S260-20-9
11
Figure 26.
Measuring fixed contact holding force.
Figure 25.
Final contact clearance.
H. To confir m proper contact
engagement, crank the actuator
mechanism to the fully closed
position.
Check clearance
between the moving contact bar
and the contact rod guide block,
Figure 25. Clearance must be
between 1/32 and 1/16 inch.
If clearance is outside these
limits adjust the hex nuts on the
bushing rods to move the station-
ary contact assembly up or down
as required. Often, a half turn of
each nut provides the adjustment
required
Be careful to move the contact
housing evenly so as not to dis-
turb its vertical alignment.
I. With the housing adjusted to pro-
vide the required gap, tighten the
bushing rod nuts securely. Hold
the inner nut in place with one
wrench while tightening the outer
nut with another wrench.
NOTE: Recheck the clearance (Step
H) and the vertical alignments (Steps
A and B) after bushing rod nuts are
tight.
J. After all three phases have been
reworked, reconnect the closing
spring to the drive stud.
Figure 27.
Stationary contact gap.
8. Check contact pressure.
A. Using a pressure gage as shown
in Figure 26 check the contact
pressure. Force on the gage rod
must be applied at right angles
to the contact surface. The force
required to separate a stationary
contact from its moving contact
should be 7.5 ± 0.5 lb.
NOTE: To help determine when the
applied force causes contact separa-
tion, an electrical continuity check
can be used. The faces of all contacts
except the set being measured are
isolated with strips of thin insulating
material.
B. The separating force on a new set
of contacts is generally greater
than 7.5 lb. Therefore, the adjust-
ment of new contacts will be in
the direction of reducing contact
pressure.
C. To reduce contact pressure:
(1 ) Insert a screwdriver between
the stationary and moving
contact tips and pry in the
direction to move the station-
ary contact away from the
moving contact tip. Adjust the
pressure toward the high
side.
NOTE: A “feel” for applying prop-
er leverage is easily determined
after the first trial. Make smalI
changes in pressure until experi-
ence has been gained.
D. To increase contact pressure:
(1 ) With the switch open, bend
each contact finger inward.
Then close switch and repeat
step C.
E. Equalize the pressure on each
side of a set of contacts as close-
ly as possible.
F. After all contact pressure adjust-
ments have been made, check
that the contacts have a gap of
1/4 (+1/32 -1/16) inch. (See Fig-
ure 27.)
9. Manually operate the switch a few
times to observe contact alignment
and clearances to verify that all parts
have been properly secured.
TYPE VLR SWITCH
If it has been determined that the con-
tacts must be replaced, refer to Figure
28 and proceed as follows:
1. Remove the movable contact yoke
assembly.
A. Remove the stop nut and flat
washer from the end of the con-
tact rod.
B. Remove the yoke positioning
spacers and drive out the roll
pin.
C. Note the flat washer arrange-
ment above and below the mov-
able contact yoke. Be sure to
replace in the same order.
D. Remove and discard the mov-
able contact yoke assembly.
2. Remove the stationary contact as
sembly.
A. Remove the brass hex nuts, lock-
washers and flatwashers attach-
ing the mounting brackets to the
bushing rods.
