Allis-Chalmers BWX-6637-5, Instruction Book

Page: 35 / 88

E.
REPLACEMENT
Refer to figure 6.
of main current carrying contacts and arcing
initial contact make and final contact break
contacts. The main contacts are not subject
surfaces
are
clad with an alloy facing which
wear and arc erosion.
The contact structure consists
contacts arranged so that
is by means of the arcing
to arcing. The actual contact
greatly reduces mechanical
When Inspection of the alloy facing Indicates that the
contacts
should be
replaced, It should be noted that hinge contact fingers
(6 1 4),
main
contact fingers (619) and
arcing
contacts {b20) are
spring
loaded.
There­
fore, care must be exercised in removal and installation of any of the
contacts.
I.
Main Contact
With the breaker contacts open and the stored-energy springs dis­
charged, main contact fingers {619) may be
removed
by loosening
screws (624) enough to
relieve
the compression on springs (623)
as
shown in Octal I 11A11•
There
are two springs behind each finger
a
n
d
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 (119- Figure I} may be
removed from each phase and the breaker inverted to rest on the ends
of connectors (629) and (630).
After the contact fingers are replaced, connector (629) should be
positioned fn the center of the slot in the molded base to assure
correct alignment of the primary disconnect
fingers.
2. Contact
The stationary arcing contact Is a part of connector {629) and may
be replaced by proceeding
as
above. In this case, screws (624)
must be removed.
However,
to provide clearance for
removal
of
connector (b29) first insert a
. 1 87''
diameter rod at least 211 long
through the opening in support (bl5)
as
shown in Detai
1
11811• It
may be necessary to compress contact (614) opposite arcing
c
o
n
t
a
ct
(620)
in order to insert the
rod . This
wi
II
hold hinge contact
fingers
(614)
in position to permit removal of pin (603). After
removal
of pin (603), main contact
(617)
and arcing contact (620)
can be positioned so that connector
(b29)
can be removed.
3. Contact
Hinge contact
fingers
{bl4) may be re�noved as follows:
Remove top
screw
(b27)
from support (615) and replace It with
a
.2)0-20 screw at least
1.511
long.
Remove
lower screw (627) and then
gradually back
off
the 1.511 screw as shown in Detai
I
11811, to relieve
the loading from springs (628). The hinge contact fingers can now be
removed.
To provide
easier
a
c c
e
s
s
to
the hinge contact fingers, pin
(603) may be removed after the loading is rei ieved from springs (628).
Be
certain
to replace
the 1.511 long screws with the
original
screws
after
replac�nent
of the contact fingers.
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