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180 2010 Lttlfu POWR-GARD Product Catalogwww.lttlfu.co
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.
sELECTION CONsIDErATIONs
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.
sELECTION CONsIDErATIONs
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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.
sELECTION CONsIDErATIONs
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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
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(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
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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
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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.)
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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
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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
CURRENT RATINGS: 0-600 amps
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
CURRENT RATINGS: 0-600 amps
INTERRUPTING RATING: 200,000 amps rms symmetrical
Not interchangeable with any other UL use class.
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
CURRENT RATINGS: 0-60 amps
INTERRUPTING RATING: 100,000 amps rms symmetrical
Not interchangeable with any other UL use class.
Time delay optional: Minimum o 12 seconds at 200% current rating.
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
CURRENT RATINGS: 0-1200 amps
900 to 1200 amps UL Recognized or 600V version
INTERRUPTING RATING: 200,000 amps rms symmetrical
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
Time delay optional: Minimum o 12 seconds at 200% current rating.
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.
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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
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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.
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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
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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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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
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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