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SPD - Selecting Protective Devices Based on the 2008 NEC ® $ 49 95 Value

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  • SPD - Selecting ProtectiveDevices

    Based on the 2008 NEC

    $4995Value

  • INSIDE FRONTCOVER

    BLANK

  • 32008 Cooper Bussmann

    Selecting Protective Devices Handbook (SPD)Based on the 2008 NEC

    Welcome to the Cooper Bussmann Selecting Protective Devices Handbook (SPD). This is a comprehensive guide to electrical overcurrent protection and electrical design considerations.Information is presented on numerous applications as well as the requirements of codes and standards for a variety of electrical equipment and distribution systems.

    How to Use:The SPD is comprised of major sections which are arranged by topic. There are three methods forlocating specific information contained within:

    1. Table of Contents: The table of contents sequentially presents the major sections and their contents. New or revised sections are noted in red text.

    2. Index: The index, found on page 265, is more detailed than the table of contents and is organized alphabetically by topic with corresponding page number references.

    3. 2008 NEC Section Index: The NEC Section Index, found on page 264, makes it easy to find information associated with specific National Electrical Code section references.

    For other technical resources and product information visit www.cooperbussmann.com.

    This handbook is intended to clearly present product data and technical information that will help the end user with design applications. Cooper Bussmann reserves the right, without notice, to change design orconstruction of any products and to discontinue or limit their distribution. Cooper Bussmann also reserves the right to change or update, without notice, any technical information contained in this handbook. Oncea product has been selected, it should be tested by the user in all possible applications. Further, Cooper Bussmann takes no responsibility for errors or omissions contained in this handbook, or for mis-applicationof any Cooper Bussmann product. Extensive product and application information is available online at: www.cooperbussmann.com.National Electrical Code is a trademark of the National Fire Protection Association, Inc., Batterymarch Park, Quincy, Massachusetts, for a triennial electrical publication. The term, National Electrical Code, asused herein means the triennial publication constituting the National Electrical Code and is used with permission of the National Fire Protection Association, Inc.

    Introduction

  • 4 2008 Cooper Bussmann

    2008 SPD Introduction . . . . . . . . . . . . . . . . . . .3Benefits Offered By Fuses . . . . . . . . . . . . . . .5Fuseology . . . . . . . . . . . . . . . . . . . . . . . . .6 - 31

    Overcurrents and Voltage Ratings . . . . . . . . . . . . . . .6Voltage Ratings & Slash Voltage Ratings . . . . . . . . .7Amp Rating and Interrupting Rating . . . . . . . . . .8 - 10Selective Coordination & Current Limiting . . . . . . . .11Non Time-Delay Fuse Operation . . . . . . . . . . . . . . .12Dual-Element, Time-Delay Fuse Operation . . . . . . .13Dual-Element Fuse Benefits . . . . . . . . . . . . . . .14 - 15Branch Circui & Application Limited

    Overcurrent Protective Devices . . . . . . . . . . .16 - 20Branch Circuit Fuse Selection Chart (600V or less) 21Branch Circuit Fuse Dimensions . . . . . . . . . . .22 - 23Cooper Bussmann Branch Circuit,

    Power Distribution Fuses . . . . . . . . . . . . . . . .24 - 25Disconnects, Panelboards, & One-Time Fuses . . . .26Fuse Holders, Fuse Blocks, Power Distribution

    Blocks & Surge Suppression . . . . . . . . . . . . . . . .27High Speed Fuses . . . . . . . . . . . . . . . . . . . . . .28 - 29Medium Voltage Fuses . . . . . . . . . . . . . . . . . . .30 - 31

    Applying Interrupting Rating: Circuit Breakers . . . . . . . . . . . . . . . . . .32 - 57Interrupting Rating Vs. Interrupting Capacity . .32 - 34Single-Pole Interrupting Capability . . . . . . . . . .35 - 40Series Rating: Protecting Circuit Breakers . . . .41 - 46- Square D Series Rating Chart . . . . . . . . . . . .47 - 48- Cutler-Hammer Series Rating Chart . . . . . . .49 - 51- General Electric Series Rating Chart . . . . . . .52 - 55- Siemens Series Rating Chart . . . . . . . . . . . . .56 - 57

    Conductor Protection General . . . . .58 - 60General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58Small Conductors . . . . . . . . . . . . . . . . . . . . . . . . . . .58Tap Conductors . . . . . . . . . . . . . . . . . . . . . . . . . .58-59

    Cable Limiters Applications . . . . . . . . . . .61Conductors & Terminations

    Applications . . . . . . . . . . . . . . . . . . . . .62 - 64Equipment Protection . . . . . . . . . . . . . . .65 - 75

    General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64 - 68Transformers 600V or Less . . . . . . . . . . . . .69 - 70Transformers Over 600V . . . . . . . . . . . . . . .71 - 72Photovoltaic (PV) Systems . . . . . . . . . . . . . . .73 - 75

    Component Protection . . . . . . . . . . . . . .76 - 86Introduction and Current-Limitation . . . . . . . . . . . . .76How To Use Current-Limitation Charts . . . . . . .77 - 78Wire & Cable . . . . . . . . . . . . . . . . . . . . . . . . . .79 - 81Tap Conductor Sizing . . . . . . . . . . . . . . . . . . . . . . . .81Small Wire (16 & 18 AWG) . . . . . . . . . . . . . . . . . . .81Busway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82-83HVAC and Refrigeration Equipment . . . . . . . . . . . .84Transfer Switches . . . . . . . . . . . . . . . . . . . . . . . . . .85Ballasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86

    Industrial Control Panels . . . . . . . . . . .87 - 107Short-Circuit Current Rating

    Marking Requirements . . . . . . . . . . . . . . . . . . .87-88Determining Assembly SCCR:

    Two Sweep Method . . . . . . . . . . . . . . . . . . . .89 - 90Umbrella Fuse Limits . . . . . . . . . . . . . . . . . . . .91 - 93Determining Assembly SCCR: Example . . . .94 - 104Increasing Assembly SCCR . . . . . . . . . . . . . .105-107

    Selective Coordination . . . . . . . . . . . .108 - 146Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108Fuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109 - 111Fuse Selectivity Ratio Guide . . . . . . . . . . . . .112 -113Fusible Lighting Panels . . . . . . . . . . . . . . . . . . . . .114Fuse Selective Coordination Example . . . . . . . . . .115Circuit Breakers: Operation Basics . . . . . . . .116 -118Circuit Breakers:

    Achieving Selective Coordination . . . . . . . .119 -125Fuse & Circuit Breaker Mixture . . . . . . . . . . . . . . .126Mandatory Selective Coordination Requirements .127Why Selective Coordination is Mandatory . . .128 -130System Considerations . . . . . . . . . . . . . . . . .131 -135OCPD Choices for Selective Coordination . .136 -137Inspection Checklist . . . . . . . . . . . . . . . . . . . . . . . .138Objections & Misunderstandings . . . . . . . . . .139-144Elevator Circuits . . . . . . . . . . . . . . . . . . . . . .145 -146

    Ground Fault Protection . . . . . . . . . .147 - 157Introduction & Requirements . . . . . . . . . . . .147 - 149Overcurrent Protective Devices . . . . . . . . . . . . . . .150GFPR Considerations . . . . . . . . . . . . . . . . . .151 - 155Current-Limitation . . . . . . . . . . . . . . . . . . . . .156 - 157

    Electrical Safety . . . . . . . . . . . . . . . . .158 - 170Introduction . . . . . . . . . . . . . . . . . . . . . . . . . .158 -159Arc-Flash Protection . . . . . . . . . . . . . . . . . . .160 -162Maintenance Considerations . . . . . . . . . . . . . . . . .163Arc-Flash Hazard Analysis . . . . . . . . . . . . . . . . . . .164Arc-Flash Incident Energy Calculator . . . . . .165 -167Arc-Flash Hazard Analysis . . . . . . . . . . . . . .168 -169Arc-Flash Protection Marking . . . . . . . . . . . .168 -170

    Devices for Motor Circuits . . . . . . . . .171 - 180Branch Circuit Devices and Disconnect

    Selection Tables: . . . . . . . . . . . . . . . . . . . .171 - 173Motor Branch Circuit Devices . . . . . . . . . . . .174 -179Motor Circuit Branch Circuit Protection

    Is Resettability of Value? . . . . . . . . . . . . . . . . . .180

    Motor Protection . . . . . . . . . . . . . . . . .181 - 189Voltage Unbalance & Single-Phasing . . . . . .181 - 186Basic Explanation . . . . . . . . . . . . . . . . . . . . .187 - 189

    Motor Branch Circuit Protection NEC 430.52 Explanation . . . . . . . . . . . . .190

    Motor Circuit Notes . . . . . . . . . . . . . . . . . . .191Motor Circuits Group Switching . . . . . .192Motor Circuit Protection Tables . . . .193 - 207

    NEC Article 430 and Tables Explanation . .193 - 194200Vac Three-Phase Motors & Circuits . . . .194 - 195208Vac Three-Phase Motors & Circuits . . . .195 - 196230Vac Three-Phase Motors & Circuits . . .197 - 198460Vac Three-Phase Motors & Circuits . . .198 - 199575Vac Three-Phase Motors & Circuits . . .200 - 201115Vac Single-Phase Motors & Circuits . . . . . . . .202230Vac Single-Phase Motors & Circuits . . . . . . . .20390Vdc Motors & Circuits . . . . . . . . . . . . . . . . . . . .204120Vdc Motors & Circuits . . . . . . . . . . . . . . . . . . .205180Vdc Motors & Circuits . . . . . . . . . . . . . . . . . . .206240Vdc Motors & Circuits . . . . . . . . . . . . . . .206 - 207

    Motor Protection Tips For Electricians & Maintenance Crews . . . . . . . . . . . . . . . .208

    Motor Starter Protection . . . . . . . . . .209 - 212Graphic Explanation . . . . . . . . . . . . . . . . . . .209 - 210Low Voltage Motor Controllers . . . . . . . . . . . . . . . .211Type 1 Versus Type 2 Protection . . . . . . . . . . . . . .212

    Table of Contents (Red indicates NEW or significantly REVISED information)

    Motor Controller & Fuse Selection For Type 2 Protection . . . . . . . . . . . .213 - 227General Electric Company IEC . . . . . . . . . . . . .213General Electric Company NEMA . . . . . .214 - 216Rockwell Automation, Allen-Bradley IEC . . . . . .217Rockwell Automation, Allen-Bradley NEMA . . .218Square D Company IEC . . . . . . . . . . . . .219 - 221Square D Company NEMA . . . . . . . . . . . . . . . .222Siemens IEC . . . . . . . . . . . . . . . . . . . . . . . . . . .223Siemens NEMA . . . . . . . . . . . . . . . . . . . . . . . . .224Cutler Hammer Freedom Series IEC . . . .225 - 226Cutler Hammer Freedom Series NEMA . . . . . .227

    Motor Circuits With Power Electronic Devices Power Electronic Device Circuit Protection . . . . . . . . . . . . . . .228 - 230

    Motor Circuit Protection Group Motor Protection . . . . . . . . . . . . . .231

    Motor Control Circuit Protection . . . .232 - 235Medium Voltage Motor Circuits

    R-Rated Medium Voltage Fuses . . . . . . . .236Cost of Ownership . . . . . . . . . . . . . . .237 - 238

    Fusible Equipment vs. Circuit Breaker Equipment 237Preventive Maintenance . . . . . . . . . . . . . . . . . . . .238

    Short Circuit Current Calculations . .239 - 245Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .239Three-Phase Short Circuits . . . . . . . . . . . . . . . . . .241Single-Phase Short Circuits . . . . . . . . . . . . .242 - 243Impedance & Reactance Data . . . . . . . . . . . . . . . .244Conductors & Busways "C" Values . . . . . . . . . . . .245

    Voltage Drop Calculations . . . . . . . . .246 - 248Ratings of Conductors and Tables to

    Determine Volt Loss . . . . . . . . . . . . . . . . . . . . . .246Copper Conductors Ratings & Volt Loss . . . . . .247Aluminum Conductors Ratings & Volt Loss . . .248

    Fuse Diagnostic Sizing Charts . . . . .249 - 253Ballasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .249Capacitors (NEC 460) . . . . . . . . . . . . . . . . . . . . .249Electric Heat (NEC 424) . . . . . . . . . . . . . . . . . . . .250Mains, Feeders, Branches . . . . . . . . . . . . . . . . . . .250Motor Loads (NEC 430) . . . . . . . . . . . . . . . . . . . .251Solenoids (Coils) . . . . . . . . . . . . . . . . . . . . . . . . . .251Transformers 600V Nominal or Less . . . . . . . . . . .252Transformers Over 600V Nominal . . . . . . . . . . . . .253Solid State Devices . . . . . . . . . . . . . . . . . . . . . . . .253

    Fuse Sizing Guide Building Electrical Systems . . . . . . . . . . .254

    Fuse Specifications . . . . . . . . . . . . . .255 - 256Suggestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .255Suggested Fuse and Fusible

    Equipment Specifications . . . . . . . . . . . . . . . . . .256

    Cooper Bussmann Current-Limiting Fuse Let-Through Data . . . . . . . . . .257 - 261

    Glossary . . . . . . . . . . . . . . . . . . . . . . . .262 - 263Electrical Formulas . . . . . . . . . . . . . . . . . . .2632008 NEC Section Index . . . . . . . . . . . . . .264Index . . . . . . . . . . . . . . . . . . . . . . . . . . . .265-266Fuse Cross Reference & Low-Peak

    Fuse Upgrade . . . . . . . . . .Inside Back Cover

    Cooper Bussmann Selecting Protective Devices

  • 2008 Cooper Bussmann 5

    Benefits Offered By Fuses

    High Interrupting Rating of 200,000 Amps or More

    Modern current-limiting fuses have high interrupting ratings at no extra cost.Whether for the initial installation or system updates, a fusible system canmaintain a sufficient interrupting rating. This helps with achieving high assembly short-circuit current ratings. See pages 6 to 8 for FuseologyInterrupting Rating details.

    Type 2 Protection

    Type 2 No Damage protection of motor starters when applied properly. Seepage 164 for details on Type 1 versus Type 2 protection.

    High SCCR

    High assembly short-circuit current ratings can be achieved. See pages 78 to88 for Industrial Control Panels.

    Rejection Features

    Modern current-limiting fuses have rejection features which assure replacement with a device of the same voltage rating and equal or greaterinterrupting rating. In addition, rejection features restrict the fuses used forreplacement to ones of the same class or type.

    Flexibility

    Increased flexibility in panel use and installation. Valuable time that was spentgathering information for proper application is drastically reduced with fusessince:

    Fuses can be installed in systems with available fault currents upto 200kA or 300kA covering the majority of installations that exist.

    Fuses can handle line-to-ground fault currents up to their markedinterrupting rating where mechanical devices often have singlepole interrupting capabilities far less than their marked IR (typically 8,660 amps for any marked IR) See pages 6 to 8 and33 to 34 for Fuse Single Pole Interrupting Ratings and pages 29to 34 for Circuit Breaker Single Pole Interrupting Capabilities.

    Fuses have a straight voltage rating instead of a slash voltage rating. A device with a slash voltage rating is limited to installationin ONLY a solidly grounded wye type system. Fuses can beinstalled in any type of installation independent of the groundingscheme used. See pages 5 to 6 for Slash Voltage Rating.

    Reliability

    Fuses provide reliable protection throughout the life of the installation. After afault occurs, fuses are replaced with new factory calibrated fuses assuring thesame level of protection that existed previous to the fault. Resettable devicesmay not provide the same level of protection following a fault and need to betested for calibration and possibly replaced.

    No Venting

    Fuses do not VENT. Therefore fuses will not affect other components in thepanel while clearing a fault. Additional guards or barriers which isolate devicesthat vent from other components are not required.

    Helps Regulation Compliance

    Eliminates invitation to reset into a fault and potential OSHA violation.Resetting or manually reenergizing a circuit without investigating the cause isprohibited in OSHA CFR29:1910-334. Fuses are not resettable and eliminatethe invitation to reset. See page 132 for Is Resettability of Value?

    Workplace Safety

    Superior current limitation provides enhanced workplace safety. See pages116 to 126 for Electrical Safety.

    Component Protection Via Current Limitation

    Superior current limitation provides protection of circuit components for eventhe most susceptible components such as equipment grounding conductors.See pages 67 to 77 for Component Protection and pages 78 to 88 forIndustrial Control Panels.

    Selective Coordination

    Achieving selective coordination is simple. Typically selective coordination canbe achieved between current-limiting fuses by simply maintaining a minimumamp ratio between upstream and downstream fuses. This can aid in diagnostics within the building electrical system or machine panel as only theeffected circuit is isolated. Selective coordination helps isolate faulted circuitsfrom the rest of the system and prevents unnecessary power loss to portionsof a building. See pages 9 and 88 to 105 for Selective Coordination.

    Specify the Cooper Bussmann

    Low-Peak System

    Safety Built-in rejection features Selective coordination with a

    minimum 2:1 ratio Maximum current-limiting protection

    for distribution equipment Type "2" Protection for motor starters Only one type of fuse throughout building Reduces inventory 300,000A interrupting rating May reduce arc-flash hazard

    M

    M

    KRP-C_SP

    KRP-C_SP KRP-C_SP

    LP-CC

    LPS-RK_SPLPS-RK_SP

    LPS-RK_SP

    LPJ_SPI

    LPJ_SP

    LPJ_SP

    FeederFor MCC

    Branch ForLarge Motor

    Feeder ForMLO Lighting

    Panel

    Branch ForResistance

    Load

    ResistanceLoad

    20A CircuitBreakersReduced

    VoltageStarter For

    Large Motor

    LP1

    Selecting Protective Devices

  • 6Electrical distribution systems are often quite complicated. They cannot beabsolutely fail-safe. Circuits are subject to destructive overcurrents. Harshenvironments, general deterioration, accidental damage or damage from natural causes, excessive expansion or overloading of the electrical distribution system are factors which contribute to the occurrence of suchovercurrents. Reliable protective devices prevent or minimize costly damageto transformers, conductors, motors, and the other many components andloads that make up the complete distribution system. Reliable circuit protectionis essential to avoid the severe monetary losses which can result from powerblackouts and prolonged downtime of facilities. It is the need for reliable protection, safety, and freedom from fire hazards that has made the fuse awidely used protective device.

    field stresses. The magnetic forces between bus bars and other conductorscan be many hundreds of pounds per linear foot; even heavy bracing may notbe adequate to keep them from being warped or distorted beyond repair.

    Fuses

    The fuse is a reliable overcurrent protective device. A fusible link or linksencapsulated in a tube and connected to contact terminals comprise the fundamental elements of the basic fuse. Electrical resistance of the link is solow that it simply acts as a conductor. However, when destructive currentsoccur, the link very quickly melts and opens the circuit to protect conductorsand other circuit components and loads. Modern fuses have stable characteristics. Fuses do not require periodic maintenance or testing. Fuseshave three unique performance characteristics:

    1. Modern fuses have an extremely high interrupting ratingcan open very high faultcurrents without rupturing.

    2. Properly applied, fuses prevent blackouts. Only the fuse nearest a fault opens with-out upstream fuses (feeders or mains) being affectedfuses thus provide selectivecoordination. (These terms are precisely defined in subsequent pages.)

    3. Fuses provide optimum component protection by keeping fault currents to a lowvalueThey are said to be current- limiting.

    2008 Cooper Bussmann

    Fuseology

    Overcurrents and Voltage Ratings

    Fuses are constructed in an almost endless variety of configurations. These photosdepict the internal construction of Cooper Bussmann Dual-Element, Semi-Tron andLow-Peak Class L fuses.

    Overcurrents

    An overcurrent is either an overload current or a short-circuit current. Theoverload current is an excessive current relative to normal operating current,but one which is confined to the normal conductive paths provided by the conductors and other components and loads of the distribution system. As thename implies, a short-circuit current is one which flows outside the normalconducting paths.

    Overloads

    Overloads are most often between one and six times the normal current level.Usually, they are caused by harmless temporary surge currents that occurwhen motors start up or transformers are energized. Such overload currents,or transients, are normal occurrences. Since they are of brief duration, anytemperature rise is trivial and has no harmful effect on the circuit components.(It is important that protective devices do not react to them.)

    Continuous overloads can result from defective motors (such as worn motorbearings), overloaded equipment, or too many loads on one circuit. Such sustained overloads are destructive and must be cut off by protective devicesbefore they damage the distribution system or system loads. However, sincethey are of relatively low magnitude compared to short-circuit currents,removal of the overload current within a few seconds to many minutes willgenerally prevent equipment damage. A sustained overload current results inoverheating of conductors and other components and will cause deteriorationof insulation, which may eventually result in severe damage and short circuitsif not interrupted.

    Short Circuits

    Whereas overload currents occur at rather modest levels, the short-circuit orfault current can be many hundred times larger than the normal operating current. A high level fault may be 50,000A (or larger). If not cut off within amatter of a few thousandths of a second, damage and destruction canbecome rampantthere can be severe insulation damage, melting of conductors, vaporization of metal, ionization of gases, arcing, and fires.Simultaneously, high level short-circuit currents can develop huge magnetic-

    The Louisiana Superdome in New Orleans is the worlds largest fully enclosed stadium. The overall electrical load exceeds 30,000,000 VA. Distribution circuits areprotected with Cooper Bussmann Low-Peak fuses.

    Voltage Rating - General

    This is an extremely important rating for overcurrent protective devices(OCPDs). The proper application of an overcurrent protective device accordingto its voltage rating requires that the voltage rating of the device be equal to orgreater than the system voltage. When an overcurrent protective device isapplied beyond its voltage rating, there may not be any initial indicators.Adverse consequences typically result when an improperly voltage rateddevice attempts to interrupt an overcurrent, at which point it may self-destructin an unsafe manner. There are two types of OCPD voltage ratings: straightvoltage rated and slash voltage rated.

    The proper application is straightforward for overcurrent protective deviceswith a straight voltage rating (i.e.: 600V, 480V, 240V) which have been evaluated for proper performance with full phase-to-phase voltage used duringthe testing, listing and marking. For instance, all fuses are straight voltagerated and there is no need to be concerned about slash ratings. However,some mechanical overcurrent protective devices are slash voltage rated (i.e.:480/277, 240/120, 600/347). Slash voltage rated devices are limited in theirapplications and extra evaluation is required when they are being considered for use. The next section covers fuse voltage ratings followed by asection on slash voltage ratings for other type devices.

  • 7Fuses are a universal protective device. They are used in power distribution systems,electronic apparatus, vehiclesand as illustrated, our space program. The SpaceShuttle has over 600 fuses installed in it protecting vital equipment and circuits.

    Voltage Rating-Fuses

    Most low voltage power distribution fuses have 250V or 600V ratings (otherratings are 125, 300, and 480 volts). The voltage rating of a fuse must be atleast equal to or greater than the circuit voltage. It can be higher but neverlower. For instance, a 600V fuse can be used in a 208V circuit. The voltagerating of a fuse is a function of its capability to open a circuit under an overcurrent condition. Specifically, the voltage rating determines the ability ofthe fuse to suppress the internal arcing that occurs after a fuse link melts andan arc is produced. If a fuse is used with a voltage rating lower than the circuitvoltage, arc suppression will be impaired and, under some overcurrent conditions, the fuse may not clear the overcurrent safely. 300V rated fuses canbe used to protect single-phase line-to-neutral loads when supplied fromthree-phase, solidly grounded, 480/277V circuits, where the single-phase line-to-neutral voltage is 277V. This is permissible because in this application, a300V fuse will not have to interrupt a voltage greater than its 300V rating.Special consideration is necessary for semiconductor fuse applications, wherea fuse of a certain voltage rating is used on a lower voltage circuit.

    Slash Voltage Ratings

    Some multiple-pole, mechanical overcurrent protective devices, such as circuitbreakers, self-protected starters, and manual motor controllers, have a slashvoltage rating rather than a straight voltage rating. A slash voltage rated overcurrent protective device is one with two voltage ratings separated by aslash and is marked such as 480Y/277V or 480/277V. Contrast this to astraight voltage rated overcurrent protective device that does not have a slashvoltage rating limitation, such as 480V. With a slash rated device, the lower ofthe two ratings is for overcurrents at line-to-ground voltages, intended to becleared by one pole of the device. The higher of the two ratings is for overcurrents at line-to-line voltages, intended to be cleared by two or threepoles of the circuit breaker or other mechanical overcurrent device.

    Slash voltage rated overcurrent protective devices are not intended to openphase-to-phase voltages across only one pole. Where it is possible for fullphase-to-phase voltage to appear across only one pole, a full or straight ratedovercurrent protective device must be utilized. For example, a 480V circuitbreaker may have to open an overcurrent at 480V with only one pole, such asmight occur when Phase A goes to ground on a 480V, B-phase, cornergrounded delta system.

    The NEC addresses slash voltage ratings for circuit breakers in 240.85restricting their use to solidly grounded systems where the line to ground voltage does not exceed the lower of the two values and the line voltage doesnot exceed the higher value.

    430.83(E) was revised for the 2005 NEC to address the proper application ofmotor controllers marked with a slash voltage rating. The words "solidlygrounded" were added to emphasize that slash voltage rated devices are notappropriate for use on corner grounded delta, resistance grounded andungrounded systems.

    Slash voltage rated OCPDs must be utilized only on solidly grounded systems.This automatically eliminates their usage on impedance-grounded andungrounded systems. They can be properly utilized on solidly grounded, wyesystems, where the voltage to ground does not exceed the devices lower voltage rating and the voltage between any two conductors does not exceedthe devices higher voltage rating. Slash voltage rated devices cannot be usedon corner-grounded delta systems whenever the voltage to ground exceedsthe lower of the two ratings. Where slash voltage rated devices will not meetthese requirements, straight voltage rated overcurrent protective devices arerequired.

    Overcurrent protective devices that may be slashed rated include, but are notlimited to:

    Molded case circuit breakers UL489 Manual motor controllers UL508 Self protected Type E combination starters UL508 Supplementary protectors UL1077 (Looks like a small circuit

    breaker and sometimes referred to as mini-breaker. However,these devices are not a circuit breaker, they are not rated forbranch circuit protection and can not be a substitute where branchcircuit protection is required.)

    What about fuses, do they have slash voltage ratings? No, fuses do not havethis limitation. Fuses by their design are full voltage rated devices; thereforeslash voltage rating concerns are not an issue when using fuses. For instance,Cooper Bussmann Low-Peak LPJ (Class J) fuses are rated at 600V. Thesefuses could be utilized on systems of 600V or less, whether the system issolidly grounded, ungrounded, impedance grounded, or corner groundeddelta.

    If a device has a slash voltage rating limitation, product standards requirethese devices, such as circuit breakers, manual motor controllers, self protected starters, or supplementary protectors to be marked with the ratingsuch as 480Y/277V. If a machine or equipment electrical panel utilizes a slashvoltage rated device inside, it is recommended that the equipment nameplateor label designate this slash voltage rating as the equipment voltage rating.UL508A industrial control panels requires the electrical panel voltage markingto be slash rated if one or more devices in the panel are slash voltage rated.

    2008 Cooper Bussmann

    Fuseology

    Voltage Ratings and Slash Voltage Ratings

    A

    B

    C

    480Y/277 Voltthree phase,four wire,solidlygrounded,wye system

    Circuit breaker 480Y/277 slash voltage rating 480 volts

    Line-to-line

    Ground

    N

    277 voltsLine-to-ground

  • 8Slash voltage devices are limited in application to solidly grounded, wye systems due to the nature of the way that these devices are tested, listed andlabeled. Any piece of equipment that utilizes a slash voltage rated overcurrentprotective device is therefore, limited to installation only in a solidly grounded,wye system and should require marking that notes this limitation.

    Equipment that utilizes straight voltage rated overcurrent protective devicesprovides more value and utilization to the owner or potential future ownersthan equipment that utilizes slash voltage rated devices. In todays businessenvironment, machinery and equipment may be moved several times duringits useful life. Equipment utilizing slash voltage rated overcurrent devices isnot suitable for many electrical systems found in industrial environments.

    Amp Rating

    Every fuse has a specific amp rating. In selecting the amp rating of a fuse,consideration must be given to the type of load and code requirements. Theamp rating of a fuse normally should not exceed the current carrying capacityof the circuit. For instance, if a conductor is rated to carry 20A, a 20A fuse isthe largest that should be used. However, there are some specific circumstances in which the amp rating is permitted to be greater than the current carrying capacity of the circuit. A typical example is motor circuits;dual-element fuses generally are permitted to be sized up to 175% and non-time-delay fuses up to 300% of the motor full-load amps. As a rule, the amprating of a fuse and switch combination should be selected at 125% of thecontinuous load current (this usually corresponds to the circuit capacity, whichis also selected at 125% of the load current). There are exceptions, such aswhen the fuse-switch combination is approved for continuous operation at100% of its rating.

    Testing Knife-Blade Fuses

    A common practice when electricians are testing fuses is to touch the endcaps of the fuse with their probes. Contrary to popular belief, fuse manufacturers do not generally design their knife-blade fuses to have electrically energized fuse caps during normal fuse operation. Electrical inclu-sion of the caps into the circuit occurs as a result of the coincidental mechanical contact between the fuse cap and terminal extending through it. Inmost brands of knife-blade fuses, this mechanical contact is not guaranteed;therefore, electrical contact is not guaranteed. Thus, a resistance readingtaken across the fuse caps is not indicative of whether or not the fuse is open.

    In a continuing effort to promote safer work environments, Cooper Bussmannhas introduced newly designed versions of knife-blade Fusetron fuses (ClassRK5) and knife-blade Low-Peak fuses (Class RK1) for some of the amp rat-ings. The improvement is that the end caps are insulated to reduce the possi-bility of accidental contact with a live part. With these improved fuses, theinformed electrician knows that the end caps are isolated. With older stylenon-insulated end caps, the electrician doesnt really know if the fuse is hotor not. A portion of all testing-related injuries could be avoided by proper test-ing procedures. Cooper Bussmann hopes to reduce such injuries by informingelectricians of proper procedures.

    Interrupting Rating

    A protective device must be able to withstand the destructive energy of short-circuit currents. If a fault current exceeds a level beyond the capability of theprotective device, the device may actually rupture, causing additional damage.Thus, it is important when applying a fuse or circuit breaker to use one whichcan sustain the largest potential short-circuit currents. The rating which definesthe capacity of a protective device to maintain its integrity when reacting tofault currents is termed its interrupting rating. The interrupting rating of mostbranch-circuit, molded case, circuit breakers typically used in residential service entrance panels is 10,000A. (Please note that a molded case circuitbreakers interrupting capacity will typically be lower than its interrupting rating.) Larger, more expensive circuit breakers may have interrupting ratingsof 14,000A or higher. In contrast, most modern, current-limiting fuses have aninterrupting rating of 200,000 or 300,000A and are commonly used to protectthe lower rated circuit breakers. The National Electrical Code 110.9, requiresequipment intended to break current at fault levels to have an interrupting rating sufficient for the current that must be interrupted. The subjects of interrupting rating and interrupting capacity are treated later in more detail.

    2008 Cooper Bussmann

    Fuseology

    Amp Rating and Interrupting Rating

    Always Test atthe Blade

    InsulatedCaps A continuity test across

    any knife-blade fuse

    should be taken ONLYalong the fuse blades.

    Do NOT test a knife-blade fuse

    with meter probes

    to the fuse caps.

    This photograph vividly illustrates theeffects of overcurrents on electrical components when protective devices arenot sized to the amp rating of the component.

    Non-Insulated

    Caps

  • 2008 Cooper Bussmann 9

    Fuseology

    Interrupting Rating

    The following series of images from high-speed film demonstrate the destructive power associated with short-circuit currents.

    The first group of photos depicts a test conducted on a 480V circuit breaker. The breaker has an interrupting rating of 14,000A, however, the test circuit was capable of delivering50,000A of short-circuit current at 480V. The results can be seen below.

    1 2 4

    4321

    Before FaultDuring Interruption After Interruption

    3

    This second group of photos uses the same test circuit as the previous test, however, the test subjects are a pair of 600V, one-time fuses with an interrupting rating of 10,000A. Notice in this test, as well as the circuit breaker test, the large amount of destructive energy released by these devices. Misapplying overcurrent protective devices in this manner is a serious safety hazard as shrapnel and molten metal could strike electricians or maintenance personnel working on equipment, or anyone whohappens to be nearby.

    This last group depicts the same test circuit as the previous two tests, which is 50,000A available at 480V. This time the test was performed with modern current-limiting fuses. Thesehappen to be Cooper Bussmann Low-Peak fuses with a 300,000A interrupting rating. Notice that the fault was cleared without violence.

  • 10

    The table below depicts four different situations involving an overcurrentdevice with a normal current rating of 100A and an interrupting rating of only10,000A.

    As depicted in the diagram that follows, when using overcurrent protectivedevices with limited interrupting rating, it becomes necessary to determine theavailable short-circuit currents at each location of a protective device. The faultcurrents in an electrical system can be easily calculated if sufficient information about the electrical system is known. (See the Point-to-PointMethod for Short Circuit Calculations, pages 192 to 198.) With modern fuses,these calculations normally are not necessary since the 200,000A or 300,000Ainterrupting rating is sufficient for most applications.

    Also, if using circuit breakers or self-protected starters, it may be necessary toevaluate the devices individual pole interrupting capability for the level of faultcurrent that a single pole of a multi-pole device may have to interrupt. This iscovered in-depth in the Single-Pole Interrupting Capability section on pages29 to 34.

    2008 Cooper Bussmann

    Fuseology

    Interrupting Rating

    P rote ct ive De v ic

    In the first three instances above, the circuit current condition is within the safeoperating capabilities of the overcurrent protective device. However, the fourthcase involves a misapplication of the overcurrent device. A short circuit on theload side of the device has resulted in a fault current of 50,000A flowingthrough the overcurrent device. Because the fault current is well above theinterrupting rating of the device, a violent rupture of the protective device andresulting damage to equipment or injury to personnel is possible. The use ofhigh interrupting rated fuses (typically rated at 200,000 or 300,000A) wouldprevent this potentially dangerous situation.

    The first paragraph of NEC 110.9 requires that the overcurrent protectivedevice be capable of interrupting the available fault current at its line terminals.

  • 11

    Selective Coordination Prevention of Blackouts

    The coordination of protective devices prevents system power outages orblackouts caused by overcurrent conditions. When only the protective devicenearest a faulted circuit opens and larger upstream fuses remain closed, theprotective devices are selectively coordinated (they discriminate). The wordselective is used to denote total coordinationisolation of a faulted circuit bythe opening of only the localized protective device.

    Current-Limitation Component Protection

    2008 Cooper Bussmann

    Fuseology

    Selective Coordination & Current Limitation

    Fuse opens and clearsshort-circuit in lessthan 1/

    2 cycle

    Initiation ofshort-circuit current

    Normalload current

    Areas within waveformloops represent destructiveenergy impressed uponcircuit components

    Circuit breaker tripsand opens short-circuitin about 1 cycle2:1 (or more)

    LPS-RK600SP

    LPS-RK200SP

    KRP-C1200SP

    2:1 (or more)

    This diagram shows the minimum ratios of amp ratings of Low-Peak fuses that arerequired to provide selective coordination (discrimination) of upstream and down-stream fuses.

    Unlike electro-mechanical inertial devices (circuit breakers), it is a simple matter to selectively coordinate fuses of modern design. By maintaining a minimum ratio of fuse-amp ratings between an upstream and downstreamfuse, selective coordination is achieved. Minimum selectivity ratios for CooperBussmann fuses are presented in the Selectivity Ratio Guide in FuseSelective Coordination section. Adherence to the tabulated selectivity ratiosnormally proves adequate.

    This book has an indepth discussion on coordination. See sections FuseSelective Coordination and Circuit Breaker Coordination.

    This burnt-out switchboard represents the staggering monetary losses in equipmentand facility downtime that can result from inadequate or deteriorated protectivedevices. It emphasizes the need for reliable protective devices that properly functionwithout progressive deterioration over time.

    A non-current-limiting protective device, by permitting a short-circuit current to buildup to its full value, can let an immense amount of destructive short circuit heat energy through before opening the circuit.

    In its current-limiting range, a current-limiting fuse has such a high speed of responsethat it cuts off a short circuit long before it can build up to its full peak value.

    If a protective device cuts off a short-circuit current in less than one-half cycle,before it reaches its total available (and highly destructive) value, the devicelimits the current. Many modern fuses are current-limiting. They restrict faultcurrents to such low values that a high degree of protection is given to circuitcomponents against even very high short-circuit currents. They permit breakers with lower interrupting ratings to be used. They can reduce bracingof bus structures. They minimize the need of other components to have highshort-circuit current withstand ratings. If not limited, short-circuit currents canreach levels of 30,000 or 40,000A or higher (even above 200,000A) in the firsthalf cycle (0.008 seconds, 60Hz) after the start of a short circuit. The heat thatcan be produced in circuit components by the immense energy of short-circuitcurrents can cause severe insulation damage or even explosion. At the sametime, huge magnetic forces developed between conductors can crack insula-tors and distort and destroy bracing structures. Thus, it is important that a protective device limit fault currents before they reach their full potential level.

    See Current-Limitation section and Fuse Let-Through Charts Analysis sectionfor in-depth discussion. See Fuse Current-Limiting Let-Through Charts sectionfor Cooper Bussmann fuse data.

  • 12

    The principles of operation of the modern, current-limiting Cooper Bussmannfuses are covered in the following paragraphs.

    Non-Time-Delay Fuses

    The basic component of a fuse is the link. Depending upon the amp rating ofthe fuse, the single-element fuse may have one or more links. They are electrically connected to the end blades (or ferrules) (see Figure 1) andenclosed in a tube or cartridge surrounded by an arc quenching filler material.Cooper Bussmann Limitron and T-Tron fuses are both single-element fuses.

    Under normal operation, when the fuse is operating at or near its amp rating, itsimply functions as a conductor. However, as illustrated in Figure 2, if an overload current occurs and persists for more than a short interval of time, thetemperature of the link eventually reaches a level that causes a restricted segment of the link to melt. As a result, a gap is formed and an electric arcestablished. However, as the arc causes the link metal to burn back, the gapbecomes progressively larger. Electrical resistance of the arc eventually reaches such a high level that the arc cannot be sustained and is extinguished. The fuse will have then completely cut off all current flow in thecircuit. Suppression or quenching of the arc is accelerated by the filler material.

    Single-element fuses of present day design have a very high speed ofresponse to overcurrents. They provide excellent short circuit component protection. However, temporary, harmless overloads or surge currents maycause nuisance openings unless these fuses are oversized. They are bestused, therefore, in circuits not subject to heavy transient surge currents andthe temporary overload of circuits with inductive loads such as motors, transformers, solenoids, etc. Because single-element, fast-acting fuses suchas Limitron and T-Tron fuses have a high speed of response to short-circuitcurrents, they are particularly suited for the protection of circuit breakers withlow interrupting ratings.

    Whereas an overload current normally falls between one and six times normalcurrent, short-circuit currents are quite high. The fuse may be subjected toshort-circuit currents of 30,000 or 40,000A or higher. Response of current-limiting fuses to such currents is extremely fast. The restricted sections of thefuse link will simultaneously melt (within a matter of two or three-thousandthsof a second in the event of a high-level fault current).

    The high total resistance of the multiple arcs, together with the quenchingeffects of the filler particles, results in rapid arc suppression and clearing of thecircuit. (Refer to Figures 4 & 5) Short-circuit current is cut off in less than ahalf-cycle, long before the short-circuit current can reach its full value (fuseoperating in its current-limiting range).

    2008 Cooper Bussmann

    Fuseology

    Non Time-Delay Fuse Operation

    With continued growth in electricalpower generation, the higher levelsof short-circuit currents made available at points of consumptionby electrical utilities have greatlyincreased the need for protectivedevices with high short-circuit interrupting ratings. The trend islower impedance transformers dueto better efficiencies, lower costs,and utility deregulation. Utilities routinely replace transformers serving customers. These transformers can have larger kVAratings and/or lower impedance,which results in higher availableshort-circuit currents. Devices thatcan interrupt only moderate levels ofshort-circuit currents are beingreplaced by modern fuses havingthe ability to cut-off short-circuit currents at levels up to 300,000amps.

    Figure 1. Cutaway view of typical single-element fuse.

    Figure 2. Under sustained overload, a section of the link melts and

    an arc is established.

    Figure 3. The open single-element fuse after opening a circuit

    overload.

    Figure 4. When subjected to a short-circuit current, several

    sections of the fuse link melt almost instantly.

    Figure 5. The open single-element fuse after opening a shorted

    circuit.

  • 13

    There are many advantages to using these fuses. Unlike single-element fuses,the Cooper Bussmann dual-element, time-delay fuses can be sized closer toprovide both high performance short circuit protection and reliable overloadprotection in circuits subject to temporary overloads and surge currents. ForAC motor loads, a single-element fuse may need to be sized at 300% of anAC motor current in order to hold the starting current. However, dual-element,time-delay fuses can be sized much closer to motor loads. For instance, it is generally possible to size Fusetron dual-element fuses, FRS-R and FRN-Rand Low-Peak dual-element fuses, LPS-RK_SP and LPN-RK_SP, at 125%and 130% of motor full load current, respectively. Generally, the Low-Peakdual-element fuses, LPJ_SP, and CUBEFuse, TCF, can be sized at 150% ofmotor full load amps. This closer fuse sizing may provide many advantagessuch as: (1) smaller fuse and block, holder or disconnect amp rating and physical size, (2) lower cost due to lower amp rated devices and possiblysmaller required panel space, (3) better short circuit protection less short-circuit current let-through energy, and (4) potential reduction in the arc-flashhazard.

    When the short-circuit current is in the current-limiting range of a fuse, it is notpossible for the full available short-circuit current to flow through the fuse itsa matter of physics. The small restricted portions of the short circuit elementquickly vaporize and the filler material assists in forcing the current to zero.The fuse is able to limit the short-circuit current.

    Overcurrent protection must be reliable and sure. Whether it is the first day ofthe electrical system or thirty, or more, years later, it is important that overcurrent protective devices perform under overload or short circuit conditions as intended. Modern current-limiting fuses operate by very simple,reliable principles.

    2008 Cooper Bussmann

    Fuseology

    Dual-Element, Time-Delay Fuse Operation

    Short circuit element

    Overload element

    Spring

    Filler quenches the arcs

    Small volume of metal to vaporize

    Filler materialInsulated end-caps to help preventaccidental contact with live parts.

    Before

    After

    Figure 6. This is the LPS-RK100SP, a 100A, 600V Low-Peak, Class RK1, dual-element fuse that has excellent time-delay, excellent current-limitation and a300,000A interrupting rating. Artistic liberty is taken to illustrate the internal portion ofthis fuse. The real fuse has a non-transparent tube and special small granular, arc-quenching material completely filling the internal space.

    Figure 7. The true dual-element fuse has distinct and separate overload element andshort circuit element.

    Figure 8. Overload operation: Under sustained overload conditions, the trigger spring fractures the calibrated fusing alloy and releases the connector.The insets represent a model of the overload elementbefore and after. The calibrated fusing alloy connectingthe short circuit element to the overload element fractures at a specific temperature due to a persistentoverload current. The coiled spring pushes the connector from the short circuit element and the circuitis interrupted.

    Figure 9. Short circuit operation: Modern fuses are designed with minimum metal inthe restricted portions which greatly enhance their ability to have excellent current-limiting characteristics minimizing the short circuit let-through current. Ashort-circuit current causes the restricted portions of the short circuit element tovaporize and arcing commences. The arcs burn back the element at the points of thearcing. Longer arcs result, which assist in reducing the current. Also, the special arcquenching filler material contributes to extinguishing the arcing current. Modern fuseshave many restricted portions, which results in many small arclets all workingtogether to force the current to zero.

    Figure 10. Short circuit operation: The special small granular, arc-quenching materialplays an important part in the interruption process. The filler assists in quenching thearcs; the filler material absorbs the thermal energy of the arcs, fuses together andcreates an insulating barrier. This process helps in forcing the current to zero.Modern current-limiting fuses, under short circuit conditions, can force the current tozero and complete the interruption within a few thousandths of a second.

  • 14

    Advantages of Cooper Bussmann

    Dual-Element, Time-Delay Fuses

    Cooper Bussmann dual-element, time-delay fuses have four distinct advantages over single-element, non-time-delay fuses:

    1. Provide motor overload, ground fault and short circuit protection.

    2. Permit the use of smaller and less costly switches.

    3. Give a higher degree of short circuit protection (greater current limitation) in circuitsin which surge currents or temporary overloads occur.

    4. Simplify and improve blackout prevention (selective coordination).

    Motor Overload and Short Circuit Protection

    provides ground fault and short-circuit protection, requiring separate overloadprotection per the NEC. In contrast, the 40A dual-element fuse providesground fault, short circuit and overload protection. The motor would be protected against overloads due to stalling, overloading, worn bearings,improper voltage, single-phasing, etc.

    In normal installations, Cooper Bussmann dual-element fuses of motor-running, overload protection size, provide better short circuit protection plus ahigh degree of back up protection against motor burnout from overload or single-phasing should other overload protective devices fail. If thermal overloads, relays, or contacts should fail to operate, the dual-element fuseswill act independently and thus provide back-up protection for the motor.

    When secondary single-phasing occurs, the current in the remaining phasesincreases to a value of 173% to 200% of rated full-load current. When primarysingle-phasing occurs, unbalanced voltages that occur in the motor circuit alsocause excessive current. Dual-element fuses sized for motor overload protection can help protect motors against the overload damage caused bysingle-phasing. See the section Motor ProtectionVoltage Unbalance/Single-Phasing for discussion of motor operation during single-phasing.

    2008 Cooper Bussmann

    Fuseology

    Dual-Element Fuse Benefits

    When used in circuits with surge currents such as those caused by motors,transformers, and other inductive components, the Cooper Bussmann Low-Peak and Fusetron dual-element, time-delay fuses can be sized close to full-load amps to give maximum overcurrent protection. Sized properly, they willhold until surges and normal, temporary overloads subside. Take, for example,a 10 HP, 200 volt, three-phase motor with a full-load current rating of 32.2A.

    The preceding table shows that a 40A, dual-element fuse will protect the32.2A motor, compared to the much larger, 100A, single-element fuse thatwould be necessary. It is apparent that if a sustained, harmful overload of200% occurred in the motor circuit, the 100A, single-element fuse would neveropen and the motor could be damaged. The non-time-delay fuse, thus, only

    Permit the Use of Smaller and Less Costly Switches

    Aside from only providing short-circuit protection, the single-element fuse alsomakes it necessary to use larger size switches since a switch rating must beequal to or larger than the amp rating of the fuse. As a result, the larger switchmay cost two or three times more than would be necessary were a dual-element Low-Peak or Fusetron fuse used. The larger, single-element fuseitself could generate an additional cost. Again, the smaller size switch that canbe used with a dual-element fuse saves space and money. (Note: where larger switches already are installed, fuse reducers can be used so that fusescan be sized for motor overload or back-up protection.)

    Better Short Circuit Component Protection

    (Current-Limitation)

    The non-time-delay, fast-acting fuse must be oversized in circuits in whichsurge or temporary overload currents occur. Response of the oversized fuseto short-circuit currents is slower. Current builds up to a higher level before thefuse opensthe current-limiting action of the oversized fuse is thus less thana fuse whose amp rating is closer to the normal full-load current of the circuit.Therefore, oversizing sacrifices some component protection.

  • 15

    In the table above, it can be seen that the 40A Low-Peak dual-element fuseused to protect a 10Hp (32.2 FLA) motor keeps short-circuit currents toapproximately half the value of the non-time-delay fuse.

    Better Selective Coordination (Blackout Prevention)

    The larger an upstream fuse is relative to a downstream fuse (for example,feeder to branch), the less possibility there is of an overcurrent in the downstream circuit causing both fuses to open (lack of selective coordination).Fast-acting, non-time-delay fuses require at least a 3:1 ratio between the amprating of a large upstream, line-side Low-Peak time-delay fuse and that of thedownstream, loadside Limitron fuse in order to be selectively coordinated. Incontrast, the minimum selective coordination ratio necessary for Low-Peakdual-element fuses is only 2:1 when used with Low-Peak loadside fuses.

    Better Motor Protection in Elevated Ambients

    The derating of dual-element fuses based on increased ambient temperaturesclosely parallels the derating curve of motors in an elevated ambient. Thisunique feature allows for optimum protection of motors, even in high temperatures.

    2008 Cooper Bussmann

    Fuseology

    Dual-Element Fuse Benefits

    The use of time-delay, dual-element fuses affords easy selective coordinationcoordination hardly requires anything more than a routine checkof a tabulation of required selectivity ratios. As shown in the preceding illustration, close sizing of Cooper Bussmann dual-element fuses in the branchcircuit for motor overload protection provides a large difference (ratio) in theamp ratings between the feeder fuse and the branch fuse, compared to thesingle-element, non-time-delay Limitron fuse.

    Affect of ambient temperature on operating characteristics of Fusetron and Low-Peak dual-element fuses.

    Below is a rerating chart for single element fuses or non dual element fuses.

    Ambient affect chart for non-dual-element fuses.

  • 16 2008 Cooper Bussmann

    Fuseology

    Branch-Circuit & Application Limited OCPDs

    Branch-Circuit OCPDs & Application Limited OCPDsIn most cases, branch circuit overcurrent protective devices (OCPD) are theonly type of overcurrent protective devices permitted to be used to protectelectrical building system mains, feeders and branch circuits, and in utilizationequipment mains, feeders and branch circuits. Yet, too often OCPDs whichare not branch circuit rated are misapplied where a branch circuit rated OCPDis required. However, the branch circuit overcurrent protective device termcan be difficult to grasp due to the multiple ways the electrical industry usesthe phrase branch circuit, and since most manufacturers do not identify theirovercurrent protective devices with the specific wording branch circuit overcurrent protective device.Not using a branch circuit OCPD where required could result in potentiallyserious electrical safety hazards to people or damage to property. In additionNational Electrical Code violations could be tagged by the authority havingjurisdiction (AHJ), resulting in project delays and unplanned costs.

    There are three types of overcurrent protective devices discussed in this section:

    1. Branch circuit overcurrent protective devices: can be used for protection of the entire circuit on a main, feeder or branch of an electrical system

    2. Application limited: the device is suitable for specific branch circuit applications under limited conditions per the NEC(often listed or recognized for the specific use)

    3. Application limited: supplementary protective device (cannot be used for branch circuit applications under any circumstances)

    NEC Article 100 offers the following definition for a branch circuit overcurrentdevice:

    With the definition, it becomes clear that a branch circuit overcurrent protectivedevice is suitable for use at any point in the electrical system to protect branchcircuits, as well as feeder circuits and mains. The definition also illustrates thata branch circuit overcurrent device must be capable of protecting against thefull range of overcurrents which includes overloads and short-circuits as wellas have an interrupting rating sufficient for the application (this reflects theinterrupting rating requirements of 110.9). In addition to the traits described inthe definition, branch circuit overcurrent devices meet minimum common standardized requirements for spacings and operating time-current characteristics.

    Branch-Circuit Overcurrent Device. A device capable of providing protection for service, feeder, and branch-circuits and equipment over thefull-range of overcurrents between its rated current and its interrupting rating. Branch-circuit overcurrent protective devices are provided with interrupting ratings appropriate for the intended use but no less than 5,000 amperes.

    Table 1 lists acceptable branch circuit overcurrent device types along withCooper Bussmann fuse part numbers. Branch circuit OCPDs can be used inany circuit, unlike the application limited OCPDs.

    Listed Branch Circuit OCPDs

    Product standards establish the minimum level of safety for a given producttype by having certain minimum product performance criteria and physicalspecifications. The commercial products listed to a product standard mustmeet the minimum performance criteria of that specific product standard.However, in addition, commercial products may have performance better thanthe minimum of the standard or other performance criteria not addressed inthe product standard.

    Fuses and circuit breakers each have their own separate product standards.There are significant differences in the minimum level of safety performanceincorporated in the product standards for current-limiting fuses versus productstandards for circuit breakers. Specifically, the discussion will focus on current-limiting fuses and molded case circuit breakers. The safety system ofeach of these product technologies differs considerably. Table 2 identifies several key characteristics of the electrical safety system offered by fuses andmolded case circuit breakers.

    Device Type Acceptable DevicesCooper Bussmann

    Branch Circuit FusesClass J Fuse LPJ_SP, JKS, DFJ, TCF*

    Class RK1 FuseLPN-RK_SP, LPS-RK_SP

    KTN-R, KTS-RClass RK5 Fuse FRN-R, FRS-R

    UL 248 Fuses Class T Fuse JJN, JJSClass CC Fuse LP-CC, KTK-R, FNQ-RClass L Fuse KRP-C_SP, KLU, KTUClass G Fuse SCClass K5 Fuse NON, NOS (0-60A)Class H Fuse NON, NOS (61-600A)

    UL 489 Molded Case CBsCircuit Breakers Insulated Case CBs

    UL 1066 Low VoltageCircuit Breakers Power CBs

    *TCF fuse have Class J performance and special finger-safe dimensions

    Table 1

    Acceptable Branch Circuit Overcurrent

    Protective Device Types

  • 172008 Cooper Bussmann

    Branch-Circuit & Application Limited OCPDs

    Equipment Has Rejects Replacement Rejects Replacement Rejects Replacement Rejects ReplacementFuse Mounting of Other UL Fuse of Lower Voltage of Fuses with IR Less of Fuses Classes with

    for UL Fuse Fuse Classes Rated Fuses Than 200kA Greater Short-CircuitClass Below Energy Let Through

    L, J, CC, T, G Yes Yes Yes Yes

    Class RYes Yes Yes Yes(RK1 and RK5)

    Equipment Has Rejects Replacement Rejects Replacement Rejects Replacement Rejects ReplacementCB Mounting with Other CB Type with Lower Voltage with Lower Interrupting of CB Having Higher

    for Type Below Rated CB Rated CB Short-CircuitEnergy Let Through

    Molded CaseNo No No NoCircuit Breaker

    Molded CaseCircuit Breaker

    No No No NoMarked

    Current-limiting

    Fu

    se

    Sa

    fety

    Sy

    ste

    m p

    er

    Pro

    du

    ct

    Sta

    nd

    ard

    s

    Mo

    lded

    -Case C

    ircu

    it B

    reake

    r

    Safe

    ty S

    yste

    m p

    er

    Pro

    du

    ct

    Sta

    nd

    ard

    s

    Molded-Case Circuit Breakers (MCCB) & Fuse Safety Systems

    Table 2

    Fuseology

  • 18 2008 Cooper Bussmann

    Fuseology

    Listed Branch Circuit Fuses: Current-LimitingUL248 Standards cover distinct classes of low-voltage (600 volts or less)fuses. Of these, modern current-limiting fuse Classes J, CC, L, R, T and G arethe most important. The rejection feature of current-limiting fuses ensures asafety system for the life of the electrical system. Listed current-limiting fuseshave physical size rejection features that help prevent installation of fuses thatcannot provide a comparable minimum level of protection for critical ratingsand performance. This is inherent in all current-limiting fuse classes. Eachfuse class found in Table 1 on page 14 has certain criteria that must be met.These include

    1. Maximum let-through limits (Ip and I2t ) during fault conditions

    2. Minimum voltage ratings3. Minimum interrupting ratings (200kA for Class J, T, R, CC and L)4. Physical rejection of larger fuse amperages* 5. Physical rejection of non-current limiting fuses *Amperages greater than fuse holder rating (i.e. 30A fuse holder will notaccept 35A fuse)

    By meeting these product standard requirements, the fuse industry providesbranch circuit fuses that ensure a minimum specific level of circuit protection,when current-limiting fuses and equipment are used. Using a given fuse classwill secure the voltage rating, interrupting rating and degree of current limitation for the life of the electrical system. This can be thought of as asafety system since the physical mounting configuration only permits thesame specific fuse class to be installed. Each class of current-limiting fuseshas its own unique physical dimensions so that fuses of a different class arenot interchangeable. For instance, Class R fuses cannot be installed in ClassJ fuse equipment. Modern Class J, CC, L, R, T, and G fuse equipment rejectsthe installation of any other fuse class. The fuse class dimensions on page 21exhibit the dimensional rejection characteristic of modern current-limitingfuses. Class R has two categories: Class RK5 and RK1 which are interchangeable, but no other fuse class can be installed. Class H, an olderstyle fuse class, is not considered current-limiting and is not recommended fornew installations. Class R fuses can be installed in Class H fuse equipmentas an upgrade. However, Class H fuses cannot be installed in Class R fuse equipment. Class R equipment physically rejects the installation of Class Hfuses.

    Listed Branch Circuit Molded-Case Circuit BreakersThe safety system for circuit breakers is not near as stringent. The initialthought of many people is that this is acceptable, since circuit breakers areresettable. However, that is faulty thinking. Circuit breakers frequently needto be replaced and in addition, circuit breakers are often added to existingequipment in spare spaces for new circuits. Or in the industrial control panelmarket, during the procurement process, a lower cost circuit breaker is mistakenly thought to be equivalent to an existing specified circuit breaker. It is easy to mistakenly substitute a lesser rated molded case circuit breakerfor a higher rated molded case circuit breaker since there is not a physicalrejection protocol in the product standard to prevent the installation of thelesser rated device. This can create a serious safety hazard. It can negatethe voltage rating protection, the interrupting rating protection and the short-circuit protection of equipment. In existing installations this may not be realized until the protective device fails to operate properly. For a given framesize circuit breaker, there are various part numbers for different interruptingratings which are physically interchangeable. So its possible to install a 10kAinterrupting rated molded case circuit breaker in a panel that is listed for 65kAand which requires only circuit breakers with a 65kA interrupting rating beinstalled. Similarly it may be possible to replace a higher voltage rating circuitbreaker with a circuit breaker of the same physical dimensions with a lowervoltage rating. A listed current-limiting molded case circuit breaker has to betested and marked as current-limiting. Most molded case circuit breakers arenot current-limiting. Yet a current-limiting circuit breaker and a standard (non-current-limiting) circuit breaker can be physically interchangeable.

    Here is an example of how simple it is: use Class J fuses and equipment, andonly Class J fuses can be installed. This ensures the voltage rating is 600V(whether the system is 120, 208, 480, or 575V), the interrupting rating is atleast 200kA, and the short-circuit protection is provided by the current-limitinglet-through characteristics of the Class J. If the fuse has to be replaced, onlya Class J fuse physically fits into the equipment.

    The illustration above shows Class R type fuse rejection clips, which accept only theClass R rejection type fuses.

    Three circuit breakers of the same frame size which are physically interchangeable.The 240V CB could be substituted for the 600V CB, the 100A CB could be substituted for the 20A CB, and the 10kA CB could be substituted for the 65kA CB.

    Branch-Circuit & Application Limited OCPDs

  • 192008 Cooper Bussmann

    Branch circuit overcurrent protective devices can also be used to provide theadditional protection that a supplementary overcurrent protective device provides: see Figure 2. Rather than using a supplementary overcurrent protective device for supplementary protection of the luminaire, a branch-circuit overcurrent protective device is used. The fact that a branch-circuitovercurrent device (KTK-R-3) is used where a supplementary device is permitted does not turn the circuit between the lighting panel and the fixturefrom a branch-circuit to a feeder. In the case of Figure 2, the branch circuitstarts on the loadside of the 20A fuse in the lighting panel.

    Application Limited OCPDsThe preceding paragraphs covered branch circuit overcurrent protectivedevices. There are two other categories to be considered:

    (1) Permitted for specific branch circuit applications under limited conditions per the specific reference in the NEC: These OCPDs havesome limitation(s) and are not true branch circuit devices, but may be permitted, if qualified for the use in question. For example, most high speedfuses are not branch circuit OCPDs, however high speed fuses are allowed tobe used for short circuit protection on motor circuits utilizing power electronicdevices by 430.52(C)(5). Motor Circuit Protectors (MCPs) are recognizeddevices (not listed) and can be used to provide short-circuit protection formotor branch circuits, if used in combination with a listed combination starterwith which the MCP has been tested and found acceptable [per 430.52(C)(3)].Self protected starters are another application limited OCPD; they are listedonly for use as protection of motor branch circuits. These examples are onlysuitable for use on motor branch circuits; they cannot be used on other branchcircuit types or for main or feeder protection. When considering the use ofapplication specific devices, special attention must be paid to the circuittype/application, NEC requirements, and the devices product listing or recognition. In other words, these types of overcurrent devices are onlyacceptable for use under special conditions.

    (2)Supplementary overcurrent protective devices: These devices have limited applications and must always be in compliance with 240.10

    The NEC definition for a supplementary overcurrent protective device isshown below. Supplementary protective devices can only be used as additional protection when installed on the load side of a branch circuit overcurrent device. Supplementary devices must not be applied where branchcircuit overcurrent protective devices are required; unfortunately this unsafemisapplication is prevalent in the industry. Supplementary devices are properlyused in appliance applications and for additional, or supplementary protectionwhere branch circuit overcurrent protection is already provided. In applianceapplications, the supplementary devices inside the appliance provide protection for internal circuits and supplement the protection provided by thebranch circuit protective devices.The use of supplementary overcurrent protective devices allowed by 240.10 isfor applications such as lighting and appliances shown in Figure 1. The supplementary protection is in addition to the branch circuit overcurrent protection provided by the device protecting the branch circuit (located in thelighting panel in Figure 1).

    240.10 Supplementary Overcurrent Protection. Where supplementaryovercurrent protection is used for luminaires, appliances, and other equipment...it shall not be used as a substitute for required branch-circuitovercurrent devices or in place of the required branch-circuit protection

    NEC Article 100Supplementary Overcurrent Protective Device.A device intended to provide limited overcurrent protection for specific applications and utilization equipment such as luminaires (lighting fixtures)and appliances. This limited protection is in addition to the protection provided in the required branch circuit by the branch-circuit overcurrent protective device.

    Figure 1

    Figure 2

    Fuseology

    Branch-Circuit & Application Limited OCPDs

  • 20 2008 Cooper Bussmann

    Fuseology

    One example of the difference and limitations is that a supplementary overcurrent protective device may have creepage and clearance spacings thatare considerably less than that of a branch circuit overcurrent protectivedevice.

    Example: A supplementary protector, recognized to UL1077, has spacings that are 38

    inch through air and 12 inch over surface at 480V. A branch circuit rated UL489 molded case circuit breaker has spacings that

    are 1 inch through air and 2 inches over surface at 480V.

    Another example of differences and limitations of supplementary protectivedevices is that branch circuit overcurrent protective devices have standardoverload characteristics to protect branch circuit, feeder, and service entranceconductors. Supplementary overcurrent protective devices do not have standard overload (time-current) characteristics and may differ from the standard branch circuit overload characteristics. Also, supplementary overcurrent protective devices have interrupting ratings that can range from 32amps to 100,000 amps. When supplementary overcurrent protective devicesare considered for proper use, it is important to be sure that the device's interrupting rating equals or exceeds the available short-circuit current and thatthe device has the proper voltage rating for the installation (including compliance with slash voltage rating requirements, if applicable).

    Reasons Why Supplementary Protectors (UL1077 Devices) cannot beused to Provide Branch Circuit Protection1. Supplementary protectors are not intended to be used or evaluated for

    branch circuit protection in UL1077.2. Supplementary protectors have drastically reduced spacings, compared to

    branch circuit protective devices, and often depend upon the aid of a separate branch circuit protective device upstream.

    3. Supplementary protectors do not have standard calibration limits or overload characteristic performance levels and cannot assure proper protection of branch circuits.

    4. Multi-pole supplementary protectors for use in 3 phase systems are not evaluated for protection against all types of overcurrents. Supplementary protectors are not tested to protect circuits from all types of fault conditions (for example line-ground faults.)

    5. Most supplementary protectors are short-circuit tested with a branch circuit overcurrent device ahead of them and rely upon this device for proper performance.

    6. Supplementary protectors are not required to be tested for closing into a fault.

    7. Recalibration of a supplementary protector is not required and depends upon the manufacturers preference. There is no assurance of performance following a fault or resettability of the device. The product standard does not require supplementary devices to be recalibrated and operational after interrupting a fault.

    8. Considerable damage to a supplemental protector is allowed following short-circuit testing.

    9. Supplementary protectors are not intended to be used as a disconnecting means.

    10. Supplementary protectors are not evaluated for short-circuit performance criteria, such as energy let-through limits or protection of test circuit conductors.

    UL248-14 UL1077 SupplementalSupplemental Fuses Protectors (Mini Circuit Breakers)

    Branch-Circuit & Application Limited OCPDs

    Supplementary overcurrent protective devices are not general use devices, asare branch-circuit overcurrent devices, and must be evaluated for appropriateapplication in every instance where they are used. Supplementary overcurrentprotective devices are extremely application oriented and prior to applying thedevices, the differences and limitations for these devices must be investigatedand found acceptable. Examples of supplementary overcurrent protectivedevices include, but are not limited to the following:

  • 212008 Cooper Bussmann

    Selective Coordination

    Branch Circuit Fuse Selection Chart (600V or less)

    Power electronicsapplicationssuch asdrives and SSRs

    Drive Fuse(High Speed,Class J)

    DFJ 600V J 200 Where branch protection isneeded with high speed fusecharacteristics

    ****

    Limitron

    **** For many of these fuse types, there are indicating and non-indicating versions, each with different symbols.

    Fuseology

  • 22 2008 Cooper Bussmann2008 Cooper Bussmann

    Branch Circuit Fuse Dimensions

    Class RK1 & RK5 - in (mm)

    Basic dimensions are same as Class H (formerly NEC) One-Time (NON & NOS) and Superlag Renewable RES & REN fuses. NOTE: These fuses can be usedto replace existing Class H, RK1 and RK5 fuses relating to dimensional compatibility.

    Ferrule StylesAmp 250V 600VRange A B A B110-30 2 (50.8) 0.56 (14.3) 5.0 (127.0) 0.81 (20.6)35-60 3 (76.2) 0.81 (20.6) 5.5 (139.7) 1.06 (27.0)

    Fusetron (FRN-R & FRS-R) & Limitron (KTN-R & KTS-R)Amp 250V 600VRange A B A B70-100 5.88 (149.2) 1.06 (26.9) 7.88 (200.0) 1.34 (34.0)110-200 7.13 (181.0) 1.56 (39.6) 9.63 (244.5) 1.84 (46.7)225-400 8.63 (219.1) 2.06 (52.3) 11.63 (295.3) 2.59 (65.8)450-600 10.38 (263.5) 2.59 (65.8) 13.38 (339.7) 3.13 (79.5)

    Low-Peak (LPN-RK & LPS-RK)Amp 250V 600VRange A B A B70-100 5.88 (149.2) 1.16 (29.5) 7.88 (200.0) 1.16 (29.5)110-200 7.13 (181.0) 1.66 (42.2) 9.63 (244.5) 1.66 (42.2)225-400 8.63 (219.1) 2.38 (60.5) 11.63 (295.3) 2.38 (60.5)450-600 10.38 (263.5) 2.88 (73.2) 13.38 (339.7) 2.88 (73.2)

    A

    B

    A

    B

    A

    B

    Class J Dimensions - in (mm)

    Low-Peak, Limitron and Drive Fuses

    LPJ, JKS & DFJ 600VAmp Range A B C D E F G H I1-30 2.25 (57.2) 0.81 (20.6) 0.50 (12.7) 35-60 2.38 (60.3) 1.06 (27.0) 0.63 (15.9) 65-100 4.63 (117.5) 1.13 (28.6) 3.63 (92.1) 2.63 (66.7) 1.00 (25.4) 0.75 (28.6) 0.13 (3.2) 0.41 (10.4) 0.28 (7.1)110-200 5.75 (146.1) 1.63 (41.4) 4.38 (111.1) 3.00 (76.2) 1.38 (34.9) 1.13 (28.6) 0.19 (4.8) 0.38 (9.5) 0.28 (7.1)225-400 7.12 (181.0) 2.11 (53.6) 5.25 (133.3) 1.51 (38.3) 1.87 (47.6) 1.62 (41.2) 0.25 (6.4) 0.56 (14.2) 0.40 (10.3)450-600 8.00 (203.2) 2.60 (66.0) 6.00 (152.4) 1.52 (38.6) 2.12 (54.0) 2.00 (50.8) 0.53 (13.5) 0.72 (18.3) 0.53 (13.5)

    Class CC - in (mm)

    LP-CC, FNQ-R & KTK-R

    600V, 1-30A

    Class T - in (mm)

    T-Tron Fuses

    JJN 300VAmp Range A B C D1-30 0.88 (22.2) 0.41 (10.3) 35-60 0.88 (22.2) 0.56 (14.3) 70-100 2.16 (54.8) 0.75 (19.1) 1.56 (39.7) 0.84 (21.4)110-200 2.44 (61.9) 0.88 (22.2) 1.69 (42.9) 0.84( 21.4)225-400 2.75 (69.9) 1.00 (25.4) 1.84 (46.8) 0.86 (21.8)450-600 3.06 (77.8) 1.25 (31.8) 2.03 (51.6) 0.88 (22.2)601-800 3.38 (85.7) 1.75 (44.5) 2.22 (56.4) 0.89 (22.6)801-1200 4.00 (101.6) 2.00 (50.8) 2.53 (64.3) 1.08 (27.4)

    JJS 600VAmp Range A B C D1-30 1.50 (14.3) 0.56 (38.1) 35-60 1.56 (20.6) 0.81 (39.7) 70-100 2.95 (19.1) 0.75 (75.0) 2.36 (59.9) 1.64 (41.7)110-200 3.25 (22.2) 0.88 (82.6) 2.50 (63.5) 1.66 (42.1)225-400 3.63 (25.4) 1.00 (92.1) 2.72 (69.1) 1.73 (44.1)450-600 3.98 (31.8) 1.25 (101.2) 2.96 (75.0) 1.78 (45.2)601-800 4.33 (44.5) 1.75 (109.9) 3.17 (80.6) 1.88 (47.6)

    Fuseology

  • 232008 Cooper Bussmann

    Fuseology

    Branch Circuit Fuse Dimensions

    Class L - in (mm)

    Low-Peak (KRP-C_SP) and Limitron (KTU & KLU) Fuses, 600VAmpRange A B C1 C2 D F G I J1 J2 J3 J4601-800 8.63 (219.1) 2.40 (61.0) 6.75 (171.5) 5.75 (146.1) 3.75 (95.3) 2.00 (50.8) 0.38 (9.5) 0.63 (15.9) 801-1200 10.75 (273.1) 2.40 (61.0) 6.75 (171.5) 5.75 (146.1) 3.75 (95.3) 2.00 (50.8) 0.38 (9.5) 0.63 (15.9) 1350-1600 10.75 (273.1) 3.00 (76.2) 6.75 (171.5) 5.75 (146.1) 3.75 (95.3) 2.38 (60.3) 0.44 (11.1) 0.63 (15.9) 1800-2000 10.75 (273.1) 3.50 (88.9) 6.75 (171.5) 5.75 (146.1) 3.75 (95.3) 2.75 (69.9) 0.50 (12.7) 0.63 (15.9) 2001-2500 10.75 (273.1) 4.80 (122.0) 6.75 (171.5) 5.75 (146.1) 3.75 (95.3) 3.50 (88.9) 0.75 (19.1) 0.63 (15.9) 1.75 (44.5) 1.38 (34.9) 0.88 (22.2) 0.81 (20.6)3000 10.75 (273.1) 5.00 (127.0) 6.75 (171.5) 5.75 (146.1) 3.75 (95.3) 4.00 (101.6) 0.75 (19.1) 0.63 (15.9) 1.75 (44.5) 1.38 (34.9) 0.88 (22.2) 0.81 (20.6)3500-4000 10.75 (273.1) 5.75 (146.1) 6.75 (171.5) 5.75 (146.1) 3.75 (95.3) 4.75 (120.7) 0.75 (19.1) 0.63 (15.9) 1.75 (44.5) 1.38 (34.9) 1.63 (41.3) 0.88 (22.2)4500-5000 10.75 (273.1) 6.25 (158.8) 6.75 (171.5) 5.75 (146.1) 3.75 (95.3) 5.25 (133.4) 1.00 (25.4) 0.63 (15.9) 1.75 (44.5) 1.38 (34.9) 1.63 (41.3) 0.88 (22.2)6000 10.75 (273.1) 7.13 (181.0) 6.75 (171.5) 5.75 (146.1) 3.75 (95.3) 5.75 (146.1) 1.00 (25.4) 0.63 (15.9) 1.75 (44.5) 1.38 (34.9) 1.63 (41.3) 0.88 (22.2)

    NOTE: KRP-CL (150A to 600A) fuses have same dimensions as601-800A case size. KTU (200-600A) have same dimensions,except tube 3 length x 2 diameter (76.2 x 50.8mm); terminal158 width x 114 thick (41.3 x 31.8mm).

    Low-Peak CUBEFuse Fuse and Fuse Holder - in (mm), 600V

    Dimension 30A 60A 100AA 1.88 (47.75) 2.13 (54.10) 3.01 (76.45)B 0.75 (19.05) 1.00 (25.40) 1.00 (25.40)C 1.00 (25.40) 1.13 (28.58) 1.26 (32.00)D 0.31 (7.94) 0.44 (11.11) 0.57 (14.48)E 0.04 (1.02) 0.04 (1.02) 0.06 (1.60)F 0.63 (15.88) 0.63 (15.88) 0.63 (15.88)G 0.27 (6.86) 0.38 (9.65) 0.39 (9.93)H 2.30 (58.42) 2.60 (66.04) 2.91 (73.91)I 0.76 (19.30) 1.03 (26.16) 1.05 (26.75)J 1.27 (32.18) 1.53 (38.86) 2.01 (51.05)K 0.15 (3.81) 0.17 (4.32) 0.16 (4.06)L N/A N/A 0.80 (20.32)M N/A N/A 2.51 (63.75)

    See Data Sheet 9000 for complete dimensional data and details on holderrejection features for the 30A, 60A and 100A holders.

  • 24 2008 Cooper Bussmann2008 Cooper Bussmann

    CUBEFuse (Dual-Element, Time-Delay)

    TCF (600Vac), 1 to 100A,

    Current-Limiting, UL Listed

    Special Purpose Fuse, STD

    248-8 Class J Performance

    UL Guide # JFHR, UL File #

    E56412, 300,000AIR AC,

    (300Vdc 100,000AIR), CSA

    Class #1422-02, CSA File

    #53787, 200,000AIR AC,

    (300VDC 100,000AIR)

    TCF fuses meet UL Class J

    time-delay electrical performance

    requirements. It is the worlds first

    finger-safe fuse with the smallest installed

    footprint of any power class fuse including Class J, CC, T

    and R fuses. Satisfies requirements of IEC 60529 for

    IP20 finger safe-rating and provides Type 2 No Damage

    protection for motor starters when sized properly. The

    TCF provides open fuse indication and is 35mm DIN rail

    and panel mountable.

    Data Sheet No. 9000

    Low-Peak (Dual-Element, Time-Delay)

    LPS-RK_SP (600Vac), LPN-RK_SP (250Vac), 110 to 600A,

    Current-Limiting, STD 248-12 Class RK1

    LPN-RK_SP 0-60A (125Vdc, 50,000AIR), 65-600A (250Vdc,

    50,000AIR), LPS-RK_SP 0-600A (300Vdc, 50,000AIR)

    UL Guide #JFHR, UL File #E56412, 300,000AIR AC, CSA

    Class #1422-02, CSA File #53787, 200,000AIR AC

    High performance, all purpose fuses. Provide the very high

    degree of short-circuit limitation of Limitron fuses plus the

    overload protection of Fusetron fuses in all types of

    circuits and loads. Can be closely sized to full-load motor

    currents for reliable motor overload protection, as well as

    backup protection. Close sizing permits the use of smaller

    and more economical switches (and fuses); better selective

    coordination against blackouts; and a greater degree of

    current limitation (component protection), Low-Peak fuses

    are rejection type but also fit non-rejection type fuse

    holders. Thus, can be used to replace Class H, K1, K5,

    RK5 or other RK1 fuses.

    Data Sheet No. 1001, 1002, 1003, 1004Low-Peak (Time-Delay)KRP-C_SP (600Vac), 601 to 6000A, Current-Limiting

    STD 248-10 Class L

    UL Guide #JFHR, UL File #E56412, 300,000AIR AC, 601-

    2000A (300Vdc 100,000AIR), CSA Class #1422-02, CSA

    File #53787, 200,000AIR AC

    The all purpose fuse for both overload and short-circuit

    protection of high capacity systems (mains and large

    feeders). Time-delay (minimum of four seconds at five

    times amp rating) for close sizing. Unlike fast-acting fuses,

    time-delay fuses pass harmless surge currents of motors,

    transformers, etc., without overfusing or any sacrifice of

    short-circuit current limitation (component protection).

    The combination use of 110 to 600A Low-Peak dual-element time-delay fuses and 601 to 6000A KRP-C Low-

    Peak fuses is recommended as a total system specification.

    Easily selectively coordinated for blackout protection. Size

    of upstream fuse need only be twice that of downstream

    Low-Peak fuses (2:1 ratio). Low-Peak fuses can reduce

    bus bracing; protect circuit breakers with low interrupting

    rating as well as provide excellent overall protection of

    circuits and loads.

    Data Sheet No. 1008, 1009

    Low-Peak (Dual-Element, Time-Delay)LPJ_SP (600Vac), 1 to 600A, Current-Limiting,

    STD 248-8 Class J

    UL Guide #JFHR, UL File #E56412, 300,000AIR ac, 1 to

    600A (300Vdc 100,000AIR), CSA Class #1422-02, CSA

    File #53787, 200,000AIR AC

    Space saving LPJ fuses have the advantage of time- delay, permitting them to pass temporary overloads, offering overload,back-up overload, and short-circuit protection. Ideal for IECstarter protection.

    Data Sheet No. 1006, 1007

    Low-Peak (Time-Delay)LP-CC (600Vac), 12 to 30A Current-Limiting 200,000AIR

    AC,

    STD 248-4 Class CC

    UL Guide #JDDZ, UL File #E4273, 12 -2.25A (300Vdc

    20,000AIR), 3-15A (150Vdc 20,000AIR), 20-30A (300Vdc

    20,000AIR), CSA Class #1422-02, CSA File #53787

    The Cooper Bussmann Low-Peak Class CC fuse (LP-CC) was

    developed specifically for a growing need in the industry - a

    compact, space saving branch circuit fuse for motor circuits.

    Data Sheet No. 1023

    Low-Peak Fuses* Now Offer

    Indication That's As Clear As Black

    And WhiteLow-Peak current-limiting fuses offer optional permanent

    replacement fuse indication. The indicator is either

    black or white; no in between coloring so no second-

    guessing whether to replace the fuse or not.

    Proven TechnologyLow-Peak fuses offer the same replacement fuse indication

    technology that s proven itself on the Cooper Bussmann

    CUBEFuse fuse and fuse holder system. Its the most

    reliable technology on the market today.

    * Indication available on Cooper Bussmann LPJ_SPI, LPN-RK_SPI

    (250V) and LPS-RK_SPI (600V).

    Good

    Replace

    Cooper Bussmann Branch Circuit, Power Distribution Fuses

    For Data Sheets: www.cooperbussmann.com

    Fusetron (Dual-Element, Time-Delay)FRS-R (600Vac), FRN-R (250Vac), 110 to 600A, 200,000AIR

    AC, FRN-R 0-600A (125Vdc, 20,000AIR), FRS-R 0-600A

    (300Vdc, 20,000AIR), Current-Limiting

    STD 248-12 Class RK5

    UL Guide #JDDZ, UL File #E4273, CSA Class #1422-02,

    CSA File #53787

    Time-delay affords the same excellent overload protection

    as Low-Peak fuses of motors and other type loads and

    circuits having temporary inrush currents such as those

    caused by transformers and solenoids. (In such circuits,

    Limitron fuses can only provide short-circuit protection).

    Fusetron fuses are not as fast-acting on short-circuits as

    Low-Peak fuses and therefore cannot give as high a

    degree of component short-circuit protection. Like the

    Low-Peak fuse, Fusetron fuses permit the use of smaller

    size and less costly switches. Fusetron fuses fit rejection

    type fuse holders and can also be installed in holders for

    Class H fuses. They can physically and electrically

    replace Class H, K5, and other Class RK5 fuses.

    Data Sheet No. 1017, 1018, 1019, 1020

    Fuseology

  • 252008 Cooper Bussmann

    Fuseology

    Cooper Bussmann Branch Circuit, Power Distribution Fuses

    Limitron (Fast-Acting)KTU (600Vac), 601 to 6000A, 200,000AIR AC, Current-

    Limiting STD 248-10 Class L

    UL Guide #JDDZ, UL File #E4273, CSA Class #1422-02,

    CSA File #53787

    Single-element fuses with no intentional time-delay. Very

    fast-acting with a high degree of current limitation; provide

    excellent component protection. Can be used for short

    circuit protection in circuits with inrush currents. Must be

    oversized to prevent opening by the temporary harmless

    overloads with some sacrifice of current limitation. In

    motor circuits, is sized at approximately 300% of