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Section OverviewThis Technical Application Guide or Fuseology section provides the

inormation needed to select the correct types o Litteluse POWR-GARD

uses or most applications. I there are any questions or i additional

data is needed or a specic use, call the Litteluse Technical Supportand Engineering Service Group at 1-800-TEC-FUSE (1-800-832-3873)

or visit us online at www.litteluse.com.

Fuseology Fundamentals.................................................... 181-182

Selection Considerations .................................................... 182-186

Time-current Curves and Peak Let-through Charts ............. 187-189

Selective Coordination ........................................................ 189-191

UL/CSA Fuse Classes and Applications .............................. 192-193

Electrical Saety Guide ........................................................ 194-195

Terms and Defnitions ......................................................... 196-202

Motor Protection Tables ..................................................... 203-205

Alphanumeric Index o Catalog Numbers ........................... 206-207

Condensed Fuse Cross Reerence ............................................ 208

TECHNICAL APPLICATION GUIDE

Table o Contents

Additional Technical Information

An expanded Technical

Application Guide andFuseology section,

white papers, and

a library o technical

inormation is

available online at

www.litteluse.com/technicalcenter.

ourtesy of Steven Engineering, Inc.-230 Ryan Way, South San Francisco, CA 94080-6370-Main Office: (650) 588-9200-Outside Local Area: (800) 258-9200-www.stevenengineeri


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FUsEOLOGy FUNDAmENTALs

I. OVERCURRENT PROTECTION

FUNDAMENTALS(FUSES AND HOW THEY WORK)

IntroductionAn important part o developing quality overcurrent protection

is an understanding o system needs and overcurrent

protective device undamentals. This section discusses these

topics with special attention to the application o uses. I

you have additional questions, call our Technical Support and

Engineering Services Group at 1-800-TEC-FUSE (1-800-832-

3873). Denitions o terms used in this section are located

towards the end o this Technical Application Guide.

Why Overcurrent Protection?All electrical systems eventually experience overcurrents.

Unless removed in time, even moderate overcurrents

quickly overheat system components, damaging insulation,

conductors, and equipment. Large overcurrents may melt

conductors and vaporize insulation. Very high currents

produce magnetic orces that bend and twist bus bars.

These high currents can pull cables rom their terminals and

crack insulators and spacers.

Too requently, res, explosions, poisonous umes and

panic accompany uncontrolled overcurrents. This not only

damages electrical systems and equipment, but may cause

injury or death to personnel nearby.

To reduce these hazards, the National Electrical Code(NEC), OSHA regulations, and other applicable design and

installation standards require overcurrent protection that will

disconnect overloaded or aulted equipment.

Industry and governmental organizations have developed

perormance standards or overcurrent devices and testing

procedures that show compliance with the standards and

with the NEC. These organizations include: the American

National Standards Institute (ANSI), National Electrical

Manuacturers Association (NEMA), and the National

Fire Protection Association (NFPA), all o which work in

conjunction with Nationally Recognized Testing Laboratories

(NRTL) such as Underwriters Laboratories (UL).

Electrical systems must meet applicable code requirements

including those or overcurrent protection beore electric

utilities are allowed to provide electric power to a acility.

What is Quality Overcurrent Protection?A system with quality overcurrent protection has the

ollowing characteristics:

Meets all legal requirements, such as NEC, OSHA, local1.

codes, etc.

Provides maximum saety or personnel, exceeding2.

minimum code requirements as necessary.

Minimizes overcurrent damage to property, equipment,3.

and electrical systems.Provides coordinated protection. Only the protective4.

device immediately on the line side o an overcurrent

opens to protect the system and minimize unnecessary

downtime.

Is cost eective while providing reserve interrupting5.

capacity or uture growth.

Consists o equipment and components not subject to6.

obsolescence and requiring only minimum maintenance

that can be perormed by regular maintenance personnel

using readily available tools and equipment.

Overcurrent Types and Eects

An overcurrent is any current that exceeds the ampere rating oconductors, equipment, or devices under conditions o use. The

term overcurrent includes both overloads and short-circuits.

OverloadsAn overload is an overcurrent conned to normal current

paths in which there is no insulation breakdown.

Sustained overloads are commonly caused by installing

excessive equipment such as additional lighting xtures

or too many motors. Sustained overloads are also caused

by overloading mechanical equipment and by equipment

breakdown such as ailed bearings. I not disconnected

within established time limits, sustained overloads

eventually overheat circuit components causing thermaldamage to insulation and other system components.

Overcurrent protective devices must disconnect circuits and

equipment experiencing continuous or sustained overloads

beore overheating occurs. Even moderate insulation

overheating can seriously reduce the lie o the components

and/or equipment involved. For example, motors overloaded

by just 15% may experience less than 50% o normal

insulation lie.

Temporary overloads occur requently. Common causes

include temporary equipment overloads such as a machine

tool taking too deep o a cut, or simply the starting o an

inductive load such as a motor. Since temporary overloads

are by denition harmless, overcurrent protective devices

should not open or clear the circuit.

It is important to realize that uses selected must have

sucient time-delay to allow motors to start and temporary

overloads to subside. However, should the overcurrent

continue, uses must then open beore system components

are damaged. Litteluse POWR-PRO and POWR-GARD

time-delay uses are designed to meet these types o

protective needs. In general, time-delay uses hold 500% o

the rated current or a minimum o ten seconds, yet will still

open quickly on higher values o current.

Technical Application Guide



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Even though government-mandated high-eciency motors

and NEMA Design E motors have much higher locked rotorcurrents, POWR-PRO time-delay uses such as the FLSR_

ID, LLSRK_ID, or IDSR series have sucient time-delay to

permit motors to start when the uses are properly selected

in accordance with the NEC.

Short-CircuitsA short-circuit is an overcurrent fowing outside o its normal

path. Types o short-circuits are generally divided into

three categories: bolted aults, arcing aults, and ground

aults. Each type o short-circuit is dened in the Terms and

Denitions section.

A short-circuit is caused by an insulation breakdown or

aulty connection. During a circuits normal operation, theconnected load determines current. When a short-circuit

occurs, the current bypasses the normal load and takes a

shorter path, hence the term short-circuit. Since there is

no load impedance, the only actor limiting current fow is

the total distribution systems impedance rom the utilitys

generators to the point o ault.

A typical electrical system might have a normal load impedance

o 10 ohms. But in a single-phase situation, the same system

might have a load impedance o 0.005 ohms or less. In order

to compare the two scenarios, it is best to apply Ohms Law (I

= E/R or AC systems). A 480 volt single-phase circuit with the

10 ohm load impedance would draw 48 amperes (480/10 = 48).

I the same circuit has a 0.005 ohm system impedance when

the load is shorted, the available ault current would increase

signicantly to 96,000 amperes (480/0.005 = 96,000).

As stated, short-circuits are currents that fow outside

o their normal path. Regardless o the magnitude o

overcurrent, the excessive current must be removed quickly.

I not removed promptly, the large currents associated

with short-circuits may have three proound eects on an

electrical system: heating, magnetic stress, and arcing.

Heatingoccurs in every part o an electrical system when

current passes through the system. When overcurrents

are large enough, heating is practically instantaneous. The

energy in such overcurrents is measured in ampere-squared

seconds (I2

t). An overcurrent o 10,000 amperes that lasts or0.01 seconds has an I2t o 1,000,000 A2s. I the current could

be reduced rom 10,000 amperes to 1,000 amperes or the

same period o time, the corresponding I2t would be reduced

to 10,000 A2s, or just one percent o the original value.

I the current in a conductor increases 10 times, the I2t

increases 100 times. A current o only 7,500 amperes

can melt a #8 AWG copper wire in 0.1 second. Within

eight milliseconds (0.008 seconds or one-hal cycle), a

current o 6,500 amperes can raise the temperature o #12

AWG THHN thermoplastic insulated copper wire rom its

operating temperature o 75C to its maximum short-circuit

temperature o 150C. Any currents larger than this may

immediately vaporize organic insulations. Arcs at the pointo ault or rom mechanical switching such as automatic

transer switches or circuit breakers may ignite the vapors

causing violent explosions and electrical fash.

Magnetic stress(or orce) is a unction o the peak current

squared. Fault currents o 100,000 amperes can exert orces

o more than 7,000 lb. per oot o bus bar. Stresses o this

magnitude may damage insulation, pull conductors rom

terminals, and stress equipment terminals suciently such

that signicant damage occurs.

Arcingat the point o ault melts and vaporizes all o the

conductors and components involved in the ault. The arcs

oten burn through raceways and equipment enclosures,

showering the area with molten metal that quickly starts resand/or injures any personnel in the area. Additional short-circuits

are oten created when vaporized material is deposited on

insulators and other suraces. Sustained arcing-aults vaporize

organic insulation, and the vapors may explode or burn.

Whether the eects are heating, magnetic stress, and/or

arcing, the potential damage to electrical systems can be

signicant as a result o short-circuits occurring.

II. SELECTION CONSIDERATIONSSelection Considerations or Fuses (600 volts and below)

Since overcurrent protection is crucial to reliable electricalsystem operation and saety, overcurrent device selection

and application should be careully considered. When

selecting uses, the ollowing parameters or considerations

need to be evaluated:

Current Rating

Voltage Rating

Interrupting Rating

Type o Protection and Fuse Characteristics

Current Limitation

Physical Size

Indication

Current RatingThe current rating o a use is the AC or DC current,

expressed in amperes, which the use is capable o carrying

continuously under specied conditions. Fuses selected

or a circuit must have ampere ratings that meet NEC

requirements, namely those ound in NEC Articles 240 and

430. These NEC requirements establish maximum ratings

and in some cases, minimum ratings. When selecting a

use, it is generally recommended to select a current rating

as close as possible to the systems normal running current.

FUsEOLOGy FUNDAmENTALs



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Voltage Rating

The voltage rating o a use is the maximum AC or DCvoltage at which the use is designed to operate. Fuse

voltage ratings must equal or exceed the circuit voltage

where the uses will be installed, and uses used in DC

circuits must be specically rated or DC applications. In

terms o voltage, uses may be rated or AC only, DC only, or

both AC and DC. However, exceeding the voltage ratings or

using an AC only use in a DC circuit could result in violent

destruction o the use.

The standard 600 volt rated uses discussed in this section

may be applied at any voltage less than or equal to their

rating. For example, a 600 volt use may be used in a 277

volt or even a 32 volt system, but not any system exceeding

600 volts.

NOTE: This does not apply to semiconductor fuses and medium

voltage fuses. See the semiconductor and medium voltage

fuse application information on www.littelfuse.com for voltage

limitations of these fuses.

Interrupting RatingThe interrupting rating o a use is the highest available

symmetrical rms alternating current that the use is required

to saely interrupt at its rated voltage under standardized test

conditions. A use must interrupt all overcurrents up to its

interrupting rating without experiencing damage. Standard

UL uses are available with interrupting ratings o 10,000 A,

50,000 A, 100,000 A, 200,000 A, and 300,000 A.

NEC Article 110.9 requires that all equipment intended

to break current at ault levels have an interrupting rating

sucient or the system voltage and current available at

the equipments line terminals. Reer to Figure 1. It is vitally

important to select uses with interrupting ratings which

equal or exceed the available ault current.

The recommendation to standardize on uses with at least

a 200,000 ampere interrupting rating (AIR) ensures that alluses have an adequate interrupting rating while providing

reserve interrupting capacity or uture increases in available

ault current.

300,000 AIR Fuses

Litteluse POWR-PRO use series have a Litteluse Sel-

Certied interrupting rating o 300,000 amperes rms

symmetrical. The 300,000 ampere testing was perormed

in a Nationally Recognized Testing Laboratory, and the tests

were UL witnessed. UL has ruled that uses with a UL

interrupting rating greater than 200,000 amperes must be

marked as Special Purpose Fuses and may not be labeled

as UL Listed Class RK5, RK1, L, etc.

Type o Protection and Fuse CharacteristicsTime current characteristics determine how ast a use

responds to overcurrents. All uses have inverse time

characteristics; that is, the use opening time decreases as

the magnitude o overcurrent increases. When properly rated

in accordance with NEC requirements, uses provide both

overload and short-circuit protection to system conductors

and components. However, in some instances such as when

uses are used to backup circuit breakers or to provide motor

branch circuit short-circuit and ground ault protection, uses

provide only short-circuit protection. A uses response to

overcurrents is divided into short-circuits and overloads.

Short-CircuitsA uses short-circuit response is its opening time on higher-

value currents. For power uses, higher-value currents are

generally over 500-600% o the uses current rating. As

stated earlier, all uses have inverse time characteristics: the

higher the current, the aster the opening time. Since short-

circuits should be removed quickly, inverse time is especially

important or short-circuit protection.

Overloads

While uses must disconnect overloaded conductors and

equipment beore the conductors and components are

seriously overheated, they should not disconnect harmless

temporary overloads. To provide sucient overloadprotection or system conductors, UL has established

maximum use opening times at 135% and 200% o a

uses current rating. All UL Listed uses or application in

accordance with the National Electrical Code must meet

these limits whether they are ast-acting or time-delay uses.

As just stated, a use is designed to respond to two types

o overcurrents short circuits and overloads. As a result,

selecting the proper use or a given application usually

involves deciding whether to use a time-delay use or a

ast-acting use. A more in-depth review o both possible

scenarios is important at this time.

sELECTION CONsIDErATIONs

Main Switchboard

Available Fault

Current = 125,000A

Available Fault

Current = 85,000AAll fuses in main switchboard

must have an A.I.R. of at least

125,000A. Next higher standard

rating is 200,000A.

Fuses in panel must have at

least an 85,000 A.I.C. Next higher

standard rating is 100,000A., but

best choice is time-delay fuses

with 200,000 A.I.R.

Figure 1 Interrupting Rating Requirements per NEC



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Fast-Acting (Normal-Opening) Fuses

Fast-acting uses (sometimes called Normal-openinguses) have no intentional time-delay. Typical opening

times at 500% o the use ampere rating range rom 0.05

second to approximately 2 seconds. Fast-Acting uses

are suitable or non-inductive loads such as incandescent

lighting and general-purpose eeders, or branch circuits

with little or no motor load. When protecting motors and

other inductive loads, ast-acting uses must be rated at

200-300% o load currents to prevent nuisance opening on

in-rush currents. Fuses with such increased ratings no longer

urnish adequate protection rom overloads and only provide

short-circuit protection. Overload relays or other overload

protection devices must be provided to properly protect

conductors and equipment rom overload conditions.

All ast-acting uses provide ast short-circuit response

within their interrupting rating. Some are considered current-

limiting, such as UL Class T and Class J. Others are non-

current-limiting, such as UL Class H.

Time-Delay (SLO-BLO) Fuses

Most UL Class CC, CD, G, J, L, RK5 and RK1 uses, plus

some o the UL Listed Miscellaneous uses are considered

time-delay. I so, they are identied as such on the use

label with the words Time-Delay, T-D, D, or some

other suitable marking. Minimum time-delay varies with

the use class, and to some degree with the use ampere

rating. UL standards or POWR-GARD use series FLNR,

FLNR_ID, FLSR, FLSR_ID, IDSR (UL Class RK5), LLNRK,LLSRK, LLSRK_ID (UL Class RK1), and JTD, JTD_ID (UL

Class J) require these uses to carry 500% rated current or a

minimum o 10 seconds. Standards or CCMR and KLDR (UL

Class CC and CD) and SLC (UL Class G) uses require them

to carry 200% rated current or a minimum o 12 seconds.

Although there is no UL Classication or time-delay Class

L uses, it is still permissible or them to be marked Time-

Delay. The amount o time-delay is determined by the

manuacturer. Litteluse KLPC series and KLLU series uses

will hold 500% current or 10 seconds or more.

In addition to providing time-delay or surges and short time

overloads, time-delay uses meet all UL requirements or

sustained overload protection. On higher values o current,

time-delay uses are current-limiting; meaning they remove

large overcurrents in less than one-hal cycle (0.00833

seconds). Time-delay uses provide the best overall protection

or both motor and general purpose circuits, and eliminate

nuisance use opening and most situations o downtime.

Compared to ast-acting uses, time-delay uses can be

selected with ratings much closer to a circuits operating

current. For example, on most motor circuits Class RK5 and

RK1 uses can be rated at 125-150% o a motors ull load

current (FLA). This provides superior overload and short-

circuit protection, and oten permits the use o smaller,

less expensive disconnect switches. Time-delay useshave gradually replaced most one-time (UL Class K5) and

renewable (UL Class H) uses. Today, more than 50% o all

uses sold by electrical distributors are time-delay uses.

Dual Element Fuses

Litteluse time-delay FLNR, FLNR_ID, FLSR, FLSR_ID, IDSR

(UL Class RK5), and LLNRK, LLSRK, LLSRK_ID (UL Class RK1),

and some JTD, JTD_ID (UL Class J) series uses have true

dual-element construction meaning the use has an internal

construction consisting o separate short-circuit and overload

sections or elements. Time-delay elements are used or

overload protection, and separate ast acting use elements or

links are used to provide current-limiting short-circuit protection.

Very Fast-Acting Fuses

This category o uses exists or limited applications. The

principle use o very ast acting uses is to protect solid-

state electronic components, such as semiconductors. Fuse

series designated as Semiconductor Fuses have special

characteristics including quick overload response, very

low I2t and Ipeak currents, and peak transient voltages, that

provide protection or components that cannot withstand

line surges, low value overloads, or short-circuit currents.

Very ast-acting uses are designed or very ast response to

overloads and short-circuits, and are very current-limiting.

Effect of Ambient Temperature on Fuses

The current carrying capacity o uses is 110% o the use

rating when installed in a standard UL test circuit and tested

in open air at 25C ambient. This allows or derating to 100%

o rating in an enclosure at 40C ambient. At higher ambient

temperatures, the continuous current carrying capacity will

be decreased as shown in Figure 2. This closely ollows

the derating tables or all electrical equipment and can help

reduce equipment burnout due to high ambient conditions.


A

A

B

B

0 0

20

40

60

20

40

60

AMBIENT TEMPERATURE

PERCENT

OFUPRATING

PERCENTOFDOWNRATING

KEY TO CHART:

Curve A - Slo-Blo Fuse

Curve B - Medium and Fast-Acting Fuses

-60C

-76F

-40C

-40F

-20C

-4F

0C

32F

20C

68F

40C

104F

60C

140F

80C

176F

100C

212F

120C

248F

140C

264F

Figure 2 Fuse Rerating Curve



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Litteluse time-delay (SLO-BLO) uses derate quicker in

higher ambient conditions, thus acting as sel-protectingdevices that maintain their integrity until ater opening.

Current LimitationA current-limiting use is one that opens and clears a ault

in less than 180 electrical degrees, or in other words, within

the rst hal electrical cycle (0.00833 seconds). See the

denition o Current-limiting Fuse and Figure 13in the Terms

and Denitions section.

NEC Article 240.2 states that a current-limiting overcurrent

protective device must reduce the peak let-through current to a

value substantially less than the potential peak current that would

have occurred i the use were not used in the circuit or were

replaced with solid conductors o the same impedance. The totaldestructive heat energy (I2t) to the circuit and its components is

greatly minimized as a result o using current-limiting uses.

It is important to note that UL Class H Renewable uses

designed decades ago are considered non-current limiting. Other

than Midget uses, almost all other use types used in todays

electrical systems and applications are considered current-

limiting per the above parameters. This selection consideration

now involves determining the degree or level o current

limitation required to properly protect a given device or system.

It is also important to point out that matching useholders

and/or useblocks must reject non-current-limiting uses and

accept only current-limiting uses o the stated UL Class.

Physical SizeWhile oten overlooked, the physical size or overall

dimensions o the use to be used in a given application is

another important selection consideration to evaluate. There

is a trend toward reduction o size in almost everything, and

electrical equipment is no exception. Fuse size is actually

determined by the size and dimensions o the useblock or

disconnect switch in which it is installed.

While saving space may be an important actor when

selecting the proper uses, other considerations should not

be overlooked. Some o these include:

Does the smallest use have the most desirablecharacteristics or the application?

Does the equipment in which the use will be installed

provide adequate space or maintenance?

Do smaller uses coordinate well with the systems other

overcurrent protection?

I looking at just physical dimensions, a 600 volt, 60 ampere,

200,000 AIR, time-delay, dual-element UL Class CD use is smaller

than a similarly rated UL Class J use, which is in turn, considerably

smaller than a similarly rated UL Class RK1 or Class RK5 use.

However, smaller-sized uses can sometimes have less time-delay

or more nuisance openings than their larger counterparts, so it is

always important to consider all actors involved.

IndicationThe newest consideration or selecting the best use or a

given application is indication. Many o the more commonly

used UL use classes are now available in both indicating

and non-indicating versions. Built-in, blown-use indication

that quickly identies which use or uses within an electrical

panel or system have blown can be ound on the Litteluse

POWR-PRO LLSRK_ID Class RK1, FLNR_ID, FLSR_ID and

IDSR Class RK5, and JTD_ID Class J use series.

The indicating eature on these uses provides reduced

downtime, increased saety, and reduced housekeeping or

troubleshooting headaches and delays. Litteluse Indicator

uses will help lower the costs associated with downtime,

provide longer use lie by minimizing nuisance openings,

increase system perormance by minimizing equipment

damage, and improve saety by minimizing accidents.

III. GENERAL FUSING RECOMMENDATIONSBased on the above selection considerations, the ollowing

is recommended:

Fuses with ampere ratings rom 1/10 through 600 amperes

When available ault currents are less than 100,000

amperes and when equipment does not require the morecurrent-limiting characteristics o UL Class RK1 uses,

FLNR and FLSR_ID Series Class RK5 current-limiting uses

provide superior time-delay and cycling characteristics

at a lower cost than RK1 uses. I available ault currents

exceed 100,000 amperes, equipment may need the

additional current-limitation capabilities o the LLNRK,

LLSRK and LLSRK_ID series Class RK1 uses.

Fast-acting JLLN and JLLS series Class T uses possess

space-saving eatures that make them especially suitable

or protection o molded case circuit breakers, meter

banks, and similar limited-space applications.

Time-delay JTD_ID and JTD series Class J uses are used

in OEM motor control center applications as well as otherMRO motor and transormer applications requiring space-

saving IEC Type 2 protection.

Class CC and Class CD series uses are used in control

circuits and control panels where space is at a premium.

The Litteluse POWR-PRO CCMR series uses are best

used or protection o small motors, while the Litteluse

KLDR series uses provide optimal protection or control

power transormers and similar devices.

For questions about product applications, call our Technical

Support Group at 800-TEC-FUSE.




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Fuses with ampere ratings rom 601 through 6,000 amperes

For superior protection o most general-purpose and motor

circuits, it is recommended to use the POWR-PRO KLPC

series Class L uses. The Class L uses are the only time-

delay use series available in these higher ampere ratings.

Inormation on all the Litteluse use series reerenced above

can be ound on the UL/CSA Fuse Classes and Applications

Charts ound later in this Technical Application Guide.

IV. SELECTION CONSIDERATIONS FORFUSEHOLDERSEqually important to the selection o the proper use is the

correct selection o the proper useholder or use block ora given application. Fuseholders are available using most o

the same Selection Considerations outlined above or UL

use classes. Considerations or useholders include:

Current Rating

Voltage Rating

Interrupting Rating

Physical Size

Indication

Additional selection considerations or useholders and

useblocks include:

Number o poles

Mounting conguration

Connector type

Number o PolesThe number o poles or each set o uses is determined by

the characteristics o the circuit. Most use block series are

available in 1, 2, or 3 pole congurations, although some are

also available with our or more poles. The option to gang

individual useblocks into longer strips will be determined by

the available space and type o wire being used.

Mounting Confguration

Depending on the use block design, another selectionconsideration to evaluate is how the useblock is mounted

or inserted into the panel. Historically, useblocks simply

screwed into the back o the panel, but many newer designs

have now added (or replaced the screw-in design with) a DIN

rail mounting capability. The DIN rail mounting eature allows

the blocks to be quickly installed and removed rom the rails.

Connector TypeFor Litteluse useblocks, a choice o three connector types

or wire terminations is available:

Screw or use with spade lugs or ring terminals.

Screw with Pressure Plate or use with solid orstranded wire without terminal and recommended or

applications where vibration will be a actor.

Box Lug the most durable o the three options and

used with all types o solid wire and Class B and Class C

stranded wire.

There are a ew additional aspects to keep in mind when

selecting the useholder or useblock needed or a given

application. UL Class H blocks accept Class H, Class K5, and

Class R uses. Similarly, Midget-style useblocks accept both

Midget and UL Class CC uses.

Both UL Class R and Class CC useholders contain a

rejection eature which prevents the insertion o a dierentClass or type o use. The physical size and dimensions o

UL Class J and Class T uses accomplish the same thing in

preventing the insertion o a dierent Class o use as well.

V. CIRCUIT PROTECTION CHECKLISTTo select the proper overcurrent protective device or an

electrical system, circuit and system designers should ask

themselves the ollowing questions beore a system is

designed:

What is the normal or average current expected?

What is the maximum continuous (three hours or more)

current expected?What inrush or temporary surge currents can be

expected?

Are the overcurrent protective devices able to distinguish

between expected inrush and surge currents, and open

under sustained overloads and ault conditions?

What kind o environmental extremes are possible? Dust,

humidity, temperature extremes and other actors need

to be considered.

What is the maximum available ault current the

protective device may have to interrupt?

Is the overcurrent protective device rated or the system

voltage?

Will the overcurrent protective device provide the saest

and most reliable protection or the specic equipment?

Under short-circuit conditions, will the overcurrent

protective device minimize the possibility o a re or

explosion?

Does the overcurrent protective device meet all the

applicable saety standards and installation requirements?

Answers to these questions and other criteria will help to

determine the type overcurrent protection device to use or

optimum saety, reliability and perormance.




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The perormance capabilities o various uses are graphically

represented by two dierent types o use characteristiccurves: time-current curves and peak let-through charts.

These curves and charts dene the operating characteristics

o a given use, and assist system designers and engineers

in selecting the proper use to protect equipment and

electrical systems.

Understanding Time-current CurvesTime-current curves provide a graphical representation

or plot o a uses average melting (opening) time at any

current. Time-current curves or Litteluse POWR-GARD

uses can be ound online at

www.litteluse.com/technicalcenter .

In order to make the curves more readable, the perormanceinormation is presented on log-log paper. The overcurrent

values appear across the bottom and increase in magnitude

rom let to right. Average melting times appear on the

let-hand side o the curve and increase in magnitude rom

bottom to top. The ampere ratings o the individual uses

or a given series are listed at the top and increase in rating

rom let to right. Figure 4shows the average melting time

curves or a typical time-delay use series.

As discussed earlier in the Fuseology Fundamentals

section, time-delay, ast-acting, and very ast-acting uses

all respond dierently based on the overcurrents occurring

in the systems each is protecting. To illustrate the basic

dierences between each type o use, Figure 5compares

the average melting times or 100 and 600 amp ratings

o three use types: Litteluse dual-element, time-delay

LLSRK series RK1 uses; Litteluse normal opening NLS

series uses; and Litteluse very ast acting L60S series

semiconductor uses.

To better illustrate this point, Table 3also compares the

opening times or each o these uses.

Peak Let-through ChartsPeak let-through charts illustrate the maximum instantaneous

current through the use during the total clearing time. Thisrepresents the current limiting ability o a use.

Fuses that are current-limiting open severe short-circuits

within the rst hal-cycle (180 electrical degrees or 0.00833

seconds) ater the ault occurs. Current-limiting uses also

reduce the peak current o the available ault current to a

value less than would occur without the use. This reduction

is shown in Figure 6.

A uses current-limiting eects are shown graphically on

Peak Let-through charts such as the one shown in Figure 7.

The values across the charts bottom represent the available

FUsE CHArACTErIsTIC CUrvEs AND CHArTs

1000800

600

400

300

200

10080

60

40

30

20

108

6

4

3

2

1.8

.6

.4

.3

.2

.1.08

.06

.04

.03

.02

.01

200

300

400

600

800

1000

2000

3000

4000

6000

8000

10000

20000

30000

40000

60000

80000

100000

10

20

30

40

60

80

100

15A

30A

60A

100A

200A

400A

600A

TIME

INSECONDS

CURRENT IN AMPERES

1000800600

400

300

200

1008060

40

30

20

108

6

4

3

2

1.8

.6

.4

.3

.2

.1.08

.06

.04

.03

.02

.01

200

300

400

600

800

1000

2000

3000

4000

6000

8000

10000

20000

30000

40000

60000

80000

100000

10

20

30

40

60

80

100

100 AMP

600 AMP

GREEN = TIME DELAY FUSE

RED = NORMAL OPENING FUSEBLUE = VERY FAST ACTING FUSE

TIMEINSECONDS

CURRENT IN AMPERES

AmPErErATING

FUsE TyPEOPENING TImE IN sECONDs

500% rATING 800% rATING 1200% rATING

100

Time-DeLAy 12 c. 0.9 c. 0.14 c.

NORmAL OPeNiNG 2 c. 0.7 c. 0.3 c.

VeRy FAsT-ACTiNG 1.3 c. 0.02 c. >0.01 c.

600

Time-DeLAy 14 c. 0 .7 c. 0 .045 c.

NORmAL OPeNiNG 10 c. 3 c. 1.1 c.

VeRy FAsT-ACTiNG 2 c. 0 .05 c. >0.01 c.

Figure 4 Average Melting Time Curves for Typical Time-Delay

Fuse Series

Figure 5 Comparison of Average Melting Times for Three Fuse

Types

Table 3 Comparative Opening Times for Time-Delay, Fast-

Acting, and Very Fast-Acting Fuses



9/26

188



(also reerred to as potential or prospective) rms symmetrical

ault current. The values on the charts let side represent

the instantaneous available peak current and the peak let-

through current or various use ratings.

To better explain the unction o these charts, lets run

through an example. Start by entering the chart on the

bottom at 100,000 rms symmetrical amperes and read

upwards to the A-B line. From this point, read horizontally

to the let and read the instantaneous peak let-thru current

o 230,000 amperes. In a circuit with a typical 15% short-

circuit power actor, the instantaneous peak o the available

current is approximately 2.3 times the rms symmetrical

value. This occurs since the A-B line on the chart has a2.3:1 slope.

The diagonal curves that branch o the A-B line illustrate the

current-limiting eects o dierent use ampere ratings ora given use series. To continue the example rom above,

enter the chart in Figure 7on the bottom at 100,000 rms

symmetrical amperes and read upwards to the intersection

o the 200 ampere use curve. Now read rom this point

horizontally to the let and read a peak let-through current o

approximately 20,000 amperes.

What this tells us is that the 200 ampere use has reduced

the peak current during the ault rom 230,000 amperes to

20,000 amperes. In other words, this is the current-limiting

eect o the 200 ampere use. 20,000 amperes is less than

one-tenth o the available current. This is important because

the magnetic orce created by current fow is a unction o

the peak current squared. I the peak let-through current oa current-limiting use is one-tenth o the available peak, the

magnetic orce is reduced to less than 1/100 o what would

occur without the use.

Using the Peak Let-through Charts

(Up-Over-and-Down)Peak Let-through Charts or Litteluse POWR-GARD uses

can be ound online at www.litteluse.com/technicalcenter.

These charts are useul in determining whether a given use

can properly protect a specic piece o equipment.

For example, given an available ault-current o 100,000

rms symmetrical amperes, determine whether 600 amp

250 volt time-delay Class RK1 uses can suciently protectequipment that has a 22,000 amp short-circuit rating. Reer

to Figure 8.

Start by locating the 100,000 A available ault-current on the

bottom o the chart (Point A) and ollow this value upwards

to the intersection with the 600 amp use curve (Point B).

Next, ollow this point horizontally to the let to intersect

with the A-B line (Point C). Finally, read down to the bottom

o the chart (Point D) to read a value o approximately

18,000 amps.

Can the use selected properly protect the equipment or

this application? Yes, the POWR-PRO LLNRK 600 ampere

RK1 current-limiting uses have reduced the 100,000amperes available current to an apparent or equivalent

18,000 amps. When protected by 600 amp LLNRK RK1

uses, equipment with short-circuit ratings o 22,000 amps

may be saely connected to a system having 100,000

available rms symmetrical amperes.

This method, sometimes reerred to as the Up-Over-and-

Down method, may be used to:

Provide back-up short-circuit protection to large air1.

power circuit breakers.

Enable non-interrupting equipment such as bus duct to be2.

FUsE CHArACTErIsTIC CUrvEs AND CHArTs

Peak Let-through Current

Peak Current which would occur

without current limitationCurrent

Time

100

1000000

200000

300000

400000

600000

800000

100000

20000

30000

40000

60000

80000

10000

2000

30004000

6000

8000

1000

200

300

400

600

800

100

200

300

400

600

800

1000

2000

3000

4000

6000

8000

10000

20000

30000

40000

60000

80000

100000

200000

FUSE

AMPERE

RATING

600

400

200

10060

30

A

B

AVAILABLE FAULT CURRENT

SYMMETRICAL R.M.S. AMPERES

PEAKLET-THRUINAMPERES

Figure 7 Peak Let-through Charts

Figure 6 Current limiting effect of fuses



10/26

189



installed in systems with available short-circuit currents

greater than their short circuit (withstand) ratings.

However, this method may not be used to select uses or

backup protection o molded case or intermediate ramecircuit breakers. National Electrical Code (NEC) Article

240.86 requires Series Ratings. Reer to the NEC or more

inormation.

UL Listed use-to-circuit breaker series ratings are now

available rom most national load center and panelboard

manuacturers. Listings are shown in their product digests,

catalogs, and online. Many local builders have also obtained

use-to-circuit breaker series ratings. For additional

inormation contact the Litteluse Technical Support Group at

1-800-TEC-FUSE (1-800-832-3873).

Short-Circuit Current Rating (SCCR)Since 2005, the NEC has required Industrial Control Panels

to be labeled with their SCCR. These labels allow users and

inspectors to compare the SCCR o the equipment to the

available ault current in order to avoid potential hazards in

acilities. For additional inormation, the latest specic NEC

requirements, and solutions on how to increase the SCCR

or a panel, visit www.litteluse.com/SCCR.

Selective CoordinationA coordinated or selective system is a system whose

overcurrent protective devices have been careully chosen and

their time-current characteristics coordinated.

Only the overcurrent device immediately on the line side o an

overcurrent will open or any overload or short-circuit condition.

To urther clariy, reer to the Terms and Denitions section

or the denition o Selective Coordination and Figure 15or a

graphical example.

Since the advent o electrical and electronic equipment,

businesses have become entirely dependent on the

continuous availability o electric energy. Loss o power

halts all production and order processing, yet expenses

continue to increase. Even many UPS systems become

unintentionally non-selective causing power loss to

computers and other critical equipment. Non-selectivity may

deeat otherwise well-engineered UPS systems.

In a selective system, none o this occurs. Overloads andaults are disconnected by the overcurrent protective device

immediately on the line side o the problem. The amount o

equipment removed rom service is minimized, the aulted

or overloaded circuit is easier to locate, and a minimum

amount o time is required to restore ull service.

For these and many other reasons, selectivity is the

standard by which many systems are judged and designed.

Fuse SelectivityTo get a better sense o how to ensure that uses are

selectively coordinated within an electrical system, reer

to Figure 4shown earlier in this Technical Application

Guide. This gure shows typical average melting time-current curves or one class o uses. Note that the curves

are roughly parallel to each other and that or a given

overcurrent, the smaller use ratings respond quicker than

the larger ratings. The heat energy required to open a use

is separated into melting I2t and arcing I2t (see denition o

Ampere-Squared-Seconds). The sum o these is the total

clearing I2t.

For a system to be considered coordinated, the smaller

use total clearing I2t must be less than the larger use

melting I2t. In other words, i the downstream (branch)

use opens the circuit beore the overcurrent aects

the upstream (eeder) use element, the system will be

considered selective. This can be determined by analyzing

curves displaying melting and total clearing I2t, or rom

minimum melting and maximum clearing time-current

curves.

But the simplest method o coordinating low voltage power

uses is by using a Fuse Coordination Table such as the

one shown in Table 4. This table is only applicable or the

Litteluse POWR-PRO and POWR-GARD use series listed.

Tables such as this greatly reduce design time. For example,

the coordination table shows that POWR-PRO KLPC Class

L uses coordinate at a two-to-one ratio with other Class L

uses, with POWR-PRO LLNRK / LLSRK / LLSRK_ID series

FUsE CHArACTErIsTICs CUrvEs AND CHArTs

100

1000000

200000

300000

400000

600000

800000

100000

20000

30000

40000

60000

80000

10000

2000

3000

4000

6000

8000

1000

200

300

400

600

800

100

200

300

400

600

800

1000

2000

3000

4000

6000

8000

10000

20000

30000

40000

60000

80000

100000

200000

FUSE

AMPERE

RATING

600

400

200

100

60

30

A

B

D A

BC

AVAILABLE FAULT CURRENT

SYMMETRICAL R.M.S. AMPERES

PEAKLET-THRUINAMPERES

Figure 8 Peak Let-through Chart for POWR-PRO LLNRK Class

RK1 Dual-Element Fuses Using the Up-Over-and-Down Method



11/26

190



Class RK1 uses, and POWR-PRO JTD / JTD_ID series Class

J uses.

In the system shown in Figure 9, the 3000 amp Class L

main uses are at least twice the ratings o the 1500, 1200,

and 1000 amp Class L eeder uses. Using the 2:1 ratio

just reerenced above, it is determined that these uses

will coordinate. The Coordination Table also shows that the

LLSRK_ID series time-delay RK1 eeder and branch circuit

uses coordinate at a two-to-one ratio with the Class L

eeder uses, so the entire system in Figure 9would be

considered 100% coordinated.

Circuit Breaker CoordinationAs a result o the numerous types o circuit breakers

and circuit breaker trip units available in todays market,developing a coordinated circuit breaker system or

coordinating circuit breakers with uses is beyond the scope

o this Technical Application Guide. For urther questions,

contact the Litteluse Technical Support Group.

NEC Requirements or SelectiveCoordination

Component Short-Circuit Protecting Ability

As shown in Figure 10, the NEC requires equipment

protection to be coordinated with overcurrent protective

devices and the available ault current in order to prevent

extensive damage to the equipment. Essentially, this

means that electrical equipment must be capable owithstanding heavy overcurrents without damage or be

properly protected by overcurrent protective devices that

will limit damage.

When a severe ault occurs in an unprotected circuit, current

immediately increases to a very high value. This is the

available or prospective ault current. Some uses respond

so quickly to the increasing current that they interrupt

current within the rst hal-cycle - or beore the current even

reaches its rst peak. This is illustrated in Figure 6ound

earlier in the Technical Application Guide. Such uses are

termed current-limiting uses.

Current-limiting uses stop damaging current aster than

any other protective device, and greatly reduce or totally

prevent component damage rom high ault currents. This

perormance capability helps users meet the NEC Article

110.10 requirements listed in Figure 10.

Pre-Engineered SolutionsApplicable code requirements also continue to expand with

each new edition o the National Electrical Code. As o the

2008 edition o the NEC, the ollowing requirements need to

be met and can be, utilizing Litteluse POWR-GARD Pre-

Engineered Solutions:

NEC 517.26 Healthcare Essential Electrical Systems

NEC 620.62 Elevators

NEC 700.27 Emergency Systems

NEC 701.18 Legally Required Standby Systems

NEC 708.54 Critical Operations Power Systems

sELECTIvE COOrDINATION

LINE-sIDE FUsEs LOAD-sIDE FUsEs

AmPErE

rANGEUL CLAss

LITTELFUsE

CATALOG NO.

TImE-DELAy FUsEs

AmPErE rANGE, UL CLAss AND CATALOG NO.

FAsT-ACTING FUsEs

AmPErE rANGE, UL CLAss AND CATALOG NO.

601-6000 601-4000 30-600 30-600 30-600 30-600 30-1200 30-600 1-60

L L RK1 J RK5 RK1 T J G

KLPC

LDCKLLU

LLNRK

LLsRK_iD

JTD_iD

JTD

FLNR_iD

FLsR_iD

iDsR

KLNR

KLsR

JLLN

JLLsJLs sLC

601-6000 L KLPC 2:1 2:1 2:1 2:1 4:1 2:1 2:1 2:1 N/A

601-4000 L KLLU 2:1 2:1 2:1 2:1 4:1 2:1 2:1 2:1 N/A

601-2000 L LDC 2:1 2:1 2:1 2:1 4:1 2:1 2:1 2:1 N/A

30-600 RK1 LLNRK N/A N/A 2:1 2:1 8:1 3:1 3:1 3:1 4:130-600 RK1 LLsRK_iD N/A N/A 2:1 2:1 8:1 3:1 3:1 3:1 4:1

30-600 J JTD_iD N/A N/A 2:1 2:1 8:1 3:1 3:1 3:1 4:1

30-600 RK5 iDsR N/A N/A 1.5:1 1.5:1 2:1 1.5:1 1.5:1 1.5:1 1.5:1

30-600 RK5 FLNR_iD N/A N/A 1.5:1 1.5:1 2:1 1.5:1 1.5:1 1.5:1 1.5:1

30-600 RK5 FLsR_iD N/A N/A 1.5:1 1.5:1 2:1 1.5:1 1.5:1 1.5:1 1.5:1

30-600 RK1 KLNR N/A N/A 3:1 3:1 8:1 3:1 3:1 3:1 4:1

30-600 RK1 KLsR N/A N/A 3:1 3:1 8:1 3:1 3:1 3:1 4:1

30-1200 T JLLN N/A N/A 3:1 3:1 8:1 3:1 3:1 3:1 4:1

30-1200 T JLLs N/A N/A 3:1 3:1 8:1 3:1 3:1 3:1 4:1

30-600 J JLs N/A N/A 3:1 3:1 8:1 3:1 3:1 3:1 4:1

1-60 G sLC N/A N/A 3:1 3:1 4:1 2:1 2:1 2:1 2:1

Table 4 Fuse Coordination Table. Selecting the Correct Fuse Ampere Ratio to Maintain Selectively Coordinated Systems. (Ratios are

expressed as Line-Side Fuse to Load-Side Fuse.)



12/26

191



The Litteluse product line o Pre-Engineered Solutions

includes:

LPS Series POWR-Switch (single elevator shunt-trip

disconnect switch)

LPMP Series POWR-Switch Panel (multiple elevator

shunt-trip disconnect switches)

LCP Selective Coordination Panel

These products continue to gain in popularity because they

meet NEC requirements and oer simple, economical

solutions or a variety o applications.

Visit www.litteluse.com/lcp or more inormation

on Litteluse Pre-Engineered Solution products and

corresponding selective coordination requirements.

sELECTIvE COOrDINATION

KLPC

3000

KLPC

1500

KLPC

1200

KLPC

1000

LLSRK

200

LLSRK

200

LLSRK

400

LLSRK

400

Figure 9 Example of Selectively Coordinated Fused System

NATIONAL ELECTRICAL CODE

ARTICLE 110 Requirements or Electrical Installations

I. General

110.3. Examination, Identiication, Installation, and Use o Equipment.

(A)Examination. In judging equipment, considerations such as the ollowing shall be evaluated:

(5) Heating eects under normal conditions o use and also under abnormal conditions likely to arise in service.

(6) Arcing eects.

(B)Installation and Use. Listed or labeled equipment shall be used or installed in accordance with any instructions included in the listing

or labeling.

110.9 Interrupting Rating. Equipment intended to interrupt current at ault levels shall have an interrupting rating not less than the

nominal circuit voltage and the current that is available at the line terminals o the equipment.

Equipment intended to interrupt current at other than ault levels shall have an interrupting rating at nominal circuit voltage not less than

the current that must be interrupted.

110.10 Circuit Impedance, Short-Circuit Ratings, and Other Characteristics. The overcurrent protective devices, the total

impedance, the equipment short-circuit current ratings, and other characteristics o the circuit to be protected shall be selected and

coordinated to permit the circuit protective devices used to clear a ault to do so without extensive damage to the electrical equipment o

the circuit. This ault shall be assumed to be either between two or more o the circuit conductors or between any circuit conductor and

the equipment grounding conductor(s) permitted in 250.118. Listed equipment applied in accordance with their listing shall be considered

to meet the requirements o this section.

ARTICLE 240 Overcurrent Protection

240.1 Scope. Parts I through VII o this article provide the general requirements or overcurrent protection and overcurrent protective

devices not more than 600 volts, nominal. Part VIII covers overcurrent protection or those portions o supervised industrial installations

operating at voltages o not more than 600 volts, nominal. Part IX covers overcurrent protection over 600 volts, nominal.

(FPN): Overcurrent protection or conductors and equipment is provided to open the circuit i the current reaches a value that

will cause an excessive or dangerous temperature in conductors or conductor insulation. See also Articles 110.9 or requirements or

interrupting ratings and 110.10 or requirements or protection against ault currents.

(Reproduced by permission o NFPA)

Figure 10 National Electrical Code Requires Effective Overcurrent Protection



13/26

192



UL/CsA FUsE CLAssEs AND APPLICATIONs

CLASS LSTANDARDS: UL Standard 248-14,

CSA Standard C22.2, No. 106, classied as HRCI-L

VOLTAGE RATING: 600 volts, AC and/or DC

CURRENT RATINGS: 601-6000 amps

KLPC also available 200-600A; LDC also available 150-600A

INTERRUPTING RATING: AC: 200,000 amps rms symmetrical

DC: 50,000, 100,000, or 200,000 amps

Not interchangeable with any other UL use class.

Time delay: Class L uses may be marked Time-Delay although UL does not

investigate time-delay characteristics o Class L uses.

KLPC & KLLU: 10 seconds at 500% current rating

LDC: 4 seconds at 500% current rating

LF SERIES: KLPC, KLLU, LDC

PAGES: 11-13

CLASS RSTANDARDS: UL Standard 248-12,

CSA Standard C22.2, No. 106, classied as HRCI-R

VOLTAGE RATINGS: 250 and 600 volts, AC; 125 and 300 volts DC


INTERRUPTING RATING: 200,000 amps rms symmetrical

TWO CLASSES: RK1 and RK5

Time delay is optional or Class R uses.

Time Delay uses are required to hold 500% current rating or a minimum o ten seconds.

Same dimensions as UL Class H uses, terminals modied to provide rejection eature.

Fits UL Class R useholders which reject non Class R uses.

Physically interchangeable with UL Class H, NEMA Class H, and UL Classes K1 &

K5 when equipment has Class H useholders.

CLASS KSTANDARDS: UL Standard 248-9; No CSA Standard

VOLTAGE RATINGS: 250 and 600 volts, AC

CURRENT RATING: 0-600 amps

INTERRUPTING RATINGS: Three permitted: 50,000, 100,000, and 200,000 amps

rms symmetrical

Time delay is optional or Class K uses.

Time Delay uses are required to hold 500% current rating or a minimum o ten seconds.

Same Dimensions and Physically interchangeable with UL Class H useholders.Class K uses are not permitted to be labeled Current Limiting because there is no rejec-

tion eature as required by NEC Article 240-60(B).

CLASS JSTANDARDS: UL Standard 248-8,

CSA Standard C22.2, No. 106, classied as HRCI-JVOLTAGE RATING: 600 volts, AC




Time delay optional: Minimum o 10 seconds at 500% current rating.

LF SERIES: Time Delay: JTD_ID, JTD

Fast Acting: JLS

PAGES: 27-29

CLASS G

STANDARDS: UL Standard 248-5CSA Standard C22.2, No. 106, classied as HRCI Misc.

VOLTAGE RATING: 480 volts, AC





LF SERIES: SLC

PAGE: 32

CLASS RK1High degree o current limitation.

Provides IEC Type 2 (no damage)

protection or motor starters and

control components. Time Delay

optional, LLSRK_ID Series provides

visual indication o blown use.

LF SERIES: Time Delay: LLNRK,

LLSRK, LLSRK_ID

Fast Acting: KLNR, KLSR

PAGES: 16-18

CLASS RK5Moderate degree o current limita-

tion, adequate or most applica-

tions. Time delay optional.

FLNR_ID, FLSR_ID and IDSR series

provides visual indication o blown

use.

LF SERIES: FLNR, FLNR_ID,

FLSR, FLSR_ID, and IDSR

PAGES: 19-22

CLASS K5Same prescribed degree o current

limitation as RK5 uses when

tested at 50,000 or 100,000 amps

rms symmetrical.

LF SERIES: NLN, NLS

PAGE: 24

CLASS TSTANDARDS: UL Standard 248-15

CSA Standard C22.2, No. 106, classied as HRCI-T

VOLTAGE RATINGS: 300 and 600 volts AC, 125 and 300 volts DC


900 to 1200 amps UL Recognized or 600V version


Fast-Acting uses. High degree o current limitation.

Very small uses; space-saving and non-interchangeable with any other UL use class.

LF SERIES: JLLN, JLLS

PAGES: 30-31

CLASS CC/CDSTANDARDS: UL Standard 248-4,

CSA Standard C22.2, No. 106, classied as HRCI Misc.

VOLTAGE RATING: 600 volts, AC

CURRENT RATINGS: UL Class CC: 0-30 amps

UL Class CD: 35-60 amps

INTERRUPTING RATINGS: 200,000 amps rms symmetrical


LF SERIES: Time Delay: CCMR (motors), KLDR (transormers)

Fast Acting: KLKR

PAGES: 33-35

CLASS K1Same prescribed degree o current

limitation as RK1 uses when

tested at 50,000 or 100,000 amps

rms symmetrical.

LF SERIES: Time Delay: LLNRK,

LLSRK

Fast Acting: KLNR,

KLSR

PAGE: 16

Overcurrent and short-circuit protection o power and lighting eeders and branch circuits

Current Limiting

Fuses which meet the requirements or current limiting uses are required to be labeled Current Limiting. Fuse labels must

include: UL/CSA use class, manuacturers name or trademark, current rating, AC and/or DC voltage rating, and AC and/or DC

interrupting rating. Time Delay, D, TD or equivalent may also be included on the label when the use complies with the

time delay requirements o its class.



14/26

193



UL/CsA FUsE CLAssEs AND APPLICATIONs

FUSES FOR SUPPLEMENTARY OVERCURRENT PROTECTIONSTANDARDS: UL Standard 248-14; CSA Standard C22.2,

No. 59-1. Three Classications covered:

NOTE: Fuses may be rated or AC and/or DC when suitable or

such use.

(1) MICRO FUSES

Voltage ratings: UL, 125 volts; CSA, 0-250 volts

Current ratings: UL, 0-10 amps; CSA, 0-60 amps

Interrupting rating: 50 amps rms symmetrical

(2) MINIATURE FUSES (CSA classies these as Supplemental Fuses)

Voltage ratings: UL, 125 or 250 volts; CSA, 0-600 volts

Current ratings: UL, 0-30 amps; CSA, 0-60 amps

Interrupt ing rating: 10,000 amps rms symmetrical

(3) MISCELLANEOUS CARTRIDGE FUSES (CSA classies these as

Supplemental Fuses)

Voltage ratings: UL, 125 to 600 volts; CSA, 0-600 volts

Current ratings: UL, 0-30 amps; CSA 0-60 amps

Interrupting ratings: 10,000, 50,000, or 100,000 amps rms symmetrical

Time delay (Optional); Minimum delay at 200% use rating:5 seconds or uses rated 3 amps or less

12 seconds or uses rated more than 3 amps

LF SERIES: BLF, BLN, BLS, FLA, FLM, FLQ, FLU, KLK, KLKD (600 Volts DC), SPF

NOTE: Litteluse electronic uses are also covered by these standards; see

electronic section o this catalog, or request Electronic Designers Guide (Publication

No. EC101) or complete listing.

PAGES: 37-39

SPECIAL PURPOSE FUSESThere are no UL Standards covering this category o uses. These uses have

special characteristics designed to protect special types o electrical or electronic

equipment such as diodes, SCR, transistors, thyristors, capacitors, integrally used

circuit breakers, parallel cable runs, etc.

Fuses may be UL Recognized or use as a component in UL Listed equipment.

UL Recognized uses are tested or characteristics such as published interrupting

capacity. They are also covered by UL re-examination service.

Non-renewable

VOLTAGE RATINGS: up to 1000 volts AC and/or DC

AMPERE RATINGS: up to 6000 amperes

INTERRUPTING RATINGS: up to 200,000 amperes

Many o these uses are extremely current limiting. When considering application o

these uses, or i you have special requirements, contact Litteluse Technical Support

Group or assistance.

LF SERIES: KLC, LA15QS, LA30QS, LA50QS, LA60QS, LA60X, LA70QS, LA100P,

LA120X, LA070URD, LA130URD, L15S, L25S, L50S, L60S, L70S, JLLS 900 amp

through 1200 amp

PAGES: 62-81

CLASS HSTANDARDS: UL Standard 248-6

CSA Standard C22.2, No. 59.1

Also known as NEMA Class H, and sometimes reerred to as NEC or Code

uses

VOLTAGE RATINGS: 250 and 600 volts, AC

AMPERE RATINGS: 0-600 amps

INTERRUPTING RATINGS: 10,000 amps rms symmetrical

Two types: one-time and renewable

Physically interchangeable with UL Classes K1 & K5;

Fits UL Class H useholders which will also accept K1, K5, RK5, and RK1 uses.

Manuacturers are upgrading Class H One-time uses to Class K5 per UL Standard

248-9D, See Class K uses.

ONE-TIME FUSES

(NON-RENEWABLE)Time delay: Optional

Time-delay uses must hold 500%

current rating or a minimum o ten

seconds.

LF SERIES: NLKP

PAGES: 25-26

RENEWABLE FUSESOnly Class H uses may be renew-

able. While time delay is optional,

no renewable uses meet require-

ments or time delay.

Some renewable uses have a mod-

erate amount o time delay, reerredto as time lag to dierentiate

rom true time delay.

LF SERIES: RLN, RLS

REPLACEABLE LINKS SERIES:

LKN, LKS

PAGES: 25-26

PLUG FUSESSTANDARDS: UL Standard 248-11,

CSA Standard C22.2, No. 59.1

VOLTAGE RATINGS: 125 volts AC only

AMPERE RATINGS: 0-30 amps

INTERRUPTING RATINGS: 10,000 amps rms symmetrical. Interrupting rating

need not be marked on use.

Two types: Edison-base and Type S

EDISON-BASE: Base is same as standard light bulb. All amp ratings interchange

able. NEC permits Edison-base plug uses to be used only as replacements or

existing uses, and only when there is no evidence o tampering or overusing.

TYPE S: Not interchangeable with Edison-base uses unless non-removable Type

S use adapter is installed in Edison-base use socket. To prevent overusing,

adapters have three ampere ratings: 10-15, 16-20, and 21-30 amps.

Time delay: Fuses may be time delay, i so, they are required to hold 200% o rating

or 12 seconds minimum.

NOTE: Plug uses may be used where there is not more than 125 volts between

conductors or more than 150 volts rom any conductor to ground. This permits their

use in 120/240 volts grounded, single-phase circuits.

LF SERIES: Edison-base: TOO, TLO

Type S: SOO, SLO

Type S Adapters: SAO

PAGE: 63

Non-Current Limiting

Overcurrent and short-circuit protection o power and lighting eeders and branch circuits



15/26

194



ELECTrICAL sAFETy GUIDE

Introduction

Electrical saety is an important issue or employers andemployees alike. Unortunately, thousands o electrical

accidents continue to occur each year resulting in permanent

disabilities to personnel and excessive medical and

equipment replacement costs.

OSHA requirements are oten the motivating actor

increasing electrical saety in the workplace. OSHA

continues to increase enorcement activities and is seeking

to increase penalties or violations.

Typical OSHA violations related to electrical saety include

improper Lockout/Tagout, aulty electrical wiring, ailure to

ollow electrical sae work practices, ailure to assess and

identiy hazards, ailure to train employees and ailure to

provide PPE (personal protective equipment) to workers.

Industry consensus standards such as NFPA 70E, Standard

or Electrical Saety in the Workplace, has been created

at the request o OSHA to dene and quantiy electrical

hazards including Shock, Arc-Flash and Arc-Blast.

Steps to Electrical Saety Compliance

Dene the project scope and identiy any current saetyprogram gaps

Collect data and document your electrical system

Evaluate your electrical system through engineering

analysis

Identiy hazards and re-engineer to reduce hazards

Label equipment to communicate hazards

Update or develop an Electrical Saety Program

Obtain Personnel Protective Equipment (PPE) and

insulated tools

Train Personnel

Maintain and Audit One-Line Drawings and Electrical

Saety Programs

OSHA Standard 29 Part 1910 Subpart S (electrical)

generally addresses electrical saety standards, work

practices, and maintenance requirements.

NFPA 70E Standard for Electrical Safety in the Workplace

is an industry consensus standard that ocuses on saety

requirements to protect employees. OSHA commonly is

reerred to as the What or Shall and NFPA 70E as the

How with regards to electrical saety compliance.

You MUST assess and identiy all hazards above 50 volts NFPA 70E explains how to perorm a Shock & Arc-Flash Hazard

Assessment down to 50 volts using tables and calculations

You MUST put saeguards in place or hazards above 50 volts

NFPA 70E establishes Hazard Risk Categories, ProtectionBoundaries, LO/TO, PPE requirements and the use o Energized

Work Permits

You MUST train employees on sae work practices NFPA 70E denes Qualied and Unqualied workers along with

training requirements

WHAT: OSHA REQUIRES YOU...

TO COMPLY WITH 1910 SUBPART S

HOW: NFPA 70E MUST BE FOLLOWED...

TO COMPLY WITH 1910 SUBPART S

Tabl 5 - Coparon of OsHA and NFPA 70e

OSHA and NFPA 70E reinorce the need or Electrical

Hazard Analysis. Electrical Hazard Analysis should address

all potential hazards including Shock, Arc-Flash, Arc-Blast

and burns. OSHAs general duty clause requires a workplace

ree rom hazards and OSHA 1910.132(d) requires employersto identiy hazards and protect workers. NFPA 70E Article

110.8(B)(1) specically requires Electrical Hazard Analysis

within all areas o the electrical system that operate at 50

volts or greater.



16/26

195



ELECTrICAL sAFETy GUIDE

Sources o Electrical Hazards and Faults

Exposed energized parts

Equipment atigue or ailure

Accidental contact with energized parts

Worn or broken insulation

Loose connections

Improperly maintained equipment or circuit breakers

Water or liquid near electrical equipment

Obstructions near or on equipment

Improper grounding

Types o Electrical Faults

It is well documented and estimated that 95% o electricalaults start as ground aults. The remaining 5% are either

phase-to-phase or three-phase aults. So in essence, i we

are able to eliminate phase-to-ground aults, or 95% o all

aults, we have essentially reduced the potential or 95%

o the Arc-Flash Hazard, making the electrical system much

saer.

Reducing Electrical Hazards

There are many methods and practices or reducing Arc-Flash and other electrical hazards while conorming to

OSHA, NEC, and NFPA 70E regulations and guidelines.

Circuit designers and electrical engineers should careully

consider the ollowing recommendations:

Design the hazard out o the system through engineering

design and component selection

Identiy and assess electrical hazards

Use and upgrade to current-limiting overcurrent

protective devices

Implement an Electrical Saety Program

Observe sae work practices

Use properly selected Personal Protective Equipment

(PPE) including insulated tools

Use Warning Labels to identiy and communicate

electrical hazards

Enorce Lockout/Tagout procedures and use Energized

Electrical Work Permits

Increase system protection by achieving Selective

Coordination and using Ground Fault Protection devices.LEADING INITIATOrs OF FAULTs % OF ALL FAULTs

Exposure to moisture 22.5%

Shortening by tools, rodents, etc. 18.0%

Exposure to dust 14.5%

Other mechanical damage 12.1%Exposure to chemicals 9.0%

Normal deterioration from age 7.0%

Tabl 6 - Ladng ntator of lctrcal fault

exapl of warnng labl

WARNINGArc-Flash and Shock Hazard

Appropriate PPE Required

Warning: Changes in equipment settings or systemconfiguration will invalidate the calculated values andPPE requirements

Equipment: TX-38 Pri

Protection: NE-38

9 inches Flash Hazard Boundary0.35 cal/cm2 Flash Hazard at 18 inches

Untreated Cotton LS Shirt/ Pants,Category 0 Safety Glasses, Ear Plugs, V-Rated Tools/

Gloves (AN), Leather Gloves (AN)

480 VAC Shock Hazardwhen cover is removed00 Glove Class42 inches Limited Approach12 inches Restricted Approach1 inch Prohibited Approach

Prepared on: 7/26/10 By:

For more inormation on Electrical Saety, visit

www.litteluse.com/services



17/26

196



Adjustable Alarm Level A setting on a protection relay at

which an LED or an output contact operates to activate a visualor audible alarm.

Adjustable Time Delay A setting on a protection relay that

determines the time between the ault detection and relay

operation.

AIC or A.I.C. See Interrupting Capacity.

AIR or A.I.R. See Interrupting Rating.

Alarm Relay Contact The output o the relay that acts as a

switch and is connected to a visual or audible alarm.

Ambient Temperature The air temperature surrounding a

device. For uses or circuit breakers in an enclosure, the air

temperature within the enclosure.

Ampacity The current in amperes that a conductor can carry

continuously under the conditions o use without exceeding

its temperature rating. It is sometimes inormally applied to

switches or other devices which are more properly reerred to

by their ampere rating.

Ampere Rating The current rating, in amperes, that is

marked on uses, circuit breakers, or other equipment.

Ampere-Squared-Seconds (I2t) A means o describing the

thermal energy generated by current fow. When a use is

interrupting a current within its current-limiting range, the term

is usually expressed as melting, arcing, or total clearing I2t.

Melting I 2t is the heat energy passed by a use ater anovercurrent occurs and until the use link melts. It equals

the rms current squared multiplied by the melting time in

seconds. For times less than 0.004 seconds, melting I2t

approaches a constant value or a given use.

Arcing I 2t is the heat energy passed by a use during its

arcing time. It is equal to the rms arcing current squared (see

denition below), multiplied by arcing time.

Clearing I 2t (also Total Clearing I2t) is the ampere-squared

seconds (I2t) through an overcurrent device rom the

inception o the overcurrent until the current is completely

interrupted. Clearing I2t is the sum o the Melting I2t plus the

Arcing I2t.

Analog Output A 01 mA, 420 mA or 05 Vdc signal rom

a protection relay used to pass inormation to a device or

controller.

Arc-Blast A pressure wave created by the heating, melting,

vaporization, and expansion o conducting material and

surrounding gases or air.

Arc-Flash The sudden release o heat energy and intense

light at the point o an arc. Can be considered a short-circuit

through the air, usually created by accidental contact between

live conductors.

Arc Gap The distance between energized conductors or

between energized conductors and ground. Shorter arc gapsresult in less energy being expended in the arc, while longer

gaps reduce arc current. For 600 volts and below, arc gaps o

1.25 inches (32 mm) typically produce the maximum incident

energy.

Arc Rating A rating assigned to material(s) that relates to the

maximum incident energy the material can resist beore break

open o the material or onset o a second-degree burn. The arc

rating is typically shown in cal/cm.

Arcing Current (See Figure 11) The current that fows

through the use ater the use link has melted and until the

circuit is interrupted.

Figure 11 Arcing and melting currents plus arcing, melting and

clearing times

Arcing I2t See Ampere-Squared-Seconds (I2t).

Arcing Fault A short-circuit that arcs at the point o ault. The

arc impedance (resistance) tends to reduce the short-circuit

current. Arcing aults may turn into bolted aults by welding o

the aulted components. Arcing aults may be phase-to-phase

or phase-to-ground.

Arcing Time (See Figure 11) The time between the melting

o a use link or parting o circuit breaker contacts, until the

overcurrent is interrupted.

Arc Voltage (See Figure 12) Arc voltage is a transient voltage

that occurs across an overcurrent protection device during

the arcing time. It is usually expressed as peak instantaneous

voltage (Vpeak or Epeak), or on rare occasion as rms voltage.

Asymmetrical Current See Symmetrical Current.

Available Short-Circuit Current (also Available or

Prospective Fault Current) The maximum rms Symmetrical

Current that would fow at a given point in a system under

bolted-ault conditions. Short-circuit current is maximum during

the rst hal-cycle ater the ault occurs. See denitions o

Bolted Fault and Symmetrical Current.

TErms AND DEFINITIONs

Peak Let-through Current

Peak Current which would occur

without current limitationCurrent

Time

MeltingTime

ArcingCurrent

ArcingTime

MeltingCurrent

Arcing Energy (l2t)

Melting Energy (l2t)



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197



Blade Fuse See Knie Blade Fuse.

Body The part o a use enclosing the use elements and

supporting the contacts. Body is also reerred to as cartridge,

tube, or case.

Bolted Fault A short-circuit that has no electrical resistanceat the point o the ault. It results rom a rm mechanical

connection between two conductors, or a conductor and

ground. Bolted aults are characterized by a lack o arcing.

Examples o bolted aults are a heavy wrench lying across two

bare bus bars, or a crossed-phase condition due to incorrect

wiring

Boundaries o Approach Protection boundaries established

to protect personnel rom shock and Arc-Flash hazards.

Calorie The amount o heat needed to raise the temperature

o one gram o water by one degree Celsius.1 cal/cm is

equivalent to the exposure on the tip o a nger by a cigarette

lighter or one second.

Cartridge Fuse A use that contains a current-responsive

element inside a tubular use body with cylindrical errules (end

caps).

Case Size (also Cartridge Size) The maximum allowable

ampere rating o a cartridge use having dened dimensions

and shape. For example, case sizes or UL Listed Class H, K, J,

RK1, and RK5 are 30, 60, 100, 200, 400, and 600 amperes. The

physical dimensions vary with use class, voltage, and ampere

rating. UL Standards establish the dimensions or each UL

Fuse Class. This catalogs product section contains case size

dimensions or all Litteluse POWR-GARD uses.

Clearing I2t See Ampere-Square-Seconds (I2t).

Clearing Time (see Figure 11) The time between the

initiation o an overcurrent condition to the point at which the

overcurrent is interrupted. Clearing Time is the sum o Melting

Time and Arcing Time.

Conormal Coating Coating used to protect circuit boards

rom pollutants, corrosion, and mildew.

Contacts (Fuse) The external metal parts o the use used to

complete the circuit. These consist o errules, caps, blades or

terminals, as shown in this catalog.

Coordination or Coordinated System See Selective

Coordination.Continuous Load An electrical load where the maximum

current is expected to continue or three hours or more.

CT Loop The electrical circuit between a current transormer

and a protection relay or monitoring device.

Current-Based Protection Protection parameters (trip-levels/

data collection etc.) derived rom current levels in a circuit.

Current-limiting Fuse (See Figure 13) A use which, when

interrupting currents within its current-limiting range, reduces

the current in the aulted circuit to a magnitude substantially

less than that obtainable in the same circuit i the device was

replaced with a solid conductor having comparable impedance.

To be labeled current limiting, a use must mate with auseblock or useholder that has either a rejection eature or

dimensions that will reject non-current-limiting uses.

Figure 13 Current-limiting Fuse

Current-limiting Range - For an individual overcurrent

protective device, the current-limiting range begins at the

lowest value o rms symmetrical current at which the device

becomes current-limiting (the threshold current) and extends

to the maximum interrupting capacity o the device. See

denitions o Threshold Current and Interrupting Capacity.

Current Rating See Ampere Rating.

Current Transormer (CT) A transormer that produces a

current in its secondary circuit in a known proportion to current

in its primary circuit.

Data Logging Collecting and storing inormation in a

ormat that can be reviewed or trending, troubleshooting and

reporting.

DFT (Discrete Fourier Transorm) Harmonic Filter An

algorithm used to measure the undamental component o

current and voltage and reject harmonics. This allows lower trip

settings and eliminates nuisance trips due to harmonics.

TErms AND DEFINITIONs

INSTANTANEOUS ARC VOLTAGE

183% OF CYCLEPEAK

RESTORED VOLTAGE

PEAK

Current

TimeFault occurs

Arc is extinguished

Current which

would flow if

not interrupted

Current before fault

Fuse opens andclears short circuit

in less than cycle

Figure 12 Transient overvoltage during arcing time



19/26

198



Distance to Arc Reers to the distance rom the receiving

surace to the arc center. The value used or most calculationsis typically 18 inches.

Dual-Element Fuse A use with internal construction

consisting o a separate time-delay overload element(s) that

interrupts overcurrents up to approximately 500%-600% o its

nominal rating, plus separate use links that quickly open higher

value currents. All dual-element uses have time delay, but,

since there are other methods o achieving time delay, not all

time-delay uses have dual-element construction. See Time-

Delay Fuse.

EFCT (Earth Fault Current Transormer) A current

transormer engineered to accurately detect low level ground-

ault current.

Electrical Hazard Analysis A study perormed to identiy the

potential electrical hazards to which personnel may be exposed.

The analysis should address both shock and Arc-Flash hazards.

Electrically Sae Work Condition Condition where the

equipment and or circuit components have been disconnected

rom electrical energy sources, locked/tagged out, and tested to

veriy all sources o power are removed.

Element A uses internal current-carrying components that

melt and interrupt the current when subjected to an overcurrent

o suc

Documents

28pg Technical Info