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POWR-GARD Electrical Fuseology & Application Guide

POWR-GARD Electrical Fuseology & Application Guide

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POWR-GARD Electrical Fuseology & Application Guide

Product catalog summary

Fuseology Fundamentals

Overcurrent Protection: Essential for preventing damage to electrical systems from overcurrents, which can cause overheating, fires, and explosions. Overcurrent protection is mandated by standards such as NEC and OSHA.
Quality Overcurrent Protection: Must meet legal requirements, ensure safety, minimize damage, provide coordinated protection, be cost-effective, and require minimal maintenance.
Overcurrent Types: Includes overloads (excessive current in normal paths) and short-circuits (current flowing outside normal paths). Both require timely disconnection to prevent damage.

Selection Considerations

Current Rating: Fuses must match the system's normal running current and comply with NEC requirements.
Voltage Rating: Fuses must operate at or below their rated voltage. Exceeding this can cause fuse destruction.
Interrupting Rating: Indicates the maximum current a fuse can safely interrupt. Fuses should have ratings that exceed the available fault current.
Type of Protection: Fuses provide both overload and short-circuit protection, with inverse time characteristics ensuring faster response to higher currents.

Time-current Curves and Peak Let-through Charts

These tools help in understanding the response time of fuses to different levels of overcurrent, aiding in the selection of appropriate fuses for specific applications.

Selective Coordination

Ensures that only the protective device closest to the fault opens, minimizing system downtime and maintaining system integrity.

UL/CSA Fuse Classes and Applications

Different classes of fuses are designed for specific applications, each with unique characteristics and compliance requirements.

Terms and Definitions

Provides clarity on technical terms used throughout the guide, essential for understanding fuse application and selection.

Motor Protection Tables

Offers guidance on selecting fuses for motor protection, considering factors like starting currents and overload conditions.

UL Fuse Classes & Selection Chart

Aids in selecting the appropriate fuse class based on application requirements and system specifications.

Condensed Fuse Cross Reference

Provides a quick reference for comparing different fuse types and their applications.

Overview: The document provides a comprehensive guide on selecting the appropriate fuses for electrical applications, focusing on time-delay and fast-acting fuses. It discusses selection considerations, fuse types, and recommendations for various applications.

Selection Considerations: Key factors in selecting fuses include the available fault current, interrupting rating, and the specific application requirements. For instance, fuses in a main switchboard must have an A.I.R. of at least 125,000A, with a preference for time-delay fuses with 200,000 A.I.R.

Fast-Acting Fuses: These fuses open quickly without intentional delay, suitable for non-inductive loads. They provide fast short-circuit response but require additional overload protection devices for inductive loads.

Time-Delay Fuses: These fuses offer a delay to handle surges and short-time overloads, providing superior protection for motor and general-purpose circuits. They are current-limiting and can be rated closer to a circuit's operating current.

Dual Element Fuses: These fuses have separate elements for overload and short-circuit protection, offering enhanced protection and minimizing nuisance openings.

Very Fast-Acting Fuses: Designed for protecting solid-state electronic components, these fuses respond quickly to overloads and short-circuits, providing current-limiting protection.

Effect of Ambient Temperature: The current carrying capacity of fuses is affected by ambient temperature, requiring derating in higher temperatures.

Current Limitation: Current-limiting fuses open faults quickly, reducing peak let-through current and minimizing destructive heat energy.

Physical Size: The size of the fuse is determined by the fuse block or disconnect switch, with smaller fuses offering space-saving benefits but potentially less time-delay.

Indication: Indicating fuses provide visual identification of blown fuses, reducing downtime and improving safety.

General Fusing Recommendations: Recommendations are provided for fuses with ampere ratings from 1/10 to 6,000 amperes, emphasizing the use of time-delay fuses for superior protection.

Selection Considerations for Fuse Holders: Important factors include current and voltage ratings, physical size, and indication features. Additional considerations involve the number of poles, mounting configuration, and connector type.

Circuit Protection Checklist: A checklist is provided to guide the selection of overcurrent protective devices, considering factors like expected current, environmental conditions, and safety standards.

Understanding Time-current Curves: These curves graphically represent a fuse's operating characteristics, aiding in the selection of the appropriate fuse for specific applications.

Overview: The document provides a detailed technical guide on Littelfuse POWR-GARD® fuses, focusing on their performance characteristics, application, and coordination within electrical systems. It includes graphical representations and tables to illustrate fuse behavior under different conditions.

Specifications and Performance: The document explains the use of log-log paper to present performance information, with overcurrent values increasing from left to right and average melting times from bottom to top. It highlights the differences in response times between time-delay, fast-acting, and very fast-acting fuses, using figures and tables to compare average melting times and opening times for different amp ratings.

Peak Let-through Charts: These charts demonstrate the current-limiting ability of fuses by showing the maximum instantaneous current during the total clearing time. The document explains how current-limiting fuses reduce peak current during faults, using graphical examples to illustrate this effect.

Fuse Coordination: The document discusses selective coordination, emphasizing the importance of choosing overcurrent protective devices that ensure only the device immediately upstream of a fault opens. It provides guidance on using Fuse Coordination Tables to achieve selective coordination, ensuring that smaller fuses open before larger ones in a system.

NEC® Requirements: The document outlines NEC® requirements for selective coordination and short-circuit current ratings (SCCR), emphasizing the need for equipment to withstand overcurrents or be protected by current-limiting devices. It also mentions pre-engineered solutions to meet specific NEC® requirements for various systems.

Conclusion: The document serves as a comprehensive guide for selecting and coordinating Littelfuse POWR-GARD® fuses within electrical systems, providing technical insights and practical examples to ensure effective overcurrent protection.

Fuse Coordination and Selection
The document provides a detailed guide on selecting the correct fuse ampere ratio to maintain selectively coordinated systems. It includes a table (Table 4) that outlines the ratios expressed as Line-Side Fuse to Load-Side Fuse. The Littelfuse product line offers pre-engineered solutions like the LPS Series POWR-Switch and LCP Selective Coordination Panel, which comply with NEC requirements.

National Electrical Code (NEC) Requirements
The document references NEC Article 110, which covers the examination, identification, installation, and use of equipment, emphasizing the importance of interrupting ratings and circuit impedance. Article 240 discusses overcurrent protection, highlighting the need for effective protection to prevent excessive temperatures in conductors.

UL/CSA Fuse Classes and Applications
The document categorizes various fuse classes, including Class L, R, K, J, G, RK1, RK5, K5, T, CC/CD, K1, H, and plug fuses. Each class is described with its standards, voltage ratings, current ratings, interrupting ratings, and specific features like time delay and interchangeability. For instance, Class L fuses have a voltage rating of 600 volts and current ratings from 601-6000 amps, with an interrupting rating of up to 200,000 amps.

Supplementary Overcurrent Protection
Fuses for supplementary overcurrent protection are classified into micro fuses, miniature fuses, and miscellaneous cartridge fuses, each with specific voltage and current ratings. These fuses are designed for special applications and may be UL Recognized for use in UL Listed equipment.

Technical Definitions
The document includes definitions of technical terms such as adjustable alarm level, ampacity, ampere rating, and ampere-squared-seconds (I2t), which describe the thermal energy generated by current flow. It also explains concepts like arc-blast and arc-flash, which are critical for understanding the safety implications of electrical systems.

Arc Current and Arc Rating: The document discusses arc current for voltages of 600 volts and below, noting that arc gaps of 1.25 inches typically produce maximum incident energy. Arc rating is defined as the maximum incident energy a material can resist before breaking open or causing a second-degree burn, measured in cal/cm².

Arcing Current and Faults: Arcing current flows through a fuse after the fuse link melts until the circuit is interrupted. Arcing faults are short-circuits that arc at the fault point, reducing short-circuit current due to arc impedance. These faults can evolve into bolted faults.

Fuse Components and Types: The document defines various fuse components such as the body, contacts, and elements. It describes different types of fuses, including blade fuses, cartridge fuses, and dual-element fuses, each with specific characteristics and applications.

Protection Boundaries and Analysis: Boundaries of approach are established to protect personnel from shock and arc-flash hazards. Electrical hazard analysis identifies potential electrical hazards, addressing both shock and arc-flash risks.

Ground-Fault Protection: Ground-fault protection systems protect equipment from damaging ground-fault currents by opening all ungrounded conductors of a faulted circuit. Ground-fault relays detect phase-to-ground faults and trip when current exceeds set thresholds.

Incident Energy and Protection: Incident energy is the thermal energy generated during an electrical arc, measured in cal/cm². Flash hazard analysis determines exposure levels and establishes protection boundaries to prevent second-degree burns.

Interrupting Capacity and Ratings: Interrupting capacity is the highest symmetrical current a protective device can safely interrupt. The document explains the difference between interrupting capacity and interrupting rating, emphasizing the importance of standardized test conditions.

Grounding Systems: High-resistance grounding limits current to low levels using a neutral-ground resistor, while low-resistance grounding allows higher currents during ground faults. The document also discusses neutral grounding resistors and their role in current limitation.

Technical Application Guide Summary

1. Specifications and Definitions
This section provides definitions of key terms related to electrical systems and fuse applications. Important terms include:

Open CT Hazard: High voltage risk when CT secondary is open-circuited.
Overcurrent: Current exceeding equipment's rated capacity.
Overload: Overcurrent within normal path causing potential damage.
Peak Let-through Current: Maximum current passing through a protective device during clearing time.
Power Factor (X/R): Relationship between inductive reactance and resistance during faults.
Protection Boundaries: Boundaries to protect personnel from electrical hazards.
Selective Coordination: System where only the immediate protective device opens during a fault.

2. Fuse Applications and Ratings
This section discusses the selection and application of fuses for motor protection:

Time-Delay Fuses: Designed to withstand temporary overcurrents without opening immediately.
Motor Protection Tables: Guidelines for selecting fuse ratings based on motor horsepower and full load amperes (FLA).
Voltage Rating: Maximum voltage at which a fuse is designed to operate.

3. Motor Protection
Guidelines for selecting fuses for motor running protection based on motor horsepower and actual full load currents. The tables provide recommendations for:

Motor Running Protection: Fuse ratings without overload relays.
Back-up Motor Running Protection: Fuse ratings with overload relays.

4. Key Figures and Charts
Figures and charts illustrate concepts such as peak let-through current, symmetrical and asymmetrical currents, and threshold current determination. These visual aids help in understanding the behavior of electrical currents and the role of fuses in protection.

Specifications and Recommendations:

Ensure to check specific mounting dimensions before substituting components.
Verify fuse characteristics and mounting dimensions for the specific application before substitution.
For amperages between 1/10 and 30, order non-indicating FLNR series fuses.
Confirm voltage suitability for DC applications.
Littelfuse has discontinued Class H fuses and recommends upgrading to RK1 or RK5 Class fuses.

Voltage Rating Guidelines:

A fuse can be used in circuits where its voltage rating is equal to or greater than the circuit voltage, unless otherwise specified.
Example: The FLSR_ID indicating fuse has a voltage rating of 75-600 volts and can be used on circuits with voltages of 600, 480, 250, 125, or 75 volts.
Never use a fuse in a circuit with a higher rated voltage than the fuse itself.

Additional Information:

For more technical information and application data, visit littelfuse.com.
Contact the Technical Support Group at 800-TEC-FUSE for inquiries.
Specifications and descriptions are accurate as of the publication date but are subject to change without notice.

Catalog excerpts

POWR-GARD Electrical Fuseology & Application Guide-1

Application Guide POWR-GARD Technical Application Guide

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POWR-GARD Electrical Fuseology & Application Guide-2

This Technical Application Guide or ‘Fuseology’ provides the information needed to select the correct types of Littelfuse POWR-GARD® fuses for most applications. If there are any questions or if additional data is needed for a specific use, call the Littelfuse Technical Support and Engineering Service Group at 1-800-TEC-FUSE (1-800-832-3873), email them at [email protected] or visit us at littelfuse.com. Technical Information White papers, and a library of technical information is available online at littelfuse.com/technicalcenter © 2014 Littelfuse POWR-GARD® Products

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POWR-GARD Electrical Fuseology & Application Guide-3

Technical Application Guide FUSEOLOGY FUNDAMENTALS I. OVERCURRENT PROTECTION FUNDAMENTALS (FUSES AND HOW THEY WORK) Introduction 3. Minimizes overcurrent damage to property, equipment, and electrical systems. 4. Provides coordinated protection. Only the protective device immediately on the line side of an overcurrent opens to protect the system and minimize unnecessary downtime. An important part of developing quality overcurrent protection is an understanding of system needs and overcurrent protective device fundamentals. This section discusses these topics with special attention to the application...

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POWR-GARD Electrical Fuseology & Application Guide-4

Technical Application Guide FUSEOLOGY FUNDAMENTALS temperature of 150°C. Any currents larger than this may immediately vaporize organic insulations. Arcs at the point of fault or from mechanical switching such as automatic transfer switches or circuit breakers may ignite the vapors causing violent explosions and electrical flash. Even though government-mandated high-efficiency motors and NEMA Design E motors have much higher locked rotor currents, POWR-PRO® time-delay fuses such as the FLSR_ ID, LLSRK_ID, or IDSR series have sufficient time-delay to permit motors to start when the fuses are properly...

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POWR-GARD Electrical Fuseology & Application Guide-5

Technical Application Guide SELECTION CONSIDERATIONS Voltage Rating The recommendation to standardize on fuses with at least a 200,000 ampere interrupting rating (AIR) ensures that all fuses have an adequate interrupting rating while providing reserve interrupting capacity for future increases in available fault current. The voltage rating of a fuse is the maximum AC or DC voltage at which the fuse is designed to operate. Fuse voltage ratings must equal or exceed the circuit voltage where the fuses will be installed, and fuses used in DC circuits must be specifically rated for DC applications....

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POWR-GARD Electrical Fuseology & Application Guide-6

Technical Application Guide SELECTION CONSIDERATIONS circuit protection, and often permits the use of smaller, less expensive disconnect switches. Time-delay fuses have gradually replaced most one-time (UL Class K5) and renewable (UL Class H) fuses. Today, more than 50% of all fuses sold by electrical distributors are time-delay fuses. Fast-Acting (Normal-Opening) Fuses Fast-acting fuses (sometimes called “Normal-opening” fuses) have no intentional time-delay. Typical opening times at 500% of the fuse ampere rating range from 0.05 second to approximately 2 seconds. Fast-Acting fuses are suitable...

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POWR-GARD Electrical Fuseology & Application Guide-7

Technical Application Guide SELECTION CONSIDERATIONS Current Limitation Indication The newest consideration for selecting the best fuse for a given application is indication. Many of the more commonly used UL fuse classes are now available in both indicating and non-indicating versions. Built-in, blown-fuse indication that quickly identifies which fuse or fuses within an electrical panel or system have blown can be found on the Littelfuse POWR-PRO® LLSRK_ID Class RK1, FLNR_ID, FLSR_ID and IDSR Class RK5, and JTD_ID Class J fuse series. A current-limiting fuse is one that opens and clears a fault...

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POWR-GARD Electrical Fuseology & Application Guide-8

Technical Application Guide SELECTION CONSIDERATIONS Fuses with ampere ratings from 601 through 6,000 amperes • Screw – for use with spade lugs or ring terminals. For superior protection of most general-purpose and motor circuits, it is recommended to use the POWR-PRO® KLPC series Class L fuses. The Class L fuses are the only timedelay fuse series available in these higher ampere ratings. • Screw with Pressure Plate – for use with solid or stranded wire without terminal and recommended for applications where vibration will be a factor. • Box Lug – the most durable of the three options and used...

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POWR-GARD Electrical Fuseology & Application Guide-9

Technical Application Guide The performance capabilities of various fuses are graphically represented by two different types of fuse characteristic curves: time-current curves and peak let-through charts. These curves and charts define the operating characteristics of a given fuse, and assist system designers and engineers in selecting the proper fuse to protect equipment and electrical systems. Understanding Time-current Curves Time-current curves provide a graphical representation or plot of a fuse’s average melting (opening) time at any current. Time-current curves for Littelfuse POWR-GARD®...

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POWR-GARD Electrical Fuseology & Application Guide-10

Technical Application Guide FUSE CHARACTERISTIC CURVES AND CHARTS Peak current which would occur without current limitation The diagonal curves that branch off the A-B line illustrate the current-limiting effects of different fuse ampere ratings for a given fuse series. To continue the example from above, enter the chart in Figure 7 on the bottom at 100,000 rms symmetrical amperes and read upwards to the intersection of the 200 ampere fuse curve. Now read from this point horizontally to the left and read a peak let-through current of approximately 20,000 amperes. Peak Let-Thru Current What this...

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POWR-GARD Electrical Fuseology & Application Guide-11

Technical Application Guide FUSE CHARACTERISTICS CURVES AND CHARTS Only the overcurrent device immediately on the line side of an overcurrent will open for any overload or short-circuit condition. In a selective system, none of this occurs. Overloads and faults are disconnected by the overcurrent protective device immediately on the line side of the problem. The amount of equipment removed from service is minimized, the faulted or overloaded circuit is easier to locate, and a minimum amount of time is required to restore full service. Since the advent of electrical and electronic equipment, businesses...

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