Contact Assembly
The contacts should be checked periodically for wear and
adjustment. Under normal conditions, the contacts should be
good for a large number of operations. A small amount of
surface pitting on the main contacts will not impair the normal
current carrying capacity of the breaker. Any excess roughness
can be smoothed with fine aluminum oxide paper making cer
tain that at least 70% of the line contact surface is effective.
The arcing contacts are subject to the intense heat of the arc
when interrupting current. Each arc interruption will burn away
some of the arcing contact metal. When they have reached the
point where only
Va
inch of contact material remains, the con
tact block or moving contact finger should be replaced.
The moving contact assembly is illustrated in Fig. 6. The fol
lowing steps are necessary to remove the complete assembly
from the breaker for servicing:
1. Remove the pin A, Fig. 3, which disconnects the toggle
linkage.
2. Remove the pin fastening the opening spring guide to the
top of the contact arm casting. Remove pinT, Fig. 3.
3. Remove the bolts holding the hinge block to lower stud.
4. Lift the contact assembly out of the breaker.
Adjustments
Contact Adjustment
To completely re-adjust the contacts, start by loosening the bolts
holding the stationary arcing contact and backing off the jack
screw so that the contact is free to slide back on the upper
stud. It is best to make the following adjustments with the lock
ing-bar in place as shown in Fig. 4. If a locking-bar is not avail
able, then the holding coil must be energized with 200mA D.C.
current.
Make certain that the armature does not pull away -from the
holding magnet as the breaker is closed.
Contact adjustments should be started by checking the com
pression of the main contact finger springs on each side of
the moving contact arm assembly. This can be done by com
paring the measurements of dimension
L,
Fig. 3, with the
breaker open and with it closed. The main contact spring
compression should be .063±.020 as indicated by the differ
ence in dimension L. If these measurements are not within tol
erance, open the breaker, loosen the lock nut on the eccentric
pin D, Fig. 3, and ascertain that the eccentric is down and for
ward (closer to pole unit). The exposed right-hand side of the
pin has been machined to indicate location. Turn the pin
clockwise to decrease the spring compression, or counter-clock
wise to increase it. In general, only a few degrees of rotation will
be required. Lock the eccentric pin and close the breaker to re
check the main contact finger spring compression.
The next adjustment to be checked is the length of the pull
rod
G,
Fig. 3, which controls the amount that pin C moves
over toggle. If pin C moves too far over toggle position, then
the contact arm will close and then re-open slightly as the
closing handle reaches its final closed position. If pin C does
6
not move far enough, then the breaker will tend to slam open
during electrical closing. The pull rod length should be ad
justed so that the operator can feel a definite snap as pin C
goes over toggle, but cannot notice any return motion of the
moving contact support. The correct adjustment is 1112 turns
over toggle.
The pull rod length can be adjusted, if necessary, by loosening
the lock nut R, removing pin
Q,
and rotating the universal joint
P to shorten or lengthen the pull rod assembly. The universal
joint has R.H. threads. After adjustment. place a screw-driver
blade between the frame of the universal joint and the inside
of the slot in the closing solenoid plunger to keep the universal
joint centered in the slot, and tighten the lock nut R. Recheck
main contact spring compression.
The stationary arcing contact should be set last. This can be
done by closing the breaker by hand until a 1/8-inch shim can
be placed between the main contacts at dimension M, Fig. 3,
and moving the stationary arcing contact forward until it just
touches the moving arcing contact. Then tighten the mount
ing bolts on the stationary arcing contact. Re-check the gap
between the main contacts to make certain that the 1/8 shim
is a snug fit when the arcing tips just touch.
As a final check, the breaker should be tested for electrical clos
ing and for holding coil drop-out. The breaker should be ca
pable of closing at 100 volts and as high as 140 volts without
slamming out. The closing voltage figures are obtained by
measuring the closing coil cold resistance and multiplying it
by the measured closing coil current. This method must be
used since the closing coil resistance will change due to heat
ing and make measured closing coil voltages meaningless. The
closing coil current times the cold coil resistance will give the
voltage conditions corresponding to the initial operation of the
breaker regardless of the present temperature of the coil. Dur
ing electrical closing tests, the closing coil should be checked
occasionally to make sure that it does not reach temperatures
high enough to burn out the coil. This coil is intended for mo
mentary duty only and should not have a current applied for
more than a few seconds at a time.
The drop-out can be checked by connecting the holding coil
to a source of variable direct current. Set the current to 200
milliamperes and close the breaker. Reduce the current slowly
until the breaker opens. The measured value of current should
be within the range of 32 to 100 milliamperes. If the drop-out
current is not within these limits, re-check the breaker adjust
ments. If adjustments are properly made and the drop-out cur
rent is still not within tolerance, the factory should be consulted.
lubrication
All pins and bearing surfaces except the moving contact hinge
joint are coated at the factory with molybdenum disulphide. If
the breaker linkage is dismantled, the pins and bearing sur
faces should be wiped clean and coated with molybdenum
disulphide dissolved in alcohol and applied with a small brush.
The alcohol will evaporate rapidly and leave a deposit of
molybdenum disulphide on the surface.
The moving contact hinge joint must be lubricated only with
a good grade of graphite grease such as WEMCO PDS 1022-
1. Do not apply molybdenum disulphide to the moving contact
hinge joint, since this lubricant is not a good electrical conductor.
/.B. 201
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