TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
always be successful. Too much opening spring pres-
millivolt drop test. Partial maintenance can then be
sure can cause excessive friction at the tripping
performed annually and complete maintenance ev-
latch and should be avoided. Electromagnetic
ery 5 years.
forces, due to the flow of heavy short-circuit cur-
(1) Inspection schedule for new circuit break-
rents through the circuit breaker, may cause extra
ers. A temporary schedule of frequent inspections is
pressure on the tripping latch.
necessary after the erection of new equipment, the
(2) Lubricate the bearing surfaces of the oper-
modification or modernization of old equipment, or
the reapplication of old equipment under different
ating mechanism as recommended in the manufac-
turer's instruction book. Avoid excessive lubrication
conditions. The temporary schedule is required to
because oily surfaces collect dust and get stiff in
correct internal defects, which may appear in the
cold weather, resulting in excessive friction.
first year of service, and to correlate external check
procedures with internal conditions as a basis for
(3) If possible, observe the circuit breaker op-
establishing a more conservative maintenance pro-
eration under load.
gram thereafter. If a circuit breaker shows no seri-
(4) Operate the circuit breaker manually and
ous defects during early internal and external in-
electrically, and look for malfunctions. Determine
spections, and no heavy interrupting duty is
the presence of excessive friction in the tripping
imposed, the following inspection schedule is recom-
mechanism and the margin of safety in the tripping
function by testing the minimum voltage required
(a) Twelve months after erection. External
to trip the circuit breaker. This can be accomplished
inspection and checks.
by connecting a switch and rheostat in series with
(b) Twelve months after the first inspection.
the trip-coil circuit at the circuit breaker (across the
Complete inspection and adjustment.
terminals to the remote control switch) and a volt-
(c) Twelve months after previous inspection.
meter across the trip coil. Starting below 50 percent
If no problems, perform regular maintenance. If
of rated trip-coil voltage, gradually increase the
there are problems, another inspection should be
voltage until the trip-coil plunger picks up and suc-
performed after 12 months; then return to the
cessfully trips the circuit breaker. Make several
maintenance schedule for existing circuit breakers.
trial tripping operations of the circuit breaker, and
(2) Inspection schedule for existing circuits
record the minimum tripping voltage. Most circuit
breakers. Normally, no more than 1 year should
breakers should trip at about 56 percent of rated
elapse between external inspections and 5 years
trip-coil voltage. Measure the trip-coil resistance
and compare it with the factory test value to dis-
between internal inspections. It is advisable to
close shorted turns. Many modern circuit breakers
make a complete internal inspection after the first
have trip coils which will overheat or burn out if left
severe fault interruption.
energized for more than a short period. An auxiliary
c. Medium-voltage circuit breakers in metalclad
switch is used, in series with the coil, to open the
switchgear. Inspection and maintenance should be
circuit as soon as the circuit breaker has opened.
The auxiliary switch must be properly adjusted to
d. Circuit breakers in low-voltage switchgear. In-
successfully break the arc without damage to the
spection and maintenance should be performed ev-
contacts. Record the minimum voltage that will
ery 5 years.
close the breaker and the closing coil resistance.
8-14. Maintenance of nonmetalclad switch-
(5) Trip the circuit breaker by protective relay
gear circuit breakers.
(6) Check adjustments by measuring the me-
Maintenance requirements include both general ex-
chanical clearances of the operating mechanism as-
ternal and internal inspection guidelines. Also
sociated with each tank or pole. Appreciable varia-
guidelines specific to the insulating medium (oil and
tion between the clearance measured and the
SF, gas) are given.
previous setting usually indicates mechanical
a. General external inspection guidelines. The fol-
trouble. Temperature, and difference of tempera-
lowing items should be included in an external in-
ture, between parts of the mechanism affect the
clearances. The manufacturer's recommended toler-
(1) Visually inspect the circuit breaker and the
ances usually allow for these effects.
operating mechanism. Carefully examine tripping
(7) Check the power factor of bushings and the
latches, since small errors in adjustments, clear-
ances, and roughness of the latching surfaces may
(8) The measurement of the electrical resis-
cause the circuit breaker to latch improperly or in-
tance between external bushing terminals of each
crease the force necessary to trip the circuit
pole can indicate whether maintenance is required.
breaker, such that the electrical tripping will not