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SECTION I - IMPORTANCE OF
ADEQUATE MAINTENANCE
ADEQUATE MAINTENANCE
The maintenance of circuit breakers deserves
special consideration because of their
importance for routine switching and for
protection of other equipment. Electric
transmission system breakups and equip-
ment destruction can occur if a circuit breaker
fails to operate because of a lack of
preventive maintenance. The need for
maintenance of circuit breakers is often not
obvious as circuit breakers may remain idle,
either open or closed, for long periods of
time. Breakers that remain idle for 6 months
or more should be made to open and close
several times in succession to verify proper
operation and remove any accumulation of
dust or foreign material on moving parts and
contacts.
special consideration because of their
importance for routine switching and for
protection of other equipment. Electric
transmission system breakups and equip-
ment destruction can occur if a circuit breaker
fails to operate because of a lack of
preventive maintenance. The need for
maintenance of circuit breakers is often not
obvious as circuit breakers may remain idle,
either open or closed, for long periods of
time. Breakers that remain idle for 6 months
or more should be made to open and close
several times in succession to verify proper
operation and remove any accumulation of
dust or foreign material on moving parts and
contacts.
SECTION 2 - MAINTENANCE OF
MOLDED CASE CIRCUIT BREAKERS
MOLDED CASE CIRCUIT BREAKERS
2.1. FREQUENCY OF MAINTENANCE.-
Molded case circuit breakers are
designed to require little or no routine
maintenance throughout their normal life-
time. Therefore, the need for preventive
maintenance will vary depending on
operating conditions. As an accumulation
of dust on the latch surfaces may affect
the operation of the breaker, molded case
circuit breakers should be exercised at
least once per year. Routine trip testing
should be performed every 3 to 5 years.
Molded case circuit breakers are
designed to require little or no routine
maintenance throughout their normal life-
time. Therefore, the need for preventive
maintenance will vary depending on
operating conditions. As an accumulation
of dust on the latch surfaces may affect
the operation of the breaker, molded case
circuit breakers should be exercised at
least once per year. Routine trip testing
should be performed every 3 to 5 years.
2.2. ROUTINE MAINTENANCE TESTS.-
Routine maintenance tests enable
personnel to determine if breakers are
able to perform their basic circuit
protective functions. The following tests
may be performed during routine
maintenance and are aimed at assuring
that the breakers are functionally
operable. The following tests are to be
made only on breakers and equipment
that are deenergized.
Routine maintenance tests enable
personnel to determine if breakers are
able to perform their basic circuit
protective functions. The following tests
may be performed during routine
maintenance and are aimed at assuring
that the breakers are functionally
operable. The following tests are to be
made only on breakers and equipment
that are deenergized.
2.2.1. Insulation resistance test.- A
megohmmeter may be used to make
tests between phases of opposite
polarity and from current-carrying
parts of the circuit breaker to ground.
A test should also be made between
the line and load terminals with the
breaker in the open position. Load
and line conductors should be dis-
connected from the breaker under
insulation resistance tests to prevent
test mesurements from also showing
resistance of the attached circuit.
Resistance values below 1 megohm
are considered unsafe and the
breaker should be inspected for pos-
sible contamination on its surfaces.
megohmmeter may be used to make
tests between phases of opposite
polarity and from current-carrying
parts of the circuit breaker to ground.
A test should also be made between
the line and load terminals with the
breaker in the open position. Load
and line conductors should be dis-
connected from the breaker under
insulation resistance tests to prevent
test mesurements from also showing
resistance of the attached circuit.
Resistance values below 1 megohm
are considered unsafe and the
breaker should be inspected for pos-
sible contamination on its surfaces.
2.2.2. Millivolt drop test.- A millivolt
drop test can disclose several abnor-
mal conditions inside a breaker such
as eroded contacts, contaminated
contacts, or loose internal connec-
tions. The millivolt drop test should be
made at a nominal direct-current volt-
age at 50 amperes or 100 amperes
for large breakers, and at or below
rating for smaller breakers. The
millivolt drop is compared against
manufacturer's data for the breaker
being tested.
drop test can disclose several abnor-
mal conditions inside a breaker such
as eroded contacts, contaminated
contacts, or loose internal connec-
tions. The millivolt drop test should be
made at a nominal direct-current volt-
age at 50 amperes or 100 amperes
for large breakers, and at or below
rating for smaller breakers. The
millivolt drop is compared against
manufacturer's data for the breaker
being tested.
2.2.3. Connections test.- The con-
nections to the circuit breaker should
be inspected to determine that a good
joint is present and that overheating is
not occurring. If overheating is indi-
cated by discoloration or signs of
arcing, the connections should be re-
moved and the connecting surfaces
cleaned.
nections to the circuit breaker should
be inspected to determine that a good
joint is present and that overheating is
not occurring. If overheating is indi-
cated by discoloration or signs of
arcing, the connections should be re-
moved and the connecting surfaces
cleaned.
2.2.4. Overload tripping test.- The
proper action of the overload tripping
components of the circuit breaker can
be verified by applying 300 percent of
proper action of the overload tripping
components of the circuit breaker can
be verified by applying 300 percent of
(FIST 3-16 1/92)