Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 48,020
TEST STRI)CTURE FOR GROUND ~AULT
CIRCUIT INTERRUPTERS
BACKGROUND OF THE INVE~TION
.
Field of the Invention:
This invention relates to a ground fault circuit
interrupter and, more particular-]y, to a simplified test
circuit con-Eiguration.
Description of the Prior Art:
.
Essentially the basic condition for which known
types of ground fault interrupters of the differential
- transformer type are intended to be effective is that in
~which there is a ground fault between the hot or line
`conductor and ground. A ground fault between the neu~tral
conductor of a multi-wire A.C. system on the load side of
the differential transformer and ground does not itself
present a safety hazard of the type for which protection is
required. However~ such a grounded neutral condition has
the effect of rendering the apparatus inoperable, particu-
larly in the absence of a load on the circuit.
In the past, most ground fault circuit breaker
manufacturers chose to connect their test circuit function
with small flexible leads, in which the connection to the
ungrounded load side of the ground fault circuit breaker
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<:Incl the i.nput line ne~lt:ral were connecte~ to two contact
tesl c:l.ips. D:isa(lvant:ages of that type o~ connection
involved numerous welds or soklered joints from the under-
ground loac] circuit term-inal to the res.Llient contact
melnber as we:L1 as probl.ems of circuit concl~lctor insulation.
Ground fault ci.rcuit interruplers of the type involved are
disclosed ill IJ.S. Pat.ent Nos. 3,7~5,414; 3,930,189;
3,959,693; 3,999,103; 4,015,169; and 4,081,852.
SUMM~R~' OF THE INVENTION
0 lt has been found in accordance with this inven-
tion that some disaclvantages of ground fault circuit
breakers of prior construction may be overcome by providing
a ground fault circuit interrupter for use in a load center
and comprising a circuit breaker, a ground fault detector,
and an i.nsulation housing therefor; the circuit breaker
comprising a pair of cooperable contacts operahle between
open and closed positions, an operating mechanism for
operating the contacts and comprising a latched pivotally
supported trip member, trip mèans for latching the~ trip
2u member, a load terminal structure, a line terminal struc-
ture, a line conductor of an AC electrical distribution
system connec~.ing the trip means to the load terminal
structure; the ground fault detector comprising a current
monitoring core, a plurality of primary windings on the
core, each being one of the line and a neutral conductor of
the AC electrical distribution system, a secondary winding
sensing current imbalance between currents in the primary
windings, means responsive to a predetermined sensing
signal OIl said sensing winding to open said line conductors;
test means to test the ability of the apparatus to trip
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3 ~,020
u~on occurrence of either line to ground :Eault conclitions
or neutral to ground ~ault conditions, said test means
comprising a circùi~ branch connecled from a first point on
a line conductor on the load side of said di~fe~ential
current transfor~er an(l a seconcl point electricall,y proxi-
mate to the neutral conductor on the supply side of said
differential current transformer, said circuit branch
including a normally open test switch that is closable to
cause unbalanced currents in said primary windings, said
0 circuit branch connected from said first point on a line
conductor comprising a wire-like conductor extending from
said first point to said test switch, said insulating
housing having groove means in which the wire-like conduc-
tor is secured by a pressure fit, the wi.re-like conductor
being in a pressure-fit connection with a load circuit
terminal, and said wire-like conductor having a portion in
line with the path of movement of the test switch.
. The advantage of the ground fault circuit inter-
.
rupter of` this invention is that it eliminates welded or
2u soldered joints from ungrounded load circuit terminals to
resilient contact members, reduces the chance of failure
due to mass incompatibility in which small gauge wire used
for flexibility is connected to conductor gauge wire of a
larger size, and enables the use of pressure-fit connec-
tions for retaining a conductor in place'as well as provid-
ing good electrical contact with associated electrical
conductors.
BRIEF DESCRIPTION OF THF DRAWINGS
Figure 1 is a perspective view of the ground
fault circuit breaker structure of this invention;
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Eig. 2 is a vertical sectional view taken on the
line Il-II of Fig. 1 and showing the circuit breaker side
of the inventio~ and in the closecl position;
Fig. 3 is a view similar to Fig. 2 with the
breaker shown in the tripped position;
Fig. 4 is a vertical sectiorlal view taken on the
line IV-IV of Fig. 1 showing the ground fault detector side
of the invention;
Fig. 5 is a sectional view taken along the line
O V-V of Fig. 4;
Fig. S is a sectional view taken on the line
- VI-VI of Fig. 4;
Fig. 7 is a diagram showing th~e electrical cir-
~` cuit of the invention; and
; Fig. 8 is an isometric view of the conductor
' mounted within the housing.
- DESCRIPTION OF THE PREFERRED EMBODIMENT
; ~ In Fig. 1 a ground fault circuit breaker struc-
ture~is generally indicated a~ 3 and it comprises a housing
~2~ 5 which is composed of electrically insulating material
such as a thermosetting resin. The housing 5 includes a
- pair of tray portions 7 and 9 and a side cover 11, which- are secured-in place by suitable means such as rivets 12 in
; a conventional manner. The tray portion 7 (Fig. 5) com-
~prises a back wall 8 and the tray portion 9 comprises a
back wall 13 that serves as a partition wall which extends
~- ~ between compartments 15 and 17 formed between the back
.
walls 8 and 13 and the side cover 11.
In Figs. 2 and 4 a circuit breaker mechanism is
disposed within the compartment 15 (Fig. 2) and a ground
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fault circuit interrupter is disposed within the compar-t-
ment 17 (Fig. 4). The circuit breaker s~ructure is of the
type disclosed in Pa-tent No. 3,566,318, to which reference
is made for a complete description of the structure an~
operation. Briefly, the circuit breaker mechanism COM-
prises a stationary contact ~1, a movable contact 23s a
supporting metal frame ~5, an operating mechanism 27, and a
trip device 29. The stationary contact 21 is welded, or
otherwise secured to a line terminal 31.
10The stationary contact 21 (Figs. 2 and 3) cooper-
ates with the movable contact 23 that is welded or other-
wise secured to a small flange portion 33 of a flat metal-
lic generally C-shaped contact arm 41. M~ans for operating
the contact arm 41 to the open and closed positions com-
prises an operating member indicated generally at 43 having
a V-shaped opening 45 therein, which opening receives a
projection 47 of the stationary metallic frame 25.. The
operating member 43 is biased outwardly or upwardly (~igs.
- 2 and 3) to a position wherein the lower edges of the
projection 47 pivotally engage the lower side walls of the
V-shaped opening 45. The contact arm 41 is bent over at
its upper end at 48, and a slot is provided in the part 48.
Depressions 51 are formed in the part 48 on opposite sides
of the slot.
When the parts are in operating position, a
molded projection integral with the operating member 43
extends into the slot of the contact arm 41 to position the
operating member 43 relative to the contact arm 41, and
pivoting portions 55 on opposite sides of the projection
3 pivotally engage in the depressions 51 of the con~act arm
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41. The operating member 43 has a handle portion 57 molded
integral therewith which extends through an opening 61 in
the housing, whereby the mechanism may be manually operated
to open and close the breaker. Arcuate surfaces 63 on
opposite sicles of the handle 57 substantially close the
opening 61 in all positions of the operating member 43.
Motion is transmitted from the operating member 43 to the
contact arm 41 when the breaker is manually operated and
from the contact arm 41 to the operating member 43 when the
breaker is automatically tripped.
The frame 25 supports an insulating pivot 65. A
releasable member 67 is pivotally supported at one end
thereof on the pivot 65. The other end ~69 of the releas-
able member 67 is latched by the trip device 29 in a manner
to be hereinafter specifically described. Except for the
trip device 29, the operating mechanism is more specific-
ally described in the Patent No. 3,~54,176.
As is more specifically described in said Patent
No. 3,254,176, the ends of the releasable member 67 are
offset and disposed along a plane which is parallel to a
plane in which the main body portion of the releasable
member 67 is disposed. A spring 71 is connected under
tension at one end in a slot 73 in contact arm 41, and at
the other end in a slot in a projection 75 that extends
from the main body portion of the releasable member 67.
The contact arm 41 is electrically connected to
the lower end of a bimetal 77 by means of a flexible con-
ductor 79. The bimetal 77 is part of the trip device 29.
A flexible conductor 81 connects the upper end of the
~ 30 bimetal 77 with a terminal strap 83 that extends th~owgh an
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opening l83 in the end wall o~ the housing. A terminal
connector 85 is connected to the external end of the term-
inal strap 83 to permit connection o~ the circuit brealcer
in a circuit in a manner well known in he ar~. The closed
circuit through ~he circuit breaker 9 extends from t`he
terminal 31 through the stationary contact 21, movable
contact 23, contact arm 41, flexible conductor 79, current-
carrying bimetal 77, flexible conductor 81, to the terminal
strap 83 by means of the terminal connector 8S. Since the
movable contact arm 41 extends downwardly from lts pivot,
the arc is established adjacent the bottom of the housing
in an arc chamber 87 which is connected by a vent passage
89 to an opening in the end of the ho~sing beneath the
terminal comlector 85.
When the releasable member 67 is in the latched
position (Fig. 2), the circuit breaker may be manually
operated by operation of the operating member 43. Movement
of the operating member 43 in a clockwise direction (Fig.
3) from the "on" (closed position) to the "of" (open
position). The spring 71 biases the contact arm 41 upward
into engagement with the operating member 43 to bias the
operating member 43 against the lower edges of the projec-
tion 47 about which the operating member 43 pivots. Move-
ment of the operating member 43 in a counterclockwise
direction from "off" to "on" moves the upper end of the
switch arm to the right of the line of action of the spring
71 to move the contact arm 41 to the closed position.
The trip device 29 comprises the elongated bi-
metal 77~ The bimetal 77 is a flat member that is secured
- 3 at the upper end thereof to a projection 93 of the sta-
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tionary frame 25. The frame 25 is a flat member that is
~ecured in place in the housing between proje~tions of the
molded insulating housing, and the projection 93 over to
extend and in a direction generally normal to the plane o
the flat supporting plate 25. An elongated rigid magne~ic
armature or latch member 95 is mounted on a spring 97 that
is welded to the high expansion side of the bimetal 77.
The armature 95 extends upward along the high expansion
side of the bimetal 77 in a parallel relationship with the
bimetal 77 when the bimetal is in the cold or straightened
condition. The armature 95 has an opening 99 therein to
form a latch surface 101 at the base of the opening.
The latch end 69 of the releas~able member 67 is
formed with a latch surface 103 thereon and a stop surface
or fulcrum part 105 thereon. The armat~re 95 serves as a
stop to engage the fulcrum part 105 of the releasable
member 67 in the latched position of the releasable member.
A U-shaped magnetic member 109 is mounted on the bimetal 77
with opposite legs being posi-tioned on opposite sides of
the bimetal.
The circuit breaker is in the reset position
(Fig. 2) wherein the releasable member 67 is latched on the
armature 95. The circuit breaker can be manually operated
only when the releasable member 67 is in the reset or
latched position. In the reset position (Fig. 2)~ the
bimetal 77 is biased toward the releasable member 67 and
engages the fulcrum part 105 of the rigid releasable member
67. In this position, the latch surface 103 of the releas-
able member 67 rests on the latch surface 101 of the arma-
-~ 30 ture 95 to latch the releasable member~67~ thereby prevent-
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ing clockwise movement of the releasable member 67 about
the pivot 6S. The high expansion side of the bimetal 77 is
on the left as seen in Fig. 2. Upon the occur-rence of a
sustained lesser overload current above a first predeter-
mined value, the bimetal 77, which is heated by the cwrrent
flowing therethrough, deflects from the position (Fig. 2
to a thermally-tripped position.
The bias of the complete bimetal 77 toward the
left maintains the armature 95 against the fulcrum part lOS
during the deflection of the bimetal 77 to a thermally-
tripped position. The bimetal 77 deflects to a curvature
such as that during movement when the rigid armature 95 is
angled to the position with the lower end of the ridig
armature 95 being carried by the lower end of the bimetal
77, and the armature 95 moves about the fulcrum part 105
with a levering action to move the latch surface 101 of the
armature 95 free of the latch 103 of the releasable member
67 to thereby release the releasable member 67.
When the releasable member 67 is released, the
spring 71 rotates the releasable member 67 in a clockwise
direction about the pivot 65 until the releasable member 67
is stopped by engagement thereof with a molded projection
: 177 on the housing part 13. During this movement, the line
- of action of the spring 71 is to the right on the pivot 55,
51, whereupon the spring 71 biases the contact arm 41 in
~the opening direction and moves the contac~ arm 41 so that
the line of action of the force exerted by the spring on
the oerating member 43 shifts across the pivot 45, 47 and
- actuates~ the operating Inember h3 to the tripped position
: 30 ~Fig 3). The tripped position of the operating member 43
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is intermediate the "on" and "off" positions. The operat-
ing member 73 is stopped in the intermediate or tripped
position (Fig. 3) when an insulating projection 119 thereon
engages the projection 75 on the releasa'b~e member 67. The
contact arm 41 is stopped in the open position (Fig. 3)
when it engages an insulating projection 121 molded inte-
gral with the partition wall 13. Positive separation of
the contacts is provided during a tripping operation by
means of a projection 123 extending from the releasable
member 67. If the contacts are slow in opening due to
sticking, drag or other reasons, the projection 123 engages
the inner edge of the contact arm 41 to start the contact
arm in the opening direction. The circuit breaker is
trip-free in that the breaker will automatically -trip open
even if the handle 57 is held in the closed position.
Following a tripping operation, it is necessary
to reset the brea'ker 'before the breaker can be operated.
This is accomplished by moving the operating member 43 from
the tripped position (Fig. 3) slightly beyond the full
"off" position. During this movement, the projection 119
on the operating member 43 operates against the projection
of the releasable member 67 to move the releasable
member 67 counterclockwise to a position, wherein the latch
surface 103 of the releasable member 67 is just above the
latch surface lOl of the armature 95. 'The spring 91 then
moves the bimetal 77, which cools and straightens when in
non-current carrying tripped condition, and armature 95
toward the releasable member to latch the trip member in an
initial 0perating position With the releasable member 67
reset in the operating position, the circuit breaker can be
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manually operated in the same manner as was hereinbefore
described.
The circuit breaker is instantaneou~ly tripped
upon the occurrence of a short circuit or 5evere overload
current above a second predetermined value, higher the the
first predetermined value, by operation of the magrletic
trip of the trip means 29. The current passing through the
bimetal 77 (Fig. 2) generates magnetic flux which operates
through the armature 95, the air gaps between the armature
95 and the magnetic member 109, and through the stationary
magnetic member 109. When the current reaches the second
predetermined value, this magnetic flux is strong enough to
attract the armature 95 toward the st~ationary magnetic
member 109, and the spring 97 flexes permitting the arma-
ture 95 and bimetal 77 to move as a unit to the magneti-
cally-tripped position (Fig. 3) wherein the releasable
member 67 is releasable to trip the breaker in the same
manner as was hereinbefore described.
Following a magnetic tripping operation, the
circuit breaker is reset and relatched in the same manner
as was hereinbefore set forth with regard to the time-delay
thermal tripping operation. The bimetal 77 and armature 95
are shown in the attached position in Fig. 3. It can be
understood that when the circuit is interrupted the arma-
ture 95 will no longer be atracted to the stationary magne-
tic member lQ9 and returns the bimetal 77 and armature 95
to the unattracted position.
The ground fault de-tec-tor or actuator in compart-
ment 17 tis generally indicated at 127 in Fig. 4 and is em-
ployed to avoid the adverse effects of the grounded neutral
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12 48,020condition. In Fig. 7, the ground fault detector 127 of thedifferential transformer type is shown schematicall.y where-
in a differential transformer 129 having a toroidal core
131 is provided with conductors including a line condwctor
81 and a neutral conductor 135. The conductors 81 and 135
extend through the core 131 as primary windings, each pre-
ferably of a single turn although multiple turn windings
may be used if desired. The .illustration of the conductors
is merely schematic and in accordance with a preferred
10form. The conductors 81 and 135 are in coaxial arrangement
as they pass through the core 131 as disclosed in U.S.
Patent No. 3,736,463.
A sensing winding or sensor 137, usually of a
plurality of turns, is provided on the core 131 for sensing
an imbalance in the conduction current levels of the pri-
mary conductors. Such an imbalance produces a sensed
current in the winding 137 which, if of sufficient magni-
tude and occurring for a sufficient time, actuates a trip
circuit 139 in order to actuate the circuit breaker on the
20conductors 81 and 135 on the input side of the differential
transformer 129. The trip circuit 139 may be of various
known types including, for example, those disclosed in -the
above-mentioned U.S. Patent No. 3,73~,468. The ground
fault circuit interrupter 127, the trip circuit 139, and
the circuit breaker are shown in ~.S. Patent No. 3J745,414.
The circuit illustrated is merely exemplary. The
invention may also be embodied in a circuit having more
than two conductors, such as a single phase, three wire
system or a three phase, four wire system. Terminals 141
3and 143 on the input side are for connection to a power
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source or supply. One or more loads to be energized by the
system may be connected to terminals 145 and 147 on the
output side.
If a ground fault occurs on the line condwctor
133 in the load circuit, without a grownded newtral condi~
tion, the operation of the apparatus is essent.ially
straightforward in accordance with past practice. If a
leakage path to the ground occurs from the neutral conduc-
tor on the load side of the transformer, as indicated by
the path 149 to ground, which may have some impedance, the
apparatus so far described would no-t be sensitive to line
conductor grounds and would prevent an unknown hazard to
those relying on the protection of the apparatus. The
problems resulting from a grounded neutral condition are
particularly serious when a load is not connected in the
system. - -
As shown in U.S. Patent NQ. 3,736,468, an ou-tput
transformer 151 of the current sensing type is provided on
the load side of the sensor or differential transformer
129. The output transformer 151 has a core 153 on which a
primary winding 155 is provided. The winding 155 is a
conductor connected between the line and neutral conductors
81 and 135 of the system. To minimize the losses in the
primary winding 155 and to enable use of a small cross-
section conductor, a current limiting means, such as a
resistance 157, is interposed in series with ~he primary on
the side of the line conductor 81. In most applications a
resistance of 10~000 to 35,000 ohms is suitable.
~ In operation~ in the absence of any load on the
output terminals and also in the absence of any ground on
14 48,~20
the neutral condllctor, a current path with minor losses is
completed ~hrough the l-in~ concluctor 81, the primar~ wind-
ing 155, and the neutral conductor 135. The polarities of
the windings of the output transformer 151 are not signifi-
cant and -the benefits are obtained whether or not they are
the same as the primary windings of the transformer 129.
Structurally the ground Eault detector 127 is
shown in Fig. 4. The several parts including the differen- i
tial transformer 129, the trip circuit 139, and the output
transformer 151 are mounted within spaced formed projec-
tions comprising integral parts of the intermediate portion
7 of the housing on the side of the compartment 17 Accord-
ingly, the several elements are retain~ed in place upon
attachment of the cover 11
More particularly, the -trip circuit 139 includes
a solenoid 159 having a plunger with an outer end 161. A
lever 163 is mounted on a pivot pin 165 which is a molded
portion of the back wall 8. The lever 163 has a notch 167
(Fig. 5) which engages the solenoid plunger adjacent the
outer end 161 thereof. The lower end of the lever 163
includes an integral projection or prong 169 (Fig. 5) which
extends through an opening 171 in the partition wall 13.
The end of the projection 169 is contiguous to the bimetal
77 of the circuit breaker in the compartment 15 (Fig. 2).
When the solenoid 159 is actuated, the lever 163 rotates
slightly cownterclockwise, whereupon the projection 169
moves the bimetal 77 a .suf-ficient distance to trip the
circuit breaker.
. The lever 163 is free from any binding forces and
3~ suitable for easy assembly. Moreover, tbe lever being com-
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posed of insulating material preven-ts electrical currents
from 1Owing from the solenoid to the bimetal 77. The
grounded neutral conductor 135 is ho-used withLn the restric-
ted con~ines of the molded housing so that essentially a
suitable mechanical insulation is achieved, The adapter
173 is constructed to enhance electrical a~taehment and to
provide for strain relief of the assembled members. The
test circuit means is arranged to exclude the need for a
separate housing. By providing molded housing members
adapted to confine the various parts in place a restricted
movement of the parts including the transformer coils, the
trip circuit, and the associated resistor enhanee reliabil-
ity and positional individuality.
The portion of the neutral conductor 135 extend-
ing through the core 153 of the output transformer 151
comprises an adapter 173, the right end of which (Fig. 4)
is connected at 175 to the cable portion of the conductor
135. The left end of the adapter 173 is connectecl to a
wire-like conductor 177 (Fig. 7). An intermediate portion
20of the adapter 173 includes a U-shaped part 179 which
extends through the core 153 as the secondary winding
thereof -and which is connected at 181 to a continuation o~
the cable portion of the conductor 135. As shown in Figs.
4 and 6, the cable portion 135 extends through the core 131
of the transformer 129 and continues to the terminal 147.
As shown in Figs. 2 and 6, the flexible conductor
81 extends through an opening 183 from the upper end of the
bimetal 77 and around and through the toroidal core 131 in
thè comp~rtment 27 and then through an opening or aperture
3means 183 in the partition wall 13, where it re-enters the
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compartment 15 and is connected to the terminal strap 83 as
set forth above. An insulating cover 187 covers the flexi-
ble conductor 81 to prevent its electrlcal contact with any
portion of the ground fault circuit interrupter such a5 ~he
neutral conductor 135 in the core 131 o~ the transformer
129.
To provide a mechanical advantage, the lower
portion of the lever 163 is slightly lon~er than the upper
portion thereof so that a solenoid 159 of lesser force is
required for the desired movement of the lower end of the
lever against the bimetal 77. After tripping a conven-
tional latch spring on the bimetal 77 automatically reposi-
tions the solenoid lever for the next strQke.
The toroidal core 131 (Fig. 6) comprises a stack
of laminated rings 189 of an iron base composition which
rings are encased within a cover 191 of an electrically in-
sulating material. A coil 193-encircles the assembly of
the laminated rings 189 and the cover 191 and the assembly
of the rings, cover and coil are encased within an outer
cover 195. The outer cover 195 has an outwardly ~xtending
arm portion 197 in which the two leads of the coil 193 are
embedded and extend through the trip circuit 139 (Fig. 7).
To enable periodic verification of the ground
fault circuit breaker structure 3, a test circuit 199 (Fig.
7) is provided and excludes the need for a separate housing
for the test switch means. The test circuit includes a
manual button 201 which closes a circuit between the conduc-
tor 177 (Fig. 7) and a wire 203 3 the latter of which leads
to the ~eutral conductor 135 ahead of the differential
transformer L29 as we:Ll as to the trip circuit 139.
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In accordance with this invention, the housing 5
(~ig. 2) comprises a groove 205 that extends from the area
of the test button 201 to the terminal 147. The conductor
177 is located in the groove 205 and the ri~id, wi~e-like
conductor 177 comprises two end portions 207 and 209 (Fig.
8). The lower end portion 209 is in electrical contact at
211 with the load terminal 147 where said portion 209 is
secured by a pressure fit, or clamping connection, between
the insulation housin~ 5 and the terminal 147.
10The upper end portion 207 extends across a sur-
face of the housing 5 at 213 where said portion 207 is
aligned with the test button 201. When the button 201 is
pressed, ~he test circuit which includes c~onductors 211 and
213~ is closed between the circui~ 199 and the conductor
177.
Accordingly, the rigid wire-like conductor pro-
- vides a mechanical contact surface for completing the
electrical connection by using a pressure fit connection to
the ungrounded load circuit terminal, thereby eliminating
welded or soldered joints with small flexible loads. By
imbedding the wire-like conductor in the groove, there is
no need for insulation on the conductor.
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