TM 5-683/NAVFAC M116/AFJMAN 32-1083
ALL POWER DISCON-
READY FOR REMOVAL
Figure 2-2. Drawout circuit breaker positions.
ac/dc control block contacts. Verify correct operation
Repair moderate damage to bushing insulation by
of "trip free" and anti-pump mechanisms.
sanding smooth and refinishing with a clear insu-
b. Fixed circuit breakers. Maintenance on fixed-
lating varnish. Check insulating parts for evidence
or bolter-type circuit breakers is normally per-
of overheating and for cracks that indicate excessive
formed with the breaker in place inside its cubicle.
Special precautions must be exercised to assure
(2) Contacts. The major function of the power
circuit breaker depends among other things upon
equipment is de-energized and the circuit in which
it is connected is properly secured from a safety
correct operation of its contacts. These circuit
standpoint. All control circuits should be de-
breakers normally have at least two distinct sets of
energized. Stored energy closing mechanisms
contacts on each pole, main and arcing (fig 2-3).
should be discharged.
Some have an intermediate pair of contacts which
c. Power circuit breaker components. Mainte-
open after the main contacts and before the arcing
nance on all power circuit breakers will encompass
maintenance on the following components.
(a) Main contacts. When the breaker is
closed, practically the entire load current passes
(1) Insulation. The general rule for insulation
is keep it clean and dry. Remove interphase barriers
through the main contacts. Also, short circuit cur-
and clean them and all other insulating surfaces
rent must pass through them during opening or
with dry compressed air and a vacuum cleaner.
closing faulted lines. If the resistance on these con-
Wipe insulation with clean lint-free rags and sol-
tacts becomes high, they will overheat. Increased
vents as recommended by the manufacturer if hard-
contact resistance can be caused by pitted contact
ened or encrusted contamination must be removed.
surfaces, foreign material embedded on contact sur-