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SECTION 8-Contact Maintenance
Breakers subjected to frequent interruption of high cur
rents may eventually require replacement of their contacts.
The general rule for determining need of replacement is
the loss of one-half or more of the mass of the contact tip
material. Roughening or light pitting of the contact surface
does not indicate loss of ability to carry or interrupt current.
When contacts are replaced, they must be adjusted to
ensure that the proper amount of force is developed be
tween the movable and stationary contacts when the
breaker is closed. This is called the "wipe" adjustment.
"Wipe" is the distance through which the stationary con
tacts move when the breaker closes. It is measured bet
ween the point of contact on a stationary contact when the
breaker is open, and the position of the same point when
the breaker is closed. The actual wiping motion is greater
because the contacts over-travel. "Wiping" imparts a slid
ing or "scrubbing" action to the contacts.
The wipe adjustment influences proper arc transfer dur
ing interruption of fault currents. "Transfer" of the arc is its
forced sequential movement from the intermediate con
tacts to the arcing contacts to the arc runner and finally to
the arc quencher where it is dissipated and extinguished. It
is recommended that contact wipe be checked periodically
during normal maintenance inspections.
BEFORE DOING ANY OF THE FOL
CAUTION :
L O WING CONTA C T A DJUSTMENT AND RE
PLA CEMENT
WOR K,
CONNEC T THE CLOSING SPRING FROM THE
MECHANISM CAM SHAFT AS DESCRIBED UN
DER SLOW CLOSING THE BREAKER, SECTION
7.4
MECHANICAL L Y DIS
ARC CHUTE REMOVAL
8.1
AND INSPECTION
There are two types of arc chute construction used on
800
2000
the
thru
ampere breakers. They are the ceramic
type shown in Fig. 5 and the molded type shown in Fig. 6.
The ceramic type uses a two piece porcelain frame to
enclose its internal parts. The molded type uses a one
piece, glass-filled polyester frame.
800
The
ampere arc chute is different from the
2000
ampere arc chute, which are identical. Therefore, the
800
ampere arc chute cannot be interchanged with the
1 600120 00
ampere arc chute. Also note that a breaker must
have either all ceramic or all molded type
ed, do not intermix on the same breaker.
The arc chutes are held in place by retainers secured by
bolts through the mechanism frame. The ceramic type
uses two retainers and the molded type uses only one. To
remove the arc chutes:
1 .
Loo se n and back off the retainer bolt locking nut from
the mechanism frame. They do not have to be removed.
2.
Loo se n the retainer bolts until the retainer(s)
removed.
3.
With the retainer(s) removed, lift the
inspection.
Inspect each arc chute for excessive burning and erosion
of the arc plates and
arc
damage to the liner material used in the molded arc chute
and damage to the insulation material used in both
chutes. Check for any missing parts.
To install the
arc
chutes:
1 .
Replace the arc chutes over each pole unil
2.
Locate the retainer(s).
3.
Tighten the retainer bolts until the
secure. There may be some side to side motion of . t he
chutes, but there must not be any front to back motion.
Torque the retainer bolts to
60
to 1 00 in·lbs for the ceramic type.
chutes and
over tighten.
4. Tighten the locknuts against the mechanism frame
with
150
to 175 in-lbs torque.
1600
arc
chutes install
can
arc
chutes off for
runner. Also look for fractures,
arc
chutes
30
in-lbs for the molded type
Do
and
be
arc
are
arc
arc
not
33
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