Más contenido relacionado La actualidad más candente (20) Similar a Littelfuse Fuseology Basics (20) Littelfuse Fuseology Basics3. 3Confidential and Proprietary | Littelfuse, Inc. © 2020 3
Why Fuses Are Required
A fuse is a thermally responsive device that:
Protects wires and prevents fires
Prevents damage to equipment
Protects equipment and personnel
Provides overcurrent fault protection
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The Two Type of Overcurrents
There are two types of
overcurrents:
1. Short Circuits (top)
2. Overloads (bottom)
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What Is a Short-Circuit?
Flows outside intended path
> 600% of rated current
Typically caused by accidents,
dropped tools, bad wiring, or
worn insulation
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What Is an Overload Fault?
Confined to a normal path
< 600% of rated current
Typically caused by mechanical
obstructions or jammed equipment
10. 10Confidential and Proprietary | Littelfuse, Inc. © 2020 10
NEC® 240.2. The proper localization of a fault condition to
restrict outages to the equipment affected, accomplished
by the choice of selective fault-protective devices.”
NEC 240.4. Requires the branch circuit, feeder, and
service conductors to be protected against overcurrent in
accordance with their ampacities as specified in 310.15.
Driving Factors for Using OCPDs
12. 12Confidential and Proprietary | Littelfuse, Inc. © 2020 12
Class L
Industrial Fuse Family and Accessories
Class RK1 Class RK5 Class L Class J Class T
Telecom Miscellaneous Fuseblocks & HoldersMidget Class CC/CD Medium Voltage
13. 13Confidential and Proprietary | Littelfuse, Inc. © 2020 13
Indicator
Assembly
Thermal Overload
Element
Precision Formed
Short-Circuit Element
Elastomeric EPR
Overload Module
Dual-element Fuse Design
No moving parts
No air chambers
All sand filled
Clears faster
Reliable indication
Runs cool, cycles longer
Blown Fuse Indication – The Inside Story
14. 14Confidential and Proprietary | Littelfuse, Inc. © 2020 14
Selecting the Proper Fuse
250 V? 600 V? Other?Voltage Rating
1/10 – 6,000 ACurrent Rating
10 – 200 k A.I.R.Interrupting Rating
Time-delay/fast-actingFuse Characteristics
How much space?Physical Size
No? Yes? How much?Current Limiting
Littelfuse InnovationIndication
Selection Considerations
15. 15Confidential and Proprietary | Littelfuse, Inc. © 2020 15
600 VAC
UL Fuse Classes
Class L “Large”
Voltage Rating:
150 – 6000 ACurrent Rating:
200,000A (self-cert @ 300kA)Interrupting Rating:
Time-DelayCharacteristics:
as large as 10-3/4” x 7-1/8”Physical Size:
VeryCurrent Limiting:
NoIndication:
LF Series: KLPC, KLLU, LDC
Typical Applications
Services Entrances
Large motors
Switchboard mains & feeders
General purpose circuits
Back-up protection to circuit breakers
LDC = 600VAC/VDCWhat’s Unique?
16. 16Confidential and Proprietary | Littelfuse, Inc. © 2020 16
250 and 600 VAC
UL Fuse Classes
Class RK1, RK5 “Rejection”
Voltage Rating:
1/10 – 600 ACurrent Rating:
200,000A (self-cert @ 300kA)Interrupting Rating:
Time-Delay/Fast-ActingCharacteristics:
6 Different Case SizesPhysical Size:
RK1 more than RK5Current Limiting:
Yes (4 of 10 Series)Indication:
LF Series
250V: LLNRK, FLNR, FLNR_ID, KLNR
600V: LLSRK_ID, LLSRK, FLSR_ID, FLSR,
IDSR, KLSR
Typical Applications
Services entrances
Switchboard mains and feeders
General purpose circuits
Circuit with high in-rush currents
(motors, transformers, compressors, pumps)
RK5 = most common fuseWhat’s Unique?
17. 17Confidential and Proprietary | Littelfuse, Inc. © 2020 17
250 and 600 VAC
UL Fuse Classes
(Not For Design-In Purposes)
Class K5 “One-Time”
Voltage Rating:
1 – 600 ACurrent Rating:
50,000A (K5)Interrupting Rating:
Time-DelayCharacteristics:
Same as RK1 / RK5Physical Size:
Yes (K5)Current Limiting:
NoIndication:
LF Series: NLN, NLS
Typical Applications
General purpose residential and
commercial circuits with little or no
motor loadNo rejection featureWhat’s Unique?
18. 18Confidential and Proprietary | Littelfuse, Inc. © 2020 18
600 VAC
UL Fuse Classes
Class J “Junior”
Voltage Rating:
8/10 – 600 ACurrent Rating:
200,000A (self-cert @ 300kA)Interrupting Rating:
Time-Delay/Fast-ActingCharacteristics:
Smaller than Class RPhysical Size:
More than Class RK1Current Limiting:
Yes (JTD_ID)Indication:
LF Series: JTD_ID, JTD, JLS
Typical Applications
Motor control centers
Transformer protection
Molded case circuit-breaker panels
General purpose circuits
Anywhere space is at a premium
LDC = 600VAC/VDCWhat’s Unique?
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1000 VDC
UL Fuse Classes
Class J (Solar rated)
Voltage Rating:
125 – 450 ACurrent Rating:
200kAIR (AC) / Varies (DC)Interrupting Rating:
Time-DelayCharacteristics:
Same as other Class JPhysical Size:
VeryCurrent Limiting:
NoIndication:
LF Series: SPFJ
Typical Applications
Inverters
Re-combiner boxes
Anywhere space is a premium in
photovoltaic (PV) systems
Meets UL & IEC StdsWhat’s Unique?
20. 20Confidential and Proprietary | Littelfuse, Inc. © 2020 20
300 and 600 VAC
UL Fuse Classes
Class T “Tiny”
Voltage Rating:
1 – 1200 ACurrent Rating:
200,000A (self-cert @ 300kA)Interrupting Rating:
Fast-ActingCharacteristics:
Smallest for 70–1200APhysical Size:
VeryCurrent Limiting:
NoIndication:
LF Series: JLLN, JLLS
Typical Applications
Individual electric services, meters
Main switch meter stacks
UPS equipment
Equipment containing variable speed
drives, rectifiers, and other surge-
sensitive components
1/3 the size of Class RWhat’s Unique?
21. 21Confidential and Proprietary | Littelfuse, Inc. © 2020 21
600 VAC
UL Fuse Classes
Class CC “Control Circuit”
Class CD (for CCMR 35-60)
Voltage Rating:
2/10 – 60 ACurrent Rating:
200,000A (self-cert @ 300kA)Interrupting Rating:
Time-Delay/Fast-ActingCharacteristics:
1-1/2” x 13/32” (0 – 30A)Physical Size:
ExtremelyCurrent Limiting:
NoIndication:
LF Series: CCMR, KLDR (Time-Delay)
KLKR (Fast-Acting)
Typical Applications
CCMR: Motor branch circuits up to
40hp, motor controllers/contactors
KLDR: Transformer, solenoids and
similar inductive components
KLKR: Control panels with solid-state
devices needing fast open
CCMR goes up to 60AWhat’s Unique?
22. 22Confidential and Proprietary | Littelfuse, Inc. © 2020 22
480 and 600 VAC
UL Fuse Classes
Class G “Graduated (length)”
Voltage Rating:
1/2 – 60 ACurrent Rating:
100,000AInterrupting Rating:
Time-DelayCharacteristics:
Varies x 13/32”Physical Size:
YesCurrent Limiting:
NoIndication:
LF Series: SLC
Typical Applications
Cost-effective, space-saving
alternative to other fuse classes
Meets NEC requirement for branch-
circuit protection
Varying length prevents over-fusing
Varying lengthsWhat’s Unique?
23. 23Confidential and Proprietary | Littelfuse, Inc. © 2020 23
125 thru 600VAC
UL Fuse Types
Midget Fuses
Voltage Rating:
1/10 – 30 ACurrent Rating:
Range: 10k – 200kAIRInterrupting Rating:
Time-Delay/Fast-ActingCharacteristics:
1-1/2” x 13/32” (10x38mm)Physical Size:
NoCurrent Limiting:
FLA (pin indication)Indication:
LF Series: BLF, BLN, BLS, FLA, FLM, FLQ,
FLU, KLK, KLKD, SPF
Typical Applications
UL supplemental protection
Small motors and transformers
Control circuits
Street and HID lighting
Multimeters and similar DC circuits
instruments
BLS is only 1-3/8” longWhat’s Unique?
and solenoids
24. 24Confidential and Proprietary | Littelfuse, Inc. © 2020 24
1000 VDC
UL Fuse Types
Midget Fuses (Solar rated)
Voltage Rating:
1 – 30 ACurrent Rating:
20,000AInterrupting Rating:
Fast-ActingCharacteristics:
1-1/2” x 13/32”Physical Size:
NoCurrent Limiting:
NoIndication:
LF Series: SPF
Typical Applications
Combiner boxes
Inverters
Battery charge controllers
Anywhere space is a premium in
photovoltaic (PV) systems
Meets UL & IEC StdsWhat’s Unique?
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2,400 thru 38,000VAC
Fuse Types > 600 Volts
Medium Voltage Fuses
Voltage Rating:
2R – 36R / 1/2E – 600ECurrent Rating:
up to 80,000AInterrupting Rating:
Fast-ActingCharacteristics:
up to 30-5/8” x 3” dia.Physical Size:
YesCurrent Limiting:
Some have pin indicationIndication:
E-Rated, R-Rated, Potential Transformer
Typical Applications
R-rated for motor protection
E-rated for transformer protection
E-rated PT for protection of potential transformers
Conventional, clip-lock and bolt-in style configurations
Double/Triple barrel designWhat’s Unique?
Approved for use in hazardous environments
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170VDC
Fuses Types – Telecom
Telecom Fuses
Voltage Rating:
1 – 1200 ACurrent Rating:
100,000AInterrupting Rating:
Fast-ActingCharacteristics:
Various stylesPhysical Size:
ExtremelyCurrent Limiting:
NoIndication:
LF Series: L17T, TLN, TLS
Typical Applications
L17T: Telecom circuits & DC power
distrib systems up to 1200A
TLN: Telecom circuits & DC power
distrib systems up to 600A
TLS: Telecom equipment, cables and
components up to 125A
Unique ratings, holderWhat’s Unique?
27. 27Confidential and Proprietary | Littelfuse, Inc. © 2020 27
Current Rating (or Ampere Rating)
Maximum amperes the fuse is
capable of carrying continuously
under specified conditions
When selecting a fuse, choose a
current rating as close as possible to
the system’s normal running current
1/10 – 6000A
Available Ratings
Current Rating
Fuse Ratings – Current
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Defines the characteristics of a fuse
Assists a system designer in selecting the proper
fuse to protect equipment within system
Types include:
Time current (T-C) curves plots the fuse’s average melting
or opening time
Peak let-thru (PLT) curves illustrates the maximum
instantaneous current through the fuse during the total
clearing time, which is the current limiting ability of a fuse
Fuse Characteristic Curve
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Start with 1000A
Overcurrent
Go up until
intersects 200A
fuse curve
Results in
average melting
time of ~18 sec.
Fuse Rating: 200A
Reading a Time-Current Curve
31. 31Confidential and Proprietary | Littelfuse, Inc. © 2020 31
Reading a Peak Let-Through Current Curve
Ip
If the available
fault current is
100 kA rms
The instantaneous peak
current can reach 35,000A
The apparent RMS
current is 16,500 A
Fuse Rating: 200A
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Maximum AC or DC voltage at which
fuse is designed to operate
Fuse voltage ratings must equal or
exceed the circuit voltage where fuses
will be installed
Fuses can be used at voltages lower
than maximum design voltage
Example: 250V fuse can be used at
240, 120 or 12 volts…but not 480V
125 – 38,000VAC Voltage Rating
Available Ratings
125 – 1500VDC Voltage Rating
Industry Standards: 250 and 600VAC
DC voltage rating is typically (but not always) ½
of corresponding AC rating.
Fuse Ratings – Voltage
34. 34Confidential and Proprietary | Littelfuse, Inc. © 2020 34
Maximum current fuse is required to
interrupt under specified conditions
Standard UL fuse interrupting ratings:
10,000A (Class H)
50,000A (Class K5)
100,000A (Class G)
200,000A (Class L, R, J, T, CC, CD, Semis)
300,000A (not a UL Standard)
10kA – 200kAAC Interrupting Rating
Available Ratings
10kA – 50kADC Interrupting Rating
Littelfuse Self-certified for 300kA
Fuse Ratings – Interrupting
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Fuse Reaction Times
Fuses are classified based on their operating characteristics and how quickly
they are designed to react.
Time delay fuses are designed to carry a specific overload for a specified
duration of time
Fast-acting fuses do not intentionally have time delay feature designed
into them
Very fast-acting fuses do not intentionally have time delay designed into
them, but are designed to react extremely fast to overcurrent
36. 36Confidential and Proprietary | Littelfuse, Inc. © 2020 36
Fuses designed to carry specific overload for specified
amount of time before opening.
UL Standard for most UL Classes: withstand 500% of
fuse’s rated current for minimum of 10 seconds.
(Class CC: 200 % for 12 sec min.)
If sized properly, Time-Delay fuses are designed to
protect against both overloads and short-circuits.
Time-Delay fuses are necessary and used for
protection of inductive loads with initial in-rush of
current when energized.
Inductive loads are generated by equipment with coils.
Time-Delay Fuses
(Class L, RK1, RK5, J, CC, CD and some Midgets)
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Used to protect extremely sensitive equipment
Used where loads typically have very little or no initial in-
rush of current when energized
Not designed to carry any specific amount of time-delay
Devices with Non-Inductive Loads
Resistance Heaters, Ovens
UPS Equipment
DC Power Supplies
Variable Speed Drives
Diodes & Thyristors
Triacs & Transistors
Rectifiers
Other Solid State Devices
Fast-Acting Fuses
(Class RK1, K5, J, T, CC and some Midgets)
38. 38Confidential and Proprietary | Littelfuse, Inc. © 2020 38
Dual-element fuse design – a fuse with an internal construction consisting of
separate overload and short-circuit sections.
Diffusion fuse design – a fuse with an internal construction that combines alloys to
create a desired time-current characteristic.
Fuse Terms – Dual-Element
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A current limiting device
opens and clears a fault
within the first half electrical
cycle (0.00833 seconds)
To be labeled “current
limiting,” a fuse must mate
with fuse block or holder that
either has rejection feature or
dimensions that reject non-
current-limiting fuses.
Current-Limiting Device – Overview
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Non Current-limiting Fuses or Circuit Breakers
With Current-limiting UL Class RK5 Fuses
With Current-limiting UL Class RK1 Fuses
With Current-limiting UL Class J or T Fuses
Standard Circuit
Breaker
5 electrical cycles
Current-Limiting Fuses Reduce Time and Energy
47. 47Confidential and Proprietary | Littelfuse, Inc. © 2020 47
Design in Safety with Current-Limiting Fuses
Older facilities used UL Class H “renewable” fuses
– No current limitation
– Interrupting rating of only 10,000 A
Designing in current-limiting fuses provides better protection
Class RK5Class RK1Class J Comparing performance
between the three…
RK5 => 6,400 A
RK1 => 4,100 A
J => 3,500 A
48. 48Confidential and Proprietary | Littelfuse, Inc. © 2020 48
Lower I2t let-thru energy
Lower Ipeak (instantaneous peak let-thru current)
Reduces arc-flash incident energy
Aids in selective coordination
Can increase Short-Circuit Current Ratings (SCCR) of industrial
control panels (NEC 409 and UL508A)
Advantages of Current Limitation
50. 50Confidential and Proprietary | Littelfuse, Inc. © 2020 50
Fuse Sizing
When sizing fuses, don’t forget to evaluate…
Mixed fuses – in 3-phase circuit, all three fuses should be same current
rating, UL Class and manufacturer
Type of load – need to assess if load requires inductive (time-delay) or
non-inductive (fast-acting) protection
Ambient temperature – need to look for any abnormal temperatures near
or surrounding the fuses
Cycling – need to assess if application is requiring repetitive ‘on’ and ‘off’
actions that could prematurely cause nuisance opening
Codes & Standards – need to assess applicable local and national
standards to confirm compliance
51. 51Confidential and Proprietary | Littelfuse, Inc. © 2020 51
Motor Protection Tables
1/2
3/4
1
1-1/2
2
3
5
7-1/2
10
15
20
25
30
40
50
60
75
100
125
150
200
1
1.4
1.8
2.6
3.4
4.8
7.6
11
14
21
27
34
40
52
65
77
96
124
158
180
240
1-1/4
1-6/10
2-1/4
3-2/10
4
5-6/10
9
12
17-1/2
25
30
40
50
60
80
90
110
150
175
225
300
1-1/8
1-6/10
2
2-6/10
3-1/2
5
8
12
15
20
30
35
45
60
70
80
110
125
175
200
250
1-1/4
1-8/10
2-1/4
3-1/2
4-1/2
6
10
15
17-1/2
30
35
45
50
70
90
100
125
175
200
225
300
1-1/4
1-8/10
2-1/4
3
4
5-6/10
9
15
15
17-1/2
25
35
40
50
60
75
90
125
150
200
225
300
30
30
30
30
30
30
30
30
30
60
60
60
100
100
100
200
200
200
400
400
460 Volt 3 Phase Motors (480 Volt Circuit)
Motor
HP
Full
Load
Amps
Without Overload Relays
S.F. = Less
Than 1.15
Or Temp
Rise More 40C
With Overload Relays
S.F. = 1.15
Or More,
Temp Rise
Not Over 40 C
S.F. = Less
Than 1.15
Or Temp
Rise More 40C
S.F. = 1.15
Or More,
Temp Rise
Not Over 40 C
Switch
or Fuse
Clip
Rating
Class R Fuses
52. 52Confidential and Proprietary | Littelfuse, Inc. © 2020 52
How Are These Products Identified?
…plus labeling requirements!
UL Listed UL Recognized
UL Classes include: L, RK1, RK5, K5, J, T, G, CC, and CD
Midget fuses are UL Listed as “Supplementary Overcurrent Protection Fuses”
High-Speed fuses are UL Recognized as “Special Purpose Fuses”
250V? 600V? Other?
UL Classes Determine a Fuse’s
Selection Considerations
Voltage Rating
1/10 – 6000ACurrent Rating
10k – 200kA.I.R.Interrupting Rating
Time-Delay/Fast-ActingFuse Characteristics
How much space?Physical Size
Yes? No? How much?Current Limiting
Littelfuse InnovationIndication
54. 5454Confidential and Proprietary | Littelfuse, Inc. © 2020
Selective Coordination Overview
If one circuit is overloaded or faulted, it will not cause a blackout or
other critical circuits to lose power
Only the protective device that is immediately on the line side of an
overcurrent fault location opens
Time-current curves provide the amount of time the device will take to
clear a fault at a given value of fault current
When designing the circuit, place the fastest-clearing devices closest to
the load.
55. 5555Confidential and Proprietary | Littelfuse, Inc. © 2020
Fuses Simplify Selective Coordination
Fuse Coordination Table
Coordination tables:
make it easier to
define what will be
selectively coordinated
prevent the system
designer from needing
to overlay the time-
current curves
save time
58. 58Confidential and Proprietary | Littelfuse, Inc. © 2020 58
Number of poles (1, 2, 3 or 4)
Mounting configuration (Screw-in or DIN-rail mounted)
Connector type (Screw, Screw w/ Pressure Plate, Box Lug)
UL Classes R, J, T, G, CC, and CD
Midgets
Semiconductors (module design)
Panel Mount fuseholders
Dead Front fuseholders
Inline fuseholders
Available configurations include…
The same factors are also used when selecting the
proper fuseholder or fuse block, plus…
Fuseholder / Fuseblock Selection Considerations
59. 59Confidential and Proprietary | Littelfuse, Inc. © 2020 59
Case Size – The maximum allowable ampere rating of a fuse
with defined dimensions and shape.
0–30 Amps 35–60 Amps 70–100 Amps 110–200 Amps 225–400 Amps 450–600 Amps
Cartridge Design Knife-blade Design
Fuse / Fuseblock Term – Case Size
60. 60Confidential and Proprietary | Littelfuse, Inc. © 2020 60
Distribution Blocks
Can terminate up to 12 load wires
in single point
Can be supplied by 1 or 2 line-side
wires
Vs.
Splicer Blocks
Combines either 1 or 2 load wires
with same number of line wires
LD and LFD Series
Distribution Blocks
Distribution Block vs. Splicer Block
LS and LFS Series
Splicer Blocks
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Easy-to-Find Online Resources
Littelfuse University
Fuses White PaperPOWR-GARD Technical
Application Guide
SCCR White Paper
Industrial Fuses Webpage
Motor Protection Guide
63. 63Confidential and Proprietary | Littelfuse, Inc. © 2020 63
Committed to Supporting You
Cross Reference & Technical Support
LuAnn Lange and Melody York
Phone: 1-800-TEC-FUSE (1-800-832-3873)
Email: techline@littelfuse.com
Product Management Support
Craig Greeson
Email: cgreeson@littelfuse.com
Engineering Support
Ryan Blackford
Email: rblackford@littelfuse.com
Marketing Support
Debra Jayson
Email: djayson@littelfuse.com
Mike Sims
Email: msims@littelfuse.com
64. 64Confidential and Proprietary | Littelfuse, Inc. © 2020 64
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