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Патент USA US2399406

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îApril '30, 1946.
l
J, TQTH
ELECTRICAL APPARATUS
Filed July 28, 1943
2,399,406
2,399,406
Patented Àpr. 30,- 1946
UNITED “_ s'rA'rEs
PATENT oFncE
2,399,403'
.
ELECTRICAL APPARATUS
.Julius Toth, East McKeespol-t, Pa., assigner te
Westinghouse vElectric Corporation. East Pitts
burgh, Pa., acorporatlon el Pennsylvania
Appunti» .my es, 194s, sum No. 496,411
s emma (c1. soo-'1in
This invention relates to electrical apparatus
in general, and especially to electric circuit inter
rupting apparatus for the protection of electric
apparatus adapted to be plugged into an electric
circuit. This invention contemplates, in its spe
ciñc aspect, the incorporation of automatic elec
tric circuit interrupting apparatus in electric
plugs.
it has been proposed heretofore that electric
attachment plugs be provided with some protec
tive means such as a fuse element, or even a sim
ple thermal strip element for automatically inter
exterior of the plus without disturbing the plug.
Another object of this invention is to provide
aplug of the type described having automatic cir
cuit interrupting means incorporated therein,
with resetting means accessible at the exterior of
the' plug, which resetting means. is trip-free of
the interrupier contacts.
a still further object of this invention is to
provide a novel plug structure or the type de
scribed having a snap-acting bimetal element in
corporated therein, with novel means for adiust~
ing the automatic operation of said element.
These and other objects of this invention will
rupting the circuit on overloads. The reason why
become more apparent after consideration of the
such a protective means is desirable for electric
plugs, is that the cords attached to electric ap 15 following detailed description or preferred em-v
bodiments thereof, when taken in connection with
paratus, such as household appliances, are gen
the attached drawing in which:
erally of smaller size than the permanent wiring
Figure 1 is a longitudinal section of an electric
into which they are plugged, so that the protective
plug constructed in accordance> with this inven
devices usually designed to protect such perma
”
`
nent wiring, may not be adequate inl all cases to 20 tion:
Fig. 2 is a longitudinal section of the plug
protect the. apparatus plugged in and its attached
shown in Fig. 1 taken substantially at right angles
cord. Moreover, while the apparatus itself may
to the section oi! Fig. l;
be adequately protected by built-in protective
Fig. 3 is _a longitudinal section of the plug
means, this still provides no protection for their
25A shown in Figs. 1 and 2 looking at the opposite side
extension cords.
Y
of the structure within the plug from that shown
Attachment plugs having fuse elements ltherein
in FIZ. 1;
,
are objectionable because of the time and expense
Pig. 4 is a longitudinal section of an electric
involved in the renewal of fuse elements, and
plug illustrating a modiiled form of the invention:
while plugs having simple bimetal strips therein
do not. require renewal on each operation, these 30 Fig. 5 is a longitudinal section of the plug
shown in Fig. 4 taken at right angles to Fig. 4;
are essentially slow-make and slow-breakdevices
Fig. 6 is a transverse section of the plug shown
and consequently are limited in interrupting
ability, and are subject to relatively rapid deteri
oration of the contacts due to excessive arcing.
AttemptsA have also been made in the past to
provide in attachment plugs circuit interrupting
means having relativelyv complex snap-acting
mechanisms for actuating the contacts of the in
terrupte'r, but because oi space limitations, such
devices have not been practical.
‘in Pigs. 4 and 5 taken substantially on the line
VI--VI of Fig. 5; and
Fig. "I vis a longitudinal section like Fig. ‘5, but
illustrating certain of the parts in a diiierent
The invention is illustrated on the drawing as
being embodied in an electric connection plug
40 .adapted to be plugged into the conventional wir
ing outlet. The plug illustrated comprises a gen
Accordingly, it is one object of this invention
erally tubular plug body 2, having a closure disk
I for closing one end of the plug body. The plug
body and closure disk l may be of any desired in
sulating material, preferably a molded insulating
terialiy increasing the plug dimensions.
'
material. Closure disk 4 is provided with spaced
Another object of this invention is to utilize a
openings for receiving contact prongs 8 and 8,
snap-acting bimetal element in an electric at
respectively, with at least the contact prong 6 be
tachment plug in a novel manner, to provide
ing »secured against movement relative to the
automatic protection for the cord and apparatus
closure disk, for example as by a locking pin l0
attached to the plug.
which may be driven into the disk and _into an
Another object of this invention is to provide
aperture provided in the contact prong. Closure
a novel plug structure of the type described hav- ‘
disk 4I may be removably secured in place at the
ing novel snap-acting automatic circuit interrupt-l
ing means therein which is resettable from the 55 open end of the plug body, as viewed in the draw
to incorporate relatively simple yet etlicient cir
cuit interrupting means having snap-acting con
tacts in an electric attachment plug, without ma
I
2,399,406
2
ing, by any desired releasable securing means,
by one or more screws I2.
a predetermined magnitude, bimetal element 2B
being in series in the circuit, will be eventually
When closure disk 4 :is assembled in position in
the upper end oi’ the plug body 2, contact prongs
heated an amount suiilcient to cause reversal’ oi'
E and 8 have their inner ends positioned within
the plug body, and a supporting bloc-lr I6 is se
quent movement of contact 4I carried by the bi
metal element out of engagement with stationary
cured in. position within the plug body between
the inner ends of the Contact prongs. Supporting
contact 42. lBimetal element 2o has two static
positions, one being the position shown in
2
bloeit it may also be of any desired insulating
material, such for example as fiber or a molded
wherein contacts «l2 and M are in, engagement,
and the other being a position wherein co> ct
M is disengaged from contact «it and who
f
such for example
insulating material. Supporting block it may be
secured
Contact in
prongs
position
ii and
between
E, bythe inner
desired.
endsmeans,
oi?
such for example as screws i o used to secure con
tact prong to the supporting block, and a screw
it used to secure contact prong b to the support
ing bloeit. in order to prevent pivotal movement
of the contact prongì i5 relative to the supporting
bloeit. about screw i il, the inner end oi” this contact
prong
a cavi is
„ turned.
provided
inwardly
in the supporting
as at 2li to be
block.
seated
îi‘he
curvature of central leg 3D thereof, and consen
the curvature of central leg Bil is reversed.
. cause it is necessary to reverse the curvature oi'
central leg ¿lll or the bimetal element in order
to separate
rating'
movement
contacts
oi the
42 and
contacts
1li, the
willactual
taire p ce
at e, very rapid rate, because enerod will,
stored
movement
up in the bimetai
thereof element
until central
with subste
leg " tiaily
:is
c.
a
neutral point in reversing its curvature
therrz~
it will quickly snap to its reverse curvature
position in a toggle-like manner, to thereby sejcan
Contact prong d is provided at
inner end
with a laterally extending supporting portion Mi
rate the contacts with a snap action.
Zin order to reclose contacts ¿il? and
t.
automatic circuit interrupting ope
:i "y “`
binietal element such
that describ l above, l.
inner end of contact [email protected] il is provided
terminal screw 2i :tor directly securing e. con
ductor thereto.
on which. may be mounted one end ci a snap-uct»
ing bimetai element
as by screws
‘The bl»
metal element
is made to operate with a snap»
action, by
provision oi? a, pair oi.’ spaced slot'ter‘l
openings .tti
'i“ extending longitudinally of.’ the elewv
meut and. terminating siro *it oi.' the ends thereof.
These slotted openings divide the intermediate
portions ci’ the bimetal element into a central
leg 3u and. side legs
and the side legs have their
intermediate portions corrugated as at 3i, or
otherwise deformed to foreshorten these legs und
cause central leg iii
as clearly shown in
may be constructed
in the art, of a pair
to assume o, bowed position
Zelig. 2. Bimota! element 26
in any manner well known
ol? laminations 2l and 2S oi“
conducting materials having different coeflicients
aperture is provided ip. plug body l2 at a jooiut or»
j_oosite the contacts for receiving c, reciprocating
rod [email protected] having an enlarged head lili termed on be
inner
generally
end cup~shapecl
thereoipv and in
having
form,a ‘threaded
push button
on. the
outer end thereof for sliding in the couutersunir
portion iii through the aperture of the plug body.
li coil compression spring 52 is
between
push button lili and the plug body to ormally
bias the push' button to a raised positi .. ..-lative
‘to the plug body and to maintain head ou out of
engagement with bimetal element
will be readily apparent that when. biuietal
element 2li has been heated an amount sulilcicnt
to cause reversal oi' curvature of central iegr .it
thereof, to move contact M out ci engagement
of thermal expansion, with the laminations se
with fixed contact 42, that the contacts muy be
cured in intimate engagement by any desired
reengagecl merely by depressing push button fill
means, such for example us by welding 0r the like. 45 to engage the upper end oi the bimetai element
For this particular application, bimetal lamina
and move it towards Contact 42 so
to move the
tion
should be ci" a material. having a low co
upper end of blmctal element an amount sur"
efficient of thermal expansion compared withv the
ñcient to move the upper ends of side legs 3l
coefdcíent of thermal expansion or bimetal lami
overcenter with respect to central leg 3u and
nation 29, so that upon heating of the blmetal
cause it to reverse its curvature bacia to the Dosi~
element the curvature of central leg 30 will be
tion shown in Fig. 2 thereby causing a snap-act~
reversed from the position shown in Fig. 2.
ing closure of contacts ll2 and 44.
Ari angled conducting bar 36 is mounted ou the
In order to calibrate the bimetal element so as
opposite side of supporting block I4 from bímetal
to be automatically responsive to a certain value
element 26, with one leg thereof having its end 55 of current and separate contacts di'. and M to ln.
portion deflected as at 38 into a cavity formed in
terrupt the circuit, an adjusting screw 56 is
the supporting block, and may, ii’ desired, be
threaded into an opening provided in the plug
molded therein, when the block is formed vof a
body opposite substantially the mid portion of
molded insulating material. The other les of
central les 30 of the blmetal element, so that
conducting bar 36 extends above supporting block 60 the curvature of the central leg may be lessened
M and terminates in an enlarged contact head
by taking up screw 54, thereby prestressing the
42 adapted to cooperate with a. contact M secured
bimetal element, and lessening the force required
to the upper end of bimetal element 26.
to reverse the curvature of central leg 30. This,
of course, means that as adjusting screw 54 is
is provided with a terminal 22 directly mounted 65 taken up, less heating of the bimetal is necessary
thereon, the circuit between terminal 40 and con
'to effect reversal of the curvature on the central
’ It will be noted that while the contact prong 6
tact prong 8 extends from terminal 40 through
conductor bar 36, contact I2, contact 4I, andy
leg, and consequently the bimetal element will op»
crate tdinterrupt the circuit at progressively
lower currents. The head of the screw 5l is
through bimetal element 26 to contact prong 8.
Accordingly. contacts l2 and 44 and blmetal ele 70 sealed with wax 55 or the like to prevent tam
ment 26 are connected in series circuit relation
pering with calibration whenthe plug is in use.
between terminal l0 and contact prong 8.
The end of plug body 2 opposite closure disk 4
With the parts positioned as shown in Figs. 1
is provided with a. smaller ‘opening 56, for re
to 3 of the drawing, it will be apparent that upon
ceiving a conductor cord 58 having conductors 60
the passage through the circuit of currents above 76 and 82 therein for connection to terminals 22
'
9,399,406
.
-
3
and 4l, respectively. With the structure illus
trated in Figs. 1. 2 and 3, an extremely simple
device is provided within the small dimensional
amount sufficient to cause reversal of curvature
thereof and move the free end thereof,` for ex
ample from the position in Fig. 2 to that shown
limitations of an electrical connector plug. in-t
volving the use of -but a single moving part Ato
automatically interrupt the circuit in response to
the presence of overloads, with interruption and
in Fig. 5, it will not be immediately reset by push
button 50 if the push button is depressed right
away, because under these conditions, a greater
force is required to reverse the curvature of the
circuit closing occurring at a rapid rate or with a
bimetal .element,_ and consequently side legs 32
snap-acting opening of the circuit, to provide an
extremely efllcient protective means of small size.
Moreover, it will be noted that the entire struc
would have to be moved to the left a greater
~ ture is supported by closure disk 4 so that the
contact prongs 6 and I, bimetal element 2t, con
tacts 42 and 44, and terminals 22 and 40 are re
movable with the closure disk as a unit from plug
body 2.
The plug construction illustrated in Figs. 4 to 7
distance than they are capable of being moved
by the push button 50- in the embodiment of the
invention shown in Figs. 4 to 7, in order to effect `
reversal of curvature. It will be observed that
push button 50 in Fig. 'I is prevented from mov
ing any further to the left by engagement with
the bottom of countersunk portion 5i of the aper
_ture in the plug body, and »at this position the
- is like that shown in Figs. 1 to 3 in most respects,
push button cannot reverse the curvature o! the
and consequently, like reference characters will
central leg of» the bimetal element when it is
be used to designate like parts. This plug struc 20 heated enough to cause it to separate the con
ture differs from that previously described in that
tacts. In other words, if push button 50 is main
the conductor bar 84 mounted on the side of
tained depressed, bimetal element 26 will auto
supporting block I4 opposite bimetal element 26,
matically open the circuit, and after some cool
is provided at its upper end above the upper end
ing thereof will automatically reclose the circuit, ^
of the supporting block with a threaded opening 25 and this will continue as long as the button is
for receiving a threaded shank 6l on contact 42,
held depressed. Push button 50 therefore is in
and a lock nut 10 is provided for shank 88 to lock'
effect trip` free of the bimetal element, because
contact 42 in any position to which it is adjusted
the bimetal element is capable of opening the
relative to conductor bar 84. Another difference
circuit even when the push button is held in its
is that bimetal element 26 is adapted to be man 80 contact closing position.
'
ually reset by push button 50 having the head 48
Calibration of the bimetal element is obtained
thereof engageable with a bridge member 12 se
in this embodiment of the invention by adjusting
cured to side legs 32 of the bimetal element.
contact 42 toward and away from contact 44 car
Bridge member 12 is substantially channel shaped
ried on the bimetal element to exert more or
in form and has the leg portions thereof secured 35 less stress on the bimetal element at the closed
to the outside edges of side leg 32 of the bimetal
circuit position of the contacts. As previously
element in any desired manner, such for example
indicated, contact 42 lmay be locked in any ad
as by lugs 14 integral with the bimetal element.
justed position by tightening lock nut 10.
Operating bridge 12 for the bimetal element is
It will be apparent from the foregoing, that
secured to the side legs of the element substan
this invention provides different forms of pro
tially at their midpoint, and push button 50, in
tective means for incorporation in an electric
this embodiment of the invention, is located on
plug, which are capable of efficiently protecting
the .wall of the plug body at a point opposite
the electric cord and apparatus with which the
bridge 12.
.
A circuit interrupting operation of the device 45 plug is associated, without, however, substantially
increasing the dimensions of conventional types
shown in Figs. 4 to 7 takes place in substantially
_ the same manner as a circuit interrupting opera
of plugs. y Moreover, in both embodiments of the
invention disclosed, there is provided» means for
tion in the embodiment of the invention pre
adjusting the current at which interruption will
viously described, and accordingly, will not be
automatically occur, as well as means for man
repeated.` This embodiment of the invention
ually reclosing the circuit following an automatic
differs, however, in the operation of manually re
interruption. Moreover, in the embodiment of
closing the circuit breaker contacts in that when
the invention shown in Figs. 4 to 'I of the draw
the circuit has been opened and the parts as
ing, interruption will occur upon predetermined
sume the position shown in Fig. 5 of the drawing,
current. conditions even though the manual reset
it will be apparent that when push button 50 is 55 means is held in its circuit closing position.
depressed to engage operating bridge member 12,
Having described preferred embodiments of
that the side >legs 32 of the bimetal element will
the
invention as required by the patent statutes,
be moved to the left to bring the outer end (if
it should be understood that the invention is not
the bimetal element over-center with respect to
to be limited to the paricular embodiments dis~
middle leg 30 and cause the latter to reverse its`
closed herein, inasmuch as it will be obvious, par
curvature suddenly with a snap action, and close
contacts 42 and 44 very rapidly. In the event ' ticularly to persons skilled in the art, that many
changes and modifications may be made in these
that push button 50 is held in the depressed po
sition shown in Fig, 7, the bimetal element may t particular structures without departing from the
broad spirit and scope of this invention as de~
still operate to interrupt the circuit, because
fined in the appended claims.
middle leg 30 may still reverse its curvature, and
I claim as my invention:
cause a separation of the contacts, with the bi
l. In a plug, a hollow plug body of insulating
metal element pivoting substantially about the
material, spaced contact members at >one end of
center thereof rather than about the supported
end, as is the case when push button 50 is not 70 said body, a pair of conductors extending into
said body from substantially the opposite end
held depressed. This separation, as viewed in
lthereof for connection to said contact members,
Fig. 7, is not as great as the separation obtained
respectively, separable contacts in the connection
when the push button is »not held depressed, but
it will be sufilcient to interrupt the circuit in all f of at least one of said conductors and its corre
cases. When bimetal element 26 is heated an 75 spending contact member, a snap-acting‘bimetal
4
2,399,406
elemenfy in said body having a movable portion
for actuating said separable contacts, said mov
able portion of the bimetal element being mov
able between spaced static positions at which
said separable contacts are engaged and disen
gaged, respectively, said bimetal element being
bowed leg portion in a direction to cause engage
ment of said contacts when said bimetal element
has .cooled down, and means limiting resetting
heated in response to currents above a predeter
of said'bowed leg when said bimetal element is
said legs to cause reversal of curvature of said
movement of said reset means to an amount less
than that necessary to cause reversal of curvature
mined value in at least one of said conductors to
heated said predetermined amount. whereby said
actuate said movable portion from the static
bimetal element may automatically operate to
position where said contacts are closed to the 10 open said contacts even though said reset means
‘other of said static positions to separate said con
is held at its resetting position.
tacts with a snap action, said bimetal element
4. In apparatus of the type described, a bi
remaining at said other static position irrespec
metal element having spaced, generally longi
tudinally extending openings intermediate the
tive of the amount it cools down, manual reset
means movable through a side wall of said plug
body for actuating said bimetal element to move
said movable portion from said other static posi
tion to said one static position to close said con
tacts with a snap action, and said reset means
ends thereof forming side legs and a central leg
with said central leg having a greater eilective
length than said side legs to normally be longi
tudinally bowed in form, means rigidly support
ing one end of said element, a contact mounted
being trip-free of said bimetal element, whereby 20 on said supporting means, a cooperating contact
said element may separate said contacts even
mounted on the opposite end of said bimetal ele
though said reset means is held in its contact
ment, said opposite end oi said bimetal element
closing position.
being movable from one static position to another
2. In apparatus of the type described, a bi
metal element which is longitudinally slotted to
form legs at least one of which _is deformed to be
of a different length than another leg so that
'
the longer of said legs is longitudinally bowed in
form, means rigidly supporting one end of said
element, a contact mounted on said supporting 30
with a snap action upon reversal of curvature of
means, a cooperating contact mounted on the op
posite end of said bimetal element. said opposite
end of said bimetal element being movable from
said bowed leg to open and close said contacts
with a snap action, said bimetal element being
responsive to predetermined heating thereof to
reverse the curvature of said bowed leg in a di
rection to cause movement of said opposite end
of said element from the static position at which
said contacts are closed to the other static posi
tion at which said contacts are open and cause
snap-action separation of said contacts, said bi
one static position to another with a snap action
metal element remaining at said other static po
upon reversal of curvature of said bowed leg to 35 sition irrespective of the amount it cools down,
open and close said contacts with a snap action,
and manually operable reset means engageable
said bimetal element being responsive to prede
with said side legs to cause reversal of curvature
termined heating thereof to reverse the curvature
of said bowed leg portion in a direction to cause
of said bowed leg in a direction to cause move
engagement of said contacts.
ment of said opposite end of said element from 40
5. In apparatus of the type described, a bimetal
the static position at which said contacts are
closed to the other static position at which
element having spaced, generally longitudinally
extending openings intermediate the ends there
said contacts are open and cause snap-action
of forming side legs and a central leg with said
separation of said contacts, said bimetal element
central leg having a greater effective length than
remaining at said other static position irrespec 45 said side legs to normally be longitudinally bowed
tive of the amount it cools down, and manually
in form, means rigidly supporting one end of said
operable reset means engageable with the shorter
element, a contact mounted on said supporting
of said legs to cause reversal of curvature of said
means, a cooperating contact mounted on the op
bowed leg portion in a direction to cause en
50 posite end of said bimetal element, said opposite
gagement of said contacts.
end of said bimetal element being movable from
3. In apparatus of the type described, a bimetal
one static position to another with a snap action
element which is longitudinally slotted to form
legs at least one of which is deformed to be of
a different length than another leg so that the
upon reversal of curvature of said bowed leg to
open and close said contacts with a snap action,
said bimetal element being responsive to prede
longer of said legs is longitudinally bowed in 55 termined heating thereof to reverse the curvature
form, means rigidly supporting one end of said
of said bowed leg'in a direction to cause move
element, a contact mounted on said supporting
ment of said opposite end of said element from
means, a cooperating contact mounted on the
the static positionI at which said contacts are
opposite end of said bimetal element, said oppo
closed to the other static position at which said
60
site end of said bimetal element being movable
contacts are open and cause snap-action separa
from one static position to another with a snap
action upon reversal of curvature of said bowed
leg to open and close said contacts with a snap
tion of said contacts, said bimetal element re
maining at said other static position irrespective
of the amount it cools down, manually operable
action, said bimetal element being responsive to 65
reset means engageable with said side legs to
predetermined heating thereof to reverse the
causevreversal of curvature of said bowed leg por
curvature of said bowed leg in a direction to cause
tion in a direction to cause engagement oi said
movement of said opposite end of said element
contacts when said bimetal element has cooled
from the static position at which said contacts
down, and means limiting resetting movement of
-are closed to the other static position at which
said contacts are open and cause snap-action
separation of said contacts, said bimetal element
remaining at said other static position irrespec
tive of the amount it cools down, manually oper
able reset means engageable with the shorter of 'Il
said reset means to an amount less than that
necessary to_ cause reversal of curvature of said
bowed leg when said bimetal element is heated
said predetermined amount, whereby said bimetal
element may automatically operate to open said
asaasos
contacts even though said reset means is held at
a position to close said opening, an opening in ’
its resetting position.
said body for cord conductors spaced from said
first mentioned opening, spaced contact members
extending through said closure member, ter
minals for said contact members to which said
cord conductors may be secured, means serially
'
6. In a plug, a hollow plug body of insulating
material, spaced contact members at one end of
said body, a pair of conductors extending into
said body from substantially the opposite end
connected between at least one of said terminals
thereof for connection to said contact members,
and its corresponding contact member which is
respectively, separable contacts in the connection
responsive to currents above a predetermined
of at least one of said conductors and its corre
sponding contact member, a snap-acting bimetal
value in at least one of said contact members for
element in said body having a movable portion 10 interrupting the circuit, and said contact mem
bers, terminals and interrupting means being
i'or actuating lsaid separable contacts, said mov.
able portion oi' the bimetal element being mov~
supported from said closure member so as to be
able between spaced static positions at which
removable as a unit with said closure member
said separable contacts are engaged and disen
gaged, respectively, said bimetal element being
from said plug body.
i
8. In a plug,`a hollow plug body having an
opening, a closure member of insulating mate
heated in response to currents above a predeter
rial adapted to be removably secured to said body
mined value in at least one of said conductors to
in a position to close said opening, an opening
actuate said movable portion from the static
in said body for cord conductors spaced from said
position where said contacts are closed to the
other of said static positions to separate said con~ 20 first mentioned opening, spaced contact members
extending through said closure member and se
tacts with a snap action, said bimetal element
remaining at >said other static position irrespec
cured thereto. terminals for 4said contact mem
bers to which said cord conductors may be se'
tive of the amount it cools down. manual reset
means movable through a side wall of said plug
cured, means serially connected between at least
one of said terminals and its corresponding con
body for actuating said bimetal element to move
tact member which is responsive to currents
said movable portion from said other static posi
tion to said one static position to close said con
above a predetermined value in at least one of
said contact members for interrupting the cir
tacts with a snap action, and means accessible
from the exterior of said plug body for adjusting
cuit, and said terminals and interrupting means
being supportedlby said contact members so as
said bimetal element to vary the value of current
to which said element will respond.
to be removable as a unit with said closure mem
ber from said plug body.
7. In a plug, a hollow plug 'body having an
opening, a closure member of insulating material
JULI‘UB TOTH.
adapted to be removably secured to said body in
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