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 TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
FIXED ARCING CONTACT
MOVABLE ARCI
CONTACT
MOVABLE MAIN
CONTACT
Figure 2-3. Power circuit breaker main and arcing contacts.
(c) Contact maintenance. The general rules
faces, or weakened contact spring pressure. This
for maintaining contacts on all types of breakers
will cause excessive current to be diverted through
are: keep them clean, aligned and well adjusted. To
the arcing contacts, with consequent overheating
inspect the circuit breaker contacts, the arc chutes
and burning.
must be removed. When doing this, check the arc
(b) Arcing contacts. Arcing contacts are the
chutes for evidence of damage, and replace dam-
last to open; any arcing normally originates on
aged parts. If not damaged, then blow off dust or
them. In circuit interruption, they carry current
loose particles. Once the main contacts are exposed,
only momentarily, but that current may be equal to
inspect their condition. Slight impressions on the
the interrupting rating of the breaker. In closing
stationary contacts caused by the pressure and wip-
against a short circuit, they may momentarily carry
ing action of the movable contacts is tolerable. Con-
considerably more than the short circuit interrupt-
tacts which have been roughened in service should
ing rating. Therefore, they must make positive con-
not be filed but large projections, caused by unusual
tact when they are touching. If not, the main con-
arcing, should be removed by filing. When filing,
tacts can be badly burned or may result in a failure
take care to keep the contacts in their original de-
to interrupt a fault.
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