Component Protection
Introduction and Current-Limitation
Component Protection and
The National Electrical Code®
110.10 Circuit Impedance and Other Characteristics: The overcurrent
protective devices, the total impedance, the component short-circuit current
ratings, and other characteristics of the circuit to be protected shall be
selected and coordinated to permit the circuit-protective devices used to
clear a fault to do so without extensive damage to the electrical
components of the circuit. This fault shall be assumed to be either between
two or more of the circuit conductors or between any circuit conductor and
the grounding conductor or enclosing metal raceway. Listed products
applied in accordance with their listing shall be considered to meet the
requirements of this section.
This requires that overcurrent protective devices, such as fuses and circuit
breakers be selected in such a manner that the short-circuit current
(withstand) ratings of the system components will not be exceeded should a
short circuit occur.
The “short-circuit withstand rating” is the maximum short- circuit current that a
component can safely withstand. Failure to provide adequate protection may
result in component destruction under short circuit conditions.
After calculating the fault levels throughout the electrical system, the next step
is to check the withstand rating of wire and cable, circuit breakers, transfer
switches, starters, etc., under short circuit conditions.
Note: The let-through energy of the protective device must be equal to or less
than the short-circuit withstand rating of the component being protected.
CAUTION: Choosing overcurrent protective devices strictly on the basis of
voltage, current, and interrupting rating alone will not assure component
protection from short-circuit currents. High interrupting capacity electromechanical overcurrent protective devices (circuit breakers), especially
those that are not current-limiting, may not be capable of protecting wire,
cable or other components within high short circuit ranges. The interrupting
rating of a protective device pertains only to that device and has absolutely
no bearing on its ability to protect connected downstream components.
Quite often, an improperly protected component is completely destroyed
under short circuit conditions while the protective device is opening the
faulted circuit.
Before proceeding with the study of component withstandability, the
technology concerning “current-limitation” will be reviewed.
©2005 Cooper Bussmann
Current-Limitation Defined
Today, most electrical distribution systems are capable of delivering very high
short-circuit currents, some in excess of 200,000A. Many circuit components
have relatively low short circuit withstandability of a few thousand amps. If the
components are not capable of handling these short-circuit currents, they
could easily be damaged or destroyed. The current-limiting ability of today’s
modern fuses allows components with low short-circuit withstand ratings to be
specified in spite of high available fault currents.
NEC® 240.2 offers the following definition of a current-limiting device:
Current-Limiting Overcurrent Protective Device: A device that, when
interrupting currents in its current-limiting range, reduces the current flowing
in the faulted circuit to a magnitude substantially less than that obtainable in
the same circuit if the device were replaced with a solid conductor having
comparable impedance.
The concept of current-limitation is pointed out in the following graph, where
the prospective available fault current is shown in conjunction with the limited
current resulting when a current-limiting fuse clears. The area under the
current curve is representative of the amount of short circuit energy being
dissipated in the circuit. Since both magnetic forces and thermal energy are
directly proportional to the square of the current, it is important to limit the
short-circuit current to as small a value as possible. The maximum magnetic
forces vary as the square of the “PEAK” current and thermal energy varies as
the square of the “RMS” current.
Current-Limiting Effect of Fuses
Prospective available short-circuit
current that would flow when a
fuse is not used.
100,000
Current
This issue analyzes the protection of electrical system components from fault
currents. It gives the specifier the necessary information regarding the shortcircuit current or withstand rating of electrical circuit components, such as
wire, bus, motor starters, etc. Proper protection of circuits will improve
reliability and reduce the possibility of injury. Electrical systems can be
destroyed if the overcurrent devices do not limit the short-circuit current to
within the withstand rating of the system’s components. Merely matching the
amp rating of a component with the amp rating of a protective device will not
assure component protection under short circuit conditions.
The National Electrical Code® covers Component Protection in several
sections. The first section to note is 110.10.
Peak Let-Through
Current of Fuse
10,000
0
Time
tc
Total Clearing Time of Fuse
Thus, the current-limiting fuse in this example (above waveform) would limit
the let-through energy to a fraction of the value which is available from the
system. In the first major loop of fault current, standard non-current-limiting,
electro-mechanical protective devices would let-through approximately 100
times* as much destructive energy as the fuse would let-through.
2
*
= 100
(100,000
10,000 )
67
Component Protection
How To Use Current-Limitation Charts
Prior to using the Fuse Let-Through Charts, it must be determined what letthrough data is pertinent to equipment withstand ratings.
Equipment withstand ratings can be described as: How Much Fault Current
can the equipment handle, and for How Long? Based on standards presently
available, the most important data that can be obtained from the Fuse LetThrough Charts and their physical effects are the following:
Analysis of Current-Limiting Fuse Let-Through Charts
The degree of current-limitation of a given size and type of fuse depends, in
general, upon the available short-circuit current that can be delivered by the
electrical system. Current-limitation of fuses is best described in the form of a
let-through chart that, when applied from a practical point of view, is useful to
determine the let-through currents when a fuse opens.
Fuse let-through charts are plotted from actual test data. The test circuit that
establishes line A-B corresponds to a short circuit power factor of 15%, that is
associated with an X/R ratio of 6.6. The fuse curves represent the cutoff value
of the prospective available short-circuit current under the given circuit
conditions. Each type or class of fuse has its own family of let-through curves.
The let-through data has been generated by actual short- circuit tests of
current-limiting fuses. It is important to understand how the curves are
generated, and what circuit parameters affect the let-through curve data.
Typically, there are three circuit parameters that can affect fuse let-through
performance for a given available short-circuit current. These are:
A. Peak let-through current: mechanical forces
B. Apparent prospective RMS symmetrical let-through current: heating effect
C. Clearing time: less than 1⁄2 cycle when fuse is in it’s current-limiting range (beyond
where fuse curve intersects A-B line).
This is a typical example showing the short-circuit current available to an 800A
circuit, an 800A Low-Peak current-limiting time-delay fuse, and the let-through
data of interest.
800 Amp Low-Peak® Current-Limiting Time-Delay
Fuse and Associated Let-Through Data
1. Short-circuit power factor
2. Short-circuit closing angle
3. Applied voltage
Current-limiting fuse let-through curves are generated under worst case
conditions, based on these three variable parameters. The benefit to the user
is a conservative resultant let-through current (both Ip and IRMS). Under
actual field conditions, changing any one or a combination of these will result
in lower let-through currents. This provides for an additional degree of
reliability when applying fuses for equipment protection.
Current-Limiting Let-Through Charts for Cooper Bussmann fuses are near the
back of this book.
B
400,000
300,000
Available Peak ShortCircuit Current = 198,000A
I
200,000
Available RMS ShortCircuit Current = 86,000A
100,000
80,000
60,000
Peak Let-Through Current
of Fuse= 49,000A
800A
RMS Let-Through Current
of Fuse = 21,000A
30,000
20,000
tm
10,000
8000
6000
TIME
ta
tc
tm = Fuse Melt Time
ta = Fuse Arc Time
tc = Fuse Clearing Time
AMP
RATING
4000
3000
A
200,000
100,000
60,000
80,000
30,000
40,000
20,000
6000
4000
3000
2000
1000
8000
10,000
2000
1000
INSTANTANEOUS PEAK LET-THROUGH CURRENT IN AMPS
Analysis of a Current-Limiting Fuse
PROSPECTIVE SHORT-CIRCUIT CURRENT – SYMMETRICAL RMS AMPS
68
©2005 Cooper Bussmann
Component Protection
How To Use Current-Limitation Charts
How to Use the Let-Through Charts
Using the example given, one can determine the pertinent let-through data for
the KRP-C-800SP amp Low-Peak fuse. The Let-Through Chart pertaining to
the 800A Low-Peak fuse is illustrated.
A.
Determine the PEAK let-through CURRENT.
Step 1.
Enter the chart on the Prospective Short-Circuit current scale
at 86,000 amps and proceed vertically until the 800A fuse
curve is intersected.
Follow horizontally until the Instantaneous Peak Let-Through
Current scale is intersected.
Read the PEAK let-through CURRENT as 49,000A. (If a fuse
had not been used, the peak current would have been
198,000A.)
Step 2.
Step 3.
Most electrical equipment has a withstand rating that is defined in terms of an
RMS symmetrical-short-circuit current, and in some cases, peak let-through
current. These values have been established through short circuit testing of
that equipment according to an accepted industry standard. Or, as is the case
with conductors, the withstand rating is based on a mathematical calculation
and is also expressed in an RMS short-circuit current.
If both the let-through currents (IRMS and Ip) of the current-limiting fuse
and the time it takes to clear the fault are less than the withstand rating
of the electrical component, then that component will be protected from
short circuit damage.
The following Table shows typical assumed short-circuit current ratings for
various unmarked components.
B.
Determine the APPARENT PROSPECTIVE RMS
SYMMETRICAL let-through CURRENT.
Typical Short-Circuit Current Ratings For Unmarked
Components*
Step 1.
Enter the chart on the Prospective Short-Circuit current scale
at 86,000A and proceed vertically until the 800A fuse curve is
intersected.
Follow horizontally until line A-B is intersected.
Proceed vertically down to the Prospective Short-Circuit
Current.
Read the APPARENT PROSPECTIVE RMS SYMMETRICAL
let-through CURRENT as 21,000A. (The RMS
SYMMETRICAL let-through CURRENT would be 86,000A if
there were no fuse in the circuit.)
Component
Step 2.
Step 3.
Step 4.
Current-Limitation Curves — Cooper Bussmann
Low-Peak Time-Delay Fuse KRP-C-800SP
Short- Circuit
Rating, kA
Industrial Control Equipment:
a. Auxiliary Devices
b. Switches (other than Mercury Tube Type)
c. Mercury Tube Switches
Rated over 60 amperes or over 250 volts
Rated 250 volts or less, 60 amperes or less, and over 2kVA
Rated 250 volts or less and 2kVA or less
Meter Socket Base
Photoelectric Switches
Receptacle (GFCI Type)
Receptacle (other than GFCI Type)
Snap Switch
Terminal Block
Thermostat
5
5
5
3.5
1
10
5
10
2
5
10
5
*Based upon information in UL 891 (Dead-Front Switchboards)
The following components will be analyzed by establishing the short-circuit
withstand data of each component and then selecting the proper currentlimiting fuses for protection:
• Wire and Cable
• Bus (Busway, Switchboards, Motor Control Centers and Panelboards)
• Transfer Switches
• HVAC Equipment
• Ballasts
• Circuit Breakers
A detailed analysis of motor circuit component protection is provided later in
the section on motor circuits.
C. Clearing time
If the RMS Symmetrical available is greater than the point where the fuse
characteristic curve intersects with the diagonal A-B line, then the fuse
clearing time is 1⁄2 cycle or less. In this example, the intersection is
approximately 9500A; so for short-circuit currents above approximately 9500A,
this KRP-C-800SP fuse is current-limiting.
The current-limiting charts and tables for Cooper Bussmann fuses are in the
rear of this book under “Current-Limiting Let-Through Charts.” Refer to these
tables when analyzing component protection in the following sections.
©2005 Cooper Bussmann
69
Ground Fault Protection
Current-Limitation
The Need for Current-Limitation
If ground fault protection is required, then the best protection is a switch
equipped with a ground fault relay scheme, a shunt trip mechanism, and
current-limiting fuses. The reason is that this system will offer protection for
high magnitude ground faults as well as low magnitude ground faults. Ground
fault relay schemes and shunt trip mechanisms on switches or circuit breakers
can protect equipment against extensive damage from low magnitude ground
faults - this is their intended purpose. However, burn downs still occur in
switchboards, large motor control centers, and large distribution panels
generally located in equipment rooms where high available ground fault
currents are present.
The National Electrical Code® requires ground fault protection for intermediate
and high ground faults as well as low grade ground faults. For high magnitude
ground faults, ground fault relay schemes operate too slowly to prevent
extensive equipment damage. The main or feeder overcurrent devices, such
as fuses or circuit breakers must clear the circuit. Current-limiting fuses
substantially limit the energy let-through for higher magnitude ground faults
and thereby offer a higher degree of protection. Conventional circuit breakers
are not current-limiting protective devices and during higher magnitude ground
faults can let-through large amounts of damaging energy.
1,000
800
600
1,000
800
400
300
600
400
300
200
200
100
80
60
100
80
60
40
KRP-C1600SP
30
20
10
8
6
TIME IN SECONDS
30
40
TIME IN SECONDS
1600A CB
20
10
8
6
4
3
4
2
3
2
1
.8
.6
1
.8
.6
.4
.3
.4
.2
.3
.2
.1
.08
.06
.1
.08
.04
.06
.03
.04
.02
CURRENT IN AMPS
Clearing characteristic for a 1600A fuse. A 20,000 amp fault is cleared by the KRP-C1600SP fuse in 0.019 to 0.039 seconds (between one and two cycles). For currents
greater than 25,000A the fuse enters its current-limiting range. Then the clearing time
is less than one half cycle (less than 0.008 seconds).
114
60,000
80,000
100,000
40,000
30,000
20,000
6,000
8,000
10,000
4,000
3,000
600
400
300
200
100
000,001
000,08
000,06
000,04
000,03
000,02
000,01
000,8
000,6
000,4
000,3
000,2
000,1
008
006
004
003
002
001
08
.01
.01
2,000
.02
800
1,000
.03
CURRENT IN AMPS
Clearing characteristic for 1600A circuit breaker. A 20,000A fault is cleared by the
1600A circuit breaker in 0.05 seconds. The circuit breaker has a fixed operating time
for high values of current. This time is approximately 0.05 seconds (three cycles).
Therefore, high magnitude ground faults and short circuits are permitted to flow for at
least three cycles.
©2005 Cooper Bussmann
Ground Fault Protection
Current-Limitation
The previous two figures illustrate the time-current characteristics for a 1600A
current-limiting fuse and a 1600A circuit breaker. The higher the fault current
the faster the fuse operates. Notice, the mechanical overcurrent protective
device reaches an irreducible operating time. For large conventional service
entrance circuit breakers this fixed operating time varies from 11⁄2 cycles to five
cycles depending on the type and size. (If short-time-delay trip settings are
used, the operating time can be as long as 30 cycles.)
Of importance is the fact that modern, rejection type fuses are current-limiting
protective devices. For faults above approximately 25,000A, the 1600A fuse
operates in its current-limiting range; clearing the circuit in less than 1⁄2 cycle
and limiting the peak current and energy let-through to the circuit components.
Current-Limitation
Current-Limitation
No Current-Limitation
Available current that would flow
without a fuse.
Fuse CurrentLimiting Effect
The effect of a fuse protecting the circuit is to limit the instantaneous peak
current and thermal or heating effect current to a value less than that which
would flow in the first half cycle had the fuse not been in the circuit. Currentlimitation for high level ground faults can substantially reduce the damaging
effect.
The large conventional mechanical overcurrent protective device reaches an
irreducible minimum clearing time and therefore permits the full fault current
flow for several cycles. The damaging peak current and thermal or heating
effect current flow unrestricted without limitation for several cycles. At higher
magnitude fault currents, large amounts of heating energy and magnetic
forces are permitted to flow and the equipment must absorb the full available
fault current energy.
Available current flows for
operating time of circuit breaker.
3 Cycle Clearing Time
Compare the Difference
Arc-flash when circuit protected by 601A Class L current-limiting fuses.
©2005 Cooper Bussmann
Arc-flash when circuit protected by a 1600A non-current limiting circuit breaker set at
640A with short time delay: circuit interrupted in six cycles.
115
Cooper Bussmann Current-Limiting Fuse Let-Through Data
See pages 67 to 69 for current-limiting definition and how to analyze these charts.
Low-Peak Class L Time-Delay Fuses
KRP-C_SP
KRP-C_SP Fuse – RMS Let-Through Currents (kA)
1000000
900000
800000
700000
600000
Prosp.
Short
C.C.
B
500000
400000
6000A
5000A
4000A
3000A
200000
2500A
2000A
1600A
1200A
601
800
1200 1600
2000 2500 3000 4000
5000
6000
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
5,000
5
5
5
5
5
5
5
5
5
5
10,000
8
10
10
10
10
10
10
10
10
10
15,000
9
12
15
15
15
15
15
15
15
15
13
17
20
20
20
20
20
20
20
20,000 10
25,000 11
14
19
22
25
25
25
25
25
25
30,000 11
14
20
24
27
30
30
30
30
30
35,000 12
15
21
25
29
35
35
35
35
35
40,000 13
16
22
26
30
35
40
40
40
40
50,000 14
17
23
28
32
37
50
50
50
50
60,000 15
18
25
30
34
40
49
60
60
60
70,000 15
19
26
32
36
42
52
62
70
70
10000
9000
8000
7000
6000
80,000 16
20
27
33
38
44
54
65
76
80
90,000 17
21
29
34
39
45
56
67
79
90
5000
100,000 17
22
30
36
41
47
58
70
81
100
3000
150,000 20
25
34
41
47
54
67
80
93
104
A
200,000 22
27
37
45
51
59
73
87
102
114
250,000 24
29
40
49
55
64
79
94
110
123
300,000 25
31
43
52
59
68
84
100
117
30
100000
90000
80000
70000
60000
800A
601A
50000
40000
AMPERE
RATING
INSTANTANEOUS PEAK LET THRU CURRENT IN AMPERES
300000
Fuse Size
30000
20000
4000
2000
300000
200000
60000
70000
80000
90000
100000
50000
40000
30000
20000
5000
6000
7000
8000
9000
10000
4000
3000
2000
1000
1000
Note: For IRMS value at 300,000 amperes, consult Factory.
PROSPECTIVE SHORT CIRCUIT CURRENT - SYMMETRICAL RMS AMPERES
Low-Peak Class J, Dual-Element Time-Delay Fuses
LPJ_SP
LPJ_SP Fuse – RMS Let-Through Currents (kA)
15
30
60
100
200
400
600
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
400A
1,000
1
1
1
1
1
1
1
200A
3,000
1
1
1
2
2
3
3
100A
5,000
1
1
1
2
3
5
5
60A
10,000
1
1
2
2
4
6
8
30A
15,000
1
1
2
3
4
7
9
15A
20,000
1
1
2
3
4
7
10
25,000
1
1
2
3
5
8
10
30,000
1
1
2
3
5
8
11
35,000
1
1
2
4
5
9
12
40,000
1
2
3
4
6
9
12
50,000
1
2
3
4
6
10
13
60,000
1
2
3
4
6
11
14
80,000
1
2
3
5
7
12
15
100,000
1
2
4
5
8
12
17
150,000
1
2
4
6
9
14
19
200,000
2
3
4
6
9
16
21
250,000
2
3
5
7
10
17
23
300,000
2
3
5
7
11
18
24
600A
50000
40000
10000
9000
8000
7000
6000
5000
4000
3000
AMPERE
RATING
INSTANTANEOUS PEAK LET-THROUGH CURRENT IN AMPERES
30000
20000
2000
1000
900
800
700
600
500
400
300
A
200
PROSPECTIVE SHORT-CIRCUIT CURRENT - SYMMETRICAL RMS AMPERES
300000
200000
60000
70000
80000
90000
100000
50000
40000
30000
20000
6000
7000
8000
9000
10000
4000
5000
3000
2000
600
700
800
900
1000
500
400
300
200
100
100
Fuse Size
Prosp.
Short
C.C.
B
100000
90000
80000
70000
60000
Note: For IRMS value at 300,000 amperes, consult Factory.
210
©2005 Cooper Bussmann
Cooper Bussmann Current-Limiting Fuse Let-Through Data
See pages 67 to 69 for current-limiting definition and how to analyze these charts.
Low-Peak Class RK1 Dual-Element Time-Delay Fuses
LPN-RK_SP
LPN-RK_SP – RMS Let-Through Currents (kA)
Prosp.
Short
C.C.
B
Fuse Size
30
60
100
200
400
600
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
1,000
1
1
1
1
1
1
2,000
1
1
2
2
2
2
3,000
1
1
2
3
3
3
5,000
1
2
2
3
5
5
10,000
1
2
3
4
7
9
15,000
1
2
3
5
8
11
20,000
1
3
3
5
8
11
25,000
1
3
3
5
9
12
30,000
2
3
4
6
9
12
35,000
2
3
4
6
10
13
40,000
2
3
4
6
10
13
50,000
2
3
4
7
11
14
4,000
60,000
2
3
4
7
11
16
3,000
70,000
2
3
4
7
12
16
80,000
2
4
5
8
12
16
90,000
2
4
5
7
13
17
100,000
2
4
5
8
13
17
150,000
2
4
6
9
15
19
200,000
3
5
6
11
16
20
250,000
3
5
7
11
17
21
300,000
3
6
7
12
18
22
600
400,000
300,000
AMPERE
RATING
INSTANTANEOUS PEAK LET-THROUGH CURRENT IN AMPERES
200,000
100,000
90,000
80,000
70,000
60,000
50,000
600A
40,000
400A
30,000
200A
20,000
100A
60A
10,000
9,000
8,000
7,000
6,000
30A
5,000
A
2,000
300,000
200,000
80,000
100,000
60,000
40,000
30,000
20,000
8,000
10,000
6,000
4,000
3,000
2,000
1,000
1,000
PROSPECTIVE SHORT-CIRCUIT CURRENT - SYMMETRICAL RMS AMPERES
Low-Peak Class RK1 Dual-Element Time-Delay Fuses
LPS-RK_SP
LPS-RK_SP – RMS Let-Through Currents (kA)
Prosp.
Short
C.C.
Fuse Size
30
60
100
200
400
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
1,000
1
1
1
1
1
1
2,000
1
1
2
2
2
2
AMPERE
RATING
B
3,000
1
1
2
3
3
3
5,000
1
2
2
3
5
5
600A
10,000
1
2
3
4
7
10
400A
15,000
1
2
3
5
8
11
200A
20,000
2
3
3
5
9
12
25,000
2
3
4
6
9
12
30,000
2
3
4
6
10
13
35,000
2
3
4
6
10
13
40,000
2
3
4
6
10
14
50,000
2
3
5
7
11
15
4,000
60,000
2
4
5
7
12
15
3,000
70,000
2
4
5
8
13
16
80,000
2
4
5
8
13
16
90,000
2
4
5
8
13
17
100,000
2
4
6
9
14
17
150,000
3
5
6
10
15
19
200,000
3
5
7
11
16
21
250,000
3
6
7
12
17
22
300,000
3
6
7
12
18
23
400,000
300,000
INSTANTANEOUS PEAK LET-THROUGH CURRENT IN AMPERES
200,000
100,000
90,000
80,000
70,000
60,000
50,000
40,000
30,000
20,000
100A
60A
10,000
9,000
8,000
7,000
6,000
30A
5,000
A
2,000
200,000
300,000
100,000
80,000
60,000
40,000
30,000
20,000
10,000
8,000
6,000
4,000
3,000
2,000
1,000
1,000
PROSPECTIVE SHORT-CIRCUIT CURRENT - SYMMETRICAL RMS AMPERES
©2005 Cooper Bussmann
211
Cooper Bussmann Current-Limiting Fuse Let-Through Data
See pages 67 to 69 for current-limiting definition and how to analyze these charts.
Fusetron Class RK5 Dual-Element Time-Delay Fuses
FRN-R
300000
Prosp.
Short
C.C.
200000
100000
90000
80000
70000
60000
50000
30
60
100
200
400
600
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
5,000
1
2
3
5
5
5
10,000
2
3
4
7
10
10
15,000
2
3
5
8
11
15
600A
20,000
2
4
5
8
12
16
25,000
2
4
6
9
13
17
30,000
2
4
6
10
14
18
100A
35,000
2
4
6
10
15
19
60A
40,000
2
5
7
11
15
20
50,000
3
5
7
11
17
21
60,000
3
5
8
12
18
22
70,000
3
6
8
13
19
23
80,000
3
6
8
13
19
24
90,000
3
6
9
14
20
25
100,000
3
6
9
14
21
26
150,000
4
7
10
16
24
29
200,000
4
8
11
18
26
32
400A
200A
40000
30000
Fuse Size
AMPERE
RATING
B
400000
INSTANTANEOUS PEAK LET-THROUGH CURRENT IN AMPERES
FRN-R – RMS Let-Through Currents (kA)
20000
10000
9000
8000
7000
6000
5000
30A
4000
3000
A
2000
200000
50000
60000
70000
80000
90000
100000
30000
40000
20000
4000
5000
6000
7000
8000
9000
10000
3000
2000
1000
1000
PROSPECTIVE SHORT-CIRCUIT CURRENT - SYMMETRICAL RMS AMPERES
Fusetron Class RK5 Dual-Element Time-Delay Fuses
FRS-R
30
60
100
200
400
600
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
5,000
1
1
3
4
5
5
10,000
1
2
4
5
9
10
15,000
1
2
4
6
10
14
20,000
2
2
5
7
11
15
600A
25,000
2
2
5
7
12
17
400A
30,000
2
3
5
8
13
18
200A
35,000
2
3
5
8
13
18
40,000
2
3
6
9
14
19
50,000
2
3
6
9
14
20
60A
60,000
2
3
6
10
15
22
30A
70,000
3
4
7
11
17
23
80,000
3
4
7
12
17
23
90,000
3
4
7
12
17
24
100,000
3
4
8
13
18
25
150,000
3
5
9
14
21
27
200,000
4
6
9
16
23
32
300000
INSTANTANEOUS PEAK LET-THROUGH CURRENT IN AMPERES
200000
100000
90000
80000
70000
60000
50000
Fuse Size
AMPERE
RATING
Prosp.
Short
C.C.
B
400000
FRS-R – RMS Let-Through Currents (kA)
40000
30000
100A
20000
10000
9000
8000
7000
6000
5000
4000
3000
A
2000
200000
60000
70000
80000
90000
100000
50000
40000
30000
20000
6000
7000
8000
9000
10000
5000
4000
3000
2000
1000
1000
PROSPECTIVE SHORT-CIRCUIT CURRENT - SYMMETRICAL RMS AMPERES
212
©2005 Cooper Bussmann
Cooper Bussmann Current-Limiting Fuse Let-Through Data
See pages 67 to 69 for current-limiting definition and how to analyze these charts.
JJN – RMS Let-Through Current (kA)
Prosp.
Short
C.C.
B
30
60
100
200
400
600
800
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
500
1
1
1
1
1
1
1
1
1
1,000
1
1
1
1
1
1
1
1
1
5,000
1
1
1
1
2
3
5
5
5
10,000
1
1
1
2
2
4
6
7
9
15,000
1
1
1
2
3
4
6
9
10
20,000
1
1
1
2
3
5
7
10
11
25,000
1
1
2
2
3
5
7
10
12
30,000
1
1
2
2
3
5
8
11
13
35,000
1
1
2
3
4
6
8
11
13
40,000
1
1
2
3
4
6
9
11
13
50,000
1
1
2
3
4
7
9
12
15
1,000
800
600
60,000
1
1
2
3
4
7
10
13
16
70,000
1
1
2
3
5
7
10
14
17
400
300
80,000
1
2
2
3
5
8
11
15
17
90,000
1
2
2
3
6
8
11
15
18
100,000 1
2
2
4
6
8
12
16
19
150,000 1
2
3
4
6
9
13
17
22
200,000 2
2
3
4
7
9
15
19
23
200,000
100,000
80,000
60,000
1200
800
600
40,000
30,000
400
200
100
20,000
10,000
8,000
6,000
60
30
15
4,000
3,000
2,000
200,000
60,000
80,000
100,000
30,000
40,000
20,000
6,000
8,000
10,000
3,000
4,000
2,000
600
800
1,000
300
400
200
200
100
A
PROSPECTIVE SHORT-CIRCUIT CURRENT–SYMMETRICAL RMS AMPS
Tron Class T Fast-Acting Fuses
JJS
1200
JJS – RMS Let-Through Current (kA)
B
400,000
300,000
AMPERE
RATING
INSTANTANEOUS PEAK LET-THROUGH CURRENT IN AMPS
Fuse Size
15
400,000
300,000
AMPERE
RATING
INSTANTANEOUS PEAK LET-THROUGH CURRENT IN AMPS
Tron Class T Fast-Acting Fuses
JJN
200,000
100,000
80,000
60,000
40,000
30,000
60
100
200
400
600
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
500
1
1
1
1
1
1
1
1
800
1
1
1
1
1
1
1
1
5,000
1
1
1
2
3
4
5
5
400
10,000
1
1
1
2
3
6
8
9
15,000
1
1
2
3
4
7
10
11
20,000
1
1
2
3
4
7
10
12
25,000
1
1
2
3
5
7
11
13
30,000
1
1
2
3
5
8
12
14
35,000
1
1
2
3
5
9
13
15
40,000
1
2
2
4
5
9
13
15
15
4,000
3,000
30
IRMS
1,000
100
60
30
10,000
8,000
6,000
15
IRMS
800
600
200
20,000
Fuse Size
Prosp.
Short
C.C.
2,000
50,000
1
2
2
4
6
10
14
17
1,000
800
600
60,000
1
2
3
4
6
10
16
18
70,000
1
2
3
4
7
11
17
19
400
300
80,000
1
2
3
4
7
11
17
20
90,000
200,000
60,000
80,000
100,000
30,000
40,000
20,000
6,000
8,000
10,000
3,000
4,000
2,000
600
800
1,000
300
400
200
200
100
A
PROSPECTIVE SHORT-CIRCUIT CURRENT–SYMMETRICAL RMS AMPS
©2005 Cooper Bussmann
1
2
3
4
7
12
18
21
100,000 2
2
3
5
7
12
19
22
150,000 2
3
4
6
8
14
22
25
200,000 2
3
4
6
9
16
24
28
213
Cooper Bussmann Current-Limiting Fuse Let-Through Data
See pages 67 to 69 for current-limiting definition and how to analyze these charts.
Low-Peak Class CC Time-Delay Fuses
LP-CC
LP-CC – RMS Let-Through Currents (A)
INSTANTANEOUS PEAK LET-THROUGH CURRENT IN AMPS
Prosp.
Short
C.C.
Fuse Size
11/4
2 8/10
15
20
25
30
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
1,000
100
135
240
305
380
435
3,000
140
210
350
440
575
580
5,000
165
255
420
570
690
710
10,000
210
340
540
700
870
1000
20,000
260
435
680
870
1090
1305
30,000
290
525
800
1030
1300
1520
40,000
315
610
870
1150
1390
1700
50,000
340
650
915
1215
1520
1820
60,000
350
735
1050
1300
1650
1980
80,000
390
785
1130
1500
1780
2180
100,000
420
830
1210
1600
2000
2400
200,000
525
1100
1600
2000
2520
3050
600
PROSPECTIVE SHORT-CIRCUIT CURRENT–SYMMETRICAL RMS AMPS
Limitron Class J Fast-Acting Fuses
JKS
JKS – RMS Let-Through Currents (kA)
30
60
100
200
400
300,000
IRMS
IRMS
IRMS
IRMS
IRMS
IRMS
200,000
5,000
1
1
2
3
4
5
10,000
1
2
3
4
6
9
15,000
1
2
3
4
7
10
20,000
1
2
3
5
8
11
600
25,000
2
3
3
6
9
12
400
30,000
2
3
3
6
9
13
200
35,000
2
3
4
6
9
13
40,000
2
3
4
7
10
14
50,000
2
3
4
7
10
15
60,000
2
3
5
7
11
16
70,000
2
3
5
8
11
17
80,000
2
3
5
8
12
17
90,000
2
4
6
9
13
18
100,000
2
4
6
9
13
18
150,000
2
5
6
9
14
22
200,000
3
5
7
10
16
24
AMPERE
RATING
100,000
80,000
60,000
50,000
40,000
30,000
20,000
100
60
10,000
8,000
30
6,000
5,000
4,000
3,000
A
200,000
80,000
100,000
40,000
50,000
60,000
30,000
20,000
8,000
10,000
4,000
5,000
6,000
3,000
1,000
2,000
2,000
1,000
INSTANTANEOUS PEAK LET-THROUGH CURRENT IN AMPS
Fuse Size
Prosp.
Short
C.C.
B
400,000
PROSPECTIVE SHORT-CIRCUIT CURRENT–SYMMETRICAL RMS AMPS
214
©2005 Cooper Bussmann