide an interference fit
with the connecting tabs 43a, 44a, 45a ~o
secure the first frame plate 42 to the second
frame plate 89. The first frame plate 42
cooperates with the second frame plate to form
an assembly frame. In the preferred embodi-
ment the first and second frame plates 42, 89,
respectively, are separate pieces; however it
is to be understood that the assembly frame
could be formed from of a single piece folded
over to form the opposing frame surfaces
without departing from the spirit and scope of
the present invention. With the first frame
plate 42 secured to the second frame plate 89,
all elements of the unitary breaker assembly
40 are secured together.
As illustrated in Fig. 5, operating
elements of the circuit breaker l0 can simply
be dropped into the circuit breaker housing,
and require no special attachment thereto.
The housing 11 has a base 11a and a
cover 11b. The base.lla defines an x-y plane
and includes internal walls directed perpen-
WO 92/Ofr4~4 PCT/US90l056G6
rC~~i~~~'~J
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dicular to the base lla along a z-axis. The
internal walls define generally an arc stack
section 90, a unitary breaker assembly section
92 and coil section 94.
End portions 18a and b of the himetal
support 18 are slid into and retained within
respective bimetal support slots 96a, b. The
line-side arc arresting plate 29a is slid into
and retained within an arc runner slot 98.
.
The unitary breaker assembly 40 is then simply
placed in the unitary breaker assembly section
92, and requires no attachments to the housing
11. The load conductor 34 is slid into~and
retained in a load conductor slot 99.
The blade 24 is a tapered plate on
edge, operating structurally as a beam so as
to pre~rent flexing. If additional current
carrying capacity is required, the width of
the blade 24 is simply increased.
It will be recalled that clockwise
rotation of the trip lever 50 by the bimetal
element 20 trips the breaker, causing the
breaker assembly 40 to be tripped from the
closed position shown in FIG. 2 to the open
position shown in FIG. 3: A tripping pin 100
is affixed to the trip lever 50 to extend
perpendicularly outwardly therefrom, through
an arcuate cut--out 111 in the blade 24. Upon
tripping, the pin 100 will follow the arcuate
path 103 shown in dotted outline in FIG. 2.
From the previous discussion, it is equally
clear that if the tripping pin 100 is urged
downward as shown in FIGS. 1, 2 and 4, that
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14- ~v'~~~~.~~
tripping of the breaker assembly 40 will also
occur.by rotating the trip lever 50.
It will be further noted that in all
cases, the pin 100 is effectively carried
along with the blade 24 so that the position
of the pin 100 thus indicates whether the
breaker is in a closed or open condition., It
will be noted in FIGS. 2 and 3 that the pin
100 iw both situations is located slightly
. below the edge of the cut-out portion 111 of
the blade 24. Considering the breaker in the
reset position shown in FIG. 2, and with
further reference to FIG. 14, in the event
that the contacts 26, 28 have become welded
, together, then immediately upon a slight
clockwise rotation of the trip lever 50, pawl
72 disengages from the engaging surface 78 of
the blade 24: however, clockwise rotation of
the blade 24 is prevented by the
aforementioned welding of the contacts 26, 28.
Only a minimal clockwise motion of the blade
24 occurs until arrested by engagement with
pin 48. The lacking engagement between the
pawl 72 and the engaging surface 78 having
been released, the cam p4 immediately rotates
clockwise under the fore of the cam spring
68, unsuccessfully attempting to rotate the
blade 24 clockwise, anti finally adopting the
intermediate position shown in FIG. 14. The
trip lever 50 is urged counter-clockwise by
the force of its biasing spring 60; however,
the immediate engagement of the pin 100 with
the edge of the cut-out portion 111 prevents
such motion. There is thus negligible
W~ 92/0644 PCTf US90/05666
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movement of the pin 100 under such
circumstances.
Thus, a slight movement of the pin 100
will cause the engaging surface 78 to release
S from engagement with the pawl 72. In the
event that the contacts 26, 28 are not welded
shut, the subsequent position of the pin 100
will serve as a positive indication 'that the
breaker assembly 40 has in fact been operated
. to an open condition. Thus, pin 100 may be
used to trip the breaker, and may also serve
as a sensing element indicating the subsequent
status of the contacts. ,
Use is made of the foregoing to allow
the employment of an add-on accessory module
104 which can be provided with a position
sensor indicating the position of the pin 100
and which also includes an actuating mechanism
providing remote tripping of the breaker
assembly 40. To achieve this, the housing
cover plate lla (FIG. 5) is provided with an
arcuate cut-out 120 providing access to the
end of the pin 100 along its entire range of
positions.
Thus, referring also to FIG. 6, the
outer surface 112 of the housing cover plate
lla i~ provided with a recess 114 in the form
of a circular sector having the cut-out 110
generally close to one edge thereof,-and
having a post 116 outwardly extending from the
.
recess 114, the post being
surface of the
positioned to be generally co-axial with the
pivot pin 48 of the breaker assembly 40. A
coupling member 118 (see also FIGS. 12, 13j
is
WO 92/064..84 PCT/US90l05666
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tCm ~.., ~ .J..y '~ a~
similarly configured as a planar circular
sector and has a guide hole 120 at the radius
point configured to accept the post 116. A
pair of pin-engaging bosses, 122, 124 extend
outward from one face of the coupling member
118. The coupling member 118 is configured so
that when emplaced over the post 116, the
bosses 122, 124 axe disposed, on,either side of
. the pin 100 as indicated by dotted outline in
FIG. 13. Thus rotation of the coupling member
118 will trip the circuit breaker assembly 40,
and the movement of the pin 100 thereafter
will further rotate the coupling member ,118.
The accessory module 104 includes a
housing 126 having a face 129 configured for
flush engagement with the outer face 112 of
the breaker housing 21. An arcuate cutout 128
similar to cutout 110 of the housing cover
plate lla as provided giving access to the
interior of the housing 126, a similar post
130 and recess 132 being provided. The
coupling member 118 is provided on the face
opposite the bosses 122, 124 with a similar
pair of bosses 134, 136. With the auxiliary
device housing 226 in place over the coupling
me~aber 118 and affixed to the housing 11,
bosses 134, 136 are then similarly coupled to
move, or be moved by, the pin 100. The
coupling member bos$es 134, 136 are configured
to extend into the housing 126, and to engage
with a pair of boss-accepting passages 138,
140 (see also FIGS. 8-I1) in a rotor 142
mounted within the housing 126.
WO 92/06484 PGT/U590/05666
17 ;G'~~~~~J
The breaker housing portions 11, lla
are preferably held together by hollow rivets
172, 174, 176 (FIGS. 6, 7). The auxiliary
device assembly housing 106 and rear wall 146
are similarly assembled by means of hollow
rivets 180, 190 positioned :~o that through
bolts may be passed between both the auxiliary
device housing 104 and the.breaker l0 to
assemble the units together. In the
.
alternative, self-tapping screws may be
employed, or the units may be hot-staked
together.
Referring next also to FIG. 7, the
rotor 142 is rotatably secured about (See
FIGS. 8-11) its central passage 143 by an
interior mounting post 144 extending outward
from the interior of the housing 126 and
secured in place by confrontation of the rear
housing wall 146. Disposed in the housing 126
are a solenoid coil 148 coupled to a plunger
150 to rotate the rotor 142, and thus trip the
breaker, and a micro-switch 152 disposed to
sense the position of the rotor 142. The
plunger 150 has at the outer end thereof a
generally radially extending shoulder flange
154. The plunger 150 extends through a
plunger passage 157 in the rotor 142, and the
shoulder flange 154 generally confronts a
flange-engaging face 156 on the rotor 142.
. The plunger 150 is freely movable and without
spring bias, as a result of which the rotor
142 is freely movable, as for example by
movement of the pin 100 when the breaker is
reset or tripped by overcurrent, and.the rotor
CA 02069505 1999-O1-26 '
-18-
142 imparts no motion to the plunger 150 upon tripping. Retraction of the
plunger 150,
however, will trip the breaker by moving pin 100.
The micro-switch 152 is positioned so that its actuating member 166 will be
engaged
by a caroming surface 162 on the rotor 142 when the rotor 142 is carried to
its extreme
clockwise position attendant to normal tripping of the breaker, either by
thermal means, or
by means of actuation of the solenoid 148. The micro-switch sensing is relayed
by micro-
switch leads 164-166 to a connector block 168. Similarly, the solenoid coil
148 is connected
by leads 169, 171 to the connector block 168. Remote sensing of the state of
the breaker
may thus be obtained via the connector 168, and remote tripping of the breaker
may be
carried out by applying an appropriate control signal to the connector 168.
Alternatively, the micro-switch 152 may be connected in series with the
solenoid coil
148 to be operated to the open position upon terminal rotation of the rotor
142 upon solenoid-
induced tripping of the breaker assembly 40. The solenoid coil is thus self de-
energizing
when so employed, and is therefore not subject to burnout by over-excitation.
A very small
solenoid coil 148 may thus be used. Such a feature may also be achieved by
providing a
second micro-switch affixed to the opposite side of the breaker housing 11 and
similarly
~mmlarl tn tho ,".,
WO 92106484 PCTlUS90/OS666
-19-
r~~~~~'~ '~J
100. In such an arrangement, one achieves not
only solenoid de-energization but also a blade
position indication. It is equally evident
that the micro-switch 152 could be configured
as a double-pole single-throw unit
incorporating such a feature4
It will be understood that the
invention may be embodied in other specific
forms'without departing from the spirit or
, central characteristics thereof. The present
examples and embodiments, therefore; are to be
considered in all respects as illustrative and
not restrictive, and the invention is nod to
be limited to the details given herein,
