Table of Contents
Advertisement
Types NR, NRV Maintenance Instructions
TEST RESULTS: These high potential withstand tests provide
information on the dielectric condition of the switch.
1. If the switch passes the closed-contacts test (Test 1) but
fails the open-contacts test (Test 2) the cause is likely to be
in the main contact assembly.
2. If the switch fails the closed-contacts test (Test 1) the cause
is likely to be a diminished electrical clearance or failed
insulation.
3. After correcting the problem, retest to confirm the repair.
SHOP REPAIR PROCEDURES
The operations described in this section should be performed
under the cleanest conditions possible. The repair work, except
for bushing replacement, will be simplified if the work bench is
arranged so the mechanism/head assembly can be inverted
(bushings down). No special tools are required for any of the
repair procedures.
Bushings
Bushing maintenance generally consists of a thorough clean-
ing and a careful examination for chips, cracks, or other
mechanical damage during the periodic maintenance inspec-
tion. Bushings must be replaced whenever damage is discov-
ered.
The NR-NRV switch bushings are oil-filled. The special fixtur-
es and procedures required to assemble these bushings is
beyond the scope of normal shop maintenance repair. There-
fore if a bushing is in any way damaged, the complete bushing
assembly must be replaced. Refer to Figure 8 and proceed as
follows:
1. Disconnect the appropriate bushing lead from the bottom
end of the bushing rod.
2. Remove the three hex head capscrews and bushing clamps
that secure the bushing to the head casting and lift out the
complete bushing assembly.
3. Remove and discard the lower bushing gasket.
4. Twist off the split aluminum ring from the old bushing and
install on the new bushing assembly if ring is in good condi-
tion; replace ring if damaged.
NOTE: The clamping ring cushions and distributes the pressure
between the porcelain and the clamps. DO NOT OMIT.
5. Install the new bushing assembly into the head using a new
lower bushing gasket. Position the bushing with the stud-
end of the terminal pointing outward.
6. Position the clamping ring with the split centered between
two clamping bolts.
7. Reassemble the bushing to the head casting. Tighten the
clamping bolts evenly, a little at a time, to a torque of 3-7 ft-
lbs.
NOTE: Clamping forces must be applied gradually and equally, in
rotation, to each bolt. This results in an evenly distributed gasket
pressure.
8. Reconnect the lead to the bushing rod.
Contacts
The Type NR and NRV switches have an open-type, double-
break contact arrangement as shown in Figure 9. Depending
upon the extent of damage, the stationary and moving con-
tacts only, the moving contact and arm assembly, or the com-
plete contact box assembly may be replaced.
6
Figure 8.
Bushing removal.
Figure 9.
Open-type double-break contact arrangement of Type
NR and NRV switches.
89995KMA
89996KMA
Advertisement
Table of Contents
