15
Circuit breakers interrupt electrical current to stop power flow both for switching
operations and during fault conditions.
operations and during fault conditions.
·
Molded case circuit breakers are usually located in low voltage distribution panels
and in control boards. These are typically 120-volts alternating current (Vac),
125-volts direct current (Vdc), 240-Vac, and 480-Vac breakers for control,
protection, and auxiliary power. Molded case breakers in panel boards should not
be loaded more than 80 percent of rating per NFPA 70B, 11-2.
and in control boards. These are typically 120-volts alternating current (Vac),
125-volts direct current (Vdc), 240-Vac, and 480-Vac breakers for control,
protection, and auxiliary power. Molded case breakers in panel boards should not
be loaded more than 80 percent of rating per NFPA 70B, 11-2.
·
Low voltage air breakers are usually located in motor starter cabinets, motor
control centers, station service switchgear, or similar enclosures. These are
typically 480 Vac for auxiliary power.
control centers, station service switchgear, or similar enclosures. These are
typically 480 Vac for auxiliary power.
·
Medium voltage circuit breakers are generally located in station-service metal
clad switchgear or in separate enclosures as unit breakers. Examples are
4160-Vac station service, 11.95-kV and 13.8-kV unit breakers. These breakers
may be air, air blast, vacuum, or SF6.
clad switchgear or in separate enclosures as unit breakers. Examples are
4160-Vac station service, 11.95-kV and 13.8-kV unit breakers. These breakers
may be air, air blast, vacuum, or SF6.
·
High voltage circuit breakers are located in separate breaker enclosures, either
indoors or outdoors. These are oil, air-blast, or SF6 breakers. Examples are
115-kV and 230-kV breakers located in the switchyard.
indoors or outdoors. These are oil, air-blast, or SF6 breakers. Examples are
115-kV and 230-kV breakers located in the switchyard.
·
Extra high voltage (EHV) circuit breakers are not addressed in this FIST volume.
Reference the manufacturer's instruction books.
Reference the manufacturer's instruction books.
Most breaker maintenance (except infrared scanning) must be performed with
equipment de-energized.
equipment de-energized.
Maintenance or Test
Recommended Interval
Reference
Review equipment ratings
5 years
NERC Planning Standard
Visual inspection
3-6 years
NFPA 70B, 11-8 and
Appendix H
Appendix H
Mechanical operation
by hand
by hand
3-6 years
NFPA 70B, 11-8 and
Appendix H
Appendix H
Infrared scan
Annually
NFPA 70B 18-17