Circuit Breakers

While there are numerous types and variations of circuit breakers, they all have the same function: protecting the distribution system and utilization devices from overloads and short circuits. However, for breakers to adequately perform their intended function, they must be able to trip within the manufacturer's design parameters from the time that they are installed until they are replaced.

10/01/2004


While there are numerous types and variations of circuit breakers, they all have the same function: protecting the distribution system and utilization devices from overloads and short circuits. However, for breakers to adequately perform their intended function, they must be able to trip within the manufacturer's design parameters from the time that they are installed until they are replaced.

To assure this, the breakers should be exercised and tested on a regular basis. At least once per year, breaker handles should be operated to keep those portions of the mechanism operating freely. Every two years the breakers should be tested and tripped using primary current injection. This test will confirm that each breaker is operating within the manufacturer's tripping curves and it will also exercise all internal parts of the breaker, including the unlatching and tripping components that do not get exercised with the aforementioned handle operation.

Circuit Breaker Types

Molded Case Breakers

Insulated Case Breakers

Current Limiting Breakers

Power Air Circuit Breakers

Fused Circuit Breakers

Description

Molded plastic case, 80% or 100 % rated in larger sizes, interrupting duties from 10 to 100kAIC; commonly used for residential and most branch circuit applications, also used in retail and commercial switchboards

Glass reinforced case, 100% rated from 100 to 5,000 amps; interrupting duties from 42 to 150kAIC, solid-state digital tripping; typical uses are in commercial and light industrial applications

Generally molded or insulated case breakers, interrupting duties from 10 to 200kAIC, trip sizes from 15 through 600 amps

Rigid, open metal frame for longer life,100% rated, interrupting duties from 42 to 100kAIC, trip ranges from 200 to 5,000 amps

Interrupting duty of 200kAIC, generally molded case breaker

Advantages

Smaller size, lowest in cost

Fiberglass reinforced case fully adjustable; limited short time rating

Inherently current limiting both for themselves and for downstream devices; same case size as molded case breakers; digital, adjustable trip unit

Fully adjustable, microprocessor trip unit; may be fully repaired, maintained and adjusted; expected life on the order of 40 to 50 years; depending on usage and maintenance, short time rating allows better coordination with downstream equipment

High interrupting duty, small size for maximum interrupting duty

Disadvantages

Cannot be maintained or repaired; limited adjustability without selecting operational tripping unit; useful life in the 10- to 20-year range; may not be operational after a fully rated fault interruption

Cannot be maintained or repaired; useful life from 20 to 25 years; may not be operational after a fully rated fault interruption

Same disadvantages as other molded case breakers.

Large size, highest cost breaker

Protects only selected downstream lower rated over-current devices

Options

Electronic trip unit

May be electrically opened or closed

Variations

Ground fault circuit interrupting, arc-fault interrupting, heating/refrigeration rating DC rating

Every possible option is available

Same concept can be found on power air circuit breakers





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