Maintenance
tightening the nuts agai nst the stop washer (1 09}, the two nuts
(110) should be locked against each other.
During maintenance inspections, the following items should
be
checked to ensure that the original settings are maintained:
IMPORTANT: The procedure in T able
4
should
be
used for
maintenance closing only. The circuit breaker must
be
on
a table with the arc chutes removed during any main
tenance close operation. Maintain a
firm
grip on the
manual charging handle during the closing stroke-the
circuit breaker may suddenly latch fully closed and apply
unexpected force to the charging handle.
Main Contact Make
(See
Figure 6)
Compression of the contact fingers ( 46) must
be
between .093'
and .125' (2.4-3.2mm). This is the difference in the 1) meas
urement from the breaker base to the tip of the finger contact
surface when the breaker is open, 2) the measurement in the
same place when the breaker is closed. For RLE version
breakers, the measurement is made .25' from bottom edge of
the finger contact surface. This is checked with a normal
closing operation-not maintenance closing. Adjustment is
provided by positioning screws (78) after loosening nuts (80).
Counterclockwise rotation of screws (78) increases compres
sion. Care should be taken to retighten nuts (80) after adjust
ment. If it is desired to check contact pressure, a push-type
spring scale can be used to compress contact fingers ( 46) with
breaker open. Contact pressure should be between 20 and 30
pounds (9.1-13.6 kg) on each finger.
Arcing Contact Make
(See
Figure 6)
With the movable arcing contact (61) in any one phase
touching the mating stationary contact when the circuit
breaker is closed by the maintenance closing method (see
Table
4),
the phase-to-phase variation should not exceed
.062' (1 .6mm). Adjustment may be made by positioning
screws (78) as in the previous paragraph. It is essential that
the
main contact
compression be maintained within the
tolerance listed in the previous paragraph. Arcing contact
pressure should be between 20 and 40 pounds (9.1-18.2 kg)
when checked with a pull-type spring scale at the base of the
arcing contact tip insert with the circuit breaker contacts
closed. Measure the pressure on each blade separately.
Contact Replacement
(See
Figure 6)
The contact structure consists of main current carrying con
tacts and arcing contacts arranged so that initial contact
make and final contact break is by means of the arcing
contacts. The actual contact surfaces are clad with an alloy
facing which greatly reduces mechanical wear and arc
erosion.
When inspection of the alloy facing indicates that the contacts
should be replaced, it should be noted that hinge contact
fingers (53, 55) main contact fingers (46) and arcing contacts
(61) are spring loaded. Therefore, care must be used in
removal and installation of any of the contacts.
Main Contact Fingers
(See
Figure 6)
With the circuit breaker contacts open and the stored energy
springs discharged, the main contact fingers (46) may be
removed by loosening screws (44, 45) enough to relieve the
com pression on spri ngs (47, 48) . There are two springs
behind each finger. It is important that they be positioned
properly upon reinstallation. If difficulty is experienced in
correctly positioning these springs, the upper and lower
primary disconnects (168
Figure 16, Page
30),
may be
removed from each phase and the circuit breaker tipped to
rest on the ends of connectors (37) and ( 49). After the contact
fingers are replaced, connector (37) should be positioned in
the center of the slot in the molded base to assure correct
alignment of the primary disconnect fingers.
Stationary Arcing Contact
(See
Figure 6)
The stationary arcing contact is a part of a connector (37) and
may be replaced by proceeding as above. In this case,
screws (44, 45) must be removed. However, to provide
clearance for removal of connector the backpanel
(33)
may
have to be loosened by removing screws 58, 59 and 23,
Figure 15, Page
28).
By removing pin (98 and 99
Figure 16,
Page
30)
the entire assembly can be lifted out.
Hinge Contact Fingers
(See
Figure 6)
H inge contact fingers (53, 55) may be removed as follows:
Remove backpanel. Remove lower connector (49) and
moving contacts by removing screws (59). The springs ( 54,
56) are unloaded by rotating the moving contacts toward a
horizontal position relative to the stationary contact (49).
Remove screws (70) to remove moving contacts. Slide fingers
(53, 55) sideways to remove. Replace fingers by compress
ing spring (56, 54) in position and inserting the fingers from
the side. Holding connector (49) in a vise aids the operation.
Movable Arcing and ,.,ain Contact
(See
Figure 6)
Either movable arcing contact (61), or main contact (62), or
both, may be removed and replaced as follows:
IMPORTANT: Extreme care should
be
taken to hold the
assembly firmly to retain spring seat (83,
84)
and spring
(81, 82) upon removal of the screws (78).
Remove lower connectors and moving contacts as described
in the preceding section. The complete movable contact
assembly may now be brought to the bench. The location of
spacers should be noted. Loosen nuts (80) and remove
screws (78) from pin (71 ), alternate several turns each side
to prevent binding.
The movable arcing contact or main contact may now be
replaced. Compress spring (81, 82) to engage screws (78).
The reverse procedure is followed for reinstallation. Care
should be taken to replace spacers correctly. Check align
ment and adjustment of contacts upon reassembly.
Tripping Actuator Operation and Replacement
When the overcurrent trip device senses a circuit condition
that requires the circuit breaker to open, it produces an output
that is fed to the tripping actuator. This device then causes
the circuit breaker contacts to open and isolate the circuit.
Mounted on the circuit breaker, the tripping actuator is held
in a charged position by a permanent magnet. It contains a
coil that is energized by the output of the trip device. When
energized, the coil causes the magnetic flux to shift to a new
path, releasing the stored energy of a spri ng located i nside
the tripping actuator. The spri ng provides the energy to trip
the breaker, moving the trip-flap clear of the toggle latch.
If the spring-loaded armature does not reset during trip opera
tion, spacer washers may be added to obtain positive reset
of the armature. If adding spacers does not cause the arma-
13
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