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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 - 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 techline@littelfuse.com 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...

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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...

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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...

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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...

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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...

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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...

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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...

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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...

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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,...

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