I.B. 48003
Page 17
Effective 11/97
CONTACTOR MAINTENANCE
All work on this contactor should be done with the main
circuit disconnect device open, and using a separate
source of control power to operate the magnet. Before
applying external control circuit power, make certain that
the contactor coil circuit is electrically isolated, to prevent
feedback into a control power transformer that could be
hazardous. Disconnect power from any other external
circuits. Also, discharge any hazardous capacitors.
The basic principles to be followed in the maintenance of
all electrical equipment are: (1) keep conducting parts as
good conductors and (2) keep insulating parts as good
insulators, i.e., tighten and clean.
Much routine maintenance on the low-voltage portion can
be done with the contactor partially withdrawn to the
balanced position, rather than completely removed.
However, the contactor can also be completely removed
and taken to a bench.
A bottle wrench and a .020-inch (.51mm) feeler guage
are screw-mounted to the right-hand sidesheet of the
contactor when the Ampgard
®
controller is shipped. The
feeler gauge is used to determine the vacuum bottle end-
of-life by virtue of contact erosion. One end of the bottle
wrench is used to adjust the operating arm associated
with the Type L64 auxiliary contacts (see Auxiliary
Contact Adjustment below) and the other end of the
wrench is for use with pre-1983 vintage vacuum bottles.
Insulation Level
Refer to the insulation resistance measurements between
contactor poles and from each pole to ground that were
recorded at start-up and subsequent intervals. Measure
the same points in the same manner and record. Investi-
gate any abrupt reduction in resistance or any unusually
low reading.
Dust and moisture are detrimental to electrical equipment
and industrial equipment is designed to tolerate a less-
than-perfect environment. However, excessive dust can
cause trouble, and should be wiped or blown off at appro-
priate intervals. If the contactor is wet for any reason, dry
it until the insulation resistance between poles and from
each pole to ground has returned to normal.
The contacts inside the interrupters are immune to dust
and moisture and require no attention of this type.
Vacuum Interrupters
Gross loss of vacuum is highly unlikely, but it can be
checked easily. With the contactor open, pull upward on the
bottle nuts, one pole at a time, using an effort of about 20
pounds (9 kilograms). If the bottle nuts move easily away
from their pivot, the vacuum has probably failed and the
bottle sub-assemblies must be replaced.
It is also unlikely, but possible, to have a very slight leak
that does not change the bottle force appreciably, but
which might seriously damage the ability of the bottle to
interrupt. In this regard, it must be remembered that in
a three-phase circuit, it is possible for any two good
interrupters to successfully interrupt the circuit even if
the third interrupter is weak. But this condition should
not be allowed to continue. It can be detected only by a
dielectric test.
Check the dielectric strength of the interrupters before
the contactor is energized for the first time and regularly
thereafter to detect, at the earliest possible date, any
deterioration in the dielectric strength of the contact gap
since this may result in an interruption failure. The
vacuum interrupters should be tested as specified in the
section CHECK-OUT, VACUUM INTERRUPTERS.
Fig. 14 Controller With Doors Open
