Voltage drop calculation, Cable size
and resistance
An approximate
check can be made on voltage drop by means of the following formulae-
For DC and single phase AC two
wire systems
Voltage drop = (2xIxLxRxt)/1000
Where I = current in ampere
L = length of cable
in meter 9one conductor only)
R = resistance of
one conductor from table
t = temperature
correction factor
For three phase AC systems
Voltage drop = (1.732xIxLxRxt)/1000
Note: formula is applied when
power factor is unity. Power factor to be considered in load and reactance to
be considered.
i).Cable size and resistance
Cross sectional
area in sqmm.
|
Sq. inch
|
Copper
|
Aluminium
|
||
Weight kg/km
|
Resistance at 20 deg.C , ohm/km
|
Weight kg/km
|
Resistance at 20 deg.C , ohm/km
|
||
1
|
0.00155
|
8.89
|
17.86
|
2.7
|
30.3
|
1.5
|
0.00230
|
13.34
|
11.91
|
4.04
|
20.2
|
2.5
|
0.0038
|
22.33
|
7.1444
|
6.74
|
12.12
|
4
|
0.0062
|
35.56
|
4.46
|
10.8
|
7.575
|
6
|
0.0093
|
53.34
|
2.977
|
16.2
|
5.05
|
10
|
0.0155
|
88.9
|
1.786
|
27
|
3.03
|
16
|
0.0248
|
142.2
|
1.116
|
43.2
|
1.894
|
25
|
0.0388
|
222.3
|
0.714
|
67.4
|
1.212
|
35
|
0.0543
|
311.2
|
0.510
|
94.4
|
0.866
|
50
|
0.078
|
444.5
|
0.357
|
135
|
0.608
|
70
|
0.108
|
622.3
|
0.255
|
189
|
0.433
|
95
|
0.147
|
844.6
|
0.188
|
256
|
0.319
|
120
|
0.186
|
1067
|
0.1488
|
323
|
0.2525
|
150
|
0.233
|
1334
|
0.1191
|
404
|
0.202
|
185
|
0.286
|
1645
|
0.0965
|
498
|
0.1638
|
240
|
0.372
|
2134
|
0.0744
|
646
|
0.1263
|
300
|
0.465
|
2677
|
0.0595
|
808
|
0.101
|
400
|
0.620
|
3556
|
0.0447
|
1016
|
0.0758
|
500
|
0.780
|
4445
|
0.0357
|
1356
|
0.0606
|
625
|
0.956
|
5556
|
0.0286
|
1688
|
0.0485
|
For building
wires and flex cord, add 5% more
ii) Resistance correction factor at different temperature
ii) Resistance correction factor at different temperature
Temperature in
deg.C
|
Temperature
Correction Factor
|
|
Copper
|
Aluminium
|
|
5
|
0.9411
|
0.9396
|
10
|
0.9607
|
0.9597
|
15
|
0.9804
|
0.9798
|
20
|
1.0000
|
1.000
|
25
|
1.0197
|
1.0202
|
30
|
1.0392
|
1.0403
|
35
|
1.0589
|
1.0604
|
40
|
1.0786
|
1.0806
|
45
|
1.0982
|
1.1008
|
50
|
1.1179
|
1.1209
|
55
|
1.1375
|
1.1410
|
60
|
1.1572
|
1.1610
|
65
|
1.1768
|
1.1814
|
70
|
1.1965
|
1.2015
|
75
|
1.2161
|
1.2216
|
80
|
1.2358
|
1.2418
|
Book
reference: a practical guide to cable installation and toolbox talk
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