SHORT CIRCUIT PERFORMANCE
OF
METALLIC SHIELDS AND SHEATHS
ON
INSULATED CABLE
ICEA PUBLICATION
P-45-482-2013
Revised February 27, 2013
2013 by
INSULATED CABLE ENGINEERS ASSOCIATION, Inc.
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ICEA P-45-482-2013
Approved as an American National Standard
ANSI Approval Date: February 27, 2013
Insulated Cable Engineers Assoc., Publication No. P-45-482-Revised 2013
Published by
Insulated Cable Engineers Association
P.O. Box 1568
Carrollton, Georgia 30112
www.icea.net
© Copyright 2013 by the Insulated Cable Engineers Association, Incorporated.
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Short Circuit Performance of Metallic Shields and Sheaths on Insulated Cable
ICEA P-45-482-2013
NOTICE AND DISCLAIMER
The information in this publication was considered technically sound by the consensus of persons
engaged in the development and approval of the document at the time it was developed. Consensus does
not necessarily mean that there is unanimous agreement among every person participating in the
development of this document.
The Insulated Cable Engineers Association, Inc. (ICEA) standards and guideline publications, of which the
document contained herein is one, are developed through a voluntary consensus standards development
process. This process brings together persons who have an interest in the topic covered by this
publication. While ICEA administers the process and establishes rules to promote fairness in the
development of consensus, it does not independently test, evaluate, or verify the accuracy or
completeness of any information or the soundness of any judgements contained in its standards and
guideline publications.
ICEA disclaims liability for personal injury, property, or other damages of any nature whatsoever, whether
special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use
of, application, or reliance on this document. ICEA disclaims and makes no guaranty or warranty,
expressed or implied, as to the accuracy or completeness of any information published herein, and
disclaims and makes no warranty that the information in this document will fulfill any of your particular
purposes or needs. ICEA does not undertake to guarantee the performance of any individual
manufacturer or seller’s products or services by virtue of this standard or guide.
In publishing and making this document available, ICEA is not undertaking to render professional or other
services for or on behalf of any person or entity, nor is ICEA undertaking to perform any duty owed by any
person or entity to someone else. Anyone using this document should rely on his or her own independent
judgment or, as appropriate, seek the advice of a competent professional in determining the exercise of
reasonable care in any given circumstances. Information and other standards on the topic covered by this
publication may be available from other sources, which the user may wish to consult for additional views
or information not covered by this publication.
ICEA has no power, nor does it undertake to police or enforce compliance with the contents of this
document. ICEA does not certify, test, or inspect products, designs, or installations for safety or health
purposes. Any certification or other statement of compliance with any health or safety-related information
in this document shall not be attributable to ICEA and is solely the responsibility of the certifier or maker of
the statement.
ICEA P-45-482-2013
Page i
CONTENTS
Page
Foreword .....................................................................................................................................ii
Section 1
Section 2
GENERAL .................................................................................................................................. 1
1.1
SCOPE ......................................................................................................................... 1
1.2
REFERENCES ............................................................................................................. 1
FORMULAE AND CALCULATIONS.......................................................................................... 3
Section 3
Tabulated Parameters ............................................................................................................... 5
LIST OF TABLES
Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
Formulas for Determining Metallic Shield/Sheath Cross-sectional Area……………………4
Parameters for Use in Equations (1), (2) or (3)...................................................................5
Values of T1, Approximate Shield or Sheath Operating Temperature, ºC at Various
Conductor Temperatures....................................................................................................5
Values for T2, Maximum Allowable Shield or Sheath Transient Temperature, ºC..............6
M Values for T2 Temperature of 200 ºC………………………………………………………..6
M Values for T2 Temperature of 350 ºC………………………………………………………..7
© Copyright 2013 by the Insulated Cable Engineers Association, Incorporated.
ICEA P-45-482-2013
Page ii
Foreword
This publication discusses factors for consideration in approximating the operability of insulated and/or
covered wire and cable under the influence of uninterrupted short circuit currents encountered as a result
of cable or other equipment faults. The duration of such a fault is considered to be up to approximately 2
seconds. Calculation for single short circuits of longer durations will yield increasingly conservative
results.
The following items must be considered in order to estimate the short circuit performance of a specific
circuit:
1. The magnitude and duration of the fault current including any fault current division due to available
conducting paths.
2. The capability of joints, terminations and other accessories in the affected circuit to withstand the
thermal and mechanical stresses created by the fault.
3. The interaction between the faulting circuit and surrounding equipment, such as supports, ties and
clamps.
4. The capability of the affected cable circuit, as installed, to withstand the electromagnetic forces
created during the fault.
5. The maximum temperature that cable components can withstand without incurring damage due to
heating caused by fault current flow.
6. Damage to adjacent equipment due to arcing at the site of the fault.
7. For limitations imposed on the short-circuit current in the cable phase conductor see ICEA
Publication P-32-382, Short Circuit Characteristics of Insulated Cable.
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An important simplifying assumption in the formula is the adiabatic nature of the heat generated, i.e., the
duration of the fault is so short that all the heat developed by the fault current during this time is assumed
to be completely contained within the sheath or shield. The amount of heat dissipated from the sheath or
shield during continuous, single fault occurrences of relatively short duration is small. A significant amount
of heat may be dissipated because of the relatively long cooling periods involved for faults interrupted and
reestablished with automatic reclosing of circuit protective devices. A non-adiabatic calculation may be
more suitable for these situations and for single, uninterrupted short circuits in excess of 2 seconds
requiring close accuracy. Non-adiabatic calculation methods are described in several published works
listed in Section 1.2 “References”.
The formula (1) described in this publication is based on the thermal capacity of the metallic sheath/shield
material and the transient temperature limit of the adjacent cable component materials. The quantity of
heat contained in the metallic sheath/shield is that created by the fault current and is also a function of the
temperature rise in the metallic sheath/shield. The magnitude of the temperature rise is the difference
between the upper temperature of the cable material in contact with the sheath/shield and the operating
temperature of the sheath/shield immediately prior to the initiation of the fault.
The operating temperature of the sheath or shield depends on the temperature of the conductor and the
insulation thickness which is determined by the cable voltage rating. See Section 3, Table 3 for suggested
estimated values.
ICEA P-45-482-2013
Page iii
The maximum transient temperature limits of the cable component materials are those which cause no
significant change in the materials. These limits were extrapolated from laboratory test data.
Suggestions for improvements in this publication are welcome, and should be sent to ICEA at the address
below.
Insulated Cable Engineers Association, Inc.
P.O. Box 1568
Carrollton, GA 30112
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© Copyright 2013 by the Insulated Cable Engineers Association, Incorporated.
ICEA P-45-482-2013
Page iv
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ICEA P-45-482-2013
Page 1
Section 1
GENERAL
1.1
SCOPE

Wires, applied ether helically, as braid or serving; or longitudinally with corrugations.

Helically applied flat tape, not overlapped.

Helically applied, overlapped, flat tape.

Corrugated tape, longitudinally applied.

Tubular sheath.
The types of cable materials in contact with the sheath or shield are: crosslinked (thermoset),
thermoplastic, impregnated paper, and varnished cloth.
The materials which determine the maximum allowable short circuit temperatures are: paper, varnished
cloth and several thermoplastic and thermosetting materials presently appearing in ICEA standards.
Temperature limits, considered safe, were established for the various coverings and insulation materials.
The equations may be used to determine:
1.2

The maximum short circuit current permitted for a specific sheath/shield and short circuit duration.

The sheath/shield size necessary to carry a specific short circuit current for a given duration.

The maximum duration a specific sheath/shield can carry a specific short circuit current.
REFERENCES
The following references were reviewed in preparing this document.
The Transient Temperature Rise of Round Wire Shields of Extruded Dielectric Cables Under Short Circuit
Conditions, M. A. Martin Jr., A.W. Reczek Jr., IEEE-ICC Open Forum at 57 Meeting Nov. 17-19, 1975.
Optimization of Design of Metallic Shield-Concentric Conductors of Extruded Dielectric Cables Under Fault
Conditions, EPRI EL-3014, Project 1286-2, final Report 4/83.
Optimization of Metallic Shields for Extruded Dielectric Cables Under Fault Conditions, IEEE Paper 86
T&D 339-B.
© Copyright 2013 by the Insulated Cable Engineers Association, Incorporated.
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Equations and parameters have been established for short circuit calculations for sheaths or shields made
of aluminum, bronze, copper, lead, steel, zinc and cupro-nickel alloys. The types of sheaths or shields
included are:
ICEA P-45-482-2013
Page 2
Normal and Short Circuit Operating Characteristics of Metallic Shielded Solid Dielectric Power Cable.
M.A. Martin Jr., D. A. Silver, R. G. Lukac, R. Suarez, IEEE Paper 973 495-9.
Fault Test on Embedded Copper Wire and Copper Tape Shielded Single Conductor Cables. C.
Landinger, L. D. Cronin, IEEE Paper C73-124-5.
Buried Power and Telephone Distribution Systems-Analysis of Primary Cable Fault Tests and Evaluations
of Experience With Random Separation, EEI Pub. 68-62.
The Short Circuit Rating of Thin Metal Tape Cable Shields, AIEE Trans, Vol. 87, pp. 740-758, March 1968.
Fault Current Rating of Metallic Cable Screens, T. M. White, S. E. Philbrick, JICABLE 1087, Paper B6.2.
Are Cable Shields Being Damaged During Grounds Faults?, P. S. Hamer, B. M. Wood. IEEE Transactions
on Industry Applications, Paper PID-86-6.
Design of Metallic Shields for Extruded Dielectric Cables, 1984 IEEE IAS Pulp and Paper Conference, D.
A. Silver, M. D. Buckweitz, Paper PPI-84-14.
Calculations of Thermally Permissible Short Currents Taking Into Account Non-Adiabatic Heating Effects,
IEC Publication 60949-9-1988.
Standard Handbook for Electrical Engineers, Tenth Edition, Page 4-87, paragraph 211.
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ICEA P-45-482-2013
Page 3
Section 2
FORMULAE AND CALCULATIONS
Short circuit current, short-circuit time or effective cross-sectional area of shield or sheath can be
calculated from the basic equation where the materials surrounding the shield/sheath are not damaged:
 T  λ 
 T2  λ  
(1)
 247.0x10 6 SGSH 0
 Log10 
 
P
A
0
 T1  λ  


Where:
I0 = Short-circuit current, amperes.
A = Effective cross-sectional area of the shield or sheath, circular mils.
t
= Time for short circuit, seconds.
SG = Specific gravity of shield or sheath material.
SH = Specific heat of shield or sheath material.
T0 = Arbitrary temperature (usually considered 20ºC).
P0 = Specific resistivity of shield or sheath material at temperature T 0, microhm-cm.
λ = Inferred temperature of zero resistance for the shield/sheath material, ºC below zero.
T2 = Maximum allowable shield or sheath transient temperature, ºC.
T1 = Operating shield or sheath temperature, ºC.
I02 t
Letting:
T  λ
K  247.0 x10-6 SGSH 0

 P0 
(2)
Then the Equation (1) becomes:
T  λ
 K Log10  2

A
 T1  λ 
I02 t
(3)
2
Working Equations may be derived from equation (3) giving:
I
A
t
T  λ
K Log10  2

 T1  λ 
(4)
Letting:
T  λ
M  K Log10  2

 T1  λ 
(5)
The Equation becomes:
MA
I
t
(6)
Or:
 MA 
t

 I 
Or:
A
I
t
2
(7)
(8)
M
Refer to Section 3 for tabulation values of the various parameters.
© Copyright 2013 by the Insulated Cable Engineers Association, Incorporated.
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2
ICEA P-45-482-2013
Page 4
For Equations (6) and (7) effective cross-sectional area, A, may be calculated from the formulas in Table
1. If A is determined from (8), these formulas may be used to determine characteristics of the shield or
sheath.
Table 1
Formulas for Determining Metallic Shield/Sheath Cross-sectional Area
FORMULA FOR
CALCULATING A (SEE
NOTES 1 & 2)
1. Wires applied either helically, as a braid or serving; or longitudinally with
corrugations.
2. Helically applied tape, not overlapped.
3. Helically applied flat tape, overlapped. See NOTE 3.
4. Corrugated tape, longitudinally applied.
5. Tubular sheath.
NOTE 1: Meaning of Symbols: A
B
b
dis
dm
ds
w
n
L
nd2s
1.27 nwb

100 
4bdm 
 2100  L  



 
1.27 π dis  50  B b
4 bdm
= Effective cross-sectional area of shield or sheath, cmil.
= Tape overlap, mils (usually 375).
= Thickness of tape, mils.
= Diameter over extruded insulation screen, mils.
= Mean diameter of shield or sheath, mils.
= Diameter of wires, mils.
= Width of tape, mils.
= Number of serving or braid wires, or tapes.
= Overlap of tape, percent.
NOTE 2:
The effective area of composite shields is the sum of the effective areas of the
components. For example, the effective area of a composite shield consisting of a
helically applied tape and a wire serving would be the sum of the area calculated from
Formula 2 (or 3) and Formula 1.
NOTE 3:
The effective area of thin, helically applied overlapped tapes depends, also, upon the
degree of electrical contact resistance of the overlaps. Formula 3 may be used to
calculate the effective cross-sectional area of the shield for new cable. An increase in
contact resistance may occur after cable installation, during service exposed to moisture
and heat. Under these conditions the contact resistance may approach infinity, where
Formula 2 could apply.
© Copyright 2013 by the Insulated Cable Engineers Association, Incorporated.
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TYPE OF SHIELD OR SHEATH
ICEA P-45-482-2013
Page 5
Section 3
TABULATED PARAMETERS
Table 2
Parameters for Use in Equations (1), (2) or (3)
Suggested Values for Properties of
K
Material§
Metals at T0 = 20 ºC
Calculated from
Equation (2)
SG
SH
Po
λ
Aluminum*
2.70
0.22
2.83
228
0.013
Bronze**
8.80
0.094
3.95
564
0.030
Copper†
8.93
0.092
1.72
234
0.030
Lead††
11.3
0.031
20.6
236
0.0011
Steel‡
7.85
0.11
12.0
180
0.0036
Zinc‡‡
7.14
0.093
5.91
268
0.0080
Cupro-Nickel Alloy
8.94
0.09
1800
90Cu-10Ni (C70600)
19.1
0.019
80Cu-20Ni (C71000)
26.6
0.014
70Cu-30Ni (C71500)
37.5
0.010
*
**
†
††
‡
‡‡
§
Three quarter hard, 1350 aluminum.
Commercial Bronze, 90% copper, 10% zinc.
annealed 100% conductivity copper.
Pure lead (99.99%).
Mild or low carbon steel.
Commercial rolled zinc, 0.08% lead.
These values are believed accurate for the materials shown. Variations may occur due to small
changes in composition.
Table 3
Values of T1, Approximate Shield or Sheath Operating
Temperature, ºC at Various Conductor Temperatures
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Rated
Voltage
(kV)
5-15
25
35-46
69-345
105 ºC
100
95
95
90
Shield or Sheath Temperature, ºC, at Conductor Temperatures
100 ºC 95 ºC 90 ºC 85 ºC
80 ºC
75 ºC
70 ºC
95
90
85
80
75
70
65
90
90
85
80
75
70
65
90
85
80
75
70
65
60
85
80
75
70
65
60
55
65 ºC
60
60
55
50
NOTE: The maximum conductor temperature should not exceed the normal temperature
rating of the insulation used. For more accurate shield/sheath temperatures, contact the cable
manufacturer.
© Copyright 2013 by the Insulated Cable Engineers Association, Incorporated.
ICEA P-45-482-2013
Page 6
Table 4
Values for T2, Maximum Allowable
Shield or Sheath Transient Temperature, ºC
Cable Material in Contact
with Shield or Sheath
T2
Crosslinked (thermoset)
350*
Thermoplastic
200
Impregnated Paper
200
Varnished Cloth
200
NOTE: The temperature of the shield or sheath shall be limited by the material in contact with it. For
example, a cable having a crosslinked semi-conducting shield under the metallic shield and a crosslinked
jacket over the metallic shield would have a maximum allowable shield temperature of 350 ºC. With a
thermoplastic jacket it would be 200 ºC.
*For lead sheaths this temperature is limited to 200 ºC.
Table 5
M Values for T2 Temperature of 200 ºC
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Shield/Sheath
Material
Aluminum
Commercial
Bronze
Copper
Lead
Steel
Zinc
90Cu-10Ni
(C70600)
80Cu-20Ni
(C71000)
70Cu-30Ni
(C71500)
100
0.039
Values for M for the Limiting Conditions Where T2 = 200 ºC
Shield/Sheath Operating Temperature (T1), ºC
95
90
85
80
75
70
65
60
55
0.040 0.041 0.042 0.043 0.044 0.045 0.046 0.047 0.048
50
0.049
0.043
0.058
0.011
0.022
0.029
0.044
0.060
0.011
0.022
0.030
0.045
0.062
0.012
0.023
0.030
0.046 0.047 0.048
0.063 0.065 0.066
0.012 0.012 0.012
0.024 0.024 0.025
0.031 0.032 0.033
Cupro-Nickel
0.049
0.068
0.013
0.026
0.034
0.050
0.070
0.013
0.026
0.034
0.051
0.071
0.014
0.027
0.035
0.052
0.073
0.014
0.027
0.036
0.053
0.074
0.014
0.028
0.037
0.021
0.021
0.022
0.022
0.023
0.023
0.023
0.024
0.024
0.025
0.025
0.017
0.018
0.018
0.019
0.019
0.020
0.020
0.020
0.021
0.021
0.021
0.015
0.015
0.016
0.016
0.016
0.017
0.017
0.017
0.018
0.018
0.018
© Copyright 2013 by the Insulated Cable Engineers Association, Incorporated.
ICEA P-45-482-2013
Page 7
100
0.056
Table 6
M Values for T2 Temperature of 350 ºC
Values for M for the Limiting Conditions Where T2 = 350 ºC
Shield/Sheath Operating Temperature (T1), ºC
95
90
85
80
75
70
65
60
55
0.057 0.058 0.059 0.060 0.060 0.061 0.062 0.063 0.063
50
0.064
0.065
0.085
0.031
0.042
0.066
0.086
0.032
0.043
0.066
0.088
0.032
0.044
0.067 0.068 0.068
0.089 0.090 0.091
0.033 0.033 0.034
0.044 0.045 0.045
Cupro-Nickel
0.069
0.092
0.034
0.046
0.070
0.093
0.035
0.046
0.070
0.094
0.035
0.047
0.071
0.096
0.036
0.047
0.072
0.097
0.036
0.048
0.032
0.032
0.033
0.033
0.033
0.034
0.034
0.034
0.034
0.035
0.035
0.027
0.027
0.028
0.028
0.028
0.028
0.029
0.029
0.029
0.030
0.030
0.023
0.023
0.024
0.024
0.024
0.024
0.025
0.025
0.025
0.025
0.026
Shield/Sheath
Material
Aluminum
Commercial
Bronze
Copper
Steel
Zinc
90Cu-10Ni
(C70600)
80Cu-20Ni
(C71000)
70Cu-30Ni
(C71500)
© Copyright 2013 by the Insulated Cable Engineers Association, Incorporated.