TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
2M RUN CONTACTOR
TR PNEUMATIC TIMER
three-wire ungrounded or three and four-wire
sizes should be stocked in the regular shop supply
grounded circuits. Multiple units should be of the
common trip type having a single operating handle.
a. Enclosures. Enclosures do not normally re-
quire maintenance when employed in a clean, dry
The need for maintenance on molded case breakers
will vary depending on operating conditions.
and noncorrosive atmosphere. But in a marginal
Molded case breakers are relatively trouble-free de-
atmosphere, enclosures should be inspected and
vices requiring little maintenance. For the most
maintained as recommended in paragraph 2-2. The
frequency of these inspections should be dictated by
part, maintenance will require only that conductor
the corrosiveness of the atmosphere.
terminations are tight and free from corrosion, and
that the breaker is kept dry and free from excessive
b. Electrical connections. Experience indicates
that failures of electrical connections are the cause
accumulations of dirt and dust. Because most
of many equipment burnouts and fires. Refer to
breakers employ welded internal construction, they
paragraph 23 for recommended maintenance.
require no internal servicing. An exception to this is
c. Molded case breakers. A wide variety of circuit
the trip unit, which is replaceable on breakers in
breakers are used in the military services. Thermal-
larger frame sizes. Periodic inspection should be
magnetic molded case circuit breakers (fig 5-10) are
made to ensure that the trip unit hold-down bolts
predominant in building panel boards and motor
are tight. For breakers rated 100 amps and below,
control centers. They are available in bolt-in or
and where inspection indicates some type of repair
plug-in types and in single-pole for two-wire
is in order, "repair by replacement" is advisable.