30/1049
30
Properties and
ratings of currentcarrying
conductors
Contents
30.1 Properties for aluminium and copper conductors 30/1051
30.1.1 Important definitions of properties of a metal 30/1051
30.1.2 Physical and mechanical properties 30/1051
30.1.3 Electrical properties 30/1051
30.1.4 Measuring the conductivity 30/1054
30.2 Current-carrying capacity of copper and aluminium conductors 30/1054
Copper sections 30/1055
Aluminium sections 30/1059
Relevant Standards 30/1065
Further Reading 30/1065
Properties and ratings of current-carrying conductors 30/1051
30.1 Properties for aluminium and
copper conductors
In Table 30.1 we provide the general properties of
aluminium and copper conductors. The table also makes
a general comparison between the two widely used metals
for the purpose of carrying current.
30.1.1 Important definitions of properties of a metal
For ease of application of the above table we give below
important definitions of the mechanical and electrical
properties of a metal.
30.1.2 Physical and mechanical properties
1 Specific heat (This is a physical property) The specific
heat of a substance is the heat required to raise the
temperature of its unit mass by 1∞C.
2 Stresses
This is the force per unit area expressed in kgf/mm2
and is represented in a number of ways, depending
upon the type of force applied, e.g.
• Tensile stress: the force that will stretch or lengthen
the material and act at right angles to the area
subjected to such a force.
• Ultimate tensile strength: the maximum stress value
as obtained on a stress–strain curve (Figure 30.1).
• Compressive stress: the force that will compress
or shorten the material and act at right angles to
the area subjected to such a force.
• Shearing stress: the force that will shear the
material and act in the plane of the area and at
right angles to the tensile or compressive stress.
• Modulus of elasticity (E): the ratio of the unit
stress to the unit strain within the proportional
limits of a material in tension or compression.
– Proportional limit: the point on the stress–strain
curve at which will commence the deviation in
Ultimate tensile
strength
the stress–strain relationship from a straight line
to a parabolic curve (Figure 30.1).
• Elastic limit: the maximum stress a test specimen
may be subjected to and which may return to its
original length when the stress is released.
– Yield point: a point on the stress–strain curve
that defines the mechanical strength of a material
under different stress conditions at which a sudden
increase in strain occurs without a corresponding
increase in the stress (Figure 30.1).
– Yield strength or tensileproof stress: the
maximum stress that can be applied without
permanent deformation of the test specimen.
For the materials that have an elastic limit (some
materials may not have an elastic region) this
may be expressed as the value of the stress
on the stress–strain curve corresponding to a
definite amount of permanent set (elongation)
of, say, 0.1% or 0.2% of the test specimen.
30.1.3
Electrical properties
Resistivity of metal of a current-carrying conductor
A metal being used for the purpose of current carrying
must be checked for its conductivity. This is proportional
to its current-carrying capacity. This will ascertain the
correctness of size and grade of the metal chosen for a
particular duty. It is necessary to avoid over-heating
of the conductor during continuous operation beyond
the limits in Table 28.2. The electrical conductivity of a
metal is reciprocal to its resistivity. The resistivity may
be expressed in terms of the following units:
• Volume resistivity or specific resistance: this is the
resistance of a conductor of unit length and unit crosssectional area, i.e.
W ◊ m 2 or W · m (or m · W · m)
m
2
and 1m ◊ W ◊ cm = 10 2 W ◊ mm
m
• Mass resistivity: this is the resistance of a conductor
of unit length and unit mass; i.e. W · gm/m2
which is also equal to the volume resistivity multiplied
by the density:
i.e. (W · m) ¥ (gm/m3) = W · gm/m2
Yield point
*
Stress
Elastic limit
Proportional limit
• Length resistivity: this is the resistance of a conductor
per unit length, i.e. W/m.
• Conductivity: therefore, the electrical conductivity
with reference to say, volume conductivity, can be
expressed by
m
W ◊ m2
or
Strain
* Tensileproof strength = 0.6 to 0.8 of ultimate tensile strength
Figure 30.1
Stress–strain curve
1
etc.
W◊m
The resistivity and conductivity of standard annealed
copper and a few recommended aluminium grades being
used widely for electrical applications are given in Table
30.1. Their corresponding current-carrying capacities in
(∞C)
Melting point
60–80% of the
tensile strength
kgf/mm2
0.2% tensile-proof strength
2
(b) in W ◊ mm
m
1.7241 ¥ 10
–2
12,000
kgf/mm2
Modulus of elasticity E
1.7241
16 to 19
kgf/mm2
Ultimate shearing strength
Electrical properties
Volume resistivity or specific resistance (r)
(a) in m · W · cm.
22 to 26
kgf/mm2
Ultimate tensile strength
Mechanical properties
8.89
(gm/cm3)
Density
1083
0.092
gm.cal/∞C
–
99.9% pure
Specific heat
Aluminium
%
%
%
%
%
100% IACS
–
–
Standard grades
(a) As in BS
(b) As in BS 2898 (ISO 209-1)
(c) Equivalent Indal grades
Copper (Cu)
Magnesium (Mg)
Silicon (Si)
Iron (Fe)
Cr, Ti, Zn and Mn
IEC 60028
Relevant Standards
Physical properties
(a) Chemical composition
Standard copper
(IACS)a
Selected properties (average) of copper and aluminium at 20∞C
Parameters
Table 30.1
2
3
2.70
2.873 ¥ 10
2.873
–
7000
5.5
6.5/7.0
–2
–2
3.1 ¥ 10 /3.6 ¥ 10
3.1/3.6
11/19.5
6700
16.5
–2
3.133 ¥ 10–2
3.133
16.5/22
6700
15
20.5/25
æææææææææææææææÆ
2.71
ææææææææææææææææÆ
15.5/23.5
¨æææææææææææææ 660
2.71
0.05
0.4–0.9
0.3–0.7
0.4
0.1
E – 91Ec
6101A
D 50S – WPb
¨ææææ Rest is all aluminium æææææÆ
0.1
0.6–0.9
0.3–0.6
0.15–0.35
0.6
HE9c – WPb
6063 A
50S – WPb
¨æææææææææææææ 0.220
99.5%
Mg, Cr, Sn, Zn and Mn ⯝ Nil
Cu, Si, Fe – Not more than 0.5%
EIEc – Mb
1350
CIS – Mb
¨––––––––––––––––––––––––––– IEC 60105 –––––––––––––––––––––––––––––––Æ
ISO 209-1,2
1
Commercial purity aluminium (for electrical use)
30/1052 Electrical Power Engineering Reference & Applications Handbook
% IACS*
Conductivity
4.03 ¥ 10–3/3.96 ¥ 10–3
2.3 ¥ 10–5
7.786
1.73 ¥ 10–5
15.328
61/60
34.80
8.37/9.72
2.3 ¥ 10–5
3.3 ¥ 10–3/3.168 ¥ 10–3
50/48
32.26/27.8
Commercial purity aluminium (for electrical use)
3.93 ¥ 10–3
100
58
Standard copper
(IACS)a
31.90
8.49
2.3 ¥ 10–5
3.63 ¥ 10–3
55
c
b
a
IACS – International Annealed Copper Standard
Suffix M (now F) or WP (now T6) represents the type of tempering.
EIE, HE9 and E91E are old designations. They have now been replaced by 1350, 6063 A and 6101 A respectively.
Notes
1 When using the above metals for the purpose of current carrying, their mechanical suitability must be checked with the data provided above to withstand, without permanent deformation,
the electrodynamic forces that may develop during a short-circuit condition (Section 28.4.2).
2 For important definitions, refer to Section 30.1.1.
3 These values are based on the mean values of a number of tests carried out on specimens of standard copper and aluminium conductors.
Coefficient of linear expansion (thermal),
(mm/∞C)
(applicable over a working range of 20–200∞C)
Mass resistivity = volume resistivity ¥ density (m·W·gm/cm2)
Temperature coefficient of electrical resistance
per ∞C (applicable over a working range of
a20
100–200∞C)
a20 at a particular conductivity
= a20 at 100% conductivity ¥ actual conductivity
of the metal
m/W·mm2
Volume conductivity
Parameters
Properties and ratings of current-carrying conductors 30/1053
30/1054 Electrical Power Engineering Reference & Applications Handbook
per cent, with respect to a standard reference (say, 100%
IACS) are also provided in the table.
30.1.4 Measuring the conductivity
For this purpose, a simple conductivity meter based on the
principle of eddy current may be used for a direct reading
of conductivity. The meter operates on the basis of relative
variance, in the impedance of the test piece compared to
the reference standard piece of aluminium or copper having
a conductivity of 100% or 31.9 m/Wmm2 for aluminium
and 58.0 m/Wmm2 for IACS (International Annealed Copper
Standard) in terms of conductivity unit. The test probes,
that sense the impedance of the test piece, induce an eddy
current in the test piece at a fixed frequency. The magnitude
of this current is directly proportional to the conductivity
of the metal. This eddy current develops an electromagnetic
field around the test piece and varies the impedance of the
test probe (skin effect). The conductivity is thus determined
by measuring the corresponding change in the impedance
of the probe. Figure 30.2 shows a simple and portable
conductivity meter.
30.2 Current-carrying capacity of
copper and aluminium
conductors
Earlier practice was to use copper in most applications
in view of its rigidity and high conductivity. With the
easier availability of aluminium and being more viable
economically, aluminium is now preferred wherever
possible. It is employed particularly where the metal has
to simply carry power such as for the transmission and
distribution of power at any voltage and as the main
current-carrying conductor in power distribution or control
equipment, such as a bus system or a switchgear assembly.
Similarly, it is also used to feed high currents to an
% I.A.C.S.
10
OFF ON
50 40
HI-SET
5 6
4
7
3
2
1
0
LOW–SET
5 6
7
4
3
2
1
0
VITY
SENSITI
6 7
5
4
3
2
1
0
induction or a smelting furnace, electroplating plant or a
rectifier plant. For main current-carrying components,
however, as required for switching or interrupting devices
(breakers, switches, fuses, contactors and relays) copper
and copper alloys are preferred. The alloys of copper are
compact in size and are a much harder metal, suitable
for making and breaking contacts frequently and yet
retaining their shape and size over long years of operation.
Copper is also used for low ratings, up to 100 A or so,
required for the internal wiring of power and control
circuits in a switchgear or a controlgear assembly, where
the wires have to bend frequently. Aluminium, being
brittle, is unsuitable for such applications. The use of
copper is also recommended for areas that are humid,
saline and chemically aggressive which may corrode
aluminium quickly. As aluminium is highly oxidizing
and a very susceptible metal to such environments it
may loosen at the joints. Typical locations are mines,
ships, textile mills and chemical and petrochemical
processing units. But for such applications also, the latest
practice is to instal electrical equipment and switchgears
in separate rooms, away from the affected areas, thus
making it possible to use aluminium. In the following
tables we have provided data for both copper and
aluminium conductors. Copper current ratings are shown
in Tables 30.2 (a, b and c) for flat bars, tubes and channel
sections respectively. Derating factors as shown in Table
30.3 may be applied to account for skin effect when
more than one bar is used in parallel. No separate skin
effect factor need be calculated when this factor is applied.
Below we give the recommended sizes and ratings:
• Copper wires/cables: refer to Table 13.15 for current
ratings up to 100 A, as recommended for the internal
wiring of a power switchgear or a controlgear assembly.
• Copper solid conductors: Tables 30.2 a, b and c and
30.3 for general engineering purposes.
• Aluminium solid conductors: Tables 30.4, 30.5, 30.6,
30.7, 30.8 and 30.9 for general engineering purposes.
The following factors must be taken into account while
deciding on the most appropriate and economical sections
of the metal conductors for the required current rating;
For the same thickness, a smaller cross-section will
have a relatively higher heat-dissipating area compared to
a larger cross-section. The latter therefore will have a higher
deration compared to a smaller cross-section on account
of poorer heat dissipation. This can be illustrated as follows.
Consider a 25.4 ¥ 6.35 mm conductor with a crosssectional area of 25.4 ¥ 6.35 mm2 and a surface area of 2
(25.4 + 6.35) ¥ l (l being the length, in mm) = 63.5l mm2.
A conductor with twice the width (i.e. 50.8 ¥ 6.35
mm) will have a cross-sectional area of 50.8 ¥ 6.35 mm2,
and a surface area of 2 (50.8 + 6.35) ¥ l = 114.3l mm2.
Thus the larger section having twice the cross-sectional
area in the same thickness will have 114.3/(2 ¥ 63.5) or
only 90% surface area compared to the smaller section
and consequently less heat dissipation in the same ratio
and will require a higher derating.
Corollary
Figure 30.2 Conductivity meter (Courtesy: Technofour)
1 Thinner sections will have a relatively higher surface
2.856
3.571
200
320
50 ¥ 4.0
80 ¥ 4.0
1.339
2.678
8.570
1.785
8.570
11.43
14.27
2.232
150
300
480
600
720
960
200
400
640
800
960
1280
1600
250
500
800
1000
1200
1600
25 ¥ 6.0
50 ¥ 6.0
80 ¥ 6.0
100 ¥ 6.0
120 ¥ 6.0
160 ¥ 6.0
25 ¥ 8.0
50 ¥ 8.0
80 ¥ 8.0
100 ¥ 8.0
120 ¥ 8.0
160 ¥ 8.0
200 ¥ 8.0
25 ¥ 10
50 ¥ 10
80 ¥ 10
100 ¥ 10
120 ¥ 10
160 ¥ 10
14.28
10.71
8.928
7.142
4.464
7.142
5.713
3.571
6.428
5.356
4.285
0.703
400
78.75
100 ¥ 4.0
12.5 ¥ 6.3
1.785
0.893
100
25 ¥ 4.0
0.446
kg/m
Weight
50
X-Sectional
area
mm2
10.7
14.3
17.2
21.5
34.4
68.9
10.8
13.4
17.9
21.5
26.9
43.1
86.2
17.9
23.9
28.7
35.9
57.4
114
218
43.1
53.8
86.2
172
344
Approx d.c.
resistance 20∞C
mW/m
2930
2285
1950
1615
1090
625
3170
2610
2032
1735
1435
965
545
2250
1750
1490
1230
825
460
275
1210
995
665
365
210
A
Still air
3380
2610
2225
1840
1235
695
3570
2935
2290
1955
1595
1070
610
2535
1970
1680
1370
915
515
305
1365
1120
740
410
230
A
Free air
Approx. d.c. rating
2620
2100
1800
1525
1060
580
2760
2230
1760
1595
1420
950
545
2130
1700
1480
1220
815
460
275
1185
980
660
365
210
A
Still air
3040
2395
2065
1735
1200
645
3110
2510
1985
1800
1580
1055
605
2400
1915
1670
1355
910
515
305
1340
1105
735
410
230
A
Free air
Approx. a.c. rating
Current ratings, moments of inertia and section moduli for strips and bars
(For more sections see CDA Pub.22)
12.5 ¥ 4.0
mm
Busbar size
Table 30.2a
8333
341 ¥ 103
13330
10000
6667
3
144 ¥ 103
833 ¥ 10
427 ¥ 10
4167
2083
8533
6827
5120
4267
3413
2133
1067
2880
2160
1800
1440
900.0
450.0
260.5
533.3
426.7
266.7
133.3
3
104 ¥ 103
13020
5.33 ¥ 106
2.73 ¥ 10
6
1.15 ¥ 106
667 ¥ 103
341 ¥ 103
83300
10420
2.05 ¥ 106
864 ¥ 103
500 ¥ 103
256 ¥ 103
62500
7813
1025
333 ¥ 10
3
170 ¥ 103
41660
5208
66.67
mm4
mm4
651.0
Flat
Edgewise
Moment of inertia, I
42660
23980
16670
10670
4168
1042
53330
34140
19200
13330
8533
3333
833.6
25600
14400
10000
6400
2500
625.0
164.0
6666
4268
1666
416.6
104.2
mm3
Edgewise
2666
2000
1667
1333
833.4
416.6
2133
1707
1280
1067
853.3
533.3
266.7
960.0
720.0
600.0
480.0
300.0
150.0
82.70
266.7
213.4
133.4
66.65
33.34
mm3
Flat
Modulus of Section, Z
Tables of properties of high conductivity (HC) copper conductors
160 ¥ 10
120 ¥ 10
100 ¥ 10
80 ¥ 10
50 ¥ l0
25 ¥ 10
200 ¥ 8.0
160 ¥ 8.0
120 ¥ 8.0
100 ¥ 8.0
80 ¥ 8.0
50 ¥ 8.0
25 ¥ 8.0
160 ¥ 6.0
120 ¥ 6.0
100 ¥ 6.0
80 ¥ 6.0
50 ¥ 6.0
25 ¥ 6.0
12.5 ¥ 6.3
100 ¥ 4.0
80 ¥ 4.0
50 ¥ 4.0
25 ¥ 4.0
12.5 ¥ 4.0
mm
Busbar size
Properties and ratings of current-carrying conductors 30/1055
X-Sectional
area
mm2
Busbar size
26.78
21.43
17.14
12.85
5.74
7.18
8.97
11.9
14.3
17.9
28.7
57.4
6.89
8.62
Approx d.c.
resistance 20∞C
mW/m
4750
3910
3225
2520
2155
1785
1210
700
4320
3550
A
Still air
5440
4480
3650
2880
2420
2000
1330
710
5030
4150
A
Free air
Approx. d.c. rating
4060
3380
2860
2310
2010
1670
1160
640
3710
3140
A
Still air
4650
3870
3235
2640
2255
1870
1275
650
4310
3630
A
Free air
Approx. a.c. rating
512 ¥ 10
4.10 ¥ 10
15.6 ¥ 106
8.00 ¥ 106
6
1.73 ¥ 106
1.00 ¥ 106
3
125 ¥ 103
15630
13.0 ¥ 10
6
35990
28790
23040
17280
14390
11519
7199
3599
20830
16670
mm4
mm4
6.67 ¥ 106
Flat
Edgewise
Moment of inertia, I
125 ¥ 103
80000
51200
28800
20000
12800
5000
5998
4798
3840
2880
2398
1919
1199
599.8
4166
104 ¥ 10
1250
3334
3
mm3
Flat
66670
mm3
Edgewise
Modulus of Section, Z
250 ¥ 12
200 ¥ 12
160 ¥ 12
120 ¥ 12
100 ¥ 12
80 ¥ 12
50 ¥ 12
25 ¥ 12
250 ¥ 10
200 ¥ 10
mm
Busbar size
Notes
1. The ratings are based on a 50∞C rise over 40∞C ambient temperature in still but unconfined air.
2. AC ratings are for frequencies up to 60 Hz. At 50 Hz ratings may be enhanced by 2.5–5% in large cross-sections (see Section 28.7.2).
3. AC ratings are based on spacings at which the proximity effect is considered almost negligible (≥ 300 mm Section 28.8).
4. These are the basic maximum ratings, that a current-carrying conductor can carry under ideal operating conditions. The rating is influenced by the service conditions and other design
considerations, as discussed in Section 28.5. Apply suitable derating factors to arrive at the actual current ratings of these conductors under actual operating conditions.
5. Ratings may be improved by approximately 20% if the busbars are painted black with a non-metallic matt finish paint. This is because heat dissipation through a surface depends upon
temperature, type of surface and colour. A rough surface dissipates heat more readily than a smooth surface and a black body more quickly than a normal surface. Also refer to Section
31.4.4 and Table 31.1. Black paint also prevents the metal from oxidation and improves cooling. Oxidation is a thermal insulating film and a hindrance in the natural heat dissipation.
6. The above ratings are for single bars. When multiple bars are used, apply the skin effect factor as per Table 30.3. This factor will account for the restricted heat dissipation and additional
skin effect due to the large number of bars.
Based on Copper Development Association, Pub. 22
3000
250 ¥ 12
1440
120 ¥ 12
1920
1200
2400
8.570
960
80 ¥ 12
100 ¥ 12
160 ¥ 12
5.356
600
200 ¥ 12
2.678
300
25 ¥ 12
50 ¥ 12
10.71
22.30
2500
250 ¥ 10
17.84
2000
kg/m
Weight
200 ¥ 10
mm
(Contd.)
Table 30.2a
30/1056 Electrical Power Engineering Reference & Applications Handbook
Properties and ratings of current-carrying conductors 30/1057
r1
r2
Table 30.2b Current ratings, moments of inertia and section moduli for tubes
(For more metric and imperial sections and rods see CDA Pub. 22)
Outside Wall
diameter thickness
Cross
sectional area
Approx.
weight
Moment of
inertia of section
Modulus
of section
Approx. resistance
per m 20∞C
Approx. d.c. current rating
mm
mm
mm2
kg/m
mm4
mm3
mW
Indoor A
22
1.0
65.98
0.587
3645
331.4
263
320
22
1.5
96.61
0.859
5102
463.8
179
385
500
22
2.0
125.7
1.12
6346
576.9
138
440
570
Outdoor A
410
22
2.5
154.1
1.37
7399
672.7
112
490
630
22
3.0
179.1
1.59
8282
752.9
97.0
525
680
28
1.5
124.9
1.11
11000
785.5
139
480
620
28
2.0
163.4
1.45
13890
991.8
106.3
550
700
28
2.5
200.3
1.78
16440
1157
86.7
605
780
28
3.0
235.6
2.10
18670
1334
73.7
660
850
35
1.5
157.9
1.40
22190
1268
110
585
750
35
2.0
207.4
1.84
28330
1619
83.7
670
850
35
2.5
255.3
2.27
33900
1937
68.0
740
950
35
3.0
301.6
2.68
38940
2225
57.5
805
1030
54
1.5
247.4
2.20
85300
3160
70.2
855
1090
54
2.0
326.7
2.91
110600
4096
53.1
980
1250
54
2.5
404.5
3.60
134400
4978
42.9
1090
1390
54
3.0
480.7
4.27
156800
5808
36.1
1190
1520
76.1
2.0
465.6
4.14
319800
8404
37.3
1330
1690
76.1
2.5
578.1
5.14
392000
10300
30.0
1480
1880
76.1
3.0
689.0
6.13
461000
12110
25.2
1610
2050
76.1
3.5
798.3
7.10
527200
13850
21.7
1740
2210
6
108
2.5
828.6
7.37
1.153 ¥ 10
21360
20.9
2010
2550
108
3.0
989.6
8.80
1.365 ¥ 106
25280
17.5
2190
2790
108
3.5
1149
10.2
1.570 ¥ 106
29080
15.1
2360
3010
133
3.0
1225
10.9
2.590 ¥ 106
38940
14.1
2630
3350
133
3.5
1424
12.7
2.987 ¥ 106
44920
12.1
2830
3610
159
3.0
1470
13.1
4.474 ¥ 106
56280
11.8
3070
2910
159
3.5
1710
15.2
5.171 ¥ 106
65040
10.1
3310
4420
Based on Copper Development Association, Pub. 22
Notes
1. The ratings are based on a 50∞C rise over 40∞C ambient temperature in still but unconfined air.
2. AC ratings are for frequencies up to 60 Hz. At 50 Hz ratings may be enhanced by 2.5–5% in large cross-sections (see Section 28.7.2).
3. AC ratings are based on spacings at which the proximity effect is considered almost negligible (≥300 mm Section 28.8)
4. These are the basic maximum ratings, that a current-carrying conductor can carry under ideal operating conditions. The rating is
influenced by the service conditions and other design considerations, as discussed in Section 28.5. Apply suitable derating factors to
arrive at the actual current ratings of these conductors under actual operating conditions.
5. Ratings may be improved by approximately 20% if the busbars are painted black with a non-metallic matt finish paint. This is because
heat dissipation through a surface depends upon temperature, type of surface and colour. A rough surface dissipates heat more readily
than a smooth surface and a black body more quickly than a normal surface. Also refer to Section 31.4.4 and Table 31.1. Black paint
also prevents the metal from oxidation and improves cooling. Oxidation is a thermal insulating film and a hindrance in the natural heat
dissipation.
6. The above ratings are for single bars. When multiple bars are used, apply the skin effect factor as per Table 30.3. This factor will account
for the restricted heat dissipation and additional skin effect due to the large number of bars.
Y
X
33.3
33.3
33.3
44.5
44.5
44.5
55.6
55.6
68.3
68.3
68.3
81.0
81.0
81.0
105
63.5 ¥ 63.5
76.2 ¥ 76.2
76.2 ¥ 76.2
88.9 ¥ 88.9
102 ¥ 102
114 ¥ 114
114 ¥ 114
127 ¥ 127
152 ¥ 152
76.2
76.2
76.2
102
102
102
127
127
152
152
152
178
178
203
228
89.9
108
108
126
144
162
162
180
216
4.91
5.49
7.21
5.08
6.10
8.59
6.60
8.61
7.01
9.75
12.5
8.26
13.2
11.9
12.7
4.76
4.76
6.35
6.35
6.35
6.35
7.94
7.94
7.94
mm
5.06
6.30
7.78
14.5
16.9
22.3
36.4
45.4
68.9
90.9
111
129
191
272
413
3.62
6.41
8.08
13.3
17.5
29.1
35.5
49.2
86.5
0.543
0.673
0.822
1.60
1.86
2.42
4.05
5.02
7.30
10.7
12.9
15.9
23.7
34.3
51.7
0.957
1.71
1.92
3.33
5.00
7.33
9.20
12.4
21.6
0.133
0.165
0.204
0.286
0.333
0.439
0.573
0.796
0.901
1.19
1.45
1.46
2.18
2.68
3.61
0.0806
0.119
0.150
0.211
0.243
0.359
0.439
0.549
0.803
0.0226
0.0286
0.0358
0.0497
0.0583
0.0780
0.102
0.127
0.147
0.220
0.270
0.272
0.417
0.513
0.688
0.0533
0.0583
0.0637
0.0957
0.128
0.167
0.208
0.251
0.370
¥ 105 mm3
¥ 105 mm3
¥ 105 mm4
¥ 105 mm4
Modulus of section
x–x
y–y
ONE CHANNEL
Moment of inertia
x–x
y–y
b
f
X
t
Y
2200
2500
2800
3200
3500
4000
4500
5000
5600
6300
6700
7000
7900
8900
10000
2750
3300
3650
4200
4800
5400
6000
6750
8000
3000
3400
3800
4400
4800
5550
6150
6850
7700
8600
9200
9650
10850
12300
13750
3000
3600
4100
4500
5200
5850
6550
7400
8700
A
A
31.8
24.9
19.5
19.4
16.4
12.0
11.9
9.35
9.15
6.76
5.41
6.59
4.29
4.04
3.35
31.8
35.7
18.9
16.1
14.1
12.4
10.4
9.32
7.61
mW/m
X
Approx a.c. rating
Test a
Calculated b
TWO CHANNELS
h1
Y
Approx. d.c.
resistance at 20∞C
30∞C rise over 40∞C ambient
50∞C rise over 40∞C ambient. For approximate values for ambients below or above 40∞C increase or decrease rating by 0.25% per ∞C respectively.
c
Weights based on copper density of 8.89 g/cm3
Notes
As in Table 30.2a
a
4.82
6.15
7.86
7.92
9.35
12.7
12.9
16.4
16.8
22.7
28.3
23.2
35.7
38.0
45.7
4.81
5.95
8.08
9.52
10.9
12.3
14.7
16.4
20.1
kg/m
mm2
542
690
884
890
1050
1430
1450
1850
1850
2550
3180
2610
4010
4280
5140
542
671
910
1070
1230
1390
1650
1850
2260
Approx.
weight c
Area
A
Based on Copper Development Association, Pub. 22
mm
mm
Thickness
t
Current ratings, moments of inertia and section moduli for channel sections
t
Width of
flange f
X
Y
Height
h
Table 30.2c
h
f
30/1058 Electrical Power Engineering Reference & Applications Handbook
Properties and ratings of current-carrying conductors 30/1059
Table 30.3
Multiplying factors for copper sections
No. of bars
Multiplying factor
1
2
3
4
5
6
8
1.0
1.8
2.5
3.2
3.9
4.4
5.5
Source: Copper Development Association, Pub. 22.
Note
The space between the bars is considered to be equal to the thickness
of the bars.
area to dissipate heat compared to thicker sections.
The thinner the section, the better will be metal
utilization and vice versa.
2 More bars in parallel will reduce the heat dissipation
further and will require yet higher deratings.
Table 30.4
3 Skin effect – the same theory is usually true for the
skin effect. The thinner the surface, the smaller will
be the nucleus resulting in a higher concentration
of current at the surface and better utilization of
metal.
We can derive the same inference from Tables 30.2(a, b
and c), 30.4 and 30.5, specifying current ratings for
different cross-sections. The current-carrying capacity
varies with the cross-section not in a linear but in an
inconsistent manner depending upon the cross-section
and the number of conductors used in parallel. It is not
possible to define accurately the current rating of a
conductor through a mathematical expression. This can
be established only by laboratory tests.
Mechanical and electrical data for important rectangular,
circular and channel sections are also provided in Tables
30.2a, b and c for copper and Tables 30.7, 30.8 and 30.9
for aluminium conductors respectively for reference. For
more details one may contact the manufacturer.
Current ratings for rectangular aluminium sections, grade E91-E (6101 A)
Size
mm
1 bar
D.C.
1 bar
50 Hz
A.C.
2 bars
D.C.
2 bars
50 Hz
A.C.
3 bars
D.C.
3 bars
50 Hz
A.C.
4 bars
D.C.
4 bars
50 Hz
A.C.
Approximate ratings (A)
25.4
38.1
50.8
63.5
76.2
¥
¥
¥
¥
¥
6.35
6.35
6.35
6.35
6.35
355
520
670
820
970
355
520
670
810
960
710
1030
1315
1550
1805
705
1020
1290
1510
1740
980
1380
1765
2100
2440
970
1350
1705
2000
2310
1120
1585
2050
2430
2860
1100
1535
1940
2260
2620
101.6 ¥ 6.35
127.0 ¥ 6.35
152.4 ¥ 6.35
1260
1545
1840
1235
1505
1780
2260
2700
3130
2140
2510
2860
3060
3660
4290
2800
3240
3680
3640
4410
5250
3200
3700
4240
50.8 ¥ 9.53
76.2 ¥ 9.53
840
1210
830
1180
1560
2180
1500
2050
2090
2940
1970
2660
2460
3510
2260
3030
101.6
127.0
152.4
203.2
76.2
¥
¥
¥
¥
¥
9.53
9.53
9.53
9.53
12.7
1550
1940
2260
2940
1405
1495
1860
2120
2750
1355
2710
3290
3770
4800
2450
2480
2930
3340
4150
2240
3660
4450
5140
6500
3290
3150
3660
4080
4900
2830
4400
5400
6300
8060
4000
3560
4200
4680
5740
3240
101.6
127.0
152.4
203.2
254.0
¥
¥
¥
¥
¥
12.7
12.7
12.7
12.7
12.7
1830
2230
2620
3380
4080
1740
2080
2420
3060
3640
3100
3720
4300
5450
6500
2720
3120
3500
4450
5000
4170
5040
5850
7420
8860
3360
3900
4400
5300
6000
5100
6170
7200
9110
10900
3900
4550
5100
6150
6850
Source: Indalco
Notes
1 The ratings are indicative and based on a 50∞C rise over 35∞C ambient temperature in still but unconfined air.
2 For a multiple-bar arrangement, the space between the bars is considered to be equal to the thickness of the bar.
3 A.C. ratings are based on spacings, at which the proximity effect is considered almost negligible (≥ 300 mm, Section 28.8).
4 These are the basic maximum ratings that a current-carrying conductor can carry under ideal operating conditions. They are influenced
by the service conditions and other design considerations, as discussed in Section 28.5. Apply suitable derating factors to arrive at the
actual current ratings of these conductors under actual operating conditions.
5 Ratings may be improved approximately by 20% if the busbars are painted black with a non-metallic matt finish paint. This is because the
heat dissipation through a surface depends upon its temperature, type of surface and colour. A rough surface dissipates heat more readily
than a smooth surface and a black body more quickly than a normal surface. See also Section 31.4.4 and Table 31.1. Black paint also
prevents the metal from oxidation and improves cooling. Oxidation is a thermal insulating film and a hindrance in the natural heat dissipation.
6 Other grades as in BS EN 755-3 (ISO 209–1,2), for electrical purposes, and as produced by the leading manufacturers, are provided in Table
30.6.
7 To obtain the current rating for any other grade of busbar, multiply the above figures by the appropriate factor defined in Table 30.6.
30/1060 Electrical Power Engineering Reference & Applications Handbook
Table 30.5
Conductor
size
(mm)
Current ratings for rectangular aluminium sections, Grade EIE-M (1350)
Cross-sectional
area
(mm2)
1 bar
2 bars
3 bars
4 bars
5 bars
6 bars
Approximate ratings (A)
2.5 ¥ 12
16
20
25
30
40
30
40
50
62.5
75
100
118
151
183
223
263
342
210
275
320
390
480
610
285
395
450
540
660
860
360
490
575
685
840
1080
425
580
675
800
990
1260
480
655
770
910
1115
1425
4 ¥ 12
16
20
25
30
40
50
48
64
80
100
120
160
200
156
198
238
290
339
434
532
290
340
410
530
600
750
905
420
470
570
755
845
1050
1260
536
600
720
950
1060
1320
1575
620
710
850
1110
1245
1550
1825
700
815
955
1250
1400
1750
2035
6 ¥ 12
16
20
25
30
40
50
60
80
100
120
160
72
96
120
150
180
240
300
360
480
600
720
960
200
252
301
364
424
545
660
782
995
1215
1415
1830
350
450
550
640
730
935
1130
1350
1700
2090
2415
3100
480
640
790
900
1025
1310
1580
1870
2310
2770
3180
4050
610
805
1000
1120
1290
1630
1950
2200
2745
3190
3640
4600
720
960
1170
1315
1520
1900
2255
2630
3070
3490
3985
5025
825
1075
1320
1485
1720
2130
2505
2885
3330
3745
4270
5340
10 ¥ 40
50
60
80
100
120
160
200
250
400
500
600
800
1000
1200
1600
2000
2500
720
870
1015
1250
1565
1810
2310
2795
3365
1230
1500
1750
2215
2650
3050
3940
4750
5720
1710
2060
2350
2940
3465
4010
5170
6160
–
2110
2505
2795
3355
3940
4560
5870
–
–
2425
2850
3120
3675
4315
4980
6300
–
–
2670
3100
3380
3950
4635
5290
6620
–
–
16 ¥ 100
120
160
200
250
1600
1920
2560
3200
4000
1950
2255
2840
3395
4095
3260
3850
4830
5780
6500
4250
5030
6260
–
–
4890
5700
–
–
–
5340
6130
–
–
–
5660
6450
–
–
–
Source:
The Aluminium Federation
Notes
1 Current ratings for E-91E (6101 A) bars are about 3% lower than EIE-M (1350); refer to Table 30.6.
2 The ratings are indicative and based on a 50∞C rise over 35∞C ambient temperature in still but unconfined air.
3 For a multiple-bar arrangement the space between the bars is considered to be equal to the thickness of the bar.
4 AC ratings are based on spacings at which the proximity effect is considered almost negligible (≥ 300 mm, Section 28.8).
5 These are the basic maximum ratings that a current-carrying conductor can carry under ideal operating conditions. They are influenced
by the service conditions and other design considerations, as discussed in Section 28.5. Apply suitable derating factors to arrive at the
actual current ratings of these conductors under actual operating conditions.
6 Ratings may be improved approximately by 20% if the busbars are painted black with a non-metallic matt finish paint. This is because,
the heat dissipation through a surface depends upon its temperature, type of surface and colour. A rough surface dissipates heat more
readily than a smooth surface and a black body more quickly than a normal body. See also Section 31.4.4 and Table 31.1. Black paint
also prevents the metal from oxidation and improves cooling. Oxidation is a thermal insulating film and a hindrance in the natural heat
dissipation.
7 Other grades as in BS EN 755–3 (ISO 209–1, 2), for electrical purposes, and as produced by the leading manufacturers, are provided
in Table 30.6.
8 To obtain the current rating for any other grade of busbar, multiply the above figures by the appropriate factor defined in Table 30.6.
Properties and ratings of current-carrying conductors 30/1061
Table 30.6
Grades of aluminium alloys for electrical purposes
Grades as the old
designation
Grades as in BS EN 755-3
(ISO 209-1)
Equivalent grades of Indian
Aluminium (Indal) alloys
Multiplying factor to ratings
of Table 30.4
EIE–M
EIC–M
E–91E
HE–9–WP
1350
–
6101 A
6063 A
CIS–M
2 S–M
D 50 S–WP
50 S–WP
1.03
1.02
1.00
0.94
Notes
1 Aluminium conductors for engineering application are produced in commercial grade quality, having an electrical conductivity varying
from 70% to 94% (approx.) as well as electrical grade quality having a purity in electrical conductivity as 94% and higher, as noted
above, varying slightly from manufacturer to manufacturer. Commercial grade, not below HE–9–WP (6063A), can be used for current
carrying, say, up to 1000 A, although electrical grade is preferred. For higher currents, however, electrical grade only should be
preferred.
2 When the short-circuit forces are likely to be high, say, 1500 kgf or more, per metre run, such as on a main power circuit the electrolytic
grade aluminium of type EIE–M (1350) may not be recommended. It is a soft metal mechanically, as noted in Table 30.1, which will
require busbar supports at very close spacing, defeating the economics of the selection. The grade type E-91E (6101 A), which has a
better mechanical strength, would be a better choice for all types of power applications. The selection of busbars, shape and grade, is
thus governed by mechanical considerations and economics, rather than the purity of the alloy alone.
6.35
6.35
6.35
9.53
9.53
101.6 ¥
127.0 ¥
152.4 ¥
50.8 ¥
76.2 ¥
Notes
As in Table 30.4
Indalco
12.70
12.70
12.70
12.70
12.70
¥
¥
¥
¥
¥
101.6
127.0
152.4
203.2
254.0
Source:
9.53
9.53
9.53
9.53
12.70
¥
¥
¥
¥
¥
101.6
127.0
152.4
203.2
76.2
25.4
38.1
50.8
63.5
76.2
6.35
6.35
6.35
6.35
6.35
1290.32
1612.90
1935.48
2580.64
3225.80
968.25
1210.31
1452.37
1936.50
967.74
645.16
806.45
967.74
484.12
726.19
161.29
241.30
322.58
403.23
483.87
mm2
mm
¥
¥
¥
¥
¥
Crosssectional
area
Size
3.848
4.355
5.226
6.968
8.710
2.614
3.268
3.921
5.228
2.613
1.742
2.177
2.613
1.307
1.961
0.435
0.652
0.871
1.089
1.306
kg/m
Weight
22.28
17.81
14.83
11.12
8.89
29.69
23.75
19.82
14.83
29.69
44.55
35.63
29.69
59.38
39.60
24.28
19.42
16.21
12.14
9.71
32.38
26.21
21.59
16.21
32.38
48.59
38.88
32.38
64.80
43.18
194.35
129.56
97.18
77.82
64.80
mW/m
mW/m
178.15
118.76
89.07
71.26
59.38
D 50 SWP d.c.
resistance
(max.)
at 20∞C
CISM d.c.
resistance
(max.)
at 20∞C
155.84
143.04
132.54
115.81
96.78
157.48
144.36
134.18
117.45
170.93
159.45
146.00
134.51
195.86
174.21
236.22
215.22
199.14
186.35
175.85
mW/m
y
x
111.009
216.773
374.608
887.822
1734.436
83.246
162.580
280.956
665.970
46.826
55.484
108.387
187.304
10.406
35.130
0.874
2.914
6.951
13.569
23.434
(cm4)
Ix–x
x
1.748
2.164
2.622
3.455
4.329
0.749
0.916
1.082
1.457
1.290
0.208
0.291
0.333
0.374
0.541
0.012
0.033
0.125
0.125
0.166
(cm4)
Iy–y
Reactance Xa Moment of inertia
at 305 mm
y
spacing at
50 Hz
Table 30.7 Indal CIS - M and D 50 S - WP rectangular busbars equivalent to EIE - M (1350) and E - 91E (6101 A) as in
BS EN 755-3 (ISO 209-1,2) (mechanical and electrical data)
21.844
34.134
49.161
87.376
136.570
16.387
25.613
36.871
65.548
12.290
10.930
17.075
24.581
4.097
9.226
0.688
1.540
2.737
4.261
6.145
(cm3)
Zx–x
2.737
3.409
4.097
5.441
6.817
1.540
1.917
2.311
3.064
2.048
0.688
0.852
1.032
0.787
1.147
0.131
0.262
0.393
0.426
0.508
(cm3)
Zy–y
Section modulus
2.936
3.670
4.404
5.872
7.341
2.936
3.670
4.404
5.872
2.202
2.936
3.670
4.404
1.466
2.202
0.734
1.102
1.468
1.836
2.202
(cm)
Kx–x
0.368
0.368
0.368
0.368
0.368
0.274
0.274
0.274
0.274
0.368
0.183
0.183
0.183
0.274
0.274
0.183
0.183
0.183
0.183
0.183
(cm)
Ky–y
Radius of gyration
30/1062 Electrical Power Engineering Reference & Applications Handbook
33.40
42.16
48.26
60.33
73.03
88.90
101.60
114.30
127.00
141.30
1
11/4
11/2
2
2 1/ 2
3
3 1/ 2
4
4 1/ 2
5
73.66
85.44
97.18
108.96
122.24
24.30
32.46
38.10
49.25
59.01
77.92
90.12
102.26
114.46
128.20
26.64
35.04
40.90
52.51
62.71
7.62
8.08
8.56
9.02
9.53
4.55
4.85
5.08
5.54
7.01
5.49
5.74
6.02
6.27
6.55
3.38
3.56
3.68
3.91
5.16
mm
1946
2374
2844
3343
3947
412
568
689
954
1454
1439
1729
2048
2379
2724
319
432
515
693
1100
mm2
5.254
6.410
7.678
9.027
10.656
1.113
1.535
1.861
2.575
3.926
3.884
4.667
5.529
6.423
7.490
0.861
1.166
1.392
1.871
2.970
kg/m
cm3
cm
28.258
39.227
52.675
68.454
89.326
2.957
3.396
3.835
4.275
4.770
1.068
1.371
1.581
1.999
2.406
162.093
261.393
399.998
584.938
860.350
4.395
10.064
16.283
36.125
80.183
36.466
51.455
69.989
92.115
121.772
2.632
4.774
6.748
11.977
21.954
2.885
3.320
3.752
4.183
4.671
1.033
1.330
1.537
1.947
2.347
(extra-heavy pipe sizes)
125.606
199.279
301.039
434.683
631.007
0.857
3.844
5.345
9.186
17.451
(standard pipe sizes)
3.634
8.104
12.899
27.709
63.683
cm4
Radius of
gyration
4.178
4.801
5.431
6.045
6.746
1.521
1.951
2.245
2.835
3.414
4.267
4.877
5.514
6.160
6.853
1.560
1.991
2.291
2.878
3.475
cm
G.M.D.
Ds.
16.1
13.2
11.0
9.4
8.0
76.0
55.1
45.4
32.9
21.5
21.8
17.4
15.3
13.2
11.3
98.1
72.7
60.7
45.1
28.4
D.C.
resistance
(max.) at
20∞C
mW/m
124.7
116.1
108.3
100.7
94.5
188.3
172.6
164.0
149.3
137.1
123.7
115.2
107.6
100.1
93.8
186.7
171.3
162.7
148.3
136.2
Reactance
Xa at 300 mm
spacing at
50 Hz
mW/m
2470
2850
3260
3700
4190
745
975
1125
1465
1955
2130
2510
2800
3160
3550
675
845
960
1245
1720
Indoors
2700
3160
3590
4040
4550
925
1170
1335
1680
2230
2350
2750
3050
3420
3810
815
1010
1160
1440
1950
Outdoors
Current rating at 50 Hz
(Amps)
r1
Notes
1 These data are indicative and provided for typical standard sizes from a manufacturer. Busbars larger than the above are generally not manufactured in tubular sections but in sections and
configurations that are convenient by extrusion (Figure 31.15). By welding such sections, one can form any desired size of tubular or any other conductor shape (hexagonal or octagonal).
Such large sections are required for isolated phase bus (IPB) systems, discussed in Chapter 31.
2 Other notes as in Table 30.4.
Indalco
88.90
101.60
114.30
127.00
141.30
3
3 1/ 2
4
4 1/ 2
5
Source:
33.40
42.16
48.26
60.33
73.03
1
11/4
11/2
2
2 1/ 2
mm
Section
modulus
mm
Moment
of inertia
in.
Inside
Nominal
weight
Outside
Area
Nominal diameter
Pipe
nominal
size IPS
Wall
thickness
Indal D50S WP tubular busbars (mechanical and electrical data and current rating)
Table 30.8
r2
Properties and ratings of current-carrying conductors 30/1063
Notes
As in Table 30.4.
Indalco
Source:
65.00
11.84
13.18
9.98
177.8
203.2
8.10
152.4
254.0
58.40
8.00
127.0
92.07
51.66
48.00
41.83
6.68
38.10
6.35
B
76.2
t
101.6
b
mm
199.06
154.12
135.62
113.98
92.00
69.20
45.08
C
mm
9.50
9.52
7.62
14.29
12.70
11.11
11.11
f
mm
mm
5515
3734
2794
1993
1695
1187
1013
77.42
629.34
375.44
171.07
82.59
59.16
33.76
20.48
74.09 132.74
42.04
31.63
17.07
12.07
Zx – x
14.89
4924.43 400.41 387.72
10.082 2033.29 120.29 200.09
7.544 1179.18
5.381
4.576
3.205
2.735
Ix – x
Iy – y
cm3
cm4
mm2
kg/m
Section
modulus
56.70
25.07
17.21
10.98
9.18
5.74
4.59
Zy – y
One channel
9.45
7.39
6.50
5.61
4.70
3.78
2.84
Kx – x
cm
2.64
1.78
1.63
1.45
1.37
1.19
1.12
Ky – y
Radius of
gyration
11.9
24.1
17.0
15.2
13.5
13.2
11.7
33.07
5.68
8.40
11.23
15.72
18.41
26.41
254.0
203.2
177.8
152.4
127.0
101.6
76.2
b
Distance D.C.
Depth
to
Resisneutral tance
axis x (max.)
at 20∞C
mm
mW/m mm
Channel busbar: mechanical and electrical data and current ratings (Grade E – 91E)
Section Weight Moment of
area
inertia
Table 30.9
mm
y
x C
Web
Flange Inner
Fillet
and
width flat
radius
flange
surface
thickness
x
t
f
Size
bx
B
y
254.0
203.2
177.8
152.4
127.0
106.4
100.0
a
mm
Width
48.56
62.99
70.54
80.38
92.52
106.96
114.83
Xa
Reactance at
305 mm
spacing
at 50 Hz
mW/m
Two channels
b
12800
9850
8200
6500
5540
4250
3380
Amps
11450
9150
7800
6340
5440
4190
3340
Amps
D.C.
A.C.
current current
rating rating
at 50 Hz
a
30/1064 Electrical Power Engineering Reference & Applications Handbook
Properties and ratings of current-carrying conductors 30/1065
Relevant Standards
IEC
Title
IS
BS
ISO
60028/1925
International standard of resistance for copper.
–
–
–
60105/1958
Recommendation for commercial purity aluminium busbar material.
–
–
–
–
Copper rods and bars for electrical purposes.
613/2000
–
–
–
Wrought aluminium and aluminium alloys, drawn tubes for general
engineering purposes.
738/1999
–
–
–
Aluminium and aluminium alloys, extruded rod/bar, tube and profiles.
1285/2002
BS EN 755 (8 parts)
–
–
Specification for copper strip for electrical purposes.
1897/2001
–
–
–
Copper for electrical purposes. Rods and bars.
4171/1988
BS 1433/1970
–
–
Specification for wrought aluminium and aluminium alloys for
electrical purposes, bars, extruded round tube and sections.
5082/2003
BS EN 755-3/1996
209-1,2/1989
–
Specification for high conductivity copper tubes for electrical
purposes.
–
BS EN 13600/2000
–
–
Copper for electrical purposes. High conductivity copper rectangular
conductors with drawn or rolled edges.
–
BS EN 13601/2002
–
Notes
1 In the table of relevant Standards while the latest editions of the Standards are provided, it is possible that revised editions have become
available or some of them are even withdrawn. With the advances in technology and/or its application, the upgrading of Standards is a
continuous process by different Standards organizations. It is therefore advisable that for more authentic references, one may consult the
relevant organizations for the latest version of a Standard.
2 Some of the BS or IS Standards mentioned against IEC may not be identical.
3 The year noted against each Standard may also refer to the year it was last reaffirmed and not necessarily the year of publication.
Further Reading
1 Alcoa, Aluminium Bus Conductor Hand Book.
2 British Aluminium Co. Ltd, Aluminium Busbars, Pub. No. L4.
3 British Aluminium Co. Ltd, Aluminium for busbars, earthing
and lightning conductors, Pub. No. M4.
4
Copper Development Association, Copper Busbar (available in
FPS and MKS systems), Pub. No. 22, U.K.
5 Dwight, H.B., Electrical Coils and Conductors, McGraw-Hill,
New York (1945).
6 Indian Aluminium Co., Indal Aluminium Busbar (Collaborators
Alcan, Canada).