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 fi nally 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 AND RE
PLA CEMENT WO R 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 C H UTE R E M OVAL
AND I N S P ECTIO N
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.
Arc chutes should not be interchanged between
frame sizes or i nterru pting ratings.
The arc chutes are held in place by retainers se
cured by bolts through the mechan ism frame. The
ceramic type uses two retainers and the m olded type
uses only one.
To remove the arc c hutes:
1 . Loosen and back off the retainer bolt locking nut
from the mechanism frame. They do n ot have to be
removed .
2 . Loosen the retainer bolts until the retainer(s) can
be removed .
3. With the retainer(s) removed , l ift the arc chutes
off for inspection.
I nspect each arc chute for excessive burning and
erosion of the arc plates and arc runner. Also look for
fractures, d amage to the l iner material used in the
molded arc chute and d amage to the insu lation
material used in both arc chutes. Check for any
m issing parts.
To install the arc chutes:
1 . Replace the arc chutes over each pole u n it.
2 . Locate the retainer(s).
3. Tighten the retainer bolts until the arc chutes are
secu re. There may be some side to side motion of the
arc chutes, but there must not be any front to back
motio n . Torque the retainer bolts to 30 i n - l bs for the
molded type arc chutes and 60 to 1 00 i n - l bs for the
ceramic type. Do not over tighten .
4 . Tighten the locknuts against the mechanism
frame with 1 50 to 1 75 in-lbs torque.
33
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