Heavy-duty power circuit breakers employ spring-operated, stored-energy
mechanisms for quick-make, quick-break manual or electric operation.
Generally, these breakers have draw-out features whereby individual
breakers can be put into test and fully de-energized position for testing
and maintenance purposes. The electrically operated breakers are actuatedby a motor and cam system or a spring release solenoid for closing. Tripping
action is actuated by one or more trip solenoids (shunt trip coil) or fl uxoperated
devices; generally one for the protective devices on the breaker
itself, and another for externally mounted controls or protective devices. The
continuous frame ratings for these breakers range from 400 to 4000 A. Some
manufacturers have introduced breakers with 5000 and 6000 A frames; however,
the long-term benefi ts and overall reliability of these designs have yet to
be proven in the fi eld. Short-circuit interrupting capabilities for these breakers
are usually 50,000–85,000 A root-mean-square (rms) for frame sizes up to
4000 A. Larger designs have approached 100 kA. These breakers can be
extended for applications up to 200 kA interrupting when equipped with
assemblies or trucks designed to hold Class L, current-limiting power fuses.