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 TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
ACRING CONTACTS
TOUCHING
CON
Figure 2-5 Intermediate contact gap.
for closing, and contains one or more small sole-
contacts found on older circuit breakers should be
noids or other types of electro-magnets for tripping.
replaced when badly burned. Repairs are not prac-
Tripping is accomplished mechanically, independent
tical because the laminations tend to weld together
from the closing device, so that the breaker contacts
when burning occurs, and contact pressure and
will open even though the closing device still may be
wipe are greatly reduced. These contacts may be
in the closed position. This combination is called a
filed to remove large projections or to restore their
mechanically trip-free mechanism. After closing,
original shape. They should be replaced when they
the primary function of the operating mechanism is
are burned sufficiently to prevent adequate circuit
to open the breaker when it is desired, which is
breaker operation or when half of the contact sur-
whenever the tripping coil is energized at above its
face is burned away. Carbon contacts, used on older
rated minimum operating voltage. The breaker op-
circuit breakers, require very little maintenance.
erating mechanism should be inspected for loose or
However, inadequate contact pressure caused by
broken parts; missing cotter pins or retaining keep-
erosion or repeated filing may cause overheating or
ers; and missing nuts and bolts. It should also be
interfere with their function as arcing contacts.
examined for damage or excessive wear on cam,
(3) Operating mechanism. The purpose of the
latch, and roller surfaces. Excessive wear usually
operating mechanism is to open and close the
results in loss of travel of the breaker contacts. It
breaker contacts. This usually is done by linkages
can affect operation of latches; they may stick or
connected, for most power breakers, to a power op-
slip off and prematurely trip the breaker. Adjust-
erating device such as a solenoid or closing spring
2-8
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