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14 Cards in this Set
- Front
- Back
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CIRCUIT BREAKER DEFINITION
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A Circuit breaker is a device designed to open and close a circuit by non-automatic means and to open the circuit automatically on a predetermined overcurrent without injury to itself when properly applied within its rating.
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TYPES OF ABNORMAL CURRENT
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1. Overload current
2. Short circuit current 3. Ground fault current a. Leakage b. Arcing c. Bolted |
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Advantages of Fuses
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Fuse interrupting ratings are greater
Less expensive Simpler (mechanically) Less space requirement Current-limiting fuses limit fault current Easier to coordinate (more consistent) Fail-safe device |
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DISADVANTAGES OF FUSES
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Less accurate than protective relays
Single phasing possible No remote operation More hazardous ( during replacement) Destroys itself ( stock on hand) |
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CIRCUIT BREAKER FUNCTIONS
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1. Must be capable of closing onto and carrying full load current for long periods of time
2. Under prescribed conditions, it must open automatically to disconnect the load or small overloads 3. It must successfully and rapidly interrupt the heavy currents that flow when a short circuit exists in a system. 4. When its contacts open, the gap must be able to withstand circuit voltage. An arc should not be able to perpetuate itself in the gap. Necessary gap distance is a direct function of the arc extinguishing medium. 5. It must be capable of closing onto a fault current and immediately reopen to clear the fault. This is known as trip-free or release free operation. This is a condition where the CB trip/opening operation can prevail over the closing operation during specific parts of the closing operation. 6. It must be capable of carrying current of short-circuit magnitude until, and for such time, as the fault is cleared by another protective device (Fuse, Circuit breaker) nearer to the poi |
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FIVE FUNCTIONAL RATINGS OF CIRCUIT BREAKERS
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Voltage Rating
Frame Rating Continuous Rating Momentary Rating Interrupting Rating |
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VOLTAGE RATING
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The highest RMS voltage at which the device is designed to operate. (distance)
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FRAME RATING
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The maximum continuous current rating in amps of all parts except the overcurrent device.
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MOMENTARY RATING
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The current value which represents the mechanical strength limits of the device.
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CONTINUOUS CURRENT RATING
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A current value equal to or less than the frame rating.
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INTERRUPT RATING
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The highest current at rated voltage that the device can interrupt without external damage.
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CIRCUIT BREAKER TYPES
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Molded Case Circuit Breakers
Low Voltage Power Circuit Breakers High Voltage Power Circuit Breakers |
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FOUR METHODS OF ARC EXTINCTION
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Air
Oil Vacuum Gas ( Sulfur Hexafluoride/ SF6) |
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Applications
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Generator Circuit Breaker
Load Tie Breaker Feeder Breaker Load Service Breaker |
