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 TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
Figure 5-9. Typical motor control center.
dence of internal heating, or reason to suspect high
line and load terminals with the breaker in the open
contact resistance or improper calibration, the
position. Resistance values below one megohm per
breakers should be replaced. It is recommended
kV of test voltage are considered unsafe and should
that molded-case breakers with removable covers be
be investigated for possible contamination on the
checked for contact and latch cleanliness as well as
surfaces of the molded case of the circuit breaker.
connection tightness. L u b r i c a t i o n should be
Clean the molded case surface and retest. If low
checked. If the operating mechanism appears dry,
megohm readings persist, then replace the breaker.
apply a drop of heavy oil or light grease at the wear
For individual breaker resistance readings, load
points. Do not apply lubricant to the contacts or to
and line conductors should be disconnected from the
the trip unit. If the contacts are badly pitted, they
breaker under test. If not disconnected, the test
should be cleaned with a fine file or sandpaper. Be
measurements will also show resistance of the at-
sure to avoid any accumulation of filings in the
tached circuit. During routine testing, all circuit
breaker. Do not tamper with factory sealed break-
breakers should be operated (while documenting)
ers.
several times to ensure that the contacts are not
frozen and that the mechanical components func-
(2) Verification field testing. Verification field
tion without undue friction. This action will also
testing of molded case circuit breakers is intended
lessen the effect of any film that might have built up
to check breaker operation versus manufacturer's
on the contacts. Check for cracked, warped or bro-
published data. If molded case circuit breaker per-
ken case and replace if necessary. If there is evi-
formance characteristics are to be tested in the
5-9
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