As briefly discussed earlier, low voltage power circuit breakers are usually available in the two following mounting configurations:
• Fixed
• Drawout
Total usage of low voltage power circuit breakers today is dominated by the drawout configuration because it provides for easier maintenance and continuity of service. Most circuit breaker manufacturers, however, offer both types.
Fixed Circuit Breaker
Fixed low voltage power circuit breakers usually have fixed primary conductor stabs protruding from the rear of the circuit breaker. The circuit breaker is bolted in position within its assembly compartment, and the rear conductor stabs are bolted to primary bus connections (Figure 30). Secondary connections are also made manually. Power must be turned off to the assembly to connect a fixed circuit breaker into the system or to remove it from the system.
Drawout Circuit Breaker
Drawout low voltage power circuit breakers have a levering device to move the circuit breaker from one compartment position to the next. Usually part of the levering mechanism is on the circuit breaker with a corresponding part is in its compartment. Working together, they provide the mechanical means required to move the circuit breaker. Drawout circuit breakers are designed to be removed and connected without cutting power to the entire assembly under load conditions because the circuit breaker, by design, automatically opens before racking can take place. This means that power to the assembly does not have to be turned off when a circuit breaker is removed from or inserted into the assembly, thus ensuring continuity of service.
Drawout circuit breaker compartments are provided with extension rails which, when not in use, are stored inside the compartment (Figure 31). The extension rails provide a means by which a drawout circuit breaker can be easily removed from its compartment for inspection, maintenance or movement to another area.
Primary electrical connections between the circuit breaker and the primary bus are automatically made or broken as the circuit breaker is moved into or out of the "Connected" position within the circuit breaker compartment. Primary connectors mounted to the back of the circuit breaker slide onto the primary bus connectors. These primary connectors, often called finger clusters or disconnect contacts, are frequently composed of a number of spring loaded fingers (contacts) . The number of fingers (contacts) used is dictated by the amount of current they will carry. Fingers (contacts) are made of an excellent conducting material or material combination, such as silver plated copper.
Secondary electrical connections are usually automatically made or broken as the circuit breaker is moved into and out of its compartment. As the circuit breaker is moved into the "Test" position from the "Disconnect" position, the secondary connections are made providing the required secondary power for testing or operating the breaker, but no primary power. The secondaries remain connected as the breaker moves into the "Connected" position. When the circuit breaker is moved out of the "Connected" position, the secondaries remain connected and stay connected until the circuit breaker is moved farther out of its compartment past the "Test" position. The graphics of the four positions presented earlier in the module demonstrate the movement and connections.
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Circui Breaker Operation
• Fixed
• Drawout
Total usage of low voltage power circuit breakers today is dominated by the drawout configuration because it provides for easier maintenance and continuity of service. Most circuit breaker manufacturers, however, offer both types.
Fixed Circuit Breaker
Fixed low voltage power circuit breakers usually have fixed primary conductor stabs protruding from the rear of the circuit breaker. The circuit breaker is bolted in position within its assembly compartment, and the rear conductor stabs are bolted to primary bus connections (Figure 30). Secondary connections are also made manually. Power must be turned off to the assembly to connect a fixed circuit breaker into the system or to remove it from the system.
Drawout Circuit Breaker
Drawout low voltage power circuit breakers have a levering device to move the circuit breaker from one compartment position to the next. Usually part of the levering mechanism is on the circuit breaker with a corresponding part is in its compartment. Working together, they provide the mechanical means required to move the circuit breaker. Drawout circuit breakers are designed to be removed and connected without cutting power to the entire assembly under load conditions because the circuit breaker, by design, automatically opens before racking can take place. This means that power to the assembly does not have to be turned off when a circuit breaker is removed from or inserted into the assembly, thus ensuring continuity of service.
Drawout circuit breaker compartments are provided with extension rails which, when not in use, are stored inside the compartment (Figure 31). The extension rails provide a means by which a drawout circuit breaker can be easily removed from its compartment for inspection, maintenance or movement to another area.
Primary electrical connections between the circuit breaker and the primary bus are automatically made or broken as the circuit breaker is moved into or out of the "Connected" position within the circuit breaker compartment. Primary connectors mounted to the back of the circuit breaker slide onto the primary bus connectors. These primary connectors, often called finger clusters or disconnect contacts, are frequently composed of a number of spring loaded fingers (contacts) . The number of fingers (contacts) used is dictated by the amount of current they will carry. Fingers (contacts) are made of an excellent conducting material or material combination, such as silver plated copper.
Secondary electrical connections are usually automatically made or broken as the circuit breaker is moved into and out of its compartment. As the circuit breaker is moved into the "Test" position from the "Disconnect" position, the secondary connections are made providing the required secondary power for testing or operating the breaker, but no primary power. The secondaries remain connected as the breaker moves into the "Connected" position. When the circuit breaker is moved out of the "Connected" position, the secondaries remain connected and stay connected until the circuit breaker is moved farther out of its compartment past the "Test" position. The graphics of the four positions presented earlier in the module demonstrate the movement and connections.
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