Questions and Answers
What typically consists of a conductive link or links encapsulated in a tube for physical protection?
Fuse
The electrical resistance of the fuse link is so low, it simply acts as a(n) ___ during normal circuit operation.
Conductor
Overcurrent devices used in photovoltaic (PV) system DC circuits must be listed for use per 690.9(B) in the NEC.
True
Class RK1, Class J, and Class CF fuses rated 100 amperes are all physically interchangeable.
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The majority of commercially available fuses sold provide visual open fuse indication.
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Cartridge fuses in circuits of any voltage must be provided with a disconnecting means on their supply side.
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Typically, non-time-delay fuses use a(n) ___ element fuse construction.
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Certain Class J dual-element time-delay fuses can be sized closer than Class RK5 dual-element time-delay fuses for high-inrush loads.
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Dual-element time-delay fuses consist of two types of elements connected in parallel inside the fuse.
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The overload element of a 600-ampere or less branch-circuit dual-element time-delay fuse will hold an overload that is five times the ampere rating of the fuse for a minimum time of ___ seconds.
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Fuses can be identified as being a branch-circuit overcurrent protective device marked with ___ .
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Which is not a performance requirement for a Class J, time-delay fuse?
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Listed current-limiting fuses have ___ features that help prevent the installation of unsuitable fuses.
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Match the correct memory word for each type of fuse.
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Match the correct ampere rating range for each type of fuse.
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Match the correct interrupting rating for each type of fuse.
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For each type of fuse, identify whether it is current-limiting, non-current-limiting, or N/A (not applicable).
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Semiconductor fuses can be used to provide motor branch-circuit short-circuit and ground-fault protection.
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Supplementary fuses used to protect individual luminaires are allowed to be considered the final branch-circuit overcurrent protective device.
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The energy-reducing maintenance switch (ERMS) can reduce the energy released during an arcing fault current.
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Study Notes
Overview of Fuses
- A fuse consists of conductive links encased in a protective tube filled with granulated filler, such as silica sand, and includes connections for installation.
- In normal operation, the fuse link behaves as a conductor due to its very low electrical resistance.
Benefits of Current-Limiting Fuses
- Current-limiting fuses are known for high interrupting ratings suitable for high fault current applications.
- They ensure reliable overcurrent protection and provide effective short-circuit protection without the need for periodic calibration testing.
Fuse Applications and Standards
- Fuses listed to UL 248-19 are specifically designed for use in photovoltaic (PV) systems and are compliant with NEC requirements.
- While Class RK1, Class J, and Class CF fuses are rated for 600 volts AC, they must not be physically interchangeable due to differences in dimensions.
Fuse Visibility and Disconnection
- Most commercially available fuses do not indicate a visual failure when opened.
- A disconnecting means is required on the supply side for cartridge fuses in circuits over 150 volts to ground.
Fuse Types and Construction
- Non-time-delay fuses typically feature a single element construction, while dual-element time-delay fuses have both overload and short-circuit elements connected in series.
- The overload element of a dual-element time-delay fuse can handle overloads up to five times its rated amperage for at least 10 seconds.
Performance and Identification
- Fuses used for protecting services, feeders, and branch circuits are identifiable through specific UL classifications.
- Class J time-delay fuses are not resettable after a fault interruption, marking a key distinction from other fuse classes.
Features and Types of Fuses
- Current-limiting fuses include physical rejection features to prevent improper installations.
- Various classes of fuses have designated ampere rating ranges, e.g., Class CC fuses range from fractional to 30 A, while Class L fuses cover 601 to 6,000 A.
Interrupting Ratings
- Class CC fuses have interrupting ratings of 200 kA, while Class J and Class L fuses may have even higher ratings (200 kA or more).
- Non-current-limiting fuses, such as Class H fuses, are specifically noted for their lower interrupting capabilities compared to current-limiting fuses.
Special Conditions and Compatibility
- Semiconductor fuses, or high-speed fuses, provide essential protection for motor circuits equipped with electronic drives but require separate overload protection.
- Supplementary fuses for devices like luminaires cannot serve as the primary branch-circuit protection required by code.
Energy-Reducing Maintenance Switch (ERMS)
- The ERMS is designed to minimize energy release during arcing faults while an electrician works on energized circuits, enhancing safety during maintenance activities.
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Description
This quiz covers the fundamental aspects of fuses, including their structure, benefits, and specific applications in systems like photovoltaics. You'll learn about current-limiting fuses and the relevant standards that govern their usage, emphasizing the importance of reliable protection in electrical circuits.
