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Sunday, 22 September 2013

Voltage drop calculation, Cable size and resistance


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
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
In India-

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Tel: +91-11-23279245 / 43596064 / 43596065
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info@discoverypublishinggroup.com
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out of India 



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