Control Voltage
The Control Voltage (or secondary voltage), is usually secondary with respect to the voltage rating of the circuit in which the circuit breaker is applied. Control voltage is used to operate secondary devices. The voltage used to run the motor that charges a circuit breaker's springs automatically is an example.
Drawout
A drawout circuit breaker refers to a circuit breaker that can be moved within a compartment from one defined position to another without manually disconnecting any connections or turning off the line side power. This is usually accomplished through the use of a mechanical levering device, sometimes in combination with the manual assistance of an operator. This is called racking the circuit breaker into or out of a position. The circuit breaker is first opened, and then automatic main disconnect devices on a drawout circuit breaker allow for the circuit breaker to connect or disconnect from the bus. These automatic main disconnect devices are often referred to as Finger Clusters. The phrase finger cluster comes from the fact that many designs utilize a number of conductive pieces (fingers) assembled into one cluster. The four typical defined positions are:
• Connected
• Test
• Disconnect
• Remove (Withdrawn)
In the Connected position, the circuit breaker is into its compartment as far as it will go with both primary and secondary electrical connections made. The circuit breaker is now ready for normal operation .
In the Test position, the circuit breaker is farther out of its compartment with the primary electrical connections no longer made (Figure 9). Secondary electrical connections are still made in this position to provide the secondary power required to test the circuit breaker's operation, including the trip unit.
In the Disconnect position, the circuit breaker is even farther out of its compartment with the main Contacts open (Figure 10). Neither the primary nor secondary electrical connections are made. This is a typical compartment storage position for a circuit breaker not in use.
In the Remove (or Withdrawn) position, the circuit breaker is out of the compartment on extension rails with the main contacts open and the closing springs discharged (Figure 11). There are neither primary nor secondary electrical connections. This is the typical last position for a circuit breaker to be in before it is physically removed from its rails to another location.
Behind Door Drawout
This is related to the specific drawout breaker design (Figure 12). Behind the door drawout means that the breaker compartment door usually must be opened to Lever (or "rack") the breaker from one position to another as just discussed under "Drawout."
The breaker normally has a Faceplate Shield (or "deadfront shield") to protect the operator from dangerous voltages while the door is open. This type of design usually permits the breaker to be in any of three positions (Disconnect, Test, Connected) with the door closed. This design does not permit an individual to know the status of the circuit breaker or its trip unit without opening the compartment door.
Through Door Drawout
This is also a drawout related circuit breaker design (Figure 13). Through the door drawout permits the operator to lever the circuit breaker from the "Connected" position to the "Test" position to the "Disconnect" position and vice versa without opening the compartment door. The door has a hole in it to accommodate protrusion through the door of some small portion of the circuit breaker as it reaches a position well to the front of the compartment. The operator is also protected by a deadfront shield, usually a combination of the door and the faceplate of the circuit breaker. The benefits associated with this design are that a full view of the circuit breaker front is given along with access to the racking (drawout) device without opening the compartment door.
Continuous Current Rating
The Continuous Current Rating of a circuit breaker is the maximum current rating the breaker is designed to carry on a continuous basis and remain within the applicable guidelines for the breaker. It is also referred to as the "Frame Rating" or the "Frame Size."
100% Rated ANSI specifies that low voltage power circuit breakers are to be rated for continuous operation at 100% of their current ratings in their compartment. To meet these requirements, they are tested for operation within a specific enclosure and, therefore, do not need to be de-rated.
Interrupting Rating
The interrupting rating is the maximum short-circuit current that the circuit breaker can safely interrupt. ANSI prescribes its minimum preferred ratings for power circuit breakers to meet.
Short Time Rating
The short time rating of a low voltage power circuit breaker is the maximum value of current the circuit breaker is designed to handle safely for a short period of time (30 cycles or 0.5 seconds) in the closed position, without damage to the circuit breaker. This test is repeated twice for a total of one (1) second. The short time rating is usually equal to the 600 volt interrupting capacity. This attribute is one of the main features that differentiates a power circuit breaker from other types of circuit breakers and allows for system selectivity. The short time rating was also discussed earlier in this module.
Trip Free
When a circuit breaker is in a Trip Free condition, it cannot, by design, be closed. Even when intentional efforts are made to close the circuit breaker and it is in a trip free condition, the main contacts will not touch and the circuit breaker will automatically return to the tripped position. This is an important safety feature specific to power circuit breakers.
Current Sensor
Sensor, as used with respect to a circuit breaker, is a common term for a current transformer which steps current down to useful levels for a specific purpose, such as providing an input to a trip unit (circuit breaker's intelligence package).
The Control Voltage (or secondary voltage), is usually secondary with respect to the voltage rating of the circuit in which the circuit breaker is applied. Control voltage is used to operate secondary devices. The voltage used to run the motor that charges a circuit breaker's springs automatically is an example.
Drawout
A drawout circuit breaker refers to a circuit breaker that can be moved within a compartment from one defined position to another without manually disconnecting any connections or turning off the line side power. This is usually accomplished through the use of a mechanical levering device, sometimes in combination with the manual assistance of an operator. This is called racking the circuit breaker into or out of a position. The circuit breaker is first opened, and then automatic main disconnect devices on a drawout circuit breaker allow for the circuit breaker to connect or disconnect from the bus. These automatic main disconnect devices are often referred to as Finger Clusters. The phrase finger cluster comes from the fact that many designs utilize a number of conductive pieces (fingers) assembled into one cluster. The four typical defined positions are:
• Connected
• Test
• Disconnect
• Remove (Withdrawn)
In the Connected position, the circuit breaker is into its compartment as far as it will go with both primary and secondary electrical connections made. The circuit breaker is now ready for normal operation .
In the Test position, the circuit breaker is farther out of its compartment with the primary electrical connections no longer made (Figure 9). Secondary electrical connections are still made in this position to provide the secondary power required to test the circuit breaker's operation, including the trip unit.
In the Disconnect position, the circuit breaker is even farther out of its compartment with the main Contacts open (Figure 10). Neither the primary nor secondary electrical connections are made. This is a typical compartment storage position for a circuit breaker not in use.
In the Remove (or Withdrawn) position, the circuit breaker is out of the compartment on extension rails with the main contacts open and the closing springs discharged (Figure 11). There are neither primary nor secondary electrical connections. This is the typical last position for a circuit breaker to be in before it is physically removed from its rails to another location.
Behind Door Drawout
This is related to the specific drawout breaker design (Figure 12). Behind the door drawout means that the breaker compartment door usually must be opened to Lever (or "rack") the breaker from one position to another as just discussed under "Drawout."
The breaker normally has a Faceplate Shield (or "deadfront shield") to protect the operator from dangerous voltages while the door is open. This type of design usually permits the breaker to be in any of three positions (Disconnect, Test, Connected) with the door closed. This design does not permit an individual to know the status of the circuit breaker or its trip unit without opening the compartment door.
Through Door Drawout
This is also a drawout related circuit breaker design (Figure 13). Through the door drawout permits the operator to lever the circuit breaker from the "Connected" position to the "Test" position to the "Disconnect" position and vice versa without opening the compartment door. The door has a hole in it to accommodate protrusion through the door of some small portion of the circuit breaker as it reaches a position well to the front of the compartment. The operator is also protected by a deadfront shield, usually a combination of the door and the faceplate of the circuit breaker. The benefits associated with this design are that a full view of the circuit breaker front is given along with access to the racking (drawout) device without opening the compartment door.
Continuous Current Rating
The Continuous Current Rating of a circuit breaker is the maximum current rating the breaker is designed to carry on a continuous basis and remain within the applicable guidelines for the breaker. It is also referred to as the "Frame Rating" or the "Frame Size."
100% Rated ANSI specifies that low voltage power circuit breakers are to be rated for continuous operation at 100% of their current ratings in their compartment. To meet these requirements, they are tested for operation within a specific enclosure and, therefore, do not need to be de-rated.
Interrupting Rating
The interrupting rating is the maximum short-circuit current that the circuit breaker can safely interrupt. ANSI prescribes its minimum preferred ratings for power circuit breakers to meet.
Short Time Rating
The short time rating of a low voltage power circuit breaker is the maximum value of current the circuit breaker is designed to handle safely for a short period of time (30 cycles or 0.5 seconds) in the closed position, without damage to the circuit breaker. This test is repeated twice for a total of one (1) second. The short time rating is usually equal to the 600 volt interrupting capacity. This attribute is one of the main features that differentiates a power circuit breaker from other types of circuit breakers and allows for system selectivity. The short time rating was also discussed earlier in this module.
Trip Free
When a circuit breaker is in a Trip Free condition, it cannot, by design, be closed. Even when intentional efforts are made to close the circuit breaker and it is in a trip free condition, the main contacts will not touch and the circuit breaker will automatically return to the tripped position. This is an important safety feature specific to power circuit breakers.
Current Sensor
Sensor, as used with respect to a circuit breaker, is a common term for a current transformer which steps current down to useful levels for a specific purpose, such as providing an input to a trip unit (circuit breaker's intelligence package).
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