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  • Contents

    Description Page

    Fuseology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11

    Bussmann Power Distribution Fuses. . . . . . . . . . . . . . . . . . . . 12-14

    Bussmann Fuseblocks, Holders, and Disconnect Switches. . . . . . 14

    General Data Selection Chart . . . . . . . . . . . . . . . . . . . . . . . . . 15

    General Data Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

    Conductor Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-18

    Equipment Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-21

    Transformer Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-24

    Cable Limiter Applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

    High Speed Fuse Applications . . . . . . . . . . . . . . . . . . . . . . . . 26-27

    3 Short-Circuit Calculations . . . . . . . . . . . . . . . . . . . . . . . . . 28-30

    1 Short-Circuit Calculations . . . . . . . . . . . . . . . . . . . . . . . . . 31-32

    Short-Circuit, Impedance and Reactance Data. . . . . . . . . . . . . . . 33

    C Values for Conductors and Busway . . . . . . . . . . . . . . . . . . . . 34

    Voltage Drop Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-37

    Selective Coordination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

    Selective Coordination Reading Time-Current Curves . . . . . 39-41

    Selective Coordination Current-Limiting Fuses . . . . . . . . . . 42-44

    Selective Coordination Elevator Circuits . . . . . . . . . . . . . . . 45-46

    Component Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47-49

    Component Protection Wire and Cable . . . . . . . . . . . . . . . 50-51

    Component Protection Bus Short-Circuit Rating and Bracing

    Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52-53

    Component Protection Low Voltage Motor Controllers . . . . . . . 54

    Component Protection Ballasts. . . . . . . . . . . . . . . . . . . . . . . . 55

    Component Protection Circuit Breakers . . . . . . . . . . . . . . . 55-56

    Component Protection Transfer Switches . . . . . . . . . . . . . . . . 57

    Component Protection HVAC Equipment . . . . . . . . . . . . . . . . 57

    Component Protection Let-Through Charts . . . . . . . . . . . . 58-62

    Description Page

    Flash Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63-64

    Ground Fault Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65-74

    Motor Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75-77

    Motor Protection Voltage Unbalance/Single-Phasing . . . . . . 78-83

    Motor Circuit Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

    115 Volt Single-Phase Motor Circuits. . . . . . . . . . . . . . . . . . . . . . 85

    230 Volt Single-Phase Motor Circuits. . . . . . . . . . . . . . . . . . . . . . 86

    200 Volt Three-Phase Motor Circuits . . . . . . . . . . . . . . . . . . . 87-88

    208 Volt Three-Phase Motor Circuits . . . . . . . . . . . . . . . . . . . 89-90

    230 Volt Three-Phase Motor Circuits . . . . . . . . . . . . . . . . . . . 91-92

    460 Volt Three-Phase Motor Circuits . . . . . . . . . . . . . . . . . . . 93-94

    575 Volt Three-Phase Motor Circuits . . . . . . . . . . . . . . . . . . . 95-96

    90 Volt DC Motor Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

    180 Volt DC Motor Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

    120 Volt DC Motor Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

    240 Volt DC Motor Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

    Main, Feeder, and Branch Circuit Protection. . . . . . . . . . . . . . . . 100

    Protection of Motor Starters . . . . . . . . . . . . . . . . . . . . . . . . 101-103

    Motor Circuit Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

    Group Motor Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

    Group Switching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

    Overcurrent Devices for Motor Circuit Protection . . . . . . . . . 107-108

    Motor Circuit Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109-110

    Motor Control Circuit Protection . . . . . . . . . . . . . . . . . . . . . 111-113

    Fuse Diagnostic Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114-116

    Main, Feeder, and Branch Circuit Fuse Sizing. . . . . . . . . . . . . . . 117

    Suggested Fuse Specification . . . . . . . . . . . . . . . . . . . . . . . . . . 118

    Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119-120

    Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inside Back Cover

    This handbook is intended to clearly present product data and technical information that will help the end user with design applications. Bussmann reserves the right,without notice, to change design or construction of any products and to discontinue or limit their distribution. Bussmann also reserves the right to change or update,without notice, any technical information contained in this handbook.

    National Electrical Code is a trademark of the National Fire Protection Association, Inc., Batterymarch Park, Quincy, Massachusetts, for a triennial electrical pub-lication. The term, National Electrical Code as used herein means the triennial publication constituting the National Electrical Code and is used with permission of the National Fire Protection Association, Inc.Copyright 1998 by Cooper Bussmann, Inc. http://www.bussmann.com Printed in U.S.A.

  • ELECTRICAL PROTECTION HANDBOOK

    SelectingProtective

    Devices BasedOn the NationalElectrical Code

    Bussmann

  • Fuseology

    Circuit ProtectionElectrical distribution systems are often quite complicated. Theycannot be absolutely fail-safe. Circuits are subject to destructiveovercurrents. Harsh environments, general deterioration, acciden-tal damage or damage from natural causes, excessive expansionor overloading of the electrical distribution system are factorswhichproteformeloadscuit pwhichfacilitfrom devic

    FusesTheseEleme

    OvercAn ovrent. mal ocondnentsshort-ing p

    OverloOverlcurresurgeers amal orise is(It is i

    Cas wloadsmust tributtivelythe oequipheatinrioratage a

    Short-CircuitsWhereas overload currents occur at rather modest levels, theshort-circuit or fault current can be many hundred times largerthan the normal operating current. A high level fault may be 50,000amperes (or larger). If not cut off within a matter of a few thou-sandths of a second, damage and destruction can become ram-

    tthere can be severe insulation damage, melting of conduc-, vaporization of metal, ionization of gases, arcing, and fires.ultaneously, high level short-circuit currents can develop hugegnetic-field stresses. The magnetic forces between bus bars other conductors can be many hundreds of pounds per linear

    t; even heavy bracing may not be adequate to keep them fromn

    e in

    iswlts

    rq

    huure

    aau

    aim

    Llotr contribute to the occurrence of such overcurrents. Reliablective devices prevent or minimize costly damage to trans-rs, conductors, motors, and the other many components and that make up the complete distribution system. Reliable cir-rotection is essential to avoid the severe monetary losses can result from power blackouts and prolonged downtime of

    ies. It is the need for reliable protection, safety, and freedomfire hazards that has made the fuse a widely used protectivee.

    are constructed in an almost endless variety of configurations. photos depict the internal construction of Bussmann Dual-nt and SEMI-TRON fuses.

    urrentsercurrent is either an overload current or a short-circuit cur-The overload current is an excessive current relative to nor-perating current, but one which is confined to the normal

    uctive paths provided by the conductors and other compo- and loads of the distribution system. As the name implies, acircuit current is one which flows outside the normal conduct-aths.

    adsoads are most often between one and six times the normalnt level. Usually, they are caused by harmless temporary currents that occur when motors are started-up or transform-re energized. Such overload currents, or transients, are nor-ccurrences. Since they are of brief duration, any temperature trivial and has no harmful effect on the circuit components.

    mportant that protective devices do not react to them.)ontinuous overloads can result from defective motors (such

    orn motor bearings), overloaded equipment, or too many on one circuit. Such sustained overloads are destructive andbe cut off by protective devices before they damage the dis-ion system or system loads. However, since they are of rela- low magnitude compared to short-circuit currents, removal ofverload current within a few seconds will generally preventment damage. A sustained overload current results in over-g of conductors and other components and will cause dete-

    ion of insulation, which may eventually result in severe dam-nd short-circuits if not interrupted.

    pantorsSimmaandfoobei

    FusTheor lcomresHomecomnotuni

    1. Tro

    2. Pnmnp

    3. Ffl

    TheencDis1g warped or distorted beyond repair.

    sfuse is a reliable overcurrent protective device. A fusible linkks encapsulated in a tube and connected to contact terminalsprise the fundamental elements of the basic fuse. Electricaltance of the link is so low that it simply acts as a conductor.ever, when destructive currents occur, the link very quickly and opens the circuit to protect conductors and other circuit

    ponents and loads. Fuse characteristics are stable. Fuses doequire periodic maintenance or testing. Fuses have three

    ue performance characteristics:

    ey are safe. Modern fuses have an extremely high inter-pting ratingcan withstand very high fault currents with-t rupturing.operly applied, fuses prevent blackouts. Only the fusearest a fault opens without upstream fuses (feeders or

    ains) being affectedfuses thus provide selective coordi-tion. (These terms are precisely defined in subsequentges.)ses provide optimum component protection by keeping

    ult currents to a low value. . .They are said to be current-iting.

    ouisiana Superdome in New Orleans is the worlds largest fullysed stadium. The overall electrical load exceeds 30,000,000 VA.

    ibution circuits are protected with BUSS LOW-PEAK fuses.

  • Fuseology

    VoltaMostratinging ovoltafuse is a fcondthe fumeltsing loand,the ocondis us

    AmpeEverratingand shouinstafuse specbe gcal eperm300%of a the ccapaTherappr

    Interrupting Rating - Safe OperationA protective device must be able to withstand the destructive ener-gy of short-circuit currents. If a fault current exceeds a levelbeyond the capability of the protective device, the device mayactually rupture, causing additional damage. Thus, it is importantwhen applying a fuse or circuit breaker to use one which can sus-

    the largest potential short-circuit currents. The rating whiches the capacity of a protective device to maintain its integrity reacting to fault currents is termed its interrupting rating.

    interrupting rating of most branch-circuit, molded case, circuitkers typically used in residential service entrance panels is00 amperes. (Please note that a molded case circuit breakersrupting capacity will typically be lower than its interrupting rat- Larger, more expensive circuit breakers may have interrupt-atings of 14,000 amperes or higher. In contrast, most modern,nt-limiting fuses have an interrupting rating of 200,000 or

    000 amperes and are commonly used to protect the lower circuit breakers. The National Electrical Code, Section 110-9,ires equipment intended to break current at fault levels to an interrupting rating sufficient for the current that must berupted. The subjects of interrupting rating and interruptingcity are treated later in more detail.

    sne

    This the eelectproteto thecompge Rating low voltage power distribution fuses have 250 volt or 600 volts (other ratings are 125 volts and 300 volts). The voltage rat-f a fuse must be at least equal to or greater than the circuitge. It can be higher but never lower. For instance, a 600 voltcan be used in a 208 volt circuit. The voltage rating of a fuseunction of its capability to open a circuit under an overcurrentition. Specifically, the voltage rating determines the ability ofse to suppress the internal arcing that occurs after a fuse link and an arc is produced. If a fuse is used with a voltage rat-wer than the circuit voltage, arc suppression will be impaired

    under some fault current conditions, the fuse may not clearvercurrent safely. Special consideration is necessary for semi-uctor fuse application, where a fuse of a certain voltage ratinged on a lower voltage circuit.

    re Ratingy fuse has a specific ampere rating. In selecting the ampere

    of a fuse, consideration must be given to the type of loadcode requirements. The ampere rating of a fuse normallyld not exceed the current carrying capacity of the circuit. Fornce, if a conductor is rated to carry 20 amperes, a 20 ampereis the largest that should be used. However, there are someific circumstances in which the ampere rating is permitted toreater than the current carrying capacity of the circuit. A typi-xample is the motor circuit; dual-element fuses generally areitted to be sized up to 175% and non-time-delay fuses up to of the motor full-load amperes. As a rule, the ampere rating

    fuse and switch combination should be selected at 125% ofontinuous load current (this usually corresponds to the circuitcity, which is also selected at 125% of the load current).

    e are exceptions, such as when the fuse-switch combination isoved for continuous operation at 100% of its rating.

    tain definwhenThe brea10,0intering.)ing rcurre300,ratedrequhaveintercapa

    Fusebutiospactectin

    photograph vividly illustratesffects of overcurrents onrical components when ctive devices are not sized ampere rating of the onent.

    Considerable damage to electricalequipment can result if the inter-rupting rating of a protectivedevice is inadequate and isexceeded by a short-circuit current.2 are a universal protective device. They are used in power distri- systems, electronic apparatus, vehicles. . .and as illustrated, our program. The Space Shuttle has over 600 fuses installed in it pro-g vital equipment and circuits.

  • Fuseology

    The table below depicts four different situations involving anovercurrent device with a normal current rating of 100 amperesand an interrupting rating of only 10,000 amperes.

    Circuit with Overcurrent Circuit ApplicationProtective Device Conditions And ActionCurrent Rating= 100A and of ProtectiveInterrupting Rating= 10,000A Device

    Normal Proper

    Overload Proper-SafeCurrent InterruptionGreater Than of CurrentDevices

    in thdevicoverchas the ointerrdevicposs200,0tion.

    rent curre

    rentnec

    atc

    f

    Available fault current50,000 amps

    Fuse must have short-circuitinterrupting rating of at least50,000 amperes.

    ,

    acoo

    80

    AMMETER100

    AmperesLOAD

    Available fault current50,000 amps

    Circuit breaker must havecapability of interrupting at least50,000 amperes. AmpereRating

    Short-Circuit Proper-SafeCurrent InterruptionWithin Device of CurrentInterruptingRating

    Short-Circuit ImproperCurrent Explosion orExceeds RuptureDevice Could ResultInterruptingRating

    In the first three instances, the circuit current condition is with-e safe operating capabilities of the overcurrent protectivee. However, the fourth case involves a misapplication of theurrent device. A short-circuit on the load side of the device

    resulted in a fault current of 50,000 amperes flowing throughvercurrent device. Because the fault current is well above theupting rating of the device, a violent rupture of the protectivee and resulting damage to equipment or injury to personnel isible. The use of high interrupting rated fuses (typically rated at00 amperes) would prevent this potentially dangerous situa-

    The first paragraph of Section 110-9 requires that the overcur-protective device be capable of interrupting the available faultnt at its line terminals.

    locsyselecircaresuf

    50,000

    25

    Aveashpr

    200

    10,0003As depicted in the diagram that follows, when using overcur- protective devices with limited interrupting rating, it becomesessary to determine the available short-circuit currents at eachtion of a protective device. The fault currents in an electricalem can be easily calculated if sufficient information about thetrical system is known. See the Point-to-Point Method for short-uit calculations. With modern fuses, these calculations normallynot necessary since the 200,000 ampere interrupting rating isicient for most applications.

    75,000 Amperes

    75,000 Amperes

    30,000 Amperes

    15,000 Amperes

    000 Amperes

    ilable short-circuit current (indicated by X) ath panel location must be determined to assurert-circuit interrupting rating of overcurrenttective devices is not exceeded.

  • Fuseology

    SeleThe ages or blackouts caused by overcurrent conditions. When onlythe protective device nearest a faulted circuit opens and largerupstream fuses remain closed, the protective devices are selec-tivelusedthe o

    ThisPEAtion

    design. By maintaining a minimum ratio of fuse-ampere ratingsbetween an upstream and downstream fuse, selective coordina-tion is assured.

    General Fuse Application Data For Compliance With NEC, Section 110-9.Guideline Features Benefits Commonly Used

    Fuse Types

    New 1. Use modern, high interrupting 300,000 ampere interrupting Assure proper interrupting All modern current-limiting Install- rated fuses throughout electrical rating, on LOW-PEAK YELLOW rating compliance currently fuses (most have 200,000ations system. fuses. 200,000 ampere interrupting and future. ampere interrupting

    rating on other classes of modern Usually a short-circuit rating). LOW-PEAK YELLOW

    current-limiting fuses. current calculation study is fuses have a 300,000

    unnecessary. ampere interrupting rating.

    2. Use current-limiting fuses to Correct type and size Compliance with NEC LOW-PEAK YELLOW

    protect low withstand rated current-limiting fuse can 110-9. Dual-Elementcomponents. protect low withstand rated T-TRON Fast-Acting

    equipment against high LIMITRON Fast-Acting

    Syst Provide safer electrical LOW-PEAK YELLOWUp- system protection with Dual-ElementGrad simple direct retrofit. FUSETRON Dual-Element

    Easily achieved since older LIMITRON Fast-Acting

    style fuses can physically bereplaced with modern fusesy coordinated (they discriminate). The word selective is to denote total coordination. . .isolation of a faulted circuit bypening of only the localized protective device.

    diagram shows the minimum ratios of ampere ratings of LOW-K YELLOW fuses that are required to provide selective coordina- (discrimination) of upstream and downstream fuses.

    2:1 (or more)

    LPS-RK600SP

    LPS-RK200SP

    KRP-C1200SP

    2:1 (or more)

    sented in a com15). Adherenceadequate.4 Minimum selectivity ratios for BUSS fuses are pre-posite table (see the Selectivity Ratio Guide, page to the tabulated selectivity ratios normally provesctive Coordination - Prevention of Blackoutscoordination of protective devices prevents system power out-

    Uis a s

    short-circuit currents. (Seefuse protection of circuitbreakers).

    em 3. Where available fault current 200,000 amperehas increased or is questionable, interrupting rating.

    ing replace old style fuses such asOne-Time and Renewable withmodern high interrupting ratedfuses.

    4. Where existing equipment may Correct type and sizehave questionable withstand current-limiting fuses can be rating due to deterioration, or the put in switch, cut-in system oravailable fault current has sometimes fuses can be cut inincreased, install modern current- bus structure.limiting fuses.nlike electro-mechanical inertial devices (circuit breakers), itimple matter to selectively coordinate fuses of modern

    with no system modification.

    Provide sale electrical T-TRON Fast-Actingsystem protection. LOW-PEAK YELLOW

    Small size of T-TRON fuse Dual-Element

    permits easy cut-in strategy. LIMITRON Fast-Acting

    LOW-PEAK YELLOW

    Time-Delay

  • Fuseology

    This in eqdetertectivover

    Current-Limitation - Component Protection

    A noncurrendestru

    r s

    phrue p

    rrg0nr

    t-oeinf

    Normload c

    Areas within waveformloops represent destructiveenergy impressed uponcircuit componentsburnt out switchboard represents the staggering monetary lossesuipment and facility downtime that can result from inadequate oriorated protective devices. It emphasizes the need for reliable pro-e devices that properly function without progressive deteriorationtime.

    A cuoff a

    If a one-destmodsuchcompermcan otheratin30,0secobe pshorexplbetwbraclimit 5-current-limiting protective device, by permitting a short-circuitt to build up to its full value, can let an immense amount ofctive short-circuit heat energy through before opening the circuit.

    rent-limiting fuse has such a high speed of response that it cutshort-circuit long before it can build up to its full peak value.

    rotective device cuts off a short-circuit current in less thanalf cycle, before it reaches its total available (and highlyctive) value, the device is a current-limiting device. Mostrn fuses are current-limiting. They restrict fault currents tolow values that a high degree of protection is given to circuitonents against even very high short-circuit currents. Theyit breakers with lower interrupting ratings to be used. Theyeduce bracing of bus structures. They minimize the need of components to have high short-circuit current withstands. If not limited, short-circuit currents can reach levels of0 or 40,000 amperes or higher in the first half cycle (.008ds, 60 hz) after the start of a short-circuit. The heat that canoduced in circuit components by the immense energy ofcircuit currents can cause severe insulation damage or evension. At the same time, huge magnetic forces developeden conductors can crack insulators and distort and destroyg structures. Thus, it is important that a protective device

    ault currents before they reach their full potential level.

    Fuse opens and clearsshort-circuit in lessthan cycle

    Initiation ofshort-circuit current

    alurrent

    Circuit breaker tripsand opens short-circuitin about 1 cycle

  • Fuseology

    OperThe fuse

    Non-The ampmoreferrurounand

    its aillustmoretuallyto mlishegap eventaineoff aarc i

    speecirculoadthescuitsrary formsuchrespthe p

    six tfuseamprentssimua seating Principles of BUSS Fusesprinciples of operation of the modern, current-limiting BUSS

    s are covered in the following paragraphs.

    Time-Delay Fusesbasic component of a fuse is the link. Depending upon theere rating of the fuse, the single-element fuse may have one or links. They are electrically connected to the end blades (orles) (see Figure 1) and enclosed in a tube or cartridge sur-ded by an arc quenching filler material. BUSS LIMITRON

    T-TRON fuses are both single-element fuses.Under normal operation, when the fuse is operating at or near

    mpere rating, it simply functions as a conductor. However, asrated in Figure 2, if an overload current occurs and persists for than a short interval of time, the temperature of the link even- reaches a level which causes a restricted segment of the linkelt. As a result, a gap is formed and an electric arc estab-d. However, as the arc causes the link metal to burn back, thebecome progressively larger. Electrical resistance of the arctually reaches such a high level that the arc cannot be sus-d and is extinguished. The fuse will have then completely cutll current flow in the circuit. Suppression or quenching of thes accelerated by the filler material.Single-element fuses of present day design have a very highd of response to overcurrents. They provide excellent short-it component protection. However, temporary, harmless over-s or surge currents may cause nuisance openings unlesse fuses are oversized. They are best used, therefore, in cir- not subject to heavy transient surge currents and the tempo-overload of circuits with inductive loads such as motors, trans-ers, solenoids, etc. Because single-element, fast-acting fuses as LIMITRON and T-TRON fuses have a high speed ofonse to short-circuit currents, they are particularly suited forrotection of circuit breakers with low interrupting ratings.Whereas an overload current normally falls between one and

    imes normal current, short-circuit currents are quite high. The may be subjected to short-circuit currents of 30,000 or 40,000eres or higher. Response of current-limiting fuses to such cur- is extremely fast. The restricted sections of the fuse link willltaneously melt (within a matter of two or three-thousandths ofcond in the event of a high-level fault current).

    quenprescircushorcurre

    Figur

    Figurarc is

    Figurload.

    Figurthe fu

    Figucircu

    Withof shelecdevicinterreplacurre6The high total resistance of the multiple arcs, together with theching effects of the filler particles, results in rapid arc sup-

    sion and clearing of the circuit. (Refer to Figures 4 & 5) Short-it current is cut off in less than a half-cycle, long before thet-circuit current can reach its full value (fuse operating in itsnt-limiting range).

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

    e 2. Under sustained overload, a section of the link melts and an established.

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

    e 4. When subjected to a short-circuit current, several sections ofse link melt almost instantly.

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

    continued growth in electrical power generation, the higher levelsort-circuit currents made available at points of consumption by

    trical utilities have greatly increased the need for protectivees with high short-circuit interrupting ratings. Devices that canrupt only moderate levels of short-circuit currents are beingced by the modern fuse having the ability to cut-off short-circuitnts at levels up to 300,000 amperes.

  • Fuseology

    Figand

    Figtur

    Figcon

    Figresburque

    Figcirc

    -kpelo dtweolee

    h noaetrct loyc

    e Ara

    lo

    Buindwoure 6. The true dual-element fuse has distinct and separate overload short-circuit elements.

    ure 7. Under sustained overload conditions, the trigger spring frac-es the calibrated fusing alloy and releases the connector.

    ure 8. The open dual-element fuse after opening under an overloaddition.

    ure 9. Like the single-element fuse, a short-circuit current causes thetricted portions of the short-circuit elements to melt and arcing ton back the resulting gaps until the arcs are suppressed by the arcnching material and increased arc resistance.

    ure 10. The open dual-element fuse after opening under a short-uit condition.

    DualUnlibe asurgoveringstwo the thostectilow-is fivmum

    per heatexteoppger to thmenFigulink shorfuseovertuallthe circuis elpathed. chadatio

    andover7

    ssmann high performance fuses are used in tens of thousands ofustrial plants, commercial buildings, and homes throughout therld.Element, Time-Delay Fuses as Manufactured by Bussmanne single-element fuses, the dual-element, time-delay fuse canplied in circuits subject to temporary motor overloads and currents to provide both high performance short-circuit andad protection. Oversizing in order to prevent nuisance open-

    is not necessary. The dual-element, time-delay fuse containsistinctly separate types of elements (Figure 6). Electrically,o elements are series connected. The fuse links similar to

    used in the non-time-delay fuse perform the short-circuit pro-n function; the overload element provides protection againstvel overcurrents or overloads and will hold an overload which times greater than the ampere rating of the fuse for a mini-

    time of 10 seconds.As shown in Figure 6, the overload section consists of a cop-eat absorber and a spring operated trigger assembly. Theabsorber bar is permanently connected to the heat absorbersion (left end of illustration) and to the short-circuit link on thesite end of the fuse by the S-shaped connector of the trig-ssembly. The connector electrically joins the short-circuit link heat absorber in the overload section of the fuse. These ele-s are joined by a calibrated fusing alloy. As depicted ine 7, an overload current causes heating of the short-circuitonnected to the trigger assembly. Transfer of heat from the-circuit link to the heat absorbing bar in the mid-section of thebegins to raise the temperature of the heat absorber. If thead is sustained, the temperature of the heat absorber even-

    reaches a level which permits the trigger spring to fracturealibrated fusing alloy and pull the connector free of the short-it link and the heat absorber. As a result, the short-circuit linkctrically disconnected from the heat absorber, the conductingthrough the fuse is opened, and overload current is interrupt- critical aspect of the fusing alloy is that it retains its originalcteristic after repeated temporary overloads without degra-

    n.BUSS dual-element fuses, typically LOW-PEAK YELLOWFUSETRON fuses, utilize the spring-loaded design in thead element.

  • Fuseology

    Advantages of Bussmann Dual-Element, Time-Delay Fuses

    Busadva

    1. Pr2. Pe3. G

    taoc

    4. Si

    Moto

    WhemotBusstimemaxsurgple, ratin

    FuseFuse

    Dual(LOWFUSESingDela*Per Per

    The preceding table shows that a 40 ampere, dual-elementfuse will protect the 32.2 ampere motor, compared to the muchlarger, 100 ampere, single-element fuse that would be necessary.It is apparent that if a sustained, harmful overload of 300%occurred in the motor circuit, the 100 ampere, single-element fusewould never open and the motor could be damaged. The non-

    -delay fuse, thus, only provides ground fault and short-circuitection, requiring separate overload protection per the NEC. Inrast, the 40 ampere dual-element fuse provides ground fault,t-circuit and overload protection. The motor would be protect-gainst overloads due to stalling, overloading, worn bearings,

    200V3 Ph

    *smann Dual-Element, Time-Delay fuses have four distinctntages over single-element, non-time-delay fuses:

    ovide motor overload, ground fault and short-circuit protection.rmit the use of smaller and less costly switches.

    ive a higher degree of short-circuit protection (greater current limi-tion) in circuits in which surge currents or temporary overloadscur.mplify and improve blackout prevention (selective coordination).

    r Overload and Short-Circuit Protection

    n used in circuits with surge currents such as those caused byors, transformers, and other inductive components, themann LOW-PEAK YELLOW and FUSETRON dual-element,

    -delay fuses can be sized close to full-load amperes to giveimum overcurrent protection. Sized properly, they will hold untiles and normal, temporary overloads subside. Take, for exam-a 10 HP, 200 volt, three-phase motor with a full-load currentg of 32.2 amperes.

    and Switch Sizing for 10 HP Motor (200V, 3, 32.2 FLA)Type Maximum Fuse Required Switch

    Size (Amperes) Size (Amperes)-Element, Time-Delay 40A* 60A-PEAK YELLOW or TRON)

    le-Element, Non-Time- 100A 100Ay (LIMITRON)N.E.C. Section 430-32. N.E.C. Section 430-52.

    timeprotcontshored aimpr

    motoprotburnprotshouly an

    remfull-lvoltaDuamoto

    Perm

    AsidelemsincratinthreLOWsingthe saveinstamoto

    ase

    Dual-ElementLOW-PEAK YELLOWor FUSETRON Fuse

    32.2 Full Load Amperes(10 HP)

    M

    2003 Ph

    1

    M8oper voltage, single-phasing, etc.In normal installations, Bussmann dual-element fuses ofr-running, overload protection size, provide better short-circuit

    ection plus a high degree of back up protection against motorout from overload or single-phasing should other overload

    ective devices fail. If thermal overloads, relays, or contactsld fail to operate, the dual-element fuses will act independent-d thus protect the motor.When secondary single-phasing occurs, the current in the

    aining phases increases to a value of 170% to 200% of ratedoad current. When primary single-phasing occurs, unbalancedges that occur in the motor circuit cause excessive current.

    l-element fuses sized for motor overload protection can protectrs against the overload damage caused by single-phasing.

    it the Use of Smaller and Less Costly Switches

    e from only providing short-circuit protection, the single-ent fuse also makes it necessary to use larger size switches

    e a switch rating must be equal to or larger than the ampereg of the fuse. As a result, the larger switch may cost two ore times more than would be necessary were a dual-element-PEAK YELLOW or FUSETRON fuse used. The larger,

    le-element fuse itself could generate an additional cost. Again,smaller size switch that can be used with a dual-element fuses space and money. (Note: where larger switches already arelled, fuse reducers can be used so that fuses can be sized forr overload protection.)

    32.2 F.L.A.(10 HP)

    Vase

    200V3 Phase

    100ANon-Time-DelayLIMITRON Fuse

    40ADual-ElementFUSETRONorLOW-PEAK YELLOWFuse

    32.2 F.L.A.(10 HP)

    00A Switch 60A Switch

    M

  • Fuseology

    Better Short-Circuit Component Protection (Current-Limitation)The in whthe oup toactioratinTherOver

    CurreUsedFuse T

    Dual-(40A)

    Non-T(100A

    PEAKFLA)value

    BetteThe examcurreof serequupstrthat selecnatiofusesfuses

    tive ca roushow

    element fuses in the branch circuit for motor overload protectionides a large difference (ratio) in the ampere ratings betweeneeder fuse and the branch fuse, compared to the single-ent, non-time-delay LIMITRON fuse.

    r Motor Protection in Elevated Ambientsderating of dual-element fuses based on increased ambienteratures closely parallels the derating curve of motors in ele- ambient. This unique feature allows for optimum protection

    otors, even in high temperatures.

    ct of ambient temperature on operating characteristics ofTRON and LOW-PEAK YELLOW Dual-Element Fuses.

    208V3 Ph

    1ELYoFnon-time-delay, fast-acting fuse must be oversized in circuitsich surge or temporary overload currents occur. Response ofversized fuse to short-circuit currents is slower. Current builds a higher level before the fuse opens. . .the current-limitingn of the oversized fuse is thus less than a fuse whose ampereg is closer to the normal full-load current of the circuit.efore, oversizing sacrifices some component protection.sizing should not exceed NEC requirements.

    nt-Limitation of Dual-Element Fuses Versus Non-Time-Delay Fuses to Protect 10 HP Motor (32.2 FLA).ype Fuse Name Let-Through Current Versus

    Prospective Short-Circuit Currents(RMS Symmetrical)25,000A 50,000A 100,000A

    Element FUSETRON 2000A 3300A 4400A

    LOW-PEAK 1800A 2200A 3000AYELLOW

    ime-Delay LIMITRON 3100A 4100A 5000A)

    In the table above, it can be seen that the 40 ampere LOW- YELLOW dual-element fuse used to protect a 10 HP (32.2

    motor keeps short-circuit currents to approximately half the of the non-time-delay fuse.

    r Selective Coordination (Blackout Prevention)larger an upstream fuse is relative to a downstream fuse (forple, feeder to branch), the less possibility there is of an over-nt in the downstream circuit causing both fuses to open (lacklective coordination). Fast-acting, non-time-delay fuses

    ire at least a 3:1 ratio between the ampere rating of a largeeam, line-side LOW-PEAK YELLOW time-delay fuse andof the downstream, loadside LIMITRON fuse in order to betively coordinated. In contrast, the minimum selective coordi-n ratio necessary for LOW-PEAK YELLOW dual-element is only 2:1 when used with LOW-PEAK YELLOW loadside.

    The use of time-delay, dual-element fuses affords easy selec-oordinationcoordination hardly requires anything more thantine check of a tabulation of required selectivity ratios. Asn in the preceding illustration, close sizing of BUSS dual-

    provthe felem

    BetteThe tempvatedof m

    AffeFUSE

    M M

    ase

    50A Dual-lementOW-PEAKELLOWr LIMITRONuse

    90ANon-Time-DelayLIMITRONFuse

    32.2 F.L.A.(10 HP)

    150/90 = 1.67:1Inadequate(Minimum ratio must be at least 3:1 forSelective Coordination)

    150/40 = 3.75:1Adequate(Minimum ratio need only be 2:1 forSelective Coordination)

    208V3 Phase

    150ADual-ElementLOW-PEAKYELLOWFuse

    40ADual-ElementLOW-PEAKYELLOWFuse

    32.2 F.L.A.(10 HP)9

  • Fuseology

    Classes of FusesSafety is the industry mandate. However, proper selection, overallfunctional performance and reliability of a product are factorswhich are not within the basic scope of listing agency activities. Inorder to develop its safety test procedures, listing agenciesdevelop basic performance and physical specifications or stan-dards for a product. In the case of fuses, these standards haveculminated in the establishment of distinct classes of low-voltage(600 volts or less) fuses, Classes RK1, RK5, G, L, T, J, H and CCbeing the more important.

    The fact that a particular type of fuse has, for instance, a clas-sification of RK1, does not signify that it has the identical functionor performance characteristics as other RK1 fuses. In fact, theLIMITRON non-time-delay fuse and the LOW-PEAK YELLOWdual-element, time-delay fuse are both classified as RK1.Substantial difference in these two RK1 fuses usually require con-siderable difference in sizing. Dimensional specifications of eachclass of fuse does serve as a uniform standard.

    Class R FusesClass R (R for rejection) fuses are high performance, to 600ampere units, 250 volt and 600 volt, having a high degree of cur-rent-limitation and a short-circuit interrupting rating of up to300ClasRK5PEAfusemoupermfusefuseiting10,0a CR fuClasthe 9 anty toholdfuse

    In the above illustration, the fuse on the right has a groovedring in one ferrule providing the rejection feature of the Class Rfuse in contrast to the lower interrupting rating, non-rejection type.

    h

    ccs

    ip

    chhht

    hig,000 amperes (RMS symmetrical). BUSS Class Rs includeses RK1 LOW-PEAK YELLOW and LIMITRON fuses, and FUSETRON fuses. They have replaced BUSS K1 LOW-K and LIMITRON fuses and K5 FUSETRON fuses. Theses are identical, with the exception of a modification in thenting configuration called a rejection feature. This featureits Class R to be mounted in rejection type fuseclips. R type

    clips prevent older type Class H, ONE-TIME and RENEWABLEs from being installed. Since Class H fuses are not current-lim- and are recognized by regulatory agencies as having only a00 ampere interrupting rating, serious damage could results if

    lass R fuse were replaced by a Class H fuse. The use of Classseholders is thus an important safeguard. The application ofs R fuses in such equipment as disconnect switches permits

    equipment to have a high interrupting rating. NEC Articles 110-d 230-65 require that protective devices have adequate capaci- interrupt short-circuit currents. Article 240-60(b) requires fuse-ers for current-limiting fuses to reject non-current-limiting types.

    whic

    BranBranof fuequ

    The 1. T2. T3. T

    ra4. T

    h10The above illustration shows Class R type fuse rejection clips accept only the Class R rejection type fuses.

    h-Circuit Listed Fusesh-circuit listed fuses are designed to prevent the installationes that cannot provide a comparable level of protection toment.

    haracteristics of branch-circuit fuses are:ey must have a minimum interrupting rating of 10,000 amps.ey must have a minimum voltage rating of 125 volts.ey must be size rejecting such that a fuse of a lower voltageing cannot be installed in the circuit.ey must be size rejecting such that a fuse with a current ratingher than the fuseholder rating cannot be installed.

  • Fuseology

    Mediu

    GenerFusetions 1. GE

    A rupfus

    2. BAA rating

    3. EXA vbya s

    definis a sits intvoltagprodufuse. withindepeas a houscreatpreveexpu

    ConstCurreend f

    pressrials u

    For erule wstud In bobetwwith screw

    mostbecacurredifferaddin

    tion chan

    ApplicManyfusesmuchappli

    fuse.CAPAm Voltage Fuseology

    als above 600 volts are classified under one of three classifica-as defined in ANSI/IEEE C37.40.NERAL PURPOSE CURRENT-LIMITING FUSES

    fuse capable of interrupting all currents from the rated inter-ting current down to the current that causes melting of theible element in one hour.CK-UP CURRENT-LIMITING FUSEfuse capable of interrupting all currents from the maximumed interrupting current down to the rated minimum interrupt- current.PULSION FUSEented fuse in which the expulsion effect of gasses produced

    the arc and lining of the fuseholder, either alone or aided bypring, extinguishes the arc.

    One should note that in the definitions above, the fuses areed as either expulsion or current-limiting. A current-limiting fuseealed, non-venting fuse that, when melted by a current withinerrupting rating, produces arc voltages exceeding the systeme, which in turn forces the current to zero. The arc voltages areced by introducing a series of high resistance arcs within theThe result is a fuse that typically interrupts high fault currents the first 1/

    2cycle of the fault. In contrast, an expulsion fuse

    nds on one arc to initiate the interruption process. The arc actscatalyst, causing the generation of de-ionizing gas from its

    ing. The arc is then elongated, either by the force of the gassesed or a spring. At some point, the arc elongates far enough tont a restrike after passing through a current zero. Therefore, an

    lsion fuse may take many cycles to clear.

    ructionnt-limiting fuses have four parts common to all designs: tube,errules, element, and arc quenching filler.The tube must have a high burst strength to withstand theures generated during interruption. The most common mate-sed are fiberglass reinforced epoxy and melamine tubing.

    End ferrule designs are usually dictated by the application.xample, a clip mounted fuse would have a silver-plated fer-ith a large surface area to insure good contact. In contrast, a

    mounted fuse may be cast bronze with very little surface area.th designs it is very important that a good seal be providedeen the tube and end ferrules. This is most commonly donea gasket and magna-forming process, or with epoxy ands.

    Fuse elements are currently made from silver. Silver is the common material used for high voltage fuse elementsuse of its predictable melting properties. To achieve this lownt operation, it is necessary to either add a series element ofent material or reduce the melting temperature of the silver byg an M spot.

    Finally, an arc quenching filler is added to aid in the interrup-process. During interruption the arc quenching filler isged into an insulating material called fulgurite.

    ation of the rules for applying expulsion fuses and current-limiting are the same, but because the current-limiting fuse operates faster on high fault currents, some additional rules must be

    ed.Three basic factors must be considered when applying any These are: VOLTAGE, CONTINUOUS CURRENT CARRYINGCITY, INTERRUPTING RATING.

    VoltThenormfuseof tequ

    ConConlevethe thating fuseare prot

    InteAll fmaxBacing tantbelo

    AddEXPfuseupsthe curvproving 1. T

    min

    2. Tau

    CurrTo ithat1. A

    thsth1dple

    2. AeFbs

    tecTuc11age fuse must have a voltage rating equal to or greater than the

    al frequency recovery voltage which will be seen across the under all conditions. On three-phase systems, it is a good rule

    humb that the voltage rating of the fuse be greater than oral to the line-to-line voltage of the system.

    tinuous Current-Carrying Capacitytinuous current values that are shown on the fuse represent thel of current the fuse can carry continuously without exceedingtemperature rises as specified in ANSI C37.46. An application exposes the fuse to a current slightly above its continuous rat-but below its minimum interrupting rating, may damage the due to excessive heat. This is the main reason overload relaysused in series with back-up current-limiting fuses for motor ection.

    rrupting Ratinguses are given a maximum interrupting rating. This rating is theimum level of fault current that the fuse can safely interrupt.k-up current-limiting fuses are also given a minimum interrupt-rating. When using back-up current-limiting fuses, it is impor- that other protective devices are used to interrupt currentsw this level.

    itional RulesULSION FUSES: When choosing a fuse, it is important that the be properly coordinated with other protective devices locatedtream and downstream. To accomplish this, one must considermelting and clearing characteristics of the devices. Twoes, the minimum melting curve and the total clearing curve,ide this information. To insure proper coordination, the follow-

    rules should be used.he total clearing curve of any downstream protective deviceust be below a curve representing 75% of the minimum melt-g curve of the fuse being applied.he total clearing curve of the fuse being applied must lie below curve representing 75% of the minimum melting curve for anypstream protective device.

    ent-Limiting Fusesnsure proper application of a current-limiting fuse it is important the following additional rules be applied.s stated earlier, current-limiting fuses produce arc voltagesat exceed the system voltage. Care must be taken to make

    ure that the peak voltages do not exceed the insulation level ofe system. If the fuse voltage rating is not permitted to exceed40% of the system voltage, there should not be a problem. Thisoes not mean that a higher rated fuse cannot be used, butoints out that one must be assured that the system insulationvel (BIL) will handle the peak arc voltage produced.s with the expulsion fuse, current-limiting fuses must be prop-rly coordinated with other protective devices on the system.or this to happen the rules for applying an expulsion fuse muste used at all currents that cause the fuse to interrupt in 0.01econds or greater.

    When other current-limiting protective devices are on the sys-m it becomes necessary to use I2t values for coordination at

    urrents causing the fuse to interrupt in less than 0.01 seconds.hese values may be supplied as minimum and maximum val-es or minimum melting and total clearing I2t curves. In eitherase, the following rules should be followed.1. The minimum melting I2t of the fuse should be greater than the total clearing I2t of the downstream current-limiting device.2. The total clearing I2t of the fuse should be less than the min-imum melting I2t of the upstream current-limiting device.

  • Bussmann Power Distribution Fuses

    LOW(TimKRP601 300,CurrSTDUL GUL FCSACSA

    The fuseshorcapalarge(minfive tclosefuseharmmotowithosacrrent proteuse LOWelem601 PEArecospeccoortectioneeddownYELLOWcan tect interprovtectioBIF -PEAKe-Delay)-C_SP (600V)to 6000A000AIRent-Limiting 248-10 CLASS Luide #JFHRile #E56412 Class #1422-02 File #53787

    all-purpose silver linked for both overload andt-circuit protection of highcity systems (mains and feeders). Time-delay

    imum of four seconds atimes amp rating) for sizing. Unlike fast-acting

    s, time-delay fuses passless surge currents ofrs, transformers, etc.,ut overfusing or any

    ifice of short-circuit cur-limitation (componentction). The combination

    of to 600 ampere-PEAK YELLOW dual-ent time-delay fuses andto 6000A KRP-C LOW-K YELLOW fuses ismmended as a total systemification. Easily selectivelydinated for blackout pro-n. Size of upstream fuse only be twice that ofstream LOW-PEAK

    LOW fuses (2:1 ratio).-PEAK YELLOW fuses

    reduce bus bracing; pro-circuit breakers with lowrupting rating as well aside excellent overall pro-n of circuits and loads.

    No. 1008, 1009

    LOW-PEAK(Dual-Element, Time-Delay)LPS-RK_SP (600VAC,300VDC)LPN-RK_SP (250VAC,125VDC) to 600A300,000AIRCurrent-LimitingSTD 248-12 CLASS RK1UL Guide #JFHRUL File #E56412CSA Class #1422-02CSA File #53787

    High performance, all-purposefuses. Provide the very highdegree of short-circuit limita-tion of LIMITRON fuses plusthe overload protection ofFUSETRON fuses in all typesof circuits and loads. Can beclosely sized to full-load motorcurrents for reliable motoroverload protection, as well asbackup protection. Close siz-ing permits the use of smallerand more economical switch-es (and fuses); better selectivecoordination against black-outs; and a greater degree ofcurrent-limitation (componentprotection), LOW-PEAK YEL-LOW fuses are rejection typebut fit non-rejection type fuse-holders. Thus, can be used toreplace Class H, K1, K5, RK5or other RK1 fuses.BIF No. 1001, 1002,1003,1004

    LOW-PEAK(Dual-Element, Time-Delay)LPJ_SP (600V)1 to 600A300,000AIRCurrent-LimitingSTD 248-8 CLASS JUL Guide #JFHRUL File #E56412CSA Class #1422-02CSA File #53787

    Space saving LPJ fuseshave the advantage of time-delay, permitting them topass temporary overloads,offering overload, back-upoverload, and short-circuitprotection. Ideal for IECstarter protection.BIF No. 1006, 1007

    FUSE(Dual-EFRS-R FRN-R to 6200,00CurrenSTD 24UL GuiUL FileCSA CCSA Fi

    Time-dexcelleof LOWfuses otype loatemporsuch astransfo(In sucfuses ccircuit pFUSETfast-acYELLOcannotof comprotectPEAK YFUSETuse of costly sfuses fiholdersinstalleH fusesand eleH, K5, fuses.BIF No1020

    LOW-PEAK(Dual-Element, Time-Delay)LP-CC to 30A Current-Limiting200,000AIRSTD 248-4 CLASS CCUL Guide #JDDZUL File #E4273CSA Class #1422-02CSA File #53787

    The Bussmann LOW-PEAK YELLOW Class CC fuse (LP-CC) was developedspecifically for a growingneed in the industry - a com-pact, space saving branchcircuit fuse for motor circuits.Its superior performancecharacteristics of both time-delay and current-limitationmake it the newest memberof the LOW-PEAK YELLOWfamily of fuses.BIF No. 102312TRONlement, Time-Delay)

    (600VAC, 300VDC)(250VAC, 125VDC)00A

    0AIRt-Limiting8-12 CLASS RK5

    de #JDDZ #E4273lass #1422-02le #53787

    elay affords the sament overload protection-PEAK YELLOWf motors and otherds and circuits having

    ary inrush currents those caused by

    rmers and solenoids.h circuits, LIMITRONan only provide short-rotection).RON fuses are not asting as LOW-PEAKW fuses and therefore give as high a degreeponent short-circuition. Like the LOW-

    ELLOW fuse,RON fuses permit thesmaller size and lesswitches. FUSETRONt rejection type fuse- and can also bed in holders for Class. They can physicallyctrically replace Classand other Class RK5

    . 1017, 1018, 1019,

    DURALAG(Dual-Element, Time-Delay)Construction Grade FusesDLS-R (600VAC, 300VDC)DLN-R (250VAC, 125VDC)1 to 600A200,000 AIRCurrent-LimitingSTD 248-12 CLASS RK5UL Guide #JDDZUL File # E4273CSA Class #1422-02CSA File #53787

    Designed for contractor needs.Protects industrial equipmentand large motors.Recommended for AC powerdistribution system mains, feed-ers and branch circuits. Industrystandard time delay of 10 sec-onds at 5 times the fuse rating.BIF No. 1021, 1022

  • LIMI(Fast-AKTU (6601 to200,00CurrenSTD 2UL GuUL FileCSA CCSA F

    Silver-ment uVery fadegreeprovidprotecshort-ccircuitsMust bopeninharmlesacrificIn motsized aof motthus wload pYELLOBIF No

    LIMI(TimeKLU (601 to200,00CurrenSTD 2UL GuUL FileCSA CCSA F

    5 seco500%currenor KTUBIF NONE-(GenerNOS (6 to 60Non-Cu(NON (NOS 1STD 24UL GuiUL FileCSA CCSA Fi(NON 6(NOS 7STD 24UL GuiUL FileCSA CCSA Fi

    With an10,000not conClass Hused inable shSingle-fuses dtime-deBIF No

    CC-T(Time-DFNQ-R to 30200,00CurrenSTD 24UL GuiUL FileCSA CCSA Fi

    Ideal foprotectof NEC508. Itsbranchbe usedand shorequireBIF No

    LIMITRON(Fast-Acting)JKS (600V)1 to 600A200,000AIRCurrent-LimitingSTD 248-8 CLASS JUL Guide #JDDZ UL File #E4273CSA Class #1422-02CSA File #53787JKS LIMITRON fuses are basi-cally the same as RK1 LIMI-TRON fuses but somewhatsmaller in physical size. JKSfuses are single-element unitswith no time-delay and arethus best applied in circuitsfree of the temporary over-loads of motor and transformersurges. The smaller dimen-sions of Class J fuses preventtheir replacement with conven-tional fuses.BIF No. 1026, 1027

    TRONcting)00V)

    6000A0AIRt-Limiting48-10 CLASS Lide #JDDZ #E4273lass #1422-02ile #53787

    linked fuse. Single-ele-nits with no time-delay.st-acting with a high of current limitation;

    e excellent componenttion. Can be used forircuit protection only in with inrush currents.e oversized to preventg by the temporaryss overloads with somee of current limitation.

    or circuits, must bet approximately 300%

    or full-load current andill not provide the over-rotection of LOW-PEAKW KRP-C_SP fuses.. 1010

    LIMITRON(Fast-Acting)KTS-R (600V)KTN-R (250V)1 to 600A200,000AIRCurrent-LimitingSTD 248-12 CLASS RK1UL Guide #JDDZUL File #E4273CSA Class #1422-02CSA File #53787

    Single-element, fast-actingfuses with no time-delay. Thesame basic performance of the601-6000A KTU fast-actingLIMITRON fuses. Provides ahigh degree of short-circuit cur-rent limitation (component pro-tection). Particularly suited forcircuits and loads with noheavy surge currents ofmotors, transformers,solenoids, and welders. LIM-ITRON fuses are commonlyused to protect circuit-breakerswith lower interrupting ratings.If used in circuits with surgecurrents (motors, etc.), must beoversized to prevent openingand, thus, only provide short-circuit protection. IncorporateClass R rejection feature. Canbe inserted in non-rejectiontype fuseholders. Thus, canphysically and electricallyreplace fast-acting Class H, K1,K5, RK5, and other RK1 fuses.BIF No. 1044, 1043

    TRON-Delay)600V) 4000A0AIRt-Limiting48-10 CLASS Lide #JDDZ #E4273lass #1422-02ile #53787

    nd delay (minimum) at of rated current. Not ast-limiting as KRP-C_SP fuses.

    o. 1013

    LIMITRON(Fast-Acting)KTK-R (600V) to 30A200,000AIRCurrent-LimitingSTD 248-4 CLASS CCUL Guide #JDDZ,UL File #E4273CSA Class #1422-02CSA File #53787U.L. listed for branch circuitprotection. A very small, highperformance, fast-acting, sin-gle-element fuse for protectionof branch circuits, motor con-trol circuits, lighting ballasts,control transformers, streetlighting fixtures. . .A diameterof only and a length of1 give cost and space sav-ings. A grooved ferrule permitsmounting in rejection typefuseholders as well as standardnon-rejection type holders.BIF No. 101513TIMEal Purpose)00V) NON (250V)0Arrent-Limiting-60A) 50,000AIR-60A) 50,000AIR8-9 CLASS K5

    de #JDDZ #E4273lass #1421-01le #537875-600A) 10,000AIR0-600A) 10,000AIR8-6 CLASS H

    de #JDDZ #E4273lass #1421-01le #53787

    interrupting rating of amperes, and generallysidered current-limiting, ONE-TIME fuses are circuits with low avail-ort-circuit currents.element ONE-TIMEo not incorporatelay.. 1030

    RONelay)

    (600V)A

    0AIRt-Limiting8-4 CLASS CC

    de #JDDZ #E4273lass #1422-01le #53787

    r control transformerion. Meets requirements 430-72 (b) & (c) and UL miniature design and circuit rating allow it to for motor branch circuitrt circuit protection

    d by NEC 430-52.. 1014

    T-TRON(Fast-Acting)JJS (600V) 1-800AJJN (300V) 1-1200A200,000AIRCurrent-LimitingSTD 248-15 CLASS TUL Guide #JDDZUL File #E4273CSA Class #1422-02CSA File #53787

    The space-savers. Counter-part of the KTN-R/KTS-RLIMITRON fuses, but onlyone-third the size; thus, par-ticularly suited for criticallyrestricted space. A single-ele-ment fuse; extremely fast-act-ing. Provides a high degreeof current limitation on short-circuits for excellent compo-nent protection. Must beoversized in circuits withinrush currents common tomotors, transformers, andother inductive components(will give only short-circuitprotection). Commonlyapplied in electric heat cir-cuits, load centers, discon-nect switches, meters,stacks, etc. The small size ofT-TRON fuses permits themto be installed in panelboardsand control centers for sys-tem upgrading to protectstatic equipment with lowerwithstand ratings.BIF No. 1029, 1025

  • Bussmann Fuseblocks, Hold

    Plug Fuses125V 10,000AIR

    STD 248-11 PlugUL Guide #JFHR, #JEFV UL File #E56412, #E12112(0-6A), (7-30A)CSA Class #1423-01CSA File #53787FUSTAT Type S fuses havea size limiting feature whichprevents overfusing. Dualelement construction providesthe time-delay necessary formotor running protection.

    Type SC(Fast-Acting) 1/2-6A(Time-Delay) 8-60A SC (STDUL GUL FCSACSA

    A higpurpfor limotovoltsis amp2ture geroBIF

    OptiProt

    Compules tnatedsizedbroadfor prcationSizes from thru 30 amps.

    STD 248-11PlugUL Guide #JEFVUL File #E12112

    FUSETRON Type T fusesare similar to Type S fusesexcept for the Edison (lightbulb type) base.

    STD 248-11 PlugUL Guide #JEFVUL File #E12112

    Type W fuses are non-timedelay, used with non-induc-tive loads.BIF No. 1032, 1034, 1036

    480V) 100,000AIR 248-5 CLASS Guide #JDDZile #E4273 Class #1422-01 File #53787

    h performance general-ose branch circuit fuseghting appliance, andr branch circuits of 480 (or less). Fuse diameter; lengths vary withere rating from 1fi to(serves as rejection fea-and, thus, prevents dan-us oversizing).No. 1024

    midget BIF No

    ModuCH S

    Excellepanels,small mand simTouchsal openBIF No

    CompSwitc

    Bussmaes usesingle-AC motBIF No

    PaneFuse

    ShownBuss pThis Hrejectiorejectiofuses sCC, KTBIF Noers, and Disconnect Switches

    Fuseblocks

    Buss fuseblocks are availablein a wide range of sizes forpower distribution, high speedsemi-conductor protectionand electronic applications.UL Listed, CSA certified.Classes H (K), R, T, J andCC fuses. Standard moduleand pyramid styles available.

    SAMI Fuse Coverswith Option/OpenFuse Indication

    Dead front protection, optionalopen fuse indication. TheSAMI fuse covers fit mostfuses and fuseblocks. Coverssnap on in seconds - no specialwiring required.BIF No. 1204

    ma Overcurrentection Modules

    act, full-featured mod-hat deliver Type 2 coordi- protection, with properly fuses. Available in a range of combinationsocess control panel appli-s. Mounts Class CC and

    style fuses.. 1102, 1103

    Fusible and Non-Fusible DisconnectSwitches

    Feature packed line of fusibleand non-fusible disconnectswitches for virtually everyindustrial application.BIF No. 1139

    lar Fuseholdereries

    nt for switchboard control consoles,otors, transformersilar applications.afe design with option- fuse indication lights.. 1151

    Power DistributionBlocks

    For industrial controls, HVACand other control automationpanel applications. Availablein 1, 2, or 3-pole versions anda wide range of input/outputterminations.BIF No. 1148

    act Disconnecthes

    nn disconnect switch-d in manual control ofphase or three-phaseors.. 1120

    l-Mountholders

    above is a typicalanel-mount fuseholder.PS-RR holder is an type which acceptsn type branch circuituch as the Buss LP-K-R and FNQ-R.. 2113

    SafetyJ Fuseholderfor Class J Fuses

    Compact and touch-safedesign that meets IP 20 Std.Fuse is removed/installedexternal to circuit. Open fuseindication available. Integral35mm DIN Rail adapter.BIF No. 115214

  • General Data Selection Chart

    Circuit Load Ampere Fuse Symbol Voltage Interrupting RemarksRating Type Rating (AC) Class Rating

    (kA)Conventional DimensionsClass RK1, RK5 (0-600A), L (601-6000A)All type loads 0 LOW-PEAK LPN-RK_SP 250V RK1 300 All-purpose fuses.

    MFaB

    B

    GP(clifu

    *

    100,

    000A

    Inte

    rrup

    ting

    Ratin

    g (R

    MSsy

    mm

    etric

    al)

    or

    Gre

    ater

    Cur

    rent

    -Lim

    iting

    10,0

    005

    0,00

    0 AI

    C

    Buss Fuse Selection Chart (600 Volts or Less)heavy inrush 0 to T-TRONTM JJN 300V Tcurrents). 1200A (fast-acting) JJS 600VMotor loads 0 LOW-PEAK

    LP-CC 600V CC(circuits with to (time-delay)heavy inrush 30Acurrents.)Non-motor loads 0 LIMITRON

    KTK-R 600V CC(circuits with no to (fast-acting)heavy inrush 30Aranch currents.)Control transformer 0 TRON FNQ-R 600V CCcircuits and lighting to (time-delay)ballasts; etc. 30AGeneral purpose; 0 SC SC 480V Gi.e., lighting topanelboards. 60AMiscellaneous 0 ONE-TIME NON 250V H or K5

    to NOS 600V600A

    eneral Plug fuses can FUSTAT S 125V Surpose be used for (dual-element,

    non- branch circuits 0 time-delay)urrent and small to FUSETRON

    T 125V **

    miting component 30A (dual-element,ses) protection. time-delay)

    Buss Type W W 125V *** U.L. Listed as Edison Base Plug Fuse.Some ampere ratings are available as U.L. Class K5 with a 50,000A interrupting rating.RK1 and RK5 fuses fit standard switches, fuseblocks and holders; however, the rejection feature of Class R sw

    (RK1 and RK5) prevent the insertion of the non-rejection fuses (K1, K5, and H).200 The space saver ( the sizeof KTN-R/KTS-R).

    200 Very compact ( 1);rejection feature. Excellent for motorcircuit protection.

    200 Very compact ( 1);rejection feature. Excellent for outdoorhighway lighting.

    200 Very compact ( 1);rejection feature. Excellent for controltransformer protection.

    100 Current limiting; dia. varyinglengths per amp rating.

    10 Forerunners ofthe moderncartridge fuse.

    10 Base threads of Type Sdiffer with amp ratings. T and W have Edison base.

    10 T & S fuses recommended for motor circuits. W notrecommended for circuits

    10with motor loads.

    itches and fuseblocks designed specifically for rejection type fuses(optimum to (dual-element, LPS-RK_SP 600Vovercurrent 600A time-delay)protection). 601 to LOW-PEAK KRP-C_SP 600V L

    6000A (time-delay)Motors, welder, 0 FUSETRON FRN-R 250V RK5transformers, to (dual-element, FRS-R 600Vcapacitor banks 600A time-delay)(circuits with heavy 0 DURA-LAGTM DLN-R 250V RK5inrush currents). to (dual-element, DLS-R 600V

    600A time-delay)601 to LIMITRON KLU 600V L

    ain, 4000A (time-delay)eeder Non-motor loads KTN-R 250V RK1nd (circuits with no 0 KTS-R 600Vranch heavy inrush to

    currents). 600A LIMITRONLIMITRON fuses

    _____ (fast-acting)particularly suited 601 to KTU 600V Lfor circuit breaker 6000Aprotection.

    Reduced Dimensions For Installation in Restricted SpaceClass J(0-600A), T(0-1All type loads LOW-PEAK LPJ_SP 600V J(optimum (dual-element,overcurrent 0 time-delay)protection). to__________ 600ANon-motor loads LIMITRON JKS 600V J(circuits with no (quick-acting)Unequaled for combinedshort-circuit and

    300 overload protection.(Specification grade product)200 Moderate degree of

    current-limitation. Time-delaypasses surge-currents.

    200

    200 All-purpose fuse. Time-delay passes surge-currents.

    200 Same short-circuit protectionas LOW-PEAK fuses butmust be sized larger forcircuits with surge-currents;i.e., up to 300%.

    200 A fast-acting, highperformance fuse.

    200A), CC(0-30A), G(0-60A)300 All-purpose fuses.

    Unequaled for combinedshort-circuit and overloadprotection. (Specification grade product)

    200 Very similar to KTS-RLIMITRON, but smaller.15

  • General Data Dimensions (Inches)

    10.75

    8.6

    801A

    601A

    450A

    35A

    .881A to

    .88

    .8

    2.1.

    70A

    21

    110A

    225A

    CLAT-TRJJN (1.7

    60

    1A

    to8

    00

    A

    80

    1A

    to1

    20

    0A

    13

    50

    Ato

    16

    00

    A

    18

    00

    Ato

    20

    00

    A

    2

    2

    .5

    2.75

    .44

    2.38

    .38.38

    2

    2.5

    2

    2.5 3 3.5

    3

    3

    6.75 5.75

    .63 All Slots and Holes

    3.632.721.731

    225A to 400A

    .88

    3.252.5

    1.66

    110A to 200A

    .75

    2.952.361.64

    70A to 100A

    .81

    35A to 60A

    1.56

    .56

    1A to 30A

    1.5

    1.082.53

    4

    2

    to 1200A

    .922.223.38

    1.75

    to 800A

    .88

    to 600A

    2.03

    1.25

    3.06

    to 200A

    .86

    .75

    .84

    1

    to 400A

    .

    CLAKRP.81

    5 1.38

    .88

    .88

    1.75

    1.63

    001Ato500A

    3000A3500A

    to4000A

    4500Ato

    5000A

    1.75.75.75

    .5

    5

    4

    5

    4.75

    5.75

    5.25

    6.25

    6.08.0

    3.75

    .74 2.13 .38

    .53

    2450A to600A 2.5

    3.38

    .58

    1.63

    1.88

    .41

    2

    .25

    225A to400A

    SS L LOW-PEAK & LIMITRON Fus-C, KTU, & KLU (601 - 4000A) (600V)

    70-10110-2225-4450-6

    LOW-

    Ampe70-10

    110-2225-4450-616

    1.38

    6000A

    6.753.75

    1

    5.75

    7.13

    es

    N O T E : K R P - C L ( 1 5 0 A t o 6 0 0 A )f u ses have same d imens i ons as601A to 800A case size. KTU (400Ato 600A) have same d imens ions ,except tube 3 lgth. 2 dia.; termi-nal 1/ width 1/ thick.

    0 5.88 1.06 7.88 1.3400 7.13 1.56 9.63 1.8400 8.63 2.06 11.63 2.5900 10.38 2.59 13.38 3.13

    PEAK & FRS-R

    250V 600Vre A B A B

    0 5.88 1.16 7.88 1.16

    00 7.13 1.66 9.63 1.6600 8.63 2.38 11.63 2.3800 10.38 2.88 13.38 2.883.982.951.78

    1.25

    450A to 600A

    601A to 800A

    4.333.171.88

    1.75

    to 60A

    .56Dia.

    30A

    .41 Dia.

    4 .75

    1656

    to100A

    .84

    .44

    .69.88

    21

    7.135.25

    4.633.632.63

    70A to 100A

    .28

    .75 1.13

    .131.43

    2.38.63

    35A to 60A

    1.06

    .5

    1A to 30A

    .81

    2.25

    5.754.383.0

    43" 1.38"

    1.13.28

    .19"

    1.63110A to200A

    A

    B

    SS TON Fuses300V) JJS (600V)

    CLASS JLOW-PEAK & LIMITRON FusesLPJ & JKS (600V)

    CLASS RK5 & RK1FUSETRON, LOW-PEAK &LIMITRON Fuses (250V & 600V)FRN-R & FRS-R; LPN-RK & LPS-RK; KTN-R & KTS-RBasic dimensions are same as Class H (for-merly NEC) ONE-TIME (NON & NOS) andSUPERLAG Renewable RES & REN fuses.

    NOTE: These fuses can be used to replaceexisting Class H, RK1 and RK5 fuses relatingto dimensional compatibility.

    250V 600VAmpere A B A B-30 2 .56 5 .8135-60 3 .81 5.5 1.06

    FUSETRON & LIMITRON

    250V 600VAmpere A B A B

    A

    B

  • Conductor Protection

    GeneraAll codanceThey mas reqeconocurren

    Fthe coing dosize fuampecircuportabnot cofuse rthan 8

    S25, 30225, 21600,

    Naddedtection430-5contro

    Per SeFlexibtion raaccepmore,#16 fithe newouldconduthe neare ca

    LocatioFusesits supfeedeA) Fu

    codotrotheratmi[24coing

    B) FucophfeerecnoN

    C) Fufeesethetorplupri

    25ofppFuistoqofwbmm

    teiodradsomrd ope

    ieto

    Trteof1)2)3)

    4)

    tee

    Othp1)2)

    V

    Vlnductors must be protected against overcurrents in accor- with their ampacities, as set forth in NEC Section 240-3.ust also be protected against short-circuit current damage,

    uired by Sections 240-1 (Note) and 110-10. The safest, mostmical way to meet these requirements is through the use oft-limiting fuses.use ampere ratings must not be greater than the ampacity ofnductor. Section 240-3(b) states that if such conductor rat-es not correspond to a standard size fuse, the next largerse may be used, provided its rating does not exceed 800

    res and the conductor is not part of a multi-outlet branchit supplying receptacles for cord and plug connectedle loads. When the ampacity of busway or cable bus doesrrespond to a standard fuse size, the next larger standard

    ating may be used, even though this rating may be greater00 amperes (364-10 and 365-5).tandard fuse sizes per Section 240-6 are: 1, 3, 6, 10, 15, 20,, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200,50, 300, 350, 400, 450, 500, 600, 601, 700, 800, 1000, 1200,2000, 2500, 3000, 4000, 5000, and 6000 amperes.ote: The small fuse ampere ratings of 1, 3, 6, and 10 were to provide more effective short-circuit and ground-fault pro- for motor circuits, in accordance with Sections 430-40 and

    2 and U.L. requirements for protecting the overload relays inllers for very small motors.

    ction 240-4le cords and extension cords shall have overcurrent protec-ted at their ampacities. Supplementary fuse protection is antable method of protection. For #18 fixture wire of 50 feet or

    a 6 amp fuse would provide the necessary protection. Forxture wire of 100 feet or more, an 8 amp fuse would providecessary protection. For #18 extension cords, a 10 amp fuse provide the necessary protection for a cord where only twoctors are carrying current, and a 7 amp fuse would providecessary protection for a cord where only three conductorsrrying current.

    n of Fuses in Circuit (Section 240-21) must be installed at the point where the conductor receivesply, i.e., at the beginning or lineside of a branch circuit or

    r (240-21). ses are not required at the conductor supply if a feeder tapnductor is not over ten feet long; is enclosed in raceway;es not extend beyond the switchboard, panelboard or con-l device which it supplies; and has an ampacity not less than combined computed loads supplied, and not less than theing of the device supplied, unless the tap conductors are ter-nated in a fuse not exceeding the tap conductor ampacity0-21(b)]. For field installed taps, the ampacity of the tap

    nductor must be at least 10% of the overcurrent device rat-. See Note following D.ses are not required at the conductor supply if a feeder tapnductor is not over 25 feet long; is suitably protected fromysical damage; has an ampacity not less than 1/3 that of theder conductors or fuses from which the tap conductorseive their supply; and terminate in a single set of fuses sized

    t more that the tap conductor ampacity [240-21(c)]. Seeote following D.ses are not required at the conductor supply if a transformerder tap has primary conductors at least 1/3 ampacity, and/or

    condary conductors at least 1/3 ampacity, when multiplied by approximate transformer turns ratio of the fuse or conduc-s from which they are tapped; the total length of one primarys one secondary conductor (excluding any portion of the

    D)

    Noserconunpdamconcaurecboausetapablfromvarduc

    E)

    NoformF)

    480

    48017

    mary conductor that is protected at its ampacity) is not over th feet in length; the secondary conductors terminate in a set fuses rated at the ampacity of the tap conductors; and if therimary and secondary conductors are suitably protected fromhysical damage [240-21(d)].ses are not required at the conductor supply if a feeder tap

    not over 25 feet long horizontally and not over 100 feet longtal length in high bay manufacturing buildings where onlyualified persons will service such a system. Also, the ampacity the tap conductors is not less than 1/3 of the fuse rating fromhich they are supplied. The size of the tap conductors muste at least No. 6 AWG copper or No. 4 AWG aluminum. Theyay not penetrate walls, floors, or ceilings, and the taps areade no less than 30 feet from the floor [240-21(e)].

    : Smaller conductors tapped to larger conductors can be aus hazard. If not adequately protected against short-circuititions (as required in Sections 110-10 and 240-1), these

    otected conductors can vaporize or incur severe insulationge. Molten metal and ionized gas created by a vaporizeductor can envelop other conductors (such as bare bus),ing equipment burndown. Adequate short-circuit protection is

    mended for all conductors. When a tap is made to a switch- bus for an adjacent panel, such as an emergency panel, thef BUSS cable limiters is recommended for protection of the

    ed conductor. These current-limiting cable limiters are avail-in sizes designed for short-circuit protection of conductors#12 to 1000 kcmil. BUSS cable limiters are available in a

    ty of terminations to make adaption to bus structures or con-rs relatively simple.

    ansformer secondary conductors of separately derived sys-ms do not require fuses at the transformer terminals when all the following conditions are met. [240-21(j)]:

    Must be an industrial location.Secondary conductors must be less than 25 feet long.Secondary conductor ampacity must be at least equal tothe secondary full-load current of transformer and sum ofterminating, grouped, overcurrent devices.Secondary conductors must be protected from physicaldamage.

    : Switchboard and panelboard protection (384-16) and trans-r protection (450-3) must still be observed.utside conductors that are tapped to a feeder or connected toe secondary terminals of a transformer do not require fuserotection when all of the following are met:

    The conductors are protected from physical damage.The conductors terminate in a single set of fuses, no larger

    150 AmpFeederFuse

    50 AmpRatedConductor

    TRANS-FORMER2:1 RATIO 100 Amp

    Fuse

    150 AmpRatedConductor

    100 AmpRatedConductor 240V.

    300 AmpFeederFuse

    100 AmpRated Conductor

    TRANS-FORMER1:1 RATIO

    100 AmpFuse

    300 AmpRatedConductor 480V.

    25 Feetor Less

    .

    . 100 AmpRatedConductoran the ampacity of the conductors.

  • Conductor Protection

    3) The conductors are outside, except for point of termination.4) The overcurrent device is near or a part of the disconnect-ing means.5) The disconnecting means is readily accessible outdoors or,if indoors, nearest the point of the entrance of the conductors.[240-21(m)].

    Branch CircuitsLighting And/Or Appliance Load (No Motor Load)The branch circuit rating shall be classified in accordance with therating of the overcurrent protective device. Classifications for thosebranch circuits other than individual loads shall be: 15, 20, 30, 40,and 50 amperes (210-3).

    Branch circuit conductors must have an ampacity of the rat-ing of the branch circuit and not less than the load to be served(210-19).

    The minimum size branch circuit conductor that can be usedis No. 14 (210-19). For exceptions to minimum conductor size, see210-19.

    Bby a Basicanon-cthe cogreateBrancmore fusedaccor

    FeederThe femust bcontiner conductocompFeedefeedelightin

    ServicEach series(for exthe secent th

    Service disconnecting means can consist of one to six switch-es for each service or for each set of service entrance conductorspermitted in Section 230-2. When more than one switch is used,the switches must be grouped together (230-71).

    Service equipment must have adequate short-circuit ratingsfor the short-circuit currents available. (230-65)

    Transformer Secondary ConductorsSecondary conductors need to be protected from damage by theproper overcurrent protective device. Although 240-3(i) providesan exception for conductors supplied by a single phase trans-former with a 2-wire secondary, or a three-phase delta-delta trans-former with a 3-wire, single voltage secondary, it is recommendedthat these conductors be protected. Primary overcurrent devicescannot adequately provide protection during internal transformerfaults.

    Motor Circuit Conductor Protectionors and motor circuits have unique operating characteristics circuit components and therefore must be dealt with differently other type loads. Generally, two levels of overcurrent protec-

    are required for motor branch circuits:verload protectionMotor running overload protection istended to protect the system components and motor fromamaging overload currents.hireelhir

    re duitoraLuiranch circuit conductors and equipment must be protectedfuse with an ampere rating which conforms to 210-20.lly, the branch circuit conductor and fuse must be sized for

    ontinuous load (as calculated per Article 220) plus 125% ofntinuous load (210-22 and 220-2). The fuse size must not ber than the conductor ampacity (for exceptions, see 210-20).h circuits rated 15, 20, 30, 40, and 50 amperes with two oroutlets (other than receptacle circuits of 220-3b) must be at their rating and the branch circuit conductor sizedding to Table 210-24 (see 210-24).

    Circuits (No Motor Load)eder fuse ampere rating and feeder conductor ampacitye at least 100% of the non-continuous load plus 125% of the

    uous load as calculated per Article 220 (220-10b). The feed-ductor must be protected by a fuse not greater than the con-

    r ampacity (for exceptions, see 240-3). Motor loads shall beuted in accordance with Article 430; see subsection on Motorr Protection. For combination motor loads and other loads on

    rs, see subsection on feeder combination motor, power, andg loads.

    e Equipmentungrounded service entrance conductor shall have a fuse in with a rating not higher than the ampacity of the conductorceptions, see 230-90a-c). The service fuses shall be part ofrvice disconnecting means or be located immediately adja-ereto (230-91).

    Motandthantion1. O

    ind

    2. ScnrTc

    curtivecircmochaYELcirc18ort-circuit protection (includes ground fault protection)Short-cuit protection is intended to protect the motor circuit compo-nts such as the conductors, switches, controllers, overloadays, motors, etc. against short-circuit currents or grounds.is level of protection is commonly referred to as motor branchcuit protection.Frequently, due to inherent limitations in various types of over-nt devices for motor application, two or more separate protec-evices are used to provide overload protection and short-t protection. An exception is the dual-element fuse. For mostr applications, the beneficial features of dual-element fusecteristics allow sizing of the FUSETRON and LOW-PEAK

    OW fuses to provide both protection functions for motor ts.

  • Equipment Protection

    Listed Listedinstrucobservment lthan monly fu

    PanelbA maxinstall(384-1must btwo sethe panot retion nIndividvidua(384-1must (384-1gle swnot res

    Woperatexceethe ascontin

    Iffor theformerphaseplies determto prim

    ApplianAppliaSectiobranchapplia

    Fappliaexcee

    Erated divideeach snot to installeble (fo

    Ffrom 1ancescircuitmentsbe diva fuse

    Pplied f

    SuppleSupplNationand o

    tsub. T

    areT

    detalesivit thd ati

    Cocod p

    torrrerretents. S

    Nivip

    s, es%nce cngct

    Lmedau

    suR

    ngnuhen MC

    T d f. ake o

    Se

    nt, S

    t li a

    con ap

    chT

    -1r or Labeled Equipment or labeled equipment must be installed in accordance withtions included in the listing or labeling (110-3b). Be sure toe maximum branch circuit fuse size labels. When the equip-abel is marked with a Maximum Fuse Ampere Rating ratherarked with Maximum Overcurrent Device Ampere Rating,

    ses can be used for protection of this equipment.

    oardsimum of 42 fuses (excluding main fuses) are permitted to beed in a lighting and appliance branch circuit panelboard5). Each lighting and appliance branch circuit panelboarde individually protected on the supply side by not more thants of fuses having a combined rating not greater than that ofnelboard (384-16). Exception No. 1: Individual protection isquired when the panelboard feeder has overcurrent protec-ot greater than that of the panelboard. Exception No. 2:ual protection in existing installations is not required for indi-

    l residential occupancy service entrance panelboards 6a). Panels with snap switches rated at 30 amperes or lessbe protected by fuses not larger than 200 amperes 6b). Fusible panelboards are available with heavy duty tog-itches rated more than 30 amperes; these panelboards aretricted by this 200 ampere requirement.hen the load continues for more than 3 hours under normalion, the total load on any fuse in the panelboard should notd 80% of the fuse rating (384-16c). Exception No. 1: Wheresembly including the overcurrent device is approved foruous duty at 100% of its rating. the panelboard is supplied through a transformer, the fuses protection of the panelboard must be located on the trans- secondary (384-16d) except when the transformer is single- with a two-wire secondary and the fuse on the primary com-with Section 450-3(b)(1) and does not exceed the valueined by multiplying the panelboard rating by the secondaryary voltage ratio (384-16d Exception).

    cesnce branch circuits shall be protected in accordance withn 240-3. If a fuse rating is marked on an appliance, the circuit fuse rating cannot exceed that rating marked on the

    nce (422-6)or branch circuits which supply a single non-motor operatednce rated more than 13.3 amperes, the fuse rating shall notd 150% of the appliance rating (422-28e).lectric heating appliances using resistance heating elementsmore than 48 amperes shall have the heating elements sub-d such that each subdivision does not exceed 48 amps andubdivision shall be protected by a branch circuit listed fuseexceed 60 amperes in rating. These fuses shall be factoryd by the heater manufacturer and they should be accessi-r Exceptions, refer to Section 422-28).ixed appliances are considered protected when supplied5, 20, 25, or 30 ampere branch circuits. Fixed cooking appli- are permitted to be protected by 40 or 50 ampere branchs (210-23). Household appliances with surface heating ele- that have a maximum rating greater than 60 amperes mustided into two or more circuits, each of which is protected by of no greater than 50 amperes.ortable appliances are considered as protected when sup-rom a 15, 20, or 30 ampere branch circuit (210-23).

    mentary Protectionementary overcurrent protection is recognized by theal Electrical Code for use in lighting fixtures, appliances,ther equipment or for internal control circuits and compo-

    nena s210as

    holinstagindthableloc

    Air Air erecommoCuCuProme430

    BRAIndComCoilFus175brafusrati[Se

    eleconbecing

    ratimafurtbeeMUCIR

    tiveandriesbretyp

    nammewiththawith

    DisThecomwhi

    430roto19 of equipment. This type of protection should not be used asstitute for branch circuit protection as described in Articlehis type of protection is not required to be readily accessible branch circuit devices.here are a wide variety of supplementary fuses and fuse-rs which have small physical dimensions and are easily

    led in or on equipment, appliances, or fixtures. The advan- of supplementary protection are closer fuse sizing for betterdual protection, isolation of equipment on overcurrents soe branch circuit fuse is not disturbed, ease in locating trou-

    equipment, and generally direct access to the fuse at theon of the equipment.

    nditioning and Refrigerationnditioning and refrigeration equipment requirements are cov-

    in Article 440 of the National Electrical Code. Hermetic motor-ressors are not rated in full-load amperes as are standards. Instead, different terms are used, such as Rated Loadnt, Branch Circuit Selection Current, Maximum Continuousnt, Minimum Circuit Ampacity, and Maximum Overcurrentction. This equipment has overcurrent protection require- that differ from that for ordinary motors covered in Articleome highlights are presented here.

    CH CIRCUIT PROTECTIONdual Motor-Compressor(s) and HVAC Equipment Having Motor-ressor(s) and Other Loads (Such as Fan Motors, Electric Heaters,etc.). sized for branch circuit protection only must not exceed of the hermetic motor-compressor rated-load current orh circuit selection current (whichever is larger). If this sizeannot withstand the motor starting current, a higher ampere is permitted, but in no case can the fuse size exceed 225%ion 440-22(a)].OW-PEAK YELLOW dual-element and FUSETRON dual-nt fuses are recommended for branch circuit protection of airitioning and refrigeration hermetic motor-compressorsse these fuses have an adequate time-delay for motor start-rges.efer to the nameplate on the equipment. The sizing (ampere

    ) for the overcurrent protection has been determined by thefacturer of the equipment. It is not necessary to apply anyr multipliers to arrive at the proper size. This has alreadydone by the manufacturer. The nameplate will indicate MAXI- SIZE FUSE. . .or. . .MAXIMUM SIZE FUSE OR HACR TYPEUIT BREAKER.he marked protective device rating is the maximum protec-evice rating for which the equipment has been investigatedound acceptable by nationally recognized testing laborato-Where the marking specifies fuses, or HACR type circuiters, the equipment is intended to be protected only by thef protective device specified.ee Listed or Labeled Equipment for requirement when

    plate states MAXIMUM SIZE FUSE. This is a critical require- and must be followed without exception to be in complianceection 110-3(b) of the Code. NEC Section 110-3(b) requiressted or labeled equipment must be installed in accordanceny instructions included in the listing or labeling.

    necting Means (Individual hermetic motor compressor)mpere rating of the disconnect shall be at least 115% of theressors rated load current or branch-circuit selection current,ever is greater [Section 440-12(a)(1)].he horsepower rating can be obtained by referring to Table51 of the NEC, which shows the conversions from locked

    current to horsepower [Section 440-12(a)(2)].

  • Equipment Protection

    Disconnecting Means (Equipment that has hermetic motor-compressorand other loads)The a115%ment.

    Tleast ment.[Sectipress

    ControThe ctinuounot letion ctrollercontromuchratinglocke

    Tmaximtable Whereing rarating

    AvailaAs wil istedmaximimporthe eqfault climitequipovercrent toinform

    Short-

    110-129.8 or 9.9 - 116.1 - 34.1 - Over 8

    200-202.12 o2.13 - 3.8 - 99.6 - 2Over 2

    Table s

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    rempere rating of the disconnecting means must be at least of the sum of all of the individual loads within the equip- . .at rated load conditions [Section 440-12(b)(2)].he horsepower rating of the disconnecting means must be at

    equal to the sum of all of the individual loads within the equip- . .at rated load conditions. . .and at locked rotor conditionson 440-12(b)(1)]. The equivalent horsepower rating of the com-or can be obtained by referring to Table 430-151 of the NEC.

    llerontroller for a hermetic motor-compressor must have a con-s duty full-load current rating and locked-rotor current ratingss than the nameplate rated current or branch circuit selec-urrent (whichever is larger), (Section 440-41). Where the con- serves a hermetic motor-compressor(s) plus other loads, theller rating is determined according to Section 440-12(b), in

    the same manner as determining the disconnecting means. It may be necessary to refer to Table 430-151 to convertd rotor current values to horsepower.he branch circuit protective device rating shall not exceed theum protective device rating shown on a manufacturers heaterfor use with a given motor controller [Section 440-22(c)]. the equipment is marked MAXIMUM SIZE FUSE ampere rat-ther than stating MAXIMUM OVERCURRENT DEVICE ampere, only fuses can be used for the branch circuit protection.

    ble Short-Circuit Currentth most electrical equipment, HVAC equipment is tested and based upon circuits capable of delivering specificum values of short-circuit current. Because of this, it is

    tant that the available fault current at the line side terminals ofuipment does not exceed these values. Where the availableurrent does exceed the above levels, it will be necessary to the fault current to levels within the withstand rating of thement as tested. This is done by ins