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.
CAUTION:
BEFORE DOING ANY OF THE FOL
L O WING CONTA C T A DJ U S TMENT A N D RE
PLA CEMENT WOR K, MECHANICA L L Y DIS
CONNEC T THE CLOSING SPRING FROM THE
MECHANISM CAM SHAFT AS DESCRIBED UN
DER SLO W CLOSING THE BREAKER, SECTION
7.4
8.1
ARC CHUTE REMOVAL
AND INSPECTION
There are two types of arc chute construction used on
the 800 thru 2000 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.
The
800
ampere arc chute is different from the 1 600 and
2000 ampere arc chute, which are identical. Therefore, the
800 ampere arc chute cannot be interchanged with the
1 600/2000 ampere arc chute. Also note that a breaker must
have either all ceramic or all molded type arc chutes install
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 . Loosen and back off the retainer bolt locking nut from
the mechanism frame. They do not have to be removed.
2. Loosen the retainer bolts until the retainer(s) can be
removed.
3. With the retainer(s) removed, lift the arc chutes off for
i nspection.
Inspect each arc chute for excessive burning and erosion
of the arc plates and arc runner. Also look for fractures,
damage to the liner material used in the molded arc chute
and damage to the insulation material used in both arc
chutes. Check for any missing parts.
To install the arc chutes:
1 . Replace the arc chutes over each pole unit.
2. Locate the retainer(s).
3. Tighten the retainer bolts until the arc chutes are
secure. There may be some side to side motion of the arc
chutes, but there must not be any front to back motion.
Torque the retainer bolts to
30
in-lbs for the molded type arc
chutes and
60
to 1 00 in-lbs for the ceramic type. Do not
over tighten.
4. Tighten the locknuts against the mechanism frame
with 150 to 1 75 in-lbs torque.
33
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